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NN and Many-Body Interactions: Chiral Perturbation Theory; Effective Interactions:

Experimental Review

Ronald Gilman

Rutgers University /

Jefferson Lab

Meeting on the Physics of Nucleons and NucleiSURA, Washington, DC October 16-17, 2006

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Subject / Scope / Theme of this Talk● What can we hope to learn experimentally in the next 5 – 10

years from JLab experiments?

– Recent experiments

– Approved experiments awaiting beam time

– Possible future experiments – 12 GeV upgrade● Unfortunately, there is no easy connection between the

experiments and the theory issues discussed – it is difficult to know in advance what aspect of theory is most impacted, and to what degree

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Coverage● Cover experiments that look at nuclei as assemblies of

nucleons, mesons, ... and the limits to that picture

– A(e,e'): elastic, inelastic form factors

– A(e,e'p): spectroscopic factors, “momentum distributions”, correlations, FSI, MEC, IC, relativity, ...

– A(γ,p)

– A(e,e'K+)● Except: experiments I expect to be covered by other people

● Do not cover “DIS-type”, GDH, hadronization, neutron form factor, hadrons-in-medium, ... or published experiments

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Experiment List: Run, but Unpublished● [A, ran 2000] E97-111: 4He(e,e'p)

● [A, ran 2001] E00-102: 16O(e,e'p)

● [A, ran 2002] E01-020: d(e,e'p)

● [A, ran 2002] E00-007: d(γ,p)n

● [A, ran 2004/5] E94-107: 1p Shell Hypernuclei

● [C, ran 2004] E02-019: x>1 Inclusive Scattering

● [A, ran 2005] E02-015: 12C(e,e'pp) Short Range Correlations

● [C, ran 2005] E01-011: Hypernuclei

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Experiment List: Recently Run, or Scheduled● [A, ran 2006] E05-103: Low Energy Deuteron Photodisintegration

● [A, ran 2006] E05-004: A(Q) at low Q in ed Elastic Scattering

● [A, running] E03-104: Probing the Limits of the Standard Model of Nuclear Physics with the 4He(e,e'p) Reaction

● [A, scheduled 2006/7] E04-018: 3,4He(e,e') elastic form factors

● [A, scheduled 2007] E06-007: 208Pb(e,e'p)

● [A, scheduled 2007] E03-101: 3He(γ,pp)n

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Future Experiments: Approved, Unscheduled● [A] E04-107: 4He(e,e'p)

● [A] E05-102: pol-3He(e,e'd)

● [A] E05-110: Coulomb Sum Rule

● [C] E05-115: Hypernuclei

● [A] E06-002: PREX: Pb neutron radius through PV

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12 GeV Nuclear Program● A(e,e') at x>1 for short-range (mutli-nucleon) correlations /

superfast quarks

● Few body form factors: d, 3He, 4He

● Various ideas using nuclei that are outside our scope

– F2p/F

2n and u/d ratio at high x

– A(e,e'p), etc., Color Transparency / Nuclear Filtering

– Hadrons in the Nuclear Medium

– Hadronization

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Experiments Under Analysis

● Experiments that have run, but not published the results

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E97-111: 4He(e,e'p)

● Goal: search for the minimum expected for p

miss ~ 500 MeV/c in IA

● Used high Q2 and parallel kinematics to suppress reaction mechanism effects

● Subsequent Laget calculation indicates FSI remain important

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E00-102: 16O(e,e'p)

● Solid: E89-003● Open: expected● Improved test of

relativistic many-body calculation of Udias et al.: spinor distortions lead to interesting A

LT

behavior

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E01-020: 2H(e,e'p)● Systematic study over several kinematic regions near

quasifree peak, emphasizing / suppressing different reaction mechanism effects

● Example: xBj > 1, parallel kinematics sensitive to SR structure

● Example below: FSI interactions leads to “peak” in cross section when neutron is at 90 deg w.r.t. q-vector.

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E00-007: 2H(γ,p)n

● Study of reaction mechanism at high W and high t (four-momentum transfer)

● Bias: large W and t --> use quarks!

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E94-107: 9Be,12C,16O(e,e'K+)

● Hypernuclear spectroscopy

● ΛN effective interaction

● Vs π / K beams:

– High resolution

– Favors spin flip transitions

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E02-019: x>1 Inclusive Scattering

● I leave comments to John Arrington.

