Hampton University Graduate Studies 2003

Hampton University Graduate Studies 2003

(e,e'p) and Nuclear Structure

Paul Ulmer

Old Dominion University

Thanks to:

W. Boeglin

T.W. Donnelly (Nuclear physics course at MIT)

J. Gilfoyle

R. Gilman

R. Niyazov

J. Kelly (Adv. Nucl. Phys. 23, 75 (1996))

B. Reitz

A. Saha

S. Strauch

E. Voutier

L. Weinstein

Outline Introduction

Background Experimental

Theoretical

Nuclear Structure

Medium-modified nucleons Cross sections

Polarization transfer

Studies of the reaction mechanism

Few-body nuclei The deuteron

3,4He

A(e,e'p)B

Known: e and A Detect: e' and p

e

e'

q A

pB

Infer: pm = q – p = pB

e'

e

v

A B + p

(e,e'p) - Schematically

B =

A–1

A–2 + N

Etc.

i.e. bound

Kinematics

e

e'

x

pA–1

pq

p

(,q)

In ERLe: Q2 – qq = q2 – 2 = 4ee' sin2/2

Missing momentum: pm = q – p = pA–1

Missing mass: m = –Tp – TA–1

scattering plane

“out-of-plane” angle

reaction plane

Some (Very Few) Experimental Details …

“accidental” (uncorrelated)

e

e

e

e'

e' p

e' p“real” (correlated)

Detected

# events

relative time: te– tp

ra

Accidental)(Real)()(

xCxCxCa

r

Accidentals Rate = Re Rp /DF I 2 /DF

Reals Rate = Reep I

S:N = Reals/Accidentals DF /(I)

Compromise:

Optimize S:N and Reep

Extracting the cross section

Ne

e

e'NN (cm-2)

(e, pe)

pepeNepe ppNNpp

Counts

d ddd

σd

pe

6

(p, pp)

p

Some Theory …

)(δπ)2(

π)2(π)2(β

1σ

144

3

3

3

32___

lab

AA

e

iffi

e

PQPP

pd

E

mkd

e

mM

e

md

AJBpkjkQ

M fiμ

μ2λ λ

πα4

Cross Section for A(e,e'p)B in OPEA

where

Current-Current Interaction

“A-1”

Square of Matrix Element

___ν

*μ

___

ν

*

μ

2

2

___2

λ λ λ λ πα4

if

ififfi

AJBpAJBp

kjkkjkQ

M

W

μνμνM

pe

6

ησdω dpdd

σdW

Electron tensor

Nuclear tensor

Mott cross section

Cross Section in terms of Tensors

3 indep. momenta: Q , Pi , P (PA–1= Q + Pi – P)

target nucleus

ejectile

6 indep. scalars: Pi2, P2, Q2, Q•Pi ,Q •P , P•Pi

= MA2

= m2

Consider Unpolarized Case

Lorentz Vectors/Scalars

)ε like termsPV(

σρμνρσ

νμ10

νμ9

νμ8

νμ7

νμ6

νμ5

νμ4

νμ3

νμ2μν1

μν

pq

ppX

ppXqpXpqX

qpXpqXppX

ppXqqXgXW

i

i

ii

ii

Nuclear Response Tensor

Xi are the response functions

Impose Current Conservation

0 ,0 ,0

0 ,0 ,0 Then

0

0

μμ

μμ

μμ

νν

νν

νν

μνν

μ

μνμ

ν

TpTpTq

SpSpSq

WqT

WqS

i

i

Get 6 equations in 10 unknowns

4 independent response functions

Putting it all together …

θ/2tan 2

θ/2tan2

θ/2sin4

θ/2cosα σ with

]φ2cosφcos

[σπ)2(dω ddd

σd

22

2

2

2

2

2

22

22

2

2

42

22

M

xx

M3pe

6

q

Q

q

Qv

q

Qv

q

Qv

q

Qv

e

RvRv

RvRvpE

p

LTTT

TL

TTTTLTLT

TTLL

LAB

The Response Functions

Use spherical basis with z-axis along q:

yfi

xfifi

zfifi

iJJJ

qJJ

2

1

ρω

1

fi0

Nuclear 4-current

)()()(ρRe2

)()(Re2

)()(

)(ω

)(ρ

11fi

11

2121

202

2

qJqJqR

qJqJR

qJqJR

qJq

qR

fifiLT

fifiTT

fifiT

fifiL

Q • Pi = MA

P • Pi = E MA

Q • P = E – q p cos pq

In lab:

