The GPD program at Jefferson Lab: recent results and outlook

Transcription

1 The GPD program at Jefferson Lab: recent results and outlook Carlos Muñoz Camacho IPN-Orsay, CNRS/INP3 (France) KITPC, Beijing July 17, 1 Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 1 / 3

2 Outline Introduction 1 Experimental introduction to GPDs (how they can be accessed through experiment) Jefferson Lab overview: Complementary programs in Hall A and Hall B 3 Outlook Jefferson Lab at 1 GeV Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 / 3

3 Introduction Motivation Studying nucleon structure experimentally Elastic scattering r y Deep inelastic scattering δz ~ 1 Q xp y Hard exclusive processes δz ~ 1 Q xp r y p z x p z x p z x ρ ( r ) f ( x) f x, r ) ( r r r x Form factors Prix Nobel, 1961 x 1 Parton distributions Prix Nobel, 1969 Prix Nobel, Generalized Parton Distributions (GPDs) Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 3 / 3

4 Introduction Motivation Deeply Virtual Compton Scattering (DVCS): γ p γ p High Q Perturbative QCD Non-perturbative GPDs Bjorken limit: Handbag diagram Q = q ν } x B = Q Mν fixed Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 4 / 3

5 Introduction Generalized Parton Distributions Motivation Correlate between different partonic states Correlate momentum and position of partons Access to new fundamental properties of the nucleon Contribution of the angular momentum of quarks to proton spin: 1 = 1 Σ + L q +J g }{{} J q = 1 J q 1 1 dx x[h q (x, ξ, ) + E q (x, ξ, )] DVCS cleanest process to access GPDs Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 5 / 3

6 Introduction Experiments GPD experimentally: Compton Form Factors (CFFs) Cross-section (V) measurement and beam charge difference (ReT) integrate GPDs with 1/(x±[) weight Beam or target spin 'V contain only ImT, therefore GPDs at x = [and [ D.R. Lattice Moments ³ x n H(x,[,t)dx Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 6 / 3

7 Introduction Experiments DVCS experimentally: interference with Bethe-Heitler (BH) At leading twist: d 5 σ d 5 σ = Im (T BH T DV CS ) d 5 σ +d 5 σ = BH + Re (T BH T DV CS ) + DV CS +1 T DV CS = +1 1 H(x, ξ, t) P dx 1 x ξ }{{} Access in helicity-independent cross section H(x, ξ, t) dx x ξ + iɛ + = iπ H(x = ξ, ξ, t) +... }{{} Access in helicity-dependent cross-section Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 7 / 3

8 Accessing different GDPs Introduction Experiments Polarized beam, unpolarized target (BSA) dσ LU = sin φ Im{F 1 H + x B (F 1 + F ) H kf E}dφ Unpolarized beam, longitudinal target (ltsa) dσ UL = sin φ Im{F 1 H + xb (F 1 + F )( H + x B /E) x B kf Ẽ... }dφ Polarized beam, longitudinal target (BlTSA) dσ LL = (A + B cos φ) Re{F 1 H + xb (F 1 + F )( H + x B /E)... }dφ Unpolarized beam, transverse target (ttsa) dσ UT = cos φ Im{k(F H F 1 E) +... }dφ Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 8 / 3

9 Kinematic coverage Introduction Experiments Kinematic complementarity between different facilities: H1, ZEUS H1, ZEUS.7 Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 9 / 3

10 Introduction The DVCS program worldwide Experiments HERMES at DESY: Beam (BSA), charge (BCA) and transverse target (TSA) asymetries published Several ongoing analysis + recoil detector installed 1 year before shutdown: results to come... Hall A and Hall B partially overlapping, partially complementary, active programs: Hall A: high accuracy, limited kinematics Hall B: wide kinematic range, limited accuracy Very different systematics COMPASS at CERN The roadmap: Early results ( 1) from non-dedicated exp. (HERMES+CLAS) First round of dedicated experiments in Halls A/B in 4/5 Second round on 8 1 Compeling DVCS experiments in Halls A/B at 11 GeV ( 14-16) Exciting program at COMPASS (15 16) Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 1 / 3

11 Recent results E-11 experimental setup JLAB / Hall A High Resolution Spectrometer 1-channel scintillator array 13-block PbF electromagnetic calorimeter Carlos Mun oz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 11 / 3

