Studying Short range Correlation in Nuclei at the Repulsive Core Limit via the triple Coincidence (e, e’ p N) Reaction PAC 31 / TJNAF Jan Proposal (Next Generation of E01-015) Hall A / TJNAF e e’ p p or n

2N-Short Range Correlations (2N-SRC)  1.f Nucleons 2N-SRC 1.7f  o = 0.17 GeV/fm 3   5  o 1.7 fm ~1 fm

SRC in nuclei Dynamics of neutron star formation and structure Study of cold dense nuclear matter complementary to study of hot dense nuclear matter Quark vs. hadronic degrees of freedom in nuclei NN interaction: short range repulsive core and the role played by the tensor force Why should we care about 2N-SRC ? Coulomb sum rule

What do we want to know about 2N-SRC ? What fraction of the momentum distribution is due to 2N-SRC ? What is the relative momentum between the nucleons in the pair? What is the ratio of pp to pn pairs? Are these nucleons different from free nucleons (e.g size,shape, mass, etc.)? ·What is the pair CM momentum distribution ?

<1 fm K 1 > K F, K 2 > K F K 1 K 2  K 1 K 2 “Redefine” the problem in momentum space A pair with “large” relative momentum between the nucleons and small CM momentum. Triple – coincidence measurements of large momentum transfer high energy reactions:

p p p n EVA / BNL E / Jlab p e e n p e e p Triple – coincidence measurements:

np-SRC pairs have been observed. * 2N-SRC dominance (74-100% are partners in 2N-SRC). * np-SRC dominance: A. Tang Phys. Rev. Lett. 90, (2003) Piasetzky, Sargsian, Frankfurt, Strikman, Watson PRL (2006). Removal of a proton with momentum above the Fermi sea level from 12 C is 92± 8 18 % accompanied by the emission of a neutron with momentum equal and opposite to the missing momentum. Triple coincidence (p, p pn) measurements at EVA / BNL γ p n Directional correlation Did not observe pp-SRC. Upper limit of 13% for pp-SRC contribution to protons with momentum above 275 Mev/c in 12 C.

Identify pp-SRC pairs in nuclei. Determined the pp-SRC / np-SRC ratio. Simultaneously measurements of the (e,e’ p), (e, e’ p p) (e, e’ p n) reactions. Determined the abundance of pp-SRC pairs. E What did we want to achieve in E / Jlab ? Verify the abundance of np-SRC pairs as deteremind by the EVA / BNL experiment. (e, e’ p p) (e, e’ p p) / (e, e’ p) (e, e’ p n) / (e, e’ p) (e, e’ p p) / (e, e’ p n) It is important to identify pp-SRC pairs and to determined the pp-SRC/np-SRC ratio since they can tell us about the isospin dependence of the strong interaction at short distance scale.

Kinematics optimized to minimize the competing processes High energy, Large Q 2 MEC are reduced as 1/Q 2. Large Q 2 is required to probe high P miss with x B >1. FSI can treated in Glauber approximation. x B >1 Reduced contribution from isobar currents. Large p miss, and E miss ~p 2 miss /2M Large P miss_z E01-105: An Custom Experiment to study 2N-SRC Q 2 = 2 GeV/c, x B ~ 1.2, P m = MeV/c, E 2m <140 MeV Luminosity ~ cm -2 s -1 The large Q 2 is required to probe the small size SRC configuration.

