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Exclusive Electroproduction Analysis with Two-arm Spectrometer and Calorimeter

This analysis focuses on the exclusive electroproduction of photons using a two-arm spectrometer and calorimeter. The experiment involves a polarized electron beam, identification of DVCS events, and the measurement of various observables related to the process. The analysis also explores the validity of the one-photon exchange and tests for scaling behavior and handbag dominance.

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Exclusive Electroproduction Analysis with Two-arm Spectrometer and Calorimeter

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  1. p0 exclusive electro production Q2=2.3 GeV2, XBj=.36 P-Y BERTIN Jefferson Laboratory and Université BLAISE PASCAL- IN2P3/CNRS for the DVCS HALL A collaboration

  2. Two-arm experiment : spectrometer and calorimeter Beam energy = 5.75 GeV Beam polarization = 75% Beam current = ~ 2 and 4 μA Luminosity = 1 and 4. 1037 cm-2.s-1nucleon-1 Left HRS Scattered Electron DVCS events are identified with MX2 LH2 / LD2 target Polarized Electron Beam g • Qg>6.3° • - Čerenkov based Electromagnetic Calorimeter • Specific Scattering Chamber • Customized Electronics & Data Acquisition Exclusivity Electromagnetic Calorimeter

  3. Raw data Simulation Xcross sections p(e,e’p0)p Photon detection threshol correction p0 g g q’1 being the smallest enegy photon of (Mp+mp)2 Th= 1.00 GeV = 1.15 GeV = 1.25GeV

  4. Mp D 1232 N*1440 Q2=0 GeV2 As seen also in DIS Q2=2.0 GeV2 • At Q2=2.3 GeV2 and xbj=.36 • The continuum is significant compared to the p(e,e’p0)p • The resonancesare washed out into the continuum.

  5. (Mp+mp )2 D 1232 N*1440 (Mp+2mp )2 (Mp+3mp )2 Br=8.5%

  6. b=-2 GeV-2 From Hall B 0.03 0.02 0.01 0.1 0.2 0.3 -t GeV2

  7. in our cut ~1% p0p (Mp+mp )2 D 1232 N*1440 (Mp+2mp )2 (Mp+3mp )2 Br=8.5% Br=100% Br=85% But we detect only e’p0=> all the process interfere =>sum of the amplitudes What I am doing ?Semi inclusive DIS and Duality ??

  8. Photon’s in the inner calorimeter (99 Block from 132) Window coincidence +/- 3 ns Accidentals gg , ep0 substracted Window 105<mgg<165 MeV Foreach exclusive p0 event selected in the cut on Mx2 The physic variable are determined exactly Q2, xbj with the spectrometer t with the position in the calorimeter ( qgg ~2-3 mrd)

  9. Analyze in the formalism of on photon exchange

  10. rT 6 amplitudes complex rL rTT rTL rTL’ Reduced response functions r‘s Decomposition in CGLM amplitude: q*=p0 cm angle ~ -(t-tmin) Chew, Goldberger, Low and Nambu

  11. rTL~5x(rT+erL ) All the trivial kinematics dependence , photon flux, e, sinq,…. Taken in account in the, Monte Carlo with radiative corrections , detector resolution,…. Use the same extraction method that the used for DVCS which take in account the bin migration by a global linear fit on 10(t)x24(f) experimental bins

  12. Extrapoled at fixed: PRELIMINARY Q2=2.3 GeV2 xBj=0.36 e=0.64 c2=1.11 Corrected for real+virtual RC Corrected for efficiency Corrected for acceptance Corrected for resolution effects Systematic errors include : trigger threshold stability ( 1 to 1.2 GeV) missing mass cut ( .9 to 1.15 GeV2 ) extrapolation at fixed Q2 and fixed XBj. spectrometer, luminosity……

  13. + coupling to pn,pD with re-scattering Regge trajectory Exchange ( w, r and B1) JML x5 JML x5 JML x5 JML x5 J. M. Laget’s Prediction underestimates the cross-sections by a factor 5

  14. p0 s Next experiment 2009 will allow a full Rosenbluth separation = ??? and Factorization hold only for longitudinal amplitude

  15. sL Longitudinal part Prediction from model (VGG) based on Hand bag model and GPD VGG x 5 VGG M Vanderhaeghen P. Guichon and M Gidal

  16. p+- p+-0 p+-0 1 g 2 g But quid of two photons exchange? How to check validity of the one photon exchange ??

  17. END

  18. Photon electroproduction

  19. Analysis – Exclusivity check using Proton Array and MC Using extra recoil Proton-detector, we have checked the missing mass spectrum of double-coincidence events with those of a triple -coincidence. The missing mass spectrum using the Monte-Carlo gives the same position and width. Using the cut shown on the Fig.,the contamination from inelastic channels is estimated to be under 3%. Normalized (e,p,g) triple coincidence events Monte-Carlo (e,g)X – (e,p,g)

  20. Experimental observables linked to GPDs Experimentally, DVCS is undistinguishable with Bethe-Heitler However, we know FF at low t and BH is fully calculable Interference term allows access to linear amplitude Using a polarized beam on an unpolarized target 2 observables can be measured: At JLab energies, |TDVCS|2 was supposed small Kroll, Guichon, Diehl, Pire, …

  21. Tests of scaling 1. Twist-2 terms should dominate s and Ds 2. All coefficients have Q2 dependence which can be tested!

