PR-05002:

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

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

3. Exclusive processesare 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. 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?

4. elastic pp scattering @ 90 deg CM angle ( ) deuteron photo-disintegration at large angles ( ) (eg. E89012, C. Bochna et al., PRL 81, 4576 (1998) 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 • First derived based on dimensional analysis (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: such as

5. Pion-photoproduction Recent JLab data (E94104) 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)

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

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

8. Oscillations are Not Unique to p-p Scattering

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

10. P P P P • Born amplitude gives the dominant helicity and s dependence P P P P • Independent scattering (Landshoff) amplitude P P P P Born vs Independent ScatteringAmplitude in p-p Scattering

11. a generalized counting rule based on pQCD 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 The Latest Idea to Explain Oscillatory Scaling Behavior

12. with hel. flip no hel. flip no hel. flip with hel. flip 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 D.Dutta and H. Gao, hep-ph/0411267

13. 1 2 L. Y. Zhu et al., PRL 91, 022003 (2003) 1 G. R. Farrar, et al. , PRL 62, 2229 (1989) 2 L. I. Frankfurt, et al., PRL 84, 3045 (2000) How About Photo Reactions? • Lacks two hadrons in the initial state, but Landshoff terms can contribute at sub-leading order. - 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. • Hints of oscillation seen in pion-photoproduction. Are oscillations a general feature of QCD ?

14. 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 ,2p) data However, Brodsky and de Teramond explain the same data in terms of excitation of charm resonance states.

15. 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.

16. The Complementary Color Transparency Phenomena CT refers to the vanishing of the h-N interaction for h produced in exclusive processes at high Q • Nuclear filtering uses the medium actively to suppress the long-distance amplitude. • In CT the large momentum transfer selects the short distance amplitude which is then free to propagate through the passivemedium. • 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.

17. 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 E94104 show CT like behavior. D.Dutta et al., PRC 68, 021001R (2003)

18. Proposed Experiment • 50 muA CW beam on 6% copper radiator • LH2, LD2, He4 targets and 2% solid C target • HRS-L for pi+ detection (for LH2 target) • HRS-R for pi- and HRS-L for proton detection • (for LD2, He-4 and Carbon targets) • Gas Cerenkov detector for e/pi separation • combination of aerogels A1 and A2 for p/pi • separation.

19. Proposed Experiment • ; just two body kinematics • for LD2, He4 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 E94-104 in Hall-A . Reconstructed photon energy spectrum for from E94-104

20. Proposed Experiment • Same technique as E94104, use 100 MeV • window. • Transparency will be extracted using : Simulated photon energy spectrum for

21. Rates and Backgrounds • The H,D,He4 rates determined from observed E94-104 rates. • The Carbon rates were obtained by comparing He-4 rates from E94-104 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 E94-104 rates.

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

23. Projected Results

24. Summary • Studying the details of the agreement withquark counting rule is crucial to understand the exact mechanism behind the onset of scaling in exclusive processes. • These studies are also important to learn about the contribution of helicity non-conserving amplitudes and quark orbital angular momentum. • E94104 data show hints of oscillations about the scaling behavior. • A fine scan of the scaling region for photo-pion production is needed 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 E94104 data on Helium-4 show hints of CT like behavior.