Latifa Elouadrhiri. Phone: X Jefferson Lab. Thomas Jefferson National Accelerator Facility Page 1

Transcription

1 Deep Exclusive Processes Latifa Elouadrhiri Office: CC B121 Phone: X Jefferson Lab Thomas Jefferson National Accelerator Facility Page 1

2 Outline Some basics about the proton Generalized Parton Distributions (GPDs) and what they can tell us experiments to access GPDs CEBAF future experiments & 12 GeV Imaging of the Proton s Quark Structure Conclusions Thomas Jefferson National Accelerator Facility Page 2

3 Some well known facts about the proton Charge: Q p = +1 It has a neutral partner, the neutron, Q n = 0 Spin: s = ½ћ Magnetic moment μ p = 2.79μ N Anomalous magnetic moment m a = m N Mass: M p ~ 940 MeV/c 2 Protons + neutrons make up 99.9% 9% of the mass of the visible universe 1950 s: Does the proton have finite size? Thomas Jefferson National Accelerator Facility Page 3

4 Scattering Experiments in Nuclear Physics Uses of scattering experiments Structure target Produced system (meson, resonances) Advantages of electron scattering Structureless probe. clean Controlled energy/momentum transfer, microscope with resolution Q 2 Interaction through well-known EM current operator Thomas Jefferson National Accelerator Facility Page 4

5 Electron Scattering a clean probe of the Proton Structure elastic inclusive exclusive e e Q γ v p e e γ v Q X e π, ρ, γ γ v p e Q p p p Interaction described by: Q 2 = -(e-e ) 2 ν = E e E e x B = Q 2 /2Mν t = (p-p ) p) 2 1/ Q 2 is the space-time resolution of the virtual γ The exploration of the internal structure of the proton began in the 1950 s with Hofstadter s s experiments. Thomas Jefferson National Accelerator Facility Page 5

6 Does the Proton have finite size? e - e - Q p p dσ/dω = [dσ/dω] n.s. F(q) iqr Fq () = dre ρ() r 1955 Proton form factors, transverse charge & current densities Nobel Prize for Physics Elastic electron-proton scattering the proton is not a point-like particle, it has finite size. R. Hofstadter Thomas Jefferson National Accelerator Facility Page 6

7 Constituent Quark Model Revolutionized our way of thinking about proton structure u u d The proton is build from three quarks of spin s = 1/2 moving in the s-state t (L = 0) and having masses m q ~ 300 MeV. Proton mass: m S 3m = q 1 Proton spin: p M. Gell-Mann, 1964 G. Zweig, 1964 Solely built from the quark spins! Tremendously successful model in description of Hadron mass spectra Magnetic moments e e e.g. μ p =. p p 279 2mc 2 ( m 3 ) c Thomas Jefferson National Accelerator Facility Page 7

8 What is the internal structure of the proton? Deep inelastic electron-proton t Nobel prize 1990 scattering ep e X e e Q X J. Friedman H. Kendall R. Taylor p 1968 = 1/x B Scaling Quarks are point-like objects! Quarks carry ~ 50% of the proton momentum =>glue=>qcd The quark spins contributes only 25% to the proton spin. Thomas Jefferson National Accelerator Facility Page 8

9 Deep Inclusive Scattering (DIS) Observed Not Observed What have we learned? quarks-substructure of the nucleon 50% of the nucleon momentum is carried by quarks, the remainder by gluons quarks are spin ½ objects less than 25% of the nucleon spin is carried by quark helicity Thomas Jefferson National Accelerator Facility Page 9

10 Some Open Questions in Nucleon Physics in the Valence Quark Region Internal nucleon dynamics Transverse momentum distributions Quark-quark correlations Full (complex) quark wave functions Origin of the nucleon spin GPDs and Exclusive processes Thomas Jefferson National Accelerator Facility Page 10