Can choose: Q2, , m , pm

Note: no x dependence in response functions

Response functions depend on scalar quantities

Including electron and recoil proton polarizations

before as defined s'other and

θ/2tanθ/2 tan θ/2 tan with

)}(

]φcos)(φsin)[(

]φ2sin)(φ2cos)[(

]φsin)(φcos)[(

)()({σπ)2(dω dpdd

σd

22

2

2

2

xx

xx

xx

M3pe

6

v

q

Qv

q

Qv

SRSRhv

SRSRSRRhv

SRSRSRRv

SRSRSRRv

SRRvSRRvpE

TTTL

ttTTl

lTTTT

ttTLl

lTLn

nTLTLTL

ttTTl

lTTn

nTTTTTT

ttLTl

lLTn

nLTLTLT

nnTTTn

nLLL

LAB

)()0(

)()0(

2

)()0(

eepeep

eepeep

eepeep

xx

xx

LTM

xxLT

A

vKR

Extracting Response Functions

For instance: RLT and A (=A LT)

]φ2cosφcos[σσ xxMeep TTTTLTLTTTLL RvRvRvRvK

Plane Wave Impulse Approximation (PWIA)

e

e'

q

p

p0

A

A–1

A-1

spectator

p0

q – p = pA-1= pm= – p0

)ε,( ω

6

mmeppe

pSKdpddd

d

nuclear spectral function

In nonrelativistic PWIA:

25

)( ω

σ mep

pe

pKddd

d

For bound state of recoil system: proton momentum distribution

The Spectral Function

e-p cross section

The Spectral Function, cont’d.

energy initial ω

momentum initial where

)εδ(E)()E,(

0

0

m0

2

000

EE

pp

ApaBpS

m

ff

Note: S is not an observable!

Elastic Scattering from a Proton at Rest

p(,q) (m,0)

p(+m, q)

Proton is on-shell ( + m)2 q2 = m2

2 + 2m + m2 q2 = m2

= Q2 2m

Before

After

Scattering from a Proton , cont’d.

ifif UUsqpJsp μμ ,,

Vertex fcn

+

+n

p

p

p

pp

p

0

p

p

μμ γpoint proton

structure/anomalous moment

+ + +

Scattering from a Proton , cont’d.

Dirac FF Pauli FF

)(κ2

σ)(γ 22

νμν21

μμ QFm

qiQF

)( κ)()(

)( τκ)()(2

22

12

22

21

2

QFQFQG

QFQFQG

M

E

Sachs FF’s

Vertex fcn:

GE and GM are the Fourier transforms of the charge and magnetization densities in the Breit

frame.

2

2

4τ with

m

Q

r

k

k'

Amplitude at q: rqierArdqF )()(

rk

1 rk

2

Phase difference:

rqrkk

Form Factor

Cross section for ep elastic

2222

M 2

θtanτ2

τ1

τσ

σM

MErec G

GGf

d

d

However, (e,e'p) on a nucleus involves scattering from moving

protons, i.e. Fermi motion.

Elastic Scattering from a Moving Proton

p(,q) (E,p)

( + E)2 – (q+p)2 = m2

2 + 2E + E2 q2 2p•q p2 = m2

Q2 = 2E 2p•q

(E/m) = (Q2 2m) + p•q m

Before

p (+E, q+p)After

Cross section for ep elastic scattering off moving protons

Follow same procedure as for unpolarized (e,e'p) from

nucleus

We get same form for cross section, with 4 response

functions …

2212

22

211

12pq

22

12pq0

12pq

22

2

22

2

1

2

0

)κ( )τ(κ

with

θsin

θsin)(

θsinτW2

42

)(

FFWFFW

Wm

pR

Wm

pEER

Wm

pR

Wm

qW

m

EER

TT

LT

T

L

Response functions for ep elastic scattering off moving protons

Quasielastic Scattering

For E m:

