University of British Columbia

1. Nuclear Studies with Hard Knockout Reactions Scattered electron Incident electron Scattered proton Recoil partner July, 2010 Eli Piasetzky University of British Columbia Tel Aviv University, ISRAEL

2. 2N-SRC Nucleons Hard processes are of particular interest because they have the resolving power required to probe the partonic structure of a complex target DIS partonic structure of hadrons Scale: several tens of GeV HARD KNOCKOUT REACTIONS hadronic structure of nuclei Scale: several GeV ~1 fm

3. A description of nuclei at distance scales small compared to the radius of the constituent nucleons is needed to take into account, ~1 fm Short range repulsion (common to many other systems) Intermediate- to long-range tensor attraction (unique to nuclei) Very difficult many-body problem presents a challenge to both experiment and theory This long standing challenge for nuclear physics can experimentally be effectively addressed thanks to high momentum transfer reached by present facilities.

4. Short /intermediate Range Correlations in nuclei What SRC in nuclei can tell us about: High – Momentum Component of the Nuclear Wave Function. LRC ~RA SRC ~RN The Strong Short-Range Force Between Nucleons. tensor force, repulsive core, 3N forces Cold-Dense Nuclear Matter (from deuteron to neutron-stars). Nucleon structure modification in the medium ? EMC and SRC 2N-SRC ~1 fm 1.f 1.7f 1.7 fm o = 0.16 GeV/fm3 A~1057 Nucleons

5. Spectroscopic factors for (e, e’p) reactions show only 60-70% of the expected single-particle strength. L. Lapikas, Nucl. Phys. A553, 297c (1993) Benhar et al., Phys. Lett. B 177 (1986) 135. MISSING : Correlations Between Nucleons SRC and LRC

6. The inclusive A(e,e’) measurements e/ e pi Adapted from Ciofi degli Atti q • At high nucleon momentum • distributions aresimilarin shape for • light and heavy nuclei:SCALING. • Frankfurt and Strikman: Can be explained by 2N-SRC dominance. • Within the 2N-SRC dominance picture one can get the probability of 2N-SRC in any nucleus, from the scaling factor. Problem: In A(e,e’) the momentum of the struck proton (pi) is unknown. Deuterium Solution: For fixed high Q2 and xB>1, xB determines a minimum pi Q2=2 GeV2 Prediction by Frankfurt, Sargsian, and Strikman:

7. A(e,e’) Kinematics e' (,q) e (just kinematics!) DISoff a nucleon: xB gives the fraction of the nucleon momentum carried by the struck parton HARD KNOCKOUT REACTIONS For large Q2: xB counts the number of hadrons involved 2N-SRC 3N-SRC

8. JLab. CLAS A(e,e') Result The observed “scaling” means that the electrons probe the high-momentum nucleons in the 2(3) -nucleon phase, and the scaling factors determine the per-nucleon probability of the 2(3) N-SRC phase in nuclei with A>3 relative to 3He. K. Sh. Egiyan et al. PRC 68, 014313 (2003) K. Sh. Egiyan et al. PRL. 96, 082501 (2006) For 12C 2N-SRC (np, pp, nn) = 20 ± 4.5%. The probabilities for 3-nucleon SRC are smaller by one order of magnitude relative to the 2N SRC. More r(A,d) data: SLAC D. Day et al. PRL 59,427(1987) JLab. Hall C E02-019

9. A triple – coincidence measurement EVA / BNL E01-015 / Jlab p p A pair with “large” relative momentum between the nucleons and small CM momentum. p n “Redefine” the problem in momentum space K 1 K 1 > KF , K 2 > KF KF ~250 MeV/c K 2 (E07-006) • K 1 -K 2

10. Why several GeV and up protons are good probes of SRC ? They have small deBroglie wavelength:  = h/p = hc/pc = 2  0.197 GeV-fm/(6 GeV)  0.2 fm. Large momentum transfer is possible with wide angle scattering. The s-10 dependence of the p-p elastic scattering preferentially selects high momentum nuclear protons. For pp elastic scattering near 900 cm QE pp scattering near 900 has a very strong preference for reacting with forward going high momentum nuclear protons. 10

