Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session EC: Mini-Symposium: Overview of Two and Three-nucleon Correlations in Nuclei II |
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Chair: Or Hen, Massachusetts Institute of Technology Room: Hilton Kohala 2 |
Thursday, October 25, 2018 7:00PM - 7:30PM |
EC.00001: Studies of two-and three-nucleon interactions in nuclear reactions Invited Speaker: Tomotsugu Wakasa The modification of the properties of mesons and nucleons in the nuclear medium is one of the most interesting topics in current nuclear physics. The reduction of hadron masses in this medium has been predicted as an effect of the partial restoration of chiral symmetry in nuclear matter, and the modification of the nucleon spinor in nuclear matter has also been discussed in the framework of a Dirac approach. These modifications may result in variations of the nucleon–nucleon (NN) interaction with density. It is anticipated that it will be possible to examine these in-medium modifications of the NN interaction through proton-induced knockout reactions [(p,2p) and (p,pn)], which are regarded as NN scatterings in a nuclear field. We introduce a significant body of evidence suggesting the existence of medium effects. A recent experimental progress is the finding of the isospin dependence (difference between p-p and p-n) of the analyzing-power (Ay) suppression in nuclear medium. Note that the strongly interacting p-n pairs (p-n short-range (SR) and tensor correlations) which have been shown to be a universal aspect of high momentum nucleons in nuclei may also be responsible for the modification. Thus the two-nucleon (2N) and three-nucleon (3N) SR and tensor correlations will be also discussed in connection with the medium modifications of NN interactions. |
Thursday, October 25, 2018 7:30PM - 7:45PM |
EC.00002: Experimental Aspects of a New Generation of SRC Measurements Using Hadron Beams Georgios Laskaris, Efrain P Segarra A program of a new generation of fully exclusive SRC measurements have been designed and partially executed during the past two years using hadron beams at JINR and GSI. These hard nucleon knock-out measurements are designed to take place at normal and inverse kinematics where an accelerated nucleon or light nucleus scatters off of a standing heavier nucleus (normal) or where a heavy nucleus scatters off of a nucleon or a standing lighter nucleus (inverse). At the final state, all products of the hard knock-out reaction are detected in coincidence. In our talk, we will give a deep insight into how we study SRC pairs using normal and inverse kinematics at GSI and JINR, respectively and the motivation for fully exclusive SRC measurements. We will also present the experimental aspects of a recently executed measurement at JINR where a 4 GeV/c/u 12C beam was used on a liquid hydrogen target to knockout a proton from an SRC pair in the carbon nucleus and detect in coincidence the target-scattered proton along with the residual A-2 system. |
Thursday, October 25, 2018 7:45PM - 8:00PM |
EC.00003: Direct Observation of Proton-Neutron Short-Range Correlation Dominance in Heavy Nuclei Meytal Duer
High-momentum transfer measurements have shown that nucleons in nuclear ground state can form temporary pairs with large relative momentum and small center-of-mass momentum, referred as short range correlated (SRC) pairs. Properties of SRC pairs are primarily inferred from measurements of exclusive electron-induced triple-coincidence reactions. A high missing-momentum nucleon is knocked out of the nucleus via a high-momentum transfer reaction and detected in coincidence with the scattered probe and a recoil nucleon balancing the large missing momentum. Previous measurements of such reactions in 4He and 12C, showed that neutron-proton (np) SRC pairs are nearly 20 times as prevalent as proton-proton (pp) pairs. This was explained as being due to the dominance of the tensor part of the nucleon-nucleon force at short distances. For heavy nuclei, the predominance of np-SRC was never extracted directly from measurements of the exclusive A(e,e'pp) and A(e,e'np). Based on our data from CLAS detector at Jefferson Laboratory we present, the triple coincidence measurement on C, Al, Fe, and Pb. The data verified, for the first time on neutron rich nuclei, that the number of pp-pairs is small than the np-pairs by about a factor of 20, independent of the neutron excess in the nucleus. |
Thursday, October 25, 2018 8:00PM - 8:15PM |
EC.00004: Isospin dependence of NN correlations and the reduction of the single-particle strength in atomic nuclei Stefanos Paschalis, Augusto O Macchiavelli, Marina Petri, Or Hen, Eli Piasetzky The atomic nucleus consists of strongly interacting nucleons. It is noteworthy that for such strongly interacting quantum system the independent-particle model is proven to be a valid approximation and has provided the framework to explain many properties of nuclei. However, correlations between the nucleons, both of short- and long-range nature, modify the mean-field approximation and dilute the pure independent-particle picture. Notably, these correlations are thought to be the reason for the quenching of spectroscopic factors observed in (e,e’p), (p,2p) and transfer reactions [1]. Here we propose a phenomenological approach to examine the role of NN short- and long-range correlations and their evolution in asymmetric systems. In particular, we show that the recently observed [2] increase of the high-momentum component of the proton momentum density in a neutron-rich nucleus correlates nicely with the reduced proton occupancies for states below or near the Fermi level [3,4], as a function of the asymmetry (N-Z)/A. [1] Dickhoff and Barbieri, PPNP 52 (2004) 377 [2] Duer et al., Nature, In-Print (2018) [3] Kramer, Blok and Lapikas, NPA 679 (2001) 267 [4] Atar et al., PRL 120 (2018) 052501 |
