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Polarization study of P-wave charmonium radiative decay into a light vector meson at e+e collider experiment

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Yong-Qing Chen, Peng-Cheng Hong, Zhuo Chen, Wei Shan and Wei-Min Song. Polarization study of the P-wave charmonium radiative decay into a light vector meson at e+e collider experiment[J]. Chinese Physics C. doi: 10.1088/1674-1137/ad8ba2
Yong-Qing Chen, Peng-Cheng Hong, Zhuo Chen, Wei Shan and Wei-Min Song. Polarization study of the P-wave charmonium radiative decay into a light vector meson at e+e collider experiment[J]. Chinese Physics C.  doi: 10.1088/1674-1137/ad8ba2 shu
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Polarization study of P-wave charmonium radiative decay into a light vector meson at e+e collider experiment

Abstract: In this paper, a formalism is presented for the helicity amplitude analysis of the decays ψ(2S)γ1χcJ,χcJγ2V(V=ρ0,ϕ,ω) (subscripts 1 and 2 are used to distinguish the two radiative photons), and the polarization expressions of the P-wave charmonia χcJ and the vector mesons ρ0,ϕ,ω for experimental measurements at an electron-positron collider. In addition, we derive formulae for the angular distributions of χc1,2γV to extract the degree of transverse polarization PT of e+e pairs with symmetric beam energy as well as the ratios of two helicity amplitudes x (in χc1 decays) and x,y (in χc2 decays), which represent the relative magnitudes of transverse to longitudinal polarization amplitude. The results are validated by Monte Carlo simulation. Finally, the statistical sensitivity of PT, x, and y are estimated based on the large ψ(2S) data samples collected at current and proposed future e+e collider experiments.

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    I.   INTRODUCTION
    • Over past five decades, heavy quarkonium spectra have been established due to a collective of theorists and experimentalists working. More than 40 heavy quark-antiquark bound states, also known as charmonium and bottomonium, are observed with masses ranging from 2.9 GeV to 4.7 GeV or from 9.3 GeV to 11.1 GeV, respectively [1]. The heavy quarkonia below the open-flavor production mass-threshold are relatively well understood, providing an ideal laboratory to test perturbative and nonperturbative quantum chromodynamics (QCD) [2, 3].

      Charmonium decay is usually a focused research topic that is significant and useful for understanding the fundamental characteristics of charmonium. J/ψ and ψ(2S) are two observed charmonium states with a wealth of experimental decay information, as recently listed by the Particle Data Group (PDG) [1]. Compared to J/ψ and ψ(2S), the experimental measurement pertinent to the decay of spin singlets, such as the P-wave state hc and S-wave state ηc, and spin triplets, the P-wave state χcJ is significantly lower. Therefore, there are currently more active theoretical and experimental investigations into such charmonia decays.

      Experimental measurements of charmonium radiative decay to light-quark vector mesons would help us understand the QCD and QED mechanism between charmonium and light vector mesons by the strong and electromagnetic interactions. The previous theoretical study on radiative decays of charmonium into light vector mesons (the processes χcJγV) was based on numerical calculations of the quark-gluon loop diagrams in the perturbative QCD (pQCD) frame and nonrelativistic quantum chromodynamics (NRQCD) [4, 5]. This provides a useful starting point to investigate the interatctions between quarks and gluons in OZI suppressed processes. Furthermore, its predicted branching ratios of the decays χcJγV were tested by later e+e collider experiments.

      Measurements of the branching ratios of the P-wave charmonia χcJγV were presented by the CLEO-c and BESIII collaborations in 2008 [6] and 2011 [7], respectively. However, there are still some significant discrepancies between the experimental results and the theoretical predictions, as shown in Table 1. To resolve these discrepancies, a phenomenological model with a hadronic loop mechanism was employed [8].

      Decay Mode CLEO-c [6] BESIII [7] pQCD [4] NRQCD [5] NRQCD+QED [5]
      χc0γρ0 <9.6 < 10.5 1.2 3.2 2.0
      χc1γρ0 243±19±22 228±13±22 14 41 42
      χc2γρ0 <50 <20.8 4.4 13 38
      χc0γϕ <6.4 <16.2 0.46 1.3 0.03
      χc1γϕ <26 25.8±5.2±2.3 3.6 11 11
      χc2γϕ <13 <8.1 1.1 3.3 6.5
      χc0γω <8.8 <12.9 0.13 0.35 0.22
      χc1γω 83±15±12 69.7±7.2±6.6 1.6 4.6 4.7
      χc2γω <7.0 <6.1 0.5 1.5 4.2

      Table 1.  Comparison of experimental measurement results (CLEO-c, BESIII) and theoretical calculations (pQCD, NRQCD, NRQCD+QED) for the branching ratio of χcJγV(V=ρ0,ϕ,ω) [in units of 10−6].

      The Sokolov-Ternov effect induces self-polarization in high-energy e+e beams, which allows them to naturally become transversely polarized in a storage ring [9]. Based on the (2712±14)×106ψ(2S) data samples collected by the BESIII detector in 2009, 2012, and 2021, it is feasible to precisely measure the polarized parameters and impact of transversely polarized beams on them, enabling a thorough examination of these theoretical models and aiding in a better understanding of the properties of P-wave charmonium radiation decays [10]. Despite the measurement of the branching ratio of χcJγV, for the accurate measurement of their polarized parameters, the theoretical calculation must be validated.

      In this paper, we present a helicity amplitude formula for the process e+eψ(2S)γ1χcJγ1γ2V(V=ρ0,ϕ,ω) and construct the spin density matrix for χcJ and light vector mesons. Expressions of the joint angular distributions are obtained, and some polarization observables are given for the measurement by e+e collider. The statistical sensitivities for the relative magnitudes of transverse to longitudinal polarization amplitude of light vector mesons are also discussed with Monte Carlo (MC) simulation results in the paper. By considering the transverse polarization of e+e pairs, the angular distribution parameters will be measured with a high accuracy as well as other decay parameters.

    II.   HELICITY AMPLITUDE ANALYSIS
    • The helicity mechanism can be used to effectively build the dynamic information of entire decays [11, 12]. The decay planes and helicity angles are visually and clearly depicted in Fig. 1. In ψ(2S)γ1χcJ decay, the helicity angle θ1 is the polar angle between the directions of the momenta of e+ and γ1 in the e+e center-of-mass (CM) frame. In χcJγ2V decay, the helicity angle θ2 is chosen as the angle between the direction of momentum of γ2 in the γ1 rest frame and the direction of momentum of γ1 from e+e collision, and ϕ2 is the azimuthal angle between the χcJ production plane and its decay plane. In ρ0π+π and ϕK+K decays, there are two helicity angles: polar angle θ3 and azimuthal angle ϕ3; meanwhile, in a three-body decay ωπ+ππ0, we use the Euler angles (α,β,γ) to describe its coordinate system rotating process. Specifically, the γ1 rest frame is rotated to the γ2 rest frame by γ around z3, β around y3, and finally α around z3, where β is the angle between the momentum direction of γ2 and cross product direction of the momenta of π+ and π in the ω rest frame [13].

      Figure 1.  (color online) Definition of helicity angles at e+e collider experiment.

      These helicity angles can be constructed by the momenta of final particles. Importantly, the experimentally obtained laboratory-frame momentum must be transformed to the rest frame of the decaying parent particle for calculation.

      The helicity angles and amplitudes for sequential decays are defined in Table 2. The total amplitude M for the sequential decay ψ(2S)γ1χcJγ1γ2ρ0(ϕ)γ1γ2π+π(K+K) can be expressed as

      Decay ModeSolid AngleHelicity Amplitude
      ψ(2S)(λ0)γ(λ1)χcJ(λ2)Ω1=(θ1,ϕ1)BJλ1,λ2
      χcJ(λ2)γ(λ3)V(λ4)Ω2=(θ2,ϕ2)AJcλ3,λ4
      V(λ4)PP(ρπ+π,ϕK+K)Ω3=(θ3,ϕ3)F1
      V(λ4)PPP(ωπ+ππ0)Ω3=(α,β,γ)F10

      Table 2.  Definition of helicity angles and amplitudes, where λi indicates the helicity and energy for the corresponding particles.

