학술논문
Measurement of flavor asymmetry of light-quark sea in the proton with Drell-Yan dimuon production in $p+p$ and $p+d$ collisions at 120 GeV
Document Type
Working Paper
Author
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.; Fassi, L. El; Geesaman, D. F.; Gilman, R.; Goto, Y.; Guo, L.; Guo, R.; Hague, T. J.; Holt, R. J.; 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.; de Medeiros, M. Mesquita; 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.
Source
Subject
Language
Abstract
Evidence for a flavor asymmetry between the $\bar u$ and $\bar d$ 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 $\bar d\left(x\right) / \bar u\left(x\right)$ ratio in the $x > 0.15$ region. We report results from the SeaQuest Fermilab E906 experiment with improved statistical precision for $\bar d\left(x\right) / \bar u\left(x\right)$ 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, $\sigma^{pd} /2 \sigma^{pp}$, from the SeaQuest data give consistent results. The $\bar{d}\left(x\right) / \bar{u}\left(x\right)$ ratios and the $\bar d\left(x\right) - \bar u\left(x\right)$ differences are deduced from these cross section ratios for $0.13 < x < 0.45$. The SeaQuest and E866/NuSea $\bar{d}\left(x\right) / \bar{u}\left(x\right)$ ratios are in good agreement for the $x\lesssim 0.25$ region. The new SeaQuest data, however, show that $\bar d\left(x\right)$ continues to be greater than $\bar u\left(x\right)$ up to the highest $x$ value ($x = 0.45$). The new results on $\bar{d}\left(x\right) / \bar{u}\left(x\right)$ and $\bar{d}\left(x\right) - \bar{u}\left(x\right)$ are compared with various parton distribution functions and theoretical calculations.