11 How are the proton s charge/current densities related to its quark momentum/spin distribution? D. Mueller, X. Ji, A. Radyushkin, M. Burkardt, A. Belitsky Interpretation in impact parameter space? Proton form factors, transverse charge & current densities Correlated quark momentum and helicity distributions in transverse space - GPDs Structure functions, quark longitudinal momentum & spin distributions Thomas Jefferson National Accelerator Facility Page 11

12 GPDs & PDFs z 3-D Scotty z 2-D Scotty y x x Deeply Virtual Exclusive Processes & GPDs Deep Inelastic Scattering & Parton Distribution Functions. 1-D Scotty Water Calcium Carbon x Thomas Jefferson National Accelerator Facility Page 12

13 From Holography to Tomography mirror A. Belitsky, B. Mueller, NPA711 (2002) 118 An Apple mirror mirror A Proton mirror detector By varying the energy and momentum transfer to the proton we probe its interior and generate images of the proton s quark content. Thomas Jefferson National Accelerator Facility Page 13

14 Deeply Exclusive Scattering (DES) Inclusive Scattering Compton Scattering θ = 0 Deeply Virtual Compton Scattering (DVCS) Probes the nucleon quark structure and correlations at the amplitude level Thomas Jefferson National Accelerator Facility Page 14

15 DVCS and Generalized Parton Distributions (GPDs) ~ ~ GPDs: H, E unpolarized, H, E polarized γ γ eg tq )= Hq (x, ξ, t, Q 2 )dx e.g. H(ξ, t, 2 x-ξ + iε H q (x, ξ, t, Q 2 )dx = x-ξξ real part + iπh q (ξ, ξ, t, Q 2 ) imaginary part d 3 σ ~ ~ P ( x + ξ ) P( x ξ ) GPD s cross section difference d 3 σ dq 2 dx B dt ~[ah(ξ, t, Q2 )+be(ξ, t, Q 2 )+ch(ξ, t, Q 2 )+de(ξ, t, Q 2 )] 2 H q : Probability amplitude for N to emit a parton q with x+ξ and N to absorb it with x- ξ. Thomas Jefferson National Accelerator Facility Page 15

16 Basic Process Handbag Mechanism Deeply Virtual Compton Scattering (DVCS) hard vertices x+ξ x-ξ x γ x longitudinal quark momentum fraction 2ξ longitudinal momentum transfer t t t Fourier conjugate to transverse impact parameter GPDs depend on 3 variables, e.g. H(x, ξ, t). They probe the quark structure at the amplitude level. ξ = x B 2-x B Thomas Jefferson National Accelerator Facility Page 16

17 Link to DIS and Elastic Form Factors DIS at ξ=t=0ξ t 0 q H ( x,0,0) = q( x) ~ q H ( x,0,0) = Δq( x) Form factors 1 1 ~ dx H ] 1 q dx [ H ( x, ξ, t) = F 1 ( t) Dirac f.f. q 1 dx [ ] ) Pauli f.f. q E ( x, ξ, t) = F 2 ( t q 1 q ~ q ( x, ξ, t) = GA, q( t), dx E ( x, ξ, t) = 1 G P, q ( t) Forward limit H q q ~ q ~ q, E, H, E ( x, ξ, t) Sum rules J q = 1 J G 1 = xdx [ H q ( x, ξ,0) + E q ( x, ξ,0) ] Ji s Angular Momentum Sum Rule Thomas Jefferson National Accelerator Facility Page 17

18 Universality of GPDs Elastic form factors Parton momentum distributions Real Compton scattering at high t GPDs Deeply Virtual Compton Scattering Single Spin Asymmetries Deeply Virtual Meson production Thomas Jefferson National Accelerator Facility Page 18

19 Universality of GPDs Quark tomography Quark-quark correlations GPDs Quark angular momentum Proton s gravitational form factors Thomas Jefferson National Accelerator Facility Page 19

20 So, GPDs give access to complex Proton Structure, but How can be determine them? Thomas Jefferson National Accelerator Facility Page 20

