Nuclear Theory·nucl-th

Thursday·June 28, 2018

8 papers—6 primary·2 cross-listed

01
Energy and momentum dependence of nuclear short-range correlations - Spectral function, exclusive scattering experiments and the contact formalism
Ronen Weiss · Igor Korover🇮🇱 · Eliezer Piasetzky🇮🇱 · Or Hen🇺🇸 · Nir Barnea
Results of electron-induced one- and two-nucleon hard knockout reactions, $A (e, e^{'} p)$ and $A (e, e^{'} pN)$ , in kinematics sensitive to nuclear short-range correlations, are studied using the nuclear contact formalism. A relation between the spectral function and the nuclear contacts is derived and used to analyze the dependence of the data on the initial energy and momentum of the knocked-out proton. The ratio between the number of emitted proton-proton pairs and proton-neutron pairs is shown to depend predominantly on a single ratio of contacts. This ratio is expected to present a deep minima in the initial energy and momentum plane, associated with the node in the proton-proton wave function. The formalism is applied to analyze data from recent $^{4}$ He and $^{12}$ C electron-scattering experiments performed at Jefferson laboratory. Different nucleon-nucleon potentials were used to asses the model-dependence of the results. For the ratio of proton-proton to proton-neutron pairs in $^{4}$ He, a fair agreement with the experimental data is obtained using the two potentials, whereas for the ratio of proton-proton pairs to the total knocked-out protons in $^{12}$ C, some of the features of the theory are not seen in the experimental data. Several possible explanations for this disagreement are discussed. It is also observed that the spectral function at specific domains of the momentum-energy plane is sensitive to the nucleon-nucleon interaction. Based on this sensitivity, it might be possible to constrain the short range part of the nuclear potential using such experimental data.
nucl-thnucl-exPLB(2019)·54 citations
02
Pion and kaon valence quark distribution functions from Dyson-Schwinger equations
Chao Shi🇺🇸 · Cedric Mezrag🇮🇹 · Hong-shi Zong🇨🇳
Using realistic quark propagators and meson Bethe-Salpeter amplitudes based on the Dyson-Schwinger equations, we calculate the pion and kaon's valence parton distribution functions (PDF) through the modified impulse approximation. The PDFs we obtained at hadronic scale have the purely valence characteristic and exhibit both dynamical chiral symmetry breaking and SU(3) flavor symmetry breaking effects. A new calculation technique is introduced to determine the valence PDFs with precision. Through NLO DGLAP evolution, our result is compared with pion and kaon valence PDF data at experimental scale. Good agreement is found in the case of pion, while deviation emerges for kaon. We point out this situation can be resolved by incorporating gluon contributions into the mesons if the pion hosts more gluons than kaon nonperturbatively.
nucl-thPRD(2018)·43 citations
03
Local chiral interactions, the tritium Gamow-Teller matrix element, and the three-nucleon contact term
A. Baroni · R. Schiavilla · L.E. Marcucci · L. Girlanda · A. Kievsky · A. Lovato · S. Pastore · M. Piarulli · Steven C. Pieper · M. Viviani · R. B. Wiringa
The Gamow-Teller (GT) matrix element contributing to tritium $β$ decay is calculated with trinucleon wave functions obtained from hyperspherical-harmonics solutions of the Schrödinger equation with the chiral two- and three-nucleon interactions including $Δ$ intermediate states that have recently been constructed in configuration space. Predictions up to N3LO in the chiral expansion of the axial current (with $Δ$ 's) overestimate the empirical value by 1--4 \%. By exploiting the relation between the low-energy constant (LEC) in the contact three-nucleon interaction and two-body axial current, we provide new determinations of the LECs $c_{D}$ and $c_{E}$ that characterize this interaction by fitting the trinucleon binding energy and tritium GT matrix element. Some of the implications that the resulting models of three-nucleon interactions have on the spectra of light nuclei and the equation of state of neutron matter are briefly discussed. We also provide a partial analysis, which ignores $Δ$ 's, of the contributions due to loop corrections in the axial current at N4LO. Finally, explicit expressions for the axial current up to N4LO have been derived in configuration space, which other researchers in the field may find useful.
nucl-thPRC(2018)·100 citations
04
Landau Pomeranchuk Midgal Effect and Charm Production in $pp$ Collisions at Large Hadron Collider Energies using the Parton Cascade Model
Dinesh K. Srivastava🇮🇳 · Rupa Chatterjee🇮🇳 · Steffen A. Bass🇺🇸
We study the impact of the Landau Pomeranchuk Midgal (LPM) effect on the dynamics of parton interactions in proton proton collisions at the Large Hadron Collider energies. For our investigation we utilize a microscopic kinetic theory based on the Boltzmann equation. The calculation traces the space-time evolution of the cascading partons interacting via semihard pQCD scatterings and fragmentations. We focus on the impact of the LPM effect on the production of charm quarks, since their production is exclusively governed by processes well described in our kinetic theory. The LPM effect is found to become more prominent as the collision energy rises and at central rapidities and may significantly affect the model's predicted charm distributions at low momenta.