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E02-015: 12C(e,e'pp) Short Range Correlations

● Doug Higinbotham will discuss this experiment.

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E01-011: Hypernuclei

● Hydrogen spectrum shows good resolution and minimal offsets

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E01-011: Hypernuclei

●7Li(e,e'K+)7

ΛHe

shows s-state Λ

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E01-011: Hypernuclei

●12C(e,e'K+)12

ΛB

shows s- and p-state Λ's

● Spin-orbit splitting reduced for Λ's, compared to nucleons

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E01-011: Hypernuclei●

28Si(e,e'K+)28ΛAl

show s- and p-state Λ's

● Perhaps some additional bound-state (d-state?) strength?

● Follow up experiment, E05-115, uses new equipment to improve S/N

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E05-103: Low Energy

2H(γ,p)n

● Study how well best theory (Schwamb and Arenhövel) reproduces recoil polarizations at E

γ = 280 – 360 MeV

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E05-004: A(Q) at low Q in ed Elastics50 Years of ed Elastic Data...

● Form factors are momentum space distributions, from wave function x nucleon f.f. + ...

● Relativistic theories describe a broad range of data well – understand deuteron to short range, < 1 fm

● Theoretical issues with implementing relativity (current conservation, completeness)

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E05-004: A(Q) at low Q in ed Elastics

● Plot: A(Q)/Afit

(Q) vs Q

● Convergence of χPT, size of relativistic corrections

● Data taken for Ta, Al, C, D, H vs Q at 362 and 687 MeV

● Q = 0.1 – 0.7 GeV, 17 Q steps, in fine steps out to 0.4 GeV

● One missing systematics study: no beam energy measurement – will use kinematic fit instead

● Generally good spectra

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E05-004:A(Q) at low Q in ed

Elastics

● E = 687 MeV

● θ = 25.5 deg

● Q = 0.3 GeV

● H, D, C, Ta

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E05-004:A(Q) at low Q in ed

Elastics

● E = 687 MeV

● θ = 30.5 deg

● Q = 0.35 GeV

● H, D, C, Ta

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E05-004:A(Q) at low Q in ed

Elastics

● E = 687 MeV

● θ = 40 deg

● Q = 0.45 GeV

● H, D, C, Ta

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E03-104: Limits to Standard Nuclear Model

● 4He(e,e'p) polarization transfer ratio vs PWIA, relativistic, and relativistic + QMC theory

● Better agreement with QMC, but more definitive experiment desired

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E03-104: Limits to Standard Nuclear Model● Various

improvements improve uncertainties by factor of 2

● Improved induced polarizations will also test Schiavilla explanation: spin-dependent charge-exchange FSI

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Future Experiments

● Experiments scheduled to run during the next several months

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E04-018: 3,4He Elastic Form Factors● Form factors arise from wave function + MEC + IC + ...

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E04-018: 3,4He Elastic Form Factors

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E04-018: 3,4He Elastic Form Factors

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E06-007: 208Pb(e,e'p) – Correlations, etc.● Will be discussed by Doug Higinbotham

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E03-101: 3He(γ,pp)n● Study mechanism of pn photo-

disintegration by examining pp disintegration

● Hall B γ3He data small compared to γd, 10 – 25 % as large (s11ds/dt ~ 0.4)

● Laget: pp dipole moment● Theories, based on γd, have

100 MeV/c cut● Hint of a phase transition

starting at 1.4 GeV? But I would expect a “transition” to be complete by 1 or 1.3 GeV.

● E03-101 to measure 5-10% cross sections up to ~3.5 GeV

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Future Experiments

● Experiments likely to run in next few years, but not scheduled to run during the next several months

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E04-107: 4He(e,e'p)● Systematic study of quasifree

nucleon knockout, similar to what was done in E89-044 for 3He(e,e'p) (shown)

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E04-107: 4He(e,e'p)

● ATL

will be measured, and response functions will be separated in both parallel and perpendicular kinematics

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E05-102:pol-3He(e,e'd)

● Goal: better understanding of the 3He system, through double-polarization data

● Naïve estimate of sensitivity to wave function shown

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E05-110: Coulomb Sum Rule

● Will be covered by Doug Higinbotham.