11. p  p1   pf p0 p p n Target nucleus  p2  pn    p We can then compare pn withpfand see if they are roughly “back to back.” From p0, p1, and p2we can deduce, event-by-event what pf and the binding energy of each knocked-out proton is.    11

12. 12C(p, p’pn) measurements at EVA / BNL pf γ pn A. Tang et al. Phys. Rev. Lett. 90 ,042301 (2003) Directional correlation Piasetzky, Sargsian, Frankfurt, Strikman, Watson PRL 162504(2006). Removal of a proton with momentum above 275 MeV/c from 12C is 92±818 % accompanied by the emission of a neutron with momentum equal and opposite to the missing momentum. σCM=0.143±0.017 GeV/c

13. JLab Hall A EXP 01-015 Identify pp-SRC pairs in nuclei. (e, e’ p p) Determine the abundance of pp-SRC pairs. (e, e’ p p) / (e, e’ p) Verify the abundance of np-SRC pairs as determined by the EVA / BNL experiment. (e, e’ p n) / (e, e’ p) Determine the pp-SRC / np-SRC ratio. (e, e’ p p) / (e, e’ p n) It is important to identify pp-SRC pairs and to determine the pp-SRC/np-SRC ratio since they can tell us about the isospin dependence of the strong interaction at short distance scale. E01-015 Simultaneous measurements of the . (e,e’ p) , (e, e’ p p), and (e, e’ p n) reactions.

14. Simultaneous measurements of the . (e,e’ p) , (e, e’ p p), and (e, e’ p n) reactions. HRS EXP 01-015 Hall A JLab HRS n array p p e n e Big Bite Lead wall Dec. 2004 – Apr. 2005

15. Directional correlation p γ p 12C(e,e’pp) Simulation with pair CM motion σCM=136 MeV/c BG (off peak) Measured 2 components of and 3 kinematical setups => σCM=0.136 ± 0.020 GeV/c (p,2pn) experiment at BNL : σCM=0.143±0.017 GeV/c Theoretical prediction (Ciofi and Simula) : σCM=0.139 GeV/c

16. EXP 01-015 / Jlab +8 -18 R. Subedi et al., Science320 (2008) 1476 Preliminary Yield Ratio [%] 96 ± 23 % BNL Experiment measurment was 92 % 9.5 ± 2 % R. Shneor et al., PRL 99, 072501 (2007) Yield Ratio [%] (e,e’pp) (e,e’p) Missing momentum [MeV/c]

17. The (e, e’pn) / (e, e’pp) ratio 179 ± 39 Corrected for detection efficiency: Corrected for SCX (using Glauber): TOF for the neutrons [ns] In Carbon: 116±17 TOF for the protons [ns]

18. There are 18 ± 5 times more np-SRC than pp-SRC pairs in 12C. Why ? R. Subedi et al., Science 320, 1476 (2008). BNL / EVA 12C(e,e’pn) / 12C(e,e’p) [12C(e,e’pn) / 12C(e,e’pp)] / 2 [12C(e,e’pp) / 12C(e,e’p)] / 2

19. At 300-500 MeV/c there is an excess strength in the np momentum distribution due to the strong correlations induced by the tensor NN potential. pp/np 3He 3He np np pp pn pp V18 pp Bonn 3He Schiavilla, Wiringa, Pieper, Carson, PRL 98,132501 (2007). Ciofi and Alvioli PRL 100, 162503 (2008). Sargsian, Abrahamyan, Strikman, Frankfurt PR C71 044615 (2005).

