Hadrons and Cold Nuclear MatterRapporteur Presentation

Donald GeesamanJLAB PAC 36

24 August 2010

A person appointed by a deliberativebody to investigate an issue or a situation and report to that body

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History – as started by Mont in his ascent to Nuclear Physics

1983- EMC - Ratio of iron to deuteriumNote systematic errors are large and don’t show up onelectronic archive

1984-EMC- virtual photon energy dependence of leading hadron multiplicities

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Questions

Do we understand nuclei when probed at the partonic level? Is the nucleon modified in the nuclear medium? Are there other particles than nucleons in the nucleus? Short range correlations emphasis pairs of nucleons that are close together. Is this

the most likely place to see medium modifications?– Do we really understand short-range correlations in nuclei?– Do we understand transition from hadron picture to quark-gluon picture?

How do rapidly moving quarks become hadrons?The Essence of Confinement

How does the nuclear medium affect the passage of fast quarks?

Can we use nuclear interactions to understand the space-time evolution of hadronic states and the cross section for interactions of short-lived particles with nucleons?

How are the hyperon-nucleon interactions and nucleon-nucleon reactions related in a QCD description?

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Our visual images of a nucleus

OR

“nucleons” held apart by short range repulsionbut even in 208Pb, half the nucleons are in the surface

average spacing at ρnm ~ 1.8 fmRadius of a nucleon ~ 0.8 fmRadius of heavy nucleus at ~ 6 fm

OR ???

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We want to describe a nucleus

Hadronic Description– exemplified by ab initio calculations

with potentials• NN• NNN + NNNN +• Bare form factors• Meson exchange currents

Past two decades have shown this is remarkably successful

Pure QCD Description– what are the clusters of quarks in a

nucleus?– know the parton distributions change

• EMC effect• shadowing• x>1

One problem is always whether our description of a bare proton is good enough. The second is how to actually calculate many body effects beyond mean field?

One of my criteria for a successful theoretical description is multiple phenomena should be described, both at the hadronic and parton levels.

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Experiments Quark structure and short range correlations

– E12-06-105 Inclusive scattering from nuclei with x>1 in the quasielastic and deeply inelastic regimes

– E12-10-008 Detailed studies of nuclear dependence of F2 in light nuclei– PR12-10-012 Precision measurement of nucleon and nuclear structure functions to constrain

gluon distributions – P12-10-004 Hard photodisintegration of a proton pair– E12-10-003 Deuteron electro-disintegration at very high missing momentum

Color Transparency– E12-06-106 Study of color transparency in exclusive vector meson production off

nuclei– E12-06-107 The search for color transparency at 12 GeV

Hadronization– E12-06-117 Quark propagation and hadron formation

Hyperon interactions and other effects– E12-10-001 Study of light hypernuclei by pionic decay at JLab

Experiments where I am on proposal

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Related measurements

E12-06-113 Bonus12 The structure of the free neutron at large x-Bjorken

MeAsurement of the Fn2 /Fp2 , d/u RAtios and A=3 EMC Effect in deep inelastic electron scattering off the tritium and helium mirror nuclei.

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Nuclear modifications of parton distributions

i j y

Ax

Ax

y

NAi

A yxqyfy

dyyxqyf

y

dyxF )/()()/()()( *

2

ShadowingL ~ 2ν/Q2 ~ 1/x >2 fmDestructive interferenceor gluon recombination

EMC regionL shortEither f(y) peaks below 1or F2

N modified in nucleus

Either constructive interference or other hadrons

Nuclear motionor short-range corrections As x-> 2 ratio goes to ~6

)(

)(2

xA

xd

A

exaggerated

Most models have limited xranges

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Many of the general features of the A dependence of parton distributions are experimentally known. How do we progress?

Are binding effects included correctly? Look at light nuclei where structure changes rapidly and, in principle, can be calculated.

Nuclei with large isospin variation. Can we tag hole state in A-1 nucleus? Do we know neutron structure functions well enough? Most of data emphasizes isoscalar effects. Can we isolate isovector effects? Is there a correlation between short range correlations measured at x>1 and average

medium modification of nucleon parton distributions– Can we correlate this with other measurements of short range correlations

Can we determine A dependence of different quark flavors – flavor tagging semi-inclusive DIS

Can we look for other observables that are sensitive to changes in nucleon structure?– (e,e’p)– Spin structure functions in nuclei.

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Examples of model trade offs

QMC - mean field model. f(y) peaks near 1. Large medium modifications are necessary to explain EMC effect. Dirac structure leads to effects in spin.

