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Heavy Quarks and Nucleon Spin Structure

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Heavy Quarks and Nucleon Spin Structure Heavy Quarks and Nucleon Spin Structure Ernst Sichtermann (LBNL) With thanks to: Feng Yuan, Xin Dong Wei Zhou Qinghua Xu Ming Liu and many others... Nucleon Structure parton momentum fraction Heavy Quarks - Nucleon Structure Major limitation for spin structure: proton beam at HERA not polarized, however, HERMES had a polarized internal target. Spin - Weak Decay In probing the polarized proton, 1 1 1 2 1 4 1 1 Γ1 = g1(x)dx = eq∆q(x) dx = ∆1u + ∆1d + ∆1s !0 !0 "2 # $ 2 "9 9 9 $ 1 1 1 = (∆1u − ∆1d) + (∆1u + ∆1d − 2∆1s) + (∆1u + ∆1d + ∆1s) 12 36 9 Unique to DIS Known from weak neutron to proton decay, combined with weak ∑ to neutron decay Known from weak neutron to proton decay This becomes a prediction if ∆ 1 s = 0 , i.e. if strange quark spins do not contribute. Proton Spin Structure - circa 1985 Polarized DIS - European Muon Collaboration: Quark spins carry only a small ∆Σ ! 0.2, ∆s < 0 fraction of the proton spin, Strange sea is negatively µ µ’ polarized. γ N X SMC, E142, E143, E155, and Hermes have since confirmed the EMC data. have tested the Bjorken Sum to ~7% precision. Some Open Questions • Is the extrapolation over unmeasured small x justified? • What does gluon polarization contribute to the proton spin? • What are the quark and anti-quark polarizations by flavor? • What orbital angular momenta do quarks and gluons carry? • What is the role of transverse spins? Asymptotic Conjectures*, Asymptotically : Ji X. Ji * in leading order, if the intrinsic contributions do not overwhelm radiatively generated contributions, ... i.e. perhaps. Active Spin Experiments HERMES at DESY: 27 GeV electron beam, fixed target, PID COMPASS at CERN: 160 GeV muon beam, fixed target, open spectrometer STAR at RHIC: 200-500 GeV Ecms, large acceptance PHENIX at RHIC: high resolution, high rate Polarized DIS - Scale Dependence 0.3 AAC06 GRSV xΔΣ(x) 0.2 Ave. 0.171±0.074 BB 0.289±0.754 LSS 0.1 AAC06 0.254±0.101 0.473±1.083 0 -0.1 BB02 0.150±0.061 0.931±0.679 0.001 0.01 0.1 1 1.4 1.2 2 2 1 Q = 1 GeV GRSV01 0.204 0.420 0.8 0.6 0.4 xΔg(x) LSS05 0.165±0.048 0.2 0.179±0.267 0 -0.2 -0.4 ΔΣ Δg -0.6 0.001 0.01 0.1 1 x -0.1 0.1 0.3 0.5 -1 0 1 Polarized DIS - Heavy Quarks Measurements of: - open charm (clean, but rare), and - high-pT hadron pairs (high and low Q2) Polarized Proton Collisions at RHIC PRL 97, 252001 (2006) detector e,ν ,γ , particle π , p,etc q, g parton (∆)σ ∝ (∆)f ⊗ (∆)g ⊗ (∆)σˆ Polarized Proton Collisions at RHIC p! + p! jet(s) or π0(s) + X → Jager, Stratmann, Vogelsang - hep-ph/0404057 ∆G ∆G∆G ∆q∆G ALL ∝ ∆q First Longitudinal Double-Spin Asymmetries from STAR (σ++ + σ ) (σ+ + σ +) ALL = −− − − − (σ++ + σ ) + (σ+ + σ +) −− − − Consistent with DIS and disfavors large (Scale uncertainty from polarization not included) values for ∆G + Statistics limited measurement; systematics ~0.015 STAR - B. Abelev et al, hep-ex /0608030 PRL 97:252001 (2006) GRSV - Gluck et al, PR D63 094005 (2001). Improved statistics 2005 (2006) Similar PHENIX results on inclusive neutral pion production Future Polarized Proton Collisions at RHIC Clear need for data that are kinematically complete and process selective, (σ++ + σ ) (σ+ + σ +) ALL = −− − − − (σ++ + σ ) + (σ+ + σ +) −− − − ∆G p! + p! jet(s) + X p! + p! cc¯, b¯b + X p! + p! γ + jet → → → + 2 1 ∆q 3 8 10 pb− , P = 0.4 0.7, √s = 200 500 GeV L ! − · − − time Clear need for data that are kinematically complete and process selective, Heavy Quark and Prompt Photon Production are complementary. Heavy Quark Total Cross Section Total cross section, e.g. P. Nason et al., NPB 303 (1988) 607 Quarkonium, e.g. G. Bodwin et al., PR D51 (1995) 1125; erratum ibid D55 (1997) 