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Vector Mesons and DVCS at Jefferson

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Vector Mesons and DVCS at Jefferson Vector Mesons and DVCS at Jefferson Lab Valery Kubarovsky Jefferson Lab Newport News, VA April 12, 2001 XIX Interna)onal Workshop on Deep-Inelas)c Sca5ering and Related Subjects Outlook • IntroducEon • DVCS with unpolarized target • DVCS with polarized targets • Vector meson electroproducEon • JLAB 12 upgrade • Conclusion DescripEon of hadron structure in terms of GPDs Nucleon form factors Structure functions GPDs transverse charge & quark longitudinal correlated quark momentum current densities momentum (polarized distributions (polarized and and unpolarized) unpolarized) in transverse distribuEons space q q γ∗ γ (x + ξ)P (x ξ)P DVCS and DVMP − GP D • Factorizaon theorem (1 + ξ)P (1 ξ)P • Access to fundamental degrees of − freedom DVCS: • the clearest way to access the GPDs • Only γT photons parEcipate in DVCS ~ ~ • Interference with BH process H,E DVMP: • Factorizaon proven only for σL 2 H, E σT/σL~1/Q • Meson distribuEon amplitude • Gluon exchange required • Vector and pseudoscalar meson producEon allows to separate flavor and separate the helicity-dependent GPDs form helicity independent. Accessing GPDs through polarizaon σ+ - σ- Δσ - A = σ+ + σ = 2σ ξ ~~ xB/(2-xB) k = t/4M2 Polarized beam, unpolarized proton target: ~ ( ,t) ΔσLU ~ sinφ {F1H + ξ(F1+F2)H +kF2E }dφ H ξ Kinematically suppressed Unpolarized beam, longitudinal proton target: ~ ~ ΔσUL ~ sinφ {F1H+ξ(F1+F2)(H +ξ/(1+ξ)E ) -.. }dφ H ( ξ ,t ), H(ξ,t) Kinematically suppressed Unpolarized beam, transverse proton target: ΔσUT ~ cosφ {k(F2H – F1E ) + ….. }dφ H(ξ,t), E(ξ,t) Kinematically suppressed H(ξ,t), E(ξ,t)… are CFF JLab Site: The 6 GeV Electron Accelerator Hall-B CLAS Hall-A Hall-C 3 independent beams with energies up to 6 GeV Dynamic range in beam current: 106 Electron polarization: 85% CEBAF Large Acceptance Spectrometer CLAS 424 crystals, 18 RL, CLAS Lead Tungstate ElectromagneEc Calorimeter PoinEng geometry, APD readout σ+ - σ- Δσ - DVCS Beam Spin Asymmetry ALU ALU = σ+ + σ = 2σ • VGG parameterization CLAS data 2 reproduces –t > 0.5GeV ) 2 0.2 # sin! # behavior, and overshoots 0.1 1+" cos! 0.3 (GeV 2 0 0.2 asymmetry at small t. Q BSA -0.1 0.1 (integrated) 0 -0.2 3 • The latter could indicate that 0 90 180 270 360 VGG misses some important ! (deg) e1-dvcs contributions to the DVCS Hall-A cross section. CLAS (previous) VGG model • Regge model (J-M Laget) is in fair VGG + twist3 agreement in some kinemac bins with 2 Laget model our results. • The Regge mode seems to be working at 0.5 1 1.5 low Q2 while the GDP approach gets -t (GeV2) beeer at larger Q2. This is expected 1 F.-X. Girod et al., PRL 100 (2008) 162002 0.1 0.2 0.3 0.4 xB ExtracEon of Compton Form Factors from CLAS DVCS data • ALU and AUL CLAS results only • Im H(t) Im H~ (t) are extracted M. Guidal, Phys.Le.B689:156-162,2010 • Im H~ (t) flaer than Im H(t) The fact that H is "flaer" in t than H, hints that the axial charge of the nucleon ~ is more concentrated than the electromagneEc charge. This is related to the fact that the axial form factor is also flaer than the EM form factors. We see that via different formalism (GDPS vs FFs) and reacEon (DVCS vs elasEc), one reaches the same conclusions. "(ep #ep$) DVCS x-sections from e1dvcs F.X. Girod ! F.X. Girod Hyon-Suk Jo Alex Kubarovski Four dimensional grid 2 CLAS PRELIMINARY Q , xB, t, φ Radiative corrections and π0 contamination accounted ! ! DVCS target spin asymmetry ! (ep ! ep") eg1-dvcs - completed data taking at 2009 E. Seder Polarizations: Beam: ~80% NH3 proton ~70% Beam energy ~5.7 GeV Longitudinal Polarized target Longitudinal target SSA will be extracted in bins in Q2, x and t 11 DVCS double spin asymmetry eg1-dvcs - completed data taking at 2009 (N ++ + N !! )! (N +! + N !+ ) A = LL ++ !! +! !