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M. Guidal, IPN Orsay

Genoa, 25/02/09. Electron scattering in CLAS (selected) review. M. Guidal, IPN Orsay. Form factors. Inclusive scattering. Semi-inclusive scattering. Deep exclusive scattering. Nuclear targets. Nucleon ground state. Nucleon resonances. unpolarized. polarized.

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M. Guidal, IPN Orsay

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  1. Genoa, 25/02/09 Electron scattering in CLAS (selected) review M. Guidal, IPN Orsay

  2. Form factors Inclusive scattering Semi-inclusive scattering Deep exclusive scattering Nuclear targets Nucleon ground state Nucleon resonances unpolarized polarized AUL, ALL, ALU for p SIDIS DVCS Vector meson Color tranparency

  3. Constituent Quarks pQCD QCD Large Nc 3  8 Lattice c Symmetry p p N

  4. Many thanks, for the slides, to: M. Aghasyan (SIDIS), H. Avakyan (SIDIS), V. Burkert (FFs), E. Christy (DIS), W. Gohn (SIDIS), K. Hafidi (Nuclear), N. Guler (DIS), S. Kuhn (DIS). [N*,Spin08,ECT workshop,CLAS Coll.meetings,…]

  5. Form factors Inclusive scattering Semi-inclusive scattering Deep exclusive scattering Nuclear targets Nucleon ground state Nucleon resonances unpolarized polarized AUL, ALL, ALU for p SIDIS DVCS Vector meson Color tranparency

  6. Ground state and Transition Form Factors , e e g N N,N* N=p,n GE ,GM GE ,GM ,GC (or E1+ ,M1+ ,S1+) N*=D(1232) P11(1440) D13(1520) S11(1535) pN pN,ppN GE ,GM (or A1/2 ,S1/2) pN,ppN GE ,GM ,GC (or A1/2 ,A3/2 ,S1/2) hN,pN GE ,GM (or A1/2 ,S1/2) [Electric/Magnetic/Coulomb,Multipoles, Helicity amplitudes,…]

  7. Neutron Magnetic Form Factor Hall B CLAS Real time in-situ calibration of the neutron detection efficiency in the CLAS e.m. calorimeter EC measured online through ep→eπ+(n). Results of the neutron magnetic form factors from Q2 = 1- 5 GeV2 . No large deviation observed from dipole form. J. Lachniet et al. (CLAS) arXiv:0811.1716 (PRL)

  8. NΔ Multipole Ratios REM, RSM • There is no sign for asymptotic pQCD behavior in REM (->+1) or RSM (->Cte). • REM < 0 at low Q2 favors oblate shape of Δ(1232) and prolate shape of the proton. • Dynamical models attribute the deformation to contributions of the pion cloud at low Q2.

  9. P11(1440) amplitudes from Nπ and Nππ Nπ Nππ (preliminary) PDG First observed zero crossing of a nucleon form factor!

  10. Fits to diff. cross sections & structure functions DR DR w/o P11 UIM DR UIM Q2=3.48GeV2 Q2=2.05GeV2

  11. Transition amplitudes for D13(1520) Nπ M. Dugger et al., PRC76 025211, 2007 Nππ (preliminary) A3/2 A1/2

  12. Transition amplitudes for D13(1520) A21/2 – A23/2 Ahel = A21/2 + A23/2 S1/2 CQM predictions: A1/2 dominance with increasing Q2. Ahel pπ+π- (prel.) nπ+ nπ+ pπ0 pπ0

  13. Transition amplitudes for S11(1535) This state has traditionally been studied in the S11(1535)→pη channel, which is the prominent decay. For the study of S1/2Nπ channel is important. S1/2 difficult to extract in pη channel. A1/2 fromnπ+consistent with ph within uncertainties of b.r.

  14. Form Factors CLAS M. Vanderhaeghen, L. Tiator p->D+ p->S11(1535) p->D13(1535)

  15. Transverse Charge Densities CLAS M. Vanderhaeghen, L. Tiator The charge distribution of the p-Roper+ transition shows a dense positive core of 0.5 fm radius, and a negative outer shell up to a radius of 1 fm. p->D+ p->S11(1535) p->D13(1535)

  16. Conclusions • NΔ(1232) amplitudes are well determined at Q2 up to 6 GeV2. • No sign of transition to asymptotic QCD behavior • Roper P11(1440) amplitudes determined up to 4.5 GeV2 using two different analysis approaches (DR, UIM), and two channels • Sign change of A1/2 seen in Nπ and Nππ • S11(1535) amplitudes measured in nπ+ channel, for the first time • Hard A 1/2 form factor confirmed • First measurement of S1/2. • D13(1520) in nπ+ and pπ+π- • Helicity switch from A3/2 dominance to A1/2 dominance at Q2>0.6 GeV2 • First measurement of S1/2.

  17. Form factors Inclusive scattering Semi-inclusive scattering Deep exclusive scattering Nuclear targets Nucleon ground state Nucleon resonances unpolarized polarized AUL, ALL, ALU for p SIDIS DVCS Vector meson Color tranparency

  18. Need proton and neutron targets to pin down u/d PDFs from DIS At Leading order x[4/9u(x) + 1/9d(x)] x[4/9d(x) + 1/9u(x)] At large x proton dominated by u(x) and neutron by d(x)‏ due to charge weighting. PDF’s least well known at large x Also, proton + neutron data provides way to separate valence cleanly (Gluon comparable in size to dv at x~0.3) u(x)‏ d(x)‏

  19. Deuterium + proton data does not allow clean determination of neutron for x  1 due to nuclear corrections

  20. CLAS with the RTPC and one electron event. to CLAS n p To BoNuS RTPC φ, z from pads r from time beam Helium/DME at 80/20 ratio dE/dx from charge along track (particle ID)

  21. e n p SpectatorTagging E = 4.223 GeV <Q2> = 1.19 (GeV/c)2 *

  22. Structure function ratio PRELIMINARY Good agreement with previous data in smaller x region. Full acceptance correction method forthcoming.