21 Deeply Virtual Compton Scattering ep epγ Kinematics γγ*p plane y e ee γ* plane e γ* Θ γγ γ p φ x z Thomas Jefferson National Accelerator Facility Page 21

22 Access GPDs through Interference DVCS e e BH E o = 11 GeV E o = 6GeV E o = 4GeV p p d 4 σ dq 2 dx B dtdφ ~ T DVCS + T BH 2 T BH : given by elastic form factors F 1, F 2 T DVCS : determined by GPDs I~2(T BH )Im(T DVCS ) DVCS BH BH-DVCS interference generates beam and target polarization asymmetries that carry the proton structure information. Thomas Jefferson National Accelerator Facility Page 22

23 Model representation of GPD H(x,ξ,0) DIS measures at ξ=0 Quark distribution q(x) -q(-x) Accessed by beam/target spin asymmetry x = ± ξ H(x,ξ,0) t=0 Accessed by cross sections Thomas Jefferson National Accelerator Facility Page 23

24 Measuring GPDs through polarization A = σ + σ σ + + σ = Δσ 2σ Polarized beam, unpolarized target: Δσ LU ~ sinφ{f 1 H + ξ(f 1 +F 2 )H +kf 2 E}dφ ~ H(ξ,t) Kinematically suppressed ξ ~x~ B /(2-x B B) k = t/4m 2 Unpolarized beam, longitudinal target: ~ Δσ UL ~ sinφ{f 1 H+ξ(F 1 +F 2 )(H +ξ/(1+ξ)e) -.. }dφ Kinematically suppressed Unpolarized beam, transverse target: ~ H(ξ,t), ) H(ξ,t) ) Δσ UT ~ sinφ{k(f 2 H F 1 E) +.. }dφ UT H(ξ,t), E(ξ,t) Kinematically suppressed Thomas Jefferson National Accelerator Facility Page 24

25 Typical cross sections and rates in en/ea Thomas Jefferson National Accelerator Facility Page 25

26 Characteristics of en facilities Luminosity L: Number of possible en collisions per time [cm -2 S -1 ] dn event = Lσdt Polarization (beam, target) JLab: High luminosity frontier Thomas Jefferson National Accelerator Facility Page 26

27 Aerial View of CEBAF 3 End Stations Thomas Jefferson National Accelerator Facility Page 27

28 6 GeV CEBAF Thomas Jefferson National Accelerator Facility Page 28

29 CEBAF Actual Parameters Primary Beam: Electrons Beam Energy: 6 GeV nucleon quark transition baryon and meson excited states 100% Duty Factor (CW) Beam coincidence experiments excite system with a known (q,ω) and observe its evolution Three Simultaneous Beams with Independently Variable Energy and Intensity complementary, long experiments Polarization (85% beam (!) and reaction products) spin degrees of freedom weak neutral currents (extremely small helicity-correlated changes) > 10 6 X SLAC at the time of the original DIS experiments Thomas Jefferson National Accelerator Facility Page 29

30 Basic Process Handbag Mechanism Deeply Virtual Compton Scattering (DVCS) hard vertices x+ξ x-ξ x γ x longitudinal quark momentum fraction 2ξ longitudinal momentum transfer t t t Fourier conjugate to transverse impact parameter GPDs depend on 3 variables, e.g. H(x, ξ, t). They probe the quark structure at the amplitude level. ξ = x B 2-x B Thomas Jefferson National Accelerator Facility Page 30

31 Access GPDs through Interference DVCS e e BH E o = 11 GeV E o = 6GeV E o = 4GeV p p d 4 σ dq 2 dx B dtdφ ~ T DVCS + T BH 2 T BH : given by elastic form factors F 1, F 2 T DVCS : determined by GPDs I~2(T BH )Im(T DVCS ) DVCS BH BH-DVCS interference generates beam and target polarization asymmetries that carry the proton structure information. Thomas Jefferson National Accelerator Facility Page 31

32 Aerial View of CEBAF 3 End Stations Thomas Jefferson National Accelerator Facility Page 32

33 Hall C: A High Momentum and a Broad Range Spectrometer Set-up Space for Unique Experiments Thomas Jefferson National Accelerator Facility Page 33

