2010 Vol. 34, No. 6
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In this paper, I review recent progress in the study of the XYZ particles at Belle. I only focus on studies with charmonium and one or more light mesons in the final states. This covers the X(3872), X(3915), Y(4140), X(4350), and the charged Z states.
We report recent results on charmonium spectroscopy and decay from the CLEO-c experiment at the Cornell electron-positron storage ring accelerator, CESR. Most of the results are based on the analysis of 54 pb－1 of luminosity collected at the ψ(2S) resonance, corresponding to 27 M ψ(2S) decays. We concentrate on radiative decays of ψ(2S) and J/ψ, on two-body mesonic decay of χcJ, on hadronic decay of the hc, and on higher multipoles in the two-photon cascade ψ(2S)→γχcJ, χcJ→γJ/ψ.
Using ~14×106 ψ(2S) and ~58×106 J/ψ data collected at BESⅡ/BEPC, the branching fraction of ψ(2S)→Ω－Ω+ is measured with about 5σ statistical significance. The Λ electric dipole and Λ decay parameter are studied using the decay J/ψ→ΛΛ→pp π+π－. Using (106±3)×106 ψ(2S) decays collected at BESⅢ/BEPCⅡ, we have obtained some interesting physics results. The branching fractions of χcj→π0π0, ηη are measured with precision improved. The mass and width of hc(11P1) state, together with the branching fractions of Br(ψ(2S)→π0hc) and Br(hc→γηc) are the first measurements. Surprisingly, the decays of χc1→φφ, ωω, and ωφ are firstly observed in BESⅢ data.
The data collected by the KLOE Collaboration at the Frascati φ-factory DAΦNE from 2001 to 2006 have been used for extensive studies in meson spectroscopy. The decays of the scalar mesons a0(980) and f0(980) into two pseudoscalar mesons have been exploited to measure the relevant parameters of those resonances. The radiative decays φ→ηγ and η′γ have been used for the determination of the pseudoscalar mixing angle and to search for a possible gluonium content in the η′. The dynamics of the η→3π decay has been studied and the Dalitz Plot parameters have been measured. The large amount of η mesons produced allowed also to study interesting rare η decays.
P. Gauzzi (for the KLOE collaboration). KLOE results on scalar and pseudoscalar mesons[J]. Chinese Physics C, 2010, 34(6): 632-637. doi: 10.1088/1674-1137/34/6/004.
The BES-Ⅲ Detector is a very versatile multipurpose device located at the Institute of High Energy Physics (IHEP) in Beijing, China. Concerning the physics program it ties stringently up to the past BES and BES-Ⅱ experiments. Since start of the data taking in the middle of 2008 the accumulated dataset of 200・
106 J/ψ events and 100・106 ψ′ events already exceeds the world data on these resonances. In addition to studies of the charmonium systems the data offers great opportunity for investigations in the light hadron sector. In detail it will be reported about the confirmation of the enhancement in pp invariant mass in radiative J/ψ decays, the search for decays Y(2175)→ K*0K*0, observation of a charged κ± in K±π0 and observation of a new excited baryon N*(2065) decaying to pπ0 and charged conjugate. The first result is based on data taken by BES-Ⅱ and BES-Ⅲ, the latter three on data collected by BES-Ⅱ only.
This paper intends to shortly summarize the recent results on Spectroscopy, published from the BABAR Collaboration. The BABAR experiment is a B-factory, at SLAC, where asymmetric energy beams of electron-positron are accelerated and collide at the energy in the center of mass of Υ(4S). In 9 years of data taking, BABAR had collected 433 fb－1 equivalent luminosity on-peak-data at the Υ(4S) energy, 30 fb－1 data at the Υ(3S) energy, 15 fb－1 data at the Υ(2S) energy, and a scan around Υ(4S) was done, collecting 25 pb－1 every 5 MeV. Thanks to the high luminosity achieved, it is possible to perform high precision measurements, and spectroscopy studies. An update on the measurement of the state X(3872) will be given, as final result published by using the whole dataset available. Then, a new preliminary Y(4260) measurement is reported, and the study of the invariant mass J/ψ π+π－ in ISR events is shown, where no evidence of the state Y(4050) is highlighted. As conclusion, the results on the angular distribution analysis performed on the state Z(4430) are reported.
We report results of experiments performed with the KEDR detector at the VEPP-4M e+e－ collider. They include precise measurement of the D0 and D± meson masses, determination of the ψ(3770) resonance parameters, and a search for narrow resonances in e+e－ annihilation at center-of-mass energies between 1.85 and 3.1 GeV.