      M(ϕ1,θ1,ϕ2,θ2,ϕ3,θ3;J,M,Jc,λ1,λ2,λ3,λ4)=BJλ1λ2DJM,λ1λ2(ϕ1,θ1)AJcλ3λ4DJcλ2,λ3λ4(ϕ2,θ2)×F1D1λ4,0(ϕ3,θ3),

      (1)

      where BJλ1,λ2 ("before" the χcJ) is the helicity amplitude of ψ(2S)γχcJ decay, the superscript J is the spin of ψ(2S) with J=1, AJcλ3,λ4 ("after" the χcJ) is the helicity amplitude of the process χcJγρ0(χcJγϕ), the superscript Jc is the spin of χcJ, and F1 is the helicity amplitude of the decay ρ0π+π or ϕK+K. The helicity amplitudes are subscripted by the helicity λ1=±1 of the radiative photon from ψ(2S)γχcJ decay, the helicity λ2 (λ2=0 for χc0, λ2=0,±1 for χc1, and λ2=0,±1,±2 for χc2) of χcJ, the helicity λ3=±1 of the radiative photon from χcJγV(V=ρ0,ϕ), and the helicity λ4=0,±1 of the vector meson (ρ0 or ϕ). The indices for the helicity of the daughters (psedudoscalar mesons) from ρ0 or ϕ decay can be omitted because they are zero. The subscript M=±1 for the first Wigner D-function is the z-component of spin J of ψ(2S).

      The total amplitude M for the decay ψ(2S)γ1χcJγ1γ2ωγ1γ2π+ππ0 is

      M(ϕ1,θ1,ϕ2,θ2,ϕ3,θ3;J,M,Jc,λ1,λ2,λ3,λ4)=BJλ1λ2DJM,λ1λ2(ϕ1,θ1)AJcλ3λ4DJcλ2,λ3λ4(ϕ2,θ2)×F1μD1λ4,μ(α,β,γ),

      (2)

      where F1μ is the helicity amplitude of the decay ωπ+ππ0. μ is the z-component of the spin angular momentum J of ω, while the normal to the ω decay plane is taken as the z-axis. The symmetry relation requires only one amplitude F1μ(μ=0) [14].

      The decay rates Γ for the cascade decays ψ(2S)γ1χcJγ1γ2ρ0(ϕ)γ1γ2π+π(K+K) and ψ(2S)γ1χcJγ1γ2ωγ1γ2π+ππ0 are proportional to

      M,λ1,λ2,λ3,λ4|M(ϕ1,θ1,ϕ2,θ2,ϕ3,θ3;J,M,Jc,λ1,λ2,λ3λ4)|2.

      (3)

      The electromagnetic transitions ψ(2S)γχcJ are dominated by electric dipole (E1) transitions, and their helicity amplitudes BJλ1λ2 satisfy the E1 transition relations [15]:

      B11,1=B11,0,forψ(2S)γ1χc1decay,B11,2=2B11,1=6B11,0,forψ(2S)γ1χc2decay.

      (4)

      Parity conservation gives the relation B1λ1,λ2=B1λ1,λ2ηψ(2S)ηγηχcJ(1)sψ(2S)sγsχcJ, where η and s represents the parity and spin of the particle, respectively. Thus, we have B11,0=B11,0 for the decay ψ(2S)γχc0, B11,1=B11,1, B11,0=B11,0 for the decay ψ(2S)γχc1, and B11,2=B11,2, B11,1=B11,1, B11,0=B11,0 for the decay ψ(2S)γχc2. Angular momentum conservation |λ1λ2|1 requires that these amplitudes (B11,1,B11,1) do not exist for the decay ψ(2S)γχc1 and that B11,1,B11,1,B11,2,B11,2 do not exist for the decay ψ(2S)γχc2. The matrix of helicity amplitude can be written as

      B=[B11,0B10,0B11,0]=[B11,00B11,0],forψ(2S)γχc0decay,

      (5)

      B=[B11,1B11,00B10,1B10,0B10,10B11,0B11,1]=[B11,1B11,000000B11,0B11,1]=[B11,0B11,000000B11,0B11,0],forψ(2S)γχc1decay,

      (6)

      B=[B11,2B11,1B11,0B11,10B10,2B10,1B10,0B10,1B10,20B11,1B11,0B11,1B11,2]=[B11,2B11,1B11,0000000000B11,0B11,1B11,2]=[6B11,03B11,0B11,0000000000B11,03B11,06B11,0],forψ(2S)γχc2decay.

      (7)

      For χcJγV(ρ0,ϕ,ω) decays, only one independent helicity amplitude for χc0 decays (A01,1 or A01,1, the "so-called" transverse polarization amplitude A0V in Ref. [16]), and there are more than one independent helicity amplitudes for χc1 and χc2 decays. The helicity amplitudes can be expressed as AJcλ3,λ4=aλ3,λ4eiζλ3,λ4, where Jc is the spin of the mother particle, λi is the helicity value of daughter particles, and a and ζ are the magnitude and phase angle of helicity amplitude A, respectively. Parity conservation leads to the following symmetry relations for helicity amplitudes:

      A01,1=A01,1,forχc0decay,A11,1=A11,1,A11,0=A11,0,forχc1decay,A21,1=A21,1,A21,0=A21,0,A21,1=A21,1,forχc2decay.

      (8)

      We define a parameter for polarization observables to describe the relative magnitudes of two helicity amplitudes:

      x|A11,1||A11,0|=|A1V||A||1V|

      (9)

      for χc1γV(ρ0,ϕ,ω) decays. We define two independent parameters

      x|A21,1||A21,0|=|A2V||A||2V|,y|A21,1||A21,0|=|T2V||A||2V|

      (10)

      for χc2γV(ρ,ϕ,ω) decays, where A or T with subscript (transverse polarization) or || (longitudinal polarization) is the amplitude defined in Ref. [16]. These parameters describe the ratio of amplitudes that characterize transverse to longitudinal polarization.

      The phase differences between independent amplitudes are defined as

      Δ1=ζ1,0ζ1,1

      (11)

      for χc1 and

      Δ1=ζ1,0ζ1,1,Δ2=ζ1,1ζ1,1

      (12)

      for χc2.

    III.   SPIN DENSITY MATRIX
    • As a method to obtain the decay angular distributions, the spin density matrix (SDM) carries the dynamical information of particle decay, and its different parameterizations can clearly explain various physical phenomena. For example, when expressed in multipole parameter form rLM (L-rank index ranges from 1 to 2J, M is taken from L to L), it can provide information about particle polarization [17, 18].

      The spin density matrix of ψ(2S) from polarized e+e beams can is written as

      ρψ(2S)=12[(1Pz)(1+ˉPz)0P2T000P2T0(1+Pz)(1ˉPz)],

      (13)

      where Pz/ˉPz is the degree of longitudinal polarization of e+/e, and PT is the degree of transverse polarization of e+/e [19].

      By taking the direction of the photon's momentum as the positive z-axis direction, as shown in Fig. 1(a), the SDM of χc0 can be written as

      ρχc0=12b21,0[1+cos2(θ1)+P2Tsin2(θ1)cos(2ϕ1)],

      (14)

      while the matrix elements of ρχc1 and ρχc2 are listed in Appendix A, where b1,0 is the magnitude of helicity amplitude B1,0 in ψ(2S)γχcJ decays. In these SDM calculations, we have used the E1 transition relations in the ψ(2S)γχcJ decay [20].

      Here, we take the multipole parameters rLM to describe the SDM of vectors (V=ρ0,ϕ,ω), which is expressed as

      ρV=r003[r20+3r10+132(ir11+r11ir21+r21)3(r22ir22)32(ir11+r11+ir21+r21)12r2032(ir11+r11+ir21r21)3(r22+ir22)32(ir11+r11ir21r21)r203r10+1].

      (15)

      In χcJγV(ρ,ϕ,ω) decays, the real multipole parameters rLM have different expressions for J=0,1,2, as listed in Appendix B.

    IV.   JOINT ANGULAR DISTRIBUTION
    • To compare the experimental results from the electron-positron collider, the joint angular distribution between the production and decay of χcJ is required. The expressions of joint angular distribution can be easily obtained using the SDMs of decay particles. Here, we construct the joint angular distribution expressions for each decay level, which can be used to experimentally verify the measured results. The joint angular distributions for the processes ψ(2S)γ1χcJ, ψ(2S)γ1χcJ,χcJγ2V(V=ρ0,ϕ,ω), and ψ(2S)γ1χcJ,χcJγ2V(V=ρ0,ϕ,ω),Vfinal states are

      W(Ω1)    Tr[ρχcJ],

      (16)

      W(Ω1,Ω2)Tr[ρV]=r00,

      (17)

      W(Ω1,Ω2,Ω3)λ4,λ4ρVλ4,λ4D1λ4,0(Ω3)D1λ4,0(Ω3)|F10|216r00[23sin2θ3(r22sin2ϕ3+r22cos2ϕ3)+23sin2θ3(r21sinϕ3+r21cosϕ3)+3r20cos2θ3+r202],

      (18)

      respectively.

      Considering the experimental polarization observables, we provide the distribution formulae for polar angle θi(i=1,2,3) after integrating other polar and azimuthal angles.

