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 The title of this talk is Beam Spin Asymmetry measurements from Deeply Virtual Meson Production with CLAS at Jefferson Lab.

? 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 DIS Elastic Correlated quark momentum and helicity distributions in transverse space - GPDs Structure functions, quark longitudinal momentum & helicity distributions Proton form factors, transverse charge & current densities ? As shown in the left hand side, from elastic scattering, we can study proton’s transverse charge and current densities. As shown in right hand side, deeply inelastic scattering we probe quark’s longitudinal momentum distributions, but has no sensitivities in transverse dimension. The recently developed formalism of Generalized Parton Distributions (GPDs) now holds promise to correlate the proton charge density related to its quark momentum distribution.

[ ] ò [ Link to DIS and Elastic Form Factors ] å ò ) ( , ~ q H D = ) , Form factors (sum rules) [ ) ( , ~ ) Dirac f.f. 1 t G x E dx H F1 q P A = ] ò å - ) Pauli f.f. F2 DIS at x =t=0 ) ( , ~ q H D = ) , ( ~ t x E H q GPDs has 4 terms, H, E, H-tilde, E-tilde. They depend three kinematic variables, x, zeta, t. The second moments of GPDs and the total angular momentum carried by quarks are related via Ji’s sum rule. The quark’s total angular momentum can be decomposed in a spin part (Delta Sigma) and an orbital momentum part (Lq). If one makes enough measurements to extract the second moment of GPDs, the sum rule will determine the orbital momentum contribution to the nucleon spin. In the forward direction, the H and H-tilde reduce to the usual parton distributions q(x) and del q(x). On the other hand, the first moments of GPDs and the elastic form factors are related the following relations. Ji’s Angular Momentum Sum Rule 1 1 1 ò [ ] J q = DS+Lq = xdx H q( x , x , ) + E q( x , x , ) 2 2 - 1 X. Ji, Phy.Rev.Lett.78,610(1997)

What can we measure? Deeply Exclusive Processes: To extract GPDs, we measure deeply exclusive processes such as deeply virtual compton scattering and deeply virtual Compton scattering. DVCS is the simplest and cleanest. More detailed talk will be given by Franck later this session. Deeply virtual meson production will be complementary to DVCS and helps to separate flavor helicity components of GPDs. 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

p0, h: Unique sensitivity to polarized GPDs 0, +  For example, pi0 and eta channels are sensitive to a polarized GPDs H-tilde. Different mesons select different combinations of quark flavors. (Difficult to isolate in DVCS) Extract unique information about GPDs, complementing DVCS.

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) To extract GPDs, we measure beam asymme

Structure Functions ep->epp0, ep->eph ALU = s+ + s- ds/dWp = sT + esL + esTTcos2f + √2e(e+1)sLTcosf + h√2e(e-1)sLT’sinf ep->epp0, ep->eph s+ - s- ALU = s+ + s- N High-luminosity Large acceptance Good Resolution p, h This picture pictures shows deeply virtual meson production of pi0 and eta channels. Here Incoming and scattered electrons produce virtual photons and we measured all final states. Beam spin asymmetry ALU will be determined by measuring the ratio of the difference and sum of two electron helicity states. To measure exclusive channels, we need high luminosity. We also need a spectrometer with large acceptance and good resolution to identify all final states.

CEBAF at Jefferson Lab CLAS 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 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

Event Reconstruction p - K+ p Particles either inbend or outbend depending the polarity of particle and toroidal field. Momentum is determined from the curvature of the track and pid is done using momentum and tof. p

Additions to CLAS Inner calorimeter (PbWO4) Superconducting solenoid magnet

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

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

Preliminary Mass Reconstruction of gg Only from new forward calorimeter

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

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

Preliminary Preliminary ALU for p0 channel Q2 xB 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

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

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)

CLAS12 Superconducting 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

Hard exclusive production of  and  with CLAS12 PR12-06-108 DVMP of  and  with CLAS12 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 Hard exclusive production of  and  with CLAS12 PR12-06-108

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

Acceptance for p0 events using FASTMC for CLAS12

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.