Helicity: Experimental Status. Matthias Grosse Perdekamp, University of Illinois

Transcription

1 Helicity: Experimental Status Matthias Grosse Perdekamp, University of Illinois

2 Content o The Experimental Effort o Quark and Sea Quark Helicity è DIS, SIDIS, pp è new FFs for global analysis è results from global analysis (previous talk!) è (high x) o Gluon Helicity è DIS, SIDIS, pp è results from global analysis (previous talk!) è extending x-range at RHIC è low x at the EIC o Goals and Some Resulting Challenges for the EIC 2

3 Nucleon Spin Structure: 35 Years of Experiment Quark Helicity Gluon Helicity Transverse Spin GPDs L z SLAC à 2000 ongoing à 1995 à 2007 ongoing ongoing E80-E155 CERN EMC,SMC COMPASS FNAL DESY JLAB RHIC E704 HERMES Halls A, B, C BRAHMS, PHENIX, STAR DIS, SIDIS polarized pp 3

4 Experimental Access to Helicity Parton Distributions: polarized DIS 4

5 Polarized DIS: Kinematic Coverage 5

6 Gluon Spin Contribution ΔG(x) from Scaling Violation of g 1 (x,q 2 ) in DIS g P 1 (x,q2 ) Hirai, Kumano, Saito Phys.Rev.D74:014015,2006 ΔG= ΔG(x) dx = , Q 2 =1GeV 2 6

7 Fixed Target: Higher Twist at low Q 2? 7

8 Polarized DIS at EIC : Kinematic Coverage current data 8

9 Polarized DIS at EIC : Kinematic Coverage Sassot, Stratmann 9

10 Experimental Access to Helicity Parton Distributions: polarized SIDIS 10

11 Polarized SIDIS: Sensitivity to Quark and Sea-Quark Distributions COMPASS & HERMES proton data 11

12 Polarized SIDIS: Sensitivity to Quark and Sea-Quark Distributions COMPASS PLB 693 (2010) 227 curves from DSSV PRD 60 (2009) Good agreement but limited sensitivity for Sea-quark distributions! 12

13 Polarized SIDIS: Strange Sea Polarization vs Kaon FF Stolarski for COMPASS at DIS 13

14 Information from e + e - on Hadron FFs for Extraction of Quark-Gluon Structure in Inclusive SIDIS (and pp) Example: extraction of the quark helicity distributions from the QCD analysis of SIDIS data for A 1 with pions and kaons: π, A K in l + p (, K) + 1 π X ~FF e + e - information on charged hadron FF - little data at large z From A 1 h to Δq(x) extract COMPASS FFs partially from e + e - z = E h s / 2 14

15 Possible Improvement: Use Precision FF Information from e + e - in Belle Belle: Charged h +/-, pions, kaons, Preliminary Belle result for negative pions and kaons (Martin Leitgab for Belle at DIS) s=10.52 GeV Pions Kaons 15

16 Photon Gluon Fusion: PGF Experimentally (LO): (a) tag charm (D-Meson) SMC HERMES COMPASS (b) high p T hadron pairs 16

17 Experimental Access to Helicity Parton Distributions: polarized pp 17

18 Probing ΔG in Polarized pp Collisions pp hx A LL Δf Δf d ˆ σ aˆ fa fb fx fa f ++ + a b LL dσ dσ a, b = = ++ + fa fb fx dσ + dσ fa fb d ˆ σ a, b b fx D h f D h f Double longitudinal spin asymmetry A LL is sensitive to ΔG 18

19 Double Spin Asymmetries A LL for Inclusive Jets Observed with STAR Process Fraction STAR Preliminary Run6, s=200 GeV p T [GeV] Good discriminative power between calculations with different assumption for ΔG 19

20 ΔG: Global QCD Based Fit Phys. Rev. Lett. 101, (2008) First truly global analysis of all available polarized data including RHIC results RHIC data Uncertainty estimation: Δχ 2 =1 Δχ 2 /χ 2 =2% DSSV: Daniel de Florian Rodolfo Sassot Marco Stratmann Werner Vogelsang A node? 20

