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Experiment List: Run, but Unpublished● [A, ran 2000] E97-111: 4He(e,e'p)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