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Azimuthal dependence in unpolarized proton-induced
Drell-Yan processes
Mini-symposium on orbital motion of quarks in hard scattering
2nd joint meeting of the APS DNP and JPS
Maui, Hawaii, Sep 18-22, 2005
Lingyan Zhu, Jen-Chieh Peng
University of Illinois at Urbana-Champaign
Paul Reimer
Argonne National Laboratory
(FNAL E866/NuSea Collaboration)
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*h N X X Angular distribution for the Drell-Yan processes
Correction due to QCD is small.
In the simple parton model:
( for massless quarks and measured relative to the annihilation axis)
1 and =0
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Conway et al., PRD39,92(1989) E615 at Fermilab: 252 GeV π- + W
Azimuthal cos2 distribution in the W Drell-Yan
NA10 at CERN: 140/194/286 GeV π- + W Z. Phys. C37, 545 (1988)
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Possible explanations for the cos2 asymmetry
The high twist in terms of pion bound state effect is not enough.Brandenburg, Brodsky, Khoze & Muller, PRL73,939(1994)
The nuclear distortion of hadronic projectile wavefunction, typically a spin-orbit effect occuring on the nuclear surface. =0 for pp Drell-Yan.
Bianconi & Radici, JPG31,645(2005).
The spin correlation due to nontrival QCD vacuum.—Flavor blind.Brandenburg, Nachtmann & Mirkes, Z. Phy. C60,697(1993)Boer,Brandenburg,Nachtmann&Utermann, EPC40,55(2005).
The non-zero chiral-odd distribution function h1? .
It is equal to Sivers function f1T? in the quark-diquark spectator model.
Boer, PRD60,014012(1999); …
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Brandenburg, Nachtmann & Mirkes, Z. Phy. C60,697(1993)
•The factorization-breaking spin correlation due to nontrivial QCD vacuum may fit the NA10 data at 194 GeV
•The helicity flip in the instanton-induced contribution may lead to nontrivial vacuum. Boer,Brandenburg,Nachtmann&Utermann, EPC40,55(2005).
•This vacuum effect should be flavor blind.
QCD vacuum effects
0=0.17mT=1.5
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Boer-Mulders function h1?
Boer, PRD60,014012(1999)
•An spin-correlation approach in terms of h1? can fit the NA10
data at 194 GeV.
•On the base of quite general arguments, for |qT|<<Q(=m ),Salvo,hep-ph/0407208.
1=0.5mC=2.3T=CH=1
221 12 2
( , ) ( )T TkC HTT H
T C
M Mh x k c e f x
k M
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Models with Boer-Mulders function h1?
•The quark-spectator-antiquark model with effective pion-quark-antiquark coupling as a dipole form factor Lu & Ma, hep-ph/0504184
•Twist 2 (as well as the kinematic twist 4) contribution in a parton-spectator framework Gamberg&Goldstein, hep-ph/0506127.
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Fermi Lab E866/NuSea experiment
Drell-Yan events Analyzed (4.5<M<9, M>11) including pp+ - X; pd+ - X
High Mass Setting: dset7-39k, dset8-85k (+ polarity) dset11-25k (- polarity)
Low Mass Setting: dset5-68k (+ polarity)
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Muon momenta
Blue: simulation
Red: data
(dset8)+ !
- !
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Comparison of data and simulation
Blue: simulation
Red: data
(dset8)
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Extraction of azimuthal cos2 distribution
Data M.C. Data/M.C.
Fit Func: p1[1+p3/2 cos2+ p2cos( + p4)]
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Very Preliminary
Azimuthal cos2 distribution for Drell-Yan processes
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Summary
• Large cos2 azimuthal asymmetry has been observed in unpolarized -induced Drell-Yan.
• The are a few possible explanations including the non-trivial vacuum effect and the non-zero Boer-Mulders function h1
? . The latter is related to the Sivers function f1T
?.
• The unpolarized p-induced Drell-Yan data seem to suggest small cos2 azimuthal asymmetry. This may disfavor the flavor blind explanation such as vacuum effect.