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

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

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)

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

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

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

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

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

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

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.

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

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

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

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/ cross section affected K-factors almost spin independent

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

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

Double Spin 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) [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

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

Expected polar distributions 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.

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

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

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

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

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)

[1] L. Zhu et al, PRL 99 (2007) ; [1] D. Boer, Phys. Rew. D60 (1999) 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

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)

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

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

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

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

Primary beams: Proton Heavy Ions Factor over present in intensity Future GSI and Facility for Antiproton and Ion Research Secondary Beams: Radioactive beams Antiprotons GeV /s Storage and Cooler Rings: Radioactive beams e – A collider stored and cooled GeV antiprotons

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

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

The PANDA Detector STT Detectors Physics Performance Report for PANDA arXiv:

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, juelich.de/ikp/pax/portal /index.php?id=103

CERN NA GeV/c Fermilab E 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, (2001)

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 HESR symmetric HESR collider GeV/c 2 ≤ M  ≤ 2.5 GeV/c 2 PANDA

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

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, (2005) & D72, (2005) A. Bianconi, Nucl.Instrum.Meth. A593: , 2008

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) [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

DY 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:

R = L  ·σ· ɛ = 2·10 32 cm -2 s -1 × x 0.8· 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: DY Vertex

The Road to Polarized Antiprotons

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

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

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

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: ±

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: > 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