1. Drell-Yan Perspectives at FAIR Marco Destefanis Università degli Studi di Torino Drell-Yan Scattering and the Structure of Hadrons Trento (Italy) May 21-25, 2012 for the PANDA Collaboration

2. Overview Motivation Drell-Yan cross section and azimuthal asymmetries Experimental scenarios Drell-Yan process and background @ PANDA  A. Bianconi Drell-Yan generator  Cut studies Investigation of Drell-Yan asymmetries Towards antiproton polarized beams Summary

3. Motivation Complete description of the nucleonic structure requires: ➠ Parton Distribution Functions (PDF) ➠ Fragmentation Functions (FF) Including k T dependence ➠ Transverse Momentum Dependent (TMD) PDF and FF ➠ Test of Universality J. C. Collins and D. E. Soper, Nucl. Phys. B 194, 445 (1982)

4. Helicity base Twist-2 PDFs: 1/2 L L + R R q(x) spin averaged

5. 1/2 L L - R R Δq(x) helicity difference Helicity base Twist-2 PDFs:

6. Helicity base Twist-2 PDFs: -         δq(x) helicity flip off diagonal in the helicity base

7. Transversity δq(x): a chirally-odd, helicity flip distribution function δg(x): no gluon transversity distribution; transversely polarised nucleon shows transverse gluon effects at twist-3 (g 2 ) only SOFFER INEQUALITY An upper limit: can be violated by factorisation at NLO inequality preserved under evolution to larger scales only

8. TMD: K T -dependent Parton Distributions Twist-2 PDFs Distribution functions Chirality even odd Twist-2 ULTULT,h1,h1, Transversity Boer-Mulders Sivers

9. TMD PDF Investigation ➠ Process SIDIS → convolution with FF Drell-Yan → PDF only pp annihilations: each valence quark can contribute to the diagram ➠ Energies @ FAIR unique energy range up to s~30 GeV 2 with PANDA up to s~200 GeV 2 with PAX @ RHIC much higher energies → big contribution from sea-quarks

10. Drell-Yan Process Drell-Yan: pp ->  +  - X Collins-Soper frame Kinematics x 1,2 = mom fraction of parton 1,2  = x 1 x 2 = M 2 /s x F = x 1 - x 2 Collins-Soper frame: Phys. Rev. D16 (1977) 2219.

11. Drell-Yan Process Gives access to chirally odd functions Transversity No convolution with FF Chirally odd functions are not suppressed (as in DIS)

12. DIS Process RHIC energies: √s = 100 GeV -> τ ≤ 10 -2 -> small x 1 and/or x 2 Too small Soffer upper bound on A TT (percent level [1] ) A TT @ RHIC very small, smaller √s would help [2] [1] Martin et al, Phys.Rev. D60 (1999) 117502. [2] Barone, Colarco and Drago, Phys.Rev. D56 (1997) 527.

13. DIS Process RHIC energies: √s = 100 GeV -> τ ≤ 10-2 -> small x 1 and/or x 2 Too small Soffer upper bound on A TT (percent level [1] ): A TT @ RHIC very small, smaller √s would help [2] [1] Martin et al, Phys.Rev. D60 (1999) 117502. [2] Barone, Colarco and Drago, Phys.Rev. D56 (1997) 527.

14. QCD higher order contributions s=45 GeV 2 s=210 GeV 2 s=45 GeV 2 s=210 GeV 2 [1] Shimizu et al., hep-ph/0503270. cross section affected K-factors almost spin independent

15. QCD contributions to A TT Contributions drop increasing the energy [1] [1] Shimizu et al., hep-ph/0503270.

16. Perturbative Corrections Smaller at higher energies [1] [1] H. Shimizu et al., Phys. Rev. D71 (2005) 114007

17. Double Spin Asymmetries @ s = 30, 45 GeV 2 A TT small at large √s and M 2 due to slow evolution of h 1 a (x,Q 2 ) Large A TT expected [1] for √s and M 2 not too large and τ not too small [2] M. Anselmino et al., Phys. Lett. B594 (2004) 97. [1] Shimizu et al., Phys.Rev.D 71 (2005) 114007. [3] Efremov et al, Eur. Phys. J. C 35 (2004) 207. Q 2 = 5 GeV 2 Q 2 = 9 GeV 2 Q 2 = 16 GeV 2

18. NLO pQCD: λ  1,   0, υ  0 Lam-Tung sum rule: 1- λ = 2ν reflects the spin-½ nature of the quarks insensitive top QCD-corrections Experimental data [1] : υ  30 % [1] J.S.Conway et al., Phys. Rev. D39 (1989) 92. Di-Lepton Rest Frame Drell-Yan Asymmetries

19. Expected polar distributions E772 @ Fermilab λ, μ, ν measured [1] in p N → μ + μ - X Perfect agreement with pQCD exptectations! [1] McGaughey, Moss, JCP, Annu. Rev. Nucl. Part. Sci. 49 (1999) 217.