34 Hall A: Two High Resolution (10-4 ) Spectrometers Maximum luminosity cm -2 s -1 Thomas Jefferson National Accelerator Facility Page 34

35 Hall B: The CEBAF Large Acceptance Spectrometer (CLAS) Maximum luminosity cm -2 s -1 Thomas Jefferson National Accelerator Facility Page 35

36 CEBAF Large Acceptance Spectrometer (CLAS) Torus magnet 6 superconducting coils Liquid id D 2 (H 2 )target, t NH3, ND3 γ start counter; e - minitorus Drift chambers argon/co 2 gas, 35,000 cells Large angle calorimeters Lead/scintillator, 512 PMTs Gas Cherenkov counters e/π separation, 216 PMTs Time-of-flight counters plastic scintillators, 684 PMTs Electromagnetic calorimeters Lead/scintillator, 1296 PMTs Operating luminosity cm -2 s -1 Thomas Jefferson National Accelerator Facility Page 36

37 CLAS (forward carriage and side clamshells retracted) Large angle EC Panel 4 TOF Panel 2 & 3TOF Panel 1 TOF Region 3 drift chamber Cerenkov & Forward angle EC Thomas Jefferson National Accelerator Facility Page 37

38 Present-day CLAS Thomas Jefferson National Accelerator Facility Page 38

39 Analysis of CLAS 4.2 and 4.8 GeV data Polarized electrons, E = 4.25 GeV and 4.8 GeV An ep epx event in CLAS Separation of single γ from π 0 γγ using missing mass. γ Thomas Jefferson National Accelerator Facility Page 39

40 Background Only 2-parameter fit: N γ and N π 0 Nγ ep epx Thomas Jefferson National Accelerator Facility Page 40

41 Exclusive DVCS with CLAS Beam Spin Asymmetry Beam energy 4.25 GeV ep epγ identified by analyzing the missing mass distribution ep epx W > 2 GeV 1(GeV/c) 2 < Q 2 < 1.75(GeV/c) (GeV/c) 2 < -t < 0.3 (GeV/c) 2 Α(φ) = αsinφ + βsin2φ The measured asymmetry: α = ± stat ± sys Thomas Jefferson National Accelerator Facility Page 41

42 Exclusivity for e p e p γ Missing Mass 2 = ( p + γ* γ ) 2 Missing Mass resolution : 0.8 GeV Exclusive region: Missing Mass < 1.7 GeV Thomas Jefferson National Accelerator Facility Page 42

43 DVCS asymmetry measurement e p e p γ x B =0.11 Q 2 =2.6 GeV 2 -t =0.27 GeV 2 A LU = -0.23±0.04(stat)±0.03(syst) sin Φ dependence -Kivel, Polyakov & Vanderhaeghen (2001) Signal of DVCS process Can be described by GPD calculation Thomas Jefferson National Accelerator Facility Page 43

44 Pioneering experiments observe interference! JLab 2001 HERA e - p >e - pγ E = 4.3 GeV Q 2 = 1.5GeV 2 E = 27 GeV Q 2 = 2.5GeV 2 e + p >e + pγ A UL = αsinφ + βsin2φ Non-leading contributions ti are small! Leading term non-leading Thomas Jefferson National Accelerator Facility Page 44

45 DVCS in Hall A (E and E03-106) 75% polarized 2.5 µa electron beam 15 cm LH2 target -> L = cm -2 s -1 Left Hall A HRS with electron package 11x12 blocks PbF 2 electromagnetic calorimeter 5x20 blocks plastic scintillator array Clear DVCS identification from HRS+calo Thomas Jefferson National Clermont-Ferrand, Accelerator Facility Saclay, Grenoble, Page 45 ODU, Rutgers

46 E kinematics The calorimeter is centered on the virtual photon direction. ) 2 (GeV 2 Q x B Thomas Jefferson National Accelerator Facility Page 46

