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Spin physics in Drell-Yan processes: past and future experiments

Spin physics in Drell-Yan processes: past and future experiments. Michela Chiosso University of Torino – Dip. Fisica Generale I.N.F.N - Torino. IWHSS 2008 Torino – April 2 nd 2008. Drell-Yan dilepton production. d. d. u. u. Target p.

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Spin physics in Drell-Yan processes: past and future experiments

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  1. Spin physics in Drell-Yan processes: past and future experiments Michela Chiosso University of Torino – Dip. Fisica Generale I.N.F.N - Torino IWHSS 2008 Torino – April 2nd 2008

  2. Drell-Yan dilepton production d d u u Target p This process is electromagnetic and exactly calculable Propagator of the virtual photon in the amplitude  factor M-2 in the cross section

  3. - Omega, CERN (Corden at al, 1978, 1980) • - CIP, FERMILAB (Anderson et al 1976, Hogan et al 1979) • NA3, CERN (Badier et al 1979, 1989) • CFS, FERMILAB (Lederman et al, 1982) • CHFMNP, CERN (Antreasyan et al) • E605, FERMILAB (Moreno et al, 1989) • … 1970s - 1980s • - E615, FERMILAB (Conway et al, 1989) • - NA10, CERN (Anderson et al, 1984) • E772, FERMILAB (McGaughey et al, 1994) • NA51, CERN (Abreu et al, 1998) • E866 (E.A. Hawker et al, 1998) • … 1980s – 1990s Past Drell-Yan experiments This process was first described by Sydney Drell and Tung-Mow Yan in 1970. First quantitative Drell-Yan experiments: late 1970s  waiting for spectrometers able to measure pbarn cross-sections in the presence of much larger background.

  4. This talk Present and future Drell-Yan facilities RHIC collider S=(200)2 GeV2 J-PARC fixed targetS= 60-100 GeV2 FAIR colliderS=200 GeV2 fixed targetS=30-80 GeV2 COMPASSfixed targetS=100-400 GeV2 (CERN-SPS) NICA S=400 GeV2 (JINR) E906 fixed target S=230 GeV2 (FMI) CMS collider S=196 TeV2 (CERN-LHC) Les Bland Yuji Goto Klaus Peters Alexander Sorin

  5. Investigating PDFs with Drell-Yan processes Since many years Drell-Yan process has been playing a key role in the study of parton distribution functions (PDFs) • Flavor asymmetry of nucleon parton distribution functions E772,E866, NA51, E906 • p, k mesons parton distribution functions NA10, E615, NA3 • Boer-Mulders transverse momentum dependent parton distribution Function (TMD PDFs) E615, NA10, E866 Recently it is drawing back attention as a unique tool to directly access spin dependent parton distribution functions • Transversity • Sivers function

  6. Flavor asymmetry in the nucleon sea E772,E866, NA51, E906 Light sea-quarks flavor asymmetry

  7. Pion quarks distribution function NA10, -----E615 P.J. Sutton, A.D. Martin, Phys.Rev.D, 45 (7) 1992 • No available experimental • data at small x (x≤0.2) to • determine sea-quark distr. • unambiguously • Performed various fits with • sea carrying an increasing • fraction of pion momentum • p+p- valence distr. are the • same, but different contr. to • DY through quark charge • squared gluon distribution: Prompt photon production valence distribution: Fit to Drell-Yan data sea-quark distribution: Fit to Drell-Yan data

  8. Light mesons parton distribution functions p, k mesons parton distribution functions NA10, E615, NA3 pion structure function NA3 :

  9. Angular distribution & Boer-Mulders PDF Unpolarized angular distribution in Collin-Soper frame λ=1,μ=ν=0 at LO, in collinear approximation  transversely polarized g, no transverse momenta: Lam-Tung relation: 1-l-n=0 NLO prediction: small deviation from for Pt<3GeV/c n≠ 0: Boer-Mulders effect if PT2«M2 NLO corrections, at large qt

