The longitudinal spin transfer DLL to Λ and Λ¯ hyperons produced in high-energy polarized proton-proton collisions is expected to be sensitive to the helicity distribution functions of strange quarks and antiquarks of the proton, and to longitudinally polarized fragmentation functions. We report an improved measurement of DLL from data obtained at a center-of-mass energy of √s = 200 GeV with the STAR detector at RHIC. The data have an approximately twelve times larger figure of merit than prior results and cover |η| < 1.2 in pseudorapidity with transverse momenta pT up to 6 GeV/c. In the forward scattering hemisphere at largest pT, the longitudinal spin transfer is found to be DLL = −0.036 ± 0.048(stat) ± 0.013(sys) for Λ hyperons and DLL = 0.032 ± 0.043(stat) ± 0.013(sys) for Λ¯ antihyperons. The dependences on η and pT are presented and compared with model evaluations.
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Funded by SCOAP3.
This work was supported in part by the Office of Nuclear Physics within the U.S. DOE Office of Science, the U.S. National Science Foundation, the Ministry of Education and Science of the Russian Federation, National Natural Science Foundation of China, Chinese Academy of Science, the Ministry of Science and Technology of China and the Chinese Ministry of Education, the National Research Foundation of Korea, Czech Science Foundation and Ministry of Education, Youth and Sports of the Czech Republic, Department of Atomic Energy and Department of Science and Technology of the Government of India, the National Science Centre of Poland, the Ministry of Science, Education and Sports of the Republic of Croatia, RosAtom of Russia and German Bundesministerium für Bildung, Wissenschaft, Forschung and Technologie (BMBF) and the Helmholtz Association.
Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, James K.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I.; Anderson, D. M.; Aoyama, R.; Aparin, A.; Arkhipkin, D.; Aschenauer, E. C.; Ashraf, M. U.; Atetalla, F.; Attri, A.; Averichev, G. S.; Bai, X.; Bairathi, V.; Barish, K.; Bassill, A. J.; Behera, A.; Bellwied, R.; Bhasin, A.; Bhati, A. K.; Bielcik, J.; Bielcikova, J.; Bland, L. C.; Bordyuzhin, I. G.; Brandenburg, J. D.; Fatemi, Renee H.; and Ramachandran, Suvarna, "Improved Measurement of the Longitudinal Spin Transfer to Λ and Λ¯ Hyperons in Polarized Proton-Proton Collisions at √s = 200 GeV" (2018). Physics and Astronomy Faculty Publications. 622.