We discuss recent measurements of exclusive e+e－ cross sections for charmed hadron final states near threshold performed by Belle and BABAR. The results are based on a study of events with initial-state-radiation photons in a large data sample collected with the Belle and BABAR detectors at the Υ(4S) resonance and nearby continuum.
Experimental data from the PEP-II B-factory at 10.6 GeV center-of-mass (c.m.) energy, obtained via initial-state radiation (ISR) with the BABAR detector, are presented. The cross sections for many hadronic processes have been measured from the production threshold to 4—5 GeV of the e+e－ c.m. energy. The obtained data allow to study a number of intermediate states and determine the parameters of known resonances and their branching fractions. The exclusive cross section for some number of hadronic sub-processes are presented.
The new e+e－ storage ring, VEPP-2000, is being commissioned at Budker Institute of Nuclear Physics, Novosibirsk. Measurement of the total cross section e+e－→ hadrons in the whole VEPP-2000 energy range is one of the main goals of the new experiments. We discuss the goals of the measurement and the expected systematic errors.
The cross section for electron-positron annihilation into hadrons allows for a precise determination of the strong coupling constant and the charm- and bottom-quark masses. Recent theoretical and experimental results are presented with emphasis on the energy region accessible by B-meson factories and below.
In an experiment with the Spherical Neutral Detector at VEPP-2M collider the cross section of the process e+e－→π+π－π0π0 was measured. At energies √s<920 MeV this cross section was measured for the first time. The energy dependence of the cross section is well discribed by the vector dominance model with contributions from ρ, ρ′, ρ′′ mesons. The decay probability ρ→π+π－π0π0 was found to be Bρ=(1.60±0.74±0.18)×10－5. The upper limit for the decay ω→π+π－π0π0 was improved by two orders of magnitude compared to the previous measurements and is Bω<2×10－4 at 90% confidence level.
The KLOE experiment at the φ-factory DAΦNE has measured the pion form factor in the range between 0.1
We present a precise BABAR measurement on the cross section of the process e+e－→π+π－(γ) from threshold to an energy of 3 GeV with the initial state radiation (ISR) technique, using 232 fb－1 of data collected with the BABAR detector at e+e－ center-of-mass energies near 10.58 GeV. The ISR luminosity is determined from a study of the leptonic process e+e－→μ+μ－γ(γ). The leading-order hadronic contribution to the muon magnetic anomaly calculated using the
ππ cross section measured from threshold to 1.8GeV is (514.1±2.2(stat)±3.1(syst))×10－10.
We show that a VMD based theoretical input allows for a significantly improved accuracy for the hadronic vacuum polarization of the photon which contributes to the theoretical estimate of the muon g－2. We also show that the only experimental piece of information in the τ decay which cannot be accounted for within this VMD framework is the accepted value for Br(τ→ππντ), while the τ spectum lineshape is in agreement with expectations from e+e－ annihilations.
We review recent developments concerning the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. We first discuss why fully off-shell hadronic form factors should be used for the evaluation of this contribution to the g－2. We then reevaluate the numerically dominant pion-exchange contribution in the framework of large-NC QCD, using an off-shell pion-photon-photon form factor which fulfills all QCD short-distance constraints, in particular, a new short-distance constraint on the off-shell form factor at the external vertex in g－2, which relates the form factor to the quark condensate magnetic susceptibility in QCD. Combined with available evaluations of the other contributions to hadronic light-by-light scattering this leads to the new result aμLbyL; had=(116±40)×10－11, with a conservative error estimate in view of the many still unsolved problems. Some potential ways for further improvements are briefly discussed as well. For the electron we obtain the new estimate aeLbyL; had=(3.9±1.3)×10－14.
We describe some recent results on isospin breaking corrections which are of relevance for predictions of the leading order hadronic contribution to the muon
anomalous magnetic moment aμhadLO when using τ lepton data. When these corrections are applied to the new combined data on the π±π0 spectral function, the prediction for aμhadLO based on τ lepton data gets closer to the one obtained using e+e－ data.
Results on the lowest-order hadronic vacuum polarization contribution to the muon magnetic anomaly are presented. They are based on the latest published experimental data used as input to the dispersion integral. Thus recent results on τ→ντππ0 decays from Belle and on e+e－ annihilation to π+π－ from BABAR and KLOE are included. The new data, together with improved isospin-breaking corrections for τ decays, result into a much better consistency among the different results. A discrepancy between the Standard Model prediction and the direct g－2 measurement is found at the level of 3σ.
