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DVCS at JLab Como, 11/06/2013

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

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

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JLab Duty cycle 100% E max 6 GeV P max 80%

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LH 2 / LD 2 target Polarized Electron Beam Scattered Electron N Nucleon Detector Left HRS Charged Particle Tagger Electromagnetic Calorimeter HALL A DVCS@JLab ep ep

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

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DVCSBethe-Heitler GPDs

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Using the (first version) of the BKM formalism, one can extract a combination of the “Im” CFFs and their Q 2 -dependence

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e’ p ep ep 420 PbWO 4 crystals : ~10x10 mm 2, l=160 mm Read-out : APDs +preamps JLab/ITEP/ Orsay/Saclay collaboration HALL B DVCS@JLab

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CLAS DVCS A LU ~0.16,-t~0.31,Q 2 ~1.82 CLAS DVCS A UL

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

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

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Given the well-established LT-LO DVCS+BH amplitude DVCSBethe-Heitler GPDs Obs= Amp(DVCS+BH) CFFs Can one recover the 8 CFFs from the DVCS observables? 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)

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1/ «Brute force » fitting 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. 5xVGG) M.G. EPJA 37 (2008) 319M.G. & H. Moutarde, EPJA 42 (2009) 71 M.G. PLB 689 (2010) 156M.G. PLB 693 (2010) 17 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 2 ) for these latter CFFs. The contribution of the non-converging CFF entering in the error bar of the converging ones.

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UL ~ sin Im{F 1 H + (F 1 +F 2 )( H + x B /2 E ) – kF 2 E+… }d ~ ~ LU ~ sin Im{F 1 H + (F 1 +F 2 ) H -kF 2 E }d ~ 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. Kumericki, D. Mueller, M. Murray, arXiv:1301.1230 hep-ph, arXiv:1302.7308 hep-ph

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unpol.sec.eff. + beam pol.sec.eff. 2 minimization

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unpol.sec.eff. + beam pol.sec.eff. 2 minimization beam spin asym. + long. pol. tar. asym

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unpol.sec.eff. + beam pol.sec.eff. 2 minimization beam spin asym. + long. pol. tar. asym beam charge asym. + beam spin asym + … linearization

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unpol.sec.eff. + beam pol.sec.eff. 2 minimization beam spin asym. + long. pol. tar. asym beam charge asym. + beam spin asym + … linearization VGG model KM10 model/fit Moutarde 10 model/fit

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Current extractions of CFFs from DVCS The sea quarks (low x) spread to the periphery of the nucleon while the valence quarks (large x) remain in the center H Im :the t-slope reflects the size of the probed object (Fourier transf.) 2 minimization linearization VGG model Moutarde 10 model/fit KM10 model/fit

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Nucleon tomography

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The axial charge (~H im ) appears to be more « concentrated » than the electromagnetic charge (~H im ) ~ 2 minimization linearization VGG model

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

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CLAS : « e1-dvcs 1» (2005) and « e1dvcs2 » (2008) Analysis of the (pol. and unpol.) DVCS cross-sections Several DVCS analysis under way with JLab 6 GeV data:

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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 from whom I borrowed a lot of material/slides and whom contribution is greatly acknowledged Several DVCS analysis under way with JLab 6 GeV data:

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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 from whom I borrowed a lot of material/slides and whom contribution is greatly acknowledged « eg1dvcs » (2008) Analysis of the long.pol. target asymmetries Several DVCS analysis under way with JLab 6 GeV data:

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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 from whom I borrowed a lot of material/slides and whom contribution is greatly acknowledged « eg1dvcs » (2008) Analysis of the long.pol. target asymmetries Several DVCS analysis under way with JLab 6 GeV data: Hall A : Rosenbluth separation of the DVCS cross-section (separation of DVCS and BH contributions)

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Samples of CLAS « e1-dvcs2 » analysis 5.88 GeV beam energy

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Samples of CLAS « e1-dvcs2 » analysis 5.88 GeV beam energy

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Data MC Ratio Acceptances

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Elastic cross section from « e1-dvcs2 »

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Thanks to I. Akushevich

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

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

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JLab Upgrade to 12 GeVCHL-2 Enhance equipment in existing halls Add new hall

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GPD program at JLab 12 GeV (Halls A, B and C) (Halls A, B and C) DVCS beam asymmetry A LU on proton&neutron DVCS long. target spin asymmetry A UL on proton&neutron DVCS long. target spin asymmetry A UT on proton&neutron DVCS unpolarized cross sections on proton DVMP: pseudoscalar mesons DVMP: vector mesons

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Simulations Hall A@12GeV Precision study of the Q 2 scaling law Validation of the GPD formalism, Estimation of the higher twist corrections 90 days of DVCS L~10 38 cm -2 s -1

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E12-06-119 Similar studies for A UL,A UT,A LL,A LT,… as well

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Projections for CLAS12 for H Im

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Corresponding spatial densities

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= 60° x B = 0.2 Q 2 = 2 GeV 2 t = -0.2 GeV 2 DVCS BSA: sensitivity to J u,d DVCS on the proton J u =.3, J d =.1 J u =.8, J d =.1 J u =.5, J d =.1 J u =.3, J d =.8 J u =.3, J d =-.5 E e = 11 GeV

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= 60° x B = 0.17 Q 2 = 2 GeV 2 t = -0.4 GeV 2 n-DVCS BSA is: very sensitive to J u, J d can be as strong as for the proton According to the kinematics and Ju, Jd DVCS on the neutron J u =.3, J d =.1 J u =.8, J d =.1 J u =.5, J d =.1 J u =.3, J d =.8 J u =.3, J d =-.5 E e = 11 GeV DVCS BSA: sensitivity to Ju,Jd

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Why Studying n-DVCS ? Eric Voutier n-DVCS gives access to the least known and constrained GPD, E 0 because F 1 (t) is small 0 because of cancelation of.

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