DVCS and DVMP: results from CLAS and the experimental program of CLAS12

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1 DVCS and DVMP: results from CLAS and the eperimental program of CLAS12 e e g N N GPDs Accessing GPDs via DVCS and DVMP Recent results from Jefferson Lab Silvia Niccolai IPN Orsay & CLAS Collaboration What we have learned The JLab 12 GeV upgrade Upcoming CLAS12 eperiments INT /8/2017 Seattle WA USA)

2 Transverse momentum Impact parameter Longitudinal momentum Multi-dimensional mapping of the nucleon DVCS et al. Elastic Scattering GTMDs GPDs FFs A complete picture of nucleon structure requires the measurement of all these distributions TMDs SIDIS PDFs DIS

3 Eclusive reactions giving access to GPDs TCS) DDVCS g) Quark GPDs DVCS Gluon GPDs Quark GPDs M Q 2 = - k-k ) 2 B = Q 2 /2Mn n=e e -E e +ξ -ξ long. mom. fract. t = D 2 = p-p ) 2 B /2- B ) DVMP Quark GPDs Transversity GPDs Gluon GPDs

4 Eclusive reactions giving access to GPDs TCS) DDVCS M. Defurne s talk M. g Boer s talk Quark GPDs DVCS Gluon GPDs Quark GPDs M Q 2 = - k-k ) 2 B = Q 2 /2Mn n=e e -E e +ξ -ξ long. mom. fract. t = D 2 = p-p ) 2 B /2- B ) DVMP Quark GPDs Transversity GPDs Gluon GPDs

5 Properties and virtues of GPDs X. Ji Phy.Rev.Lett ) ) ) ) ) ) ) ) ) t G d t E t G d t H t F d t E t F d t H P A ~ ~ 2 1 ) 00) ~ ) 00) q H q H D Link with FFs Forward limit: PDFs not for E E) ~ Nucleon tomography Nucleon spin: ½ = ½ D + DL + DG J L J t E t H d D D 2 1 0)) 0) Intrinsic spin of the quarks D 25% Intrinsic spin on the gluons DG 0??) Orbital angular momentum of the quarks DL? Quark angular momentum Ji s sum rule) M. Burkardt PRD ) ) 0 ~ ) 2 ) b ) 0 ) 2 ) b 2 b b D D D D D D D H e d q H e d q i i

6 Np) e Deeply Virtual Compton Scattering and quark GPDs g* Q 2 ) +ξ e t -ξ ~ ~ H H E E ξt) g factorization Np ) «Handbag» factorization valid in the Bjorken regime: high Q 2 n fied B ) t<<q 2 At leading order QCD twist 2 chiral-even quark helicity is conserved) quark sector 4 GPDs for each quark flavor conserve nucleon spin flip nucleon spin Vector: H ξt) Tensor: E ξt) ~ Aial-Vector: H ξt) ~ Pseudoscalar: E ξt)

7 Accessing GPDs through DVCS DVCS allows access to 4 comple GPDs-related quantities: Compton Form Factors t) T DVCS 1 GPDs t) ~ P d igpds t) 1 Only and t are accessible eperimentally 1 2 q q 1 1 q q ReH q e q P H t) H t) ) d ImH q e H t) H t) 2 q 0 BH is calculable electromagnetic FFs) ~ T D A DVCS D 2 T I BH BH Re CFFs ) also DSA) I DVCS BH ) DVCS BH ) 2 2 DVCS 2 I Im CFFs ) e e g leptonic plane hadronic plane N f

8 Sensitivity to CFFs of DVCS spin observables A A LU UL) LL c BH 0 unp c s I 1 unp UL) I BH 0 unp c1 unp c c BH 0 LP BH 0 unp c sinf c c I 0 LP I 0 unp I 1 unp c c )cosf BH 1 LP BH 1 unp c c I 1 LP I 1 unp )cosf )cosf Twist-2 approimation -t<<q 2 ) = B /2- B ) k=-t/4m 2 ) Polarized beam unpolarized target: s I 1unp ~ Im{F 1 H + F 1 +F 2 )H -kf~ 2 E} ~ Im{H p H ~ p } Unpolarized beam longitudinal target: s I 1UL ~ Im{F 1 H+F 1 +F 2 )H + B /2E) kf 2 E+ } ~ Polarized beam longitudinal target: c I 1 LP ~ Re{F 1 H+F 1 +F 2 )H + B /2E) } Unpolarized beam transverse target: D UT ~ sinf s f)im{kf 2 H F 1 E) + } Proton Neutron ~ ~ Im{H p H p E p } Im{H n H n E n } Im{H n E n } ~ ~ Re{H p H p } Im{H p E p } Im{H n } Re{H n E n }

