Nuclear Theory·nucl-th

Tuesday·July 31, 2018

10 papers—4 primary·6 cross-listed

01
High Baryon Densities Achieveable at RHIC and LHC
Joseph I. Kapusta🇺🇸 · Ming Li🇺🇸
In high energy collisions nuclei are practically transparent to each other but produce very hot, nearly baryon-free, matter in the central rapidity region. Where do the baryons go? We calculate the energy loss of the nuclei using the color glass condensate model. Using a space-time picture of the collision we calculate the baryon and energy densities of the receding baryonic fireballs. For central collisions of large nuclei at RHIC and LHC we find baryon densities more than ten times that of atomic nuclei over a large volume which appear at high rapidities. These results can and are being used as initial conditions for subsequent hydrodynamic evolution and could test the equation of state of matter at very high baryon densities.
nucl-thNPA(2019)·4 citations
02
Generator-coordinate reference states for spectra and $0 ν β β$ decay in the in-medium similarity renormalization group
J. M. Yao🇺🇸 · J. Engel🇺🇸 · L. J. Wang🇺🇸 · C. F. Jiao🇺🇸 · H. Hergert🇺🇸
We use a reference state based on symmetry-restored states from deformed mean-field or generator-coordinate-method (GCM) calculations in conjunction with the in-medium similarity-renormalization group (IMSRG) to compute spectra and matrix elements for neutrinoless double-beta ( $0 ν β β$ ) decay. Because the decay involves ground states from two nuclei, we use evolved operators from the IMSRG in one nucleus in a subsequent GCM calculation in the other. We benchmark the resulting IMSRG+GCM method against complete shell-model diagonalization for both the energies of low-lying states in $^{48}$ Ca and $^{48}$ Ti and the $0 ν β β$ matrix element for the decay of $^{48}$ Ca, all in a single valence shell. Our approach produces better spectra than either the IMSRG with a spherical-mean-field reference or GCM calculations with unevolved operators. For the $0 ν β β$ matrix element the improvement is slight, but we expect more significant effects in full ab-initio calculations.
nucl-thcond-mat.str-elPRC(2018)·77 citations
03
The tensor-optimized high-momentum antisymmetrized molecular dynamics with bare interaction and its application in $^{4}$ He nucleus
Mengjiao Lyu · Takayuki Myo · Masahiro Isaka · Hiroshi Toki · Kiyomi Ikeda · Hisashi Horiuchi · Tadahiro Suhara · Taiichi Yamada
We formulate the "tensor-optimized high-momentum antisymmetrized molecular dynamics (TO-HMAMD)" framework for ab initio calculations of nuclei by hybridizing the tensor-optimized (TO-) and high-momentum (HM-) AMD approaches. This hybrid approach has advantages in both analytical simplicity and numerical efficiency comparing with other AMD-based methods which treat the bare interaction, especially for heavier nuclear systems. In this work, the $s$ -shell nucleus $^{4}$ He is calculated with TO-HMAMD by including up to double product of nucleon-nucleon ( $N N$ ) correlations, described by using high-momentum pairs and spatial correlation functions of nucleons. The total energy and radius of $^{4}$ He nucleus are well reproduced using the AV8 $^{'}$ interaction. The spin-isospin channel dependence is also discussed for $N N$ -correlations, which are found to be mostly contributed in the even-state channels, especially the triplet-even channel. Analyses of the analytical formation and numerical results suggest that TO-HMAMD could be a promising framework for general nuclear systems.
nucl-thPRC(2018)·13 citations
04
Probing the topological charge in QCD matter via multiplicity up-down asymmetry
Yifeng Sun🇺🇸 · Che Ming Ko🇺🇸
Relativistic heavy ion collisions provide the possibility to study the topological charge in QCD matter through the event-by-event fluctuating net axial charge or nonequal numbers of left- and right-handed quarks they generate in the produced quark-gluon plasma. Based on the chiral kinetic approach for nearly massless quarks and antiquarks in the strong vorticity field produced along the normal direction of the reaction plane of non-central heavy ion collisions, we show that a unique signal for the topological charge in QCD matter can be identified from the asymmetric distribution of particles with momenta pointing in the upper and lower hemispheres of the reaction plane as a result of the fluctuating net axial charge.
nucl-thPLB(2019)·4 citations
05
Coarse graining $π π$ scattering
Jacobo Ruiz de Elvira🇨🇭 · Enrique Ruiz Arriola🇪🇸
We carry out an analysis of $π π$ scattering in the $I J = 00$ , $11$ and $20$ channels in configuration space up to a maximal center-of-mass energy $s = 1.4$ GeV. We separate the interaction into two regions marked by an elementarity radius of the system; namely, a long distance region above which pions can be assumed to interact as elementary particles and a short distance region where many physical effects cannot be disentangled. The long distance interaction is described by chiral dynamics, where a two-pion-exchange potential is identified, computed and compared to lattice calculations. The short distance piece corresponds to a coarse grained description exemplified by a superposition of delta-shell potentials sampling the interaction with the minimal wavelength. We show how the so constructed non-perturbative scattering amplitude complies with the proper analytic structure, allowing for an explicit N/D type decomposition in terms of the corresponding Jost functions and fulfilling dispersion relations without subtractions. We also address renormalization issues in coordinate space and investigate the role of crossing when fitting the scattering amplitudes above and below threshold to Roy-equation results. At higher energies, we show how inelasticities can be described by one single complex and energy dependent parameter. A successful description of the data can be achieved with a minimal number of fitting parameters, suggesting that coarse graining is a viable approach to analyze hadronic processes.
