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Polarized Drell-Yan Physics at COMPASS

Polarized Drell-Yan Physics at COMPASS. IhnJea Choi University of I llinois at Urbana-Champaign For the COMPASS collaboration. Outline. TMD PDFs Sivers asymmetry results from Semi-Inclusive DIS (SIDIS) Sign change of Sivers functions between Drell -Yan (DY) and SIDIS

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Polarized Drell-Yan Physics at COMPASS

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  1. Polarized Drell-Yan Physicsat COMPASS IhnJea Choi University of Illinois at Urbana-Champaign For the COMPASS collaboration Light Cone 2014, IhnJea Choi

  2. Outline • TMD PDFs • Sivers asymmetry results from Semi-Inclusive DIS (SIDIS) • Sign change of Siversfunctions between Drell-Yan (DY) and SIDIS • Polarized DY process • COMPASS experiment • Pion-induced transversely polarized DY experiment • DY Simulation with COMPASS spectrometer • Beam test results for DY feasibility and estimation at COMPASS • Summary Light Cone 2014, IhnJea Choi

  3. Proton Spin Structure, 3 PDFs NUCLEON Spin NUCLEON, Un Pol. Longitudinal Pol. Transverse Pol. Un Pol. Unpolarized f1 (x) Quark Spin Helicity g1(x) − Long. Pol. Quark, Transversity h1(x) − Trans. Pol. • At leading twist, structure of nucleon can be described by three PDFs. • However, perturbative QCD in collinear approximation cannot explain measurements • of large azimuthal spin asymmetries from high energy collision experiments. Light Cone 2014, IhnJea Choi

  4. Proton Spin Structure, 3 PDFs (kT) Taking account the intrinsic transverse momentum of quark NUCLEON Spin NUCLEON, Un Pol. Longitudinal Pol. Transverse Pol. Un Pol. Unpolarized f1 (x) Quark Spin Helicity g1(x) − Long. Pol. Quark, Transversity h1(x) − Trans. Pol. Light Cone 2014, IhnJea Choi

  5. +5 TMDs Proton Spin Structure, 3 PDFs (kT) Taking account the intrinsic transverse momentum of quark NUCLEON Spin NUCLEON, Un Pol. Longitudinal Pol. Transverse Pol. Sivers − kT kT Un Pol. Unpolarized f1 (x) Quark Spin − kT kT Helicity g1(x) − Long. Pol. h1(x) − − Quark, Transversity h1(x) kT kT kT kT − − kT kT Trans. Pol. • 8 PDFs are needed for a full description of the nucleon, Transverse Momentum dependent PDFs • Subtle quark transvers momentum of parton embedded into the PDFs (x)  (x, kT2) • Provide essential non-perturbative information on the parton sub-structure of nucleon Light Cone 2014, IhnJea Choi

  6. Sivers in Semi-Inclusive DIS(SIDIS) Semi-Inclusive IDIS Sivers Function − kT kT • Influence of the transverse hadron spin • onto the quark transverse momentum Siversasymmetry • Lepton and produced hadron used a probe access to quark kT and transverse polarization • TMDs appears in azimuthal asymmetries in convolution of PDFs and fragmentation function (FFs) • If FFs known, TMDs are accessible for different flavor from SIDIS measurements of identified hadrons Light Cone 2014, IhnJea Choi

  7. Sivers measurement from SIDIS • COMPASS 160 GeV, HERMES 27.6 GeV • Non zero Sivers asymmetries measured in SIDIS at COMPASS and HERMES Light Cone 2014, IhnJea Choi

  8. Sign Change of SiversFunctions between SIDIS and DY SIDIS DY VS. S.J. Brodsky, D.S. Hwang, I.Schmidt, Nucl. Phys. B642 344 J.C. Collins, Phys. Lett. B536 (2002) 43 Direction of the gauge-link of the kT dependent PDF is process-dependent and it changes to the opposite in SIDIS w.r.t DY Crucial test of non-perturbative QCD! arXiv:0805.2677v2 [hep-ph] 9 Jan 2009 M.Anselmino et al, PRD 79 054010 Light Cone 2014, IhnJea Choi

