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arXiv 1801.01487hep-exhep-ph
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Drell-Yan过程中与横向自旋相关的方位角不对称性的首次测量

First measurement of transverse-spin-dependent azimuthal asymmetries in the Drell-Yan process

Bakur Parsamyan

摘要:

欧洲核子研究中心的COMPASS实验作为其方案的一部分,通过测量半包容性DIS和最近的Drell-Yan过程中与自旋(in)有关的方位角不对称性,探索核子的横向自旋结构。在2002年至2010年期间,COMPASS进行了一系列SIDIS测量,使用纵向偏振μ子束撞击横向偏振$^6LiD$或$NH_3$目标。Drell-Yan测量使用$π^-$光束与横向偏振$NH_3$目标相互作用,从2015年开始运行,并将在2018年继续进行。在这封信中的第一个测量的横向自旋相关的方位角不对称性的π诱导的Drell-Yan过程的报告。利用质量不变的双μ子事件,在4.3~ \gvcw \和8.5~ \gvcw \之间提取了测量的非对称性,得到了不同的横动量相关(TMD)部分子分布函数(PDF).最近的COMPASS SIDIS测量是在硬尺度上获得的,与这些DY结果相当。这为检验在QCD中预测的Sivers TMD PDF的符号变化和其他与横向动量相关的部分子分布函数的(伪)普适特征提供了一种独特的可能性。

英文摘要:

The COMPASS experiment at CERN, as part of its programme addresses the exploration of the transverse spin structure of the nucleon by measuring spin (in)dependent azimuthal asymmetries in semi-inclusive DIS and, recently, also in Drell-Yan processes. Between 2002 and 2010 COMPASS performed a series of SIDIS measurements, using a longitudinally polarized muon beam impinging on transversely polarized $^6LiD$ or $NH_3$ targets. Drell-Yan measurements with a $π^-$ beam interacting with a transversely polarized $NH_3$ target started with the 2015 run and will be continued in 2018. In this Letter the first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan process is reported. Measured asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3~\gvcw\, and 8.5~\gvcw. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This provides a unique possibility to test predicted in QCD sign change of the Sivers TMD PDF and other (pseudo-)universal features of transvers momentum dependent parton distribution functions.

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