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Chiral 07, Osaka, November 12-16, 2007 Sea-quark flavor asymmetry in the nucleon from a relativistic analysis of the Drell-Yan scattering off nuclei A. Molochkov Far Eastern National University

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Chiral 07, Osaka, November 12-16, 2007 Drell-Yan scattering pp and pn Drell-Yan lepton pair production is sensitive to the anti- quark distribution in the nucleon The only source of information about the neutron is a nucleus. The deuteron is a simplest nucleus. Neglecting nuclear effects in the deuteron we get:

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Chiral 07, Osaka, November 12-16, 2007 Ratio of the cross-sections provide direct information on the flavor asymmetry of the light quarks in the nucleon assuming The ratio equals 1 in case of flavor symmetry of the quark sea

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Chiral 07, Osaka, November 12-16, 2007 Results for the ratio show flavor asymmetry Can binding effects change the conclusion? FNAL E866 data 2001

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Chiral 07, Osaka, November 12-16, 2007 Covariant view on the binding effect in the Drell-Yan pair production The cross section for the pD scattering within the BS formalism: Integration with respect the : 1. First order pole gives IA with off-shell nucleon. Simple, but we have to account off-mass-shell nucleon structure change. 2. Second order pole puts the struck nucleon on-shell, but produces additional corrections that originate from the dependence of the cross-section

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Chiral 07, Osaka, November 12-16, 2007 Result of the integration where the impulse approximation and the correction The derivative comes form the energy dependence of the cross-section: The variables are defined as It can produce deviations in the ratio

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Chiral 07, Osaka, November 12-16, 2007 Result of the numerical calculations The relativistic kinematics can reproduce the deviation without the flavor asymmetry of the nucleon sea Input DY nucleon cross- sections are constructed from fGRV98 parameterization with FNAL E866 data 2001

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Chiral 07, Osaka, November 12-16, 2007 A-dependence of the ratio The A-dependence of the deviations is defined by the coefficient in front of the cross-section derivative Same dependence as in case of nuclear DIS: Three A-independent points where R=1 The ratio scales as number of nucleons inside the nucleus NR interpretation: contribution of the surface nucleons to the second term is small A-dependence can clarify nature of the effect

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Chiral 07, Osaka, November 12-16, 2007 Conclusions Observed flavor asymmetry results from the relativistic kinematics of bound nucleons The bound nucleons structure change have the same nature in the DIS and DY processes A-dependence data is required High x data is required

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