ProtonAntiproton Photoproduction on a Nucleon Andrei Afanasev Hampton

Proton-Antiproton Photoproduction on a Nucleon Andrei Afanasev Hampton University and Jefferson Lab Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Plan of Talk . Available data on p-pbar photoproduction. Theoretical interpretation and problems addressed. Near-threshold p-pbar interactions; hadronic spectroscopy. Cross-channels for hard exclusive reactions; time-like form factors. Motivation for new measurements Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Proton-antiproton spectroscopy Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Recent Claims for P-anti. P states Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

BES Data Interpretation. . . BES Collab (2003): Near-threshold enhancement may be interpreted as a JPC= 0 -+ or 0++ state with M≈1850 Me. V and width <30 Me. V Sibirtsev et al. , PRD 71, 054010 (2005); Haidenbauer et al, PRD 74, 017501 (2006); p-pbar invariant-mass enhancement can be reproduced by the final-state p-pbar interactions; but other interpretations are not ruled out Entem, Fernandez, PRD 75, 014004 (2007): final-state 3 P 0 Figure from Haidenbauer et al. Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Cross Section Data on From Bodenkamp et al, PL 133 B, 275 (1983); also claimed observation of X(2020) signal in p anti-p invariant mass Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

CLAS Data vs Phase Space (comparison by A. Sibirstev) Enhancement at smaller invariant mass Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Theoretical estimates for the cross section (Afanasev, in progress) . . Pion-exchange in t-channel Constraints on the sub-process amplitude obtained from annihilation at rest; BR (=1. 5% measured at CERN PS) assumed energy-independent Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Comparison with CLAS data from B. Stokes, APS Meeting Talk, Nashville, TN, Oct. 2006 Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Theoretical Progress . Theory work in progress: Afanasev, Sibirtsev. Small invariant masses of p-pbar: spectroscopy, low-energy p-pbar interactions. Experimental requirements: PWA analysis to identify quantum numbers of states responsible for threshold enhancement=> need good energy and angular resolution, high statistics; higher beam energy provides kinematic separation of t-channel exchange; linear polarization for t-exchange naturality meas. . Large invariant masses: cross-channels for hard exclusive reactions, GPDs; reggeized baryon exchange. Experiment: higher energies, angular resolution, luminosity (to compensate for small cross sections) Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Hard Exclusive Reactions. . . 1973: Constituent counting rules: Brodsky, Farrar; Matveev, Muradyan, Tavhelidze 1979: QCD for exclusive reactions: Efremov, Radyushkin; Brodsky, Lepage 1996: GPDs: Ji, Radyushkin, et al. Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Belle Collab. , PL B 621, 41 (2005) • Hard exclusive kinematics • Compared with Kroll et al. calculations • Also γγ→pion and kaon pairs From BELLE (2006) Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Belle (2005) Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Nucleon Time-Like Form Factors. Process e+e-→p+pbar, most recently studied by BABAR Collab, PRD 73, 012005 (2006). Scanned through a broad range of p-pbar invariant masses Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Compton Scattering on a Pion. . Coriano, Radyushkin, Sterman, Nucl. Phys. B 405: 481 -506, 1993, QCD sum rules for γπ→γπ Afanasev, hep-ph/9808291; predicted scaling violations in γπ→γπ using pion GPDs from hep-ph/9808291 Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08

Summary . . Photoproduction of p-pbar pairs allows studies of. p-pbar interaction near threshold; hadronic spectroscopy. Access cross-channels of hard exclusive reactions on a nucleon Compton scattering on a pion at large transverse momenta: a test of the mechanism of hard exclusive scattering Andrei Afanasev, Workshop on Photon-Hadron Physics with Glue. X, 3/6/08