1. 1 Azimuthal dependence in unpolarized proton-induced Drell-Yan processes Mini-symposium on orbital motion of quarks in hard scattering 2 nd 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)

2. 2 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

3. 3 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)

4. 4 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 h 1 ?. It is equal to Sivers function f 1T ? in the quark-diquark spectator model. Boer, PRD60,014012(1999); …

5. 5 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 =0.17 m T =1.5

6. 6 Boer-Mulders function h 1 ? Boer, PRD60,014012(1999) An spin-correlation approach in terms of h 1 ? can fit the NA10 data at 194 GeV. On the base of quite general arguments, for |q T |<<Q(=m   ), Salvo,hep-ph/0407208.  1 =0.5 m C =2.3  T =C H =1

7. 7 Models with Boer-Mulders function h 1 ? 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.

8. 8 Fermi Lab E866/NuSea experiment Drell-Yan events Analyzed (4.5 11) including pp   +  - X; pd   +  - X High Mass Setting: dset7-39k, dset8-85k (+ polarity) dset11-25k (- polarity) Low Mass Setting: dset5-68k (+ polarity)

9. 9 Muon momenta Blue: simulation Red: data (dset8) + !+ ! - !- !

10. 10 Comparison of data and simulation Blue: simulation Red: data (dset8)

11. 11 Extraction of azimuthal cos2  distribution Data M.C. Data/M.C. Fit Func: p 1 [1+p 3 /2 cos2  + p 2 cos(  + p 4 )]

12. 12 Very Preliminary Azimuthal cos2  distribution for Drell-Yan processes

13. 13 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 h 1 ?. The latter is related to the Sivers function f 1T ?. 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.