47 H(e,e γ) Exclusivity [H(ee γ)x H(e,e - H(e,e γ)γy ]: Missing Mass 2 H(e,e γ)p 2 M X cut H(e,e γ)δ H(e,e γp) sample, Normalized to H(e,e γ) (GeV ) 2 M X <2% in estimate of H(e,eγ)Nπ eγ)nπ below threshold M X2 <(M+m) 2 H(e,e γp) simulation, Normalized to data Thomas Jefferson National Accelerator Facility Page 47

48 Difference of cross sections PRL97, (2006) 2 2 Q x B = 23GeV 2.3 = 0.36 Corrected for real+virtual RadCor Corrected for efficiency Corrected for acceptance Corrected for resolution effects Checked elastic cross ~1% New work by P. Guichon Thomas Jefferson National Accelerator Facility Page 48

49 PRL97, (2006) Total cross section Q 2 = 23G 2.3 GeV 2 x B = 0.36 Corrected for real+virtual RC Corrected for efficiency Corrected for acceptance Corrected for resolution effects Thomas Jefferson National Accelerator Facility Page 49

50 Q 2 -dependence: averaged over t: <t>=-0.23 GeV 2 Im[C I (F )]: sinϕ term Im[C I ]: VGG Average of three Q 2 points. No Q 2 dependence: strong indication for scaling behavior and handbag dominance Thomas Jefferson National Accelerator Facility Page 50

51 Jefferson Laboratory Newport News, USA I max ~ 200 μa Duty Factor ~ 100% σ -5 E /E ~ Beam Pol ~ 80% Continuous Electron Beam Accelerator Facility E max = 6 GeV Hall B CEBAF Large Acceptance Spectrometer Thomas Jefferson National Accelerator Facility Page 51

52 The CLAS detector Toroidal magnetic field (6 supercond. coils) Drift chambers (argon/co 2 gas, cells) Time-of-flight scintillators Electromagnetic calorimeters Cherenkov Counters (e/π separation) Performances: large acceptance for charged particles 8 <θ<142, p p >0.3 GeV/c, p π >0.1GeV/c good momentum and angular resolution Δp/p 0.5%-1.5%,.5%, Δθ, Δφ 1 mrad Thomas Jefferson National Accelerator Facility Page 52

53 Channel selection TOF ep e p γ in CLAS All 3 particles are detected DC CC e γ EC electron ID: EC, CC, DC and TOF proton ID: DC and TOF photon ID: IC or EC p IC Thomas Jefferson National Accelerator Facility Page 53

54 The e1-dvcs experiment at CLAS Experiment: March - May 2005 E e = 5.77 GeV Polarization: 76% - 82% Current: na Integrated luminosity: nb PbWO 4 crystals 16cm x 1.3cm x 1.3cm 18 radiation lengths APD light readout CLAS solenoid IC Standard CLAS acceptance for photons: θ [ 17 o ; 43 o ] Superconducting solenoid magnet (shielding for Moeller electrons) Inner calorimeter: θ [ 4 o ; 15 o ] Thomas Jefferson National Accelerator Facility Page 54

55 Magnetic Shielding for Møller Electrons without magnetic field with magnetic field Thomas Jefferson National Accelerator Facility Page 55

56 Kinematics and Acceptance with CLAS + IC Thomas Jefferson National Accelerator Facility Page 56

57 CLAS e1-dvcs Results Thomas Jefferson National Accelerator Facility Page 57

58 Exclusive DVCS with CLAS Beam Spin Asymmetry Beam energy 4.25 GeV ep epγ identified by analyzing the missing mass distribution ep epx W > 2 GeV 1(GeV/c) 2 < Q 2 < 1.75(GeV/c) (GeV/c) 2 < -t < 0.3 (GeV/c) 2 Α(φ) = αsinφ + βsin2φ The measured asymmetry: α = ± stat ± sys Thomas Jefferson National Accelerator Facility Page 58

