Present and Future Exploration of the Nucleon Spin and Structure at COMPASS

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1 Present and Future Exploration of the Nucleon Spin and Structure at COMPASS Longitudinal spin structure Transverse spin structure Gluon polarization Primakov: pion polarizabilities DY: Transverse Momentum Dependent PDF DVCS: Generalized Parton Distributions July 5, 2010 Claude Marchand - INPC2010 1

2 COMPASS phase I Compass setup Beam: 160 GeV µ +, pol. 80% from π decay µ filter longitudinally or transversely polarized fixed target RICH µ filter ECal & HCal Straws MWPC SciFi Silicon Micromegas GEMs Drift chambers July 5, 2010 Claude Marchand - INPC2010 2

3 Longitudinal Spin structure Parton distribution functions Three leading twist-2 PDFs after integration over k T q(x) f 1 q (x) Δq(x) g 1q (x) unpolarised PDF quark with momentum xp in a nucleon well known unpolarised DIS helicity PDF quark with spin parallel to the nucleon spin in a longitudinally polarised nucleon known polarised DIS Δ T q(x) h 1q (x) transversity PDF quark with spin parallel to the nucleon spin in a transversely polarised nucleon chiral odd, poorly known July 5, 2010 Claude Marchand - INPC2010 3

4 Longitudinal Spin structure Double-spin asymmetries g 1 F 2 2x(1+ R) A 1 Phys. Lett. B 690 (2010) 466 Phys. Lett. B 647 (2007) 8 Proton data - world Deuteron data - world Σ=a 0 = 0.33±0.03±0.05 (evol. to Q 2 = ) ( s+ s)=1/3(a 0 -a 8 ) = ± 0.01 ± 0.02 July 5, 2010 Claude Marchand - INPC2010 4

5 Longitudinal Spin structure Test of Bjorken sum rule 3 Par. NLO Fit 0.7 C 1 NS up to 3 rd order in α s (Q 2 ) : Larin et al. PLB 404 (1997)153 dx.g NS 1 (x,q 2 ) extrapolated to with NLO fit g A g V =1.28 ± 0.07 ± 0.10 ( ± from β decay) July 5, 2010 Claude Marchand - INPC2010 5

6 Transverse Spin structure Transversity PDF Couple to chiral odd Collins FF Azimuthal cross-section asymmetry: + July 5, 2010 Claude Marchand - INPC2010 6

7 Transverse Spin structure Collins assymetry - proton Spin dependent fragmentation of transversely polarised quarks into hadrons Comparison with HERMES COMPASS data with x>0.050 Sub. Phys. Lett. B (hep-ex/ ) July 5, 2010 Claude Marchand - INPC2010 7

8 Transverse Spin structure Sievers function Sivers Asymmetry: proposed (1990, Sivers) though to vanish (1993, Collins) resurrected (2002, Brodsky, Hwang, Schmitt) different sign in DY and SIDIS July 5, 2010 Claude Marchand - INPC2010 8

9 Transverse Spin structure Sievers assymetry - proton Intrinsic k T dependence of the quark distribution correlated to nucleon transverse spin Comparison with HERMES COMPASS data with x>0.032 Sub. Phys. Lett. B (hep-ex/ ) Additional data in 2010 July 5, 2010 Claude Marchand - INPC2010 9

10 Gluon Polarization Gluon polarization via PGF Principle: Gluon polarisation enters via photon-gluon fusion (PGF) A µn LL = R PGF PGF a LL ΔG G q=c (open charm): no physics bgd measure for events with D calculate µn A LL R PGF,a LL PGF by MC July 5, 2010 Claude Marchand - INPC

11 Gluon Polarization G/G data D Kπ ; D Kππ ; D Kπππ ; D sub(k )π (all D * tagged) D Kπ (untagged) : proton+ deuteron data July 5, 2010 Claude Marchand - INPC

12 COMPASS phase II COMPASS II proposal July 5, 2010 Claude Marchand - INPC

13 Pion polarizabilities Primakov experiment π (or Κ) (190 GeV) Q 2 0 π (or Κ) γ ( GeV) July 5, 2010 Claude Marchand - INPC

14 Pion polarizabilities π polarizability and ChPT α π > 0 S=0 diamagnetic contr. β π <0 Present experiments: α π - β π from 4 to fm 3 2-loop ChPT prediction 5.70 ± ± COMPASS accuracy ±0.66 ±0.025 ±1.94 July 5, 2010 Claude Marchand - INPC

15 Drell-Yann TMDs Transverse Mom. Dep. PDF 8 intrinsic transverse momentum dependent PDFs at LO Asymmetries with different angular dependences on hadron and spin azimuthal angles, Φ h and Φ s Sivers Boer Mulders Transversity July 5, 2010 Claude Marchand - INPC

16 Drell-Yann TMDs Pure valence u dominance because of the π - beam July 5, 2010 Claude Marchand - INPC

17 Drell-Yann TMDs Drell-Yan cross section at LO Boer-Mulders Sivers The T-odd character of the Boer-Mulders and Sivers function implies that these functions are process dependent Boer-Mulders Sivers July 5, 2010 Claude Marchand - INPC

18 Drell-Yann TMDs Background estimates July 5, 2010 Claude Marchand - INPC

19 Drell-Yann TMDs DY COMPASS setup µ - π GeV ( s -1 ) µ + 1. Absorber to reduce secondary particle flux 2. COMPASS Polarised Target (2x55cm cells) 3. Tracking system and beam telescope 4. Muon trigger (LAS of particular importance - 60% of the DY acceptance) 5. RICH1, Calorimetry also important to reduce the background July 5, 2010 Claude Marchand - INPC

