The large COMPASS polarized solid ammonia target for Drell?Yan measurements with a pion beam
The large COMPASS polarized solid ammonia target for Drell?Yan measurements with a pion beam
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用于使用介子束进行 Drell?Yan 测量的大型 COMPASS 偏振固体氨目标
DOI：
10.1016/j.nima.2021.166069
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Ru
中科院分区：
文献类型：
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作者：
Andrieux V.;Berlin A.;Doshita N.;Finger M.;Finger M.;Gautheron F.;Horikawa N.;Ishimoto S.;Iwata T.;Kisselev Y.;Koivuniemi J.;Kondo K.;Magnon A.;Mallot G.K.;Matou?ek J.;Matsuda T.;Meyer W.;Miyachi Y.;Nukazuka G.;Pe?ek M.;Pires C.;Quintans C.;Reicherz G.;Ru
CERN 的 COMPASS (NA58) 合作项目的横向偏振靶 (PT) 已用于 2015 年和 2018 年的 Drell-Yan 测量。使用负介子束和固体氨靶研究了质子的横向自旋结构。采用动态核极化（DNP）方法，在 2.5 T 均匀磁场和 3 He/4 He 稀释制冷机下，一天后通常可以达到 80% 以上的质子极化值。在数据采集过程中，目标在0.6 T的横向磁偶极场中运行。这种没有DNP泵浦过程的所谓冻结自旋运行模式会导致目标材料缓慢去极化，π介子束的热量输入进一步加速去极化，产生二次粒子并对目标材料产生辐射损伤效应。在已知的固体靶材中，氨对辐射引起的去极化具有最高的抵抗力。质子极化已通过核磁共振（NMR）测量。观察到质子极化的弛豫时间约为 1100 小时，导致在约两周长的数据采集期间平均极化在 68% 至 76% 之间。为了实现极化 Δ P/P 低至 3.2% 的系统不确定性和小于 1.8% 的统计不确定性，建造了两个具有适当定位 NMR 线圈的大型目标单元。
The transversely polarized target (PT) of the COMPASS (NA58) collaboration at CERN has been used for Drell–Yan measurements in 2015 and 2018. The transverse spin structure of the proton has been studied using a negative pion beam and a solid ammonia target. Employing the dynamic nuclear polarization (DNP) method, proton polarization values of more than 80% have been routinely achieved after one day, at a homogeneous magnetic field of 2.5 T and using a 3 He/4 He dilution refrigerator. During the data-taking the target operates in a transversely oriented magnetic dipole field at 0.6 T. This so-called frozen spin operation mode without the DNP pumping process leads to a slow depolarization of the target material, which is further accelerated by the heat input of the pion beam, produced secondary particles and radiation damage effects to the target material. Ammonia has the highest resistance against radiation-induced depolarization among known solid target materials. The proton polarization has been measured by the nuclear magnetic resonance (NMR). Relaxation times of about 1100 h have been observed for the proton polarization resulting in an average polarization between 68% and 76% during about two weeks long data-taking periods. To achieve a systematic uncertainty of the polarization Δ P/P as low as 3.2% and a statistical one of less than 1.8% two large target cells with appropriate positioning of the NMR-coils have been built.