1 / 31

Marc Vanderhaeghen Jefferson Laboratory / College of William & Mary

Overview of nucleon structure studies. Marc Vanderhaeghen Jefferson Laboratory / College of William & Mary. INPC07 Tokyo, June 3-8, 2007. nucleon form factors. (generalized) parton distributions spin, tomography. nucleon resonances Δ (1232),…. Pun05. Gay02.

pillan
Download Presentation

Marc Vanderhaeghen Jefferson Laboratory / College of William & Mary

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Overview of nucleon structure studies Marc Vanderhaeghen Jefferson Laboratory / College of William & Mary INPC07 Tokyo, June 3-8, 2007

  2. nucleon form factors (generalized) parton distributions spin, tomography nucleon resonances Δ(1232),…

  3. Pun05 Gay02 proton e.m. form factor : status green : Rosenbluth data (SLAC, JLab) JLab/HallA recoil pol. data new JLab/HallC recoil pol. exp. (2008) : extension up to Q2 ≈ 9 GeV2

  4. neutron e.m. form factor : status MAMI JLab/HallC JLab/CLAS JLab/HallA new MIT-Bates (BLAST) data for both p and n at low Q2 : see talk M. Kohl (D1-1) new JLab/HallA double pol. exp. (spring 07) : extension up to Q2 ≈ 3.5 GeV2 completed

  5. nucleon form factors : pion cloud Friedrich, Walcher (2003) phenomenological fit : “smooth” part (sum of 2 dipoles) + “bump” (gaussian) 6 parameter fit for each FF pion cloud pronounced structure in all FF around Q  0.5 GeV/c

  6. nucleon FF : lattice prospects F1V state of art : connected diagrams -> OK for isovector quantities LHPColl. full QCD lattice calculations Pion masses down to less than 300 MeV √(r2)1V chiral extrapolation to physical mass Leinweber, Thomas, Young (2001) next step : inclusion of disconnected diagrams see talks S. Ohta (D4-5), A. Schäfer

  7. Two-photon exchange effects Rosenbluth vs polarization transfer measurements of GE/GM of proton SLAC, Jlab Rosenbluth data Jlab/Hall A Polarization data Jones et al. (2000) Gayou et al. (2002) Two methods, two different results ! 2γ exchangeproposed as explanation Guichon, Vdh (2003)

  8. Two-photon exchange calculations partonic calculation elastic contribution N GPDs Chen, Afanasev, Brodsky, Carlson, Vdh (2003) Blunden, Melnitchouk, Tjon (2003, 2005)

  9. Generalized Parton Distributions * Qhard2 large t = Δ2 low –t process : -t << Qhard2 Ji , Radyushkin (1996) x + ξ x - ξ P - Δ/2 P + Δ/2 GPD (x, ξ ,t) (x + ξ) and(x - ξ): longitudinal momentum fractions of quarks at large Q2 : QCD factorizationtheorem hard exclusive process can be described by 4 transitions(GPDs) : ~ Vector :H (x, ξ ,t) Tensor :E (x, ξ ,t) Axial-Vector :H (x, ξ ,t) Pseudoscalar :E (x, ξ ,t) ~

  10. Δ P - Δ/2 P + Δ/2 known information on GPDs forward limit : ordinaryparton distributions unpolarized quark distr polarized quark distr : do NOT appear in DIS new information first moments : nucleonelectroweak form factors Dirac Pauli axial ξ independence : Lorentz invariance pseudo-scalar

  11. Why GPDs are interesting Unique tool to explore the internal landscape of the nucleon : 3D quark/gluon imaging of nucleon Access to static properties : constrained (sum rules) by precision measurements of charge/magnetization orbital angular momentum carried by quarks

  12. GPDs yield 3-dim quark structure of nucleon Burkardt (2000, 2003) Belitsky, Ji, Yuan (2004) Elastic Scattering transverse quark distribution in coordinate space DIS longitudinal quark distribution in momentum space DES (GPDs) fully-correlated quark distribution in both coordinate and momentum space

  13. electromagnetic form factors PROTON NEUTRON modified Regge GPD parametrization 1 : Regge slope -> protonDirac (Pauli) radius 2, 3 :large x behavior of GPD Eu, Ed ->large Q2 behavior of F2p, F2n 3-parameter fit Guidal, Polyakov, Radyushkin, Vdh (2005) world data (2006) also Diehl, Feldmann, Jakob, Kroll (2005)

  14. proton Dirac & Pauli FFs : GPD framework PQCD modified Regge GPD model data : SLAC data : JLab/HallA data : JLab/HallA Belitsky, Ji, Yuan (2003) Guidal, Polyakov, Radyushkin, Vdh (2005)

  15. GPDs : transverse image of the nucleon (tomography) Hu(x, b? ) x b?(fm)

  16. quark contribution to proton spin X. Ji (1997) with parametrizations for E q : GPD : based on MRST2002 μ2 = 2 GeV2 lattice : full QCD, no disconnected diagrams so far

  17. e e e e  Z p p p p e e 2  p p NucleonstrangenessFFs PV e-scattering APV = Q2 = 0.1 GeV2 re-analysis Young et al. (2006) GMs = 0.28 ± 0.20 GEs = -0.006 ± 0.016 GMs = -0.01 ± 0.25 GEs = +0.002 ± 0.018

  18. NucleonstrangenessFFs : Q2 dependence Forward angle e-p data • Rapid variation at low Q2 unlikely • Await backward angle measurements from A4, G0 • Deuterium running will provide constraints on GA • One high precision point at Q2~0.6 (HAPPEX III: run in 2009)

