模型参数对奇异星性质的影响

用有效质量口袋模型描述奇异夸克物质,研究了耦合常数和口袋常数的选取对奇异夸克物质的状态方程及奇异星性质的影响.结果表明,随着耦合常数和口袋常数的增大,奇异夸克物质的状态方程变软,相应的奇异星的引力质量和对应的半径均变小.当耦合常数从0.5增大到2.0时,奇异星的质量从1.43M_⊙(M_⊙=1.99×10³⁰ kg)减小到1.25M_⊙,相应的半径由8.3 km减小到7.7 km;当口袋常数B^1/4由160 MeV增大到175 MeV时,奇异星的质量和半径分别由1.47M_⊙和8.6 km减小到1.22M_⊙和7.4 km.这说明奇异夸克物质及奇异星的性质明显依赖于模型参数的取值. 关键词： 模型参数 奇异星 状态方程 质量-半径关系     

Study of the B_c→B_sπ decay with the perturbative QCD approach

The Bc→Bsπ decay is studied with the perturbative QCD approach. Three types of wave functions for Bsmeson are considered.The transition form factor FBc→Bs0(0) and the branching ratio Br(Bc→Bsπ)aresensitivetothemodelofthe Bsmeson wave functions.With appropriate inputs, our estimate on Br(Bc→Bsπ) is comparable with the recent LHCb measurement. A clear signal of Bc→Bsπ decay should be easily observed at the Large Hadron Collider.     

Study of D_s~±→μ~±V_μ at Belle

We present a preliminary measurement of the B(D_s→μν_μ)with the Belle experiment at the KEKB collider.We select D~s→μV_μdecays with a method that provides a high-purity of the selected sample and an absolute measurement of the branching fraction.The results are based on a data sample of 550 fb~(-1)and are compared to similar measurements by other experiments as well as to the predictions of LQCD.We conclude with short prospects for improvements in the accuracy of the measurement.     

有限温度下的二维暗能量星模型

研究了具有奇异物质作用的二维暗能量星模型,推导出了场方程和星体平衡方程;并获得了一些解析解,计算出了星体质量.另外,还研究了温度对星体质量的影响,发现几种情况下星体总质量都具有上限. 关键词： 暗能量星 奇异物质 有限温度     

Accelerator Disaster Scenarios, the Unabomber, and Scientific Risks

The possibility that experiments at high-energy accelerators could create new forms of matter that would ultimately destroy the Earth has been considered several times in the past quarter century. One consequence of the earliest of these disaster scenarios was that the authors of a 1993 article in Physics Today who reviewed the experiments that had been carried out at the Bevalac at Lawrence Berkeley Laboratory were placed on the FBI’s Unabomber watch list. Later, concerns that experiments at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory might create mini black holes or nuggets of stable strange quark matter resulted in a flurry of articles in the popular press. I discuss this history, as well as Richard A. Posner’s provocative analysis and recommendations on how to deal with such scientific risks. I conclude that better communication between scientists and nonscientists would serve to assuage unreasonable fears and focus attention on truly serious potential threats to humankind. Joseph I. Kapusta: Joseph I. Kapusta received his Ph.D. degree at the University of California at Berkeley in 1978 and has been on the faculty of the School of Physics and Astronomy at the University of Minnesota since 1982. He is the author of over 150 papers in refereed journals and conference proceedings and of Finite Temperature Field Theory (Cambridge University Press, 1989; second edition with Charles Gale, 2006).     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1(13D1) and the 3(13D3) Ds agree well with those of recently observed Ds1(2700)± and DsJ(2860), respectively.     

Study of the process e+e-→π+π-π0π0 at energies √s< 1 GeV

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-π0π0was 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.     

Exclusive meson production at HERMES

The exclusive electroproduction of pseudoscalar and vector mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target.The results are compared to calculations based on generalized parton distributions,some of which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.     

K－p scattering and hyperon excitations in a chiral quark model

A chiral quark-model approach is employed to study theˉ KN scattering at low energies.The processes of Kˉp → Σ 0 π 0,Λπ 0 andˉ K 0 n at P K 800 MeV/c （i.e.the center mass energy W 1.7 GeV） are investigated.The analysis shows that the Λ（1405）S 01 dominates the processes Kˉp → Σ 0 π 0,ˉ K 0 n in the energy region considered here.Around P K 400 MeV/c,the Λ（1520）D 03 is responsible for a strong resonant peak in the cross section of Kˉp → Σ 0 π 0 andˉ K 0 n.To reproduce the data,an unexpectedly large coupling for Λ（1520）D 03 to KN is needed.In contrast,the coupling for Λ（1670）S 01 to KN appears to be weak,which could be due to configuration mixings between Λ（1405）S 01 and Λ（1670）S 01 .By analyzing Kˉ p → Λπ 0,evidences for two low mass S-wave states,Σ（1480）S 11 and Σ（1560）S 11,seem to be available.With these two states,the reaction Kˉp →ˉ K 0 n can also be described well.However,it is difficult to understand the low masses of Σ（1480）S 11 and Σ（1560）S 11 .The s-channel amplitudes for Kˉp → Λπ 0 are also larger than the naive quark model expectations.The non-resonant background contributions,i.e.t-channel and/or u-channel,also play important roles in the explanation of the angular distributions due to amplitude interferences.     

Relativistic studies of the decay constants of S wave and P wave mesons

Relativistic corrections are important in hadronic physics since even for the heavy hadrons there are sizable relativistic corrections. Therefore one should use a relativistic model to describe the higher excited states. This note summarizes our predictions for the decay constants of the S wave and P wave heavy mesons by means of the instantaneous relativistic Bethe Salpeter equation （Salpeter equation）.