DVCS at JLab Como 11062013 JLab published 6
DVCS at JLab Como, 11/06/2013
JLab published 6 Ge. V results JLab 6 Ge. V analysis in progress JLab 12 Ge. V program
JLab published 6 Ge. V results JLab 6 Ge. V analysis in progress JLab 12 Ge. V program
JLab Duty cycle 100% Emax 6 Ge. V Pmax 80%
DVCS@JLab HALL A ep ep on at Sc Polarized Electron Beam Charged Particle Tagger ed r e t tr lec E Left HRS LH 2 / LD 2 target Electromagnetic Calorimeter N Nucleon Detector
DVCS : exclusivity HRS+calorimeter ep -> ep 0 0 -> ep -> ep 0 N … HRS+calorimeter + proton array H(e, e’ )X - H(e, e’ ’)X' H(e, e’ p) H(e, e’ )N • Good resolution : no need for the proton array • Remaining contamination 1. 7%
DVCS GPDs Bethe-Heitler
Using the (first version) of the BKM formalism, one can extract a combination of the “Im” CFFs and their Q 2 -dependence
DVCS@JLab e’ HALL B g epa epg p 420 Pb. WO 4 crystals : ~10 x 10 mm 2, l=160 mm Read-out : APDs +preamps JLab/ITEP/ Orsay/Saclay collaboration
CLAS DVCS AUL x~0. 16, -t~0. 31, Q 2~1. 82 CLAS DVCS ALU
Given the well-established LT-LO DVCS+BH amplitude DVCS Bethe-Heitler GPDs Can one recover the 8 CFFs from the DVCS observables?
In general, 8 GPD quantities accessible (Compton Form Factors) with
Given the well-established LT-LO DVCS+BH amplitude DVCS Bethe-Heitler GPDs Can one recover the 8 CFFs from the DVCS observables? Obs= Amp(DVCS+BH) CFFs Two (quasi-) model-independent approaches to extract, at fixed x. B, t and Q 2 ( « local » fitting), the CFFs from the DVCS observables (leading-twist formalism)
1/ «Brute force » fitting c 2 minimization (with MINUIT + MINOS) of the available DVCS observables at a given x. B, t and Q 2 point by varying the CFFs within a limited hyper-space (e. g. 5 x. VGG) 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 c 2) for these latter CFFs. The contribution of the non-converging CFF entering in the error bar of the converging ones. 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
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/Q 2 terms, . . . ), the system can be linear (practical for the error propagation) ~-k. F 2 E}df Ds. LU ~ sinf Im{F 1 H + x(F 1+F 2)H ~ 1+F 2)(H + x. B/2 E) –xk. F 2 E+…}df ~ Ds. UL ~ sinf. Im{F 1 H+x(F K. Kumericki, D. Mueller, M. Murray, ar. Xiv: 1301. 1230 hep-ph, ar. Xiv: 1302. 7308 hepph
unpol. sec. eff. + beam pol. sec. eff. c 2 minimization
unpol. sec. eff. beam spin asym. + + beam pol. sec. eff. long. pol. tar. asym c 2 minimization
unpol. sec. eff. beam spin asym. beam charge asym. + + + beam pol. sec. eff. long. pol. tar. asym beam spin asym + c 2 minimization linearization …
unpol. sec. eff. beam spin asym. beam charge asym. + + + beam pol. sec. eff. long. pol. tar. asym beam spin asym + c 2 minimization linearization Moutarde 10 model/fit VGG model KM 10 model/fit …
Current extractions of CFFs from DVCS c 2 minimization linearization VGG model KM 10 model/fit Moutarde 10 model/fit HIm: the t-slope reflects the size of the probed object (Fourier transf. ) The sea quarks (low x) spread to the periphery of the nucleon while the valence quarks (large x) remain in the center
Nucleon tomography
