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Gluons in the proton and exclusive hard diffraction. Introduction soft, hard interactions gluons data on exclusive vector meson electroproduction sizes of gluon cloud sizes of photon configurations effective Pomeron trajectory comparison to theory. Aharon Levy - PowerPoint PPT Presentation
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Gluons in the proton and exclusive hard diffractionAharon LevyTel Aviv University and MPI Introduction soft, hard interactions gluons data on exclusive vector meson electroproduction sizes of gluon cloud sizes of photon configurations effective Pomeron trajectory comparison to theory
Aharon Levy - Hosza seminar
Aharon Levy - Hosza seminar
LHeC
Aharon Levy - Hosza seminar
Deep Inelastic kinematicsSpin[20 fb-1 /point]
Aharon Levy - Hosza seminar
McAllister, HofstadterEe=188 MeVrmin=0.4 fmBloom et al. 10 GeV 0.05 fmCERN, FNAL fixed target 500 GeV 0.007 fmHERA 50 TeV 0.0007 fmHERA KinematicsEe=27.5 GeVEP=920 GeVs=(k+P)2 = (320 GeV)2Transverse distance scale:Impact parameter:where t is the square of the 4-momentumtransferred to the proton
Aharon Levy - Hosza seminar
Proton momentum framePartons frozen during time of interaction. Virtual photon samples the quark distribution.Assume that partons form incoherent beam. The parton density distributions are meant to be universal quantities.
Aharon Levy - Hosza seminar
Proton rest-framesoft and hard studied by W (or x~1/W2) dependence of the cross section.
Aharon Levy - Hosza seminar
soft
high energy behavior tot s0.08Donnachie and Lanshoff universal behavior of total hadron-hadron cross section :
Aharon Levy - Hosza seminar
Regge trajectories
Aharon Levy - Hosza seminar
hardThe rise of F2 with decreasing x is strongly dependent on Q2.DIS:
Aharon Levy - Hosza seminar
soft hardBelow Q2 0.5 GeV2, see same energy dependence as observed in hadron-hadron interactions. Start to resolve the partons.
Aharon Levy - Hosza seminar
QCD based fits can follow the data accurately, yield parton densities. BUT: many free parameters (18-30) (only know how parton densities evolve)
form of parameterisation fixed by hand (not given by theory)
F2 parton densities. * sees partons. parton density increases with decreasing x.
Aharon Levy - Hosza seminar
From Pumplin, DIS05There are signs that DGLAP (Q2 evolution) may be in trouble at small x (negative gluons, high 2 for fits).
Need better data to test whether our parton densities are reasonable. The structure function FL will provide an important test. all is not well Can also get information on gluon density from exclusive hard processes.
Aharon Levy - Hosza seminar
Exclusive VM electroproduction(V0 = DVCS)
Aharon Levy - Hosza seminar
soft to hard transition Expect to increase from soft (~0.2, from soft Pomeron value) to hard (~0.8, from xg(x,Q2)2) Expect b to decrease from soft (~10 GeV-2) to hard (~4-5 GeV-2)
Aharon Levy - Hosza seminar
ingredientsUse QED for photon wave function. Study properties of V-meson wf and the gluon density in the proton.
Aharon Levy - Hosza seminar
Mass distributions
Aharon Levy - Hosza seminar
Photoproduction process becomes hard as scale (mass) becomes larger.
Aharon Levy - Hosza seminar
(W) 0 Fix mass change Q2
Aharon Levy - Hosza seminar
(W) - , J/,
Aharon Levy - Hosza seminar
(Q2+M2) - VM
Aharon Levy - Hosza seminar
(Q2)Fit to whole Q2 range gives bad 2/df (~70)
VMncomments2.440.09Q2>10 GeV22.750.13 0.07Q2>10 GeV2J/2.4860.0800.068All Q21.540.09 0.04Q2>3 GeV2
Aharon Levy - Hosza seminar
b(Q2) 0,
Aharon Levy - Hosza seminar
b(Q2+M2) - VM
Aharon Levy - Hosza seminar
Frankfurt - Strikman
Aharon Levy - Hosza seminar
Information on L and T Use 0 decay angular distribution to get r0400 density matrix element - ratio of longitudinal- to transverse-photon fluxes ( = 0.996)using SCHC
Aharon Levy - Hosza seminar
R=L/T (Q2)When r0004 close to 1, error on R large and asymmetric advantageous to use r0004 rather than R.