      For χc0,

      dNdcosθ11+cos2θ1,

      (19)

      dNdcosθ31cos2θ3,

      (20)

      dNdcosθ1dϕ11+cos2(θ1)+Pt2(1cos2(θ1))cos(2ϕ1)

      (21)

      The angular distribution dN/dcosθ2 is trivial because the projection of the cosine polar angle cosθ2 is flat.

      For χc1,

      dNdcosθ1113cos2θ1,

      (22)

      dNdcosθ21+2x212x2+3cos2θ2,

      (23)

      dNdcosθ31+2x2x2cos2θ3,

      (24)

      dNdcosθ1dϕ1113cos2(θ1)13Pt2(1cos2(θ1))cos(2ϕ1).

      (25)

      For χc2,

      dNdcosθ11+113cos2θ1,

      (26)

      dNdcosθ21+6x2+6y2310x2+6y2+9cos2θ2,

      (27)

      dNdcosθ31+2x2y2x2+y2cos2θ3,

      (28)

      dNdcosθ1dϕ11+113cos2θ1+113Pt2(1cos2(θ1))cos(2ϕ1)

      (29)

      To validate the above angular distribution functions, MC simulation was performed by modeling the amplitude sampling of phase space events in Eqs. (3)−(12). The phase differences were naively set to Δ1=π/3 in χc1 decays and to Δ1=π/3 and Δ2=π/4 in χc2 decays. The degree of beam polarization was simply set as PT=0.24 for all χcJ decays. The parameter x was set as 0.43 for χc1γρ0 decay, 0.63 for χc1γϕ decay, and 0.57 for χc1γω decay, as obtained from BESIII measurement in 2011 [7]. Referring to Ref. [20], the parameters for χc2γV decays were arbitrarily chosen to be x=1.55, y=2.06 for χc2γρ0 decay, x=1.55, y=2.13 for χc2γϕ decay, and x=0, y=1 for χc2γω decay. 500000 pseudo experiments were generated and fitted for each decay mode, using a probability density function derived from the full angular distributions shown in Eqs. (19)−(29).

      Here, we list some fitting results; the others can be found in Table C1, C2 and Figs. C1Fig. C6 of Appendix C. We use the function 1+αcos2θ to fit the angular distributions of ψ(2S)γχcJ(J=0,1,2) in Eqs. (19), (22), (26) and ρ0π+π, ϕK+K, ωπ+ππ0 from χc0γV(V=ρ0,ϕ,ω) decays in Eq. (21). In this case, the fitted α values are 0.992±0.009 for the decay ψ(2S)γχc0 and 0.999±0.001 for the decay ϕK+K from χc0γϕ decay in Fig. 2(a) and Fig. 2(b), respectively, which are consistent with the default values in Eqs. (19) and (21) within the standard deviation. With the measured angular distributions of χcJγV(J=0,1,2), we can extract the parameter ˆx(x,y,PT) in χcJ decays by fitting these equations of joint angular distributions to data. Given an example of fitting the angular distributions of χcJγϕ(J=1,2) based on MC simulation samples, the fitted x and PT values in χc1γϕ decays are 0.630±0.002 and 0.26±0.02, as shown in Fig. 3(b), Fig. 3(c), and Fig. 3(d), which are in agreement with the inputs x=0.63 and PT=0.24. In χc2γϕ decays, the fitted parameters of x and y are x=1.558±0.344, y=2.137±0.251, as shown in Fig. 4(b) and Fig. 4(c), respectively, which are consistant with the inputs x=1.55,y=2.13.

      Figure 2.  (color online) Fits to the angular distributions of cosθ1, ϕ1 in ψ(2S)γχc0 and cosθ3 in ϕK+K from χc0γϕ decays. Dots with error bars represent MC events, and the blue solid curve represents the fit.

      Figure 3.  (color online) Fits to the angular distributions of cosθi(i=1,2,3) and ϕ1 in ψ(2S)γχc1, χc1γϕ, and ϕK+K decays. Dots with error bars represent MC events, and the blue solid curve represents the fit.

      Figure 4.  (color online) Fits to the angular distributions of cosθi(i=1,2,3) and ϕ1 in ψ(2S)γχc2, χc2γϕ, and ϕK+K decays. Dots with error bars represent MC events, and the blue solid curve represents the fit.

      Decay mode Default α value Fitted α value Figure
      ψ(2S)γχc0 1.00 1.00±0.01 C1(a)
      ωπ+ππ0 −1.00 1.00±0.01 C1(b)
      ψ(2S)γχc0 1.00 1.02±0.01 C2(a)
      ρ0π+π −1.00 1.00±0.01 C2(b)
      ψ(2S)γχc1 (χc1γρ) −0.33 0.34±0.01 C3(a)
      ψ(2S)γχc1 (χc1γω) -0.33 0.33±0.01 C4(a)
      ψ(2S)γχc2 (χc2γρ) 0.08 0.07±0.01 C5(a)
      ψ(2S)γχc2 (χc2γω) 0.08 0.07±0.01 C6(a)

      Table C1.  Monte Carlo simulation and fitting results of the projection of the polar angles in the processes ψ(2S)γχc0 and ψ(2S)γχc1,2

      Decay modeInput valueFit valueFigure
      χc0γρPT=0.24PT=0.24±0.01C2(c)
      χc0γωPT=0.24PT=0.25±0.01C1(c)
      χc1γρx=0.43,PT=0.24x=0.43±0.01,PT=0.25±0.02C3(b),C3(c),C3(d)
      χc1γωx=0.57,PT=0.24x=0.56±0.01,PT=0.23±0.02C4(b),C4(c) C4(d)
      χc2γρx=1.55,y=2.06,PT=0.24x=1.58±0.79,y=2.09±0.77,PT=0.29±0.07C5(b),C5(c),C5(d)
      χc2γωx=0,y=1,PT=0.24x=0.00±0.02,y=1.000±0.02,PT=0.22±0.01C(b),C6(c),C6(d)

      Table C2.  Monte Carlo simulation and fitting results in the decays χc1,2γV

    V.   SENSITIVITY ESTIMATION
    • By investigating the statistical sensitivity of specific parameters, precise measurement is beneficial for evaluating the potential impact of uncertainties on the final results. The estimation aims to enhance the understanding of experimental uncertainties associated with these parameters and observed signal yields. It is necessary to estimate sensitivity to guide the data acquisition plan for current large-scale e+e experimental devices, such as BEPCII, as well as those to be built in the future, such as Super-Tau Charm Facility (STCF) [21, 22]. Through rigorous statistical analysis and simulations, the research provides valuable insights into the sensitivity of the key parameters, enabling researchers to make informed decisions and draw meaningful conclusions from experimental data.

      Assuming that the parameters will be obtained by fitting to the maximum likelihood function event-by-event, the normalized joint angular distribution can be defined as

      ˜W(Ω1,Ω2,Ω3,ˆx)=W(Ω1,Ω2,Ω3,ˆx)W()3i=1dcosθi3j=1dϕj,

      (30)

      where ˆx is a set of parameters containing PT for χc0, x,PT for χc1, and x,y,PT for χc2. The maximum likelihood function is

      L=Ni=1˜W(Ω1,Ω2,Ω3,ˆx),

      (31)

      where N is the number of observed events [23]. The estimated statistical sensitivity δxi for parameter ˆx(xi) is obtained by

      δxi=Vxi,xi|xi|×100%

      (32)

      where the covariance matrix gives

      V1xi,xj=E[2lnLxixj]=N˜W(2ln˜Wxixj)3k=1dcosθk3l=1dϕl.

      (33)

      By taking the phase difference \Delta_1= {\pi}/{3} in \chi_{c1} decays, the dependence of the statistical sensitivity for a set of different x values is plotted in Fig. 6(a). In \chi_{c2} decays, the phase differences \Delta_1 and \Delta_2 are set to {\pi}/{3} and {\pi}/{4}, respectively. The parameter y(x) is set to 1 when plotting the dependence of the statistical sensitivity for a set of different x(y) , as shown in Fig. 7(a) and Fig. 7(b).

      Figure 6.  (color online) (a) Sensitivity of x (in \chi_{c1} decay) for different x values relative to the observed events N. (b) Sensitivity of P_T (in \chi_{c1} decay) for different P_T values relative to the observed events N.

      Figure 7.  (color online) (a) Snsitivity of x (in \chi_{c2} decay) for different x values relative to the observed events N. (b) Sensitivity of y (in \chi_{c2} decay) for different y values relative to the observed events N. (c) Sensitivity of P_T (in \chi_{c2} decay) for different P_T values relative to the observed events N.

      From Fig. 5, Fig. 6(b), and Fig. 7(c), we can see that as polarization increases, the number of events required under the same statistical significance decreases. In Fig. 6(a), we can see that the ratio of the two independent helicity amplitude moduli x in \chi_{c1} decays can be measured at a statistical sensitivity of an order of 1% with at least 20,000 observed signal yields, where background, detector acceptance, and other experimental effects are not taken into account, if assuming x=1 . In comparison to the decay of \chi_{c1} , the decay of \chi_{c2} involves two independent parameters x and y, necessitating a higher number of observed events to achieve the same statistical sensitivity in the measurement of these two parameters.

