Measurement of flavor asymmetry of the light-quark sea in the proton with Drell-Yan dimuon production in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi><mml:mo>+</mml:mo><mml:mi>p</mml:mi></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi><mml:mo>+</mml:mo><mml:mi>d</mml:mi></mml:mrow></mml:math> collisions at 120 GeV
J. Dove, Bryan Kerns, C. H. Leung, R. E. McClellan, S. Miyasaka, D. H. Morton, K. Nagai, Sidharth Kumar Prasad, F. Sanftl, M. B. C. Scott, A.S. Tadepalli, C. Aidala, J. Arrington, C. Ayuso, Craig Barker, C. Brown, Tung‐Zong Chang, W. C. Chang, A. Chen, D. Christian, B. P. Dannowitz, M. Daugherity, M. Diefenthaler, L. El Fassi, D. F. Geesaman, R. Gilman, Y. Goto, L. Guo, R. Guo, T. J. Hague, R. J. Holt, D. Isenhower, E. Kinney, N. D. Kitts, A. Klein, D. Kleinjan, Y. Kudo, P.-J. Lin, Kun Liu, M. X. Liu, W. Lorenzon, N. C. R. Makins, M. Mesquita de Medeiros, P. L. McGaughey, Y. Miyachi, I. Mooney, K. Nakahara, K. Nakano, S. Nara, J. C. Peng, A. J. R. Puckett, B. Ramson, P. E. Reimer, J. Rubin, S. Sawada, T. Sawada, T.-A. Shibata, S. H. Shiu, D. Su, M. Teo, B. G. Tice, R. S. Towell, Sho Uemura, T. S. Watson, Sen Wang, A. B. Wickes, Jia-Jun Wu, Z. Xi, Z. Ye
Abstract
Evidence for a flavor asymmetry between the $\overline{u}$ and $\overline{d}$ 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 $\overline{d}(x)/\overline{u}(x)$ ratio in the $x>0.15$ region. We report results from the SeaQuest Fermilab E906 experiment with improved statistical precision for $\overline{d}(x)/\overline{u}(x)$ 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, ${\ensuremath{\sigma}}^{pd}/2{\ensuremath{\sigma}}^{pp}$, from the SeaQuest data give consistent results. The $\overline{d}(x)/\overline{u}(x)$ ratios and the $\overline{d}(x)\ensuremath{-}\overline{u}(x)$ differences are deduced from these cross section ratios for $0.13<x<0.45$. The SeaQuest and E866/NuSea $\overline{d}(x)/\overline{u}(x)$ ratios are in good agreement for the $x\ensuremath{\lesssim}0.25$ region. The new SeaQuest data, however, show that $\overline{d}(x)$ continues to be greater than $\overline{u}(x)$ up to the highest $x$ value ($x=0.45$). The new results on $\overline{d}(x)/\overline{u}(x)$ and $\overline{d}(x)\ensuremath{-}\overline{u}(x)$ are compared with various parton distribution functions and theoretical calculations.