9 DVCS eperiments worldwide JLAB Hall A pn-dvcs Bpol.) CS CLAS Hall B) p-dvcs BSAlTSADSACS DESY HERMES H1/ZEUS p-dvcs p-dvcs BSABCA CSBCA ttsaltsadsa CERN COMPASS p-dvcs CSBSABCA ttsaltsadsa S. Stepanyan et al. PRL ) C.M. Camacho et al. PRL ) CLAS CLAS: first observation of DVCS-BH interference Hall A <Q 2 -t> = ) GeV 2 Q 2 =1.25 GeV 2 < B > = 0.19 <-t> = 0.19 GeV 2 Hall A: proof of scaling for DVCS

10 GeV Continuous Electron Beam Accelerator Facility Hall B: CLAS Large acceptance Suited for multi-particle final states L~10 34 Hall A: 2 HRS High resolution High luminosity L~10 37 ) Limited coverage A B C E ma ~ 6.0 GeV I ma ~200 ma Polarization 85% MHz operation Simultaneous Hall C SOS/HMS) delivery to 3 halls Shutdown in May 2012

11 CLAS: unpolarized and beam-polarized cross sections ep epγ H.S. Jo et al. PRL ) ~ D LU ~ sinf Im{F 1 H + F 1 +F 2 )H -kf 2 E}df Largest kinematic ever covered Two observables etracted BH VGG KM10 KM10a KM10 model fits Hall A 2006 data using «anomalous» H ~ Data taken in 2005 e1-dvcs Beam energy ~ 5.75 GeV Beam polarization ~ 80% Target LH 2 Inner Calorimeter IC) 21 Q 2 - B bins 9 t bins 24 φ bins

12 CLAS: DVCS on longitudinally polarized target Data taken in 2009 eg1-dvcs Beam energy ~5.9 GeV CLAS + IC to detect forward photons Target: longitudinally polarized NH 3 P~80%) 3 DVCS observables BSA ~ Im{H p } ep epγ Beam asymmetry Target asymmetry Double asymmetry 5 Q 2 - B bins 4 t bins 10 f bins S. Pisano et al. PRD ) CLAS: <Q 2 >= 2.4 GeV/c) 2 < B >= 0.31 HERMES: <Q 2 >= GeV/c) 2 < B >= CLAS2006: <Q 2 >= 1.82 GeV/c) 2 < B >= 0.28 Improved statistics 10 at low t Etended kinematic coverage

13 CLAS: DVCS on longitudinally polarized target Data taken in 2009 eg1-dvcs Beam energy ~5.9 GeV CLAS + IC to detect forward photons Target: longitudinally polarized NH 3 P~80%) 3 DVCS observables ~ TSA ~ Im{H p H p } ep epγ Beam asymmetry Target asymmetry Double asymmetry 5 Q 2 - B bins 4 t bins 10 f bins E. Seder et al. PRL ) CLAS: <Q 2 >= 2.4 GeV/c) 2 < B >= 0.31 HERMES: <Q 2 >= GeV/c) 2 < B >= CLAS2006: <Q 2 >= 1.82 GeV/c) 2 < B >= 0.28 Improved statistics 10 at low t Etended kinematic coverage

14 CLAS: DVCS on longitudinally polarized target Data taken in 2009 eg1-dvcs Beam energy ~5.9 GeV CLAS + IC to detect forward photons Target: longitudinally polarized NH 3 P~80%) 3 DVCS observables ~ DSA ~ Re{H p H p } ep epγ Beam asymmetry Target asymmetry Double asymmetry 5 Q 2 - B bins 4 t bins 10 f bins S. Pisano et al. PRD ) Constant term and cosf term are dominated by BH

15 ep eγp) DVCS on the proton in Hall A M. Defurne et. al. PRC ) Significant deviation from Bethe-Heitler Both I BH DVCS) and DVCS 2 contribute to the cross section Twist-4 corrections TMC) may be necessary to describe the data New results from 2009 data: see M. Defurne s talk

