偏極ドレル・ヤン実験

1. 偏極ドレル・ヤン実験 偏極標的開発キックオフミーティング ＠山形大学 2010年6月30日（水） 後藤雄二（理研）

2. 内容 • イントロダクション • 陽子スピンの謎 • 横方向スピン構造 • TMD分布関数 • 偏極ドレル・ヤン実験 • FNAL-E906実験将来計画 • その他の実験計画 • 偏極標的開発

3. イントロダクション • 陽子スピンの謎 • 陽子スピン1/2の起源は何か？ • Fundamentalな対象であるにもかかわらず理解されていない。 • QCDを基盤とする研究方法が発展している • 縦偏極実験と横偏極実験 • 縦偏極 • 横偏極 • 深非弾性散乱(DIS)実験とハドロン衝突実験 • DIS実験 • Semi-inclusive DIS実験 • ハドロン衝突実験

4. lepton beam  or  g*  or  nucleon target quark 核子スピン１/２の起源 • 偏極レプトン深非弾性散乱実験 • パートン模型 偏極構造関数 非偏極構造関数

5. 核子スピン１/２の起源 • EMC実験＠CERN • 中性子およびハイペロン崩壊データを用いて • クォークスピンは核子スピンの小さな割り合いにしか寄与しない • x = 0 ~ 1 の積分による不確定性 • より広いx領域を覆う、よりよい精度のデータが必要 • SLAC/CERN/DESY/JLAB 実験 J. Ashman et al., NPB 328, 1 (1989). 「陽子スピンの危機」

6. 核子スピン１/２の起源 • なぜわかっていないのか？ • 偏極実験の難しさ • 偏極レプトンビーム • SLAC/CERN/DESY/JLab • 偏極標的 • SLAC/CERN/DESY/Jlab/FNAL • (and other low-energy facilities) • 偏極陽子ビーム • RHIC • (and other low-energy facilities)

7. 偏極レプトン深非弾性散乱実験 • 固定ターゲット実験 • Q2の範囲が限られている unpolarized DIS polarized DIS 1 < Q2< 100 (GeV/c)2 1 < Q2< 100 (GeV/c)2

8. 偏極レプトン深非弾性散乱実験 • クォークスピンの寄与 • 核子スピン１/２の起源は何か？ • グルーオンスピンの寄与？ • 軌道角運動量？

9. Transverse-spin - introduction Multi-dimensional structure of the nucleon Orbital angular momentum inside the nucleon Shape of the nucleon Extension of distribution functions GPD (Generalized Parton Distribution) TMD (Transverse-Momentum Dependent) distribution quark distribution with parallel spin to the nucleon quark distribution with anti-parallel spin to the nucleon direction of nucleon spin G. A. Miller, PRC68, 022201(R) (2003) NSAC Long Range Plan arXiv:0809.3137

10. 横偏極非対称度測定 • SSA (Single Spin Asymmetry)、左右非対称度 • 前方 xF > 0.2 • Fermilab-E704 • 固定標的実験 • s = 19.4 GeV • 非対称度 ~20% • 多くのQCDに基づく理論の開発

11. Transverse-spin – results Forward rapidity 0 at STAR at s = 200 GeV Forward identified particles at BRAHMS +  Forward rapidity 0 at PHENIX at s = 62.4 GeV K p

12. Introduction • Transverse structure of the proton • Transversity distribution function • Correlation between nucleon transverse spin and parton transverse spin • TMD distribution functions • Sivers function • Correlation between nucleon transverse spin and parton transverse momentum (kT) • Boer-Mulders function • Correlation between parton transverse spin and parton transverse momentum (kT) Leading-twist transverse momentum dependent (TMD) distribution functions

13. Transverse-spin - results • Results at forward rapidity • Explained as a mixture of Sivers effect, Collins effect, and higher-twist effect • Why similar asymmetry on K+ (valence+sea) and K- (sea+sea)? • Why large asymmetry on anti-proton? • How to distinguish Sivers effect? • Back-to-back jet • How to separate initial-state and final-state interaction with remnant partons? • Forward photon + jet • Drell-Yan process

14. Sivers function M. Anselmino, et al. EPJA 39, 89 (2009) Sivers function u-quark • Single-spin asymmetry (SSA) measurement • < 1% level multi-points measurements have been done for SSA of DIS process • Valence quark region: x = 0.005 – 0.3 • (more sensitive in lower-x region) d-quark

15. Drell-Yan process • The simplest process in hadron-hadron reactions • No QCD final state effect • FNAL-E866 • Unpolarized Drell-Yan experiment with Ebeam = 800 GeV • Flavor asymmetry of sea-quark distribution • x = 0.01 – 0.35 (valence region) • FNAL-E906 • Similar experiment with main-injector beam Ebeam = 120 GeV • x = 0.1 – 0.45 DIS Drell-Yan