      Figure 5.  (color online) Sensitivity of P_T (in \chi_{c0} decay) for different P_T values relative to the observed events N.

      The expected number of observed signal yields for the processes \psi(2S) \to \gamma_1 \chi_{c1,2} \to \gamma_1 \gamma_2 \rho^0 \to \gamma_1 \gamma_2 \pi^+ \pi^- , \psi(2S) \to \gamma_1 \chi_{c1,2} \to \gamma_1 \gamma_2 \phi \to \gamma_1 \gamma_2 K^+ K^- , and \psi(2S) \to \gamma_1 \chi_{cJ} \to \gamma_1 \gamma_2 \omega \to \gamma_1 \gamma_2 \pi^+ \pi^- \pi^0 are calculated by the following equation:

      N_{sig} = N_{\Psi(2S)} \times {\rm Br}_{\psi(2S) \to \gamma_1 \chi_{cJ}} \times {\rm Br}_{\chi_{cJ}\to\gamma_2 V} \times {\rm Br}_{V \to\rm final\; states}\times \epsilon ,

      (34)

      where N_{\rm sig} represents the expected number of observed signal events, N_{\Psi(2S)} represents the total number of \psi(2S) data samples at BESIII or STCF, and \epsilon is the expected experimental reconstruction efficiency. Additinally, {\rm Br}_{\psi(2S) \to \gamma_1 \chi_{cJ}} , {\rm Br}_{\chi_{cJ}\to\gamma_2 V} , and Br_{V \to\rm final\; states} denote the branching ratios of \psi(2S) \to \gamma_1 \chi_{cJ}\; (J=0,1,2) , \chi_{cJ}\to\gamma_2 V (V=\rho^0,\; \phi,\; \omega) , and \rho^0 \to \pi^+ \pi^- | \phi\to K^+ K^- | \omega \to \pi^+ \pi^- \pi^0 , respectively. BESIII collected approximately 2.71 billion (B) \psi(2S) events in 2009, 2012, and 2021 and plans to collect 3 billion (B) \psi(2S) events [21]. The future high-luminosity e^+e^- collider STCF will collect approximately 640 billion (B) \psi(2S) data samples each year [22]. Table 3 lists the expected numbers of observed signal yields for the processes \psi(2S) \to \gamma_1 \chi_{c0,1,2},\; \chi_{c0,1,2} \to \gamma_2 V (V=\rho^0,\; \phi,\; \omega) based on 2.71 B \psi(2S) data samples from BESIII and 640 B \psi(2S) data samples from STCF. With the expected signal yields, we can estimate the statistical sensitivity of the relative magnitudes of the transverse to longitudinal polarization amplitude and the degree of transverse polarization of e^++e^- beams, \delta_x ( \delta_y, \delta_{P_T} ) for the processes \psi(2S) \to \gamma_1 \chi_{c0,1,2} \to \gamma_1 \gamma_2 V (V=\rho^0,\; \phi,\; \omega) based on 2.71 B and 640 B \psi(2S) events, as shown in Table 4. The results of \delta_{P_T} indicate that the degree of beam transverse polarization has a large statistical uncertainty based on current data. The statistical sensitivity \delta_x is 1.4%−4.3% for \chi_{c1} \to \gamma V decays with 2.71 B \psi(2S) data samples in the current BESIII experiment, which reaches at least 5-fold improvement over the BESIII measurement in 2011 with (1.06\pm 0.04)\times10^8\; \psi(2S) data samples [7]. The processes \chi_{c2} \to \gamma V is promising to be observed at BESIII, and its statistical sensitivities \delta_x and \delta_y are conservatively estimated to be up to the levels of 10%−20% based on 2.71 B \psi(2S) data samples. The STCF experiment is expected to further improve the sensitivity \delta_x for \chi_{c1} decays and \delta_x , \delta_y for \chi_{c2} decays, with an impressive precision of less than or equal to 1% based on 640 B \psi(2S) data samples, presenting an improvement of 1 order of magnitude compared to the BESIII experiment with 2.71 B \psi(2S) data samples. The sensitivity \delta_{P_T} for \chi_{c1} and \chi_{c2} decays ranges from 2% to 20% at the STCF experiment.

      N_{sig} N_{\Psi(2S)} Br_{\psi(2S) \to \gamma_1 \chi_{cJ}} (%) [1] Br_{\chi_{cJ}\to\gamma_2 V} ( 10^{-5} ) [1] {\rm Br}_{V \to\rm final~ states} (%) [1] \epsilon (%) [7]
      537 2.71\times 10^9 (BESIII) 9.77 ( \psi(2S) \to \gamma \chi_{c0}) <0.9 ( \chi_{c0}\to\gamma \rho^0 ) 100 ( \rho^0 \to \pi^+ \pi^- ) 22.6
      253 <0.6 ( \chi_{c0}\to\gamma \phi ) 49.1 ( \phi\to K^+ K^- ) 32.4
      337 <0.8 ( \chi_{c0}\to\gamma \omega ) 89.2 ( \omega \to \pi^+ \pi^- \pi^0 ) 18.6
      11072 9.75 ( \psi(2S) \to \gamma \chi_{c1}) 21.6 ( \chi_{c1}\to\gamma \rho^0 ) 100 ( \rho^0 \to \pi^+ \pi^- ) 19.4
      1080 2.4 ( \chi_{c1}\to\gamma \phi ) 49.1 ( \phi\to K^+ K^- ) 34.6
      3493 6.8 ( \chi_{c1}\to\gamma \omega ) 89.2 ( \omega \to \pi^+ \pi^- \pi^0 ) 22.7
      788 9.36 ( \psi(2S) \to \gamma \chi_{c2} ) <1.9 ( \chi_{c2}\to\gamma \rho^0 ) 100 ( \rho^0 \to \pi^+ \pi^- ) 15.7
      339 <0.8 ( \chi_{c2}\to\gamma \phi ) 49.1 ( \phi\to K^+ K^- ) 32.6
      261 <0.6 ( \chi_{c2}\to\gamma \omega ) 89.2 ( \omega \to \pi^+ \pi^- \pi^0 ) 19.2
      1.27\times10^5 6.4\times 10^{11} (STCF) 9.77 ( \psi(2S) \to \gamma \chi_{c0}) <0.9 ( \chi_{c0}\to\gamma \rho^0 ) 100 ( \rho^0 \to \pi^+ \pi^- ) 22.6
      5.97\times10^4 <0.6 ( \chi_{c0}\to\gamma \phi ) 49.1 ( \phi\to K^+ K^- ) 32.4
      7.95\times10^4 <0.8 ( \chi_{c0}\to\gamma \omega ) 89.2 ( \omega \to \pi^+ \pi^- \pi^0 ) 18.6
      2.61\times10^6 9.75 ( \psi(2S) \to \gamma \chi_{c1}) 21.6 ( \chi_{c1}\to\gamma \rho^0 ) 100 ( \rho^0 \to \pi^+ \pi^- ) 19.4
      2.55\times10^5 2.4 ( \chi_{c1}\to\gamma \phi ) 49.1 ( \phi\to K^+ K^- ) 34.6
      8.25\times10^5 6.8 ( \chi_{c1}\to\gamma \omega ) 89.2 ( \omega \to \pi^+ \pi^- \pi^0 ) 22.7
      1.86\times10^5 9.36 ( \psi(2S) \to \gamma \chi_{c2} ) <1.9 ( \chi_{c2}\to\gamma \rho^0 ) 100 ( \rho^0 \to \pi^+ \pi^- ) 15.7
      8.01\times10^4 <0.8 ( \chi_{c2}\to\gamma \phi ) 49.1 ( \phi\to K^+ K^- ) 32.6
      6.16\times10^4 <0.6 ( \chi_{c2}\to\gamma \omega ) 89.2 ( \omega \to \pi^+ \pi^- \pi^0 ) 19.2

      Table 3.  Expected numbers of observed signal events and related parameters for calculating the expected signal yields for the processes \psi(2S) \to \gamma_1 \chi_{c0,1,2} \to \gamma_1 \gamma_2 V (V=\rho^0,\; \phi,\; \omega) at the BESIII and STCF experiments. The upper limits for \chi_{c2}\to\gamma V are at 90% C.L..