16 Etraction of Compton Form Factors from DVCS observables GPDs cannot directly be etracted from DVCS observables one can access Compton Form Factors: 8 CFF M. Guidal: Model-independent fit at fied Q 2 B and t of DVCS observables 8 parameters the CFFs) loosely bound +/- 5 VGG prediction) M. Guidal Eur. Phys. J. A ) 319 & many other papers

17 ~ Results for H Im and H Im from the fits of JLab 2015 data Fit to CLAS c.s. and beam pol. c.s. Fit to CLAS c.s. beam pol. c.s. ltsa DSA Fit to Hall A c.s. and beam pol. c.s. VGG model H Im has steeper t-slope than H Im : the aial charge ~Du-Dd) is more concentrated than the electric charge R. Dupré M. Guidal S.Niccolai M. Vanderhaegen arxiv: ~

18 From CFFs to proton tomography «Integrated» radius from elastic form factor F 1 :

19 Summary of proton-dvcs spin observables and GPDs etraction Beam charge asymmetry Beam spin asymmetry Transverse target spin asymmetry Beam-spin and tr. target spin asymmetry Longitudinal target spin asymmetry Beam-spin and long. target spin asymmetry Hall A 2015) CLAS C.S. CLAS C.S. +TSA+DSA N. d Hose S.N. A. Rostomyan EPJA ) HERMES Beam Charge Asymmetry: strong constraint for H Re

20 ed eγnp) DVCS on the neutron in Hall A M. Mazouz et al. PRL ) F. Cano B. Pire Eur. Phys. J. A ) 423 ~ D LU ~ sinf Im{F 1 H + F 1 +F 2 )H -kf 2 E} 1 1 d H t 0) E t 0)) 2 1 J S. Ahmad et al. PR D ) VGG PR D ) E03-106: First-time measurement of D LU for ndvcs model-dependent etraction of J u J d Proton and neutron GPDs and CFFs) are linear combinations of quark GPDs H H p n t) H t) H t) u t) H t) H t) u d d A combined analysis of DVCS observables for proton and neutron targets is necessary to perform a quark-flavor separation of the GPDs E08-025: Beam-energy «Rosenbluth» separation of ndvcs CS using an LD2 target

21 Deeply virtual meson production and GPDs Different mesons different sensitivity to GPDs H E ~ H ~ E Factorization proven only for longitudinally polarized virtual photons quark flavor decomposition accessible via meson production Vector mesons r w f) 0 h ρ 0 ω ρ + Pseudoscalar mesons h) 2Du+Dd 2Du-Dd 2u+d 2u-d u-d Complications: effective scale in the hard scattering process meson distribution amplitude

22 Deeply virtual meson production at CLAS Vector mesons: eclusive r 0 w f and r + electroproduction on the proton with CLAS K. Lukashin et al. Phys. Rev. C f@4.2 GeV) e1-b C. Hadjidakis et al. Phys. Lett. B r GeV) 1999) L. Morand et al. Eur. Phys. J. A w@5.75gev) J. Santoro et al. Phys. Rev. C f@5.75 GeV) S. Morrow et al. Eur. Phys. J. A r A. Fradi Orsay Univ. PhD thesis r GeV) e ) e1-dvcs 2005) Pseudoscalar mesons: eclusive 0 and h electroproduction on the proton with CLAS R. De Masi et al. Phys. Rev. C R) 2008 K. Park et al. Phys. Rev. C GeV) I. Bedlinskiy et al. Phys. Rev. Lett ) ; Phys. Rev. C ) I. Bedlinskiy et al. Phys. Rev. C ) h@5.75gev)

23 Comparison between vector mesons ) r r 0 w f CLAS preliminary

24 Comparison between vector mesons L ) Q 2 =3.8 GeV 2 GK full) GK sea and gluons) VGG valence and sea) GK valence) = The GPD models fail to reproduce L at low W for r 0 L. Favart M. Guidal T. Horn P. Kroll EPJA )

25 Chiral-odd GPDs 4 chiral-odd GPDs parton helicity flip) Difficult to access helicity flip processes are suppressed) Chiral-odd GPDs are very little constrained Anomalous tensor magnetic moment: +1 κ T = න 1 d തE T ξ t = 0 Link to the transversity distribution: തE T = 2 H T + E T H T q 00 = h 1 q H T H T E T E T Transverse Densities for u and d quarks in the nucleon Distributions of unpolarized quarks in a transversely polarized nucleon linked to E Distribution of transversely polarized quarks in an unpolarized nucleon linked to ഥE T Gockeler et al Phys. Rev. Lett ) lattice calculation

