Hadrons and Cold Nuclear Matter Rapporteur Presentation

1. Hadrons and Cold Nuclear MatterRapporteur Presentation Donald Geesaman JLAB PAC 36 24 August 2010 A person appointed by a deliberative body to investigate an issue or a situation and report to that body

2. History – as started by Mont in his ascent to Nuclear Physics 1983- EMC - Ratio of iron to deuterium Note systematic errors are large and don’t show up on electronic archive 1984-EMC- virtual photon energy dependence of leading hadron multiplicities

3. 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?

4. average spacing at ρnm ~ 1.8 fm Radius of a nucleon ~ 0.8 fm Radius of heavy nucleus at ~ 6 fm Our visual images of a nucleus OR “nucleons” held apart by short range repulsion but even in 208Pb, half the nucleons are in the surface OR ???

5. We want to describe a nucleus • 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? • 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 One of my criteria for a successful theoretical description is multiple phenomena should be described, both at the hadronic and parton levels.

6. Experiments where I am on proposal 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

7. 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.

8. Nuclear modifications of parton distributions Most models have limited x ranges Either constructive interference or other hadrons exaggerated EMC region L short Either f(y) peaks below 1 or F2N modified in nucleus Nuclear motion or short-range corrections As x-> 2 ratio goes to ~6 Shadowing L ~ 2ν/Q2 ~ 1/x >2 fm Destructive interference or gluon recombination

9. 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.

10. 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

11. 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) JLab Data Black points 3He Benhar and Pandharipande 3He Calculations by Pandharipande and Benhar for 3He and 4He Magenta points 4He I don’t like presenting Isoscalar corrected ratio Benhar and Pandharipande 4He

12. 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 F2n/F2p ratios. They advocate a 5% renormalization (~3 times published systematic error) of JLab data. I advocate reexamining isovector dependence of EMC effect.

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

14. 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

15. 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~ 0.5 Best 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

16. 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

17. 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

18. Comparison of ubar+dbar-s-sbar with dbar-ubar vs 0.25 *HERMES 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

19. 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

20. Is shadowing Q2 dependent? Have to look at x<0.05! Q2 < 1at 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

21. Relation between short range correlations and medium modifications/EMC effect? Stolen from John Arrington

22. 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?

23. (γ,pp) Quark Counting rules vs Rescattering? d(,p) scales at E>1 GeV pp(,p) may scale at E>2.5 GeV Oscillation signal rescattering picture Does not require 12 GeV

24. 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

25. 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

26. 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???

27. Jlab has the luminosity to slice and dice this:CLAS12: 12-06-117Likely not have the ν range to reach non-interacting limit to separate energy loss from attenuation?

28. lf lc 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

29. In non-diffractive channels, compact size of elementary interaction is still an issue.Many consider it a necessary condition for GPD applicability Babar *→π0 • Protons No clear effect so far Extend to Q2=16 GeV2 at 12 GeV I 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

30. 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

31. Pion decay spectra JLab goal Finuda Results

32. 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.

33. Most of the information on the sea came from deep-inelastic lepton scattering, especially charged current neutrino experiments Q2 = (k-k’)2 = mass2 of the virtual boson x= Q2/(2m) is the fractional momentum nucleon carried by the parton • = Ebeam- Escattered y =  / Ebeam muon and electron scattering~  charge current scattering ~ anti- c. c. scattering~ parity violating  scattering, F3~ parity violating anti- scattering~ The high statistics experiments are all done on nuclear targets

34. Does deuterium structure affect the results at higher x

35. Nuclear corrections in charged lepton and neutrino scattering are different Schienbein et al. Charged lepton Fe/D Neutrino Fe/D F2(Fe from neutrinos)/F2(D determined w/o neutrino data)

36. Experiments where I am on proposal 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

37. lc and lfchosen small 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 σγ→J/ψ is has strong energy dependence at ~11 GeV.