We update our Standard Model predictions for g－2 of the muon and for the hadronic contributions to the running of the QED coupling, Δα(5)had(MZ2). Particular emphasis is put on recent changes in the hadronic contributions from new data in the 2π channel and from the energy region just below 2 GeV.
After a brief review of the muon g－2 status, we discuss hypothetical errors in the Standard Model prediction that might explain the present discrepancy with the experimental value. None of them seems likely. In particular, a hypothetical increase of the hadroproduction cross section in low-energy e+e－ collisions could bridge the muon g－2 discrepancy, but it is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 135 GeV which, in conjunction with the experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.
The New Muon (g－2) Collaboration at Fermilab has proposed to measure the
anomalous magnetic moment of the muon, aμ, a factor of four better than was done in E821 at the Brookhaven AGS, which obtained aμ=[116 592 089 (63)]× 10－11±0.54 ppm. The last digit of aμ is changed from the published value owing to a new value of the ratio of the muon-to-proton magnetic moment that has become available. At present there appears to be a difference between the Standard-Model value and the measured value, at the ~3 standard deviation level when electron-positron annihilation data are used to determine the lowest-order hadronic piece of the Standard Model contribution. The improved experiment, along with further advances in the determination of the hadronic contribution, should clarify this difference. Because of its ability to constrain the interpretation of discoveries made at the LHC, the improved measurement will be of significant value, whatever discoveries may come from the LHC.
A new measurement of the anomalous magnetic moment of the positive muon aμ is proposed with a novel technique utilizing an ultra-cold muon beam accelerated to 300 MeV/c and a 66 cm-diameter muon storage ring without focusing-electric field. This measurement will be complimentary to the previous measurement that achieved 0.54 ppm accuracy with the magic energy of 3.1 GeV in a 14 m diameter storage ring. The proposed experiment aims to achieve the sensitivity down to 0.1 ppm.
Recent results on radiative K± decays from the NA48/2 experiment are reported. From the full NA48/2 data set, about a million K±→π±π0γ decays were reconstructed. Based on this sample, the first measurement of the interference between direct photon emission and inner bremsstrahlung in K±→π±π0γ decays was performed. Stringent limits on CP violation in this decay were also set. In addition, a precise measurement of the branching fraction of K±→π±γγ is presented. This measurement was based on a data sample of more than 1000 event candidates. Also the related decay K±→π±π0e+e－γ has first been observed. Results of the measurement of the decay rate and the decay parameter c are summarized.
I show that the CP-violating asymmetry in K0 vs K0→π+π－π0 decays differs from that in KL→π+π－, KL→π0π0 or the semileptonic KL transitions, if there exists CPT violation in K0-K0 mixing. A delicate measurement of this difference at a super flavor factory (e.g., the φ factory) will provide us with a robust test of CPT symmetry in the neutral kaon system.
Based on the data collected with the H1 and ZEUS detectors at HERA, recent results on strangeness, charm and beauty production in ep collision are presented.
Several recent CLEO-c results on hadronic decays of charm mesons are reviewed. Topics include measurements of precision branching fractions for exclusive modes, investigations of inclusive rates, and analyses of Dalitz plots. In addition, the quantum correlations of the DD pairs produced at the ψ(3770) are exploited to measure phase information that is of current interest for both D and B physics.
The D0-D0 mixing at Belle in different modes with corresponding methods is reported in this paper, there is a clear evidence for non-zero y D0 mixing parameter, and the measurement of D0 mixing parameter x is still a challenge. CP violation in the decays is not observed. Branching fractions of other charm decays are presented.
Studies in which BABAR data have shown evidence for mixing in the neutral charm meson system are presented. A new measurement of the lifetime difference parameter yCP=(1.16±0.22±0.18)% is described. Results are also presented from a systematic study of DK and D*K invariant mass distributions from a 470 fb－1 sample of asymmetric e+e－ interactions recorded by the BABAR detector at the PEP-Ⅱ storage rings. A new charmed-strange meson has been observed with mass [3044±8stat(+30－5)syst]MeV/c2 and width [239±35stat(+46－42)syst]MeV/c2.
We present the physics program of the open charm and heavy cc states above the DD production energy threshold, which will be studied with the BES-Ⅲ detector at the BEPC-Ⅱ collider in the coming years. Based on some full Monte Carlo simulations with the BES-Ⅲ detector, we predict the accuracy levels on measuring some physical quantities related to D0, D+ and D+s decays as well as some non-charmed decays of the heavy cc states.