  19. DIS fit :ν - ν(CDHS data) x (s – s) NucleonstrangenessFFs : interpretation lattice GMs (0) = -0.046 ± 0.019 μNLeinweber et al. (2005) GEs (0.1) = 0.001 ± 0.004 ± 0.004Leinweber et al. (2006) + charge symm. constraints GPD F1s Regge slope :α’ ≈ 0.95 GeV2 data (Young et al.) : 0.002 ± 0.024 Barone, Pascaud, Zomer (2000) CCFR + NuTeV data (2001) Vdh ( PAVI2002 )

  20. t g* g,M,... x~xB x ~ ~ H,E,H,E p p’ Beam or target spin asymmetries contain only ImT, i.e. GPDs at x = x and -x Cross sections and charge asymmetries measurements (ReT) Integral of GPDs over x link GPDs and observables

  21. DVCS : beam spin asymmetry ALU = (BH) * Im(DVCS) * sin Φ GPDs Bethe-Heitler DVCS Q2 = 1 – 1.5 GeV2 , xB = 0.15 – 0.25, -t = 0.1 - 0.25 GeV2 Q2 = 2.6 GeV2 , xB = 0.11, -t = 0.27 GeV2 JLab/CLAS (2001) HERMES (2001) twist-2 + twist-3 : Kivel, Polyakov, Vdh (2000)

  22. Bethe-Heitler DVCS on protonJLab/Hall A @ 6 GeV DVCS GPDs Difference of polarized cross sections Q2 ≈ 2 GeV2 xB = 0.36 Unpolarized cross sections Muñoz-Camacho, Camsonne (2006) -> see talk P. Bertin (D4-2)

  23. DVCS on proton : JLab/Hall A @ 6 GeV • Twist-2terms dominate the cross section and are independent ofQ2in the explored kinematical domain • The contribution to the cross section oftwist-3terms issmalland isindependent of Q2in the limit of error bars indication in favor of factorization already from Q2=2 GeV2 in the valence region

  24. DVCS on proton : JLab/CLAS @ 6 GeV Girod, Jo (2007)

  25. DVCS on neutron Mazouz (2006) 0 because F1(t) is small 0 because of cancelation of u and d quarks n-DVCSgives access to the least known and constrained GPD,E JLab /Hall A (E03-106) : preliminary data

  26. H1, ZEUS Large phase space(x,t,Q2) and High luminosity required Valence region Sea/gluon region EIC JLab12 high xB only reachable with high luminosity JLab Upgrade at 12 GeV, CEBAF will be ideal for GPD studies in valence quark regime

  27. exclusive DVCS : BSA @ JLab 12 GeV e p epg L = 1x1035 T = 2000 hrs DQ2 = 1 GeV2 Dx = 0.05 CLAS12 in HallB Projected results E = 11 GeV increase luminosity tenfold to > 1035 cm-2s-1 DsLU~sinfIm{F1H+..}df selected kinematics

  28. Sphere: Prolate: Q20=0 Q20/R2 > 0 Oblate: Q20/R2 < 0 electromagnetic N -> Δ(1232) transition J P=3/2+ (P33), M' 1232 MeV,  ' 115 MeV N ! transition:  N !  (99%),  N !  (<1%) non-zero values for E2 and C2 : measure of non-spherical distribution of charges spin 3/2 Role of quark core (quark spin flip) versus pion cloud

  29. Q2 dependence of E2/M1 and C2/M1 ratios data points : M1 MIT-Bates (Sparveris et al., 2005) MAMI : Q2 = 0 (Beck et al., 2000) Q2 = 0.06 (Stave et al., 2006) Q2 = 0.2 (Elsner et al., 2005, Sparveris et al., 2006) E2/M1 EFT calculation predicts the Q2 dependence C2/M1 no pion loops pion loops included Pascalutsa, Vdh (2005) also Gail, Hemmert

  30. mπ dependence of E2/M1 and C2/M1 ratios Q2 = 0.1 GeV2 quenched lattice QCD results : at mπ= 0.37, 0.45, 0.51 GeV linear extrapolation in mq ~ mπ2 Nicosia – MIT group :Alexandrou et al. (2005) EFT calculation discrepancy with lattice explained by chiral loops(pion cloud)! Pascalutsa, Vdh (2005) data points : MAMI, MIT-Bates

  31. Summary Nucleon form factors : -> high precision data at low Q2 : map out pion cloud of nucleon -> difference Rosenbluth vs polarization data GEp /GMp : mainly understood as due to two-photon exchange effects (new expt. planned) -> PV e-scattering : strangeness contributions to E and M distributions very small -> lattice QCD : state-of-art calculations go down to mπ~ 300 MeV, into the regime where chiral effects are important GPDs : -> unifying theme in hadron physics (form factors, parton distributions) -> provide a tomographic image of nucleon -> access to angular momentum of quarks/gluons in nucleon -> encouraging experimental results coming out of HERMES, H1/ZEUS, JLab@6 GeV indicating twist-2 dominance -> future programs : COMPASS, dedictated JLab@12 GeV, EIC… Nucleon excitation spectrum : -> precision data on NΔform factors : shape of hadrons -> chiral EFT is used in dual role : describe both observables and use in lattice extrapolations strong non-analytic behavior in quark mass due to opening of πN decay channel (interplay of scales)

More Related