Deeply Virtual Compton Scattering Studies with CLAS and

Deeply Virtual Compton Scattering Studies with CLAS and CLAS 12 Latifa Elouadrhiri Jefferson Lab g CLAS 12 t Thomas Jefferson National Accelerator Facility Page 1 August 8, 2011

Generalized Parton. Distributions(GPDs) D. Mueller, X. Ji, A. Radyushkin, (1994 -1997), … M. Burkardt, A. Belitsky (2000)… The size and structure of proton. Proton form factors, transversecharge and current distributions Nobel prize 1961 - R. Hofstadter Internal constituents of the nucleon Quark longitudinal momentum and helicity distributions Nobel prize 1990 - J. Friedman, H. Kendall, R. Taylor GPDs connect the quark distribution in transverse space and longitudinal momentum Thomas Jefferson National Accelerator Facility Page 2 August 8, 2011

Deeply Virtual Compton Scattering & GPDs Deeply Virtual Compton Scattering (DVCS) hard vertices g x-x x+x t x – longitudinal quark momentum fraction 2 x – longitudinal momentum transfer –t – Fourier conjugate to transverse impact parameter GPDs depend on 3 variables, e. g. H(x, x, t). They describe the internal nucleon dynamics. Thomas Jefferson National Accelerator Facility Page 3 August 8, 2011

Link to DIS and Elastic Form Factors Form factors (sum rules) 1 [ q dx H ( x, x, t) å ò q DIS at x =t=0 H q ( x, 0, 0) = q( x) ~ H q ( x, 0, 0) = Dq( x) ò dxå[E 1 q ( x, x, t) q 1 ~q ò dx H -1 ] = F 1 ( t )Dirac f. f. ] = F 2 ( t )Pauli f. f. 1 ~ ( x, x, t ) = GA, q ( t ) , ò dx E q ( x, x, t) = GP, q ( t ) -1 ~ q ~q x H , E , H , E ( x, , t ) q q Angular Momentum Sum Rule 1 1 1 J q= - J G = xdx H q( x, x, 0) + E q(x, x, 0) ò 2 2 -1 [ ] X. Ji, Phy. Rev. Lett. 78, 610(1997) Thomas Jefferson National Accelerator Facility Page 4 August 8, 2011

Physical content of GPD E&H Nucleon matrix element of the Energy-Momentum Tensor of QCD contains 3 scalar form factor: M 2(t) : Mass distribution inside the nucleon J (t) : Angular momentum distribution d 1(t) : Forces and pressure distribution Directly measured in elastic graviton-proton scattering! GPDs are related to these form factors through 2 nd moments Thomas Jefferson National Accelerator Facility Page 5 August 8, 2011

Accessing. GPDs. Through DVCS ØGPDs are universal, they can be determined in any suitable process d 4 ~ |TDVCS + TBH|2 2 d. Q dx. Bdtd DVCS Eo = 11 Ge. V Eo = 6 Ge. V BH BH TBH: given by elastic form factors TDVCS: determined by GPDs DVCS BH-DVCS interference generates beam and target asymmetries that carry the nucleon structure information. Thomas Jefferson National Accelerator Facility Page 6 August 8, 2011 Eo = 4 Ge. V

GPDs& DVCS (at leading order: ) Cross-sectionmeasurement and beam charge asymmetry (Re. T) integrate. GPDs over x Beam or target spin asymmetry containonly. Im. T, therefore. GPDsatx = x and -x Thomas Jefferson National Accelerator Facility Page 7 August 8, 2011

Accessing GPDsthrough polarization + - D A = + + - = 2 Polarized beam, unpolarized target: ~ H Ds. LU~ sinf. Im{F 1 H+ x(F 1+F 2)H+k. F 2 E}df x = x. B/(2 -x. B) Kinematically suppressed k = t/4 M 2 Unpolarized beam, longitudinal target: ~ ~ sinf. Im{F H+x(F +F )(H+x/(1+x)E) -. . Ds. UL 1 1 2 ~ H }df Kinematically suppressed Unpolarized beam, transverse target: Ds. UT~ cosf. Im{k(F 2 H– F 1 E) + …. . }df Kinematicallysuppressed Thomas Jefferson National Accelerator Facility Page 8 August 8, 2011 H, E

