1. e e’  GPDs NN’ Deeply virtual Compton scattering on the nucleon at 6 and 11 GeV Silvia Niccolai Soutenance HDR IPN Orsay – November 27 th 2014

2. p p n  GPDs   s u d Technical project: polarized target for electron scattering experiments at CLAS Few-body interactions among nucleons: three-body photodisintegration of 3 He at CLAS Baryon spectroscopy: pentaquark search in  d( 3 He)→  + (p) Phys. Rev. Lett. 97, 032001 (2006) Nucleon structure: GPDs PAC proposal: DVCS with polarized target at CLAS Nucleon structure: strange form factors → parity violation Radiative corrections for G0 (Hall C), forward angles Eur. Phys. J. A26, 429 (2005) GENOVA 9/97-10/98 CV: Experimental hadronic physics at JLab (junior years) 1/99-2/03 3/03-9/03 10/03-9/06 Phys. Rev. C 70, 1 (2004)

3. CV: Structure of the nucleon at CLAS (senior years) e1-dvcs experiment (2005): cross sections for ep→e’p’  0 → sensitivity of this channel to transversity GPDs (chiral-odd) Phys. Rev. Lett. 109, 112001 (2012) Phys. Rev. C 90, 039901 (2014) 3 PhD theses at IPN: H.S. Jo (DVCS cross section) B. Moreno (  DVCS asymmetry) A. Fradi (ep→e’n  + c. s.) e1-dvcs2 experiment (2008): 2 PhD theses: B. Guegan (DVCS c.s.) N. Saylor (DVCS c.s.) e1-6 experiment (2001): 1 PhD thesis, underway: B. Garillon (ep→e’p’f 0 (f 2 ) c.s.) 3 « encadrements de stagiaires »

4. Part 1: DVCS on longitudinally polarized protons at 6 GeV

5. x ee’ X p  (Q 2 ) Electron-proton scattering: yesterday ee’ pp’  (t=Q 2 )  1950: Elastic scattering ep→e’p’ ( Hofstadter, Nobel prize 1961)  1967: Deep inelastic scattering (DIS) ep→e’X ( Friedman, Kendall, Taylor, Nobel prize 1990) Discovery of the quarks (or “partons”) Measurement of the momentum and spin distributions of the partons: q(x),  q(x) The proton is not a point-like object Measurement of charge and current distributions of the proton: form factors (F 1 (t), F 2 (t)) Low Q 2 High Q 2

6. x Electron-proton scattering: today ? Form factors: transverse quark distribution in coordinate space Parton distributions: longitudinal quark distribution in momentum space F 1 (t), F 2 (t) q(x),  (x)

7. x Electron-proton scattering: today GPDs: H, E, H, E Fully correlated quark distributions in both coordinate and momentum space ~~ Form factors: transverse quark distribution in coordinate space Accessible in hard exclusive processes Parton distributions: longitudinal quark distribution in momentum space q(x),  (x) F 1 (t), F 2 (t)

8. Deeply Virtual Compton Scattering and GPDs e’ t (Q 2 ) e ** x+ξ x-ξ H, H, E, E (x,ξ,t) ~ ~  N(p) N(p’) « Handbag » factorization valid in the Bjorken regime: high Q 2,  (fixed x B ), t<<Q 2 Q 2 = - (e-e’) 2 x B = Q 2 /2M  =E e -E e’ x+ξ, x-ξ longitudinal momentum fractions t =  2 = (p-p’) 2  x B /(2-x B ) GPDs: Fourier transforms of non-local, non-diagonal QCD operators P = (p+p’)/2 Light-cone: a ± = (a 0 ± a 3 )/ √2 factorization

9. Deeply Virtual Compton Scattering and GPDs Vector: H (x,ξ,t) Tensor: E (x,ξ,t) Axial-Vector: H (x,ξ,t) Pseudoscalar: E (x,ξ,t) ~ ~ conserve nucleon spin flip nucleon spin At leading order QCD, twist 2, chiral-even (quark helicity is conserved), quark sector → 4 GPDs for each quark flavor