(Q2 2m) + p•q m

Expect peak at: (Q2 2m)

Broadened by Fermi motion: p•q m

If we “quasielastically” scatter from nucleons within nucleus:

ωd

σ2

d

d

Elastic

Quasielastic N*

Deep Inelastic

M

Q

2

2

m

Q

2

2

MeV3002

2

m

Q

Nucleus

Elastic

N*

Deep Inelastic

m

Q

2

2

MeV3002

2

m

Q

Proton

Electron Scattering at Fixed Q 2

ωd

σ2

d

d

6Li

181Ta

89Y58Ni40Ca

24Mg12C

118Sn 208Pb

R.R. Whitney et al., Phys. Rev. C 9, 2230 (1974).

Quasielastic Electron Scattering

Data: P. Barreau et al., Nucl. Phys. A402, 515 (1983).y-scaling analysis: J.M. Finn, R.W. Lourie and B.H. Cottman, Phys. Rev. C 29, 2230 (1984).

Nuclear Structure

U. Amaldi, Jr. et al.,

Phys. Rev. Lett. 13,

341 (1964).

First, a bit of history:

The first (e,e'p) measurement

Frascati Synchrotron,

Italy

12C(e,e'p)

27Al(e,e'p)

(e,e'p) advantages over (p,2p)

• Electron interaction relatively weak: OPEA is reasonably accurate.

• Nucleus is very transparent to electrons: Can probe deeply bound orbits.

However: ejected proton is strongly interacting. The “cleanness” of the

electron probe is somewhat sacrificed.

FSI must be taken into account.

)ε,( ω

6

mmeppe

pSKdpddd

d

Recall, in nonrelativistic PWIA:

where q – p = pm= – p0

FSI destroys simple connection between the measured pm and the

proton initial momentum (not an observable).

01 pppq A

e

e'

q

p

p0

FSI A–1

A

p0'

Final State Interactions (FSI)

Treat outgoing proton distorted waves in

presence of potential produced by residual

nucleus (optical potential).

Distorted Wave Impulse Approximation (DWIA)

),ε,( ω

6

ppSKdpddd

dmm

Dep

pe

“Distorted” spectral function

Optical potential is constrained by proton elastic scattering data.

Problems with this approach:

• Residual nucleus contains hole state, unlike the target in p+A

scattering.

• Proton scattering data is surface dominated, whereas ejected protons in (e,e'p) are produced within entire

nuclear volume.

J.W.A. den Herder, et al., Phys. Lett. B 184, 11 (1987).

100 MeV data is significantly overestimated by DWIA near 2nd maximum.

NIKHEF-K Amsterdam


2

α

0

*(-)α

thα

d)(ψ)exp(

),(χ),(ρ

ppp

p

r

m

rrrqi

prSppc

At pm160 MeV/c, wf is probed in nuclear interior.


Adjusting optical potential renders good agreement while maintaining agreement with

p+A elastic.

J. Mougey et al., Nucl. Phys. A262, 461 (1976).

Saclay Linac, France

12C(e,e'p)11B

J. Mougey et al., Nucl. Phys. A262, 461 (1976).


12C(e,e'p)11Bp-shell l=1

s-shell l=0

G. van der Steenhoven et al., Nucl. Phys. A484, 445 (1988).

NIKHEF-K Amsterdam

12C(e,e'p)11B

G. van der Steenhoven et al., Nucl. Phys. A484, 445 (1988).

NIKHEF-K Amsterdam

12C(e,e'p)11B

G. van der Steenhoven, et al., Nucl. Phys. A480, 547 (1988).

NIKHEF-K Amsterdam

12C(e,e'p)11B

DWIA calculations fit data reasonably

well.

Missing strength observed however.

L.B. Weinstein et al., Phys. Rev. Lett. 64, 1646 (1990).

12C(e,e'p)

Bates Linear

Accelerator

K.I. Blomqvist et al., Phys. Lett. B 344, 85 (1995).

MAMI Mainz,

Germany


MAMI Mainz,

Germany

Factorization violated. DWIA calculations

underpredict at high pm.