21 Run 9 Jet A LL : STAR Preliminary Run9: 3-4 smaller stat. uncertainties than in Run6: ü Trigger upgrade ü DAQ upgrade (increased rate, lower E T threshold) STAR Run 9 data suggest positive ΔG~0.1. These measurements will be continued in parallel to the W- data taking and the large statistic for the W-sample will lead to a precise measurements of A LL! 21

22 Extend x-range Different s π 0 at η <0.35: x g distribution vs p T bin x s=62 GeV GeV/c 4-5 GeV/c 9-12 GeV/c s=200 GeV GeV/c 4-5 GeV/c 9-12 GeV/c s=500 GeV 22

23 Probing Low x Through Forward Di-Hadrons merged π 0 s PHENIX central spectrometer magnet mid-fwd x gluon ~ 10-2 p π 0 ϕ MPC PbWO 4 Backward direction (South) ß Side View Muon Piston Calorimeter (MPC) trigger π 0 or h +/- η <0.35 fwd-fwd x gluon ~ trigger EM-cluster 3.1<η<3.9 asssociated asssociated π 0 or EM-clusters π < < η < < Forward direction (North) à p 23

24 PHENIX Muon Piston Calorimeter Technology à ALICE(PHOS) PbWO 4 avalanche photo diode readout Acceptance: 3.1 < η < 3.9, 0 < φ < 2π -3.7 < η < -3.1, 0 < φ < 2π Both detectors were installed for 2008 d-au run. PbWO4 + APD + Preamp Assembly at UIUC MPC integrated in the piston of the muon spectrometer magnet

25 Muon Piston Calorimeter (MPC): PbWO < η < 3.9, 2π azimuth Gives access to lower: x 10-3 Fully available from 2008 STAR: π 0 forward rapidity PRL 97, pqcd seems working even at forward rapidities MPC π GeV 300 pb -1 P=

26 Summary Helicity Experiment Much progress still needed: gluon distribution, gluon spin contribution reliable flavor decomposition of quark spin distribution strange polarization measure high x-region at large Q 2 only EIC can è extend kinematics to low x and high Q 2 è carry out measurements in current x-range with high statistical precision and at scales that will allow a model independent interpretation of the data 26

27 EIC: Helicity Structure, Wish List 1 2 = L q ΔΣ + L G + ΔG Goals: (I) Precise measurements of ΔΣ and ΔG and therefore total L z present ΔΣ = è 0.02? present ΔG = extrapolation uncertainty è 0.02? QCD tests! (II) Bjorken sumrule to 2% (factor 5 better than present)! (III) g 1 evolution to 2% (IV) Can L z be directly accessed (in a model independent way)? 27

28 Helicity Structure è Measurements Inclusive: Semi inclusive: Exclusive: Jets: g 1 (including evolution) and g 5 for proton and 3 He or d beams A LL for identified charged pions and kaons DVCS A LL for di-jets Heavy flavor: A LL for D 0 è Full acceptance detector with hadron pid capabilities, heavy flavor tagging, jet reconstruction, excellent momentum resolution, precise relative luminosity monitors and local polarimeters! 28

29 Helicity Structure è Needs & Input Absolute polarimeter: < 2% (both beams) Local polarimeters: < 2% (both beams) Extrapolation uncertainties: < 2% pqcd framework for PDF extraction: test with cross section è normalization (luminosity) to < 2% Fragmentation functions: need to be know to < 2% Control of radiative corrections: < 2% 29

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31 Generalized Parton Distributions to Access Orbital Angular Momentum GPDs H u, H d, E u, E d provide access to total quark contribution to proton angular momentum in exclusive processes l + N à l + N + γ Proton spin sum ½ = ½ (Δu+Δd+Δs) + L q + J g J q J q = xdx [ H q ( x, ξ, 0 ) + E q ( x, ξ, 0 )] X. Ji, Phy.Rev.Lett.78,610(1997) 31