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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

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 M_{mu+ mu-} >= 4.5 GeV/c^2 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.

Measurement of the Light Antiquark Flavor Asymmetry in the Nucleon Sea

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 M_{mu+ mu-} >= 4.5 GeV/c^2 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.

Paper Structure

This paper contains 4 equations, 3 figures, 1 table.

Figures (3)

  • Figure 1: The ratio $\sigma^{pd}/2\sigma^{pp}$ of Drell-Yan cross sections vs.$x_{2}$. Shown are next-to-leading order calculations, weighted by acceptance, of the Drell-Yan cross section ratio using the CTEQ4M (solid) and MRS(R2) (dashed) parton distributions. Also shown is a leading order calculation of the cross section ratio using CTEQ4M (dotted). In the lower CTEQ4M curve $\bar{d} - \bar{u}$ has been set to 0 as described in the text. The errors are statistical only. An additional 1% systematic uncertainty is common to all points.
  • Figure 2: The ratio of $\bar{d}/\bar{u}$ in the proton as a function of $x$ extracted from the Fermilab E866 cross section ratio. The curve is from the CTEQ4M parton distributions. The error bars indicate statistical errors only. An additional systematic uncertainty of $\pm0.032$ is not shown. The result from NA51 is also plotted as an open box.
  • Figure 3: Fermilab E866 values for (a) $\bar{d}-\bar{u}$ and (b) $\int^{0.345}_{x}\left(\bar{d}-\bar{u}\right) dx'$ in the proton versus $x$. The curves represent the corresponding values obtained by the CTEQ4M (solid) and MRS(R2) (dashed) parameterizations. The bar at $0.147\pm0.039$ on the left axis in (b) shows the result obtained by NMC for the integral from 0 to 1.