Transverse single-spin asymmetry for very forward neutral pion production in polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV
M. H. Kim, O. Adriani, E. Berti, L. Bonechi, R. D'Alessandro, Y. Goto, B. Hong, Y. Itow, K. Kasahara, H. Menjo, I. Nakagawa, J. S. Park, T. Sako, N. Sakurai, K.… 展开作者
M. H. Kim, O. Adriani, E. Berti, L. Bonechi, R. D'Alessandro, Y. Goto, B. Hong, Y. Itow, K. Kasahara, H. Menjo, I. Nakagawa, J. S. Park, T. Sako, N. Sakurai, K. Sato, R. Seidl, K. Tanida, S. Torii, A. Tricomi, M. Ueno, Y. Makino, Q. D. Zhou, J. H. Lee, T. Ljubicic, A. Ogawa
备注：
This paper submitted to PRL is the final result of arXiv:1902.07852
Transverse single-spin asymmetries of very forward neutral pions generated in polarized $p + p$ collisions allow us to understand the production mechanism in terms of perturbative and non-perturbative strong interactions. During 2017 the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized $p$+$p$ collisions at $\sqrt{s}$ = 510 GeV. The large non-zero asymmetries increasing both in longitudinal momentum fraction $x_{F}$ and transverse momentum $p_{T}$ have been observed at low transverse momentum $p_{T} < 1$ GeV/$c$ for the first time at this collision energy. The asymmetries show an approximate $x_{F}$ scaling in the $p_{T}$ region where non-perturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
我们报告的第一个结果，在反应e + p -> e + p +伽马在4.25 GeV的束流能量测量的束流自旋不对称性。观察到一个大的不对称性与sin（φ）调制，作为预测的干涉项的深虚康普顿散射和贝特-海特勒过程。该调制的幅度为α = 0.202 +/-0.028。在超前阶和超前扭曲pQCD中，α与DVCS振幅的虚部成正比。
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A complete, fundamental understanding of the proton must include knowledge of the underlying spin structure. The transversity distribution, $h_1\left(x\right)$, which describes the transverse spin structure of quarks inside of a transversely polarized proton, is only accessible through channels that couple $h_1 \left(x\right)$ to another chiral odd distribution, such as the Collins fragmentation function ($Δ^N D_{π/q^\uparrow}\left(z,j_T\right)$). Significant Collins asymmetries of charged pions have been observed in semi-inclusive deep inelastic scattering (SIDIS) data. These SIDIS asymmetrie…
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