Nuclear Theory·nucl-th

Thursday·December 1, 2016

13 papers—8 primary·5 cross-listed

01
Emergent phenomena and partonic structure in hadrons
Craig D. Roberts🇺🇸 · Cedric Mezrag🇺🇸
Modern facilities are poised to tackle fundamental questions within the Standard Model, aiming to reveal the nature of confinement, its relationship to dynamical chiral symmetry breaking (DCSB) - the origin of visible mass - and the connection between these two, key emergent phenomena. There is strong evidence to suggest that they are intimately connected with the appearance of momentum-dependent masses for gluons and quarks in QCD, which are large in the infrared: $m_{g} \sim 500$ MeV and $M_{q} \sim 350$ MeV. DCSB, expressed in the dynamical generation of a dressed-quark mass, has an enormous variety of verifiable consequences, including an enigmatic result that the properties of the (almost) massless pion are the cleanest expression of the mechanism which is responsible for almost all the visible mass in the Universe. This contribution explains that these emergent phenomena are expressed with particular force in the partonic structure of hadrons, e.g. in valence-quark parton distribution amplitudes and functions, and, consequently, in numerous hadronic observables, so that we are now in a position to exhibit the consequences of confinement and DCSB in a wide range of hadron observables, opening the way to empirical verification of their expression in the Standard Model.
nucl-thhep-lathep-phnucl-exEPJ Web Conf.(2017)·7 citations
02
Scale-Chiral Symmetry, Proton Mass and Sound Velocity in Compact-Star Matter
Won-Gi Paeng🇰🇷 · Mannque Rho🇫🇷
With a light dilaton $σ$ and the light-quark vector mesons $V = (ρ, ω)$ incorporated into an effective scale-invariant hidden local symmetric Lagrangian, scale-chiral symmetry -- hidden in QCD -- arises at a high density, $n_{1/2}$ , as an "emergent" symmetry, a phenomenon absent in standard chiral perturbative approaches but highly relevant for massive compact stars. What takes place as the density increases beyond $n_{1/2} \sim 2 n_{0}$ in compressed baryonic matter is (1) a topology change from skyrmions to half-skyrmions, (2) parity doubling in the nucleon structure, (3) the maximum neutron star mass $M ≃ 2.01 M_{⊙}$ and the radius $R ≃ 12.0$ km and (4) the sound velocity $v_{s}^{2} / c^{2} ≃ 1/3$ due to the "vector manifestation (VM)" fixed point of $ρ$ and a "walking" dilaton condensate, which is intricately connected to the source of the proton mass.
nucl-thhep-ph6 citations
03
Tritium $β$ -decay in pionless effective field theory
Hilla De-Leon🇮🇱 · Lucas Platter🇺🇸 · Doron Gazit🇮🇱
We calculate the $β$ -decay of tritium at next-to-leading order in pionless effective field theory. At this order, a low-energy parameter $L_{1, A}$ enters the calculation that is also relevant for a high-accuracy prediction of the solar proton-proton fusion rate. We use the tritium half-life to determine this parameter and provide uncertainty estimates. We show proper renormalization of our calculation analyzing the residual cutoff dependence of observables. We find that next-to-leading order corrections contribute about $4%$ to the triton decay Gamow-Teller strength. We show that these conclusions are insensitive to different arrangements of the effective range expansion.
nucl-thPRC(2019)·32 citations
04
Production of proton-rich nuclei around Z=84-90 in fusion-evaporation reactions
Peng-Hui Chen · Zhao-Qing Feng · Fei Niu · Ya-Fei Guo · Hong-Fei Zhang · Jun-Qing Li · Gen-Ming Jin
Within the framework of the dinuclear system model, production cross sections of proton-rich nuclei with charged numbers of Z=84-90 are investigated systematically. Possible combinations with the $^{28}$ Si, $^{32}$ S, $^{40}$ Ar bombarding the target nuclides $^{165}$ Ho, $^{169}$ Tm, $^{170 - 174}$ Yb, $^{175, 176}$ Lu, $^{174, 176 - 180}$ Hf and $^{181}$ Ta are analyzed thoroughly. The optimal excitation energies and evaporation channels are proposed to produce the proton-rich nuclei. The systems are feasible to be constructed in experiments. It is found that the neutron shell closure of N=126 is of importance during the evaporation of neutrons. The experimental excitation functions in the $^{40}$ Ar induced reactions can be nicely reproduced. The charged particle evaporation is comparable with neutrons in cooling the excited proton-rich nuclei, in particular for the channels with $α$ and proton evaporation. The production cross section increases with the mass asymmetry of colliding systems because of the decrease of the inner fusion barrier. The channels with pure neutron evaporation depend on the isotopic targets. But it is different for the channels with charged particles and more sensitive to the odd-even effect.
nucl-thEPJA(2017)·14 citations
05
Higher-order baryon number susceptibilities: interplay between the chiral and the nuclear liquid-gas transitions