59 BSA: coverage and distributions Data integrated over t 13 Q 2, x B bins 5 t bins 12 φ bins Fit = α sinφ/(1+βcosφ) Thomas Jefferson National Accelerator Facility Page 59 Ph.D. Thesis of F.X. Girod

60 Thomas Jefferson National Accelerator Facility Page 60

61 BSA: a vs. t a(t) Q = 2.8 = x B Q = 3.3 = x B Q = 3.7 = 0.46 x B CLAS e1-dvcs Hall A 4.3 GeV Q = 2.3 = x B 2 2 Q = 2.7 = x B 2 2 Q = 3.0 = 0.36 x B VGG(*) twist-2 (DD) VGG(*) twist-2 and Q = 1.7 = x B Q = 1.9 = x B Q = 2.2 = 0.25 x B Regge model (**) (*) Guidal, Polyakov, Radyushkin, Vanderhaegen, PRD 72 (2005) (**) Cano and Laget, PL B551 (2003) Q = 1.2 = x B Q = 1.4 = 0.17 x B Q = 1.6 = 0.18 x B 0 0 Thomas Jefferson National Accelerator Facility Page t (GeV ) GPD model overestimates the data arxiv: [hep-ex] Submitted to PRL Ph.D. Thesis of F.X. Girod

62 Unpolarized Cross Sections d dq 4 σ 2 ep epγ dx B as a function of dtdφ φ <-t<0.2 02GeV <-t< GeV <-t< GeV 2 06<t<1 0.6<-t<1 GeV 2 1<-t<1.5 GeV 2 15<t<2 1.5<-t<2 GeV 2 Thomas Jefferson National Accelerator Facility Page 62 Ph.D. Thesis of H.S. Jo

63 Difference of Polarized Cross Sections 4 r 4 s d σ ep epγ d σ ep epγ as a function of 2 2 dq dx dtdφ dq dx dtdφ B B φ <-t<0.2 02GeV <-t< GeV <-t< GeV 2 06<t<1 0.6<-t<1 GeV 2 1<-t<1.5 GeV 2 15<t<2 1.5<-t<2 GeV 2 Largest kinematical coverage ever obtained for DVCS: 0.1<x B <0.58, 1<Q 2 <4.6, 0.09<-t<2 Thomas Jefferson National Accelerator Facility Page 63 Ph.D. Thesis of H.S. Jo

64 Measuring GPDs through polarization A = σ + σ σ + + σ = Δσ 2σ Polarized beam, unpolarized target: Δσ LU ~ sinφ{f 1 H + ξ(f 1 +F 2 )H +kf 2 E}dφ ~ H(ξ,t) Kinematically suppressed ξ ~x~ B /(2-x B B) k = t/4m 2 Unpolarized beam, longitudinal target: ~ Δσ UL ~ sinφ{f 1 H+ξ(F 1 +F 2 )(H +ξ/(1+ξ)e) -.. }dφ Kinematically suppressed Unpolarized beam, transverse target: ~ H(ξ,t), ) H(ξ,t) ) Δσ UT ~ sinφ{k(f 2 H F 1 E) +.. }dφ UT H(ξ,t), E(ξ,t) Kinematically suppressed Thomas Jefferson National Accelerator Facility Page 64

65 Spin polarized proton target The separation of GPDs requires measurements on polarized hydrogen targets. Measurements on such a target are more difficult than on unpolarized hydrogen. A typical polarized target NH 3 contains only 3 protons with spins aligned out of 17 nucleons. Dynamically polarized NH3 target Magnetic field ~ 5 Tesla Temperature ~ 1 K final state particle to CLAS beam target cell Thomas Jefferson National Accelerator Facility Page 65 Helmholtz coils liquid He 1m

66 Hall B Longitudinally Polarized Target Dynamically polarized NH 3 5 Tesla magnetic field δb/b K LHe cooling bath NH 3 polarization:75% 12 C, 15 N, and 4 He targets to measure the dilution factor Thomas Jefferson National Accelerator Facility Page 66

