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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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ron gilman rutgers jefferson lab what have we learned what might we learn
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

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 are also good PT calculations near threshold

Low Energy

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

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.

Medium Energy

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

the p y 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.

The py Problem

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

high energy

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

high energy motivation

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

slide7
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

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)

Models

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

at 90 o all the models and the data fall about like s 11 at sufficiently high energy
At 90o, all the models and the data fall about like s-11, at sufficiently high energyModels vs. Data

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

models vs data ii

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

slide11
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

polarizations

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

polarizations c x c z

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

so what have we learned

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

so what might we learn

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

clas data from s niccolai note large strength for low momentum neutrons analysis ongoing
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

slide17
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

3 he ppn predictions

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

the n distribution

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

3 he ppn oscillations

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

3 he ppn predictions1

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

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 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

references acknowledgements

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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