      Decay ModeParameterInput value \delta_x (2.71B) \delta_y (2.71B) \delta_{P_T} (2.71B) \delta_x (640B) \delta_y (640B) \delta_{P_T} (640B)
      \chi_{c0}\to\gamma \rho^0 P_T 0.2\backslash 7.69%
      \chi_{c0}\to\gamma \phi P_T 0.2\backslash 7.27%
      \chi_{c0}\to\gamma \omega P_T 0.2\backslash 8.27%
      \chi_{c1}\to\gamma \rho^0 x11.4%32.5%0.1%2.1%
      P_T 0.2 (fixed)
      \Delta_1 \dfrac{\pi}{3} (fixed)
      \chi_{c1}\to\gamma \phi x14.3% \backslash 0.3%6.8%
      P_T 0.2 (fixed)
      \Delta_1 \dfrac{\pi}{3} (fixed)
      \chi_{c1}\to\gamma \omega x12.4%59.1%0.2%3.8%
      P_T 0.2 (fixed)
      \Delta_1 \dfrac{\pi}{3} (fixed)
      \chi_{c2}\to\gamma \rho^0 x18.6%8.4% \backslash 0.6%0.5%9.0%
      y1
      P_T 0.2 (fixed)
      \Delta_1 \dfrac{\pi}{3} (fixed)
      \Delta_2 \dfrac{\pi}{4} (fixed)
      \chi_{c2}\to\gamma \phi x113.7%13.3% \backslash 0.9%0.9%14.2%
      y1
      P_T 0.2 (fixed)
      \Delta_1 \dfrac{\pi}{3} (fixed)
      \Delta_2 \dfrac{\pi}{4} (fixed)
      \chi_{c2}\to\gamma \omega x115.6%15.1% \backslash 1.0%1.0%16.2%
      y1
      P_T 0.2 (fixed)
      \Delta_1 \dfrac{\pi}{3} (fixed)
      \Delta_2 \dfrac{\pi}{4} (fixed)

      Table 4.  Statistical sensitivity \delta_x ( \delta_y , \delta_{P_T} ) for the processes \psi(2S) \to \gamma_1 \chi_{c0,1,2} \to \gamma_1 \gamma_2 V (V=\rho^0,\; \phi,\; \omega) based on 2.71 billion \Psi(2S) events at BESIII and 640 billion \Psi(2S) events at STCF.

    VI.   SUMMARY AND OUTLOOK
    • To better understand the radiative decays of \psi(2S) \to \gamma \chi_{cJ}, \chi_{cJ} \to \gamma V(\rho^0, \phi, \omega) , we presented formulae for helicity amplitude analysis and derived the joint angular distribution for these decay chains. Furthermore, we provided observables for experimentally measuring the polarization of the vector mesons in \chi_{cJ} decays, performed a Monte Carlo simulation, and fitted the angular distributions to validate the theoretical calculations. Finally, we investigated the statistical sensitivity of the degree of transverse polarization P_T of e^+ e^- beams and the modulus ratio of helicity amplitudes in the decays of \chi_{c1} and \chi_{c2} , and we predicted the expected number of signal events required to achieve the relevant statistical precision in experimental measurements. Based on 3 billion planned \psi(2S) data samples at the BESIII experiment, the ratio of transverse to longitudinal polarization amplitude for the process \chi_{cJ} \to \gamma V(\rho, \phi, \omega) can be measured in the near future [21]. The fomalism in the work can be used in the near future in high-energy physics experiments, such as STCF with 640 billion \psi(2S) data samples per year [22]. Analogous to the radiative decay of a charmonium state with the same spin-parity quantum number, it also provides a reference for future measurements by the super-B factory to study the polarization effect of P-wave bottonia \chi_{bJ} \to \gamma V(\rho^0, \phi, \omega) [24].

    APPENDIX A: SPIN DENSITY MATRIX ELEMENTS OF \chi_{c1} AND \chi_{c2}

      A.1.   Spin density matrix elements of \chi_{c1}

    • \begin{aligned}[b] \rho^{\chi_{c1}}_{1,1} &=-\frac{1}{2} b_{1,0}^2 \sin ^2\left(\theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right),\\ \rho^{\chi_{c1}}_{1,0} &= \frac{b_{1,0}^2 \sin \left(\theta _1\right) \left(\cos \left(\theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)-{\rm i} P_T^2 \sin \left(2 \phi _1\right)\right)}{2 \sqrt{2}},\\ \rho^{\chi_{c1}}_{0,1} &= \frac{b_{1,0}^2 \sin \left(\theta _1\right) \left(\cos \left(\theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)+{\rm i} P_T^2 \sin \left(2 \phi _1\right)\right)}{2 \sqrt{2}},\\ \rho^{\chi_{c1}}_{0,0} &= \frac{1}{4} b_{1,0}^2 \left(\cos \left(2 \theta _1\right)+2 P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right)+3\right),\\ \rho^{\chi_{c1}}_{0,-1} &= \frac{b_{1,0}^2 \sin \left(\theta _1\right) \left(\cos \left(\theta _1\right) \left(1-P_T^2 \cos \left(2 \phi _1\right)\right)+{\rm i} P_T^2 \sin \left(2 \phi _1\right)\right)}{2 \sqrt{2}},\\ \rho^{\chi_{c1}}_{-1,0} &= -\frac{b_{1,0}^2 \sin \left(\theta _1\right) \left(\cos \left(\theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)+{\rm i} P_T^2 \sin \left(2 \phi _1\right)\right)}{2 \sqrt{2}},\\ \rho^{\chi_{c1}}_{-1,-1} &= -\frac{1}{2} b_{1,0}^2 \sin ^2\left(\theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right),\\ \rho^{\chi_{c1}}_{1,-1} &= \rho^{\chi_{c1}}_{-1,1} = 0. \end{aligned}

      (A1)
    • A.2.   Spin density matrix elements of \chi_{c2}

    • \begin{aligned}\rho_{2,2}^{\chi_{c2}} & =\frac{3}{4}b_{1,0}^2\left(\cos\left(2\theta_1\right)+2P_T^2\sin^2\left(\theta_1\right)\cos\left(2\phi_1\right)+3\right), \\ \rho_{2,1}^{\chi_{c2}} & =\frac{3}{2}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(1-P_T^2\cos\left(2\phi_1\right)\right)+{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{2,0}^{\chi_{c2}} & =\frac{1}{4}\sqrt{\frac{3}{2}}b_{1,0}^2\left(2\sin^2\left(\theta_1\right)+P_T^2\left(\left(\cos\left(2\theta_1\right)+3\right)\cos\left(2\phi_1\right)-4{\rm i}\cos\left(\theta_1\right)\sin\left(2\phi_1\right)\right)\right), \\ \rho_{1,2}^{\chi_{c2}} & =\frac{1}{2}(-3)b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right)+{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{1,1}^{\chi_{c2}} & =\frac{1}{2}(-3)b_{1,0}^2\sin^2\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right), \\ \rho_{1,0}^{\chi_{c2}} & =\frac{1}{2}\sqrt{\frac{3}{2}}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right)-{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{0,2}^{\chi_{c2}} & =\frac{1}{4}\sqrt{\frac{3}{2}}b_{1,0}^2\left(2\sin^2\left(\theta_1\right)+P_T^2\left(\left(\cos\left(2\theta_1\right)+3\right)\cos\left(2\phi_1\right)+4{\rm i}\cos\left(\theta_1\right)\sin\left(2\phi_1\right)\right)\right), \\ \rho_{0,1}^{\chi_{c2}} & =\frac{1}{2}\sqrt{\frac{3}{2}}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right)+{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{0,0}^{\chi_{c2}} & =\frac{1}{4}b_{1,0}^2\left(\cos\left(2\theta_1\right)+2P_T^2\sin^2\left(\theta_1\right)\cos\left(2\phi_1\right)+3\right),\\\rho_{0,-1}^{\chi_{c2}} & =\frac{1}{2}\sqrt{\frac{3}{2}}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(1-P_T^2\cos\left(2\phi_1\right)\right)+{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{0,-2}^{\chi_{c2}} & =\frac{1}{4}\sqrt{\frac{3}{2}}b_{1,0}^2\left(2\sin^2\left(\theta_1\right)+P_T^2\left(\left(\cos\left(2\theta_1\right)+3\right)\cos\left(2\phi_1\right)-4{\rm i}\cos\left(\theta_1\right)\sin\left(2\phi_1\right)\right)\right), \end{aligned}

      \begin{aligned}[b] \rho_{-1,0}^{\chi_{c2}} & =-\frac{1}{2}\sqrt{\frac{3}{2}}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right)+{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{-1,-1}^{\chi_{c2}} & =\frac{1}{2}(-3)b_{1,0}^2\sin^2\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right), \\ \rho_{-1,-2}^{\chi_{c2}} & =\frac{3}{2}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right)-{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{-2,0}^{\chi_{c2}} & =\frac{1}{4}\sqrt{\frac{3}{2}}b_{1,0}^2\left(2\sin^2\left(\theta_1\right)+P_T^2\left(\left(\cos\left(2\theta_1\right)+3\right)\cos\left(2\phi_1\right)+4{\rm i}\cos\left(\theta_1\right)\sin\left(2\phi_1\right)\right)\right), \\ \rho_{-2,-1}^{\chi_{c2}} & =\frac{3}{2}b_{1,0}^2\sin\left(\theta_1\right)\left(\cos\left(\theta_1\right)\left(P_T^2\cos\left(2\phi_1\right)-1\right)+{\rm i}P_T^2\sin\left(2\phi_1\right)\right), \\ \rho_{-2,-2}^{\chi_{c2}} & =\frac{3}{4}b_{1,0}^2\left(\cos\left(2\theta_1\right)+2P_T^2\sin^2\left(\theta_1\right)\cos\left(2\phi_1\right)+3\right), \\ \rho_{2,-1}^{\chi_{c2}} & =\; \rho_{2,-2}^{\chi_{c2}}=\; \rho_{1,-1}^{\chi_{c2}}=\; \rho_{1,-2}^{\chi_{c2}}=\; \rho_{-1,2}^{\chi_{c2}}=\; \rho_{-1,1}^{\chi_{c2}}=\; \rho_{-2,1}^{\chi_{c2}}=\; \rho_{-2,1}^{\chi_{c2}}=0\\\end{aligned}