Neglected MEC’s & relativistic effects.

Offshell effects uncertain at high pm.

I. Bobeldijk et al., Phys. Rev. Lett. 73, 2684 (1994).

AmPS NIKHEF-K Amsterdam

208Pb(e,e'p)

I. Bobeldijk et al., Phys. Rev. Lett. 73, 2684 (1994).

208Pb(e,e'p)


Long-range correlations important.

SRC and TC less so, but expected to

grow with m.

Some of the lessons learned:

• (e,e'p) sensitive probe of single-particle orbits.

• Proton distortions (FSI) must be accounted for to reproduce shape of spectral function. Energy dependence of FSI breaks factorization.

• Missing strength in valence orbits, even after accounting for FSI

• At high Pm significant discrepancies found relative to calculations.

Where does the “missing” strength go?

One possibility:

Detected

recoils

populates high m

C. Ciofi degli Atti, E. Pace and G. Salmè, Phys. Lett. 141B, 14 (1984).

n(k)

total

m 12.25 MeV

2-body

m 300 MeV

m 50 MeV

3He

SRC dominate high

k (=pm ) and are related to large values

of m.

C. Ciofi degli Atti, E. Pace and G. Salmè, Phys. Lett. 141B, 14 (1984).

d

Nucl. Matter

3He4He

Similar shapes for few-body nuclei

and nuclear matter at high k (=pm).

Medium-Modified Nucleons

Searching for Medium Effects on the Nucleon …

22Mσ

σMTTELLrec GkvGkvf

d

d

][σπ)2(dω ddd

σdM3

pe

6

TTLL RvRvpE

p

In parallel kinematics:

Can write ep elastic cross section as:

2

2

2

2

2 and with

m

Qk

Q

qk TL

E

M

L

TG G

G

R

R

Q

qmR ~

~2

2

PWIA

Relate RT/RL to in-medium proton FF’s

This relies on (unrealistic) model assumptions!

Nonetheless …

J.E. Ducret et al.,

Phys. Rev. C 49, 1783 (1994).

2H(e,e'p)n 6Li(e,e'p)

DWIA

NIKHEF-K Amsterdam

J.B.J.M. Lanen et al.,

Phys. Rev. Lett. 64, 2250 (1990).

12C(e,e'p) and 12C(e,e')

D. Dutta et al., Phys. Rev. C 61, 061602 (2000).

JLab Hall C

However, large FSI effects can mimic this

behavior …

Dirac PWIA

Dirac DWIASchrödinger LDA

FSI calculations for 16O 1p3/2

Data for 12C 1p3/2

Another, less model-dependent, method …

Polarization Transfer

Proton Polarization and Form Factors

2

θtan)τ1(21τ

2

θtan)τ1(τ

2

θtan)τ1(τ2

e2220

e220

e0

scattering Free

ME

Mz

MEx

GGI

Gm

eePI

GGPI

pe

2

θtan

2e

m

ee

P

P

G

G

z

x

M

E

* R. Arnold, C. Carlson and F. Gross, Phys. Rev. C 23, 363 (1981).

M

E

G

G~

~in nucleus

model assumptions

*

spectrometer + FPP

1H and (2H or 4He)

spectrometer

e

e

p

),(H

H),(He ),(H

1

342

pee

peenpee

Polarization Transfer in Hall A

Measuring the Proton Polarization: FPP

Density Dependent Form Factors

)(

))(,( )()(

3

23

2

rrwd

rQGrrwdQG

B

)(),()exp( *)( rrprqiw

For (e,eFor (e,e''p)p)

D.H. Lu, , A.W. Thomas, K. Tsushima, A.G. Williams, K. Saito, Phys. Lett. B 417, 217 (1998).

Quark-Meson Coupling Model (QMC):

D.H. Lu, K. Tsushima, A.W. Thomas, A.G. Williams and K. Saito, Phys. Lett. B417, 217 (1998) and Phys. Rev. C 60, 068201 (1999).

Quark-Meson Coupling Model

4He

npee )',(H2

Calculations by Arenhövel

H)',(He 34 pee

JLab

RDWIA calculations by Udias et al.