c 2 minimization VGG model linearization ~ The axial charge (~Him) appears to be more « concentrated » than the electromagnetic charge (~Him)
JLab published 6 Ge. V results JLab 6 Ge. V analysis in progress JLab 12 Ge. V program
Several DVCS analysis under way with JLab 6 Ge. V data: CLAS : « e 1 -dvcs 1» (2005) and « e 1 dvcs 2 » (2008) Analysis of the (pol. and unpol. ) DVCS cross-sections
Several DVCS analysis under way with JLab 6 Ge. V data: CLAS : « e 1 -dvcs 1» (2005) and « e 1 dvcs 2 » (2008) Analysis of the (pol. and unpol. ) DVCS cross-sections Four main analyzers: H. -S. Jo, F. -X. Girod, B. Guegan, N. Saylor from whom I borrowed a lot of material/slides and whom contribution is greatly acknowledged
Several DVCS analysis under way with JLab 6 Ge. V data: CLAS : « e 1 -dvcs 1» (2005) and « e 1 dvcs 2 » (2008) Analysis of the (pol. and unpol. ) DVCS cross-sections Four main analyzers: H. -S. Jo, F. -X. Girod, B. Guegan, N. Saylor from whom I borrowed a lot of material/slides and whom contribution is greatly acknowledged « eg 1 dvcs » (2008) Analysis of the long. pol. target asymmetries
Several DVCS analysis under way with JLab 6 Ge. V data: CLAS : « e 1 -dvcs 1» (2005) and « e 1 dvcs 2 » (2008) Analysis of the (pol. and unpol. ) DVCS cross-sections Four main analyzers: H. -S. Jo, F. -X. Girod, B. Guegan, N. Saylor from whom I borrowed a lot of material/slides and whom contribution is greatly acknowledged « eg 1 dvcs » (2008) Analysis of the long. pol. target asymmetries Hall A : Rosenbluth separation of the DVCS cross-section (separation of DVCS and BH contributions)
Samples of CLAS « e 1 -dvcs 2 » analysis 5. 88 Ge. V beam energy
Samples of CLAS « e 1 -dvcs 2 » analysis 5. 88 Ge. V beam energy
Data MC Ratio Acceptances
Elastic cross section from « e 1 -dvcs 2 »
Thanks to I. Akushevich
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
JLab published 6 Ge. V results JLab 6 Ge. V analysis in progress JLab 12 Ge. V program
JLab Upgrade to 12 Ge. V Add new hall CHL-2 Enhance equipment in existing halls
GPD program at JLab 12 Ge. V (Halls A, B and C) DVCS beam asymmetry ALU on proton&neutron DVCS long. target spin asymmetry AUL on proton&neutron DVCS long. target spin asymmetry AUT on proton&neutron DVCS unpolarized cross sections on proton DVMP: pseudoscalar mesons DVMP: vector mesons
Simulations Hall A@12 Ge. V Precision study of the Q 2 scaling law Validation of the GPD formalism, Estimation of the higher twist corrections 90 days of DVCS L~1038 cm-2 s-1
Similar studies for AUL, AUT, ALL, ALT, … as well E 12 -06 -119
Projections for CLAS 12 for HIm
Corresponding spatial densities
DVCS BSA: sensitivity to Ju, d DVCS on the proton Ju=. 3, Jd=. 1 Ju=. 8, Jd=. 1 Ju=. 5, Jd=. 1 Ju=. 3, Jd=. 8 Ju=. 3, Jd=-. 5 f= 60° x. B = 0. 2 Q 2 = 2 Ge. V 2 t = -0. 2 Ge. V 2 Ee = 11 Ge. V
DVCS BSA: sensitivity to Ju, Jd DVCS on the neutron Ju=. 3, Jd=. 1 Ju=. 8, Jd=. 1 Ju=. 5, Jd=. 1 Ju=. 3, Jd=. 8 Ju=. 3, Jd=-. 5 n-DVCS BSA is: • very sensitive to Ju, Jd • can be as strong as for the proton According to the kinematics and Ju, Jd Ee = 11 Ge. V f= 60° x. B = 0. 17 Q 2 = 2 Ge. V 2 t = -0. 4 Ge. V 2
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