67 DVCS eg1: Separating DVCS Photons from Polarized Protons in NH 3 before the angular cut after the angular cut Eve ents NH 3 15 N MM X GeV /c Eve ents MM X GeV /c Events from both π 0 and unpolarized target nucleons are suppressed Geometry cut: θ γx < 1 o Thomas Jefferson National Accelerator Facility Page 67

68 First DVCS measurement with spin-aligned target Unpolarized beam, longitudinally spin-aligned target: ~ Δσ UL ~ sinφim{f 1 H+ξ(F 1 +F 2 )H + }dφ S. Chen, et al., Phys. Rev. Lett 97, (2006) fit model ~ CLAS preliminary model (H=0) A UL is dominated by H and H ~ ~ H=0 ~ H=0 α = ± β = ± Planned experiment in 2008 will improve accuracy dramatically. Thomas Jefferson National Accelerator Facility Page 68

69 Target Spin Asymmetry: φ Dependence 6 GeV run with NH 3 longitudinally polarized target (CLAS + IC) 60 days of beam time CLAS eg1 (preliminary) CLAS (eg1+ic) projected A dedicated CLAS experiment with longitudinally polarized target will provide a statistically significant measurement of the kinematical Thomas Jefferson dependences National Accelerator of the Facility DVCS target Page 69SSA

70 Target Spin Asymmetry: Q 2 Dependence Thomas Jefferson National Accelerator Facility Page 70

71 Target Spin Asymmetry: t- Dependence Higher t values will also be measured. The interpretation within the handbag formalism needs to be clarified. Thomas Jefferson National Accelerator Facility Page 71

72 Target Spin Asymmetry: t- Dependence Thomas Jefferson National Accelerator Facility Page 72

73 Target Spin Asymmetry: x- Dependence Thomas Jefferson National Accelerator Facility Page 73

74 Target Spin Asymmetry: Q 2 - Dependence Thomas Jefferson National Accelerator Facility Page 74

75 JLab Upgrade to 12 GeV E= 2.2, 4.4, 6.6, 8.8, 11 GeV Beam polarization P e > 80% Add new hall 12 GeV CHL-2 Thomas Jefferson National Accelerator Facility Page 75 Experiments on exclusive reactions to extract GPDs are a central part of the physics programs of the Halls A and B Enhance equipment in existing halls

76 Hall GeV: CLAS12 Concurrent measurement of deeply virtual exclusive, semi-inclusive, and inclusive processes Forward Electromagnetic Calorimeter Forward Time-of-Flight High threshold Cerenkov Counter Low threshold Cerenkov Counter Drift Chambers Q 2 > 2.5 GeV 2 Preshower Calorimeter Central detector Inner Electromagnetic Calorimeter Design luminosity ~ cm -2 s -1 Thomas Jefferson National Accelerator Facility Page 76

77 Hall GeV: CLAS12 Concurrent measurement of deeply virtual exclusive, semi-inclusive, and inclusive processes ep eγp High threshold Cerenkov Counter Forward Electromagnetic Calorimeter Forward Time-of-Flight Low threshold Cerenkov Counter Drift Chambers Q 2 > 2.5 GeV 2 Preshower Calorimeter Central Detector Forward Detector Central detector Inner Electromagnetic Calorimeter Acceptance for charged particles: Central (CD), 40 o <θ<135 o Forward (FD), 5 o <θ<40 o Design luminosity ~ cm -2 s -1 Thomas Jefferson National Accelerator Facility Page 77

78 Hall GeV: CLAS12 Concurrent measurement of deeply virtual exclusive, semi-inclusive, and inclusive processes ep eγp High threshold Cerenkov Counter Forward Electromagnetic Calorimeter Forward Time-of-Flight Low threshold Cerenkov Counter Drift Chambers θ γ Q 2 > 2.5 GeV 2 Preshower Calorimeter x B = 0.35 EC IC Central detector Acceptance for charged particles: Central (CD), 40 o <θ<135 o Forward (FD), 5 o <θ<40 o Q 2 Inner Electromagnetic Calorimeter Acceptance for photons: IC 2 o <θ<5 o EC, 5 o <θ<40 o Design luminosity ~ cm -2 s -1 Thomas Jefferson National Accelerator Facility Page 78

