2010 Vol. 34, No. 8
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One of the first physics results that CMS will hopefully obtain will be the analysis of heavy quarkonium productions, including the Υ cross-section measurement. Since the Υ production cross-section from p-p collisions is expected to be relatively large, the analysis should be viable with rather small datasets which will be available soon after the start-up of the LHC. This paper describes the methods and plans for measuring the differential cross-section of Υ (1S)→μ+μ－ production, by using data to be collected from the CMS detector in the first LHC run. In this study, about 80 thousand Υ are reconstructed corresponding to an integrated luminosity of 6.4 pb－1 in 10 TeV proton-proton collisions by using Monte Carlo data. The precision of this measurement is estimated to be about 16%, which is limited by the systematic errors.
A combined fit is performed to the BABAR and Belle measurements of the e+e－→φπ+π－ and φf0(980) cross sections for center-of-mass energy between threshold and 3.0 GeV. The resonance parameters of the φ(1680) and Y(2175) are determined. The mass is (1681+10－12) MeV/c2 and the width is (221+34－24) MeV/c2 for the φ(1680), and the mass is (2117+59－49) MeV/c2 and the width is (164+69－80) MeV/c2 for the Y(2175). This information will shed light on the understanding of the nature of the excited φ and Y states observed in e+e－ annihilation.
The recently observed X(3872) resonance, which is difficult to assign a conventional cc charmonium state in the quark model, may be interpreted as a molecular state. Such a molecular state is a hidden flavor four quark state because of its charmonium-like quantum numbers. The s-channel one gluon exchange is an interaction which only acts in the hidden flavor multi-quark system. In this paper, we will study the X(3872) and other similiar hidden flavor molecular states in a quark model by taking into account the s-channel one gluon exchange interaction.
We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγ collisions at the International Linear Collider (ILC). We find that the cross section for ttht in γγ collisions is at the level of a few fb with the c.m. energy √s=1000 GeV, which is consistent with the results of the cross section of ttH in the standard model and the cross section of tth in the minimal supersymmetric standard model. It should be clear that hundreds of to thousands of ht per year can be produced at the ILC. This process of γγ→ttht is really interesting in testing the standard model and searching the signs of technicolor.
Abundant ψ′ events have been collected at the Beijing Electron Positron Collider-Ⅱ (BEPCⅡ) that could undoubtedly provide us with a great opportunity to study the more attractive charmonium decays. As has been noticed before, in the process of J/ψ decaying to the baryonic final states, pK－Λ, the evident Λ* and N* bands have been observed. Similarly, by using the product of χcJ from ψ′ radiative decay, we may confirm this or find some extra new resonances. χc0's data samples will be more than χc1,2, taking into account the larger branching ratio of ψ′→γχc0. Here, we provide explicit partial wave analysis formulae for the very interesting channel ψ′→γχc0→γpK－Λ.
The gl(1|1) supersymmetric vertex model with domain wall boundary conditions (DWBC) on an N×N square lattice is considered. We obtain the reduction formulae for the two-point boundary correlation functions of the model.
Using the method based on Random Matrix Theory (RMT), the results for the nearest-neighbor distributions obtained from the experimental data on 12C-C collisions at
4.2 AGeV/c have been discussed and compared with the simulated data on 12C-C collisions at 4.2 AGeV/c produced with the aid of the Dubna Cascade Model. The results show that the correlation of secondary particles decreases with an increasing number of charged particles Nch. These observed changes in the nearest-neighbor distributions of charged particles could be associated with the centrality variation of the collisions.
The proton-rich isotope 146Ho was produced via the fusion-evaporation reaction 92Mo (58Ni, 3p1n). The β-delayed proton decay of 146Ho was studied by proton-γ coincidence measurements using a He-jet tape transport system. The γ-transitions in 145Tb following the proton emissions were observed, and the β-delayed proton branching ratios to the final states in the grand-daughter nucleus 145Tb were determined. According to the relative branching ratios, the ground-state spin of 146Ho has been proposed and the possible configuration discussed.