10. Properties and “virtues” of GPDs X. Ji, Phy.Rev.Lett.78,610(1997) Link with FFs Forward limit: PDFs (not for E, E) ~ Nucleon tomography Nucleon spin: ½ = ½  +  L +  G J Intrinsic spin of the quarks  ≈ 25% Intrinsic spin on the gluons  G ≈ 0 (??) Orbital angular momentum of the quarks  L ? Quark angular momentum (Ji’s sum rule) M. Burkardt, PRD 62, 71503 (2000)

11. Accessing GPDs through DVCS   Only  and t are accessible experimentally DVCS allows access to 4 complex GPDs-related quantities: Compton Form Factors ( ,t)

12. Im{ H n, E n, E n }  = x B /(2-x B ) k=-t/4M 2 )   leptonic plane hadronic plane N’ e’ e Unpolarized beam, longitudinal target: s I 1,UL ~ sin  Im{F 1 H +  (F 1 +F 2 )( H + x B /2 E ) –  kF 2 E+… } ~ Im{ H p, H p } ~ s I 1,unp ~ sin  Im{F 1 H +  (F 1 +F 2 ) H -kF 2 E } ~ Polarized beam, unpolarized target: Im{ H p, H p, E p } ~ Sensitivity to GPDs of DVCS spin observables Polarized beam, longitudinal target: c I   LP ~ (A+Bcos  Re{F 1 H +  (F 1 +F 2 )( H + x B /2 E )…} ~ Re{ H p, H p } ~ Im{ H n, H n, E n } ~ Proton Neutron ~ Re{ H n, E n, E n } ~ Im{ H n } ~ Unpolarized beam, transverse target:  UT ~ cos  sin  s  Im{k(F 2 H – F 1 E ) +… } Im{ H p, E p } Twist 2

13. s I 1,unp ~ sin  Im{F 1 H +  (F 1 +F 2 ) H -kF 2 E } ~ Polarized beam, unpolarized target: Im{ H p, H p, E p } ~  = x B /(2-x B ) k=-t/4M 2 )   leptonic plane hadronic plane N’ e’ e Unpolarized beam, longitudinal target: s I 1,UL ~ sin  Im{F 1 H +  (F 1 +F 2 )( H + x B /2 E ) –  kF 2 E+… } ~ Im{ H p, H p } ~ Sensitivity to GPDs of DVCS spin observables Polarized beam, longitudinal target: c I   LP ~ (A+Bcos  Re{F 1 H +  (F 1 +F 2 )( H + x B /2 E )…} ~ Re{ H p, H p } ~ Im{ H n, H n, E n } Proton Neutron ~ ~ Twist 2

14. DVCS experiments worldwide Jefferson Lab (Halls A&B) HERMES COMPASS

15. The CLAS eg1-dvcs experiment ep→epγ →→ Analysis team composed of: E. Seder, U Connecticut (CEA Saclay) S. Pisano, INFNFR A. Biselli, Fairfield U S. Niccolai Also: ongoing BSA and TSA for nDVCS (D. Sokhan, Glasgow U) Target: longitudinally polarized NH 3 (polarization ~80%) Experiment approved by PAC28 (2005) with A rating Data taken from February to end of August 2009 Beam energy ~5.9 GeV CLAS + IC to detect forward photons IC (inner calorimeter): 424 lead-tungstate crystals + APD readout (built at IPNO)

16. The eg1-dvcs polarized target Dynamic Nuclear Polarization of NH 3 Free electrons ( Ṅ H 2 radicals) are implanted in crystalline beads of ammonia via electron radiation Radicals are polarized ( ~100%) at 5 T and 1 K (P=tanh(µB/kT) ) Microwaves (140 Ghz) drive electron/proton spin-flip transitions and transfer polarization to protons Polarization is measured with NMR Polarized ammonia Carbon Empty Optics

17. Experimental definition of the observables b: beam t: target FC bt : charge, from Faraday Cup B  0 : relative  0 contamination P t : target polarization P b : beam polarization D f : dilution factor c AUT, c AUL : transverse corrections Beam-spin asymmetry Target-spin asymmetry Double-spin asymmetry Im{ H p } For each 4-dimensional bin in (Q 2, x B, -t,  Charge-normalized DVCS/BH yield Im{ H p, H p } ~ Re{ H p, H p } ~

