High-t Exclusive Reactions With Real

Photons

High-t Exclusive Reactions With Real

Photons

Gerald A. Miller, UW

Outline

• Constituent counting rules-

challenge and opportunity

• (Real) Compton scattering

• Transition from hadrons to quarks, gluons using nuclear targets (with M. Strikman)

• Exclusive reactions to test exotic nature of

mesons (with M. Strikman)

1973

Remarkable success –quarks are real

Constituent Counting Rules -Assumptions

• Physical mesons, baryons –s wave bound states , finite wave function at zero separation

• Large s, -t• Disconnected Landshoff graphs unimportant

Remarkable success

Large angle pion production

Transition? at s between 3 and 6 GeV2 ,

t between 1 and 2.2

GeV2

Data from 1970’s

ntot -2= 1+3+2+3-2=7

JLab counts! (s1/2>2.5) Hall A, Zhu et alPhys. Rev. C 71, 044603 (2005)

More opportunities to check scaling

JLab range of s

11 - 21 GeV2

Challenges to

8

Kroll

Puzzle• Why does constituent counting work so

well for N→ N but NOT for N → N ?

• Kinematics are similar-another graph?

N N

s-8

Modern Interest?• AdS/CFT correspondence provides a set of solvable, non-perturbative field theories• scale (conformal) invariant• High momentum transfer exclusive reactions

obey constituent counting rules. There are NO partons, Polchinski and Strassler

• Conformal dimension plays role of nH

• Theorists playground- learn how to calculate• Renewed interest in constituent counting• If constituent counting ruled out at high s,t –

these insights are not valid 50 million high-energy theorists wrong

Summary of Constituent Counting

• Constituent counting is important

• Relates to AdS/CFT

• When occurring, provides a tool (see below)

• puzzle –pion photoproduction vs RCS

Real Compton Scattering RCS

• p elastic scattering

• simplest process?

• many diagrams –samples below

HandbagpQCD

RCS > reaction physics-GPDs

GPD

Elastic Form Factor

DIS –parton dist

DVCSRCS

RCS > reaction physics-GPDs

GPD

Elastic Form Factor

DIS –parton dist

RCS

0Pretty much all

• d/dt ~1/s8.0 +/- 0.02

constituent counting: 1/s6

Solid Handbag –KrollDashed Handbag -Miller\

Danagoulian et al Hall A

wave function,

transverse quark momentum

constituent quark mass

Hamilton et al Hall A

CQM- Miller

GPD-Huang, Kroll Morii

Regge –Cano Laget

ASY, COZ- pQCD- Brooks Dixon with different dist. amps

KLL is not ALL

=ALL (Kroll)

non-vanishing constituent quark mass causes KLL ≠ALL

Summary of RCS

• RCS has direct connection to DIS and elastic form factors

• Constituent counting not reached yet

• KLL ≠ ALL a new test of models

Constituent counting and the hadron-quark transition

• Remainder of talk

• Assume constituent counting holds at

high enough s, -t (50 million high energy theorists can’t be wrong)

• Quark degrees of freedom dominate

• How to exploit

Hadron-Quark Transition N πN

N N

high -tlow -t

)

high -t

NN

t=2/m2

Hadronic regime has long lived

How to see go away ?

N → N Transparency vs. A,

/A /A10GeV

5 GeV

-(t-t0) GeV2-(t-t0) GeV2

/A

10 GeV

5 GeV

nuclear RCS to understand puzzle

N N

in nuclei, A dependence ?

Not proportional to A

Can use (A, t) - dependence of quasielastic

N → N, to find Hadron-Quark Transition

use N →

Summary of High –t exclusive in nuclei

Constituent Counting and Exotics production at large s, angle

Exotic meson X: nX=n +1 (or 2)

ntot= 9,10

High s, angle ratio:

N → N, ntot=9

Summary of summaries

• Constituent counting CC is important• Relates to AdS/CFT• When occurring, provides a tool• RCS DIS, elastic form factors• Constituent counting not yet reached in RCS• KLL ≠ ALL new test of models in RCS• Can use (A, t) - dependence of quasielastic

N → N, to find Hadron-Quark Transition, understand RCS• Can use CC to find or verify exotics

Spares follow

Kroll 2007