Taking the conservation of baryon number into account in a non-uniform flow model, the rapidity distribution of the net protons at the LHC is predicted. The energy dependence of the rapidity distribution, baryon stopping and collective flow from BNL/AGS to CERN/LHC are systematically investigated.
In this paper, considering the quantum effect of electrons in a super-strong magnetic field, the influence of a super-strong magnetic field on the chemical potential of a non-zero temperature electron is analyzed, the rates of β decay under the super-strong magnetic field are studied, and then we compare them with the case without a magnetic field. Here, the nucleus 63Co is investigated in detail as an example. The results show that a magnetic field that is less than 1010T has little effect on the electron chemical potential and β decay rates, but the super-strong magnetic field that is greater than 1010T depresses the electron chemical potential and improves the β decay rates clearly.
The potential energy surfaces of even-even 142—156Ba are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that for the ground states, 142Ba is near spherical, 156Ba well quadrupole-deformed, and in between 144－154Ba octupole deformed. In particular, the nuclei 148,150Ba with N=92, 94 have the largest octupole deformations. By including the octupole degree of freedom, energy gaps N=88, N=94 and Z=56 near Fermi surfaces for the single-particle levels in 148Ba with β2~0.26 and β3~0.17 are found. Furthermore, the performance of the octupole deformation driving pairs (ν2f7/2, ν1i13/2) and (π2d5/2, π1h11/2) is demonstrated by analyzing the single-particle levels near Fermi surfaces in 148Ba.
The possibility of the experiment for constraining the symmetry energy Esym(ρ) at supra-densities via π－/π+ probe on the external target experiment of phase I ( ETE(I) ) with part coverage at forward angle at HIRFL-CSR is studied for the first time by using the isospin and momentum dependent hadronic transport model IBUU04. Based on the transport simulation with Au+Au collisions at 400 MeV/u, it is found that the differential π－/π+ ratios are more sensitive to Esym(ρ) at forward angles in laboratory reference, compared with the total yield ratio widely proposed. The insufficient coverage at lower transverse momentum maintains the sensitivity of the dependence of π－/π+ ratio on the Esym(ρ) at high density, indicating that the ETF (I) under construction in Lanzhou provides the possibility of performing the experiment for probing the asymmetric nuclear equation of state.
By employing the Glauber model, we give the centrality dependences of the numbers of participants and binary nucleon-nucleon collisions in nucleus-nucleus collisions. By taking into account the energy loss of the participants in their multiple collisions, we then present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as a function of beam energy and impact parameter. Finally, we analyze the centrality dependence of the pseudorapidity of the charged particles in Au+Au collisions at energies from √sNN=19.6 to 200 GeV. The theoretical results are in good agreement with the experimental observations of the RHIC-PHOBOS collaboration.
In the construction of a large area neutron detector (neutron wall) that is used to detect neutrons at GeV energies, the performances of all the sampling paddle modules prepared for the neutron wall are investigated with a specially designed test bench. Tested by cosmic rays, an average intrinsic time resolution of 222.5 ps is achieved at the center of the modules. The light attenuation length and the effective speed of the light in the module are also investigated.
This study uses Daya Bay RPCs operating in streamer mode to investigate gas mixtures of at least 50% argon, at most 6% isobutane, and with small amounts of SF6. Isobutane is reduced to 2% without degradation of performance, and SF6 reduces the noise rate and current, as well as the signal size. This study provides quantitative relationships between basic RPC operating parameters and various gas compositions.
Physical designing of the pre-chopper in CSNS LEBT is carried out, which includes the deflecting voltage, the length and the width of the deflecting plates, and the gap between the deflecting plates. The most outstanding feature of the design is that both the gap and the width vary with the beam envelope size. So both the requried deflecting voltage and the loaded capacitance are lowered. In order to avoid destruction of the space charge neutralization by the pre-chopper in the whole LEBT, an electron-trapping electrode is arranged to confine the electrostatic field of the pre-chopper to the local area. To examine the reliability of the pre-chopping design in CSNS LEBT, a similar pre-chopping design in ADS RFQ LEBT is set up and an experiment on the pre-chopper is prepared. 3-dimensional simulations are carried out to determine the loaded capacitance and the applied voltage of
the electron-trapping electrode.