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

p e e’ n or p p Pm = “300”,”400”,”500” MeV/c 99 ± 5 0 P = MeV/c Ee = GeV Ee’ = GeV Q 2 =2 (GeV/c) 2 q v =1.65 GeV/c , 35.8, p = 1.45,1.42,1.36 GeV/c The selected kinematics for the measurement X=1.245

Experimental setup HRS p e e p Big Bite n array EXP / Jlab n Lead wall

EXP Jlab / Hall A Dec – Apr BigBite Spectrometer Neutron Detector

x B >1 12 C(e,e’p) 12 C(e,e’p) 11 B “300 MeV/c” “400 MeV/c” “500 MeV/c” (e,e’∆)(e,e’p) “300 MeV/c” “400 MeV/c” “500 MeV/c”

TOF [ns] P mis =“300” MeV/c (Signal : BG= 1.5:1) P mis =“400” MeV/c (Signal : BG= 2.3:1) P mis =“500” MeV/c (Signal : BG= 1:7) (Signal : BG= 4:1) TOF [ns] (e,e’pp) (e,e’pn)

12 C(e,e’pp) γ Directional correlation p p BG (off peak) MCEEP Simulation with pair CM motion σ CM =136 MeV/c

12 C(e,e’pn) γ Directional correlation p n MCEEP Simulation with pair CM motion σ CM =136 MeV/c BG (off peak)

CM motion of the pair: (p,2pn) experiment at BNL : σ CM =0.143±0.017 GeV/c Theoretical prediction (Ciofi and Simula) : σ CM =0.139 GeV/c This experiment : σ CM =0.136±0.015 GeV/c P c.m verical, “500 MeV/c “ setup MCEEP with pair CM motion: σ CM =50 MeV/c σ CM =100 MeV/c σ CM =136 MeV/c 2 components of and 3 kinematical setups

Preliminary 9.5 ± 2 % 107 ±23 % R. Shneor et al., To be submitted R. Subedi et al., To prepared

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

For MeV/c protons in 12 C: pn - SRC 74 – 93 % 4.75 ± 1 % Assuming for 12 C nn-SRC = pp-SRC np-SRC dominance 2N –SRC dominance Notice: 100% is the sum of all the nucleons in this momentum range

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

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

The ratio of pp-SRC / pn-SRC pairs in 12 C From the EVA / BNL 12 C(p,ppn) data : From the combined EVA /BNL 12 C(p,ppn) and the E C(e,e’pp) data: From the E C(e,e’pp) / 12 C(e,e’pn) data: Why ? There are 18 ± 2 times more np-SRC than pp-SRC pairs in 12 C. Piasetzky, Sargsian, Frankfurt, Strikman, Watson PRL (2006).

At MeV/c there is an excess strength in the np momentum distribution due to the strong correlations induced by underline tensor NN potential. 3 He V18 Bonn np pn pp pp/np 3 He Schiavilla, Wiringa, Piere, Carson, nucl-th / (2006). Sargsian, Abrahamyan, Strikman, Frankfurt PR C (2005).

Proposal Measurement of the 4 He(e,e’pp) 4 He(e,e’pn) reactions over the 4 He(e,e’p) missing momentum range from 400 to 875 MeV/c. (scaled to 4 He) E C This proposal - 4 He Sargsian Laget PWIA +FSI (e,e’pN) calculations scaled to 4 He Density distribution Sargsian et al. Schiavilla et al. 3 He “d” 3 He

Shield wall 2” lead+1” iron Veto counters 4 layers of neutron detectors D(e,e’n) D(e,e’pn) The neutron-array

56Scintillators: 350x25x2.5 mm mm ∆E counters mm E counters E New for PR x25x2.5 mm 3 scintillaor bars with one PM 56 counters x2.5x2.5 mm 3 Fibers with 2 PMs Auxilary plan

The Proposed Measurements: P miss [Mev/c] days(e,e’pp) events (e,e’pn) events Setup, calibrations, checks: 4 days Total requested beam time: 29 days. Total number of triple coincidence events ~ 2000 ( E : Total number of triple coincidence events ~ 600 )

Summary E Simultaneous measurement of the (e,e’pp),(e,e’pn), and (e,e’p) reactions on 12 C over the (e,e’p) missing momentum range MeV/c. pp-SRC and np-SRC pairs were identified and their abundances were determined. Data show sensitivity to the short-range NN tensor force. PR Simultaneous measurement of these reactions on 4 He over (e,e’p) missing momentum range of MeV/c. The data is expected to be sensitive to the NN tensor force and the NN short range repulsive force. The proposed experiment uses the Hall A cryotarget, the two HRSs, BigBite, and an array of neutron counters. Total beam time request: 29 days The experiment can be ready to run in 6 month from approval. l