A. Mukherjee🇩🇪 · S. Schramm🇩🇪 · J. Steinheimer🇩🇪
We use an improved version of the SU(3) flavour parity-doublet quark-hadron model to investigate the higher order baryon number susceptibilities near the chiral and the nuclear liquid-gas transitions. The parity-doublet model has been improved by adding higher-order interaction terms of the scalar fields in the effective mean field Lagrangian, resulting in a much-improved description of nuclear ground-state properties, in particular the nuclear compressibility. The resulting phase diagram of the model agrees qualitatively with expectations from lattice QCD, i.e., it shows a crossover at zero net baryo-chemical potential and a critical point at finite density. Using this model, we investigate the dependence of the higher-order baryon number susceptibilities as function of temperature and chemical potential. We observe a strong interplay between the chiral and liquid-gas transition at intermediate baryo chemical potentials. Due to this interplay between the chiral and the nuclear liquid-gas transitions, the experimentally measured cumulants of the net baryon number may show very different beam energy dependence, subject to the actual freeze-out temperature.
nucl-thhep-phPRC(2017)·71 citations
06
Power Counting in Peripheral Partial Waves: The Singlet Channels
M. Pavón Valderrama🇨🇳 · M. Sánchez Sánchez🇫🇷 · C.-J. Yang🇫🇷 · Bingwei Long🇨🇳 · Jaume Carbonell🇫🇷 · U. van Kolck🇫🇷
We analyze the power counting of the peripheral singlet partial waves in nucleon-nucleon scattering. In agreement with conventional wisdom, we find that pion exchanges are perturbative in the peripheral singlets. We quantify from the effective field theory perspective the well-known suppression induced by the centrifugal barrier in the pion-exchange interactions. By exploring perturbation theory up to fourth order, we find that the one-pion-exchange potential in these channels is demoted from leading to subleading order by a given power of the expansion parameter that grows with the orbital angular momentum. We discuss the implications of these demotions for few-body calculations: though higher partial waves have been known for a long time to be irrelevant in these calculations (and are hence ignored), here we explain how to systematize the procedure in a way that is compatible with the effective field theory expansion.
nucl-thPRC(2017)·42 citations
07
Quasifission dynamics and stability of superheavy systems
Kazuyuki Sekizawa · Sophia Heinz
Recent experiments revealed intriguing similarities in the $^{64}$ Ni+ $^{207}$ Pb, $^{132}$ Xe+ $^{208}$ Pb, and $^{238}$ U+ $^{238}$ U reactions at energies around the Coulomb barrier. The experimental data indicate that for all systems substantial energy dissipation takes place, in the first stage of the reaction, although the number of transferred nucleons is small. On the other hand, in the second stage, a large number of nucleons are transferred with small friction and small consumption of time. To understand the observed behavior, various reactions were analyzed based on the microscopic time-dependent Hartree-Fock (TDHF) theory. From a systematic analysis for $^{40, 48}$ Ca+ $^{124}$ Sn, $^{40}$ Ca+ $^{208}$ Pb, $^{40}$ Ar+ $^{208}$ Pb, $^{58}$ Ni+ $^{208}$ Pb, $^{64}$ Ni+ $^{238}$ U, $^{136}$ Xe+ $^{198}$ Pt, and $^{238}$ U+ $^{238}$ U reactions, we find that TDHF reproduces well the measured trends. In addition, the Balian-Vénéroni variational principle is applied to head-on collisions of $^{238}$ U+ $^{238}$ U, and the variance of the fragment masses is compared with the experimental data, showing significant improvement. The underlying reaction mechanisms and possible future studies are discussed.
nucl-thnucl-exActa Phys.Polon.Supp.(2017)·8 citations
08
Novel Role of Superfluidity in Low-Energy Nuclear Reactions
Piotr Magierski · Kazuyuki Sekizawa · Gabriel Wlazłowski
We demonstrate, within symmetry unrestricted time-dependent density functional theory, the existence of new effects in low-energy nuclear reactions which originate from superfluidity. The dynamics of the pairing field induces solitonic excitations in the colliding nuclear systems, leading to qualitative changes in the reaction dynamics. The solitonic excitation prevents collective energy dissipation and effectively suppresses fusion cross section. We demonstrate how the variations of the total kinetic energy of the fragments can be traced back to the energy stored in the superfluid junction of colliding nuclei. Both contact time and scattering angle in non-central collisions are significantly affected. The modification of the fusion cross section and possibilities for its experimental detection are discussed.
nucl-thnucl-exPRL(2017)·79 citations
09
More about the light baryon spectrum
Gernot Eichmann🇩🇪