First observation of DVCS/BH beam asymmetry e+pe+g. X 2001 e-p. X CLAS 4. 3 Ge. V HERMES 27 Ge. V Q 2=2. 5 Ge. V 2 -180 0 f(deg) Q 2=1. 5 Ge. V 2 +180 Early GPD analysis of CLAS/HERMES/HERA data in LO/ NLO shows results consistent with handbag mechanism and lowest order p. QCD. A. Freund (2003), A. Belitsky, et al. (2003) A(f) = asinf + bsin 2 f b/a << 1 twist-3 << twist-2 Thomas Jefferson National Accelerator Facility Page 9 August 8, 2011

First DVCS measurement with spin-aligned target Unpolarized beam, longitudinally spin-aligned target: ~ Ds. UL~ sinf. Im{F 1 H+x(F 1+F 2)H+…}df ~ AUL is dominated by Hand H S. Chen, et al. , Phys. Rev. Lett 97, 072002 (2006) CLAS fit model ~ model (H=0) CLAS preliminary ~ H=0 a = 0. 252 ± 0. 042 b = -0. 022 ± 0. 045 Consistent with leading twist Thomas Jefferson National Accelerator Facility Page 10 August 8, 2011 ~ H=0

First Dedicated DVCS Experiments at JLab Full reconstruction of all final state particles e, p, g High luminosity CLAS Hall A s. c. solenoid Pb. WO 4 Electromagnetic calorimeter Azimuthal and Q 2 dependence of Im(TDVCS) at fixed x. Test Bjorkenscaling. x, t, Q 2 - dependence of Im(TDVCS) in wide kinematics. Constrain GPD models. Thomas Jefferson National Accelerator Facility Page 11 August 8, 2011

Results of the Hall A DVCS experiment First absolute cross section measurements in the valence quark regime. Verify Bjorken scaling of cross section in limited Q 2 range. Phys. Rev. Lett. 97: 262002, 2006 Thomas Jefferson National Accelerator Facility Page 12 August 8, 2011

Results of the CLAS E 1 -DVCS experiment Beam-spin asymmetries Ds. LU~ sinf{F 1 H+ x(F 1+F 2)H+k. F 2 E}df Phys. Rev. Lett. 100: 162002, 2008 Thomas Jefferson National Accelerator Facility Page 13 August 8, 2011

GPD extraction from truncated expansion (H only) ~ Truncation allows analysis of x and t dependences of H, but neglecting H is problematic. H. Moutarde, Phys. Rev. D 79: 094021, 2009 Thomas Jefferson National Accelerator Facility Page 14 August 8, 2011

Extractions of GPDs from full expansion A nearly model-independent GPD analysis in leading twist has become possible due the availability of beam-spin and target-spin asymmetry results at 3 values of t and fixed x. M. Guidal, Phys. Rev. Lett. B 689: 156 -162, 2010 • HIm drops with t similar to VGG model but has smaller magnitude • H-tilde tends to be larger than model prediction Thomas Jefferson National Accelerator Facility Page 15 August 8, 2011

CLAS 12 - DVCS – Dedicated longitudinally polarized target experiment To extend GPD extraction from polarization data improvement of statistics and expansion of kinematical coverage is needed. AUL Preliminary data from eg 1 -dvcs experiment have 10 times previous statistics Pioneering results from data mining Thomas Jefferson National Accelerator Facility Page 16 August 8, 2011

CLAS 12 - DVCS with transversely polarized target Transverse asymmetries AUT and ALT are sensitive to GPD E. GPDs E and H enter in the angular momentum sum rule. A precise measurement of AUT will help resolve the proton spin puzzle. Thomas Jefferson National Accelerator Facility Page 17 August 8, 2011

JLab Upgrade to 12 Ge. V At 12 Ge. V, CEBAF is an ideal laboratory for GPD studies in the valence quark regime. Add new hall CHL-2 Enhance equipment in existing halls Thomas Jefferson National Accelerator Facility Page 18 August 8, 2011

Hall B 12 Ge. V upgrade overview from CLAS to CLAS 12 CLAS will be replaced with CLAS 12 Present Day CLAS 12 is CLAS 12 designed to operate with order of magnitude higher luminosity. CLAS 12 designed to accommodate CLAS 12 polarized solid state targets NH 3, ND 3 and HD. Thomas Jefferson National Accelerator Facility Page 19 August 8, 2011