  23. Double polarized inclusive electron scattering e e p p N+ N- e’ Long. Polarized Electron qe e Pe Pt y Long. Polarized Nucleon Cross section can be expressed in terms of virtual photon asymmetries A1 and A2. A1 A2 Difference in the cross sections for two cases is expressed as “double spin asymmetry”.

  24. Q2 evolution of the GDH integral DIS pQCD G1 operator product expansion quark models Lattice QCD? ChPT 1 Q2 (GeV2) GDH sum rule • Both Bjorken and GDH sum rules are fundamental sum rules Small Q2 GDH sum rule Experiments at Mainz, Bonn Chiral perturbation theory Intermediate Q2 Extended GDH sum rule Several different models Experiments at JLAB(CLAS/Hall A/Hall C) A good test of “at what distance scale pQCD corrections and higher twist expansions will break down and physics of confinement dominate”. ? Large Q2 Bjorken Sum rule Experiments at CERN,SLAC,DESY Higher order QCD expansion EG1B has good precision data with wide Q2 coverage to answer some of these questions. • Dramatic change of sign of G1 from DIS-regime to the value at the real photon point. • At low Q2 , g1(x,Q2) is dominated by resonance excitations.

  25. A1 Deuteron Δ(1232)P33 A1 N(1520-35)D13/S13 PRELIMINARY W(GeV)

  26. Γ1 Deuteron, Comparison to world data

  27. Γ1 Deuteron, Comparison to world data

  28. Γ1 Deuteron, Comparison to world data PRELIMINARY

  29. Γ1 Proton, Comparison to world data

  30. Γ1 Proton, Comparison to world data PRELIMINARY

  31. Γ1 Proton, Comparison to world data PRELIMINARY

  32. Fit to Bjorken sum: Γ1(p-n) = gA/6[1-αs(Q)/π] Bjorken sum: Γ1(p-n) =∫(g1p-g1n)dx CLAS –Saturation of the strong coupling The saturation of s at large distances is a necessary condition for the application of the AdS5/CFT correspondence that can be used to carry out non-perturbative QCD calculations(Brodsky, de Teramond).

  33. Form factors Inclusive scattering Semi-inclusive scattering Deep exclusive scattering Nuclear targets Nucleon ground state Nucleon resonances unpolarized polarized AUL, ALL, ALU for p SIDIS DVCS Vector meson Color tranparency

  34. Unpolarized target e p Longitudinally pol. target Transversely pol. target e p SIDIS (g*p→pX) cross section at leading twist (Ji et al.) e Boer-Mulders 1998 Kotzinian-Mulders 1996 Collins-1993 structure functions = pdf × fragm × hard × soft (all universal)

  35. Longitudinal Target SSA measurements at CLAS Large sinf for all pions and no indication of sin2fforp0 ’ssuggests Sivers dominance p1sinf+p2sin2f CLAS PRELIMINARY W2>4 GeV2 Q2>1.1 GeV2 y<0.85 0.4<z<0.7 MX>1.4 GeV p1=-0.042±0.015 p2=-0.052±0.016 p1=0.082±0.018 p2=0.012±0.019 p1= 0.059±0.010 p2=-0.041±0.010 PT<1 GeV 0.12<x<0.48 36

  36. ALL PT-dependence 0.4<z<0.7 m02=0.25GeV2 mD2=0.2GeV2 M.Anselmino et al hep-ph/0608048 p+ A1 suggests broader kT distributions for f1 compared to g1 p- A1 may require non-Gaussian kT-dependence for different helicities and/or flavors

  37. ALU ALU

  38. ALU Results p0

  39. Form factors Inclusive scattering Semi-inclusive scattering Deep exclusive scattering Nuclear targets Nucleon ground state Nucleon resonances unpolarized polarized AUL, ALL, ALU for p SIDIS DVCS Vector meson Color tranparency

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

  41. VGG (1999) DVCS beam spin asymmetry JLab Hall B Collaboration, PRL 100:162002,2008

  42. Unpolarized Cross Section 0.09<-t<0.2 GeV2 0.2<-t<0.4 GeV2 0.4<-t<0.6 GeV2 POTENTIAL 0.6<-t<1 GeV2 1<-t<1.5 GeV2 1.5<-t<2 GeV2

  43. r w f

  44. BackgroundSubtraction (normalized spectra) • 1) Ross-Stodolsky B-W forr0(770),f0(980)andf2(1270) • with variable skewedness parameter, • 2)D++(1232) p+p-inv.mass spectrumandp+p- phase space.

  45. sL (g*Lp  prL0) VGG GPD model GK GPD model ep  epr 0 EPJA39 (2009)

  46. sL (g*Lp  prL0) Regge/Laget

  47. Large tmin ! (1.6 GeV2) Fit by ebt ds/dt (g*ppr0)

  48. N p+p0 Counts/20 MeV 100% e1-dvcs statistics p+p0 invariant mass =√( p p+ + p p0)2

  49. Form factors Inclusive scattering Semi-inclusive scattering Deep exclusive scattering Nuclear targets Nucleon ground state Nucleon resonances unpolarized polarized AUL, ALL, ALU for p SIDIS DVCS Vector meson Color tranparency

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