Kulagin and Petti work to cover entire x range. Yes!– Large binding effects– Still need medium/off-shell modifications to fit EMC region, assumed to vary like binding– Shadowing due to hadronic component of the photon- leads to Q2 dependence– Also include meson contributions. Small effect in Drell-Yan– Not clear if neutral current and charged current neutrino DIS are consistent

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Can we measure binding energy and spectator momentum dependence? Test technical issue of how to include binding in calculation

Do we see nuclear dependence change for high momentum spectators which involve short distance interactions- Spectator tagging?

SLAC fit to heavy nuclei(scaled to 3He)

Calculations by Pandharipande and Benhar for 3He and 4He

Benhar and Pandharipande 3He

Benhar and Pandharipande 4He

JLab DataBlack points 3HeMagenta points 4He

I don

’t lik

e pr

esen

ting

Isos

cala

r cor

rect

ed ra

tio

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Isovector EMC effect is not well tested

Kulagin and Petti (ArXiv:1004.3062v1) find in their model NMC d/p and JLab 3He/D give different F2

n/F2p ratios. They advocate a 5% renormalization (~3 times

published systematic error) of JLab data. I advocate reexamining isovector dependence of EMC effect.

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Are there data at the hadronic level that nucleon structure is changing?

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Nuclear Effects in Spin Dependence Why its big?

– Quark-Meson Coupling model: – Lower Dirac component of confined light quark modified most by the scalar field

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If one understands parton propagation in nuclei, semi-inclusive DIS and flavor tagging could give insight into flavor dependence of EMC effect as it has for spin.HERMES has a new slant on the strange quark sea distributions. A. Airapetian et al Phys. Lett. B 666, 446 (2008)

Usually s(x)+sbar(x) ~ κ (ubar+ dbar) with κ~ 0.5Best handle has been considered to be multi-muon events in neutrino scattering.HERMES looks at DIS on deuterium and compares inclusive with semi-inclusive kaon multiplicities

)()()(

)()()()()(

)()()()(),()(

)(2)(5),()(

22

2

22

2

xsxsxS

xdxdxuxuxQ

dzzDxSdzzDxQQxdxdQ

xNd

xSxQQxdxdQ

xNd

KS

KQU

K

U

DIS

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HERMES sees little strange quark content for x>0.1 and s(x)+sbar(x) ~ ubar(x)+dbar(x) at x< 0.03!

A. Airapetian et al Phys. Lett. B 666, 446 (2008) Q2=2.5 GeV2

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How is this consistent with years of neutrino multi-muon data? ν + s → μ+ + c →μ-

NUTEV, PRD 64 112006(2001) CTEQ, JHEP 42, 89 (2007) Q2=1.69

Note 5/3

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Comparison of ubar+dbar-s-sbar with dbar-ubar

)]()()()([ xsxsxdxux

Based on the HERMES result and assuming the strange quark distribution represents the gluon-splitting induced distribution, the shape of the non-perturbative

is similar to

)]()([ xuxdx vs 0.25 *HERMES

)]()([ xuxdx

)]()()()([ xsxsxdxux

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Can JLab probe the glue?

dF2(Sn)/dx / dF2(C)/dx vs Q2

R = σL / σT

The primary question is can this precision be achieved.Double ratios reduce systematics for measurements in two different spectrometers

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Is shadowing Q2 dependent? Have to look at x<0.05!

Q2 < 1 at JLab12 in shadowing region.Kulagin and Petti (1004.3062) take difference between NMC and HERMES as evidence of Q2 dependence from vector dominance description of shadowing

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Relation between short range correlations and medium modifications/EMC effect?

1

d

AK

1

d

AK

)1('

AA

NZ

dx

dRK

Stolen from John Arrington

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Direct measurements of short range correlations in deuterium

D(e.e’p)n to high missing momentum

Is kinematics chosen to emphasize/mimimize FSI and MEC?

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(γ,pp) Quark Counting rules vs Rescattering?

d(,p) scales at E>1 GeV

pp(,p) may scale at E>2.5 GeVOscillation signal rescattering picture

Does not require 12 GeV

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Using secondary interactions in a nuclear target to study cross sections for short lived objects to interact with nucleons and to determine time scales in strong interaction dynamics

Hadronization

Color Transparency

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Hadronization – the fundamental realization of confinement

Mostly taken from Accardi et al. RIVISTA DEL NUOVO CIMENTO 32, 439-553 (2009)

Other complications Resonance decay Overlap of target and projectile fragmentation regions at low z

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With so many unknowns, what can we vary or measure?