26 Eclusive 0 electroproduction e 0 f e leptonic plane hadronic plane p dσ = G dq 2 d B dϕdt Q2 1 B σ 2π T + εσ L + εcos2ϕσ TT + 2ε1 + ε)cosϕσ LT Leading twist: L is suppressed: σ T = 4πα e 2κ σ TT = 4πα e 2κ σ L = 4πα e k Q 6 1 ξ 2 < H > 2 2ξ 2 Re < H > < E > t 4m 2 ξ2 < E > 2 H π = H u + H d Generalized Compton Form Factors μ π 2 Q 4 1 ξ 2 < HT > 2 t 8m 2 < E T > 2 μ π 2 Q 4 t 8m 2 < E T > 2 < H > = 1 λ 1 d M ξ Q 2 λ H ξ t Transversity GPD models: Goloskokov-Kroll Liuti-Goldstein L << T

27 CLAS results I. Bedlinskiy et al. Phys. Rev. Lett ) ; Phys. Rev. C ) T +e L LT TT Goloskokov-Kroll model Transversity GPDs Recent Hall A results for proton and neutron 0 electroproduction flavor separation of transversity GPDs M. Defurne s T. Horn s talks)

28 Comparison 0 /h I.Bedlinskiy et al. Phys. Rev. C ) Very little dependence on B and Q 2 Chiral-odd GPD models predict this ratio to be ~1/3 at CLAS kinematics Chiral-even GPD models predict this ratio to be around 1 at low t) Potentially one can perform flavor separation of transversity GPDs combining 0 and h

29 E= GeV for the Halls A B C Beam polarization > 80% Upgrade completed in 2014 JLab upgrade to 12 GeV Add new hall 12 GeV CH L-2 Sea/gluon region H1 ZEUS H1 ZEUS Valence region COMPASS HERMES 11 GeV Study of high B domain requires high luminosity The 12-GeV upgrade is well matched to studies in the valence-quark regime 0.7

30 New capabilities in Halls A B & C A B High Resolution Spectrometer HRS) pair and specialized large installation eperiments C Super High Momentum Spectrometer SHMS) at high luminosity and forward angles CLAS12: large acceptance high luminosity GPDs eperiments at 11 GeV have been approved for each of these three halls. Complementary programs: different kinematic coverage different precisions/resolutions focus on different observables M. Defurne and T. Horn will present Halls A and C

31 Hall GeV: CLAS12 Design luminosity L ~ cm -2 s -1 Acceptance for charged particles: Central CD) 40 o <q<135 o Forward FD) 5 o <q<40 o Central Detector Acceptance for photons: Forward tagger T 2 o <q<5 o EC 5 o <q<40 o High luminosity & large acceptance: Concurrent measurement of deeply virtual eclusive semi-inclusive and inclusive processes +FT CND MM RICH Forward Detector PCAL

32 DVCS BSA and TSA with CLAS12 & 11 GeV beam BSA 85 days of beam time P beam = 85% L = cm 2 s 1 Statistical error: 1% to 10% on sinf moments Systematic uncertainties: ~6-8% 120 days of beam time P beam = 85% P target = 80% L = cm 2 s 1 Statistical error: 2% to 15% on sinf moments Systematic uncertainties: ~6-8% TSA Impact of CLAS12 DVCS-BSA data on CFF fit

33 CLAS12: p-dvcs transverse target-spin asymmetry 100 days of beam time Beam pol. = 80% ; target pol. HDIce) = 60% ; Luminosity = cm -2 s -1 1< Q 2 < 10 GeV < B < 0.66 t min < t < 1.5 GeV 2 Transverse-target spin asymmetry for p-dvcs is highly sensitive to the u-quark contributions to proton spin. JLab PAC: high-impact eperiment Proposal conditionally approved by PAC39 Tests on HDIce target are ongoing

34 From CFFs to spatial densities Projections for CLAS12 M. Guidal H. Moutarde M. Vanderhagen Rept.Prog.Phys ) )

35 -0.2 BSA 0.2 E : BSA for DVCS on the neutron with CLAS12 ~ H E) H E) u d t) 9 15 t) 9 15 ed ep)ng CLAS12 + Forward Calorimeter + Neutron Detector 80 days of data taking L = cm 2 s 1 /nucleon 4 4 H E) t) H E) p H E) t) H E) n n p t) t) -t D LU ~ sinf Im{F 1 H + F 1 +F 2 )H -kf 2 E}df The most sensitive observable to the GPD E First-time measurement Installation in 3 weeks IPN Orsay) JLab PAC: high-impact eperiment