Thursday, October 25, 2018 8:15PM - 8:30PM |
EC.00005: Probing the nuclear force with rare isotopes Rituparna Kanungo, Jason Holt, Petr Navratil, J.S. Randhawa, A. Kumar, M. Holl, A. Calci, IRIS Collaboration Understanding the nuclear force from the fundamental theory of QCD had been enabled by the chiral effective field theory. The importance of the three-nucleon force has emerged from reconciling observed fundamental properties of nuclei with the predictions. However, there are different prescriptions of the chiral interactions that need to be constrained with experiments. We will present examples from recent reaction spectroscopy studies at TRIUMF accessing rare isotopes at the drip-lines to show how observables such as excitation spectra and diffraction pattern in nuclear scattering unfold new understanding of the two- and three-nucleon forces and challenges our current knowledge. |
Thursday, October 25, 2018 8:30PM - 8:45PM |
EC.00006: Probing three-nucleon-force effects through knockout reactions Kosho Minomo, Michio Kohno, Kazuki Yoshida, Kazuyuki Ogata Understanding of the roles of three-nucleon forces (3NFs) in nuclear few- and many-body systems is one of the fundamental subjects in nuclear physics. In this talk, we propose to use proton knockout reactions (p,2p), which can be regarded as a two-proton quasielastic scattering, as a new probe into 3NF effects on reaction observables. In a many-body system, 3NF effects can be represented by the density-dependence of nucleon-nucleon effective interaction. Proton knockout reactions from a deeply bound orbit should be suitable for probing 3NF effects since such reactions occur mainly in the internal region of the target nucleus in which the density is high. We clarify the roles of 3NF for knockout reactions based on the distorted-wave impulse approximation with a nucleon-nucleon g-matrix interaction including the 3NF effects. The 3NF effects significantly change the peak height of the triple differential cross section of (p,2p) reactions. |
Thursday, October 25, 2018 8:45PM - 9:00PM |
EC.00007: Possible signature of tensor interactions observed via (p,dN) reaction at large momentum transfer Satoru Terashima, L. Yu, Hooi Jin Ong, Isao Tanihata, Satoshi Adachi, Nori Aoi, Phaikying Chan, Hiroyuki Fujioka, Mitsunori Fukuda, Hans Geissel, Chihiro Iwamoto, Takahiro Kawabata, Harutaka Sakaguchi, Akane Sakaue, Christoph Scheidenberger, Baohua Sun, Atsushi Tamii, Leung Tang, Dinh Trong Tran, Yuni Watanabe, Helmut Weick We report observation of new evidence for tensor interactions from 16O(p,dN) measurements at 392-MeV proton under quasi-free scattering kinematics but at scattering angle relevant to neutron pick up mechanism. To investigate isospin dependence of high-momentum component, an exclusive (p,dN) reaction experiment was performed recently at RCNP. Scattering deuterons and recoiled nucleons N[p or n] were measured by the spectrometer GrandRAIDEN and plastic scintillator telescopes or the newly developed stacked neutron detector BOS4. For 16O(p,dp)14N channel, the good excitation energy resolution allows to resolve several final states of the residual nuclei in the excitation energy spectra. Among the low-lying states in 14N, strong suppression for the lowest T=1 state was observed, which were observed in similar amplitudes with T=0 states in the other reactions. The missing transition to T=1 states suggests that high-momentum-correlated p-n pairs in nuclei are dominant T=0 nature. In neutron channel (p,dn), the observed cross section was found to be strongly suppressed also in comparison with (p,dp) T=0 channel. The observed clear isospin dependences can be understood by considering the tensor interactions at large-momentum transfer. Detailed reaction analysis will be discussed also. |
Thursday, October 25, 2018 9:00PM - 9:15PM |
EC.00008: Short-range correlations and momentum distributions in light nuclei Wataru Horiuchi Since the precise solution can be obtained for a four-nucleon system, 4He, the system can be a testing ground of nuclear interactions and an ideal nucleus to study many-nucleon correlations. We perform an ab initio calculation for 4He using the explicitly correlated Gaussian expansion of the wave function [1] and discuss its correlated structure in the ground state as well as in excited four-nucleon states from various viewpoints. We extract density and momentum density distributions from highly correlated wave function and discuss a role of short-range two-body interaction [2]. As a theoretical interest, we translate the short-range correlations in a language of the harmonic-oscillator wave function which is widely employed in shell model calculations [3]. We discuss how the many-body correlations appear in the momentum distributions from the viewpoint of the effective nuclear interaction [4].
References [1] J. Mitroy et al., Rev. Mod. Phys. 85, 693 (2013). [2] H. Feldmeier, W. Horiuchi, T. Neff, and Y. Suzuki, Phys. Rev. C 84, 054003 (2011). [3] W. Horiuchi and Y. Suzuki, Phys. Rev. C 90, 034001 (2014). [4] T. Neff, H. Feldmeier, W. Horiuchi, Phys. Rev C 92, 024003 (2015). |
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