      (A2)
    B.   r^L_M expressions

      B.1.   \chi_{c0}

    • The multipole parameters r^L_M for \chi_{c0} are expressed as

      \begin{aligned} r^0_0 =a_{1,1}^2 b_{1,0}^2 \left(1+\cos ^2\left(\theta _1\right)+P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right)\right), r^0_0 r^2_0 = \frac{1}{2} a_{1,1}^2 b_{1,0}^2 \left(1+\cos ^2\left(\theta _1\right)+P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right)\right). \end{aligned}

      (B1)

      The other unlisted r^L_M are equal to zero.

    • B.2.   \chi_{c1}

    • The multipole parameters r^L_M for \chi_{c1} are expressed as

      \begin{aligned}[b] r^0_0 =\;& \frac{1}{12} a_{1,0}^2 b_{1,0}^2 (-3 \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) \cos \left(\phi _2\right) +6 P_T^2 \left(1-2 x^2\right) \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) \\ &+ 6 P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right) \left(\left(2 x^2-1\right) \cos \left(2 \theta _2\right)-1\right) +3 \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) \cos \left(\phi _2\right) \left(P_T^2 \left(1-2 x^2\right) \cos \left(2 \phi _1\right)+2 x^2\right) \\ &+2 \left(2 x^2-1\right) \cos ^2\left(\theta _1\right) \left(3 \cos \left(2 \theta _2\right)+1\right)-2 \left(x^2+1\right) \cos \left(2 \theta _1\right)+10 x^2+10),\\ r^0_0 r^1_{-1} =\;& \frac{1}{4} \sqrt{3} x a_{1,0}^2 b_{1,0}^2 \sin \left(\Delta _1\right) (2 \sin \left(2 \theta _2\right) \left(\cos ^2\left(\theta _1\right)+P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right)\right) \\ &+\cos \left(2 \theta _2\right) \left(2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) +\sin \left(2 \theta _1\right) \cos \left(\phi _2\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)\right)),\\ r^0_0 r^1_1 =\;&\frac{1}{4} \sqrt{3} x a_{1,0}^2 b_{1,0}^2 \sin \left(\Delta _1\right) \cos \left(\theta _2\right) (2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \cos \left(\phi _2\right) +\sin \left(2 \theta _1\right) \sin \left(\phi _2\right) \left(1-P_T^2 \cos \left(2 \phi _1\right)\right)),\\ r^0_0 r^2_{-1} =\;& \frac{1}{4} \sqrt{3} x a_{1,0}^2 b_{1,0}^2 \cos \left(\Delta _1\right) \cos \left(\theta _2\right) (\sin \left(2 \theta _1\right) \sin \left(\phi _2\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right) -2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \cos \left(\phi _2\right)),\\ r^0_0 r^2_{0} =\;& \frac{1}{12} a_{1,0}^2 b_{1,0}^2 (3 \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) \cos \left(\phi _2\right) -6 P_T^2 \left(x^2+1\right) \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) \\ &+6 P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right) \left(\left(x^2+1\right) \cos \left(2 \theta _2\right)+1\right) -3 \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) \cos \left(\phi _2\right) \left(P_T^2 \left(x^2+1\right) \cos \left(2 \phi _1\right)-x^2\right) \\ &+2 \left(x^2+1\right) \cos ^2\left(\theta _1\right) \left(3 \cos \left(2 \theta _2\right)+1\right)-\left(x^2-2\right) \cos \left(2 \theta _1\right)+5 x^2-10), \\ r^0_0 r^2_{1} =\;& \frac{1}{4} \sqrt{3} x a_{1,0}^2 b_{1,0}^2 \cos \left(\Delta _1\right) (2 \sin \left(2 \theta _2\right) \left(\cos ^2\left(\theta _1\right)+P_T^2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _1\right)\right) \\ &+\cos \left(2 \theta _2\right) (2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) +\sin \left(2 \theta _1\right) \cos \left(\phi _2\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right))) .\\ \end{aligned}

      (B2)

      The other unlisted r^L_M are equal to zero.

    • B.3.   \chi_{c2}

    • The multipole parameters r^L_M for \chi_{c2} are expressed as

      \begin{aligned}[b] r^0_0 =\;& \frac{1}{64} \{4 x^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2+54 y^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 +108 x^2 \cos \left(4 \theta _2\right) \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 \\ &+ 18 y^2 \cos \left(4 \theta _2\right) \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 -72 \cos \left(4 \theta _2\right) \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2+72 x^2 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) P_T^2 \\ &+108 y^2 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) P_T^2-144 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) P_T^2 \\ &+48 x^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) P_T^2-72 y^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) P_T^2 \\ &+48 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) P_T^2-72 x^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) P_T^2\\ &-12 y^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) P_T^2+48 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) P_T^2\\ &+96 x^2 \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2-144 y^2 \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &+96 \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2-144 x^2 \sin \left(\theta _1\right) \sin \left(4 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &-24 y^2 \sin \left(\theta _1\right) \sin \left(4 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2+96 \sin \left(\theta _1\right) \sin \left(4 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &+48 \left(2 x^2+3 y^2-4\right) \cos \left(\theta _1\right) \sin ^2\left(\theta _2\right) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right) P_T^2+48 x^2 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right) \\ &+72 y^2 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right)-96 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right)+18 x^2 \cos \left(4 \theta _2\right) +3 y^2 \cos \left(4 \theta _2\right) \\ &+\cos \left(2 \theta _1\right) \{2 x^2+27 y^2+12 P_T^2 \left(2 x^2+3 y^2-4\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) +9 \left(6 x^2+y^2-4\right) \cos \left(4 \theta _2\right) \\ &+ 12 \cos \left(2 \theta _2\right) [-2 x^2+5 y^2 +P_T^2 \left(6 x^2+y^2-4\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right)-4]-12\}-48 x^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) \\ &+72 y^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right)+3 [50 x^2 + 67 y^2 - 8 P_T^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) - 4 \cos \left(4 \theta _2\right) - 16 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) + 52] \\ &+72 x^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) +12 y^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right)-48 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right)\\ &+12 \cos \left(2 \theta _2\right) [\cos \left(2 \phi _1\right) \left(3 \left(6 x^2+y^2-4\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right)-2 \left(2 x^2-5 y^2+4\right) \sin ^2\left(\theta _1\right)\right) P_T^2 -6 x^2+7 y^2\\ &+2 \left(6 x^2+y^2-4\right) \sin ^2\left(\theta _2\right) (2 \cos \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right) P_T^2 +\cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right))-4]\} a_{1,0}^2 b_{1,0}^2,\\r^0_0 r^1_{-1} &= \frac{3}{64} a_{1,0}^2 b_{1,0}^2 \{2 x \sin \Delta _1 \{\sin \left(2 \theta _2\right) [4 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _2\right)+\cos \left(2 \theta _1\right) \left(4 P_T^2 \cos \left(2 \phi _1\right) \cos ^2\left(\phi _2\right)-2\right) \\ &+2 P_T^2 \cos \left(2 \phi _1\right) \left(3 \cos \left(2 \phi _2\right)-1\right)-6] +18 P_T^2 \sin \left(4 \theta _2\right) \sin ^2\left(\phi _2\right) \cos \left(2 \phi _1\right)-3 \sin \left(4 \theta _2\right) [2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _2\right)+\cos \left(2 \theta _1\right) \\ &\times \left(P_T^2 \cos \left(2 \phi _1\right) \left(\cos \left(2 \phi _2\right)+3\right)-3\right)-1]-8 P_T^2 \sin \left(\theta _1\right) [\cos \left(2 \theta _2\right) -3 \cos \left(4 \theta _2\right)] \sin \left(2 \phi _1\right) \sin \left(\phi _2\right)\}\\ &+ 8 \cos \left(\theta _1\right) \{x \sin \Delta _1 [P_T^2 (2 \sin \left(2 \theta _2\right)-3 \sin \left(4 \theta _2\right)) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right)\\ &-2 \sin \left(\theta _1\right) (\cos \left(2 \theta _2\right) -3 \cos \left(4 \theta _2\right)) \cos \left(\phi _2\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)]\\ &+\sqrt{6} y \sin \left(\Delta _1-\Delta _2\right) [\sin \left(\theta _1\right) \left(3 \cos \left(2 \theta _2\right)+\cos \left(4 \theta _2\right)\right) \cos \left(\phi _2\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)\\ &-4 P_T^2 \sin \left(\theta _2\right) \cos ^3\left(\theta _2\right) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right)]\} \\ &+\sqrt{6} y \sin \left(\Delta _1-\Delta _2\right) \{6 P_T^2 \sin \left(4 \theta _2\right) \sin ^2\left(\phi _2\right) \cos \left(2 \phi _1\right)-2 \sin \left(2 \theta _2\right) [2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _2\right)\\ &+\cos \left(2 \theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right) \left(\cos \left(2 \phi _2\right)+5\right)-5\right)+P_T^2 \cos \left(2 \phi _1\right) \left(3 \cos \left(2 \phi _2\right)-5\right)-7] -\sin \left(4 \theta _2\right) (2 \sin ^2\left(\theta _1\right) \cos \left(2 \phi _2\right)\\ &+\cos \left(2 \theta _1\right) \left(P_T^2 \cos \left(2 \phi _1\right) \left(\cos \left(2 \phi _2\right)+3\right)-3\right)-1) +8 P_T^2 \sin \left(\theta _1\right) \left(3 \cos \left(2 \theta _2\right)+\cos \left(4 \theta _2\right)\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right)\}\},\\ r^0_0 r^1_1 =\;&\frac{3}{224} a_{1,0}^2 b_{1,0}^2 \{7 \sin \left(\theta _2\right) [\sin \left(2 \phi _2\right) \left(2 \sin ^2\left(\theta _1\right)+P_T^2 \left(\cos \left(2 \theta _1\right)+3\right) \cos \left(2 \phi _1\right)\right)\\ &-4 P_T^2 \cos \left(\theta _1\right) \sin \left(2 \phi _1\right) \cos \left(2 \phi _2\right)] [2 x \sin \Delta _1 \left(3 \cos \left(2 \theta _2\right)+1\right) \end{aligned}