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E05-115: Hypernuclei

● Already discussed under E01-011

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E06-002: PREX: Lead Neutron Radius Experiment

● To be discussed by Krishna Kumar

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Unapproved / Unproposed Experiments

● Several other ideas have been around, which have, for various reasons, never resulted in approved experiments, including– B structure function / G

M in ed elastic scattering – the

minimum in B is not well established

– Threshold deuteron electrodisintegration: d(e,e')pn – the low-lying unbound inelastic states are poorly understood

– Charge radii for Li, B – these are only known to ~0.05 or worse, compared to ~0.01 uncertainties on other light nuclei

– ...

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The 12 GeV Program

● The 12 GeV physics program has focused on nucleon and meson structure

● Following are a few nuclear physics experiments that have been discussed

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A(e,e') at x>1 (Superfast quarks)

● I expect John Arrington to comment.

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Few-Body Elastic Form Factors

● The few body program was studied using MAD and an electron calorimeter.

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Summary

● There has been a broad nuclear physics program at JLab● Many more results to appear in the next few years:

– 11 unpublished experiments

– 3 experiments scheduled to run in the next few months

– 5 experiments in the queue● Interest remains high over the next several years – the 12

GeV upgrade leads to measurements at higher Q, emphasizing the shorter-range structure of nuclei– It appears likely the JLab nuclear community will focus

more on issues of quark substructure

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Backup Slides Follow

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D(e,e') Elastic Scattering● Deuteron elastic scattering is a primary test case for predicting

nuclear structure from the NN interaction● Spin-1 deuteron has 3 form factors:

σ = σNS

[A(GC,G

Q,G

M) + B(G

M)tan2(θ/2)]

● Cross section data allow A and B to be determined. Polarization measurements are needed to separate out G

C and G

Q● Many theoretical tools: conventional hadronic theory (NR, rel), no-

π EFT, PT, pQCD ...● In NR approach, ff are a product of nucleon ff times body ff

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Polarization Observables

● Using S = A + Btan2(θ/2), vector and tensor polarization observables are:– Px ~ G

M(G

C+ηG

Q/3)/S

– Pz ~ GM

2/S– T

20 ~ [“G

CG

Q” + “G

Q2” + “G

M2”]/S

– T21

~ GMG

Q/S

– T22

~ GM

2/S● T

20, T

21, and T

22 have been measured, because they do

not require polarized beam, and because GM is small -

T20

mainly determines the separation of GC and G

Q

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... But Problems Remain● G

M: the minimum is difficult

● GQ: a 1% discrepancy

between theory and data for Q

d – in EFT it is missing

shorter-range physics, but noone knows what it is in conventional theory

● GC: Problems in A at low Q2

lead to questions about extracting form factors and about the role of relativity

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Upcoming Data● Improved low Q data have been measured at Bates

BLAST . Figure from Tsentalovich, Nucleon05

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Deuteron Photo-disintegration● When one probes the nucleus (nucleon) in elastic

scattering, the transferred energy and momentum match to boost the nucleus (nucleon); internal degrees of freedom are not “explicitly” excited

– With high q, but small W, perhaps we should not be surprised to not see quarks in the deuteron

● Photodisintegration provides high q AND high W: 286 channels (combinations of different allowed intermediate states of 24 baryon resonances) are explicitly excited for Eγ = 0 – 4 GeV

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Data Overview● Extensive low Eγ studies, for dσ/dΩ and polarizations,

(~1100 data points, mostly py and Σ)

– Recent measurements from LEGS, Mainz, and TUNL

– Generally good agreement between theory (Schwamb and Arenhövel) and data

● High energy studies from SLAC and JLab, mostly dσ/dΩ plus some recoil polarimetry (C

x', p

y, C

z')

– Conventional theory fails above 1 GeV; some non-perturbative quark models not ruled out

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Some Observables in d(γ,p)ndσ/dΩ, Σ, T, C

x', p

y, C

z'

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Agreement in ds/dΩ, Σ

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Disagreement in py

● The p y

problem led to dibaryon excitement in the 1970s/80s

● It remains unresolved

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The Hard Scattering RegimeSLAC NE8, NE17

JLab Hall C E89-012, E96-003

Yerevan (Σ)

JLab Hall A E89-019 (Cx', p

y, C

z'), E99-008

JLab Hall B E93-017

JLab Hall A E00-007 (Cx', p

y, C

z') (X. Jiang)

JLab Hall B: 3He (S. Strauch)

Does pQCD apply? -> Is there a good quark model? Is there a phase transition?