+ S. Pisano fPbeamPt arget (N + N )! (N + N ) Fitting function: 2 2 ALL = ! + "cos# +$cos # +%sin # N+/-: number of DVCS events with a positive (negative) target/beam polarization Pbeam/T: beam/target polarization f: diluition factor Hall A • Proton DVCS, helicity dependent and independent cross secEons were measured at Q2=(1.5, 1.9, 2.3) GeV2 -t=(0.17, 0.23, 0.28, 0.33) GeV2 xB=0.36 • Neutron DVCS, helicity dependent cross secEon on deuterium. SensiEve to E(!,t) Q2=1.9 GeV2 xB=0.36 • Completed data taking at 2010, which included measurements of DVCS on proton and deuterium at two different energies with the aim to separate Re [DVCS*BH] and |DVCS|2 terms. Imaginary Part of the Interference Term VGG model • VGG model agrees in slope with the data but lies 30% above • Q2 independent in all t bins • Provide support for the factorizaon at Q2>2 GeV2 Constraint on Jd and Ju Helicity-dependent Jlab Hall-A neutron and HERMES transversity polarized proton data constrain in a model dependent way on the total up and down quark contribuEons to the proton spin. 1 1 1 J = !" + L = x[H (x,!,t = 0)+ E (x,!,t = 0)]dx q 2 q q 2 $ #1 q q Exclusive Meson ProducEon + + + 0 ep ! en" + ep ! en" , " ! # # 0 0 + $ ep ! ep" 0, " 0 ! ## ep ! ep" , " ! # # ep ! ep$, $ ! ## ep ! ep%, % ! # +# $# 0 ep ! ep&, & ! K +K $ CLAS6: lots of data. New proposal being prepared CLAS12: Exp. # E12-06-108 for PAC 38 K. Lukashin et al., Phys.Rev.C63:065205,2001 (φ, 4.2 GeV) C. Hadjidakis et al., Phys.Lee.B605:256-264,2005 (ρ0,4.2 G eV) L. Morand et al., Eur.Phys.J.A24:445-458,2005 (ω, 5.75GeV) J. Santoro et al., Phys.Rev.C78:025210,2008 (φ, 5.75GeV) S. Morrow et al., Eur.Phys.J.A39:5-31,2009 (ρ0, 5.75GeV) A. Fradi, Orsay Univ. PhD thesis (ρ+ ,5.75 GeV) Vector Mesons Quark and Gluon GPDs New d" (# * p $en% + ) & 'tebt dt ! CLAS data. The first measurement of the ρ+ exclusive electroproducEon ρ+ t-slope parameter d" (# * p $en% + ) & 'tebt 2) dt b(xB,Q Slope parameter is ! decreasing with xB. This indicates that the size of the interacEon region decreases as xB1 xB ) 2 9 Vector mesons t-slope parameter ï CLAS (5.754 GeV) FermiLab (1977) CLAS (5.754 GeV) CLAS (5.754 GeV) CORNELL E665 CORNELL CLAS (5.754 GeV) 1 8 CORNELL 2 2 2 b (GeV HERMES H1 H1 W = Q ( !1)+ m NMC ZEUS ZEUS N 7 xB 6 5 4 New 3 2 0 + 1 l t q l 0 W 10 10 10 10 10 10 10 10 W (GeV) W (GeV) W (GeV) W (GeV) ) 2 9 ï CLAS (5.754 GeV) CLAS (5.754 GeV) CLAS (5.754 GeV) 8 CLAS (5.754 GeV) DESY 0 DESY DESY b (GeV + SLAC l SLAC t SLAC q Daresbury l 7 6 New 5 4 3 2 1 Q2 0 0123456 0123456 0123456 0123456 Q2 (GeV2 ) Q 2 (GeV2) Q 2 (GeV2) Q 2 (GeV2) • b increases with W : the size of the nucleon increases as one probes the high W values (i.e. the sea quarks). Sea quarks tend to extend to the periphery of the nucleon. * + σL, σΤ separaon ! L p ! n" S-channel helicity conservaon 2 2 σ 2 2 1.00<Q (GeV )< 1.50 L 1.50<Q (GeV )< 2.00 1 10ï1 10ï1 10ï2 2 2 Q =1.25 10ï2 Q =1.75 10ï3 10ï3 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 W(GeV) W(GeV) 2.00<Q2(GeV2)< 2.50 2.50<Q2(GeV2)< 3.00 10 1 1 Q2=2.75 10ï1 10ï1 Q2=2.25 10ï2 10ï2 0 0.5 1 1.5 2 2.5 3 2 2.5 3 3.5 4 W(GeV) W(GeV) 3.00<Q2(GeV2)< 3.50 3.50<Q2(GeV2)< 4.00 1 1 2 Q =3.25 ï1 10 10ï1 Q2=3.75 10ï2 10ï2 10ï3 2 2.5 3 3.5 4 4.5 0 0.5 1 1.5 2 2.5 3 W(GeV) W(GeV) 4.00<Q2(GeV2)< 4.50 1 + mL(l ) [[email protected] GeV] 2 + 10ï1 Q =4.25 mL(l ) [VGG] ( +) [GK] ï2 mL l 10 W 2 2.5 3 3.5 4 4.5 5 W(GeV) GPD fails to describe data by more than order of magnitude * 0 " L p # p$ Fails to describe data W<5 GeV Describes well for W>5 GeV Regge model VGG model ! σL VGG with D-term W GK model •Popular GK and VGG models can not provide the right W-dependence of the cross-secEon •This does not mean that we can’t access GPD in vector meson electroproducEon •For example, model with the addiEon of q- qbar exchange (M.Guidal) together with standard VGG model successfully describes data !"#$%&'()"**#%"(+) * φ and ρ0 * 0 " L p # p$ Goloskokov, Kroll " L p # p$ φ ρ0 CLAS ZEUS 102 Cornell ZEUS E665 HERMES 2 p) [nb] p) Cornell p) [nb] p) $ # 10 H1 ! 1 ! p-> CLAS p-> H1 * * 10 " " ( ( L L ! ! GPD GK GPD GK 100 101 4 6 81020 40 60 100 4681020 40 60 100 W[GeV] W[GeV] (a) (b) •φ mesons - gluon GPD are dominant 0 FIGURE 5. The longitudinal•ρ 0 and cross ω - sea quarks and/or gluons dominant. section for (a) exclusive $,(b)exclusive # production (adapted from Ref. [25]). The curve/error GPD approach describes well data for W>5 band show the GPD–based model calculationGeV of Ref.
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