Photodisintegration of FewBody Nuclei Ron Gilman Rutgers Jefferson

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

Low Energy ● ● ● 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 also good � PT calculations near threshold Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

Medium Energy ● ● ● 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. Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

The py Problem ● ● 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. Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

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

High-Energy Motivation Hadrons and quarks are in principle alternate basis states, and 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) ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

p. QCD The CCR work amazingly well (data: P. Rossi et al. , hepph/0405207), n ~ 11, over a large angular range, once Pt ~ 1 – 1. 3 Ge. V ● Why? ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

Models 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) ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

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

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

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

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

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

So What Have We Learned? Data are not very different from p. QCD 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? ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

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

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

CLAS Data on CLAS has 3 measured � He → ppn up to about 1. 5 Ge. V ● Note the ``spectator'' neutron peak (left), vs the three body breakup (right) 3 �He → ppn ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

3 �He → ppn Predictions Use pn < 100 Me. V/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 ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

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

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

3 �He → ppn Predictions 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 Ge. V (Brodsky) ● No existing data would test this – perhaps we need a new proposal? ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

Conclusions � 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 3 He gives several handles on the underlying physics, through the ratio � /�, the pp pn shape of the � n distribution, and the possible oscillations. ● With good luck and scheduling of E 03 -101, we will know the answer in a few years ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,

References, Acknowledgements 3 He → ppn: For more on � ● S. J. Brodsky et al. , Phys. Lett. B 578, 69 (2003) ● Hall A E 03 -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, R 37 (2002) 3 ● The � He 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 E 03 -101 collaboration ● Jefferson Lab User Group The Next Seven Years 2004 June 16 -18,