18. « Highlights » of the eg1-dvcs analysis Selection of the ep  final state: exclusivity cuts to reduce nuclear background and ep  0 →ep  (  ) contamination; different strategies to define the cuts for the IC and EC topologies NH 3, before cuts 12 C, before cuts NH 3, after cuts 12 C, after cuts

19. P t : measured during the experiment by NMR. NMR coils surrounded the target → more sensitive to polarization of its outer volume. Risk to overestimate P t « Highlights » of the eg1-dvcs analysis Extraction of P b P t P b P t deduced from elastic BSA (ep→e’p’): A theo : known function of the kinematics and of the e.m. FFs P b measured during the experiment with Moller runs

20. Beam-spin asymmetry Fit:  LU sin  /(1+  cos  ) (  constrained: equal for the 3 asymmetries)

21. Beam-spin asymmetry  LU ~ Im{ H p } Fit:  LU sin  /(1+  cos  )

22. Beam-spin asymmetry  LU ~ Im{ H p } Fit:  LU sin  /(1+  cos  ) VGG: Vanderhaegen, Guidal, Guichon KMM12: Kumericki, Mueller, Murray GK: Goloskokov, Kroll GGL: Gonzalez., Goldstein, Liuti

23. Target-spin asymmetry  UL ~ Im{ H p, H p } ~ Fit:  UL sin  /(1+  cos  ) E. Seder et al. arXiv:1410.6615, submitted to PRLarXiv:1410.6615

24. Target-spin asymmetry E. Seder et al. arXiv:1410.6615, submitted to PRLarXiv:1410.6615 Fit:  UL sin  +B sin 2  Agreement with world data Improved statistics x10 at low -t Extended kinematic coverage E. Seder et al. arXiv:1410.6615, submitted to PRLarXiv:1410.6615 CLAS: = 2.4 (GeV/c) 2, = 0.31 HERMES: = 2.459 (GeV/c) 2, = 0.096 CLAS2006: = 1.82 (GeV/c) 2, = 0.28

25. Target-spin asymmetry E. Seder et al. arXiv:1410.6615, submitted to PRLarXiv:1410.6615 E. Seder et al. arXiv:1410.6615, submitted to PRLarXiv:1410.6615 “This paper presents new data on Generalized Parton Distributions (GPDs) obtained through DVCS. The results obtained are by far (at least one order of magnitude) the most accurate and the most extensive to date on the target-spin asymmetry in DVCS. Together with earlier published data on beam-spin asymmetries they will significantly advance our knowledge about GPDs. As such, this work has indeed significant impact on the field of hadronic structure. The fact that insight in the 3D-structure of the nucleon is pushed forward by experiments and analyses today fully merits the attention of a broader audience than that served by the Physical Review journals, and I support the publication in Physical Review Letters.” PRL referee

26. Double-spin asymmetry Fit:  LL + LL cos  /(1+  cos  ) Constant term dominated by BH

27. LL ~ Re{ H p, H p } ~ Fit:  LL + LL cos  /(1+  cos  ) cos  term small and dominated by BH Double-spin asymmetry

28. Extraction of Compton Form Factors from DVCS observables 8 CFF M. Guidal: Model-independent fit, at fixed Q 2, x B and t of DVCS observables 8 unknowns (the CFFs), non-linear problem, strong correlations Bounding the domain of variation of the CFFs with model (5xVGG) M. Guidal, Eur. Phys. J. A 37 (2008) 319

29. Extraction of CFF from DVCS TSA, BSA, DSA [12] CLAS BSA (Girod et al.) [14] CLAS TSA (Chen et al.) CFFs fitting code by M. Guidal Im H has steeper t-slope than Im H : is axial charge more “concentrated” than the electromagnetic charge? ~ Some sensitivity to Re H, Re E but with big uncertainties → DSA at CLAS12 ~ ~ Slope of Im H decreasing as x B increases: fast quarks (valence) more concentrated in the nucleon’s center, slow quarks (sea) more spread out

