论文标题
LHC核冲突中Quarkonium极化的首次测量
First measurement of quarkonium polarization in nuclear collisions at the LHC
论文作者
论文摘要
在$ \ sqrt {s _ {s _ {\ rm {nn}}} = 5.02 $ TEV的PB-PB碰撞中产生的包容性J/$ψ$和$υ（1 {\ rm s}）$的两极分化。这项研究是通过重建Quarkonium通过其腐烂到速度区域的粘液对$ 2.5 <y <4 $并测量MUON的极性和方位角分布来进行的。极化参数$λ_θ$，$ λ_ϕ $和$λ_{θϕ} $在螺旋和柯林斯 - soper参考框架中测量，横向动量间隔$ 2 <p _ {\ rm t} <10 $ c $ and $ p _ $ p _ $ p _ $ c $ g $ g $ g $ g $ g $ c $ c <15 $ c。 $υ（1 {\ rm s}）$。发现J/$ψ$的极化参数与零兼容，在低$ p _ {\ rm t} $的最多大约两个标准偏差范围内，用于参考帧和整个$ p _ {\ rm t} $ range。将这些值与Alice和LHCB实验在类似的运动区域中在$ \ sqrt {s} = 7 $和8 TEV处获得的PP碰撞获得的相应结果进行了比较。尽管有更大的不确定性，但PB-PB碰撞中的$υ（1 {\ rm s}）$生产的极化参数也与零一致。
The polarization of inclusive J/$ψ$ and $Υ(1{\rm S})$ produced in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ 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 $λ_{θϕ}$ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval $2<p_{\rm T}<10$ GeV/$c$ and $p_{\rm T}<15$ GeV/$c$ for the J/$ψ$ and $Υ(1{\rm S})$, 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 $p_{\rm T}$, for both reference frames and over the whole $p_{\rm T}$ range. The values are compared with the corresponding results obtained for pp collisions at $\sqrt{s}=7$ and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for $Υ(1{\rm S})$ production in Pb-Pb collisions are also consistent with zero.
