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DVCS at JLab

DVCS at JLab. Como, 11/06/2013. JLab published 6 GeV results. JLab 6GeV analysis in progress. JLab 12 GeV program. JLab published 6 GeV results. JLab 6GeV analysis in progress. JLab 12 GeV program. JLab. Duty cycle  100% E max  6 GeV P max  80%. ep ep g.

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DVCS at JLab

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  1. DVCS at JLab Como, 11/06/2013

  2. JLab published 6 GeV results JLab 6GeV analysis in progress JLab 12 GeV program

  3. JLab published 6 GeV results JLab 6GeV analysis in progress JLab 12 GeV program

  4. JLab Duty cycle 100% Emax6 GeVPmax80%

  5. ep epg DVCS@JLab HALL A Scattered Electron Left HRS LH2 / LD2 target Polarized Electron Beam g Charged Particle Tagger Electromagnetic Calorimeter N NucleonDetector

  6. H(e,e’)X DVCS : exclusivity HRS+calorimeter ep -> ep ep -> ep0 0-> ep -> ep0 ep -> ep0N … H(e,e’)X - H(e,e’’)X' H(e,e’p) HRS+calorimeter + proton array H(e,e’)N • Good resolution : no need for the proton array • Remaining contamination 1.7%

  7. DVCS Bethe-Heitler GPDs

  8. Using the (first version) of the BKM formalism, one can extract a combination of the “Im” CFFs and their Q2-dependence

  9. g DVCS@JLab e’ HALL B epaepg p JLab/ITEP/ Orsay/Saclay collaboration 420 PbWO4 crystals : ~10x10 mm2, l=160 mm Read-out : APDs +preamps

  10. CLAS DVCS AUL x~0.16,-t~0.31,Q2~1.82 CLAS DVCS ALU

  11. Given the well-established LT-LO DVCS+BH amplitude DVCS Bethe-Heitler GPDs Can one recover the 8CFFs from the DVCS observables?

  12. In general, 8GPD quantities accessible (Compton Form Factors) with

  13. Given the well-established LT-LO DVCS+BH amplitude Obs= Amp(DVCS+BH) CFFs DVCS Bethe-Heitler GPDs Can one recover the 8CFFsfrom the DVCS observables? Two (quasi-) model-independentapproaches to extract, atfixedxB, t and Q2(« local » fitting), the CFFsfrom the DVCS observables (leading-twist formalism)

  14. M.G. EPJA 37 (2008) 319 M.G. & H. Moutarde, EPJA 42 (2009) 71 M.G. PLB 689 (2010) 156 M.G. PLB 693 (2010) 17 1/ «Brute force » fitting  c2 minimization (with MINUIT + MINOS) of the available DVCS observables at a given xB, t and Q2 point by varying the CFFs within a limited hyper-space (e.g. 5xVGG) The problem can be (largely) undersconstrained: JLab Hall A: pol. and unpol. X-sections JLab CLAS: BSA + TSA 2 constraints and 8 parameters ! However, as some observables are largely dominated by a single or a few CFFs, there is a convergence (i.e. a well-defined minimum c2) for these latter CFFs. The contribution of the non-converging CFF entering in the error bar of the converging ones.

  15. 2/ Mapping and linearization If enough observables measured, one has a system of 8 equations with 8 unknowns Given reasonnable approximations (leading-twist dominance, neglect of some 1/Q2 terms,...), the system can be linear (practical for the error propagation) ~ DsLU ~ sinfIm{F1H+ x(F1+F2)H-kF2E}df ~ ~ DsUL ~ sinfIm{F1H+x(F1+F2)(H+ xB/2E) –xkF2E+…}df K. Kumericki, D. Mueller, M. Murray, arXiv:1301.1230 hep-ph, arXiv:1302.7308 hep-ph

  16. unpol.sec.eff. + beam pol.sec.eff. c2minimization

  17. unpol.sec.eff. + beam pol.sec.eff. beam spin asym. + long. pol. tar. asym c2minimization

  18. unpol.sec.eff. + beam pol.sec.eff. beam spin asym. + long. pol. tar. asym beam charge asym. + beam spin asym + … c2minimization linearization

  19. unpol.sec.eff. + beam pol.sec.eff. beam spin asym. + long. pol. tar. asym beam charge asym. + beam spin asym + … c2minimization linearization Moutarde 10 model/fit VGG model KM10 model/fit

  20. Current extractions of CFFsfrom DVCS c2minimization VGG model linearization KM10 model/fit Moutarde 10 model/fit HIm:the t-slopereflects the size of the probedobject(Fourier transf.) The seaquarks(low x) spread to the periphery of the nucleonwhile the valence quarks (large x) remain in the center

  21. Nucleon tomography

  22. c2minimization VGG model linearization ~ The axial charge (~Him) appears to be more « concentrated » than the electromagnetic charge (~Him)

  23. JLab published 6 GeV results JLab 6GeV analysis in progress JLab 12 GeV program

  24. Several DVCS analysisunderwaywithJLab 6 GeV data: CLAS : « e1-dvcs 1» (2005) and « e1dvcs2 » (2008) Analysis of the (pol. and unpol.) DVCS cross-sections

  25. Several DVCS analysisunderwaywithJLab 6 GeV data: CLAS : « e1-dvcs 1» (2005) and « e1dvcs2 » (2008) Analysis of the (pol. and unpol.) DVCS cross-sections Four main analyzers: H.-S. Jo, F.-X. Girod, B. Guegan, N. Saylor fromwhom I borrowed a lot of material/slides and whom contribution isgreatlyacknowledged

  26. Several DVCS analysisunderwaywithJLab 6 GeV data: CLAS : « e1-dvcs 1» (2005) and « e1dvcs2 » (2008) Analysis of the (pol. and unpol.) DVCS cross-sections Four main analyzers: H.-S. Jo, F.-X. Girod, B. Guegan, N. Saylor fromwhom I borrowed a lot of material/slides and whom contribution isgreatlyacknowledged « eg1dvcs » (2008) Analysis of the long.pol. targetasymmetries

  27. Several DVCS analysisunderwaywithJLab 6 GeV data: CLAS : « e1-dvcs 1» (2005) and « e1dvcs2 » (2008) Analysis of the (pol. and unpol.) DVCS cross-sections Four main analyzers: H.-S. Jo, F.-X. Girod, B. Guegan, N. Saylor fromwhom I borrowed a lot of material/slides and whom contribution isgreatlyacknowledged « eg1dvcs » (2008) Analysis of the long.pol. targetasymmetries Hall A : Rosenbluthseparation of the DVCS cross-section (separation of DVCS and BH contributions)

  28. Samples of CLAS « e1-dvcs2 » analysis 5.88 GeVbeamenergy

  29. Samples of CLAS « e1-dvcs2 » analysis 5.88 GeVbeamenergy

  30. Data MC Ratio Acceptances

  31. Elastic cross section from « e1-dvcs2 »

  32. Thanks to I. Akushevich

  33. From CFFs to spatial densities How to go from momentum coordinates (t) to space-time coordinates (b) ? (with error propagation) Burkardt (2000) Applying a (model-dependent) “deskewing” factor: and,in a first approach, neglecting the sea contribution

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