20. Q>0 q=300-500 MeV/c pp/pn ratio as a function of pair CM momentum np pp q (fm-1) Q (fm-1) Wiringa, Schiavilla, Pieper, Carlson PRC 78 021001 (2008) Small Q  pp pair in s-wave  large tensor contribution  small pp/np ratio JLab / Hall B preliminary data Thanks to L. Weinstein 300 < q < 500 MeV/c PRELIMINARY Hall A / BNL pair CM momentum Q

21. (e,e’) 60-70% 10-20% 20±5% Thus, the deduced short range 12C structure is: 60-70 % - independent particle in a shell model potential. 80 ± 4.5 % - single particle moving in an average potential. 10-20 % - shell model long range correlations (e,e’p) 18 ± 4.5 % - SRC np pairs . (p,2pn) 20 ± 4.5 % - 2N SRC . 0.95±0.2% - SRC pp pairs. 2N-SRC n-p pairs p-p pairs 74-92 % 4.75±1% 0.95±0.2 % - SRC nn pairs. (e,e’pN) 4.75±1% n-n pairs Small ~1% - SRC of “more than 2 nucleons”. ? ~1% -non nucleonic degrees of freedom (e,e’)

22. What else did we learn recently about SRC ? The dominant NN force in the 2N-SRC is the tensor force. 2N-SRC  2N 2N-SRC mostly built of 2N not 6 quarks or NΔ, ΔΔ. All the decay strength to non-nucleonic components can not exceed 20% of the 2N-SRC. (e,e’pN)

23. Fe(e,e’pp) Pb(e,e’pp) Ein =5.014 GeV Q2=2GeV/c2 X>1.2 JLab / CLAS Data Mining, EG2 data set, Or Chen et al.

24. Directional correlation p γ p 12C(e,e’pp) Simulation with pair CM motion σCM=136 MeV/c BG (off peak) Measured 2 components of and 3 kinematical setups => σCM=0.136 ± 0.020 GeV/c (p,2pn) experiment at BNL : σCM=0.143±0.017 GeV/c Theoretical prediction (Ciofi and Simula) : σCM=0.139 GeV/c

25. Directional correlation p γ p C(e,e’pp) Hall A data PRL 99(2007)072501 Hall B JLab / CLAS Data Mining, EG2 data set, Or Chen et al. PRELIMINARY Fe(e,e’pp) Pb(e,e’pp)

26. Implications for Neutron Stars Adapted from: D.Higinbotham, E. Piasetzky, M. Strikman CERN Courier 49N1 (2009) 22. • At the core of neutron stars, most accepted models assume : • ~95%neutrons, ~5%protons and ~5% electrons (β-stability). • Neglecting the np-SRC interactions, one can assume three separate Fermi gases (n p and e). • strong np interaction the n-gas heats the p-gas. n See estimates in Frankfurt and Strikman : Int.J.Mod.Phys.A23:2991-3055,2008.

27. EMC and SRC Largest attractive force SRC Mean field High local nuclear matter density, large momentum, large off shell. large virtuality PRL 103, 202301 (2009) How big is the EMC effect in dense nuclear systems? What would be the consequences of a large EMC in these systems? Will the EMC effect reverse its sign for repulsive core dominance ? EMC effect in the deuteron ?

28. A new experiment scheduled to run 2011 at JLab (E 07-006) Measurement over missing momentum range from 400 to 875 MeV/c. Taketani,Nakamura,Saaki Prog. Theor. Phys. 6 (1951) 581. (e,e’pp) / (e,e’pn) Chiral effective field Lattice QCD Adapted form W.Wesie The data are expected to be sensitive to the NN tensor force and the NN short range repulsive force.

