arXiv 2209.047982022-09-11hep-exhep-phnucl-exphysics.data-an

LHC上ALICE中Pb-Pb碰撞中$Λ$（$\barΛ$）超子的整体和局域极化

Global and local polarization of $Λ$ ($\barΛ$) hyperons in Pb--Pb collisions in ALICE at the LHC

Debojit Sarkar

备注：: Presented at SQM 2021 - https://indico.cern.ch/event/985652/contributions/4305110/
发表信息：: EPJ Web Conf. 259 (2022) 06001
DOI：: 10.1051/epjconf/202225906001

摘要：

在大型强子对撞机（LHC）的ALICE装置上，测量了能量为$\sNN=$ 2.76 TeV和5.02 TeV的Pb-Pb碰撞中$Λ$和$\barΛ$超子（$P_{\rm H}$）的全局极化.超子的全局极化被发现是一致的，在两个碰撞能量为零。在$\sNN=5.02$ TeV的铅-铅碰撞中，还测量了$Λ$和$\barΛ$超子沿电子束（$z$）方向的局域极化（$P_{\rm z}$）.的$P_{\rm z}$，作为相对于第二谐波对称平面的超子发射角的函数测量，表现出第二谐波正弦调制，由于椭圆流的预期。报道了不同碰撞中心的全局和局部超子极化的测量结果，并作为半中心碰撞中横向动量的函数。这些结果表明，在LHC的铅-铅碰撞的非零超子$P_{\rm z}$的第一个实验证据。

英文摘要：

The global polarization of the $Λ$ and $\barΛ$ hyperons ($P_{\rm H}$) has been measured in Pb--Pb collisions at $\sNN=$ 2.76 TeV and 5.02 TeV in ALICE at the Large Hadron Collider (LHC). The hyperon global polarization is found to be consistent with zero at both collision energies. The local polarization of the $Λ$ and $\barΛ$ hyperons along the beam ($z$) direction, $P_{\rm z}$, has also been measured in Pb--Pb collisions at $\sNN=5.02$ TeV. The $P_{\rm z}$, measured as a function of the hyperon emission angle relative to the second harmonic symmetry plane, exhibits a second harmonic sine modulation, as expected due to elliptic flow. The measurements of global and local hyperon polarization are reported for different collision centralities and as a function of transverse momentum in semicentral collisions. These results show the first experimental evidence of a non-zero hyperon $P_{\rm z}$ in Pb--Pb collisions at the LHC.

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