      \begin{aligned} &+\sqrt{6} y \sin \left(\Delta _1-\Delta _2\right) \left(\cos \left(2 \theta _2\right)+3\right)] +28 \sin \left(\theta _1\right) \cos \left(\theta _2\right) [\cos \left(\theta _1\right) \sin \left(\phi _2\right) \left(1-P_T^2 \cos \left(2 \phi _1\right)\right) \\&+P_T^2 \sin \left(2 \phi _1\right) \cos \left(\phi _2\right)] [2 x \sin \Delta _1 \left(3 \cos \left(2 \theta _2\right)-1\right) +\sqrt{6} y \sin \left(\Delta _1-\Delta _2\right) \left(\cos \left(2 \theta _2\right)+3\right)]\}, \\ r^0_0 r^2_{-2} =\;& -\frac{3 x y }{8 \sqrt{2}}a_{1,0}^2 b_{1,0}^2 \cos \left(\Delta _2\right) \{-\cos \left(\theta _2\right) \left(3 \cos \left(2 \theta _2\right)+1\right) \sin \left(2 \phi _2\right) [2 \sin ^2\left(\theta _1\right) +P_T^2 \left(\cos \left(2 \theta _1\right)+3\right) \cos \left(2 \phi _1\right)] \\ &+2 P_T^2 \sin \left(2 \phi _1\right) [\cos \left(\theta _1\right) \left(5 \cos \left(\theta _2\right)+3 \cos \left(3 \theta _2\right)\right) \cos \left(2 \phi _2\right) +\sin \left(\theta _1\right) \left(7 \sin \left(\theta _2\right)+3 \sin \left(3 \theta _2\right)\right) \cos \left(\phi _2\right)] \\ &-2 \sin \left(2 \theta _1\right) \sin \left(\theta _2\right) \left(3 \cos \left(2 \theta _2\right)+5\right) \sin \left(\phi _2\right)\left(P_T^2 \cos \left(2 \phi _1\right)-1\right)\}\\ r^0_0 r^2_{-1} =\;&-\frac{3}{224} a_{1,0}^2 b_{1,0}^2 \{2 x \cos \Delta _1 \{14 \cos \left(\theta _2\right) \left(3 \cos \left(2 \theta _2\right)-1\right) (2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \cos \left(\phi _2\right) \\ &+\sin \left(2 \theta _1\right) \sin \left(\phi _2\right) \left(1-P_T^2 \cos \left(2 \phi _1\right)\right)) -7 \sin \left(\theta _2\right) \left(3 \cos \left(2 \theta _2\right)+1\right) [4 P_T^2 \cos \left(\theta _1\right) \sin \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \\ &-\sin \left(2 \phi _2\right) \left(2 \sin ^2\left(\theta _1\right)+P_T^2 \left(\cos \left(2 \theta _1\right)+3\right) \cos \left(2 \phi _1\right)\right)]\}\\&+7 \sqrt{6} y \cos \left(\Delta _1-\Delta _2\right) \{\sin \left(\theta _2\right) \left(\cos \left(2 \theta _2\right)+3\right) \sin \left(2 \phi _2\right) \left(2 \sin ^2\left(\theta _1\right)+P_T^2 \left(\cos \left(2 \theta _1\right)+3\right) \cos \left(2 \phi _1\right)\right)\\ &-2 P_T^2 \left(5 \sin \left(\theta _2\right)+\sin \left(3 \theta _2\right)\right) \cos \left(\theta _1\right) \sin \left(2 \phi _1\right) \cos \left(2 \phi _2\right) +\sin \left(2 \theta _1\right) \cos \left(3 \theta _2\right) \sin \left(\phi _2\right) \left(1-P_T^2 \cos \left(2 \phi _1\right)\right) \\ &+\cos \left(\theta _2\right) \left(4 P_T^2 \sin \left(\theta _1\right) \left(\cos \left(2 \theta _2\right)+3\right) \sin \left(2 \phi _1\right) \cos \left(\phi _2\right)-7 \sin \left(2 \theta _1\right) \sin \left(\phi _2\right) \left(P_T^2 \cos \left(2 \phi _1\right)-1\right)\right)\}\},\\ r^0_0 r^2_0 =\;& \frac{1}{128} \{4 x^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2+54 y^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 + 108 x^2 \cos \left(4 \theta _2\right) \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 \\ &+18 y^2 \cos \left(4 \theta _2\right) \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 +144 \cos \left(4 \theta _2\right) \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2+48 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) P_T^2 \\ &+72 x^2 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) P_T^2+108 y^2 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) P_T^2 +288 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) P_T^2 \\ &+48 x^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) P_T^2 -72 y^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) P_T^2\\ &-96 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) P_T^2 -72 x^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) P_T^2\\ &-12 y^2 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) P_T^2 -96 \cos \left(2 \phi _1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) P_T^2 \\ &+96 x^2 \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 -144 y^2 \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2\\ &-192 \sin \left(\theta _1\right) \sin \left(2 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 -144 x^2 \sin \left(\theta _1\right) \sin \left(4 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2\\ &-24 y^2 \sin \left(\theta _1\right) \sin \left(4 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 -192 \sin \left(\theta _1\right) \sin \left(4 \theta _2\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &+48 \left(2 x^2+3 y^2+8\right) \cos \left(\theta _1\right) \sin ^2\left(\theta _2\right) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right) P_T^2+150 x^2+201 y^2 +48 x^2 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right)\\ &+72 y^2 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right) +192 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right)+18 x^2 \cos \left(4 \theta _2\right)+3 y^2 \cos \left(4 \theta _2\right)+24 \cos \left(4 \theta _2\right) \\ &+\cos \left(2 \theta _1\right) [2 x^2+27 y^2+12 P_T^2 \left(2 x^2+3 y^2+8\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right) +9 \left(6 x^2+y^2+8\right) \cos \left(4 \theta _2\right)\\ &+12 \cos \left(2 \theta _2\right) [-2 x^2+5 y^2 +P_T^2 \left(6 x^2+y^2+8\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right)+8]+24] -48 x^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right)\\ &+72 y^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right) +96 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(2 \theta _2\right)+72 x^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) \\ &+12 y^2 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right)+96 \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \sin \left(4 \theta _2\right) +12 \cos \left(2 \theta _2\right) \{\cos \left(2 \phi _1\right) [2 \left(-2 x^2+5 y^2+8\right) \sin ^2\left(\theta _1\right) \\ &+3 \left(6 x^2+y^2+8\right) \cos \left(2 \phi _2\right) \sin ^2\left(\theta _2\right)] P_T^2-6 x^2+7 y^2 +2 \left(6 x^2+y^2+8\right) \sin ^2\left(\theta _2\right) (2 \cos \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right) P_T^2\\ &+\cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right))+8\} -312\} a_{1,0}^2 b_{1,0}^2, \\ r^0_0 r^2_1 =\;& \frac{3}{224} \{7 \sqrt{\frac{3}{2}} y \cos \left(\Delta _1-\Delta _2\right) \{-32 P_T^2 \cos \left(\theta _1\right) \sin \left(\theta _2\right) \sin \left(2 \phi _1\right) \sin \left(2 \phi _2\right) \cos ^3\left(\theta _2\right) \\ &+20 P_T^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) \sin \left(2 \theta _2\right)-4 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin \left(2 \theta _2\right)+2 [5 \cos \left(2 \theta _1\right)+\cos \left(2 \theta _2\right) +7] \sin \left(2 \theta _2\right) \\ &-6 P_T^2 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(2 \theta _2\right)-2 P_T^2 \cos \left(2 \theta _1\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(2 \theta _2\right) +6 P_T^2 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) \sin \left(4 \theta _2\right) \end{aligned}

