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Drell-Yan Perspectives at FAIR

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

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Drell-Yan Perspectives at FAIR

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

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

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

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

  7. Transversity • δq(x): a chirally-odd, helicityflipdistributionfunction • δg(x): no gluontransversitydistribution; transversely • polarisednucleonshowstransversegluoneffects • at twist-3 (g2) only • SOFFER INEQUALITY • An upper limit: • can beviolatedbyfactorisation at NLO • inequalitypreserved under evolutiontolargerscalesonly

  8. TMD: KT-dependent Parton Distributions Twist-2 PDFs Transversity Sivers Boer-Mulders

  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 GeV2 with PANDA up to s~200 GeV2 with PAX @ RHIC much higher energies → big contribution from sea-quarks

  10. Drell-Yan Process • Drell-Yan: pp -> +-X Kinematics x1,2 = mom fraction of parton1,2  = x1• x2 = M2/s xF = x1 - x2 Collins-Soper frame 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 x1 and/or x2 • Too small Soffer upper bound on ATT (percent level[1]) • ATT @ 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 x1 and/or x2 • Too small Soffer upper bound on ATT (percent level[1]): • ATT @ 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. s=45 GeV2 s=45 GeV2 s=210 GeV2 s=210 GeV2 QCD higher order contributions • cross section affected • K-factors almost spin independent [1] Shimizu et al., hep-ph/0503270 .

  15. QCD contributions to ATT • 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 GeV2 [3]Efremov et al, Eur. Phys. J. C 35 (2004) 207. • ATT small at large √s and M2 • due to slow evolution of h1a(x,Q2) • Large ATT expected[1] for √s and • M2 not too large and τ not too • small Q2 = 16 GeV2 Q2 = 9 GeV2 Q2 = 5 GeV2 [1] Shimizu et al., Phys.Rev.D 71 (2005) 114007. [2]M. Anselmino et al., Phys. Lett. B594 (2004) 97.

  18. Drell-Yan Asymmetries Di-Lepton Rest Frame • 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.

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

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

  21. Angular distribution in CS frame E615 @ Fermilab -N  +-X @ 252 GeV/c -0.6 < cos < 0.6 4 < M < 8.5 GeV/c2 Conway et al, Phys. Rev. D39 (1989) 92

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

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

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

  25. Drell-Yan Asymmetries Boer-Mulders T-odd Chiral-odd TMD [1] • 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] L. Zhu et al, PRL 99 (2007) 082301; [1] D. Boer, Phys. Rew. D60 (1999) 014012.

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

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

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

  29. UNPOLARISED Drell-Yan Cross Section SINGLE-POLARISED . DOUBLE-POLARISED 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. Future GSI andFacility for Antiproton and Ion Research • Primary beams: • Proton • Heavy Ions • Factor 100-1000 over present in intensity • Secondary Beams: • Radioactive beams • Antiprotons 3 - 30 GeV • 1-2 107 /s • Storage and Cooler Rings: • Radioactive beams • e – A collider • 1011 stored and cooled • 0.8 - 14.5 GeV antiprotons

  32. High Energy Storage Ring Injection 1011 stored and cooled 0.8-15 GeV/c antiprotons HESR 185 m 70 m Electron cooler E<8 GeV Detector Characteristics Pmax = 15 GeV/c Lmax = 2·1032 cm-2 s-1 Ø < 100 m p/p < 10-5 internal target Cooling: electron/stochastic High res. mode: L = 1031 cm-2 s-1p/p < 10-5 High lum. mode: L = 2·1032 cm-2 s-1 p/p < 10-4

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

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

  37. Phase space for Drell-Yan processes x1,2 = mom fraction of parton1,2  = x1• x2 xF = x1 - x2  = const: hyperbolae xF = const: diagonal PANDA 1.5 GeV/c2 ≤ M ≤ 2.5 GeV/c2 PAX @HESR symmetric HESR collider 1

  38. Drell-Yan Process and Background • Drell-Yan: pp -> +-X cross section   1 nb @ s = 30 GeV2 • Background: pp -> +-X, 2+2-X,…… cross section   20-30 b m = 105 MeV/c2; m 145 MeV/c2 average primary pion pairs:  1.5 • Background studies: needed rejection factor of 107

  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: • x1, x2, PT, , , 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. Dilepton Mass Distribution σ01.5≤M≤2.5~ 0.8 nb x2 σ04≤M≤9~ 0.4 pb xP Mdilepton [GeV/c2] x1 xP DY @ 15 GeV/c — pp->+-X GeV [1] A. Bianconi Drell-Yan Generator • layout studies for muon id • with ABDYG (1.5 MEv) Focus on one single Mrange 1.5 MEv in 1.5 <M< 2.5 (GeV/c2) [1]A. Bianconi and M. Radici, Phys. Rev. D71 (2005) 074014

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

  42. ) ) xP DY Asymmetries @ Vertex Statistical errors for 500KEv generated xP R = L·σ·ɛ = 2·1032cm-2s-1 × x 0.8·10-33cm2× 0.33 = 0.05 s-1~ 130 Kev/month xP Physics Performance Report for PANDA arXiv:0903.3905

  43. The Road to Polarized Antiprotons

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

  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 • Polarization lifetime: τp > 105 s • Spin-flip efficiency: 0.9887 ± 0.0001 H. Ströher, PoS(STORI11) 030 D. Oellers, PoS(STORI11) 008

  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 < Mμμ < 2.5 GeV/c2 • Cuts for background rejection • Rejection factor achieved for secondary background: > 5 106 • 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 qT,μμ • Next step: Polarized Antiprotons

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