Photon Energy Nucleus – length of nuclear material for re-interaction Hadron species Fractional energy of the hadron, z

– <tpreh>=f(z) (1-z) zν/Kstr

Transverse momentum– Gluon radiation or multiple scattering

Good news – energy loss effects are larger fractionally at low energy– Resolution is better at low energy

Need very differential cross section to try to separate these effects. – Hermes was first to see clear z dependence in nuclear ratios - EMC, E665 no z dependence– JLab offers much better statistics that can be sliced and diced in many ways

Essential for validating use of SIDIS Interesting physics of confinement Potentially valuable for comparison to hot nuclear matter

Data driven Will there ever be serious theoretical predictions???

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Jlab has the luminosity to slice and dice this:

CLAS12: 12-06-117

Likely not have the ν range to reach non-interacting limit to separate energy loss from attenuation?

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Color Transparency

Need– Compact size initial state– Small cross section with compact size– Evolution to full size take few fm

Diffractive Vector meson prepares small size q-qbar pair with small color dipole

Must pay attention to coherence length to measure formation length/transparency effects

Solid 5 GeV results

12 GeV results extend kinematic range in both Q2 and range of formation and coherence length

lc lf

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In non-diffractive channels, compact size of elementary

interaction is still an issue.Many consider it a necessary condition for GPD applicability Protons

No clear effect so far Extend to Q2=16 GeV2 at

12 GeVI am betting on no effect to

higher Q2, but it has to be measured.

Pions First hint in non-

diffractive production Extend to Q2~9 GeV2

Babar *→π0

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Study of light hypernuclei by pionic decay at JLab

Relationship of hyperon-nucleon interaction to N-N interaction remains an important clue in understanding low-energy baryon-baryon interaction

Also has impact on neutron star structure

My opinion is we have to get past the exploratory phase and into a production phase for this to realize its promise, i.e. not study one or two levels but many.

Pionic decay offers this promise if count rate and resolution is sufficient

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Pion decay spectra

Finuda Results

JLab goal

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Summary

JLab12 can make significant contributions to understanding the implications of the quark structure of nuclei on nuclear structure

I believe one needs to see consistent effects at the quark and the hadron level to believe we truly understand what is happening.

Short-range correlations may show particular sensitivity to hadron structure in the nuclear medium. We need to correlate both direct and indirect (x>1) measurements.

The space-time evolution of hadronization requires 2-3 fold differential studies that have not been possible in the past.

The lower energy at JLab emphasizes energy loss and reinteraction effects compared to high energy measurements

SIDIS may provide new insight into nuclear dependence once propagation effects are quantified.

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Most of the information on the sea came from deep-inelastic lepton scattering, especially charged current neutrino experimentsQ2 = (k-k’)2 = mass2 of the virtual boson

x= Q2/(2m) is the fractional momentum nucleon carried by the parton

= Ebeam- Escattered y = / Ebeam

)(xfdx

di

iql i

muon and electron scattering~ charge current scattering ~anti- c. c. scattering~ parity violating scattering, F3~parity violating anti- scattering~ )(2

)(2

))]()1([2

)]()1([2

])[9/1][9/4(2

2

2

sdcux

cusdx

sdycux

cuysdx

sdsdcucux

The high statistics experiments are all done on nuclear targets

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Does deuterium structure affect the results at higher x

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Nuclear corrections in charged lepton and neutrino scattering are different

Charged lepton Fe/D Neutrino Fe/D

F2(Fe from neutrinos)/F2(D determined w/o neutrino data)

Schienbein et al.

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Experiments Quark structure and short range correlations

– E12-06-105 Inclusive scattering from nuclei with x>1 in the quasielastic and deeply inelastic regimes

– E12-10-008 Detailed studies of nuclear dependence of F2 in light nuclei– PR12-10-012 Precision measurement of nucleon and nuclear structure functions to constrain

gluon distributions – P12-10-004 Hard photodisintegration of a proton pair– E12-10-003 Deuteron electro-disintegration at very high missing momentum

Color Transparency– E12-06-106 Study of color transparency in exclusive vector meson production off

nuclei– E12-06-107 The search for color transparency at 12 GeV

Hadronization– E12-06-117 Quark propagation and hadron formation– E12-07-101 Hadronization in nuclei by deep inelastic scattering

Other Nuclear effects– E12-07-106 The A Dependence of J/Psi Photoproduction near Threshold– E12-10-001 Study of light hypernuclei by pionic decay at JLab

Experiments where I am on proposal

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J/ψ Production Near Threshold

Exploratory experiment Cross section near threshold

poorly known

Small size leads to interesting dynamics

Extracting J/ψ-nucleon cross section through A dependence is of considerable interest, but handling nuclear corrections requires care because σ γ→J/ψ is has strong energy dependence at ~11 GeV.

lc and lf chosen small