30. Part 2: DVCS on the neutron at 11 GeV

31. JLab upgrade and CLAS12 CHL-2 Add new hall CLAS12 H1, ZEUS Valence region Sea/gluon region E max (A,B,C) = 11 GeV CLAS12: high luminosity (10 35 cm -2 s -1 ) and large acceptance: Charged particles, 5 o <  <135 o Photons: 2.5 o <  < 5 o (Forward Tagger) 5 o <  <40 ° (E.m. Calorimeter) 12 GeV Extensive experimental program for p-DVCS planned: BSA, lTSA, tTSA (CLAS12) Cross sections, Q 2 -scaling tests (Halls A and C)

32. (H,E) p (ξ, ξ, t) = 4/9 (H,E) u (ξ, ξ, t) + 1/9 (H,E) d (ξ, ξ, t) (H,E) n (ξ, ξ, t) = 1/9 (H,E) u (ξ, ξ, t) + 4/9 (H,E) d (ξ, ξ, t) A combined analysis of DVCS observables on proton and neutron targets is necessary for the flavor separation of the GPDs (H,E) u (ξ, ξ, t) = 9/15[4(H,E) p (ξ, ξ, t) – (H,E) n (ξ, ξ, t)] (H,E) d (ξ, ξ, t) = 9/15[4(H,E) n (ξ, ξ, t) – (H,E) p (ξ, ξ, t)] DVCS on the neutron: motivation GPDs depend on the quark’s flavor: Proton and neutron GPDs are linear combinations of quarks GPDs The BSA for nDVCS is sensitive to the GPD E, That is the least known and the least constrained of the GPDs and that appears in Ji’s sum rule → J u, J d We will intiate an experimental program at JLab on neutron DVCS at 11 GeV, by measuring the beam-spin asymmetry (BSA)  LU ~ sin  Im{F 1 H +  (F 1 +F 2 ) H -kF 2 E }d  ~ Im{ H n, H n, E n } ~

33. First nDVCS measurement: Hall A@6 GeV Subtraction of the contributions from the proton using H 2 data convoluted with Fermi motion “Impulse approximation” (no FSI) Active nucleon identified via MM(e  M. Mazouz et al., PRL 99 (2007) 242501 Model-dependent extraction of J u et J d Q 2 = 1.9 GeV 2 x B = 0.36 Im(C I n ) compatible with zero (→ too high x B ?) Big statistical and systematic uncertainties (mostly due to the H 2 subtraction and  0 background) S. Ahmad et al., PRD75 (2007) 094003 VGG, PRD60 (1999) 094017

34.  = 60° x B = 0.17 Q 2 = 2 GeV 2 t = -0.4 GeV 2 The BSA for nDVCS: is very sensitive to E depends strongly on the kinematics → a large acceptance is necessary → CLAS12 VGG model J u =.3, J d =.1 J u =.1, J d =.1 J u =.5, J d =.1 J u =.3, J d =.3 J u =.3, J d =-.1 E e = 11 GeV BSA for nDVCS at 11 GeV: sensitivity to E  LU  Hall A

35. Central Detector nDVCS@CLAS12: detector requirements More than 80% of the neutrons have  >40° → Neutron detector in the CD ~ 0.4 GeV/c ~ 60° ed→e’n  (p) Detected in forward CLAS12 Detected in EC, FT Not detected Detected in CND In the hypothesis of absence of FSI: p μ p = p μ p’ → kinematics are complete detecting e’, n (p, ,  ),  p μ e + p μ n + p μ p = p μ e′ + p μ n′ + p μ p′ + p μ  Resolution on MM(en  ) studied with nDVCS event generator + electron and photon resolutions obtained from CLAS12 FastMC + design specs for Forward Tagger → dominated by photon resolutions Resolution on MM(en  ) studied with nDVCS event generator + electron and photon resolutions obtained from CLAS12 FastMC + design specs for Forward Tagger → dominated by photon resolutions The Central Neutron Detector (CND) must ensure: good neutron/photon separation for 0.2<p n <1 GeV/c → ~150 ps time resolution (obtained from GEANT4 simulations) momentum resolution below 10% no stringent requirements for angular resolutions