20 Drell-Yann TMDs DY predictions at COMPASS Blue line with grey band: Anselmino et al., PRD79 (2009) Black solid and dashed: Efremov et al., PLB612 (2005) Black dot-dashed: Collins et al., PRD73 (2006) Squares: Bianconi et al., PRD73 (2006) Green short-dashed: Bacchetta et al., PRD78 (2008) x F =x π -x p x F =x π -x p July 5, 2010 Claude Marchand - INPC

21 Drell-Yann TMDs Results from 2009 DY test Expected: 3600±600 J/ψ and 110±22 DY Measured: 3170±70 J/ψ and 84±10 DY <Pt> = 1 GeV/c COMPASS sensitive to TMDs July 5, 2010 Claude Marchand - INPC

22 DVCS GPDs Generalized Parton Dist. µp µ p γ Elastic Form Factors γ* Q² γ x x+ξ x-ξ p GPDs t P z H,,E, (x,ξ,t) H(x,ξ,t)dx = F(t) x P b ordinary parton density x boost y x Generalized Partons Distrib. H( x,ξ,t ) ( P x, b ) H(x,0,0) = q(x) (x,0,0) = Δq(x) July 5, 2010 Claude Marchand - INPC

23 DVCS GPDs Generalized Parton Dist. µp µ p γ γ* Q² γ x+ξ x-ξ Ji s sum rule p GPDs t P z 2J q = x(h+e)(x,ξ,0)dx x P b x boost y Generalized Partons Distrib. H( x,ξ,t ) ( P x, b ) July 5, 2010 Claude Marchand - INPC

24 DVCS GPDs Nucleon tomography GPDs allow simultaneous measurement of longitudinal momentum and transverse spatial structure Impact parameter b Longitudinal momentum fraction x x x 0.03 x 0.3 Tomographic parton images of the nucleon July 5, 2010 Claude Marchand - INPC

25 DVCS GPDs Kinematical domain CERN High energy muon beam GeV µ + and µ - available 80% Polarisation with opposite polarization Will explore the intermediate x Bj region Uncovered region between ZEUS+H1 and HERMES+Jlab before new colliders may be available B July 5, 2010 Claude Marchand - INPC

26 DVCS GPDs Experimental setup µ γ SM2 ECAL2 SM1 ECAL1 µ p July 5, 2010 Claude Marchand - INPC

27 DVCS GPDs Interferences DVCS - BH dσ (µp µpγ) = dσ BH + dσ DVCS unpol + P µ dσ DVCS pol + e µ a BH Re A DVCS + e µ P µ a BH Im A DVCS Monte-Carlo Simulation for COMPASS set-up with only ECAL1+2 Missing DVCS acceptance without ECAL0 July 5, 2010 Claude Marchand - INPC

28 DVCS GPDs Beam charge and spin sum dσ (µp µpγ) = dσ BH + dσ DVCS unpol + P µ dσ DVCS pol + e µ a BH Re A DVCS + e µ P µ a BH Im A DVCS ss dσ(µ + ) + dσ(µ - ) µ µ φ γ* p γ θ dσ DVCS /dt ~ exp(-b t ) Transverse imaging Im(F 1 H) July 5, 2010 Claude Marchand - INPC

29 DVCS GPDs Transverse imaging Integrating S CS,U over Φ and substracting BH B(x B ) = ½ < r 2 (x B ) > r =b /(1 x) (0.65 fm at low x) ansatz at small x B : determination of B with 0.1 GeV 2 accuracy, α with 2.5σ acc. if α 0.12 no model dependence July 5, 2010 Claude Marchand - INPC

30 DVCS GPDs Beam charge and spin diff dσ (µp µpγ) = dσ BH + dσ DVCS unpol + P µ dσ DVCS pol + e µ a BH Re A DVCS + e µ P µ a BH Im A DVCS dσ(µ + ) - dσ(µ - ).. and Re(F 1 H) Advantage: BH contribution cancels Difficulty: needs control of absolute X-section at few % level Alternative: Beam charge and spin asymmetry dσ(µ + ) - dσ(µ - ) dσ(µ + ) + dσ(µ - ) July 5, 2010 Claude Marchand - INPC

31 DVCS GPDs Beam charge and spin diff...+c 1 Int cosϕ +... α =0.8 α =0.05 => Re ( ) July 5, 2010 Claude Marchand - INPC

32 DVCS GPDs Beam charge and spin asym July 5, 2010 Claude Marchand - INPC

33 DVCS GPDs Results from 2009 DVCS test 1m long recoil proton detector (RPD) and 40cm long LH2 target Selection of events: vertex with µ and µ (no other charged track) one high energy photon proton in RPD + exclusivity cuts July 5, 2010 Claude Marchand - INPC

34 Conclusions New results for spin structure: -precise test of Bjorken sum rule -non zero transverse spin and momentum effects -constraints on gluon polarization Future program (2012 ) submitted to CERN SPSC: -Primakov: ChPT tests and π polarizabilities -DY: TMD PDFs and univerality DY-SIDIS -DVCS: constrain GPD H, dσ/dt tranverse imaging (phase 2: GPD E, needs transv. pol. target + RPD) New groups welcome to join COMPASS July 5, 2010 Claude Marchand - INPC