Studies of γγ interactions are performed with the KLOE detector, without tagging of the outgoing e+e－. The data sample is from an integrated luminosity of 240 pb－1. It was collected at the φ-factory DAΦNE with e+e－ beams colliding at √s~1 GeV, below the φ resonance peak. We present preliminary results concerning the observation of the γγ→η process and the evidence for γγ→π0π0 production at low π0π0 invariant masses.
We review recent measurements of pure neutral final state production in the two-photon processes, γγ→π0π0 and ηπ0 at the Belle experiment. In the lower invariant mass region, properties of light scalar mesons are measured by partial wave analysis. In the higher energy region the total and differential cross section are compared with QCD models.
The surprising thing is that arising almost 50 years ago from the linear sigma model (LSM) with spontaneously broken chiral symmetry, the light scalar meson problem has become central in the nonperturbative quantum chromodynamics (QCD) for it has been made clear that LSM could be the low energy realization of QCD. First we review briefly signs of four-quark nature of light scalars. Then we show that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic P wave tensor qq mesons that are produced via two-quark transitions γγ→qq. Thus we get new evidence of the four-quark nature of these states.
We present measurements of the γγ*→π0 transition form factor for the momentum transfer range Q2=4—40 GeV2 and the γγ*→ηc transition form factor for the range Q2=2—50 GeV2. The current status of measurements of the meson-photon transition form factors for the η and η′ mesons is discussed. The results of the measurement of the ηc mass, total and two-photon widths are also presented.
A short review of experimental and theoretical results on the large angle cross sections "γγ→twomesons" and the form factors γ*γ→P=π, η, η′ is given.
We present a study of the inclusive photon spectra from 5.9 million J/ψ decays collected with the KEDR detector at the VEPP-4M e+e－ collider. We measure the branching fraction of radiative decay J/ψ→ηcγ, ηc width and mass. Our preliminary results are: M(ηc)=2979.4±1.5±1.9 MeV/c2, Γ(ηc) = 27.8±5.1±3.3 MeV, B(J/ψ→ηcγ)=(2.34±0.15±0.40)%.
We report a new precise determination of the leptonic widths of the J/psi meson performed with the KEDR detector at the VEPP-4M e+e－ collider. The measured values of the J/psi parameters are: Γee×Γee/Γ=0.3323±0.0064 (stat.)±0.0048(syst.) keV, Γee×Γμμ/Γ=0.3318±0.0052 (stat.)±0.0063 (syst.) keV. Assuming eμ universality and using the table value of the branching ratios the leptonic Γll=5.59±0.12 keV width and the total Γ=94.1±2.7 keV widths were obtained. We also discuss in detail a method to calculate radiative corrections at a narrow resonance.
We analyze the φ meson production in e+e－→ωπ0 as a probe for studying the isospin violation mechanisms. By clarifying the dynamic sources causing the isospin violation, we succeed in quantifying those mechanisms with the help of the recent KLOE data. Hence, the φ→ωπ0 branching ratio is extracted. We find that apart from the electromagnetic (EM) transitions, the strong transition via intermediate kaon loops plays an important role in understanding the cross section and its lineshape.
In this proceeding, we propose to directly measure the a00(980)-f0(980) mixing in J/ψ→φ f0(980)→φa00(980) and χc1→π0φa00(980)→π0f0(980) with the upgraded Beijing Electron Positron Collider(BEPCII) with BESIII detector. We show that a narrow peak of about 8 MeV will be produced by the φa00(980)-f0(980) mixing, and the predominant feature makes it standing out from the background contributions. The predicted branching ratios for these two reactions are both expected to be about O(10－6), which is unambiguously accessible with 109 J/ψ and 3×108 χc1 at BESⅢ.
We discuss interference effects important for the form factors extraction in the vicinity of J/ψ and ψ(2S) resonances in combination with resonance parameters determination. The implementation to the Monte Carlo event generator PHOKHARA of the J/ψ and ψ(2S) contributions to the muon, pion and kaon pairs production associated with a photon at next-to-leading order is also described.