79 CLAS12: DVCS beam-spin asymmetry e p epγ E = 11 GeV Δσ LU ~sinφim{f 1 H+..}dφ L = 1x10 35 T = 2000 hrs ΔQ 2 = 1 GeV 2 Δx = 0.05 Q 2 =5.5GeV 2 x B = t = 0.25 GeV 2 Thomas Jefferson National Accelerator Facility Page 79

80 CLAS12: DVCS target-spin asymmetry e p epγ Longitudinally polarized target ~ Δσ~sinφIm{F 1 H+ξ(F 1 +F 2 )H...}dφ E = 11 GeV Projected results L = 2x10 35 cm -2 s -1 T = 1000 hrs ΔQ 2 = 1GeV 2 Δx = 0.05 S. Chen et al., PRL 97 (2006) E e =5.75 GeV <Q 2 > = 1.82 GeV 2 <x B > = 0.16 <-t> = 0.31 GeV 2 Thomas Jefferson National Accelerator Facility Page 80 Dedicated experiment at 6 GeV scheduled for next year

81 CLAS 12: DVCS transverse target-spin asymmetry e p epγ E = 11 GeV Projected results Transversely polarized target Q 2 =2.2 2 GeV 2, x =025 t=05gev 2 B 0.25, -t 0.5GeV Δσ ~ sinφim{k 1 (F 2 H F 1 E) + }dφ A UTx Target polarization in scattering plane A UTy Target polarization perpedicular to scattering plane Transverse-target spin asymmetry is highly sensitive to the u-quark contributions to proton spin. Thomas Jefferson National Accelerator Facility Page 81 H. Avakian

82 2Δ (Im(AB*))/π CLAS12: ep epρ 0 Α UT = A ~ (2H u +H d ) Α 2 (1 ξ 2 ) Β 2 (ξ 2 +t/4m 2 ) - Re(ΑΒ )2ξ 2 ρ 0 B ~ (2E u + E d ) Q 2 =5 GeV 2 Asymmetry depends on the GPD E, necessary for Ji s sum rule L=10 35 cm -2 s -1 T=2000 hrs Thomas Jefferson National Accelerator Facility Page 82 Goeke, Polyakov, Vanderhaegen (2001) and CLAS12 will allow us to measure also DVCS polarized and unpolarized cross sections, ndvcs, vector and pseudo-scalarscalar meson electroproduction

83 GeV: DVCS setup for Hall A H(e,e γ)p Q1 e' e detected in HRS-L γ detected in PbF2 calorimeter (upgraded with 76 additional elements) LH 2 BEAM DUMP 6 7 Extraction of epγ final state for published 6 GeV Ca lori meter at 1.50 M calorimeter at 3.00 M High resolution allows exclusivity without requiring detection of recoil proton Thomas Jefferson National Accelerator Facility Page 83

84 JLab12: Hall A with 3, 4, 5 pass beam H(e,e γ)p High luminosity high accuracy Absolute measurements: dσ(λ e =±1) 250K events/setup 100 days Twist 2 & Twist 3 separation Im{DVCS*BH} +εdvcs 2 Unphysical Re{DVCS*BH} +ε DVCS 2 Thomas Jefferson National Accelerator Facility Page 84

85 JLab12: projected results for DVCS in Hall A Unpolarized cross sections (pb/gev 4 ) 400 hours E e =8.8 GeV, Q 2 = 4.8 GeV 2, x B =0.5 E e =11 GeV, Q 2 = 9 GeV 2, x B =0.6 and exclusive π 0 electroproduction will also be measured Polarized cross section differences (pb/gev 4 ) Thomas Jefferson National Accelerator Facility Page 85 C. Hyde-Wright et al., arxiv:nucl-ex/