20. E537 @ Fermilab Anassontzis et al., Phys. Rev. D38 (1988) 1377 Expected polar distributions

21. Conway et al, Phys. Rev. D39 (1989) 92 E615 @ Fermilab  -N   +  - X @ 252 GeV/c -0.6 < cos < 0.6 4 < M < 8.5 GeV/c 2 Angular distribution in CS frame

22. Conway et al, Phys. Rev. D39 (1989) 92 30% asymmetry observed for  - E615 @ Fermilab  -N   +  - X @ 252 GeV/c Angular distribution in CS frame

23. NA10 coll., Z. Phys. C37 (1988) 545 NA10 @ CERN  -N   +  - X @ 286 GeV/c Deuterium Tungsten Nuclear effects?

24. NA10 @ CERN [1] λ, μ, ν measured in π N→μ + μ – X υ involves transverse spin effects at leading twist [2] If unpolarised DY σ is kept differential on k T, cos2φ contribution to angular distribution provide: [1] NA10 coll., Z. Phys. C37 (1988) 545 Violation of Lam-Tung sum rule [2] D. Boer et al., Phys. Rev. D60 (1999) 014012.

25. [1] L. Zhu et al, PRL 99 (2007) 082301; [1] D. Boer, Phys. Rew. D60 (1999) 014012. Boer-Mulders T-odd Chiral-odd TMD ν > 0 → valence h 1  has same sign in π and N ν(π - W→μ + μ - X) ~ h 1  (π) valence x h 1  (p) valence ν(pd→μ + μ - X) ~ h 1  (p) valence x h 1  (p) sea ν > 0 → valence and sea h 1  has same sign, but sea h 1  should be significantly smaller [1] Drell-Yan Asymmetries

26. λ  1,   0 Even unpolarised beam on polarised p, or polarised on unpolarised p are powerful tools to investigate к T dependence of QDF D. Boer et al., Phys. Rev. D60 (1999) 014012.

27. Transverse Single Spin Asymmetries # of partons in polarized proton depends on PDF X X partons’ polarisation in unpolarized proton depends on FF X Hadrons’ polarisation coming from unpolarised quarks depends on X fragmentation of polarised quark depends on

28. Transverse Single Spin Asymmetries All those terms contribute to the Single Spin Asymmetry

29. SINGLE-POLARISED UNPOLARISED. DOUBLE-POLARISED Drell-Yan Cross Section R.D. Tangerman and P.J. Mulders, Phys. Rev. D51, 3357-3372 (1995)

30. Azimuthal Asymmetries Unpolarized Single polarized Double polarized U = N(cos2φ>0) D = N(cos2φ<0) Asymmetry

31. Primary beams: Proton Heavy Ions Factor 100-1000 over present in intensity Future GSI and Facility for Antiproton and Ion Research Secondary Beams: Radioactive beams Antiprotons 3 - 30 GeV 1-2 10 7 /s Storage and Cooler Rings: Radioactive beams e – A collider 10 11 stored and cooled 0.8 - 14.5 GeV antiprotons

32. High Energy Storage Ring Electron cooler E<8 GeV Injection HESR High res. mode: L = 10 31 cm -2 s -1  p/p < 10 -5 High lum. mode: L = 2·10 32 cm -2 s -1  p/p < 10 -4 Cooling: electron/stochastic P max = 15 GeV/c L max = 2·10 32 cm -2 s -1 Ø < 100  m  p/p < 10 -5 internal target Characteristics 70 m 185 m 10 11 stored and cooled 0.8-15 GeV/c antiprotons Detector

33. HESR: asymmetric collider layout Asymmetric double-polarised collider mode proposed by PAX people: APR (Antiproton Polariser Ring): polarising antiprotons, p > 0.2 GeV/c CSR (Cooled Synchrotron Ring): polarised antiprotons, p = 3.5 GeV/c HESR: polarised protons, p = 15 GeV/c

34. The PANDA Detector STT Detectors Physics Performance Report for PANDA arXiv:0903.3905

35. Cherenkov Polarized Antiproton eXperiments Asymmetric collider (√s=15 GeV): polarized protons in HESR (p=15 GeV/c) polarized antiprotons in CSR (p=3.5 GeV/c) The PAX Detector V. Barone et al., Technical Proposal for PAX, 2005 http://www2.fz- juelich.de/ikp/pax/portal /index.php?id=103