  10. Angular distribution & Boer-Mulders PDF 1.There is a sizable cos2f asymmetry (n up to 0.3) in the unpolarized pion-induced Drell-Yan: the Lam-Tung sum rule is violated beyond the QCD-improved parton model. NA10 , E615 2.l= -1 at large xf E615 3. No azimuthal asymmetry in proton-induced Drell-Yan E866

  11. Angular distribution & Boer-Mulders PDF Violation of Lam-Tung sum rule Boer-Mulders function can lead to azimuthal dependence

  12. Angular distribution & Boer-Mulders PDF E866 at Fermilab 800 GeV/c p+d 800 GeV/c p+p No noticeable flavour asymmetry between Sea-quark Boer-Mulders function is relatively small

  13. Spin dependent parton distribution functions Polarized Drell-Yan Transversity  direct access to without convolution with fragmentation function , like in SIDIS Sivers function Boer-Mulders function

  14. Spin dependent parton distribution functions Double polarization ( ) transversity Single polarization ( ) Sivers Boer-Mulders transversity No polarization ( ) Boer-Mulders

  15. Spin dependent PDFs with Drell-Yan processes polarized beam + polarized target (beam) or unpolarized beam + polarized target Valence High luminosity: very small DY cross section Larger asymmetries (SSA and DSA) in region with large valence quark content. What do we need to access spin dependent PDFs through DY?

  16. Spin physics with Drell-Yan processes in COMPASS Measures of single-spin DY asymmetries: Polarised DY SSA ~ sin(f-fs) + sin(f+fs) Beam: p - p S=100÷400 GeV2 Polarized target: NH3 / 6LiD Polarization: >80% / >40% Dilution factor: 0.15 / 0.35 Luminosity Unpolarised DY ds~cos(2f)  · Using p- beam it is necessary to make an assumption connecting pion and proton PDFs p - p ~1031 cm-2 s-1

  17. COMPASS spectrometer layout MW1 PT Beam ECAL1 HCAL1 Ibeam~ 1108 p/s 25% of current PT Polarized target 180 mrad acceptance 2 cells, 15 cm each

  18. Kinematic range M<J/y dominated by semileptonic decay of charmed hadrons M>J/yDrell-Yan dilepton production major contribution M must be large enough to apply pQCD But production rate falls off rapidly with M Safe region: Out from resonances regions dominated by strong production mechanism

  19. Kinematic range x1, x2 Sizeable single and double spin asymmetries in valence quark region COMPASS s=100-400 GeV2 M=4-9 GeV/c2 t=0.16-0.8 @ s=100 GeV2 t=0.08-0.4 @ s=200 GeV2 t=0.05-0.3 @ s=300 GeV2 t=0.04-0.2 @ s=400 GeV2

  20. Kinematic range COMPASS S=300GeV2 S=100GeV2 S=200GeV2 x2 x2 x2 x1 x1 x1 S=100GeV2 S=300GeV2 Q2 Q2

  21. Kinematic range: COMPASS acceptance x1vs x2 in “valence” region: 0.1  x1/2 0.5 t Sensitive to Sivers effect at low PT: PT<< Q PT

  22. Kinematic range: COMPASS vs other experiments x2 vs x1 COMPASS E866 E615

  23. What… Spin dependent PDFs transversity, Sivers function, Boer-Mulders function How… 1·108 p- beam on NH3/6LiD polarized target expected luminosity: 1031 cm-2 sec-1 expected events rate: ~ 34000 in 150 days of run S=300 GeV2 , M(m+m-): 4-9 GeV/c When Beyond 2010 November 11-12, 2007 Test beam at CERN SPS: verified radiation conditions, PT and spectrometer peformances with high intensity hadron beam EOI in preparation Spin physics in Drell-Yan processes at COMPASS SUMMARY

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