16. FNAL-E906 Momentum analysis • Dimuon spectrometer • Main injector beam Ebeam = 120 GeV • Higher-x region: x = 0.1 – 0.45 • Beam time: 2010 – 2013 Focusing magnet Hadron absorber Beam dump

17. Polarized Drell-Yan experiment • Many new inputs for remaining proton-spin puzzle • Single transverse-spin asymmetry • Sivers function measurement • Transversity  Boer-Mulders function • Double transverse-spin asymmetry • Transversity (quark  antiquark for p+p collisions) • Double helicity asymmtry • Flavor asymmetry of quark polarization • Other physics • Parity violation asymmetry…

18. Polarized Drell-Yan experiment • “Non-universality” of Sivers function • Sign of Sivers function determined by SSA measurement of DIS and Drell-Yan processes should be opposite each other • final-state interaction with remnant partons in DIS process • Initial-state interaction with remnant partons in Drell-Yan process • Fundamental QCD prediction • Milestone for the field of hadron physics to test the concept of the TMD factorization DIS Drell-Yan “toy” QED attractive repulsive QCD • Explanation by Vogelsang and Yuan • from “Transverse-Spin Drell-Yan • Physics at RHIC,” Les Bland, et al., • May 1, 2007

19. 偏極ドレル・ヤン実験 • FNAL-E906実験将来計画 •  ビーム、偏極標的 • その他の実験計画 • COMPASS •  ビーム、偏極標的 • RHIC • 偏極陽子ビーム • J-PARC • 偏極陽子ビーム（？）、偏極標的 • FAIR, …

20. Comparison with other experiments

21. COMPASS facility at CERN (SPS) II

22. DY@COMPASS - set-upπ- p  μ- μ X Key elements: • COMPASS PT • Tracking system (both LAS abs SAS) and beam telescope in front of PT • Muon trigger (in LAS is of particular importance - 60% of the DY acceptance) • RICH1, Calorimetry – also important to reduce the background (the hadron flux downstream of the hadron absorber ~ 10 higher then muon flux) π- 190 GeV

23. DY@COMPASS kinematics - Indication TMD PDFs – ALL are sizable in the valence quark region Sivers effect in Drell-Yan processes.
M. Anselmino, M. Boglione U. D'Alesio, S. Melis, F. Murgia, A. Prokudin 
Published in Phys.Rev.D79:054010, 2009

24. DY@COMPASS – kinematics - valence quark rangeπ- p  μ- μ X • In our case (π- p  μ- μ X) contribution from valence quarks is dominant • In COMPASS kinematics u-ubar dominance • <PT> ~ 1GeV – TMDs induced effects expected to be dominant with respect to the higher QCD corrections

25. DY@COMPASS - feasibility • Small cross section - High luminosity experiment • Polarised target is the key instrument of the program • Radioprotection issue – experiment similar to NA3 • Detector occupancies • Trigger rates • DY event rate (J/Psi as a monitoring signal) • Physics background study: • D-Dbar semi-leptonic decays • Combinatorial background from π and K • COMPASS spectrometer kinematic range

26. RHIC-IP2 (overplotted on BRAHMS) Internal target position St.4 MuID St.1 St.2 St.3 F MAG3.9 m Mom.kick 2.1 GeV/c KMAG 2.4 m Mom.kick 0.55 GeV/c 14 m 18 m

27. Requirement for the RHIC accelerator • Appropriate beam lifetime and low background • Affected by beam blow-up (small-angle scattering, beam energy loss at the target, …) • low background for collider experiments (in phase-1) • Compensation for dipole magnets in the experimental apparatus • both beams need to be restored on axis in two colliding-beam operation • Higher beam intensity at phase-2 • 1.5-times more number of bunches (assumed at eRHIC) • Otherwise, 1.5-times longer beam time is required • Radiation issues • Beam loss/dump requirement? • Experimental site issues • Magnet, civil engineering works, …

28. Experimental sensitivities • PYTHIA simulation • s = 22 GeV (Elab = 250 GeV) • luminosity assumption 10,000 pb-1 •  10 times larger luminosity necessary than that of the collider experiments • because of ~10 times smaller cross section  acceptance (in the same mass region) • 4.5 GeV < M < 8 GeV • acceptance for Drell-Yan dimuon signal is studied all generated dumuon from Drell-Yan accepted by all detectors

29. Experimental sensitivities • About 50K events for 10,000pb-1 luminosity • x-coverage: 0.2 < x < 0.5 • x1: x of beam proton (polarized) • x2: x of target proton

