Pion Photoproduction from the Nucleon and Scaling Dipangkar Dutta : Duke University & TUNL Spokespersons: Haiyan Gao, Dipangkar Dutta, Patrizia Rossi vs Pion Electroproduction from the Nucleon and Scaling Kijun Park University of South Carolina

Challenge Ana. proposal Outline Introduction Constituent quark counting JLab experiment E94-104 on photo-pion production from the nucleon [Hall-A] New proposal (can run with Super-G [E04-005] ) Challenge Ana. proposal New Window : Observe the dσ/dt in single pion electro-production with existed data [E99-107] γp→π+n vs. γ*p→π+n Original Exp. proposal

Introduction Mapping the transition from the nucleon-meson degrees of freedom to the quark-gluon degrees of freedom of QCD. In order to describe nucleons and nuclei in terms of quarks and gluons one needs to reconcile these two pictures. In trying to do that a natural questions is … Nucleon-meson degrees of freedom effective at low energies Quark-gluon degrees of freedom at high energies

Constituent Counting Rule Exclusive two body reactions (A+B C+D) at large momentum transfers should scale as: s = c.m. energy sq. n = # of constituent fields First derived based on dimensional analysis (Matveev et al., Brodsky, Farrar,….) Confirmed within short distance pQCD framework (Brodsky, LePage) Recently, derived from anti-de Sitter/Conformal Field Theory correspondence or string/gauge duality ( Polchinski, Strassler …..) Many exclusive processes exhibit global scaling behavior elastic pp scattering @ 90 deg CM angle (dσ/dt S-10) deuteron photo-disintegration at large angles (dσ/dt S-11) C. Bochna et al., PRL 81, 4576 (1998), E.C. Schulte, et al., PRL 87, 102302 (2001), M. Mirazita et al., PRC 70, 014005 (2004), P. Rossi, PRL 94,012301 (2005). Photopion production from nucleon at large angles L.Y. Zhu et al., PRL 91, 022003 (2003)

p-p elastic scattering at 900 Deuteron Photodisintegration Scaling onset: Pt~1.2 GeV/c From data compilation of Landshoff and Polkinghorn E. Schulte et al. PRL 87, 102302 (2001) Bochna et al., PRL 81, 4576 (1998)

p-p elastic scattering at 900 What is the origin for such oscillatory scaling behavior? R = s10ds/dt Global scaling in good agreement with constituent quark counting Detailed investigation reveals oscillatory scaling behavior Oscillatory Scaling Behavior The oscillations in the scaled cross-section explained as: Resonance state production near the charm threshold (Brodsky, Schmidt, etc). Interference between short distance (Born) and long distance (Landshoff) amplitudes, (Ralston & Pire and Carlson, Myhrer, …)

Exciting New Developments ``restricted locality'' of quark-hadron duality results in oscillations (Zhao & Close). a generalized counting rule based on pQCD analysis, by systematically enumerating the Fock components of a hadronic light-cone wave function. (Ji, Ma & Yuan and also Brodsky et al.) The generalized counting rule includes parton orbital angular momentum and hadron helicity flip. They provide the scaling behavior of the helicity flipping amplitudes If = 0; reduces to constituent quark counting rule of Brodsky-Farrar. number of partons orbital angular momentum projection

Generalized Counting Rule & pp Elastic Scattering Using their Generalized Counting Rule Ji et al. predict the s dependence of the helicity flipping amplitudes in pp elastic scattering as ~S-4.5 and ~S-5 no hel. flip with hel. flip D.Dutta and H. Gao, hep-ph/0411267 (accepted for publication in PRC as rapid comm. )

Photopion Production (n=9)

Transition observed (90 degree)? NN n-2=9 L.Y. Zhu, PRL 91, 022003 (2003) Scale factor of 5.4!

Limited angular distribution L.Y. Zhu et al., Nucl-exp/0409018, PRC 71, 044603 (2005)

Scaling at 90 degree between 2.0 -2.5 GeV Very narrow energy window for transition? Scaled data show resonance structure around 2.2 GeV center-of-mass energy Missing nucleon resonances from QM? Threshold associated with strange quark? Brodsky, de Teramond (1988) N bound state? Brodsky, Schmidt, de Teramond (1990) De Teramond et al. (1998) Gao, Lee and Marinov (2001) What can CLAS do? Very fine energy scan of the scaled differential cross-section in this interesting center-of-mass energy region Angular dependence of the scaled differential cross-section, important to identify the enhancement around 2.0 GeV It can also be used to investigate contributions from helicity non-conserving amplitudes. Ideally one would like to study all nucleon photopion production channels, but new proposal is to measure p+ production.

We have looked at single p+ events. During g11 running period, one run taken with one charge particle trigger.- Patrizia Rossi (priv. comm.) single p+ events at 900 C.M. angle, used to estimate projected results for new proposal.

Kinematic limitaiton : Absence of models Angular Coverage Kinematic Coverage E99-107 Experiments W & Q2 Ranges

New Proposal Projected Results Assuming same running conditions as g11a, and same target. For 1000 hrs of running as approved for superG 1. Collect pre-scaled singles (one charge particle trigger) events during super-G (E04-005) running period. 2. Analyze γp→nπ+ events for a fine energy scan of the scaled cross-section at 900 C.M.angle to verify scaling behavior seen in E94104. 3. Also investigate the angular dependence of the scaled cross-section, specially around √s= 2.0 GeV where an enhancement is seen. Collaboration Duke University / George Washington University / INFN, Laboratori Nazionali di Frascati / Carnegie Mellon University / Rensselaer Polytechnic Institute / SLAC, Stanford University / University de Costa Rica / University of Illinois, Urbana, IL

Transition observed (90 degree) in pion electroproduction

Q2 dependence

CLAS data Rossi et al,PRL 94, 012301 (2005)