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90º Excitation FunctionsCross sections fall by a factor of 30,000 from 1 – 4 GeV, ~following ``expected'' quark scaling, dσ/dt ~ s-11

Hadronic theories not satisfactory and not shown

Most quark models normalized

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The Quark ModelsQGS: Regge phenomenology to evaluate 3-quark exchange, justified by dominance of planar diagrams

RNA, HRM, TQC, CQM: Photon absorbed and quarks exchanged; might be related to NN elastic scattering – all use hard scattering approximations

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90º Excitation FunctionsCross sections fall by factor of 1.2x106 from 1 – 6 GeV

The onset of ~quark scaling, dσ/dt ~ s-11, at each angle corresponds to pT ~ 1.1 GeV: P Rossi et al, PRL 04, 012301 (2005)

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JLab Hall A Angular DistributionsBlue dash: HRM

TQC (Radyushkin):

d/dsym

= NFp2F

n2/

{[s-λ2] [ s(s-md2)]}

d/dasym

= d/dsym

/{1-Acos / [1+m

p/E]}2

Similar AD shapes -- insensitive to dynamics?

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JLab Hall B Angular DistributionsBeautiful set of angular distributions vs. energy

P. Rossi et al., E93-017

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Σ AsymmetryHHC - Hadron Helicty Conservation – leads to Σ = -1

Adamian et al. showed Σ heads away from HHC, with increasing energy

Grishina et al. pointed out iso-vector (scalar) limit is Σ = 1 (-1)

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Induced Polarization py

HHC leads to py = 0,

and py vanishes above 1

GeV

HRM predicts py small,

<0

Hadronic prediction, that D

13 + D

15 leads to

large resonance peak, falsified

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Polarization TransferSchwamb & Arenhövel prediction good at low energies

Cx' small, but not

vanishing, so no HHC

Cannot rule out or strongly support HRM / QGS / approach to HHC

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3He (pp) Disintegration?After ~20 years of high energy deuteron photo-disintegration, what have we learned?

PQCD does not apply, but also conventional hadronic models do not work: use quark d.o.f.

Cross section and polarization data different in character above vs below ~ 1 GeV in E

γ and p

T

QGS appears to be overall the best candidate quark model for the few GeV region

Is there anything we can do to better indicate the underlying physics? 2He disintegration!

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3He (pp) DisintegrationBrodsky et al, PLB 578, 69 (2003): ratio of pp to pn well determined in theory

At low energy, σ(γpp) / σ(γpn) ~ 0.1: pp dipole moment vanishes: JM Laget

Quark models predict larger ratio: slow 2nd order or fast 1st order phase transition?

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3He (pp) αn DistributionLight cone momentum fraction, α = (E-p

z)/m,

is conserved: α

γ+α

He=0+3=α

p1+α

p2+α

n

Soft FSI “do not” affect α, so α

n

reflects neutron spectator wave function

RNA short range/broad, HRM long range/narrow

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3He (pp) OscillationsProminent oscillations in pp cross section, as opposed to flatter pn cross section, reflected in oscillations in γpp, as opposed to flatter energy dependence in γd?

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3He(γ,pp)n Measured!Hall B experiment, analyzed by S. Strauch, GWU (now SC)

PRELIMINARY

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3He(γ,pp)n Neutron Spectator?Is the neutron a spectator? Cut at 0.1 – 0.25 GeV/c

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3He(γ,pp)n Cross SectionsRed: “γpp->pp”, symmetric about 90˚

Blue: γd->pn x ¼, asymmetric about 90˚

Cross sections for γpp like back-angle γd, near 1 GeV

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3He(γ,pp)n αn DistributionHard distribution from short-range physics, evidence for TQC? 1 GeV/c nucleons in c.m., probably lots of rescattering broadens distribution

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3He(γ,pp)n: Hall A E03-101Can cleanly distinguish 1/10, 1/4, ... x deuteron disintegration cross section vs “phase transition”First run: May 2007Given exciting results near 2-2.5 GeV, would want to map transition: Hall A or Hall B