1. How Does Short Distance Behavior Affect the Nucleus Don Geesaman 12 January 2007 DNP QCD Town Meeting

2. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 2 Why We built JLab and did experiments at SLAC, FNAL, DESY... because the short-distance behavior of nuclei was not understood. –the nucleus is more than mean-field and long-range correlations. High momentum transfer = short distances –short range components of N-N interaction High momentum transfer = resolve the QCD structure –where are the QCD effects in nuclei? We know at high temperature or density things must change. –how high is high –is transition continuous or abrupt? –where do neutron stars lie?

3. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 3 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 The problem is always whether our description of a bare proton is good enough and then how to actually calculate many body effects?

4. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 4 Issues in Proton Structure – new data has been critical! Nucleon form factors spin carried by the quarks and gluons and angular momentum nature of the sea

5. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 5 Our visual images OR “nucleons” held apart by short range repulsion but even in 208 Pb, half the nucleons are in the surface average spacing at ρ nm ~ 1.8 fm Radius of a nucleon ~ 0.8 fm average spacing at 3ρnm ~ 1.3 fm

6. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 6 What do we know about short distance behavior in nuclei? Strong N-N potential does have impacts NN Interaction NN Correlation Functions

7. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 7 What do we know about short distance behavior in nuclei? Impact of correlations on high momentum structure of wave functions –direct observation high momentum components in (e,e’p) x>1 correlations –indirect (quenching) effects reduction of single particle strength – Spectroscopic factors apparent changes in bare form factors – quenching of G A

8. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 8 Direct measurement JLab E97-006 Rohe et al. PRL 93, 182501 (04) 0.61+/-.06 protons in p m >240 MeV/c and E m > 40 MeV

9. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 9 Spectroscopic factors

10. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 10 Distribution of spectroscopic strength (from Dickhoff) Note ab initio calculations do very good job in, for example 7 Li – SRC+LRC.

11. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 11 Basic “facts” of nuclear physics that may be wrong in neutron-rich nuclei The radius and diffuseness of the neutron and proton distributions are similar R=1.2 A 1/3, a~ 0.55 fm The magic numbers of the shell model are fixed. The deformations of the neutrons and protons are similar The valence quasi-particles are renormalized by about 0.6 by short-range correlations. The charge-independence of the strong interaction makes isospin a good quantum number This is only illustrative. There are a number of other mechanisms that also lead to changes in the shell structure as N/Z varies.

12. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 12 Does the impact of correlations change dramatically away from valley of stability?  S = S n -S p for neutron knockout and S p -S n for proton knockout History 1960’s: Shell Model and transfer reactions assumed pure single particle states. 1970’s: electron scattering showed only 60% occupancy in valence single particle states. 1980’s: Understood based on correlations. 1990’s: Correlations viewed as universal, approximately nucleus independent. 2000’s: In nuclei far from stability, observed large changes in correlation effects. 22 O 34 Ar From Gade and Tostevin, NSCL Note R s is ratio to shell model not spectroscopic factor

13. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 13 Another way to look at high momentum components: x>1 data 2 and 3 nucleon correlations It appears that correlations dominate the deep inelastic structure functions at high x. Not likely to tell us about quark substructure! CLAS Egiyan et al.

14. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 14 Towards better understanding of short range behaviour NN, NNN Data –a number of puzzles –what is the key experiment? Lattice –very long way to go Effective field theory –Need at least N3LO – Chi 2 of order 1 Still a fit to data, but about ½ the free parameters! –3NF – still working on N3LO Other baryon-nucleon interactions: Modern lattice QCD result S.R. Beane et al, PRL 97 (2006)

15. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 15 Nucleon-Baryon Interactions Λ-NNo one pion exchange –small spin-orbit interaction –perhaps more direct window on short range behavior –Will low energy data (scattering length, hypernuclear spectroscopy) provide enough constraints? Σ – N and Ξ – N Important for neutron star matter. How to probe? P P Interactions –G parity says short range part changes –problem is absorption is so strong that little information seems to be obtainable

16. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 16 Alexa et al PRL 82, 1374 (99) e-d elastic scattering Does structure of baryons change in nuclei? So far JLAB has taught us that hadron structure/interactions do not change much (to the precision we can determine today) at normal matter densities. Schiavilla et al PRL 94, 072303 (05) Perhaps the smoking gun?

17. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 17 Quark Meson Coupling predictions

18. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 18 Parton Distributions in Nuclei 1984 – Parton distributions are different EMC effect – nucleon carries smaller fraction of momentum or changes structure Shadowing 1990 – little change in sea quarks for x>0,1 2007 –x >1 data dominated by correlations –still need flavor separation and larger x range for antiquarks. –Will we finally be able to tag parton distributions vs the momentum and binding energy of spectator particles? –predicted large effects in spin structure Alde et al (Fermilab E772) Phys. Rev. Lett. 64 2479 (1990)

19. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 19 Still only one high precision measurement of antiquarks: Where are the nuclear pions? The binding of nucleons in a nucleus modifies the x dependence. Most contemporary models still predict large effects to antiquark distributions as x increases. Models must explain both DIS-EMC effect and Drell-Yan Sufficient uncertainly that CTEQ is worried about using neutrino data on Fe to establish nucleon antiquark distributions. MINERva – neutrino A dependence Smith and Miller

20. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 20 Advantages of 120 GeV Main Injector The (very successful) past: Fermilab E866/NuSea Data in 1996-1997 1 H, 2 H, and nuclear targets 800 GeV proton beam The future: Fermilab E906 Data in 2009 1 H, 2 H, and nuclear targets 120 GeV proton Beam Cross section scales as 1/s –7 x that of 800 GeV beam Backgrounds, primarily from J/  decays scale as s –7 x Luminosity for same detector rate as 800 GeV beam 50 statistics!! 50 x statistics!! Fixed Target Beam lines Tevatron 800 GeV Main Injector 120 GeV

21. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 21 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 3 He) Calculations by Pandharipande and Benhar for 3 He and 4 He Approximate uncertainties for 12 GeV coverage

22. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 22 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

23. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 23 Neutron Stars probe densities to 6 ρ NM Is neutron matter superfluid? –low density – yes –higher density ??? Do we see transition to kaon-condensed, hyperson, or quark matter ? Nuclear Observables: –neutron skins –N/Z dependence of giant resonances –nuclear equation of state studies Astronomical observations –What are the limits on mass and radii? –cooling? Recent observation of high mass neutron stars 2.1 ± 0.2 M  Nice et al. astro-ph/0508050 2.1 ± 0.28 M , R=13.8 ± 1.8 km Ozel, Nature 441, 04858 (2006) Correlation between neutron skin thickness in finite nuclei and pressure of β-equilibrated matter in neutron stars

24. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 24 Constraints on neutron star equations of state Mass-Radius constraints from observations and model predictions for the mass- radius of nucleonic stars, hybrid stars and strange quark stars. (From Jaikumar, Page and Reddy)

25. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 25 What really happens at high density? Stone, Guichon, Matevosyan and Thomas

26. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 26 Summary Success –Two body correlations mapped out Dickhoff: “unique for a correlated many body system” –beginning to get information on three body correlations –correlations may be quite different in nuclei far from stability Still to do – and a lot harder than we had hoped –QCD description of short range N-N behavior –definitive evidence for changes in proton structure in nuclei beyond easily understood (if hard to calculate) mean-field effects. –Spin and binding/spectator momentum effects –flavor dependence - extend nuclear anti-quark measurements to regions where effects may be much larger. –a long way to go to be confident about what happens in neutron stars

27. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 27 x target x beam Detector acceptance chooses x target and x beam. Fixed target  high x F = x beam – x target Valence Beam quarks at high-x. Sea Target quarks at low/intermediate-x. Drell-Yan scattering: A laboratory for sea quarks E906 Spect. Monte Carlo

28. Don Geesaman Short Distance Behavior in Nuclei 12 January 2007 28 Separating structure and dynamics