As a promising kind of high current cold cathode, the Ferroelectric Cathode (FEC) has several significant advantages, such as a controllable trigger time, lower vacuum requirement and large emitting area fabricability. The emitting current density of the FEC fabricated at Tsinghua University was more than 200 A/cm2. In order to make the ferroelectric cathode into practical applications, a high current density diode using a ferroelectric cathode was designed, based on the PIC simulation. The performance of the FEC diode was investigated experimentally. When the applied diode voltage was 60 kV, a current density of more than 250 A/cm2 was obtained, and the current density distribution was also measured.
In order to realize high energy density physics and plasma physics research at HIRFL-CSR, a magnetic alloy (MA)-loaded cavity has been studied. According to the theoretical calculation and simulation for the MA-loaded cavity, we achieved a better result. The MA-loaded cavity had a higher μQf value, with a higher shunt impedance and a higher accelerating gradient. The accelerating gradient was about 95 kV/m at 1.8003 MHz, 130 kV/m at 0.9000 MHz. Compared with the ferrite-loaded cavities that are used at HIRFL-CSR, with about 10 kV/m accelerating gradient, the MA-loaded cavity obviously has an advantage. The results of the theoretical calculation and the simulation, which meet the design requirements are in good agreement.
A new SSC (Separated Sector Cyclotron)-Linac is being designed to serve as an injector for
the SSC at the HIRFL (Heavy Ion Research Facility Lanzhou). The beam intensity at the LEBT
(Low Energy Beam Transport) for the heavy ions after the selection is typically low and the space charge effects are inconspicuous. The space charge effects become obvious when the beam current increases to a few hundred microamperes. The emittance growth deriving from the space charge effects may be particularly troublesome for the following linac and cyclotron. An optical system containing three solenoids has been designed for the LEBT to limit the beam emittance and to avoid the unnecessary beam loss in the cyclotron, as well as for the purpose of immunizing the LEBT emittance growth due to the space charge effects. The results of the PIC (Particle-In-Cell) mode simulation illustrate that this channel could limit the beam emittance growth and increase the beam brightness.
In this paper, by using the ``frequency up-conversion'' principle with a high gain harmonic generation free electron laser and an external seed laser, we consider the possibility of modulating a relativistic electron beam on the attosecond scale, so that it can produce
coherent spontaneous radiation from the deep ultraviolet to the hard X-ray spectral region with a very short radiator. Analytical estimation and three-dimensional numerical modeling show the great potential to reach ultra-high harmonics up to several thousand. For an electron bunch with the typical quality as in the free electron laser scheme and a seed laser with 800 nm wavelength, 0.8 nm attosecond trains with alterable duration and GW scale peak power are modeled. The output radiation exhibits good shot-to-shot stability, full coherence and perfect tuning ability between the discrete harmonics of the seed frequency.
The objective of this study is to investigate a high performance and lower cost compact gamma camera module for a multi-head small animal SPECT system. A compact camera module was developed using a thin Lutetium Oxyorthosilicate (LSO) scintillation crystal slice coupled to a Hamamatsu H8500 position sensitive photomultiplier tube (PSPMT). A two-stage charge division readout board based on a novel subtractive resistive readout
with a truncated center-of-gravity (TCOG) positioning method was developed for the camera. The performance of the camera was evaluated using a flood 99mTc source with a four-quadrant bar-mask phantom. The preliminary experimental results show that the image shrinkage problem associated with the conventional resistive readout can be effectively overcome by the novel subtractive resistive readout with an appropriate fraction subtraction factor. The response output area (ROA) of the camera shown in the flood image was improved up to 34%, and an intrinsic spatial resolution better than 2 mm of detector was achieved. In conclusion, the utilization of a continuous scintillation crystal and a flat-panel PSPMT equipped with a novel subtractive resistive readout is a feasible approach for developing a high performance and lower cost compact gamma camera.
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