30. Experimental sensitivities • Phase-1 (parasitic operation) • L = 2×1033 cm-2s-1 • 10,000 pb-1 with 5×106 s ~ 8 weeks, or 3 years (10 weeks×3) of beam time by considering efficiency and live time • Phase-2 (dedicated operation) • L = 3×1034 cm-2s-1 • 30,000 pb-1 with 106 s ~ 2 weeks, or 8 weeks of beam time by considering efficiency and live time Theory calculation: U. D’Alesio and S. Melis, private communication; M. Anselmino, et al., Phys. Rev. D79, 054010 (2009) Measure not only the sign ofthe Sivers function but also the shape of the funcion 10,000 pb-1 (phase-1) 40,000 pb-1 (phase-1 + phase-2)

31. Collider vs fixed-target • x1 & x2 coverage • Collider experiment with PHENIX muon arm (simple PYTHIA simulation) • s = 500 GeV • Angle & E cut only • 1.2 < || < 2.2 (0.22 < || < 0.59), E > 2, 5, 10 GeV • (no magnetic field, no detector acceptance) • luminosity assumption 1,000 pb-1 • M = 4.5  8 GeV • Single arm: x1 = 0.05 – 0.1 (x2 = 0.001 – 0.002) • Very sensitive x-region of SIDIS data • Fixed-target experiment • x1 = 0.2 – 0.5 (x2 = 0.1 – 0.2) • Can explore higher-x region with better sensitivity PHENIX muon arm (angle & E cut only) Fixed-target experiment x2 x2 x1 x1

32. Charm/bottom background • In collider energies, there is non-negligible background from open beauty production • In fixed-target energies, background from charm & bottom production is negligible PHENIX muon arm s = 200 GeV FNAL-E866 Elab = 800 GeV charm bottom Drell-Yan

33. Polarized proton acceleration at J-PARC • How to keep the polarization given by the polarized proton source • depolarizing resonance • imperfection resonance • magnet errors and misalignments • intrinsic resonance • vertical focusing field • weaken the resonance • fast tune jump • harmonic orbit correction • intensify the resonance and flip the spin • rf dipole • snake magnet • How to monitor the polarization • polarimeters

34. Polarized proton acceleration at AGS/RHIC • Proposed scheme for the polarized proton acceleration at J-PARC is based on the successful experience of accelerating polarized protons to 25 GeV at BNL AGS BRAHMS & PP2PP PHOBOS Absolute Polarimeter (H jet) RHIC pC Polarimeters PHENIX Full Helical Siberian Snakes STAR Spin Rotators Spin Rotators Pol. H- Source LINAC BOOSTER Partial Solenoidal Snake rf Dipole AGS Warm Partial Helical Siberian Snake 200 MeV Polarimeter AGS Internal Polarimeter AGS pC Polarimeters Cold Partial Helical Siberian Snake

35. pC CNI Polarimeter Extracted Beam Polarimeter Pol. H- Source rf Dipole 30% Partial Helical Siberian Snakes 180/400 MeV Polarimeter Polarized proton acceleration at J-PARC BRAHMS & PP2PP PHOBOS Absolute Polarimeter (H jet) RHIC pC Polarimeters PHENIX STAR Pol. H- Source LINAC BOOSTER rf Dipole AGS Warm Partial Helical Siberian Snake 200 MeV Polarimeter AGS Internal Polarimeter AGS pC Polarimeters Cold Partial Helical Siberian Snake

36. Polarized Drell-Yan experiment at J-PARC analyzing magnet 51cm 127cm • Single transverse-spin asymmetry • Sivers effect measurement • Experimental condition • higher beam intensity is possible for unpolarized liquid H2 target, or nuclear target • 51012ppp = 2.510122sec in 1pulse (5sec) possible? • PYTHIA simulation • 75% polarization beam • 120 days, beam on target 51017 (with 50% duty factor) • ~5% liquid H2 target • 10000 fb-1 luminosity • ~20% nuclear target • 40000 fb-1 luminosity • mass 4 – 5 GeV/c2 polarized beam red liquid H2 target blue nuclear target 4 < M+- < 5 GeV integrated over qT Theory calculation by Ji, Qiu, Vogelsang and Yuan based on Sivers function fit of HERMES data (Vogelsang and Yuan: PRD 72, 054028 (2005))

37. J-PARC and/or RHIC • J-PARC • Advantage • High intensity = high luminosity • Disadvantage • Smaller cross section (at the same invariant mass) • Uncertainties • Availability of 50 GeV beam • Polarized proton beam? • RHIC • Advantage • Polarized proton beam available • Larger cross section (at the same invariant mass) • Disadvantage • Luminosity? • Collider or fixed-target (internal-target) experiment

38. 偏極標的開発 • KEK • 山形 • 偏極ヘリウム３

39. Polarized target at KEK • Michigan polarized target • target thickness ~3 cm (1% target) • maybe operational with 1011 ppp (luminosity ~1034 cm-2s-1)