  9. Drell-Yan Process • Quark and antiquark annihilation process. • DY, no fragmentation process required, is an excellent tool to study TMDs as it accesses directly to initial parton structure • Complementary measurement to SIDIS measurement Arnold, Metz and sion Phys. Rev. D79 (2009) 034005 Pa Hadron beam momentum Pb = 0, (fixed target) ι Lepton momenta S target polarization If the quarks intrinsic transverse momentum ≠ 0, The dilepton has also qT = kTa + kTb Light Cone 2014, IhnJea Choi

  10. Definition of azimuthal angles in DY 1) Target rest frame (TF) Angle between target spin (ST) and transverse component of outgoing lepton pair momentum Beam hadron 2) Rest frame of the virtural photon (CS : Collins-Soper frame) Angle between planes defined by hadron and lepton momenta Beam hadron Polar angle of lepton pair in the CF frame Light Cone 2014, IhnJea Choi

  11. Pol. Drell-Yan cross section DY cross section for transversely polarized nucleon target S. Arnold et al., Phys. Rev. D79 (2009) 034005. A. Kotzinian, COMPASS Note 2010-2, February 10, 2010, F: Flux of incoming hadrons, D[] depolarisation factor ϕs : TF frame ϕ, θ, CS frame DY cross section (LO QCD) Light Cone 2014, IhnJea Choi

  12. Pol. Drell-Yan cross section All these asymmetries (modulations) are expected to be sizable in the valence quark range and can be measured at COMPASS. At LO QCD Light Cone 2014, IhnJea Choi

  13. COMPASS COmmonMuon Proton Apparatus for Structure and Spectroscopy SPS M2 Beam line COMPASS II (Proposal approved by CERN on 2010) - Generalized Parton Distributions - TMDs in SIDIS - TMDs in pion induced Drell Yan • Fixed target experiment located at CERN SPS M2 beam line since 2002 • Muon and Baryon spectroscopy with high energy • 25 Institutes, ~250 people Light Cone 2014, IhnJea Choi

  14. COMPASS Experimental Hall Beam Light Cone 2014, IhnJea Choi

  15. MuonWall SM2 E/HCAL E/HCAL SM1 MuonWall Target RICH Beam The COMPASS Spectrometer • Muon/hadron beam: 160/190 GeV • High beam intensity (2x109 / spill) • Polarized proton target 50 m Small Angle Spectrometer(SAS) Large Angle Spectrometer (LAS) Light Cone 2014, IhnJea Choi

  16. Simulation for Beam Choice • Choice of beam (π-) Valence u-quark and anti-u quark dominant in Drell-Yan process TMDs are sensitive at valence quark regime (x > 0.1) • Choice of beam energy (190GeV) (PYTHIA, 4 < Mμμ< 9 GeV/c) ~ 0.1 The value s = 357 GeV2, corresponding to a pion beam momentum of 190 GeV/c, seems to be a good choice. -> As the energy increased, the phase space coverage extends to the low-x non-valence region Light Cone 2014, IhnJea Choi

  17. Simulation for DY Acceptance COMPASS Spectrometer Polar angle distribution of muon pairs from Drell-Yan events SAS LAS Large Angle Spectrometer(LAS) < 140 mrad Small Angle Spectrometer(SAS) < 15 mrad Light Cone 2014, IhnJea Choi

  18. Simulation for DY Kinematics (High Di-muon mass region, 4 < Muu < 9 GeV/c2) M. Anselmino .. Phys.Rev.D79:054010, 2009 • Valence quark range (x > 0.1) for both quarks (pure u-ubar annihilation) • (PT dimuon about 1GeV/c where TMD effects are dominant) • Acceptance is largest where the Siversfunction is expected to be largest Light Cone 2014, IhnJea Choi

  19. Simulation for DY Kinematics (Low Di-muon mass region, 2 < Muu < 2.5 GeV/c2) M. Anselmino .. Phys.Rev.D79:054010, 2009 • Maximal expected asymmetry value nearly correspond to the maximal acc. Light Cone 2014, IhnJea Choi

