sqrt{s} = 41.6 GeV质子核相互作用中粲偶素态chic_1和chic_2的产生
Production of the Charmonium States chic_1 and chic_2 in Proton Nucleus Interactions at sqrt{s} = 41.6 GeV
摘要：
本文给出了在920 GeV/c（sqrt{s}=41.6 GeV）的Feynman-x范围-0.35 < x_F（Jpsi）< 0.15的pC，pTi和pW相互作用中R_chic =（chic -> Jpsi + gam）/ Jpsi的测量结果。μ + μ-和e+ e-Jpsi衰变通道都被观测到，总的统计量约为15000个chic事件，这是迄今为止在pA碰撞中最大的可用样本。当不考虑Jpsi和chic偏振时，在不同材料上平均的结果是R_chic = 0.188+-0.013（st）（+0.024）（-0.022）（sys）。chic_1与chic_2的生产比率R_12 = R_chic1/R_chic2被测量为1.02 ± 0.40，导致截面比率sigma（chic_1）/sigma（chic_2）=0.57 ± 0.23。研究了Rchic与Jpsi的Feynman-x，x_F（Jpsi）和横动量p_T（Jpsi）的关系，以及Rchic与靶的原子序数A的关系。对于第一次，广泛的研究可能的偏见R_别致和R_12由于接受Jpsi和别致的偏振态的依赖性进行。通过改变偏振参数，λ（obs），所有产生的Jpsi的由HERA-B测量的值周围的两个西格玛，并考虑由于可能的chic_1和chic_2偏振的最大变化，它表明，R_chic可以改变一个因子之间的1.02和1.21和R_12之间的一个因子0.89和1.16。
英文摘要：
A measurement of the ratio R_chic = (chic -> Jpsi + gam)/ Jpsi in pC, pTi and pW interactions at 920 GeV/c (sqrt{s}=41.6 GeV) in the Feynman-x range -0.35 < x_F(Jpsi) < 0.15 is presented. Both mu+mu- and e+e- Jpsi decay channels are observed with an overall statistics of about 15000 chic events, which is by far the largest available sample in pA collisions. The result is R_chic = 0.188+-0.013(st)(+0.024)(-0.022)(sys) averaged over the different materials, when no Jpsi and chic polarisations are considered. The chic_1 to chic_2 production ratio R_12 = R_chic1/R_chic2 is measured to be 1.02+-0.40, leading to a cross section ratio sigma(chic_1)/sigma(chic_2)=0.57+-0.23. The dependence of R_chic on the Feynman-x of the Jpsi, x_F(Jpsi), and its transverse momentum, p_T(Jpsi), is studied, as well as its dependence on the atomic number, A, of the target. For the first time, an extensive study of possible biases on R_chic and R_12 due to the dependence of acceptance on the polarization states of Jpsi and chic is performed. By varying the polarisation parameter, lambda(obs), of all produced Jpsi's by two sigma around the value measured by HERA-B, and considering the maximum variation due to the possible chic_1 and chic_2 polarisations, it is shown that R_chic could change by a factor between 1.02 and 1.21 and R_12 by a factor between 0.89 and 1.16.
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