12 Recent results JLAB / Hall A DVCS cross section in the valence region (Hall A: E-11) < t > = -.33 GeV < t > = -.8 GeV < t > = -.3 GeV < t > = -.17 GeV ) 4 DVCS cross section (nb/gev E-11 BH+DVCS E-11 Total fit Twist - BH BH+DVCS - BH beam helicity-independent beam helicity-dependent φ (deg) φ (deg) φ (deg) φ (deg) Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 1 / 3

13 I E-11: Scaling tests Recent results JLAB / Hall A (H, H ~, E) Im C Q = 1.5 GeV Q = 1.9 GeV Q =.3 GeV VGG model Twist-: dominant contribution -t (GeV ) Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 13 / 3

14 Recent results JLAB / Hall A DVCS on the neutron: experiment E3-16 at JLab I exp ) n Im(C LD target (F n(t) F 1 n (t)!) J u=-.4 J d=-.6 J u=.3 J d=. J u=.6 J d= t (GeV ) σ σ = Γ(A sin ϕ +... ) Charged particle veto in front of scintillator array A = F 1 (t)h + x B [F 1 (t) + F (t)] x H t B 4M F (t) E }{{} Main contribution for neutron Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 14 / 3

15 Recent results JLAB / Hall A DVCS on the neutron: experiment E3-16 at JLab LD target (F n(t) F 1 n (t)!) J d JLab Hall A n-dvcs + J u J d =.18 5 ±.14 Charged particle veto in front of scintillator array - -. Lattice QCDSF HERMES Preliminary p-dvcs J u σ σ = Γ(A sin ϕ +... ) A = F 1 (t)h + x B [F 1 (t) + F (t)] x H t B 4M F (t) E }{{} Main contribution for neutron Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 14 / 3

16 Recent results JLAB / Hall B E1-113: BSA in a large kinematic domain (Hall B) CLAS+ dedicated calorimeter Q (GeV ) t =.8 GeV -t =.49 GeV A = σ σ σ + σ α sin φ 1 + β cos φ x B φ (deg) Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 15 / 3

17 Recent results JLAB / Hall B E1-113: BSA in a large kinematic domain (Hall B) CLAS+ dedicated calorimeter A = σ σ σ + σ α sin φ 1 + β cos φ Simple models do not reproduce the data Analysis of cross sections underway Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 15 / 3

18 Recent results JLAB / Hall B JLab Hall B cross-sections: preliminary nb/gev 4 Large data set under analysis Compatible within errors with Hall A in overlap region arxiv: Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 16 / 3

19 Recent results π electroproduction (ep epπ ) Deep meson electroproduction At leading twist: dσ L dt [ 1 M L = 1 Γ h N,h N dz φ π(z) z M L (λ M =, h N, h N ) 1 Q 6 σ T 1 Q 8 ] 1 dx 1 [ 1 x ξ + 1 x + ξ ] { } Γ 1 Hπ + Γ Ẽ π Different quark weights: flavor separation of GPDs π = 1 { uū d d } Hπ = 1 { 3 H u + 1 } 3 H d p = uud H DV CS = 4 9 Hu Hd Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 17 / 3

20 Recent results Deep meson electroproduction Exclusive π electroproduction cross-sections dσ L ) - (µb GeV + L dt dσ T Kin3 σ L ] σ L ] Kin Q =1.9 GeV Q =.3 GeV (a) dσ L ) - (µb GeV + L dt dσ T KinX3 σ L ] σ L ] KinX W =. GeV W =.3 GeV (a) + L [σ T + L [σ T.5 + L [σ T + L [σ T t min -t (GeV ) (b) t min -t (GeV ) (b) σ T + ɛ L σ L Q 5 (similar to σ T (ep epπ + ) measured in Hall C) GPDs predict σ L Q 6 σ T likely to dominate at these Q, but L/T separation necessary ( new experiment... ) E. Fuchey et al., Phys. Rev. C83 (11), 515 Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 18 / 3

21 E7-7 (Hall A) Recent results Near-future experiments σ(ep epγ) = BH }{{} + I(BH DV CS) }{{} + DV CS }{{} Known to 1% Linear combination of GPDs Bilinear combination of GPDs DVCS cross section has a very rich azimuthal structure: Azimuthal analysis allows the separation of the different contributions to I if DVCS is negligeble. If DVCS is important, I and DVCS terms MIX in an azimuthal analysis. The different energy dependence of I and DVCS allow a full separation. Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 19 / 3

