# PR05002 Dipangkar Dutta TUNLDuke University Hall A Collaboration

PR-05002: Dipangkar Dutta TUNL/Duke University Hall A Collaboration Experiment Spokespersons: Dipangkar Dutta, Haiyan Gao and Roy Holt

Outline l Introduction l Motivation § Oscillatory Scaling § Nuclear Filtering/ Color Transparency l Proposed Experiment § Only three different Linac energies l Projected Results l Summary

Introduction Map out the transition from the quark and gluon degrees of freedom of QCD to the Nucleon-meson degrees of freedom. What is the Energy/Momentum Threshold for the Transition? Exclusive processes are crucial in studying this transition region. Exclusive processes on Nucleons • Differential cross-sections measurements: quark counting rules, formfactors, oscillations, GPDs, generalized counting rules. • Polarization measurements: Hadron helicity conservation. Exclusive processes on Nuclei • Search for Color Transparency & Nuclear filtering effects.

The Constituent Quark 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 l l l First derived based on dimensional analysis (Brodsky, Farrar, …. ) Confirmed within short distance p. QCD framework (Brodsky, Le. Page) Recently, derived from anti-de Sitter/Conformal Field Theory correspondence or string/gauge duality ( Polchinski, Strassler …. . ) Many exclusive processes exhibit global scaling behavior: such as elastic pp scattering @ 90 deg CM angle ( deuteron photo-disintegration at large angles ( (eg. E 89012, C. Bochna et al. , PRL 81, 4576 (1998) ) )

Pion-photoproduction Recent JLab data (E 94104) on photo-pion production show scaling behavior at large C. M. angles. quark counting rule predicts L. Y. Zhu et al. , PRL 91, 022003 (2003)

Hadron Helicity Conservation Short distance p. QCD predicts helicity conservation in exclusive two-body processes (A+B C+D) l. A + l B = l l l. C + l. D Based on quark helicity conservation, neglecting quark orbital angular momentum. Experimental data tends not to agree with HHC. elastic pp scattering; Polarization Transfer 0 1 2 Eg ( Ge. V ) K. Wijesooriya et al. , PRL 86, 2975 (2001)

Quark Counting Rule vs HHC Global scaling behavior has been observed l But experimental data do not support HHC. l Short-distance physics may not be the full picture. • Detailed investigation of the agreement with quark counting rule is necessary. l Example: pp elastic scattering J. P. Ralston and B. Pire, PRL 61, 1823 (1988)

Oscillations are Not Unique to p-p Scattering

Oscillatory Scaling Behavior The large spin correlation and oscillations in the scaled cross-section explained as: q Resonance state production near the charm threshold (Brodsky, Schmidt , ……. ). q ``restricted locality'' of quark-hadron duality results in oscillations (Zhao & Close). q Interference between short distance (Born) and long distance (Landshoff) amplitudes, (Ralston & Pire and Carlson, Myhrer, ……. )

Born vs Independent Scattering Amplitude in p-p Scattering P § Born amplitude P P P gives the dominant helicity and s dependence P P P § Independent scattering (Landshoff) amplitude P P P

The Latest Idea to Explain Oscillatory Scaling Behavior q a generalized counting rule based on p. QCD analysis, by systematically enumerating the Fock components of a hadronic light-cone wave function. (Ji, Ma & Yuan) • The generalized counting rule includes parton orbital angular momentum and hadron helicity flip. • They provide the scaling behavior of the helicity flipping amplitudes which were neglected in previous derivations of the quark counting rule. 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 and no hel. flip D. Dutta and H. Gao, hep-ph/0411267 with hel. flip

How About Photo Reactions? § Lacks two hadrons in the initial state, but Landshoff terms can contribute at sub-leading order. 1 - can also contribute due to fluctuations to a vector-meson. § Oscillations can be due to final state interactions. § Similar oscillations predicted in deuteron photo-disintegration. 2 • Hints of oscillation seen in pion-photoproduction. L. Y. Zhu et al. , PRL 91, 022003 (2003) Are oscillations a general feature of QCD ? 1 G. R. Farrar, et al. , PRL 62, 2229 (1989) 2 L. I. Frankfurt, et al. , PRL 84, 3045 (2000)

What Happens to Oscillations in the Nuclear Medium? Nuclear filtering effect predicts that they are filtered out in the nuclear medium. One explaination for the BNL A(p , 2 p) data However, Brodsky and de Teramond explain the same data in terms of excitation of charm resonance states.

Nuclear Filtering with Photo-pions 12 12 T - § Large oscillations in photo-pion transparency predicted by Jain, Kundu and Ralston [PRD 65, 094027 (2002)]. § Amplitude depends on an additional nuclear phase. § Can be tested with photo-pion production from Carbon.

The Complementary Color Transparency Phenomena CT refers to the vanishing of the h-N interaction for h produced in exclusive processes at high Q l Nuclear filtering uses the medium actively to suppress the long-distance amplitude. l In CT the large momentum transfer selects the short distance amplitude which is then free to propagate through the passive medium. l The onset of CT is expected to be sooner on lighter nuclei, while nuclear filtering effect is bigger in heavier nuclei There is no unambiguous, model independent, evidence for CT in qqq systems.

Recent Transparency Data §Small size is more probable in 2 quark system such as pions. Onset of CT expected at lower Q in qq system. § Photo-pion production data from E 94104 show CT like behavior. D. Dutta et al. , PRC 68, 021001 R (2003)

Proposed Experiment • 50 mu. A CW beam on 6% copper radiator • LH 2, LD 2, He 4 targets and 2% solid C target • HRS-L for pi+ detection (for LH 2 target) • HRS-R for pi- and HRS-L for proton detection (for LD 2, He-4 and Carbon targets) • Gas Cerenkov detector for e/pi separation combination of aerogels A 1 and A 2 for p/pi separation.

Proposed Experiment • ; just two body kinematics • for LD 2, He 4 and C target we need momentum and angle of both proton and pion to reconstruct the photon energy. • The technique has been well established in experiment E 94 -104 in Hall-A. Reconstructed photon energy spectrum for from E 94 -104

Proposed Experiment • Same technique as E 94104, use 100 Me. V window. • Transparency will be extracted using : Simulated photon energy spectrum for

Rates and Backgrounds • The H, D, He 4 rates determined from observed E 94 -104 rates. • The Carbon rates were obtained by comparing He-4 rates from E 94 -104 to Monte Carlo simulations of He and carbon and an estimate of the relative transparency of carbon. • Singles rates and e/pi ratios all estimated from observed E 94 -104 rates.

Beam Time Request Need 7 different energies but with just 3 different linac energies

Projected Results

Summary § Studying the details of the agreement with quark counting rule is crucial to understand the exact mechanism behind the onset of scalin in exclusive processes. § These studies are also important to learn about the contribution helicity non-conserving amplitudes and quark orbital angular momentum. § E 94104 data show hints of oscillations about the scaling behavior. § A fine scan of the scaling region for photo-pion production is need to confirm and quantify these oscillations. § This can be performed with 7 different energies (3 linac energies) § The photo-pion transparency for Carbon can be used to test the nuclear filtering effect. While the same on Helium-4 can help look for CT. § The E 94104 data on Helium-4 show hints of CT like behavior.

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