5883 Friday morning session at this workshop ... and its Spin Dependence A ∝ ∆f ⊗ ∆g ⊗ aˆ Small total cross section asymmetry is a result from cancellation caused by mass. aˆ Contogouris et al., PLB 246 (1990) 523 Karliner and Robinett, PLB 324 (1994) 209 Lampe and Reya, Phys. Rept. 332 (2000) 1 Bojak and Stratmann, PR D67 (2003) 034010 Displaced Electrons from Charm in STAR Inclusive electrons from charm; ~100 pb-1, 70% pol. ALL GRSV best fit GRSV minimum gluon polarization GRSV maximum gluon polarization Beauty |asymmetries| are generally smaller at small pT Heavy Quark Content of Jets UA1, PLB 244 (1990) 566 CDF, PRL 64 (1990) 348 Heavy Quark Content of Jets UA1, PLB 244 (1990) 566 CDF, PRL 64 (1990) 348 Heavy Quark Content of Jets UA1, PLB 244 (1990) 566 CDF, PRL 64 (1990) 348 Some Open Questions • Is the extrapolation over unmeasured small x justified? • What does gluon polarization contribute to the proton spin? • What are the quark and anti-quark polarizations by flavor? • What orbital angular momenta do quarks and gluons carry? • What is the role of transverse spins? Quark Structure at Hadron Colliders - Leptonic W-boson Decays CDF Collaboration, Measurement of the lepton charge asymmetry in W boson decays produced by ppbar collisions, PRL 81, 5754 (1998). u + d → W → l + ν σ+ − σ− A = charge σ+ + σ− Clean measurement: - hard scale, - convolution with calculable V-A decay, - sensitive, at large |Lepton Rapidity| More recent measurements (Phys.Rev.D71 - 2005): - transverse energy ET dependence Quark Polarimetry at RHIC - Leptonic W-boson Decays Quark polarimetry with W-bosons: projections νe θ W + u d¯ e Born + + 2 2 ∆σ (pp" → W → e νe) ∝ −∆u(xa)d¯(xb)(1+cos θ) +∆d¯(xa)u(xb)(1−cos θ) Spin measurements: −∆u(xa) → ¯ ¯ , xa 1 + −∆u(xa)d(xb) + ∆d(xa)u(xb) u(xa) AL W ( ) = ¯ ¯ = ¯ u(xa)d(xb) + d(xa)u(xb) ∆d(xa) → ¯ , xb 1 d(xa) ∆d(xa) − , xa → 1 − d(xa) AL(W ) = Requires: ∆u¯(xa) , xb → 1 u¯(xa) - PHENIX and STAR upgrades - high integrated luminosity Quark Polarimetry at RHIC - Heavy Quark W-boson Decays? Hadronic decays: UA2, PLB 186 (1987) 452. + are 6x more abundant, + are kinematically complete, - have challenging QCD backgrounds. Quark Polarimetry at RHIC - Heavy Quark W-boson Decays? RHIC Hadronic decays: + are 6x more abundant, + are kinematically complete, - have challenging QCD backgrounds. mass [GeV] The requirement of charm ~10 pb-1 + reduces QCD background > 10x, + reduces Z background 5x, - reduces signal 2x. mass [GeV] ALQCD = 0, ALW ~ 0.2, S/B can be optimized, W charge? W. Zhou (LBNL), E.S. W-boson Processes - Higher Orders... Charm-associated W-boson production, gives some sensitivity to ∆s, ∆s¯ K. Sudoh, RHIC-II Science Workshop (2005) −1 L = 800 pb , P = 70%, !c = 10% Hyperon spin transfer at RHIC (Q.H. Xu, E.S.), elastic neutrino scattering (BNL E734), semi-inclusive DIS at a future Electron Ion Collider Some Open Questions • Is the extrapolation over unmeasured small x justified? • What does gluon polarization contribute to the proton spin? • What are the quark and anti-quark polarizations by flavor? • What orbital angular momenta do quarks and gluons carry? • What is the role of transverse spins? Feng Yuan Feng Yuan Feng Yuan Some Open Questions • Is the extrapolation over unmeasured small x justified? • What does gluon polarization contribute to the proton spin? • What are the quark and anti-quark polarizations by flavor? • What orbital angular momenta do quarks and gluons carry? • What is the role of transverse spins? Other Quarkonia Considerable effort to understand the production mechanism e.g. Cooper, Liu, Nayak Any spin observables? Quarkonia Spin Transfer - A correlation between the spins Λc of initial and final particles. K. Sudoh, RHIC-II Science Workshop (2005) Thanks!.
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