36.  CTOF can detect neutrons as well (3% efficiency)  Central Tracker (SVT+MM): charged-particles veto limited available space (~10 cm radially) → limited efficiency → no space for light guides in the forward direction (CTOF) strong magnetic field (~5 T) → problems for light readout CND (IPNO) CTOF Central Tracker (Micromegas SPhN) CND: constraints and early R&D studies ~ 2 years of R&D (IPNO, INFN Genova et Frascati) Three kinds of magnetic-resistant photo-detectors tested Silicon PMs: too small active surface → Too few photons → too big APDs: Too noisy  t ~ 1.5 ns Micro-channel-plate PMs: Good resolution  t ~ 100 ps Loss of gain in magnetic field B ~ 1T Short life time due to radiation damage

37. Chosen design for the CND CND design: scintillator barrel 3 radial layers, 48 bars per layer coupled two-by-two by “u-turn” lightguides, light read upstream by PMTs connected to the bar via 1.5m- long light guides Plastic scintillator: compromise between neutron efficiency (~1% /cm) and fast response Photon-neutron separation → measurement of β via Time-Of-Flight TOF: time from the interaction vertex to the impact point; l: path lenght  + PID (m) → momentum z: hit position along the scintillator bar; h: radial distance of the hit from the vertex → requires radial segmentation v eff : light velocity in the scintillator bar; t left,right : time measured at the two ends of the bar→ double readout z → θ

38. nDVCS@CLAS12 & CND history Simulations and R&D for detector conception started in 2008 (summer student project…) LOI for nDVCS@CLAS12 endorsed by PAC34 (2009) Proposal for nDVCS@CLAS12 approved by PAC37 and rated (A) by PAC38 (2011) CND project presented at Conseil Scientifique of IN2P3, obtained 300 k€ (fall 2011) Partial support also received from the HP3 program of the European 7th Framework JLab review of the CND in February 2012 R&D and choice of all components finalized the same year Completion of purchase of all detector components by end of 2013 Construction started in December 2013, almost complete!

39. PMT-N PMT-D GEANT4 simulations used to evaluate:  efficiency  PID (neutron/photon separation)  momentum and angular resolutions  definition of reconstruction algorithms  background studies Measured  t and light loss due to u-turn implemented in the simulation CND: expected performances Efficiency ~ 8-9% for a threshold of 3 MeV, TOF<8 ns and p n = 0.2 - 1 GeV/c p n =0.4 GeV/c

40. Beam-time requested and obtained: 90 days (80 of production data taking at L = 10 35 cm −2 s −1 /nucleon) CLAS12 + Forward Calorimeter + Central Neutron Detector (efficiency ~10%) 85% polarized electron beam liquid deuterium target nDVCS: expected accuracy and coverage ed→ e(p)n  -t 0 1.2 BSA -0.20.2 Relative error on the yield:  N/N~0.05%-10% Estimated systematic uncertainties: 8% J u =.3, J d =.1 J u =.1, J d =.1 J u =.3, J d =.3 J u =.3, J d =-.1 Model predictions (VGG) for different values of quarks’ angular momentum  JLab PAC: high-impact experiment E12-11-003

41. Determination of the detector components Goal: optimize the time resolution ↔ neutron/photon discrimination Components chosen via comparative tests in cosmic rays on prototypes, checking light yield and σ t (and costs…) Measured σ t fed to simulation to verify PID requirements Shielding PMT WrappingScintillator Glue U-turn - 2.5 mm- R2083- Mylar Al - BC408- MBOND 200 - Triangular - 5 mm- 9954A- VM2000 - EJ200- BC600 - Semicircular - R9779- Al foil - R10533

42. Tests on the one-layer prototype One-layer prototype used to determine: Wrapping material PMT Scintillator Direct PMT Trigger detectors Indirect PMT Ind PMT Dir PMT R2083 R9779 (EJ200 scintillator, semicircular U-turn, Al foil wrapping) R2083 gives the best σ t but is very expensive R9779 σ t is ~10% worse but a factor 3 less expensive Shape of u-turn (semicircular) was chosen using a preliminary setup (without long light guides)