We discuss the light baryon spectrum obtained from a recent quark-diquark calculation, implementing non-pointlike diquarks that are self-consistently calculated from their Bethe-Salpeter equations. We examine the orbital angular momentum content in the baryons' rest frame and highlight the fact that baryons carry all possible values of L compatible with their spin, without the restriction P=(-1)^L which is only valid nonrelativistically. We furthermore investigate the meaning of complex conjugate eigenvalues of Bethe-Salpeter equations, their possible connection with 'anomalous' states, and we propose a method to eliminate them from the spectrum.
↳ hep-phnucl-thFew Body Syst.(2017)·23 citations
10
Event patterns extracted from top quark-related spectra in proton-proton collisions at 8 TeV
Ya-Hui Chen🇨🇳 · Fu-Hu Liu🇨🇳 · Roy A. Lacey🇺🇸
We analyze the transverse momentum ( $p_{T}$ ) and rapidity ( $y$ ) spectra of top quark pairs, hadronic top quarks, and top quarks produced in proton-proton ( $pp$ ) collisions at center-of-mass energy $s = 8$ TeV. For $p_{T}$ spectra, we use the superposition of the inverse power-law suggested by the QCD (quantum chromodynamics) calculus and the Erlang distribution resulting from a multisource thermal model. For $y$ spectra, we use the two-component Gaussian function resulting from the revised Landau hydrodynamic model. The modelling results are in agreement with the experimental data measured at the detector level, in the fiducial phase-space, and in the full phase-space by the ATLAS Collaboration at the Large Hadron Collider (LHC). Based on the parameter values extracted from $p_{T}$ and $y$ spectra, the event patterns in three-dimensional velocity ( $β_{x}$ - $β_{y}$ - $β_{z}$ ), momentum ( $p_{x}$ - $p_{y}$ - $p_{z}$ ), and rapidity ( $y_{1}$ - $y_{2}$ - $y$ ) spaces are obtained, and the probability distributions of these components are also obtained.
↳ hep-phhep-exnucl-exnucl-thCPC(2018)·2 citations
11
Nuclear pasta and supernova neutrinos at late times
C. J. Horowitz🇺🇸 · D. K. Berry🇺🇸 · M. E. Caplan🇺🇸 · T. Fischer🇵🇱 · Zidu Lin🇺🇸 · W. G. Newton🇺🇸 · E. O'Connor🇺🇸 · L. F. Roberts🇺🇸
Nuclear pasta, with nucleons arranged into tubes, sheets, or other complex shapes, is expected in core collapse supernovae (SNe) at just below nuclear density. We calculate the additional opacity from neutrino-pasta coherent scattering using molecular dynamics simulations. We approximately include this opacity in simulations of SNe. We find that pasta slows neutrino diffusion and greatly increases the neutrino signal at late times of 10 or more seconds after stellar core collapse. This signal, for a galactic SN, should be clearly visible in large detectors such as Super-Kamiokande.
↳ astro-ph.HEhep-phnucl-th32 citations
12
J/psi+Z production at the LHC
Jean-Philippe Lansberg🇫🇷 · Hua-Sheng Shao🇨🇭
We briefly review recent results which we have obtained in the study of J/psi+Z production at the LHC. Considering our NLO computation in the Colour Evaporation Model (CEM) as an upper theory limit for the single-parton-scattering contributions, we claim that the existing data set from ATLAS points at a dominant double-parton-scattering contribution with an effective cross section smaller than that for jet-related observables. As a side product of our analysis, we have computed, for the first time, the one-loop QCD corrections to the J/psi P_T-differential cross section in the CEM.
↳ hep-phhep-exnucl-exnucl-thEPJ Web Conf.(2017)·1 citation
13
Kinematics of Current Region Fragmentation in Semi-Inclusive Deeply Inelastic Scattering
M. Boglione🇮🇹 · J. Collins🇺🇸 · L. Gamberg🇺🇸 · J. O. Gonzalez-Hernandez🇺🇸 · T. C. Rogers🇺🇸 · N. Sato🇺🇸
Different kinematical regimes of semi-inclusive deeply inelastic scattering (SIDIS) processes correspond to different underlying partonic pictures, and it is important to understand the transition between them. This is particularly the case when there is sensitivity to intrinsic transverse momentum, in which case kinematical details can become especially important. We address the question of how to identify the current fragmentation region --- the kinematical regime where a factorization picture with fragmentation functions is appropriate. We distinguish this from soft and target fragmentation regimes. Our criteria are based on the kinematic regions used in derivations of factorization theorems. We argue that, when hard scales are of order a few GeVs, there is likely significant overlap between different rapidity regions that are normally understood to be distinct. We thus comment on the need to take this into account with more unified descriptions of SIDIS, which should span all rapidities for the produced hadron. Finally, we propose general criteria for estimating the proximity to the current region at large Q.
↳ hep-phnucl-thPLB(2017)·57 citations

Affiliations

first authorsco-authorsvia INSPIRE