Aharon Levy - Hosza seminar
Photon configuration - sizesT: large size small size strong color forces color screening large cross section small cross section*: *T, *L*T both sizes, *L small size
Aharon Levy - Hosza seminar
L/tot(W)
Aharon Levy - Hosza seminar
L/tot(t)
Aharon Levy - Hosza seminar
(W) - DVCSFinal state is real Tusing SCHC initial * is *Tbut W dep of steep large *T configurations suppressed
Aharon Levy - Hosza seminar
Effective Pomeron trajectory0 photoproduction
Aharon Levy - Hosza seminar
Effective Pomeron trajectory0 electroproduction
Aharon Levy - Hosza seminar
Comparison to theory All theories use dipole picture Use QED for photon wave function Use models for VM wave function usually take a Gaussian shape Use gluon density in the proton Some use saturation model, others take sum of nonperturbative + pQCD calculation, and some just start at higher Q2 Most work in configuration space, MRT works in momentum space. Configuration space puts emphasis on VM wave function. Momentum space on the gluon distribution. W dependence information on the gluon Q2 and R properties of the wave function
Aharon Levy - Hosza seminar
0 data - Comparison to theoryMartin-Ryskin-Teubner (MRT) work in momentum space, use parton-hadron duality, put emphasis on gluon density determination. Phys. Rev. D 62, 014022 (2000).Forshaw-Sandapen-Shaw (FSS) improved understanding of VM wf. Try Gaussian and DGKP (2-dim Gaussian with light-cone variables). Phys. Rev. D 69, 094013 (2004).Kowalski-Motyka-Watt (KMW) add impact parameter dependence, Q2 evolution DGLAP. Phys. Rev. D 74, 074016 (2006).Dosch-Ferreira (DF) focusing on the dipole cross section using Wilson loops. Use soft+hard Pomeron for an effective evolution. Eur. Phys. J. C 51, 83 (2007).
Aharon Levy - Hosza seminar
Q2KMW good for Q2>2GeV2 miss Q2=0DF miss most Q2FSS Gauss better than DGKP
Aharon Levy - Hosza seminar
Q2Data seem to preferMRST99 and CTEQ6.5M
Aharon Levy - Hosza seminar
W dependenceKMW - closeFSS:Sat-Gauss right W-dep. wrong norm. MRT:CTEQ6.5M slightly better in W-dep.
Aharon Levy - Hosza seminar
L/tot(Q2)
Aharon Levy - Hosza seminar
L/tot(W)All models have mild W dependence. None describes all kinematic regions.
Aharon Levy - Hosza seminar
Summary and conclusions
HERA data shows transition from soft to hard interactions.The cross section is rising with W and its logarithmic derivative in W, , increases with Q2.The exponential slope of the t distribution decreases with Q2 and levels off at about b = 5 GeV-2. Transverse size of gluon density (0.6 fm) inside the charge radius of the proton (0.8 fm).The ratio of cross sections induced by longitudinally and transversely polarised virtual photons increases with Q2, but is independent of W and t. The large configurations of the transversely polarised photon are suppressed.The effective Pomeron trajectory has a larger intercept and smaller slope than those extracted from soft interactions.All these features are compatible with expectations of perturbative QCD.None of the models which have been compared to the measurements are able to reproduce all the features of the data.Precision measurements of exclusive vector meson electroproduction can help determine the gluon density in the proton.
Aharon Levy - Hosza seminar
Fixed Q2>>0 to read Q2~0 (May 16,2005)