36 -0.2 BSA 0.2 E : BSA for DVCS on the neutron with CLAS12 ~ H E) H E) u d ed ep)ng CLAS12 + Forward Calorimeter + Neutron Detector 80 days of data taking L = cm 2 s 1 /nucleon Model predictions VGG) for different values of quarks angular momentum J u =.3 J d =.1 J u =.1 J d =.1 t) 9 15 t) H E) t) H E) p H E) t) H E) n n p t) t) -t D LU ~ sinf Im{F 1 H + F 1 +F 2 )H -kf 2 E}df The most sensitive observable to the GPD E First-time measurement J u =.3 J d =.3 J u =.3 J d =-.1 f JLab PAC: high-impact eperiment

37 A E a: ndvcs target-spin asymmetry 1 P A) 1 t P N t 2 ~ ~ D UL ~ sinf Im{F 1 H+F 1 +F 2 )H + B /2E) kf 2 E+ } 1 0 -t 1.2 TSA ~ 0.2 L = 3/ cm -2 s -1 Time = 50 days P t = end 3 ep)ng CLAS12 + Long. pol. target Forward Calorimeter + Neutron Detector -1 First time measurement 4 bins in Q 2 4 bins in t 4 bins in B 12 bins in φ Same as E )

38 A E a: ndvcs double spin asymmetry 1 P P A) 1 b t P P N b t 2 ~ ~ D LL ~ A+Bcosf) Re{F 1 H+F 1 +F 2 )H + B /2E) kf 2 E+ } t 1.2 DSA up to 0.8 L = 3/ cm -2 s -1 Time = 50 days P t = 0.4; P b = 0.85 end 3 ep)ng CLAS12 + Long. pol. target Forward Calorimeter + Neutron Detector First time measurement 4 bins in Q 2 4 bins in t 4 bins in B 12 bins in φ Same as E ) Green curves: Bethe-Heitler

39 Combined analysis of all ndvcs CLAS12 projections ImH n Etraction of neutron CFFs using M. Guidal s fitting code. Fit of TSA DSA E a) and BSA E ) 7 CFFs as free fit parameters ImE ~ = 0

40 DVCS on the nucleon: past present future CLAS12 CLAS12 + Timelike Compton CLAS12 DDVCS SOLID? CLAS12?)

41 Fits done to all the projected observables for pdvcs BSA ltsa ldsa ttsa CS DCS) and ndvcs BSAlTSA ldsa) of the CLAS12 program CLAS12: projections for flavor separation ImH ImE) Quark CFFs Nucleon CFFs q q q J t E t H d )) 0 0) ) ) ) ) ) ) ) ) ) ) ) ) t E H t E H t E H t E H t E H t E H p n d n p u

42 CLAS12: eclusive f electroproduction Differential c.s. etraction of structure functions L-T separation from ϕ KK decay distributions t dependence of d L /dt Transverse distribution of gluons in the proton

43 Conclusions GPDs are a unique tool to eplore the internal dynamics of the nucleon: 3D quark/gluon imaging of the nucleon orbital angular momentum carried by quarks Their etraction from eperimental data is very difficult: there are 4 GPDs for each quark flavor they depend on 3 variables only two t) eperimentally accessible via DVCS Recently-developed fitting methods allow to etract CFFs from DVCS observables. Need to measure several p-dvcs and n-dvcs observables over a wide phase space A wealth of new results on various DVCS observables is coming from recent CLAS and Hall- A eperiments on the proton deuterium and 4 He targets) First tomographic interpretations of the quarks in the proton from DVCS: valence quarks are concentrated in its center sea quarks at its perifery aial charge more concentrated than the electric one Things are more complicate for DVMP: uneplained low-w behavior for light vector mesons transversity GPDs dominance for pseudo-scalars The 12-GeV-upgraded JLab is the only facility to perform GPD eperiments in the valence region for Q 2 up to 11 GeV DVCS and DVMP eperiments on both proton and neutron pol. and unpol.) are planned for 3 of the 4 Halls at JLab@12 GeV: quarks spatial densities flavor separation quarks orbital angular momentum gluon densities