Preliminary Preliminary

Induced Polarization – 4He

JLab E93-049

Py=0 in PWIA: test of FSI

Preliminary

PWIA DWIADWIA+spinor

distortion

DWIA+QMC

221516 (GeV/c) 8.0at N )O( Qpe,e

S. Malov et al., Phys. Rev. C 62, 057302 (2000).

Studies of the Reaction Mechanism

Correlations

MEC’s

IC’s

Correlations and Interaction Currents

Off-shell Effects

Vertex function is not well defined. The “Gordon identity” leads to alternative forms,

equivalent only when proton is on-shell.

e

e'

q

p

p0

A

A–1

initial proton is bound

D. Dutta et al., Phys. Rev. C 61, 061602 (2000).P.E. Ulmer et al., Phys. Rev. Lett. 59, 2259 (1987).

12C(e,e'p) L/T Separations

Q2=0.15 GeV2Q2=0.64 GeV2

Bates Linear Accelerator JLab Hall C

D. Dutta et al., Phys. Rev. C 61, 061602 (2000).

Excess transverse strength at high m.

Persists, though perhaps declines,

at higher Q2.

JLab Hall C

J.B.J.M. Lanen et al., Phys. Rev. Lett. 64, 2250 (1990).

6Li(e,e'p) T/L Ratio

DWIA (dashed) fails to describe overall

strength.

Scaling transverse amplitude in DWIA (solid) gives good

agreement deduce scale factor, .

NIKHEF-K Amsterdam

J.B.J.M. Lanen et al., Phys. Rev. Lett. 64, 2250 (1990).

DWIA

6Li(e,e'p) T/L Ratio

NIKHEF-K Amsterdam

The L/T separations suggest

• Additional transverse reaction mechanism above 2-nucleon emission threshold.

• MEC’s primarily transverse in character. Suggestive of two-body current.

Reminiscent of …

J.M. Finn, R.W. Lourie and B.H. Cottman, Phys. Rev. C 29, 2230 (1984).

T/L anomaly in inclusive

(e,e'):

R.W. Lourie et al., Phys. Rev. Lett. 56, 2364 (1986).

12C(e,e'p) in “Dip Region”

Data from: Bates Linear Accelerator

Bates Linear

Accelerator

L.B. Weinstein et al., Phys. Rev. Lett. 64, 1646 (1990).

H. Baghaei et al., Phys. Rev. C 39, 177 (1989).

12C(e,e'p)Quasielastic“Delta”

Q2=0.30

Q2=0.48

Q2=0.58

Between dip and Peak of

Bates Linear Accelerator Bates Linear Accelerator

Figure adapted from J.H. Morrison et al., Phys. Rev. C 59, 221 (1999).

Missing Energy (MeV)

0 100 200 300

12C(e,e'p) q=990 MeV/c, =475 MeV

ω/2

ω-ω)ε(α

dε dωdd

σd

0

0

pe

6

max

lm

l

ll

m

P

For 60<m<100 MeV, continuum cross section

increases strongly with .

Large continuum strength continues up to 300 MeV.

Bates Linear

Accelerator

Figure adapted from J.H. Morrison et al., Phys. Rev. C 59, 221 (1999).

Missing Energy (MeV)

0 100 20050 150

ω/2

ω-ω)ε(α

dε dωdd

σd

0

0

pe

6

max

lm

l

ll

m

P

12C(e,e'p) q=970 MeV/c, =330 MeV

Continuum strength increases strongly

with .

Continuum cross section is smaller at

high m.

Bates Linear

Accelerator

J.H. Morrison et al., Phys. Rev. C 59, 221 (1999).

12C(e,e'p)

For <QE, spectroscopic

factors consistent with

naïve expectations.

Bates Linear

Accelerator

C.M. Spaltro et al., Phys. Rev. C 48, 2385 (1993).

Circles (solid) – NIKHEF-K Crosses (dashed) - Saclay

Large discrepancy

for 1p3/2.

Relativistic effects

predicted to be small here.

Two-body currents

responsible??

