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Measurement of the Light Antiquark Flavor Asymmetry in the Nucleon Sea

E. A. Hawker, T. C. Awes, M. E. Beddo, C. N. Brown, J. D. Bush, T. A. Carey, T. H. Chang, W. E. Cooper, C. A. Gagliardi, G. T. Garvey, D. F. Geesaman, X. C. He, L. D. Isenhower, S. B. Kaufman, D. M. Kaplan, P. N. Kirk, D. D. Koetke, G. Kyle, D. M. Lee, W. M. Lee, M. J. Leitch, N. Makins, P. L. McGaughey, J. M. Moss, B. A. Mueller, P. M. Nord, B. K. Park, V. Papavassiliou, J. C. Peng, G. Petitt, P. E. Reimer, M. E. Sadler, J. Selden, P. W. Stankus, W. E. Sondheim, T. N. Thompson, R. S. Towell, R. E. Tribble, M. A. Vasiliev, Y. C. Wang, Z. F. Wang, J. C. Webb, J. L. Willis, D. K. Wise, G. R. Young

hep-exarXiv:hep-ex/9803011

Abstract

A precise measurement of the ratio of Drell-Yan yields from an 800 GeV/c proton beam incident on hydrogen and deuterium targets is reported. Over 140,000 Drell-Yan muon pairs with dimuon mass Mmu+ mu- >= 4.5 GeV/c2 were recorded. From these data, the ratio of anti-down (dbar) to anti-up (ubar) quark distributions in the proton sea is determined over a wide range in Bjorken-x. A strong x dependence is observed in the ratio dbar/ubar, showing substantial enhancement of dbar with respect to ubar for x<0.2. This result is in fair agreement with recent parton distribution parameterizations of the sea. For x>0.2, the observed dbar/ubar ratio is much nearer unity than given by the parameterizations.

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