Measurement of the Bottom Quark Contribution to Nonphotonic Electron Production in p plus p Collisions at root s=200 GeV

The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at root s = 200 GeV has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of p(T) >= 5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high p(T).

Understanding the branching ratios of chi(c1) -> phi phi,omega omega,omega phi observed at BES-III

In this work, we discuss the contribution of the mesonic loops to the decay rates of chi(c1) -> phi phi, omega omega, which are suppressed by the helicity selection rules and chi(c1) -> phi omega, which is a double- Okubo- ZweigIizuka forbidden process. We find that the mesonic loop effects naturally explain the clear signals of chi(c1) -> phi phi, omega omega decay modes observed by the BES Collaboration. Moreover, we investigate the effects of the omega - phi mixing, which may result in the order of magnitude of the branching ratio BR(chi(c1) -> omega phi) being 10(-7). Thus, we are waiting for the accurate measurements of the BR(chi(c1) -> omega omega), BR(chi(c1) -> phi phi) and BR(chi(c1) -> omega phi) which may be very helpful for testing the long- distant contribution and the omega - phi mixing in chi(c1) -> phi phi, omega omega, omega phi decays.

Spectra of identified high-p(T) pi(+/-) and p((p)over-bar ) in Cu + Cu collisions at root s(NN)=200 GeV

We report new results on identified (anti) proton and charged pion spectra at large transverse momenta (3 < p(T) < 10 GeV/c) from Cu + Cu collisions at root s(NN) = 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). This study explores the system size dependence of two novel features observed at RHIC with heavy ions: the hadron suppression at high-p(T) and the anomalous baryon to meson enhancement at intermediate transverse momenta. Both phenomena could be attributed to the creation of a new form of QCD matter. The results presented here bridge the system size gap between the available pp and Au + Au data, and allow for a detailed exploration of the onset of the novel features. Comparative analysis of all available 200 GeV data indicates that the system size is a major factor determining both the magnitude of the hadron spectra suppression at large transverse momenta and the relative baryon to meson enhancement.

Charged and strange hadron elliptic flow in Cu plus Cu collisions at root s(NN)=62.4 and 200 GeV

We present the results of an elliptic flow, v(2), analysis of Cu + Cu collisions recorded with the solenoidal tracker detector (STAR) at the BNL Relativistic Heavy Ion Collider at root s(NN) = 62.4 and 200 GeV. Elliptic flow as a function of transverse momentum, v(2)(p(T)), is reported for different collision centralities for charged hadrons h(+/-) and strangeness-ontaining hadrons K-S(0), Lambda, Xi, and phi in the midrapidity region vertical bar eta vertical bar < 1.0. Significant reduction in systematic uncertainty of the measurement due to nonflow effects has been achieved by correlating particles at midrapidity, vertical bar eta vertical bar < 1.0, with those at forward rapidity, 2.5 < vertical bar eta vertical bar < 4.0. We also present azimuthal correlations in p + p collisions at root s = 200 GeV to help in estimating nonflow effects. To study the system-size dependence of elliptic flow, we present a detailed comparison with previously published results from Au + Au collisions at root s(NN) = 200 GeV. We observe that v(2)(p(T)) of strange hadrons has similar scaling properties as were first observed in Au + Au collisions, that is, (i) at low transverse momenta, p(T) < 2 GeV/c, v(2) scales with transverse kinetic energy, m(T) - m, and (ii) at intermediate p(T), 2 < p(T) < 4 GeV/c, it scales with the number of constituent quarks, n(q.) We have found that ideal hydrodynamic calculations fail to reproduce the centrality dependence of v(2)(p(T)) for K-S(0) and Lambda. Eccentricity scaled v(2) values, v(2)/epsilon, are larger in more central collisions, suggesting stronger collective flow develops in more central collisions. The comparison with Au + Au collisions, which go further in density, shows that v(2)/epsilon depends on the system size, that is, the number of participants N-part. This indicates that the ideal hydrodynamic limit is not reached in Cu + Cu collisions, presumably because the assumption of thermalization is not attained.

Long-distant contribution and chi(c1) radiative decays to light vector meson

The discrepancy between the PQCD calculation and the CLEO data for chi (c1)->gamma V (V=rho (0), omega, phi) stimulates our interest in exploring other mechanisms of chi (c1) decay. In this work, we apply an important non-perturbative QCD effect, i.e., the hadronic loop mechanism, to study chi (c1)->gamma V radiative decay. Our numerical result shows that the theoretical results including the hadronic loop contribution and the PQCD calculation of chi (c1)->gamma V are consistent with the corresponding CLEO data of chi (c1)->gamma V. We expect further experimental measurement of chi (c1)->gamma V, which will be helpful to test the hadronic loop effect on chi (c1) decay.

强子的介质效应

本论文简述了强子介质效应的研究现状，理论方法以及实验探测技术。系统的介绍了相对论平均场理论和手征有效场论。利用相对论平均场研究了Pentaquark的介质效应，利用手征有效场论研究了△(1232)共振态的介质效应。 在密度相关的平均场理论基础上，计算出的Pentaquark的有效质量随核物质密度的增加而减小。一定的Pentaquark含量导致每核子的结合能减小，这使得核物质系统更加稳定。 在手征有效场论的框架下，利用泡利不相容原理对核子传播子的修正，以及核子有效质量在核物质中的改变，通过计算△共振态一阶自能，讨论了△共振态的有效质量和衰变宽度对核物质密度的依赖关系。结果表明：△共振态的有效质量随核物质密度的增加而减小，在正常核密度下为1221MeV，而在3倍正常核密度时为1186MeV，其减小幅度与美国Lawrence Berkeley国家实验室上做的58Ni+Cu（能量为1.97GeV/u）碰撞实验给出的结果大致相符；△粒子的衰变宽度在核物质中的变化主要决定于核子以及△粒子的有效质量的变化

强子有效质量与核子内夸克性质

论文包括两部分内容：利用强子动力学模型和相对论平均场近似方法研究了强子的有效质量；扩展了夸克质量密度相关的模型，讨论了核子的基本性质。 从非线性σ-ω-ρ模型拉氏量出发,给出了核物质标量密度和矢量密度的关系,利用其修正了K介子有效质量；在不变耦合系数和密度相关耦合系数下，研究了Θ+的有效质量，并发现在密度相关的耦合系数下，标量介子与重子的相互作用在高密度区域被削弱。 在改进的夸克质量密度相关(IQMDD)模型的基础上，引入了ω介子来描述夸克间排斥作用，给出了夸克和σ,ω场函数满足的方程, 通过自洽求解，分B^(1/4)=145MeV和c2=0两种情况，研究了在不同条件下夸克波函数和夸克密度的变化情况，给出了σ,ω场函数的分布。计算了rp，磁矩μp，以及核子的轴矢量与矢量的β衰变耦合系数之比gA/gv，发现与实验值有较好的吻合