Measurement of flavor asymmetry of the light-quark sea in the proton with Drell-Yan dimuon production in 𝑝+𝑝 and 𝑝+𝑑 collisions at 120 GeV

Creators: Dove, J.; Kerns, B.; Leung, C.; McClellan, R. E.; Miyasaka, S.; Morton, D. H.; Nagai, K.; Prasad, S.; Sanftl, F.; Scott, M. B. C.; Tadepalli, A. S.; Aidala, C. A.; Arrington, J.; Ayuso, C.; Barker, C. T.; Brown, C. N.; Chang, T. H.; Chang, W. C.; Chen, A.; Christian, D. C.; Dannowitz, B. P.; Daugherity, M.; Diefenthaler, M.; El Fassi, L.; Geesaman, D. F.; Gilman, R.; Goto, Y.; Guo, L.; Guo, R.; Hague, T. J.; Holt, Roy J.¹; Isenhower, D.; Kinney, E. R.; Kitts, N. D.; Klein, A.; Kleinjan, D. W.; Kudo, Y.; Lin, P.-J.; Liu, K.; Liu, M. X.; Lorenzon, W.; Makins, N. C. R.; Mesquita de Medeiros, M.; McGaughey, P. L.; Miyachi, Y.; Mooney, I.; Nakahara, K.; Nakano, K.; Nara, S.; Peng, J. C.; Puckett, A. J.; Ramson, B. J.; Reimer, P. E.; Rubin, J. G.; Sawada, S.; Sawada, T.; Shibata, T.-A.; Shiu, S. H.; Su, D.; Teo, M.; Tice, B. G; Towell, R. S.; Uemura, S.; Watson, T. S.; Wang, S. G.; Wickes, A. B.; Wu, J.; Xi, Z.; Ye, Z.

1. California Institute of Technology

Abstract

Evidence for a flavor asymmetry between the ‾𝑢 and ‾𝑑 quark distributions in the proton has been found in deep-inelastic scattering and Drell-Yan experiments. The pronounced dependence of this flavor asymmetry on 𝑥 (fraction of nucleon momentum carried by partons) observed in the Fermilab E866 Drell-Yan experiment suggested a drop of the ‾𝑑⁡(𝑥)/‾𝑢⁡(𝑥) ratio in the 𝑥>0.15 region. We report results from the SeaQuest Fermilab E906 experiment with improved statistical precision for ‾𝑑⁡(𝑥)/‾𝑢⁡(𝑥) in the large 𝑥 region up to 𝑥=0.45 using the 120 GeV proton beam. Two different methods for extracting the Drell-Yan cross section ratios, 𝜎𝑝⁢𝑑/2⁢𝜎𝑝⁢𝑝, from the SeaQuest data give consistent results. The ‾𝑑⁡(𝑥)/‾𝑢⁡(𝑥) ratios and the ‾𝑑⁡(𝑥)−‾𝑢⁡(𝑥) differences are deduced from these cross section ratios for 0.13<𝑥<0.45. The SeaQuest and E866/NuSea ‾𝑑⁡(𝑥)/‾𝑢⁡(𝑥) ratios are in good agreement for the 𝑥≲0.25 region. The new SeaQuest data, however, show that ‾𝑑⁡(𝑥) continues to be greater than ‾𝑢⁡(𝑥) up to the highest 𝑥 value (𝑥=0.45). The new results on ‾𝑑⁡(𝑥)/‾𝑢⁡(𝑥) and ‾𝑑⁡(𝑥)−‾𝑢⁡(𝑥) are compared with various parton distribution functions and theoretical calculations.

Copyright and License

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP³.

Acknowledgement

We thank G. T. Garvey for contributions to the early stages of this experiment. We also thank the Fermilab Accelerator Division and Particle Physics Division for their support of this experiment. This work was performed by the SeaQuest Collaboration, whose work was supported in part by the US Department of Energy under Grant No. DE-AC02-06CH11357, the US National Science Foundation under Grants No. PHY 1812340, No. PHY 2012926, No. PHY 1807338, No. PHY 2110229, No. PHY 2111046, and No. PHY 1506489; National Science and Technology Council of Taiwan (R.O.C.); the DP&A and ORED at Mississippi State University; the JSPS (Japan) KAKENHI through Grants No. 21244028, No. 25247037, No. 25800133, No. 20K04000, and No. 22H01244; the Bilateral Programs Joint Research Projects of JSPS; the Tokyo Tech Global COE Program, Japan; the Yamada Science Foundation of Japan; and the Ministry of Science and Technology (MOST) of Taiwan. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359.

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