22 E b =6. GeV E b =3.64 GeV Recent results Near-future experiments E7-7: Rosenbluth-like DVCS I separation in Hall A b/gev Clean separation of BH-DVCS intereference term from pure DVCS Scaling test on the real part of the DVCS amplitude Rosenbluthdseparation σ of σ L 4/σ T forsimulated (nb/gev ) ep data epπ 4 ) dq dx B dtdϕ γγ d 4 σ (nb/gev 4 Fit ) 1-σ 4 BH DVCS C (F,F*) I Re (C ) Re (C I I + C ) I Re (C ) eff <t>=-.8 <t>=-.33 GeV GeV <t>=-.3 <t>=-.8 GeV GeV I <t>=-.3 GeV Re C <t>=-.17 GeV I I Re (C + C ).14 <t I I Re.1 (C + C ) t (GeV ) t (GeV ) deg) -. ϕ (deg) eff γ γ ϕ (deg) 9 18 γ γ ϕ (deg) DVCS Re C C ϕ (deg) ϕ (deg) γ γ γγ γ γ 3 7 ϕ (deg) γ γ -..5<t>=-.8 GeV.5<t>=-.3 GeV.5<t>=-.17 GeV t (GeV ).5 <t>=-.33 GeV.5 t (GeV ) 1 <t>=-.8 GeV <t>=-.3 GeV.5<t DVCS Simulated data C (F,F*) -1 DVCS.3.4 I.3.4 C Re (C) Fit 4 I I -3 Re (C+ C ) I Re (C )..3 1-σ..3 I I I.3 Re C 3 eff I I Re (C + C ) t (GeV ) t (GeV ) Re (C + C ) <t>=-.17 GeV E7-7 Systematic uncertainty deg) ϕ (deg) ϕ (deg) (deg) γ γ γ γ γ γ 1.5 E-11: assuming DVCS = ϕ (deg) ϕ (deg) ϕ (deg) γγ γ γ γ γ -.3 t (GeV -.5 ) 7 ϕ (deg) t (GeV -. ) ϕ (deg) 36 γ γ t (GeVγ γ ) t (GeV ) eff <t>=-.17 GeV DVCS Carlos Muñoz Re C Camacho (IPN-Orsay) GPDs atc JLab KITPC, 1 / Simulated data Fit 1-σ

23 Outlook 1 GeV Upgrade of Jefferson Lab to 1 GeV Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 1 / 3

24 Outlook JLab 1 GeV DVCS experiments 1 GeV E : Hall A unpolarized protons E : Hall B unpolarized protons E1-11-3: Hall B unpolarized neutrons E : Hall B long polarized protons E1-1-1: Hall B tran polarized protons Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 / 3

25 Outlook 1 GeV E : JLab Hall A at 11 GeV JLab1 with 3, 4, 5 pass beam (6.6, 8.8, 11. GeV beam energy) DVCS measurements in Hall A/JLab ) (GeV Q 1 5 W <4 GeV Unphysical with E 11 GeV beam E beam = 6.6 GeV E beam = 8.8 GeV E beam = 11. GeV E beam = 5.75 GeV xbj 88 days 5k events/setting 1 year of operations in JLab/Hall A Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 3 / 3

26 Outlook 1 GeV E : DVCS on the proton with CLAS1 Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 4 / 3

27 Outlook 1 GeV E : DVCS on the proton with CLAS1 Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 4 / 3

28 Outlook 1 GeV E1-11-3: DVCS on the neutron with CLAS1 Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 5 / 3

29 E1-11-3: projections Outlook 1 GeV Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 6 / 3

30 Outlook 1 GeV DVCS with transversally polarized target Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 7 / 3

31 Outlook 1 GeV Time-like DVCS: Time-like Compton Scattering (TCS) TCS: Same factorization as in DVCS Test of universality of GPDs (like DIS vs Drell-Yann) Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 8 / 3

32 Outlook 1 GeV TCS experiment E1-1-1: projections R = π dϕ cos ϕ dσ π dϕ dσ dq dtdϕ dq dtdϕ Re{F 1 H + x B (F 1 + F ) H kf E} Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 9 / 3

33 Summary Conclusion DVCS golden channel for GPDs, but also accessible in: Time-like Compton Scattering (JLab proposal recently approved) Deep meson production (but higher Q are needed... ) Large set of data (cross-sections and asymmetries) is now available Compeling GPD program in the future at Jefferson Lab 1 GeV Carlos Muñoz Camacho (IPN-Orsay) GPDs at JLab KITPC, 1 3 / 3