16O(e,e'p)

J. Gao et al., Phys. Rev. Lett. 84, 3265 (2000).

16O(e,e'p) Q2=0.8 GeV2 Quasielastic

Relativistic DWIA gives

good agreement with data.

JLab Hall A

N. Liyanage et al., Phys. Rev. Lett. 86, 5670 (2001).

Two-body calculations of Ryckebusch et

al., give flat distribution, as

seen in the data, but underpredict

by a factor of two.

16O(e,e'p) Q 2=0.8 GeV2 Quasielastic

JLab Hall A

At high energies, RLT interference response function sensitive to relativistic effects.

For example, spinor distortion …

Spinor Distortions

VSmE

p

N.R. reduction

S+V Mean field

S+V relatively small

Dirac spinor

S–V affects lower components

S–V large

J. Gao et al., Phys. Rev. Lett. 84, 3265 (2000).

16O(e,e'p) Q 2=0.8 GeV2 Quasielastic

Udias fullUdias BS SD only

Udias scatt. state SD only

Udias - no SD

Kelly

1p 1/2

1p 3/2

Sensitive to “spinor

distortions”

JLab Hall A

Few-body Nuclei …

The Deuteron

Short-distance Structure

Low pm p n

High pm p n

For large overlap, nucleons may lose individual identities:

Quark/gluon d.o.f.?

M. Bernheim et al., Nucl. Phys. A365, 349 (1981).


P.E. Ulmer et al., Phys. Rev. Lett. 89, 062301 (2002).

pm (MeV/c)

Arenhövel DWBA

Arenhövel Full

PWBA Jeschonnek

or Arenhövel

JLab Hall A

Large FSI/non-nucleonic effects.

Problem at pm=0.

D. Jordan et al., Phys. Rev. Lett. 76, 1579 (1996).


MAMI Mainz,

Germany

Ducret et al.Bernheim et al.

Jordan et al.

Blomqvist et al. data cover kinematics

beyond . Also neutron

exchange diagram

important.


Calculations: H. Arenhövel

FSI

FSI+MEC+IC

Bonn Electron Synchrotron,

Germany

2H(e,e'p) Q2=0.23 GeV2 near

Calculations: Leidemann and Arenhövel

H. Breuker et al., Nucl. Phys. A455, 641 (1986).

PWBA+FSI

PWBA+FSI+MEC+IC

PWBA+FSI+MEC

clearly important

qpn

f

Final State

nf

p

Proton hit (high pm)

q

np

Final State

nf

pf

Neutron hit (low pm)

e q

fpn

f

n p

Proton spectator

pm (MeV/c)0 100 200 400 500300 600

P.E. Ulmer et al., Phys. Rev. Lett. 89, 062301 (2002).

Q2=0.67 GeV2 Quasielastic

Large FSI effects.

Also, substantial

non-nucleonic effects.

JLab Hall A

Final State Interactions Can be LARGE

p

q

fp'

fp

p'pp

actualinferred

G. van der Steenhoven, Few-Body Syst. 17, 79 (1994).

Wilbois/ArenhövelWilbois/Arenhövel

de Forest

de Forest

Hummel/Tjon

Arenhövel/Fabian

Arenhövel/Fabian

Mosconi/Ricci

NR

NR

What do all these data and curves suggest?

• Relativistic effects substantial in A (and RLT).

• de Forest “CC1” nucleon cross section gives same qualitative features as more complete calculations here, relativity more related to nucleonic current, as opposed to deuteron structure.

I. Passchier et al., Phys. Rev. Lett. 88, 102302 (2002).

),(H2 pee

Ted

dVed

de

Td

dVd

d APAPAhAPAP 21210 1σσ

D-state important


Lots more d(e,e'p) data on the way!

Perpendicular: R LT Q 2 : 0.80, 2.10, 3.50 (GeV/c)2

x=1: p m from 0 to 0.5 GeV/c

Parallel/Anti-parallel Q 2 : 2.10 (GeV/c)2

vary x: p m from 0 to 0.5 GeV/c

Neutron angular distributionQ 2 : 0.80, 2.10, 3.50 (GeV/c)2

2H(e,e'p)n E01-020 Hall A



2H(e,e'p)n with JLab 12 GeV upgrade

Preliminary Hall B E5 Data – 2H(e,e'p)

Hall B data covers large

range of Q2 and excitation as

well as coverage to

separate RLT, RLT' and RTT.