      \begin{aligned} &-2 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin \left(4 \theta _2\right)+3 \cos \left(2 \theta _1\right) \sin \left(4 \theta _2\right) -3 P_T^2 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(4 \theta _2\right)\\ &-P_T^2 \cos \left(2 \theta _1\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(4 \theta _2\right) +12 \cos \left(2 \theta _2\right) (2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &+\left(P_T^2 \cos \left(2 \phi _1\right)-1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right)) +4 \cos \left(4 \theta _2\right) (2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &+\left(P_T^2 \cos \left(2 \phi _1\right)-1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right))\} -7 x \cos \Delta _1 \{4 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) \sin \left(2 \theta _2\right) P_T^2 \\ &-2 \cos \left(2 \theta _1\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(2 \theta _2\right) P_T^2-6 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(2 \theta _2\right) P_T^2 -18 \cos \left(2 \phi _1\right) \sin ^2\left(\theta _1\right) \sin \left(4 \theta _2\right) P_T^2\\ &+3 \cos \left(2 \theta _1\right) \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(4 \theta _2\right) P_T^2 +9 \cos \left(2 \phi _1\right) \cos \left(2 \phi _2\right) \sin \left(4 \theta _2\right) P_T^2+4 \cos \left(\theta _1\right) (3 \sin \left(4 \theta _2\right)\\&-2 \sin \left(2 \theta _2\right)) \sin (2 \phi _1) \sin (2 \phi _2) P_T^2 -4 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin \left(2 \theta _2\right)+2 \left(\cos \left(2 \theta _1\right)+3\right) \sin \left(2 \theta _2\right)\\&+6 \cos \left(2 \phi _2\right) \sin ^2\left(\theta _1\right) \sin \left(4 \theta _2\right) -9 \cos \left(2 \theta _1\right) \sin \left(4 \theta _2\right)-3 \sin \left(4 \theta _2\right)+4 \cos \left(2 \theta _2\right) [2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right) P_T^2 \\ &+\left(P_T^2 \cos \left(2 \phi _1\right)-1\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right)]+12 \cos \left(4 \theta _2\right) [\left(1-P_T^2 \cos \left(2 \phi _1\right)\right) \cos \left(\phi _2\right) \sin \left(2 \theta _1\right) \\ &-2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right)]\}\} a_{1,0}^2 b_{1,0}^2,\\ r^0_0 r^2_2=\; & \frac{3 x y}{32 \sqrt{2}} a_{1,0}^2 b_{1,0}^2 \cos \left(\Delta _2\right) \{2 \sin ^2\left(\theta _1\right) \left(4 \cos \left(2 \theta _2\right)+3 \cos \left(4 \theta _2\right)+9\right) \cos \left(2 \phi _2\right) +4 \sin ^2\left(\theta _2\right) (3 \left(\cos \left(2 \theta _2\right)+3\right) \\&+\cos \left(2 \theta _1\right) \left(9 \cos \left(2 \theta _2\right)+11\right)) +P_T^2 \cos \left(2 \phi _1\right) [\left(\cos \left(2 \theta _1\right)+3\right) \left(4 \cos \left(2 \theta _2\right)+3 \cos \left(4 \theta _2\right)+9\right) \cos \left(2 \phi _2\right) \\&+4 \sin \left(2 \theta _1\right) \left(2 \sin \left(2 \theta _2\right)+3 \sin \left(4 \theta _2\right)\right) \cos \left(\phi _2\right)+8 \sin ^2\left(\theta _1\right) \sin ^2\left(\theta _2\right) \left(9 \cos \left(2 \theta _2\right)+11\right)] +4 P_T^2 \cos \left(\theta _1\right) (4 \cos \left(2 \theta _2\right)\\ &+3 \cos \left(4 \theta _2\right)+9) \sin (2 \phi _1) \sin (2 \phi _2) -4 \left(2 \sin \left(2 \theta _2\right)+3 \sin \left(4 \theta _2\right)\right) \left(\sin \left(2 \theta _1\right) \cos \left(\phi _2\right)-2 P_T^2 \sin \left(\theta _1\right) \sin \left(2 \phi _1\right) \sin \left(\phi _2\right)\right)\}. \end{aligned}

      (B3)
    C.   Monte Carlo Simulation and Fitting Results of the Angular Distributions
    • Figure C1.  (color online) {\mathrm{d}N}/{\mathrm{d}\cos\theta_1} , {\mathrm{d}N}/{\mathrm{d}\cos\theta_3} , and {\mathrm{d}N}/{\mathrm{d}\phi_1} distributions versus \cos\theta_1 , \cos\theta_3 , and \phi_1 in \psi(2S)\to \gamma \chi_{c0} and \omega \to \pi^+ \pi^- \pi^0 from \chi_{c0} \to \gamma \omega decays. Dots with error bars are filled with MC events, and the blue solid curve represents the fit.

      Figure C2.  (color online) {\mathrm{d}N}/{\mathrm{d}\cos\theta_1} , {\mathrm{d}N}/{\mathrm{d}\cos\theta_3} , and {\mathrm{d}N}/{\mathrm{d}\phi_1} distributions versus \cos\theta_1 , \cos\theta_3 , and \phi_1 in \psi(2S)\to \gamma \chi_{c0} and \rho^0 \to \pi^+ \pi^- from \chi_{c0} \to \gamma \rho decays. Dots with error bars are filled with MC events, and the blue solid curve represents the fit.

      Figure C3.  (color online) {\mathrm{d}N}/{\mathrm{d}\cos\theta_i}, i=1,2,3 , and {\mathrm{d}N}/{\mathrm{d}\phi_1} distributions versus \cos\theta_i and \phi_1 in \psi(2S)\to \gamma \chi_{c1} , \chi_{c1} \to \gamma \rho , and \rho^0 \to \pi^+ \pi^- decays. Dots with error bars are filled with MC events, and the blue solid curve represents the fit.

      Figure C4.  (color online) {\mathrm{d}N}/{\mathrm{d}\cos\theta_i}, i=1,2,3 , and {\mathrm{d}N}/{\mathrm{d}\phi_1} distributions versus \cos\theta_i and \phi_1 in \psi(2S)\to \gamma \chi_{c1} , \chi_{c1} \to \gamma \omega , and \omega \to \pi^+ \pi^- \pi^0 decays. Dots with error bars are filled with MC events, and the blue solid curve represents the fit.

      Figure C5.  (color online) Fits to the angular distributions of \cos\theta_i (i=1,2,3) and {\mathrm{d}N}/{\mathrm{d}\phi_1} versus \cos\theta_i and \phi_1 in \psi(2S)\to \gamma \chi_{c2} , \chi_{c2} \to \gamma \rho , and \rho^0 \to \pi^+ \pi^- decays. Dots with error bars represent MC events, and the blue solid curve represents the fit.

      Figure C6.  (color online) {\mathrm{d}N}/{\mathrm{d}\cos\theta_i}, i=1,2,3 , and {\mathrm{d}N}/{\mathrm{d}\phi_1} distributions versus \cos\theta_i and \phi_1 in \psi(2S)\to \gamma \chi_{c2} , \chi_{c2} \to \gamma \omega , and \omega \to \pi^+ \pi^- \pi^0 decays. Dots with error bars are filled with MC events, and the blue solid curve represents the fit.

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