29. A new experiment scheduled to run 2011 at JLab (E 08-014) A(e,e’) Spokeperson: Arrington, Day, Higonbotham, Solvingnon δp = ±4.5% Q2 δp = ±3% Q2 (GeV/c)2 29o A wide range of Q2 and XB that will allow to study the 2N, 3N scaling and the transition between them. 27o 25o 23o 21o The Inclusive (e,e’) scattering is ‘isospin-blind’ but Information on the isospin structure can be achieved by comparing targets like 40Ca and 48 Ca. 19o 17o 15o x 2N 3N 4He, 12C, 40Ca, 48ca Isospin independent: n-p (T=0) dominance: For no extra T=0 pairs with f7/2 neutron:

30. What is the role played by non nucleonic degrees of freedom in SRC ? m outlook How to relate what we learned about SRC in nuclei to the dynamics of neutron star formation and structure ? What is the role played by short range correlation of more than two nucleons ? 12 GeV JLab GSI SRC The new facilities will allow even harder knockout reactions EMC Is theory well enough established to interpret the data? QE What are the observables ? 0ptimized kinematics ? DIS

31. I would like to thank the organizers for the invitation to a great conference at a wonderful location

33. The kinematics selected for the E01-015 measurement p Pm = “300”,”400”,”500” MeV/c Ee’ = 3.724 GeV e’ Ee = 4.627 GeV 19.50 e 50.40 40.1, 35.8, 32.00 P = 300-600 MeV/c n or p p = 1.45,1.42,1.36 GeV/c Q2=2 (GeV/c)2 p qv=1.65 GeV/c 99 ± 50 X=1.245

34. E01-015: A customized Experiment to study 2N-SRC Q2 = 2 GeV/c , xB ~ 1.2 , Pm=300-600 MeV/c, E2m<140 MeV Luminosity ~ 1037-38 cm-2s-1 Kinematics optimized to minimize the competing processes High energy, Large Q2 The large Q2 is required to probe the small size SRC configuration. MEC are reduced as 1/Q2 . Large Q2 is required to probe high Pmiss with xB>1. FSI can treated in Glauber approximation. xB>1 Reduced contribution from isobar currents. Large pmiss, and Emiss~p2miss/2M Large Pmiss_z

35. Kinematics optimized to minimize the competing processes FSI FSI with the A-2 system: Kinematics with a large component of pmiss in the virtual photon direction. Small (10-20%). Pauli blocking for the recoil particle. Geometry, (e, e’p) selects the surface. Can be treated in Glauber approximation. Canceled in some of the measured ratios. FSI in the SRC pair: These are not necessarily small, BUT: Conserve the isospin structure of the pair . Conserve the CM momentum of the pair.

36. Why FSI do not destroy the 2N-SRC signature ? For large Q2 and x>1 FSI is confined within the SRC FSI in the SRC pair: Conserve the isospin structure of the pair . Conserve the CM momentum of the pair.

37. Assuming in 12C nn-SRC = pp-SRC and 2N-SRC=100% A virtual photon with xB >1 “sees” all the pp pairs but only 50% of the np pairs. 1-2x x x

39. k Fermi p e k k Fermi Fermi SRC in nuclei: implication for neutron stars • At the core of neutron stars, most accepted models assume : • ~95%neutrons, ~5%protons and ~5% electrons (β-stability). • Neglecting the np-SRC interactions, one can assume three separate Fermi gases (n p and e). At T=0 For Pauli blocking prevent direct n decay n Strong SR np interaction

40. 2 4 5 6 3 2 5 6 1 3 4 1 What did we learn recently about SRC ? The standard model for the short distance structure of nuclei CLAS / HALL B The probability for a nucleon to have momentum ≥ 300 MeV / c in medium nuclei is ~25% . PRL. 96, 082501 (2006) More than ~90% of all nucleons with momentum ≥ 300 MeV / c belong to 2N-SRC. The probability for a nucleon with momentum 300-600 MeV / c to belong to np-SRC is ~18 times larger than to belong to pp-SRC. The dominant NN force in the 2N-SRC is the tensor force. PRL 98,132501 (2007). 2N-SRC mostly built of 2N not 6 quarks or NΔΔΔ. All the non-nucleonic components can not exceed 20% of the 2N-SRC. EVA / BNL and Jlab / HALL A Three nucleon SRC are present in nuclei. PRL 162504(2006); Science 320, 1476 (2008).

41. ) Ciofi,