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PAC 31 / TJNAF Jan. 2007

e’. e. p. p or n. Studying Short range Correlation in Nuclei at the Repulsive Core Limit via the triple Coincidence (e, e’ p N) Reaction. Hall A / TJNAF. Proposal 07-006. (Next Generation of E01-015). PAC 31 / TJNAF Jan. 2007. 2N-SRC.   5  o. 1.7 fm. ~1 fm.  1.f. 1.7f.

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PAC 31 / TJNAF Jan. 2007

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  1. e’ e p p or n Studying Short range Correlation in Nuclei at the Repulsive Core Limit via the triple Coincidence (e, e’ p N) Reaction Hall A / TJNAF Proposal 07-006 (Next Generation of E01-015) PAC 31 / TJNAF Jan. 2007

  2. 2N-SRC  5o 1.7 fm ~1 fm 1.f 1.7f o = 0.17 GeV/fm3 Nucleons 2N-Short Range Correlations (2N-SRC)

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

  4. 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 pair CM momentum distribution ? • What is the ratio of pp to pn pairs? • Are these nucleons different from free nucleons (e.g size,shape, mass, etc.)?

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

  6. Triple – coincidence measurements: p EVA / BNL p p n E01-015 / Jlab e e p p e e p n

  7. p γ n Triple coincidence (p, p pn) measurements at EVA / BNL Directional correlation np-SRC pairs have been observed. Removal of a proton with momentum above the Fermi sea level from 12C is 92±818 % accompanied by the emission of a neutron with momentum equal and opposite to the missing momentum. * 2N-SRC dominance (74-100% are partners in 2N-SRC). * np-SRC dominance: Did not observe pp-SRC. Upper limit of 13% for pp-SRC contribution to protons with momentum above 275 Mev/c in 12C. A. Tang Phys. Rev. Lett. 90 ,042301 (2003) Piasetzky, Sargsian, Frankfurt, Strikman, Watson PRL 162504(2006).

  8. What did we want to achieve in E01-015 / Jlab ? Identify pp-SRC pairs in nuclei. (e, e’ p p) Determined the abundance of pp-SRC pairs. (e, e’ p p) / (e, e’ p) Verify the abundance of np-SRC pairs as deteremind by the EVA / BNL experiment. (e, e’ p n) / (e, e’ p) Determined the pp-SRC / np-SRC ratio. (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. E01-015 Simultaneously measurements of the (e,e’ p) , (e, e’ p p) (e, e’ p n) reactions.

  9. E01-105: An Custom Experiment to study 2N-SRC Q2 = 2 GeV/c , xB ~ 1.2 , Pm=250-650 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

  10. 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) select periphery. Can treated in Glauber approximation. Canceled in some of the measured ratios. FSI in the SRC pair: These are not necessary small BUT: Conserve the isospin structure of the pair . Conserve the CM momentum of the pair.

  11. The selected kinematics for the 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

  12. Experimental setup HRS HRS EXP 01-015 / Jlab n array p p e n e Big Bite Lead wall

  13. BigBite Spectrometer Neutron Detector EXP 01-015 Dec. 2004 – Apr. 2005 Jlab / Hall A

  14. 12C(e,e’p) “300 MeV/c” xB>1 “400 MeV/c” “500 MeV/c” 12C(e,e’p)11B “500 MeV/c” “300 MeV/c” (e,e’p) (e,e’∆) “400 MeV/c”

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

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

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

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

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

  20. 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

  21. For 275-600 MeV/c protons in 12C: Assuming for 12C nn-SRC = pp-SRC 74 – 93 % pn - SRC 4.75 ± 1 % 4.75 ± 1 % 2N –SRC dominance Notice: 100% is the sum of all the nucleons in this momentum range np-SRC dominance

  22. Thus, the deduced 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) (e,e’) 18.4 ± 4.5 % - SRC np pairs . (p,2pn) 20 ± 4.5 % - 2N SRC . 0.95±0.2% - SRC pp pairs. or 0.95±0.2 % - SRC nn pairs. (e,e’pp) Small ~1% - SRC of “more than 2 nucleons”. ? ~1% -non nucleonic degrees of freedom (e,e’)

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

  24. The ratio of pp-SRC / pn-SRC pairs in 12C From the EVA / BNL 12C(p,ppn) data : Piasetzky, Sargsian, Frankfurt, Strikman, Watson PRL 162504(2006). From the combined EVA /BNL12C(p,ppn) and the E01-015 12C(e,e’pp) data: From the E01-015 12C(e,e’pp) / 12C(e,e’pn) data: There are 18 ± 2 times more np-SRC than pp-SRC pairs in 12C. Why ?

  25. At 300-500 MeV/c there is an excess strength in the np momentum distribution due to the strong correlations induced by underline tensor NN potential. pp/np 3He 3He np np pp pn pp V18 pp Bonn Schiavilla, Wiringa, Piere, Carson, nucl-th /0611037 (2006). 3He Sargsian, Abrahamyan, Strikman, Frankfurt PR C71 044615 (2005).

  26. E01-105 12 C (scaled to 4He) This proposal - 4He Proposal 07-006 Measurement of the 4He(e,e’pp) 4He(e,e’pn) reactions over the 4He(e,e’p) missing momentum range from 400 to 875 MeV/c. 3He “d” Density distribution 3He Sargsian et al. Schiavilla et al. (e,e’pN) calculations scaled to 4He +FSI Sargsian PWIA +FSI Laget PWIA

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

  28. Scintillators: 350x25x2.5 mm3 24 3 mm ∆E counters 24 30 mm E counters E01-015 56 counters 12 350x2.5x2.5 mm3 Fibers with 2 PMs New for PR 07-006 56 350x25x2.5 mm3 scintillaor bars with one PM Auxilary plan

  29. The Proposed Measurements: Pmiss [Mev/c] days (e,e’pp) events (e,e’pn) events 400 5 110 200 500 5 110 200 625 5 235 160 750 5 280 150 875 5 320 140 Setup, calibrations, checks: 4 days Total number of triple coincidence events ~ 2000 ( E01-015 : Total number of triple coincidence events ~ 600 ) Total requested beam time: 29 days.

  30. Summary E01-015 Simultaneous measurement of the (e,e’pp),(e,e’pn), and (e,e’p) reactions on12C over the (e,e’p) missing momentum range 300-500 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 07-006 Simultaneous measurement of these reactions on 4He over (e,e’p) missing momentum range of 400-875 MeV/c. l 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. The experiment can be ready to run in 6 month from approval. Total beam time request: 29 days

  31. The end

  32. Theory: Frankfurt, Sargsian, and Strikman New CLAS A(e,e') Result: K. Sh. Egiyan et al. PRC 68, 014313. K. Sh. Egiyan et al. PRL. 96, 082501 (2006) 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 3He. The probabilities for 3-nucleon SRC are smaller by one order of magnitude relative to the 2N SRC. For 12 C: 2N-SRC(np,pp,nn) = 0.20 ± 0.045% 3N-SRC Less than 1% of total

  33. Why FSI are predicted to be small in the chosen kinematics? 2.4 fm p 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 pmiss (>kF) reduce the FSI. Frankfurt, Sargsian, Strikman PR C56, 1124 (1997). The absorptive (imaginary) part of the FSI amplitude does not modify the (e,e’pp)/(e,e’p) ratio. 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.

  34. 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.

  35. 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 (σcm=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.

  36. 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.).

  37. 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. We calculated the conditioned transparency as: 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.

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

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

  40. Calculations by J. M. Laget (unpublished)

  41. Calculations by J. M. Laget (unpublished)

  42. Calculations by J. M. Laget (unpublished)

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