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Photodisintegration of Few-Body Nuclei

Ron Gilman Rutgers / Jefferson Lab What have we learned? What might we learn?. Photodisintegration of Few-Body Nuclei. Jefferson Lab User Group The Next Seven Years June 16-18, 2004. Low energy theory uses nucleons + π's + ...

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Photodisintegration of Few-Body Nuclei

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  1. Ron Gilman Rutgers / Jefferson Lab What have we learned? What might we learn? Photodisintegration ofFew-Body Nuclei Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  2. Low energy theory uses nucleons + π's + ... A consistent NN force determines scattering and bound state nuclear wave functions Beautiful detailed calculations nicely explain data; there are also good PT calculations near threshold Low Energy Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  3. Conventional theory is more complicated and less successful Is there good control of: relativity? the short-range nuclear structure? meson and baryon resonances? The worst case is shown. Medium Energy Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  4. The Arenhoevel – Schwamb theory predicts large induced polarizations, but the angle dependence is wrong. The older, simpler Bonn (Kang, Erbs, Pfeil, and Rollnik) calculation also has problems. The py Problem Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  5. Conventional theory complications get worse 286 (+) on-shell baryon-baryon channels appear by 4 GeV This suggests finding good effective quark degrees of freedom to average over all the resonances. High Energy Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  6. Hadrons and quarks are in principle alternate basis states, and the theory can be formulated with either But... is there some indication of a transition or phase change, a behavior that is simple (difficult) to understand with a quark (hadronic) model? The usual choice: do the cross sections fall with energy according to the constituent counting rules of QCD: d/dt ∝ s-(n-2) High-Energy Motivation Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  7. The CCR work amazingly well (data: P. Rossi et al., hep-ph/0405207), n ~ 11, over a large angular range, once Pt ~ 1 – 1.3 GeV Why? pQCD Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  8. Most models based on upper diagram, some directly relate photodisintegration to NN scattering Quark-Gluon String (Regge) theory also applied (to NN scattering as well) Models Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  9. At 90o, all the models and the data fall about like s-11, at sufficiently high energy Models vs. Data Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  10. Data at other angles confirm the observations from the 90o data Since the cross sections do not clearly distinguish between the models, we turn to the polarizations Models vs. Data II Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  11. Simple discussion: pQCD ⇨ hadron helicity conservation ⇨py = 0 But Sargsian / HRM also predicts small py, based on NN scattering Polarizations-py Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  12. Generally expected HHC⇨∑ = -1 Kondratyuk et al. pointed out that limit depends on isoscalar vs isovector coupling, could range from -1 → 1 Polarizations-∑ Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  13. HHC⇨Cx',z'→ 0 as 1/t, 1/t2 HRM predicts Cx' small, Cz' similar to QGS Unpublished data: 2 GeV angular distribution, should be done in a few months Polarizations - Cx', Cz' Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  14. Data are not very different from pQCD expectations, even though we expect ``soft'' physics to dominate There are several more or less satisfactory approaches, in terms of describing the data, despite very different underlying mechanisms In particular, if you reproduce the NN in some model, you probably do OK on the d → pn This is not a very satisfying result How can we do better? So What Have We Learned? Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  15. The same models that more or less agree for pn photodisintegration give very different predictions for pp photodisintegration (Sargsian) Thus, we need to study 3He → ppnspectator At low energies, the (pp)S=0 system in 3He has reduced interactions, so the pp/pn cross section ratio is small (Laget) At high energies, different quark models vary So What Might We Learn? Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  16. CLAS data from S. Niccolai Note large strength for low-momentum neutrons Analysis ongoing CLAS Data on 3He → ppn Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  17. CLAS has measured 3He → ppn up to about 1.5 GeV Note the ``spectator'' neutron peak (left), vs the three body breakup (right) CLAS Data on 3He → ppn Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  18. Use pn < 100 MeV/c RNA: pp >> pn HRM: pp > pn QGS: pp ~ pn TQC: pp << pn For the first three models, there is a dramatic change in pp/pn with energy 3He → ppn Predictions Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  19. n= (E-pz)/m is the light cone momentum fraction M Sargsian showed n is ~ unaffected by FSI If photodisintegration takes place on low (high) momentum nucleons, as in HRM (RNA), then the distribution is narrow (broad) The n Distribution Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  20. One interesting prediction from HRM: due to the oscillations in pp (vs. pn) with energy, the 3He photodisintegration will appear to fall as ~s-10 rather than s-11 over a wide range 3He → ppn Oscillations Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  21. Furthermore, the interesting spin physics in pp elastic scattering might be reflected in the pp photodisintegration spin observables If the high energy spin physics in pp arises from charm threshold, then there should also be interesting spin physics in the photodisintegration near strangeness threshold, about 1.6 GeV (Brodsky) No existing data would test this – perhaps we need a new proposal? 3He → ppn Predictions Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  22. d → pn is the most promising exclusive reaction for a transition to quark degrees of freedom ... but soft physics remains important, and we have several more or less okay quark models – so what is the correct way to think about the problem? pp → pp using 3He gives several handles on the underlying physics, through the ratio pp/pn, the shape of the n distribution, and the possible oscillations. With good luck and scheduling of E03-101, we will know the answer in a few years Conclusions Jefferson Lab User Group The Next Seven Years June 16-18, 2004

  23. For more on 3He → ppn: S. J. Brodsky et al., Phys. Lett. B 578, 69 (2003) Hall A E03-101: E. Piasetzky, R. Gilman et al. For a review of the deuteron photodisintegration (including the references I could not fit in here): R. Gilman and F. Gross, J. Phys. G 28, R37 (2002) The 3He program is largely due to M Sargsian and E Piasetzky, with additional large contributions from Brodsky, Frankfurt, Hiller, Miller, and Strikman, and Radyushkin, de Sanctis, Kondratyuk, and the E03-101 collaboration References, Acknowledgements Jefferson Lab User Group The Next Seven Years June 16-18, 2004

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