43. Ind PMT Dir PMT R2083 R9779 (EJ200 scintillator, semicircular U-turn, Al foil wrapping) PMTs choice: test and simulation Photons: R2083 R9779 Neutrons: R2083 R9779 Gemc simulation of the CND: measured  t used to smear timing  vs p for photons and neutrons Error bars represent 3  R9779 still meets requirements Final choice R10533: same price and time performances of R9779, higher gain – no amplifier needed Tests on three-layer prototype confirmed all choices of components + choice of CFDs and splitters R2083 gives the best σ t but is very expensive R9779 σ t is ~10% worse but a factor 3 less expensive

44. 45° =230 G @ PMTs Relative angle B-PMT~70° Final choice is 5 mm of mild-steel shielding Magnetic field values without shielding Magnetic probe Position of photocathode Mild steel µ-metal Magnetic field tests (LAL, Orsay) JLab field simulations confirm the B~0 inside our 5mm shieldings 60° Probe Shielding Magnet Also done tests checking PMT signal amplitude vs field angle

45. Detector construction: gluing U-turn: yes, it works! 144 scintillators, 144 long light guides, 72 u-turn light guides, 144 « fish-tail » guides, 144 « connection » guides Gluing started in December 2013 Polishing before gluing The gluing room at IPN Orsay Fish-tail guide

46. Detector construction: wrapping Wrapping: Al foil Black tape Measurement of the thickness to verify clearance requirements One layer is completed

47. Detector construction and testing One block of the CND: end of the light guides Connecting the guide to the shielded PMT All PMT bases are ready and mounted One block of the CND in the cosmic-rays test room

48. Direct light Indirect light U turn drop TOP layer MIDDLE layer BOTTOM layer Raw data: TDC vs ADC

49. Characterization of the blocks One week of data taking to characterize each block, right after assembly (same 6 PMTs used): Light collection Effective light velocity in scintillator+light guides Light attenuation Time resolution

50. E.S. Smith et al. NIM A 432 (1999) 265-298 Measurement of time resolution with cosmic rays (following the method described by R.T. Giles et al. NIM A 252 (1986) 41-52) S PMT A B Time resolution with cosmic rays, trigger from triple coincidence

51. Support structure and installation tests 6 stainless steel brackets 6 aluminum arches Mock up of the solenoid Mock up of the solenoid support ring

52. 21 blocks constructed: only 3 more to go! Shipping to JLab in April ‘15 We arrived at this stage thanks to (alphabetic order): Julien Bettane, Jean-Luc Cercus, Brice Garillon, Giulia Hull, Miktat Imre, Michael Josselin, Alain Maroni, Gilles Minier, Thi Nguen-Trung, Joel Pouthas, Daria Sokhan, Claude Thèneau.

53. Conclusions and outlook  GPDs are a unique tool to explore the internal landscape of the nucleon: 3D quark/gluon imaging of the nucleon orbital angular momentum carried by quarks  Their extraction from experimental data is very difficult: there are 4 GPDs for each quark flavor they depend on 3 variables, only two ( , t) experimentally accessible they appear as integrals in cross sections  Recently-developed fitting methods allow to extract CFFs from DVCS observables We need to measure several p-DVCS and n-DVCS observables over a wide phase space  Our new measurement of 3 spin observables for p-DVCS allows the extraction of Im H p and Im H p → spatial distribution of electric and axial charge in the proton  The 12-GeV-upgraded JLab will be the only facility to perform DVCS experiments in the valence region, for Q 2 up to 11 GeV: DVCS experiments on both proton (L/T polarized and unpolarized) and deuteron targets are planned for 3 of the 4 Halls at JLab@12 GeV The CND is ready to go! nDVCS@CLAS12 experiment foreseen for the year 2018 Work ongoing on PAC proposal for nDVCS with a longitudinally-polarized target (TSA and DSA): sensitivity to Im H n and Re H n → flavor separation! ~