  20. Simulation, SIDIS vs. DY kinematic Mean value comparison There is overlap in the phase-space accessed by the 2 measurements. When comparing the extracted TMDs, QCD evolution of the TMDs must be taken into account. • The COMPASS SIDIS and DY experimental measurements have an overlapping kinematic region. Light Cone 2014, IhnJea Choi

  21. DY Feasibility – Test Setup • Pion induced DY test runs at COMPASS, year 2007, 2008, 2009 (3 days) • π- 190 GeV/c beam • Transversely polarized target simulated by two cylinders targets of polyetylene (CH2) -> NH3 • Hadron absorber installed • Beam intensity : 8 x107 pions/spill (spill length 9.6s) COMPASS Detector π- beam Transvers Pol. target Two 40cm length of Polyethylene(CH2) separated by 20cm Hadron absorber and beam plug(stop non-interacting beam) Light Cone 2014, IhnJea Choi

  22. Vertex & Di-muonDistributon Preliminary on Nov 2013 After all track quality cuts included From absorber cell1 cell2 • Bothtarget cells (40cm + 40cm, gap between cells 20cm) are visible in the distribution • (to cancel out systematic uncertainties from different location of polarized target) • Requires improved beam and vertex tracking Light Cone 2014, IhnJea Choi

  23. Dimuon Mass Distributon For 3 days of data taking in 2009 Preliminary on Nov 2013 • 6787 number of J/ψ reconstructed for 3 days of data taking (a factor two increased from the previous released data, 3170 # J/ψ) • Collected number of J/ψ is agreement with the expectations from MC simulation. Light Cone 2014, IhnJea Choi

  24. Dimuon Transverse Momentum Distribution Light Cone 2014, IhnJea Choi

  25. xp vs. xπ, and xFDistributions Light Cone 2014, IhnJea Choi

  26. Di-muon Background • Combinatorial muon BG is negligible under the J/Psi region • Beam intensity in this test was 8.3*106pions/s, which is around 10 times lower than the beam intensity expected in the future • - controllable by optimizing hadron absorber and beam plug • Open-charm semi-leptonic decays • - Seen to negligible in simulation Muu>2GeV in PYTHIA Light Cone 2014, IhnJea Choi

  27. Expected DY events at COMPASS Previous COMPASS Proposal Current estimation Beam intensity of Ibeam = 108 pion/s SPS super-cycle of 33.6s Beam intensity of Ibeam = 6 x 108pion/s Spill 9.6s 2034 DY events / day 1 year run (140days) 0.285 Million DY events estimated For dimuon high mass region, (4 < Muu < 9 GeV/c2) 892 DY events / day 2 year runs (280days) 0.2 Million DY events estimated For dimuon high mass region (4 < Muu < 9 GeV/c2) Light Cone 2014, IhnJea Choi

  28. Sivers Asymmetry Prediction (Dimuon Mass Region, 4 < Mμμ < 9 GeV/c2) Light Cone 2014, IhnJea Choi

  29. Asymmetries Prediction Light Cone 2014, IhnJea Choi

  30. Detector Upgrades • COMPASS Polarised target: • New target holder (2x55 cm, 20 cm gap) • Old/modified Micro-Wave cavity (2 cells target) • PT Pump system refurbishing • COMPASS PT has to be moved by ~2.2 meters upstream in order to release space for the Hadron Absorber • Hadron absorber (Alumina Al2O3) and beam plug (tungsten) • Radio-Protection screen (stainless steel & borated polyeth.) • New SciFi-based beam telescope • H1 trigger hodoscope modification (central hole size adjustment) • New vertex detector (SciFi based) • New Large Area tracking station in the LAS Light Cone 2014, IhnJea Choi

  31. Summary • The Sivers asymmetry has been measured in SIDIS at COMPASS • and at HERMES. • COMPASS II will test the expected sign change of Sivers and • Boer-Mulders PDFs in DY • Feasibility of Drell-Yan measurement was demonstrated • with 2009 test beam • Expected statistical precision of asymmetry measurement • is 1~2% • First ever pion induced transversely polarized Drell-Yan • experiment will start in this year (2014). Light Cone 2014, IhnJea Choi

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