  22. Difference of cross-sections PRL97, 262002 (2006) Twist-2 Twist-3 Extracted Twist-3 contribution small ! Corrected for real+virtual RC Corrected for efficiency Corrected for acceptance Corrected for resolution effects Checked elastic cross-section @ ~1% New work by P. Guichon !

  23. Twist-2 Twist-3 No Q2 dependence: strong indication for scaling behavior and handbag dominance Q2 dependence and test of scaling <-t>=0.26 GeV2, <xB>=0.36

  24. large Extracted Twist-3 contribution small ! And it is impossible to disentangle DVCS2 from the interference term Total cross-section PRL97, 262002 (2006) Corrected for real+virtual RC Corrected for efficiency Corrected for acceptance Corrected for resolution effects

  25. 1. Isolate the BH-DVCS interference term from the pure DVCS2 Contribution (as a function of Q2) • Extraction of both linear and bilinear combinaton of GPDs • Additional test of DVCS scaling ( unpolarized cross section) 2. Measure 5 response functions of the deep virtual p0 channel • First test of factorization in ep epp0 using sL • If test is positive , valuable complementary ( flavor) information in GPDs We have proposed to use different beam energies (different BH) to : ( experiment approved and planned to run end 2009)

  26. This proposal: assuming DVCS2=20

  27. On the deuterium

  28. Deuterium=proton+neutron+deuteron - Hydrogen=proton = neutron + deuteron Missing mass assuming a proton target Mn2+t/2 Mn2 Helicity Asymmetry

  29. F. Cano & B. Pire calculation Eur. Phys. J. A19, 423(2004). PRELIMINARY PRELIMINARY d-DVCS Deuteron contribution compatible with zero at large -t n-DVCS PRELIMINARY PRELIMINARY VGG Code : M. Vanderhaeghen, P. Guichon and M. Guidal Neutron contribution is small and compatible with zero Results can constrain GPD models (and therefore GPD En)

  30. To summarize the Scaling test is positive VGG model misses by 30% DVCS2 must be taken into account Agree with F. Cano B. Pire model Transverse -Transverse large. Description in terms of Quarks GPD and Hadronic description ( Regge exchange) miss by a factor 5~15 the data .

  31. New data taking in 2009 using 2 beam energies: Full extraction of linear terms and bilinear terms of GPDs Full separation ofsTandsLforp0electro production At Q2=1.5, 1.9, 2.3 GeV2 We have demonstrated that : high precision DVCS measurements are doable using a high resolution spectrometer and a calorimeter Full DVCS program in Hall A (up to Q2=9 GeV2) already approved with the 12 GeV upgrade

  32. END

  33. Raw data Simulation Xcross sections p(e,e’p0)p Photon detection threshol correction p0 g g q’1 being the smallest enegy photon of p0 Invariant mass (Mp+mp)2 FWHM=21 MeV 100 150 MeV

  34. DVCS Analysis Check of the missing mass spectrum of double-coincidence events with the a triple -coicidence using a Auxilliary Proton array The missing mass spectrum using the Monte-Carlo gives the same position and width. Using the cut shown on the Fig.,the contamination from inelastic channels is estimated to be under 3%. Raw Raw –p0 Normalized (e,p,g) triple coincidence events Monte-Carlo (e,g)X – (e,p,g) (e,p,g)

  35. After : • Normalizing H2 and D2 data to the same luminosity • Adding Fermi momentum to H2 data • 2 principle sources of systematic errors : • The contamination of π0 electroproduction on the neutron (and deuteron). • The uncertainty on the relative calibration between H2 and D2 data A. Belitsky,D Muller A Kirchner Compton form factor :

  36. F. Cano & B. Pire calculation Eur. Phys. J. A19, 423(2004). PRELIMINAY Deuteron contribution compatible with zero at large -t Neutron contribution is small and compatible with zero Results can constrain GPD models (and therefore GPD En)

  37. Analysis – Exclusivity check using Proton Array and MC Using extra recoil Proton-detector, we have check the missing mass spectrum of double-coincidence events with the a triple -coicidence . The missing mass spectrum using the Monte-Carlo gives the same position and width. Using the cut shown on the Fig.,the contamination from inelastic channels is estimated to be under 3%. Normalized (e,p,g) triple coincidence events Monte-Carlo (e,g)X – (e,p,g)

  38. Mp D 1232 N*1440 Q2=0 GeV2 As seen also in DIS Q2=2.0 GeV2 • At Q2=2.3 GeV2 and xbj=.36 • The continuum is significant compared to the p(e,e’p0)p • The resonancesare washed out into the continuum.

  39. Deuterium=proton+neutron+Deuton - • After : • Normalizing H2 and D2 data to the same luminosity • Adding Fermi momentum to H2 data Hydrogen=proton = neutron + deuton • 2 principle sources of systematic errors : • The contamination of π0 electroproduction on the neutron (and deuteron). • The uncertainty on the relative calibration between H2 and D2 data Helicity Asymety Missing masse assuming a proton target Mx2+t/2 Mx2

  40. Decomposition in CGLM amplitude: Chew, Goldberger, Low and Nambu ==> CGLM q*=p0 cm angle ~ -(t-tmin)

  41. k’ q’ f q=k-k’ k

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