BABAR has measured with unprecedented accuracy the e+e－→pp and e+e－→ΛΛ cross sections by means of the initial state radiation technique, which has the advantages of good efficiency, good energy resolution and full angular acceptance, even exactly at threshold. A peculiar feature of these cross sections is their non-vanishing values at threshold. In the case of charged baryons, this phenomenon is expected according to the Coulomb interaction between the outgoing baryon and antibaryon. Once this Coulomb enhancement factor is taken into account, the striking result is achieved that the proton form factor at threshold is |Gp(4 M2p)| = 1, that is what is expected for pointlike fermion pairs, in spite of the proton structure. However a Coulomb enhancement factor is not expected for neutral fermions, likely in contradiction with the BABAR data. Qualitatively this behaviour is consistent with Coulomb interactions at the valence quark level.
The high intensity and high energy antiproton beams which will be produced at
FAIR open the possibility to determine time-like electromagnetic form factors
in a wide kinematical range, through the annihilation reaction: p+p→e++e－. The status of the proposed experiment as well as the expected results are presented on the basis of realistic simulations. The impact of these measurements on the understanding of the nucleon structure, of the asymptotic properties of form factors and of the reaction mechanism are discussed using model independent statements based on symmetry properties of the strong and electromagnetic interactions in connection with space-like data.
The two two-photon exchange corrections to the unpolarized cross section and polarized observable PT, PL in elastic ep scattering are discussed in a simple hadronic model. Comparing with previous results, the Δ contribution are re-analysed. And the similar corrections in e+e－→pp are also discussed.
Analyticity of nucleon form factors allows to derive sum rules which, using space-like and time-like data as input, can give unique information about behaviors in energy regions not experimentally accessible. Taking advantage from new time-like data on proton-antiproton differential cross section and hence the possibility to separate electric and magnetic form factors also in the time-like region, we verify the consistency of the asymptotic behavior predicted by the perturbative QCD for the proton magnetic form factor.
A Monte-Carlo Generator Photon Jets (MCGPJ) to simulate Bhabha scattering as well as production of two charged muons and two photons events is discussed. The theoretical precision of the cross sections with radiative corrections (RC) is estimated to be smaller than 0.2%. The Next Leading Order (NLO) radiative corrections proportional to α are treated exactly, whereas the all logarithmically enhanced contributions, related to photon jets emitted in the collinear region, are taken into account in frame of the Structure Function approach. Numerous tests of the MCGPJ as well as a detailed comparison with other MC generators are presented.
The status and accuracy of the precision Monte Carlo generators used for luminosity measurements at flavour factories is reviewed. It is shown that, thanks to a considerable, long-term effort in tuned comparisons between the predictions of independent programs, as well as in the validation of the generators against the presently available calculations of the next-to-next-to-leading order QED corrections to Bhabha scattering, the theoretical accuracy reached by the most precise tools is of about one per mille. This error estimate is valid for realistic experimental cuts, appears to be quite robust and is already sufficient for very accurate luminosity measurements. However, recent progress and possible advances to further improve it are also discussed.
PHOTOS Monte Carlo is widely used for simulating QED effects in decay of intermediate particles and resonances. It can be easily connected to other main process generators. In this paper we consider decaying processes γ*→π+π－(γ) and K±→π+π－e±ν (γ) in the framework of Scalar QED. These two processes are interesting not only for the technical aspect of PHOTOS Monte Carlo, but also for precision measurement of αQED(MZ), g－2, as well as ππ scattering lengths.
We discuss recent results on τ lepton physics obtained at the BABAR, Belle and KEDR detectors. They include tests of lepton universality using new measurements of τ lepton mass and some branching fractions. Also described are selected results on τ lepton hadronic decays coming from BABAR and Belle.
We report recent results of searches for lepton flavor violation and second class current in decays of τ leptons using the data sample collected in the Belle experiment at the KEKB electron-positron asymmetric-energy collider.
The BABAR experiment has now completed data taking and with an integrated luminosity of 531 fb－1 of e+e－ collision data has recorded some 480 million tau-pair events. Various studies of suppressed, rare and forbidden decays of the tau have been conducted, including searches for high-multiplicity decays, for second-class hadronic weak currents, and for lepton-flavour violation.
The beam energy measurement system at BEPCII is composed of there parts: laser source and optics system, laser-electron interaction system and High Purity Germanium (HPGe) detector system. The special components and construction of each part are introduced, especially about radiation background measurement in the storage ring, which is of great importance for the safe commissioning of HPGe detector.
In a few months the KLOE-2 detector is expected to start data taking at the upgraded DAΦNE φ-factory of INFN Laboratori Nazionali di Frascati. It aims to collect 25 fb－1 at the φ(1020) peak, and about 5 fb－1 in the energy region between 1 and 2.5 GeV. We review the status and physics program of the project.
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