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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
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:
pnpppd
)()()()( 2191
2194 xdxdxuxupp
)()()()( 2191
2194 xuxdxdxupn
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
)()(
1
1
21
2 2
2
)2()2(
)1()1(
41
)1()1(
41
21
1 xuxd
xx xuxd
xuxd
xuxd
pp
pd
)(4)( xuxd
)()(
21
2 2
2
21
1 xuxd
xxpp
pd
assuming
The ratio equals 1 in case of flavor symmetry of the quark sea
Chiral 07, Osaka, November 12-16, 2007
Results for the ratio show flavor asymmetry
Can binding effects change the conclusion?
FNAL E866 data 2001
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 0p :
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
0p
Chiral 07, Osaka, November 12-16, 2007
Result of the integration
CorrpD
IApDpD
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
Chiral 07, Osaka, November 12-16, 2007
Result of the numerical calculations
0,05 0,10 0,15 0,20 0,25 0,30 0,350,8
0,9
1,0
1,1
1,2
1,3
R(d
/p)
x2
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
)()( xdxu
FNAL E866 data 2001
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
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
