First measurement of quarkonium polarization in nuclear collisions at the LHC
First measurement of quarkonium polarization in nuclear collisions at the LHC
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DOI：
10.1016/j.physletb.2021.136146
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发表时间：
2020-05
影响因子：
4.4
通讯作者：
Alice Collaboration
中科院分区：
文献类型：
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作者：
Alice Collaboration
用ALICE探测器测量了LHC上sNN = 5.02TeV的Pb-Pb碰撞中产生的J/π和π（1 S）的极化。通过在快度区2.5< y< 4衰变为μ子对重建夸克偶素，并测量μ子的极角和方位角分布，进行了研究。在螺旋度参考系和Collins-Soper参考系中，分别在J/π和π（1 S）的横动量区间2<pT < 10 GeV/c和pT < 15 GeV/c测量了偏振参数λ θ，λ π和λ θ π。的J/π的偏振参数被发现是兼容的零，在最大约两个标准偏差在低p T，为两个参考帧和整个p T范围内。的值进行了比较与PP碰撞在S= 7和8 TeV在一个类似的运动学区域的ALICE和LHCb实验获得的相应结果。虽然有更大的不确定性，在Pb-Pb碰撞中产生的π（1 S）的极化参数也是一致的零。
The polarization of inclusive J/ψ and ϒ (1 S) produced in Pb–Pb collisions at s NN= 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5< y< 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters λ θ, λ ϕ and λ θ ϕ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2< p T< 10 GeV/c and p T< 15 GeV/c for the J/ψ and ϒ (1 S), respectively. The polarization parameters for the J/ψ are found to be compatible with zero, within a maximum of about two standard deviations at low p T, for both reference frames and over the whole p T range. The values are compared with the corresponding results obtained for pp collisions at s= 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for ϒ (1 S) production in Pb–Pb collisions are also consistent with zero.