↳ hep-phnucl-thEPJC(2018)·14 citations
06
Generalized linear sigma model with two glueballs
Amir H. Fariborz🇺🇸 · Renata Jora🇷🇴
We present a generalized linear sigma model that includes both scalar and pseudoscalar glueballs in addition to a quark-antiquark as well as a four-quark chiral nonet. Utilizing the axial and trace anomalies of QCD (at the effective mesonic level), we aim to develope the most general structure of the Lagrangian which can be used to study the interaction of quarkonia with glueballs. We then study the effect of scalar glueball on the vacuum of the model by considering a decoupling limit in which the glueball fields are decoupled from quarkonia. This determines the properties of the pure scalar glueball and builds a practical foundation for determining the model parameters when the interactions are turned on.
↳ hep-phnucl-thPRD(2018)·11 citations
07
Comment on scalar glueball mass
Amir H. Fariborz🇺🇸 · Renata Jora🇷🇴
We study the interaction of scalar glueball with quark-antiquark and four-quark spinless meson fields within the framework of a generalized linear sigma model in which the trace anomaly of QCD is exactly realized. To determine the pure scalar glueball mass ( $m_{h}$ ), we consider the decoupling limit in which the scalar glueball decouples from the meson fields. We find the exact relationship $m_{h} = 2 h_{0}$ where $h_{0}$ is the vacuum expectation value of the scalar glueball field independent of the properties of the framework used.
↳ hep-phhep-latnucl-thPLB(2019)·9 citations
08
Spin tensor and its role in non-equilibrium thermodynamics
F. Becattini🇮🇹 · W. Florkowski🇵🇱 · E. Speranza🇩🇪
It is shown that the description of a relativistic fluid at local thermodynamic equilibrium depends on the particular quantum stress-energy tensor operator chosen, e.g., the canonical or symmetrized Belinfante stress-energy tensor. We argue that the Belinfante tensor is not appropriate to describe a relativistic fluid whose macroscopic polarization relaxes slowly to thermodynamic equilibrium and that a spin tensor, like the canonical spin tensor, is required. As a consequence, the description of a polarized relativistic fluid involves an extension of relativistic hydrodynamics including a new antisymmetric rank-two tensor as a dynamical field. We show that the canonical and Belinfante tensors lead to different predictions for measurable quantities such as spectrum and polarization of particles produced in relativistic heavy-ion collisions.
↳ hep-thgr-qcnucl-thPLB(2019)·171 citations
09
Adding vacuum branching to jet evolution in a dense medium
P. Caucal🇫🇷 · E. Iancu🇫🇷 · A.H. Mueller🇺🇸 · G. Soyez🇫🇷
We study the fragmentation of a jet propagating in a dense quark-gluon plasma. We show that the "vacuum-like" emissions triggered by the parton virtualities can be factorized from the medium-induced radiation responsible for the energy loss within a controlled, "double-logarithmic", approximation in perturbative QCD. We show that the collisions with the plasma constituents modify the vacuum-like parton shower already at leading twist, in two ways: the radiation phase-space is reduced and the first emission outside the medium can violate angular ordering. We compute the jet fragmentation function and find results in qualitative agreement with measurements at the LHC.
↳ hep-phnucl-thNPA(2019)·0 citations
10
Angular distributions in electroweak pion production off nucleons: odd parity hadron terms, strong relative phases and model dependence
J.E. Sobczyk🇪🇸 · E. Hernández🇪🇸 · S.X. Nakamura🇧🇷 · J. Nieves🇪🇸 · T. Sato🇯🇵
The study of pion production in nuclei is important for signal and background determinations in current and future neutrino oscillation experiments. The first step, however, is to understand the pion production reactions at the free nucleon level. We present an exhaustive study of the charged-current and neutral-current neutrino and antineutrino pion production off nucleons, paying a special attention to the angular distributions of the outgoing pion. We show, using general arguments, that parity violation and time-reversal odd correlations in the weak differential cross sections are generated from the interference between different contributions to the hadronic current that are not relatively real. Next, we present a detailed comparison of three, state of the art, microscopic models for electroweak pion production off nucleons, and we also confront their predictions with polarized electron data, as a test of the vector content of these models. We also illustrate the importance of carrying out a comprehensive test at the level of outgoing pion angular distributions, going beyond comparisons done for partially integrated cross sections, where model differences cancel to a certain extent. Finally, we observe that all charged and neutral current distributions show sizable anisotropies, and identify channels for which parity violating effects are clearly visible. Based on the above results, we conclude that the use of isotropic distributions for the pions in the center of mass of the final pion-nucleon system, as assumed by some of the Monte Carlo event generators, needs to be improved by incorporating the findings of microscopic calculations.
↳ hep-phhep-exnucl-exnucl-thPRD(2018)·40 citations

Affiliations

first authorsco-authorsvia INSPIRE