36. CERN NA51 450 GeV/c Fermilab E866 800 GeV/c Di-Lepton Production pp -> l + l - X A. Baldit et al., Phys. Lett. 332-B, 244 (1994) R.S. Towell et al., Phys. Rev. D 64, 052002 (2001)

37. Phase space for Drell-Yan processes x 1,2 = mom fraction of parton 1,2  = x 1 x 2 x F = x 1 - x 2  = const: hyperbolae x F = const: diagonal PAX @ HESR symmetric HESR collider 1 1.5 GeV/c 2 ≤ M  ≤ 2.5 GeV/c 2 PANDA

38. Drell-Yan Process and Background Background studies: needed rejection factor of 10 7 Drell-Yan: pp ->  +  - X cross section   1 nb @ s = 30 GeV 2 Background: pp ->  +  - X, 2  + 2  - X,…… cross section   20-30  b m  = 105 MeV/c 2 ; m  145 MeV/c 2 average primary pion pairs:  1.5

39. A. Bianconi Drell-Yan Generator for pp Antiproton beam Polarized/Unpolarized beam and target Drell-Yan cross section from experimental data Selects event depending on the variables: x 1, x 2, P T,, ,  S from a flat distribution Cross section: A. Bianconi, Monte Carlo Event Generator DY_AB4 for Drell-Yan Events with Dimuon Production in Antiproton and Negative Pion Collisions with Molecular Targets, internal note (PANDA collaboration) A. Bianconi, M. Radici, Phys. Rev. D71, 074014 (2005) & D72, 074013 (2005) A. Bianconi, Nucl.Instrum.Meth. A593: 562-571, 2008

40. DY @ 15 GeV/c — pp->  +  - X layout studies for muon id with ABDYG (1.5 MEv) A. Bianconi Drell-Yan Generator [1] A. Bianconi and M. Radici, Phys. Rev. D71 (2005) 074014 [1] GeV Dilepton Mass Distribution M dilepton [GeV/c 2 ] Focus on one single M  range 1.5 MEv in 1.5 < M  < 2.5 (GeV/c 2 ) σ 0 4≤M≤9 ~ 0.4 pb σ 0 1.5≤M≤2.5 ~ 0.8 nb xPxP xPxP x2x2 x1x1

41. DY Asymmetries @ Vertex UNPOLARISEDSINGLE-POLARISED 500KEv included in asymmetries Acceptance corrections crucial! 1 < q T < 2 GeV/c 2 < q T < 3 GeV/c xPxP xPxP xPxP xPxP xPxP xPxP Physics Performance Report for PANDA arXiv:0903.3905

42. R = L  ·σ· ɛ = 2·10 32 cm -2 s -1 × x 0.8·10 -33 cm 2 × 0.33 = 0.05 s -1 ~ 130 Kev/month Statistical errors for 500KEv generated xPxP ) ) xPxP xPxP Physics Performance Report for PANDA arXiv:0903.3905 DY Asymmetries @ Vertex

43. The Road to Polarized Antiprotons

44. How to polarize antiprotons? Intensity loss, but it works H. Ströher, PoS(STORI11) 030 D. Oellers, PoS(STORI11) 008 Spin filtering Λbar decay Not feasible Not enought intensity Spin flip Spin dependent reaction Under study

45. Experimental setup H. Ströher, PoS(STORI11) 030 D. Oellers, PoS(STORI11) 008

46. Beam Polarimenter pd elastic scattering detection in two (L-R) symmetric Silicon Tracking Telescopes Deuteron separation H. Ströher, PoS(STORI11) 030 D. Oellers, PoS(STORI11) 008

47. Results – Beam Polarization Measurements after a storing period of 5000 s H. Ströher, PoS(STORI11) 030 D. Oellers, PoS(STORI11) 008 Polarization lifetime: τ p > 10 5 s Spin-flip efficiency: 0.9887 ± 0.0001

48. Summary  New physics from unpolarized DY  Wide Single Spin Asymmetry program  Double Spin Asymmetries, if p can be polarized Interest on Drell-Yan studies 1.5 < M μμ < 2.5 GeV/c 2 Cuts for background rejection Rejection factor achieved for secondary background: > 5 10 6 Kinematically constrained refit still to be investigated Few months of data taking are enough to:  evaluate unpolarised and single-spin asymmetries with good accuracy  investigate their dependence on q T, μμ Next step: Polarized Antiprotons