nucl-thPRC(2018)·4 citations
05
Enhancement of strange baryons in high-multiplicity proton-proton and proton-nucleus collisions
Yuuka Kanakubo🇯🇵 · Michito Okai🇯🇵 · Yasuki Tachibana🇯🇵 · Tetsufumi Hirano🇯🇵
We investigate the enhancement of yields of strange and multi-strange baryons in proton-proton (p+p), proton-lead (p+Pb) and lead-lead (Pb+Pb) collisions at the Large Hadron Collider (LHC) energies from a dynamical core-corona initialization model. We first generate partons just after the collisions by using event generators. These partons dynamically generate the quark gluon plasma (QGP) fluids through the source terms in the hydrodynamic equations. According to the core-corona picture, this process tends to happen where the density of generated partons is high and their transverse momentum is low. Some partons do not fully participate in this process when they are in dilute regions or their transverse momentum is high and subsequently fragment into hadrons through string fragmentation. In this framework, the final hadrons come from either chemically equilibrated fluids as in the conventional hydrodynamic models or string fragmentation. We calculate the ratio of strange baryons to charged pions as a function of multiplicity and find that it monotonically increases up to $d N_{ch} / d η \sim 100$ and then saturates above. This suggests that the QGP fluids are \textit{partly} created and that their fraction increases with multiplicity in p+p and p+Pb collisions at LHC energies.
nucl-thhep-phnucl-exPTEP(2018)·16 citations
06
Novel shape evolution in Sn isotopes from magic numbers 50 to 82
Tomoaki Togashi🇯🇵 · Yusuke Tsunoda🇯🇵 · Takaharu Otsuka🇯🇵 · Noritaka Shimizu🇯🇵 · Michio Honma🇯🇵
A novel shape evolution in the Sn isotopes by the state-of-the-art application of the Monte Carlo Shell Model calculations is presented in a unified way for the 100-138Sn isotopes. A large model space consisting of eight single-particle orbits for protons and neutrons is taken with the fixed Hamiltonian and effective charges, where protons in the 1g9/2 orbital are fully activated. While the significant increase of the B(E2; 0+1 -> 2+1) value, seen around 110Sn as a function of neutron number (N), has remained a major puzzle over decades, it is explained as a consequence of the shape evolution driven by proton excitations from the 1g9/2 orbital. A second-order quantum phase transition is found around N=66, connecting the phase of such deformed shapes to the spherical pairing phase. The shape and shell evolutions are thus described, covering topics from the Gamow-Teller decay of 100Sn to the enhanced double magicity of 132Sn.
nucl-thPRL(2018)·99 citations
07
Application of the functional renormalization group to Bose gases: from linear to hydrodynamic fluctuations
Felipe Isaule🇬🇧 · Michael C. Birse🇬🇧 · Niels R. Walet🇬🇧
We study weakly interacting Bose gases using the functional renormalization group with a hydrodynamic effective action. We use a scale-dependent parametrization of the boson fields that interpolates between a Cartesian representation at high momenta and an amplitude-phase one for low momenta. We apply this to Bose gases in two and three dimensions near the superfluid phase transition where they can be described by statistical O(2) models. We are able to give consistent physical descriptions of the infrared regime in both two and three dimensions. In particular, and in contrast to previous studies using the functional renormalization group, we find a stable superfluid phase at finite temperatures in two dimensions. We compare our results for the superfluid and boson densities with Monte-Carlo simulations, and we find they are in reasonable agreement.
↳ cond-mat.quant-gasnucl-thphysics.atom-phPRB(2018)·12 citations
08
On operator relations for gravitational form factors of a spin-0 hadron
Kazuhiro Tanaka (Juntendo Univ.)🇯🇵
The gravitational form factors for a hadron, the form factors for the hadron matrix element of the QCD energy-momentum tensor, not only describe the coupling of the hadron with a graviton, but also serve as unique quantities for describing the shape inside the hadron reflecting dynamics of quarks and gluons, such as the internal shear forces acting on the quarks/gluons and their pressure distributions. We consider the quark contribution to the gravitational form factors for a (pseudo)scalar hadron, and derive and clarify the relations satisfied by them as direct consequences of the symmetries and the equations of motion in QCD, and connections to the generalized parton distributions. Our results reveal the connections between the gravitational form factors and the higher-twist quark-gluon correlation effects inside the hadrons.
↳ hep-phhep-exnucl-thPRD(2018)·66 citations

Affiliations

first authorsco-authorsvia INSPIRE