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B. Zhao 1 , R. De Masi 2 , K. Joo 1 , V. Kubarovsky 3 , P. Stoler 3 , M. Ungaro 1

Beam Spin Asymmetry Measurements from Deeply Virtual Meson Production. B. Zhao 1 , R. De Masi 2 , K. Joo 1 , V. Kubarovsky 3 , P. Stoler 3 , M. Ungaro 1 and the CLAS Collaboration 1. University of Connecticut, USA, 2. Saclay-CEA, France 3. RPI, USA. Introduction Experiment

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B. Zhao 1 , R. De Masi 2 , K. Joo 1 , V. Kubarovsky 3 , P. Stoler 3 , M. Ungaro 1

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  1. Beam Spin Asymmetry Measurements from Deeply Virtual Meson Production B. Zhao1, R. De Masi2, K. Joo1, V. Kubarovsky3, P. Stoler3, M. Ungaro1 and the CLAS Collaboration 1. University of Connecticut, USA, 2. Saclay-CEA, France 3. RPI, USA Introduction Experiment Preliminary Results DVMP with CLAS12 Summary

  2. How is the proton charge density related to its quark momentum distribution? D. Mueller, X. Ji, A. Radyushkin, A. Belitsky, … M. Burkardt, … Interpretation in impact parameter space ? Structure functions, quark longitudinal momentum & helicity distributions Proton form factors, transverse charge & current densities Correlated quark momentum and helicity distributions in transverse space - GPDs DIS Elastic

  3. Form factors (sum rules) ] x [ 1 DIS at =t=0 å ò x = q dx H ( x , , t ) F1 ( t )Dirac f.f. q = q H ( x , 0 , 0 ) q ( x ) ] [ 1 å ò x = q dx E ( x , , t ) F2 ( t )Pauli f.f. ~ = D q ( x , 0 , 0 ) q ( x ) H q 1 1 ~ ~ ò ò x = x = q q dx H ( x , , t ) G ( t ) , dx E ( x , , t ) G ( t ) , , A q P q ~ ~ - - 1 1 x q q q q H , E , H , E ( x , , t ) Link to DIS and Elastic Form Factors Ji’s Angular Momentum Sum Rule 1 1 1 [ ] ò = DS+Lq = x + x J q xdx H q( x , , 0 ) E q( x , , 0 ) 2 2 - 1 X. Ji, Phy.Rev.Lett.78,610(1997)

  4. Deeply Exclusive Processes: What can we measure? L Deeply Virtual (Exclusive) Meson Production (DVMP): helps to separate flavor helicity components of GPDs Deeply Virtual Compton Scattering (DVCS): Clean (Talk by F. Sabatie) , but limited flavor separation

  5.  0, + p0, h: Unique sensitivity to polarized GPDs • Different mesons select different combinations of quark flavors. (Difficult to isolate in DVCS) • Extract unique information about GPDs, complementing DVCS.

  6. How to extract GPDs • Beam spin asymmetries, longitudinal and transverse target spin asymmetries for DVCS and DVMP. • (get imaginary part of the amplitudes) • Absolute cross section measurements. • (get real part of amplitudes) • Separations of different GPDs. • (E and H and H-tilde separations)

  7. N ds/dWp = sT + esL + esTTcos2f + √2e(e+1)sLTcosf + h√2e(e-1)sLT’sinf Structure Functions ep->epp0, ep->eph • s+ - s- • ALU = • s+ + s- • High-luminosity • Large acceptance • Good Resolution p, h

  8. Emax ~ 6 GeV Imax ~ 200 mA Duty Factor ~ 100% sE/E ~ 2.5 10-5 Beam P ~ 80% Eg(tagged) ~ 0.8- 5.5 GeV CLAS CEBAF at Jefferson Lab

  9. CEBAF Large Acceptance Spectrometer (CLAS) • Six identical sectors • 5 T toroidal B-field • Δθ=15-140 degrees • Δφ= 0-50 degrees • Δp/p = 10-2-10-3

  10. Event Reconstruction K+ p - p

  11. Inner calorimeter (PbWO4) Superconducting solenoid magnet Additions to CLAS

  12. Need to reconstruct 0 and  from 2 decays New Forward Calorimeter. (E06-003 DVCS)

  13. Inner Calorimeter (IC) photon detection at small angles (4-15; 1-5 GeV) Front view from the target 424 PBWO4 crystals, 16 mm long, pointing geometry, ~ 1.4 degree/crystal, APD readout

  14. Mass Reconstruction ofgg Preliminary Only from new forward calorimeter

  15. epepp0 event selection MM2 of epepX Data Analysis by R. De Masi Preliminary

  16. Integrated ALU for p0 channel Data Analysis by R. De Masi ALU Preliminary f • Integrated for all Q2 and x • Fit to a*sinf

  17. ALU for p0 channel Q2 4.5 Data Analysis by R. De Masi 3.5 3.0 Preliminary Preliminary 2.5 2.0 1.5 1.0 xB 0.10 0.15 0.20 0.30 0.40 0.55

  18. epeph event selection MM2 of epepX Data Analysis by B. Zhao Preliminary

  19. Integrated ALU for h channel Data Analysis by B. Zhao ALU Preliminary f • Integrated for all Q2 and x • Fit to a*sinf/(1+b*cosf + c*cos2f)

  20. CLAS12 Forward Calorimeter Preshower Calorimeter Forward Cerenkov (LTCC) Forward Time-of-Flight Detectors Forward Drift Chambers Superconducting Torus Magnet Inner Cerenkov (HTCC) Central Detector Beamline Instrumentation Inner Calorimeter * Reused detectors from CLAS

  21. DVMP of  and  with CLAS12 Hard exclusive production of  and  with CLAS12PR12-06-108 PR12-06-108 K. Joo, M.Ungaro University of Connecticut, USA V. Kubarovsky, P.Stoler Department of Physics, Rensselaer, USA • High Q2, Low t • High Q2, High t

  22. Acceptance of Q2 vs xB with CLAS12 • Increase in luminosity by a factor ~5 • Larger acceptance

  23. Acceptance for p0 events using FASTMC for CLAS12

  24. Summary • An extensive program is underway to study GPDs by measuring exclusive channels. • Measured large ALU in ep ->epp0, ep->eph. • The second half of the run (e1-dvcs) is scheduled in 2008. • The new experiment (E05-114) using polarized proton target is also scheduled in 2008. • Deeply virtual meson production (DVMP) measurements with CLAS12 as well as DVCS is approved and will be one of flagship experiments with the JLAB 12 GeV upgraded program.

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