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Photoproduction in Nuclei

Photoproduction in Nuclei. Z.-E. Meziani Temple University. Photon-hadron physics with the GlueX detector at Jefferson Lab. Thursday, March 6 - Saturday, March 8, 2008. Motivation: Explore the Q C D Van der Waals interaction. The interaction is described with multiple-gluon exchange

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Photoproduction in Nuclei

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  1. Photoproduction in Nuclei Z.-E. Meziani Temple University Photon-hadron physics with the GlueX detector at Jefferson Lab Thursday, March 6 - Saturday, March 8, 2008 PHP 2008, Newport News, VA

  2. Motivation: Explore the QCD Van der Waals interaction • The interaction is described with multiple-gluon exchange • On what systems is it clean: • Interaction between color neutral systems with no quark exchange (OZI rule) • J/Psi (heavy quarkonium) and the nucleon or J/Psi and the nucleus. • What do we expect to learn • Range and magnitude of the gluonic potential • One should explore the interaction using Lattice QCD and AdS/CFT • If the interaction is attractive enough can we have Nuclear-Bound Quarkonium? PHP 2008, Newport News, VA

  3. Theoretical history • As in QED the QCD Van der Waals force is attractive. • Question: Is the force attractive enough to have in principle a bound system? • Brodsky, Schmidt and de Teramond in 1990 proposed the idea of nuclear-bound quarkonium as a consequence of QCD Van der Waals forces. PRL 64, 1011 (1990) • Binding estimated to be as large as 120 MeV in a light nucleus light He4 and as high as 400 MeV for A = 9 • Wasson, made a correction to the nuclear potential and solved the charmonium-nucleus Schrodinger equation. He concluded that the binding is less than 30 MeV for all nuclei. PRL 67 (1991) 2237 • Luke, Manohar and Savage did a calculation using OPE to describe the low energy interaction of quarkonium with nuclei in the limit where the mass of the c quark --> infinity. They find that the J/Psi binds in nuclear matter with about 10 MeV and caution about large corrections to the result due to confinement effects. PLB 288 (1992)335 PHP 2008, Newport News, VA

  4. For completeness • A. B. Kaidalov and P.E. Volkovitsky PRL 69 (1992) 3155 • S-wave quarkonia can be bound in nuclei withA>10 with binding energy of the order of some MeV • G. de Teramond and R. Espinoza, PRD 58 (1998) 034012 • Estimate a binding of about2 MeVin 12C and10 MeVin 208Pb. • V. I. ShevchenkoPhys. Lett B 392 (1997) 457. Interaction of charmonium- nucleon is so small that the potential depth for nuclear bound states may be only for A = 200 • S. Brodsky and G. Miller, PLB 412 (1997) 125. Answered the question about whether the Van der Waals force dominates the J/psi-nucleon scattering. • A. Hayashigaki, Prog.Theor. Phys.101 (1999) 923 • Applying QCD sum rules finds a 4 to 7 MeV binding of J/Psi in nuclear matter • A. Sibirtsev and M.B. VoloshinPRD 71, (2005) 076005 • “…J/Psi nucleon elastic scattering is very likely to exceed 17mb and that existence of bound state of the J/Psi in light nuclei is possible”. • K. Yokokawa, S. Sazaki, T. Hatsuda and A. Hayashigaki, PRD 74 (2006) 034504. First Lattice (quenched) study of low energy charmonium-hadron interaction PHP 2008, Newport News, VA

  5. For completeness (continued) • S.J.Brodsky,E.Chudakov,P.Hoyer,andJ.M.Laget.Photoproduction ofcharm near threshold.Phys.Lett.,B498:23–28,2001. • A. Sbirtsev, S. Krewald and A.Thomas,Journal of Physical G 30 (2004) 1427 • We attribute the J/Ψ photoproduction at low energies and large |t| to a mechanism different from pomeron or two-gluonexchange. We consider that this might be the exchange of an axial vector trajectory that couples with the axial form factor of the nucleon. • . • . • . PHP 2008, Newport News, VA

  6. The experimental situation • Many experiments at high photon energies and low t • Not much is known about threshold region and high t • A recently completed experiment (E03-008) at JLab Hall C in the subthreshold region E=5.7 GeV hasn’t seen a signal and needs to be understood. • In the subthreshold region (E<8.2 GeV) nuclei are critical to produce the J/Psi and maximize its interaction with the recoil nucleus. Not much data. PHP 2008, Newport News, VA

  7. Existing J/Psi Photoproduction Experiments Summary PHP 2008, Newport News, VA

  8. c c V Nucleon Nucleus Quarkonium Bound State • Start with an energy above the free nucleon threshold on a nuclear target (9 GeV) • Insure that the production occurs on a nucleon close to being on shell in the nucleus. • Lower the energy to 6 GeV and now measure the production in subthresold kinematics. PHP 2008, Newport News, VA

  9. Subthreshold kinematics for incoherent production in nuclei Photon energy vs nucleon initial momentum PHP 2008, Newport News, VA

  10. Kinematics (continued)relative velocity versus t Deuterium Helium PHP 2008, Newport News, VA

  11. Lab angle vs momentum of the decay pair With a cut for small relative velocity With a cut for small relative velocity PHP 2008, Newport News, VA

  12. Coherent production on Pbrelative velocity • Low relative velocity at large t PHP 2008, Newport News, VA

  13. Kinematics for Coherent Production • Pairs from J/Psi with low relative velocity with respect to the recoiling nucleus Momentum of leptons (GeV) PHP 2008, Newport News, VA

  14. Detector • Large coverage to accept slow moving J/Psi in the lab. • Pairs will have a large opening angle for kinematics where the relative velocity between the J/Psi and the recoiling nucleus is small. • J/Psi mass reconstruction needs resolution to observe any mass shift PHP 2008, Newport News, VA

  15. Conclusion • The problem of understanding Van der Waals forces in QCD is important • Lattice QCD, AdS/CFT could give a greater insight into the pure gluonic potential • Detector with large angles coverage and good resolution is important for the subthreshold J/Psi and coherent measurements • More work on simulation is needed. PHP 2008, Newport News, VA

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