Deeply Virtual Compton Scattering and Meson Production at JLab/CLAS Hyon-Suk Jo for the CLAS collaboration IPN Orsay PANIC 2011 – M.I.T. – Cambridge - July 25, 2011 19th Particles & Nuclei International Conference
Outline • Introduction • Deeply Virtual Compton Scattering (DVCS) • Deeply Virtual Meson Production (DVMP) • JLab 12GeV: DVCS/DVMP at CLAS12 • Conclusions Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Deeply Virtual Compton Scattering (DVCS) “handbag” diagram (high Q 2 , small t, fixed x B ) DVCS DVMP BH fully calculable in QED 2 (ep ep ) = + + GPDs DVCS and Bethe-Heitler (BH) experimentally undistinguishable H(x, ,t), E(x, ,t) H(x, ,t), E(x, ,t) ~ ~ ~ ~ H(x, ,t), E(x, ,t) interference between the 2 processes H(x, ,t), E(x, ,t) 4 d 2 2 2 DVCS BH DVCS BH T T T T I 2 dQ dx dtd B with BH DVCS DVCS * * BH I T T T T interference term DVCS is the most straightforward, theoretically cleanest reaction allowing to access the GPDs Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Extracting GPDs from DVCS observables 1 1 1 hadronic plane 2 q q H e Re P H ( x , , t ) H ( x , , t ) dx q q x x e ’ 0 2 q q H e Im H ( , , t ) H ( , , t ) * q q e leptonic plane d d p’ LU BSA : A ep ep LU d d d d = x B /(2-x B ) k = t/4M 2 Proton Neutron ~ • Polarized beam, Unpolarized target Im { H p , H p , E p } ~ ~ Im { H n , H n , E n } LU ~ sin Im{F 1 H + (F 1 +F 2 ) H -kF 2 E }d ~ • Unpolarized beam, Longitudinally polarized target Im { H p , H p } ~ ~ ~ UL ~ sin Im{F 1 H + (F 1 +F 2 )( H + x B /2 E ) – kF 2 E +… }d Im { H n , E n , E n } • Unpolarized beam, Transversely polarized target Im { H p , E p } UT ~ cos Im{k(F 2 H – F 1 E ) + ….. }d Im { H n } ~ • Polarized beam, Longitudinally polarized target Re { H p , H p } ~ ~ LL ~ (A+Bcos Re{F 1 H + (F 1 +F 2 )( H + x B /2 E )… }d Re { H n , E n , E n } Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Jefferson Lab (Newport News, Virginia, USA) CEBAF : C ontinuous E lectron B eam A ccelerator F acility Duty cycle 100% E max 5.8 GeV P max 80% CLAS Hall B detector in Hall B Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
A typical DVCS/BH event in the CLAS detector ep e’p’ SC e’ The DVCS/BH photon is mostly DC emitted at forward angles EC CC (EC) p’ DVCS/BH photon not (CC) detected with CLAS alone Need an electromagnetic (DC) (SC) calorimeter at forward angles for DVCS experiments ! Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
The e1-DVCS experiment (first experiment with CLAS dedicated to DVCS) with the CLAS detector + DVCS electromagnetic calorimeter + Solenoid CLAS Part 1 of the e1-DVCS experiment: • Data taken from March 11 until May 27, 2005 • Beam energy ~ 5.766 GeV • Beam current = 20-25 nA • Polarization ~ 76-82% • Integrated luminosity ~ 3.33 x 10 7 nb -1 • Target LH 2 Solenoid DVCS electromagnetic calorimeter shielding the detectors from the Møller electrons 424 lead tungstate crystals + APD readout Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
The e1-DVCS experiment (first experiment with CLAS dedicated to DVCS) with the CLAS detector + DVCS electromagnetic calorimeter + Solenoid CLAS Part 1 of the e1-DVCS experiment: • Data taken from March 11 until May 27, 2005 • Beam energy ~ 5.766 GeV • Beam current = 20-25 nA • Polarization ~ 76-82% • Integrated luminosity ~ 3.33 x 10 7 nb -1 • Target LH 2 Solenoid DVCS electromagnetic calorimeter The e1-DVCS data can be used to extract DVCS and DVMP Beam Spin Asymmetries and Cross Sections shielding the detectors from the Møller electrons 424 lead tungstate crystals + APD readout Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Kinematic coverage of the e1-DVCS data hadronic plane The kinematics of the DVCS reaction is defined by 4 independent variables : e ’ Q 2 , x B , t and * 4-dimensional bins = (Q 2 , x B , -t, ) e leptonic plane p’ Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