3,4He

C. Marchand et al., Phys. Rev. Lett. 60, 1703 (1988).

3He(e,e'p)Calculations by Laget: dashed=PWIA

dot-dashed=DWIA solid=DWIA+MEC

Saclay Linear

Accelerator

Arrows indicate

expected position for correlated

pair.

C. Marchand et al., Phys. Rev. Lett. 60, 1703 (1988).

3He(e,e'p)d 3He(e,e'p)np

3BBU similar

to dnp

JLab Hall A

Large effects from FSI and non-nucleonic

currents.

Highest pm shows excess

strength.

AL

T

JLab Hall A

General features

reproduced but not at

correct values of pm.

The most direct way to look for correlated

nucleons?

Detect both of them JLab Hall B

3He(e,e'pp)n Hall B

2 GeVPN>250 MeV/c

4 GeVPN>250 MeV/c

fast pn leading p

fast pn leading p

PR

EL

IMIN

AR

Y

0 0.5 1Tp2/

0 0.5 1Tp2/

0

0.5

1T

p1/

0

0.5

1

Tp

1/

-1 -0.5 0 10.5cos(2 fast nucleon angle)

-1 -0.5 0 10.5cos(2 fast nucleon angle)

Hall B 3He(e,e'pp)n 2 GeVpperp < 300 MeV/c

PR

EL

IMIN

AR

Y

cos(nq)

cos(pq)

Isotropic fast pairs pair not involved in reaction.

Hall B 3He(e,e'pp)n

Pair momentum along q [GeV/c] Pair momentum along q [GeV/c]

Small momentum along q pair not involved in reaction.

Little Q2 or isospin dependence.

pp

erp <

300

MeV

/cP

RE

LIM

INA

RY

2 GeV has acceptance corrections

Before

p

np

After

np

p

Direct evidence of NN correlations

A. Magnon et al., Phys. Lett. B 222, 352 (1989).

Saclay

4He(e,e'p)3HArgonne+Mod 7

Urbana+Mod 7 Data and calculations

“corrected” for MEC+IC (Laget).

Longitudinal overpredicted.pm=90 MeV/c pm=90 MeV/c

J.E. Ducret et al., Nucl. Phys. A556, 373 (1993).

Saclay

4He(e,e'p)3H

Calculations predict q

dependence.

J.E. Ducret et al., Nucl. Phys. A556, 373 (1993).

4He(e,e'p)3H

Again, calculations

predict q dependence.

J.J. van Leeuwe et al., Phys. Rev. Lett. 80, 2543 (1998).

PWIA

tree+one-loop

tree

PWIA

+FSI

+2-body

PWIA

+FSI+MEC/2B

+MEC/3B

Laget

Schiavilla

Nagorny

Minimum filled in by FSI and

2&3-body currents.

4He(e,e'p)3H


FSI: dependence on kinematics

p

q

fp'

fpp'pp

actualinferred

Large FSI

qp

fp p'

fp'

pp

Small FSI

4He(e,e'p)3H

JLab Hall A Experiment E97-111, J. Mitchell, B. Reitz, J. Templon, cospokesmen

It looks like the minimum

is filled in here as well.

Summary

• (e,e'p) sensitive to single-particle aspects of nucleus, but …

• More complicated physics is clearly important.

• Spectroscopic factors reduced compared to naïve shell model (including FSI corrections).

• Missing strength at least partly due to interaction currents: direct interaction with with exchanged mesons or interaction with correlated pairs (spreads strength over m).

Summary cont’d.

• After several decades of experimental and theoretical effort, there are still unanswered questions.

• What is the nature of the interaction of the virtual photon with the “nucleon”: medium and offshell effects?

• Handling FSI and other reaction currents still problematic, though realistic calculations are now available for the lighter systems.

• High energy program is underway, pushing to shorter distance scales, emphasizing relativistic effects, …

Documents

Hampton University Graduate Studies 2003