Kinematic reach of the 12 Ge. V Upgrade Exclusive Processes 27 200 Ge V H 1, ZEUS COMPASS HERMES 11 Ge. VJLab @ 12 V e G Study of high x. B domain requires high luminosity 0. 7 Thomas Jefferson National Accelerator Facility Page 20 August 8, 2011

CLAS 12 DVCS/BH- Beam Asymmetry at 12 Ge. V ALU With large acceptance, measure large Q 2, x. B, t ranges simultaneously. A(Q 2, x. B, t) Ds(Q 2, x. B, t) Thomas Jefferson National Accelerator Facility Page 21 August 8, 2011

CLAS 12 - DVCS/BH- Beam Asymmetry Q 2=5. 5 Ge. V 2 x. B = 0. 35 -t = 0. 25 Ge. V 2 Luminosity = 720 fb-1 Thomas Jefferson National Accelerator Facility Page 22 August 8, 2011

CLAS 12 - DVCS/BH Beam Asymmetry epepg E = 11 Ge. V Ds. LU~sin Im{F 1 H+. . }d Selected Kinematics L = 1 x 1035 T = 2000 hrs ΔQ 2= 1 Ge. V 2 Δx= 0. 05 Thomas Jefferson National Accelerator Facility Page 23 August 8, 2011

CLAS 12 - DVCS/BH Longitudinal Target Asymmetry L = 2 x 1035 cm-2 s-1 T = 1000 hrs DQ 2 = 1 Ge. V 2 Dx = 0. 05 E = 11 Ge. V epepg ~ Ds~sin Im{F 1 H+x(F 1+F 2)H. . . }d Thomas Jefferson National Accelerator Facility Page 24 August 8, 2011

CLAS 12 - DVCS/BH Transverse Target Asymmetry ep epg E = 11 Ge. V Sample kinematics Q 2=2. 2 Ge. V 2, x. B = 0. 25, -t = 0. 5 Ge. V 2 Transverse polarized target Ds ~ cos Im{k 1(F 2 H– F 1 E) +…}d AUTx Target polarization in the scattering plane AUTy Target polarization perpendicular to the scattering plane Asymmetries highly sensitive to the u-quark contributions to the proton spin. Thomas Jefferson National Accelerator Facility Page 25 August 8, 2011

CLAS 12– DVCS/BH beam spin asymmetry on neutrons This program requires adding a Central Neutron Detector (CDN) to the CLAS 12 base equipment. DVCS on neutrons is sensitive to GPD En and the d -quark content of the nucleon spin. CND European Initiative led by: Orsay University Thomas Jefferson National Accelerator Facility Page 26 August 8, 2011

Forward Detector: - TORUS magnet - Forward SVT tracker - HT Cherenkov Counter - Drift chamber system - LT Cherenkov Counter - Forward To. F System -Preshower calorimeter - E. M. calorimeter Central Detector: -SOLENOID magnet - Barrel Silicon Tracker - Central Time-of-Flight -Polarized target (NSF) Proposed upgrades: -Micromegas (CD) - Neutron detector (CD) - RICH detector (FD) - Forward Tagger (FD) CLAS 12

CLAS 12 in construction - examples 1. Super Conducting Magnets – Conductor ready – Torus Coil case being prepared for coil winding 2. Silicon Vertex Tracker – Testing of the readout chip – Sensor testing 3. Forward Time of Flight – PMT testing at USC – Scintillator testing at USC Thomas Jefferson National Accelerator Facility Page 28 August 8, 2011

CLAS 12 Under Construction - Examples 1. Drift Chambers – Wire stringing of RI at JLab – Wire stringing of RII at ODU 2. High Threshold Cerenkov – Mirror fabrication in the JLab Clean room – Mirror trimming at JLab Machine shop 3. Pre-Shower Calorimeter (MRI/NSF) – Module assembly – Fibers QA Thomas Jefferson National Accelerator Facility Page 29 August 8, 2011

12 Ge. V Upgrade Project Schedule Two short parasitic installation periods in FY 10 6 -month installation May-Oct 2011 12 -month installation May 2012 -May 2013 Hall A commissioning start October 2013 Hall D commissioning start April 2014 Halls B & C commissioning start October 2014 Project Completion June 2015 Thomas Jefferson National Accelerator Facility Page 30 August 8, 2011