DVCS Beam Spin (A LU ) and Longitudinal Target Spin (A UL ) asymmetries A LU integrated over t F.X. Girod et al. (CLAS Collaboration), Phys. Rev. Lett. 100, 162002 (2008) Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
DVCS Beam Spin (A LU ) and Longitudinal Target Spin (A UL ) asymmetries A LU A UL JLab Hall A VGG twist-3 results <Q 2 >=1.82, <-t>=0.31, < >=0.16 VGG twist-2 Regge (JML) Previous F.X. Girod et al. (CLAS Collaboration), S. Chen et al. (CLAS Collaboration), CLAS results Phys. Rev. Lett. 100, 162002 (2008) Phys. Rev. Lett. 97, 072002 (2006) VGG model: Vanderhaeghen,Guichon,Guidal Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Extraction of GPDs from fitting A LU and A UL CLAS data Having both the beam-spin and longitudinal target-spin asymmetries, a nearly model-independent GPD analysis in leading twist was achieved fitting simultaneously A LU and A UL extracted with CLAS at 3 values of t and fixed x B ~ Im H Im H M. Guidal, Phys. Lett. B 689, 156-162 (2010) • Im H : VGG model predictions reproduce the shape of the data but overestimate it, especially at lower t ~ • Im H : VGG model predictions tend to underestimate the data ~ Im H shows a steeper t-slope than Im H which would suggest that the axial charge is more concentrated than the electromagnetic charge Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Extraction of GPDs from fitting world data red circles: fit with only H Indication that we can not ~ neglect H , [Kumericki and Mueller] (blue and green curves, black triangles) K. Kumericki and D. Mueller, Proceedings of 4th Workshop on Exclusive Reactions at High Momentum Transfer, Newport News, Virginia, 18-21 May 2010 Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
DVCS cross sections Q 2 , 0.1 x 0.58, 0.09 - t 3 The fast variation of the BH cross section: 1 B Around Φ =0 (where lies the BH singularity), 21 45, p 0.8, W 2 e there can be a factor ~2 between e 4-dimensional bins = (Q 2 , x B , -t, ) neighbouring kinematics Q 2 x B The very fast variations of the BH cross section make the DVCS cross section analysis particularly difficult Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
DVCS cross sections Q 2 , 0.1 x 0.58, 0.09 - t 3 1 B PRELIMINARY 21 45, p 0.8, W 2 e e 4-dimensional bins = (Q 2 , x B , -t, ) Q 2 x B 2 independent analyses in progress JLab / IPN Orsay Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Deeply Virtual Meson Production (DVMP) “handbag” diagram (high Q 2 , small t, fixed x B ) DVMP Factorization proven only for longitudinally polarized conserve nucleon helicity virtual photons ~ H (x, ξ ,t) H (x, ξ ,t) ~ 1 E (x, ξ ,t) E (x, ξ ,t) H(x, ,t), E(x, ,t) ~ H(x, ,t), E(x, ,t) ~ ~ T L Q 2 ~ ~ H(x, ,t), E(x, ,t) flip nucleon helicity H(x, ,t), E(x, ,t) ρ 0 2u+d Vector mesons ( w ) ω 2u-d sensitive to H and E ρ + u-d DVMP allows quark flavor decomposition 0 2 u+ d Pseudoscalar mesons ( ) ~ ~ + u- d sensitive to H and E 2 u- d Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
Deeply Virtual Meson Production (DVMP) Vector mesons: exclusive 0 , w and electroproduction on the proton at CLAS 6 GeV: K. Lukashin et al. , Phys. Rev. C 63, 065205, 2001 ( @4.2 GeV) e1-b C. Hadjidakis et al. , Phys. Lett. B 605, 256-264, 2005 ( 0 @4.2 GeV) (1999) L. Morand et al. , Eur. Phys. J. A 24, 445-458, 2005 ( w @5.75GeV) e1-6 J. Santoro et al. , Phys. Rev. C 78, 025210, 2008 ( @5.75 GeV) (2001-2002) S. Morrow et al. , Eur. Phys. J. A 39, 5-31, 2009 ( 0 @5.75GeV) e1-DVCS A. Fradi, Orsay Univ. PhD thesis ( @5.75 GeV) (2005) There are also results on exclusive pseudoscalar meson electroproduction on the proton at CLAS 6 GeV: R. De Masi et al. , Phys. Rev. C 77, 042201(R), 2008 ( 0 @5.75GeV) K. Park et al. , Phys. Rev. C 77, 015208, 2008 ( @5.75 GeV) I. Bedlinskiy et al. , paper in preparation ( 0 @5.75GeV) Hyon-Suk Jo PANIC 2011 - M.I.T. – Cambridge - July 24-29, 2011 July 25, 2011
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