The end

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 2/3N-SRC phase in nuclei with A>3 relative to 3 He. K. Sh. Egiyan et al. PRL. 96, (2006) The probabilities for 3-nucleon SRC are smaller by one order of magnitude relative to the 2N SRC. New CLAS A(e,e') Result: 3N-SRC Less than 1% of total K. Sh. Egiyan et al. PRC 68, N-SRC(np,pp,nn) = 0.20 ± 0.045% For 12 C: Frankfurt, Sargsian, and Strikman Theory:

Why FSI are predicted to be small in the chosen kinematics? The FSI with the A-2 system The FSI of the recoil proton with the rest of the nucleus Suppressed due to Pauli blocking and the geometry of the (e,e’p) reaction. Pandharipande and Pierper PR C45, 791 (1992). The FSI of the fast proton with the rest of the nucleus The large anti-parallel component of p miss (>k F ) reduce the FSI. Frankfurt, Sargsian, Strikman PR C56, 1124 (1997). The small reduction in the (e,e’pp)/(e,e’p) ratio due to the transparency of the low energy proton is partially compensated by a small increase in the ratio by single charge exchange that can turn pn-SRC pairs into (e,e’pp) events. The absorptive (imaginary) part of the FSI amplitude does not modify the (e,e’pp)/(e,e’p) ratio. p 2.4 fm

Simple estimates of the FSI effects, based on a Glauber approximation show that these are small compared to the large errors of the data. Mardor,Mardor,Piasetzky,Alster, and Sargsian PR C 761 (1992) The transparency of the low momentum protons is about 0.8. i.e the measured (e,e’pp)/(e,e’p) ratio should be increased by 20% The same ratio should be decreased by 8-16% due to SCX. These two, within the errors, compensate each other.

Simple estimates of the FSI effects, based on a Glauber approximation show that these are small compared to the large errors of the data. Mardor,Mardor,Piasetzky,Alster, and Sargsian PR C 761 (1992) The data itself indicate that FSI are small. The extracted pair c.m distribution is a combination of c.m motion and FSI. The fact that we get : a narrow width (σ cm =136 MeV/c), similar in the transverse and longitudinal directions, Same as in previous measurements of the (p,2pn) reaction, Same as theoretical predications, indicates that FSI contribution are not dominant. The node in the pp / np ratio resulted from the NN-SRC Is not filled by FSI.

we adjust the effective cross section to obtain the measured Transparency: We used the measured effective cross section at 180 MeV/c and the energy dependent of the mean free path as calculated by Pandharipande and Pieper (Phys. Rev C45(1992)791.).

We calculated the conditioned transparency as: The transparency of the recoil particle in the triple coincidence experiment is higher than that calculated for (e,e’p) since the (e,e’p) already selected an interaction point in the nucleus where the transparency of the (e,e’p) proton is high and therefore the transparency of the recoil proton is also high. Single Charge Exchange (SCX) Assuming the (e,e’pn) is 5-10 times the magnitude of the (e,e’pp), the contamination of (e,e’pp) events with contribution from the np correlated pairs is 8-16%. Since the SCX is very forward peaked at these energies we assumed that each proton produced in a SCX process will be considered a correlated partner.

3 He PWIA PWIA+FSI (only in the pair) PWIA+FSI Calculations by M. Sargsian (unpublished) The FSI between the two nucleons in the SRC pair Notice: that the FSI in the SRC pair conserve the CM momentum of the pair and the isospin structure of the pair.

A B At the deep: For pp A~0  For np Since AB is negative FSI contribute more to pp M. Sargsian (private communication )

Calculations by J. M. Laget (unpublished)

Calculations by J. M. Laget (unpublished)

Calculations by J. M. Laget (unpublished)