CLAS Collaboration. Collaborai Collaboration Arizona State University, Tempe, AZ University Bari, Italy University of California, Los Angeles, CA California State University, Dominguez Hills, CA Carnegie Mellon University, Pittsburgh, PA Catholic University of America CEA-Saclay, Gif-sur-Yvette, France Christopher Newport University, Newport News, VA University of Connecticut, Storrs, CT Edinburgh University, Edinburgh, UK University Ferrara, Italy Florida International University, Miami, FL Florida State University, Tallahassee, FL George Washington University, Washington, DC University of Glasgow, UK Universityof Grenoble, France Idaho State University, Pocatello, Idaho INFN, Laboratori. Nazionalidi. Frascati, Italy INFN, Sezionedi. Genova, Italy Institut de Physique Nucléaire, Orsay, France ITEP, Moscow, Russia James Madison University, Harrisonburg, VA Kyungpook University, Daegu, South Korea University of Massachusetts, Amherst, MA Moscow State University, Moscow, Russia University of New Hampshire, Durham, NH Norfolk State University, Norfolk, VA Ohio University, Athens, OH IN 2 P 3 - JLab Meeting Old Dominion University, Norfolk, VA Rensselaer Polytechnic Institute, Troy, NY Rice University, Houston, TX University of Richmond, VA University of Rome Tor Vergata, Italy University of South Carolina, Columbia, SC Thomas Jefferson National Accelerator Facility, Newport News, VA Union College, Schenectady, NY University Santa Maria, Valparaiso, Chile Virginia Polytechnic Institute, Blacksburg, VA University of Virginia, Charlottesville, VA College of William and Mary, Williamsburg, VA Yerevan Institute of Physics, Yerevan, Armenia Brazil, Germany, Morocco and Ukraine, , have individuals or groups involved with CLAS, but with no formal collaboration at this stage.

Summary —The discovery of Generalized Parton Distributions has opened up a new and exciting avenue of hadron physics that needs exploration in dedicated experiments. — Moderate to high energy, high luminosity, and large acceptance spectrometers are needed to measure GPDs in deeply virtual exclusive processes. — The JLab 12 Ge. V Upgrade provides the tools to do this well and explore the nucleon at a much deeper level. Thomas Jefferson National Accelerator Facility Page 32 August 8, 2011

CLAS 12 Institutions Armenia: - Yerevan Physics Institute, Yerevan, Armenia Chile: - University Santa Maria, Valparaiso France: - Grenoble University, IN 2 P 3, Grenoble - Orsay University, IN 2 P 3, Paris - CEA Saclay, IRFU, Paris Italy: - INFN - LNF, Roma - INFN - Genova, Genova - INFN - University Bari, Bari - INFN - University Ferrara, Ferrara - INFN - ISS, Roma - INFN - Roma II, Tor Vergata, Roma Republic of Korea: - Kyungpook National University, Daegu, Korea Russian Federation: - MSU, Skobeltsin Institute for Nuclear Physics, Moscow - MSU, Institute for High Energy Physics, Si. Lab, Moscow - Institute for Theoretical and Experimental Physics, Moscow United Kingdom: - Edinburgh University, Edinburgh, Scotland - Glasgow University, Glasgow, Scotland United States of America: - Argonne National Laboratory, Argonne, Il - California State University, Dominguez Hills, CA - Catholic University of America, Washington, DC - College of William and Mary, Williamsburg, VA - Christopher Newport University, Newport News, VA - Fairfield University, Fairfield, CT - Florida International University, Miami, FL - Hampton University, Hampton, VA - Idaho State University, Pocatella, ID - James Madison University, Harrisionburg, VA - Norfolk State University, Norfolk, VA - Ohio University, Athens, OH - Old Dominion University, Norfolk, VA - Rensselaer Polytechnic Institute, Troy, NY - Temple University, Philadelphia, PA - Jefferson Lab, Newport News, VA - University of Connecticut, Storrs, CT - University of New Hampshire, Durham, NH - University, of Richmond, VA - University of South Carolina, Columbia, SC - University of Virginia, Charlottesville, VA 38 Institutions, November 2010 Thomas Jefferson National Accelerator Facility Page 33 August 8, 2011