Nuclear Theory·nucl-th

Tuesday·May 2, 2017

14 papers—8 primary·6 cross-listed

01
The production of primordial $J / ψ$ in p+p and relativistic heavy-ion collisions
Taesoo Song🇩🇪 · Joerg Aichelin🇩🇪 · Elena Bratkovskaya🇩🇪
$J / ψ$ observables of p+p collisions at $s =$ 200 GeV and 2.76 TeV are calculated using the PYTHIA event generator for the production of $c$ and $c ˉ$ and the Wigner density formalism. The charm quark momentum from PYTHIA is tuned in such a way that the transverse momentum and rapidity distribution correspond to the Fixed-Order Next-to-Leading Logarithm (FONLL) calculations and hence to the experimental data for open charm mesons. Using the Wigner density of the charmonium wave function we calculate for each charm quark pair the probability to form a charmonium. As a result, the experimental data on the total $J / ψ$ yield, its rapidity and transverse momentum distribution as well as the fractions of feed-down from excited states of charmonium are reproduced. Applying the same approach to relativistic heavy-ion collisions, we find, if quark gluon plasma (QGP) effects are ignored, a considerable enhancement of the primordial $J / ψ$ 's.
nucl-thhep-phPRC(2017)·30 citations
02
Multistage Monte-Carlo simulation of jet modification in a static medium
JETSCAPE Collaboration: Shanshan Cao🇺🇸 · Chanwook Park🇨🇦 · R. Alex Barbieri🇺🇸 · Steffen A. Bass🇺🇸 · Dennis Bazow🇺🇸 · Jonah Bernhard🇺🇸 · Jacob Coleman🇺🇸 · Rainer Fries🇺🇸 · Charles Gale🇨🇦 · Yayun He🇨🇳 · Ulrich Heinz🇺🇸 · Barbara V. Jacak🇺🇸 and 21 other authors
The modification of hard jets in an extended static medium held at a fixed temperature is studied using three different Monte-Carlo event generators (LBT, MATTER, MARTINI). Each event generator contains a different set of assumptions regarding the energy and virtuality of the partons within a jet versus the energy scale of the medium, and hence, applies to a different epoch in the space-time history of the jet evolution. For the first time, modeling is developed where a jet may sequentially transition from one generator to the next, on a parton-by-parton level, providing a detailed simulation of the space-time evolution of medium modified jets over a much broader dynamic range than has been attempted previously in a single calculation. Comparisons are carried out for different observables sensitive to jet quenching, including the parton fragmentation function and the azimuthal distribution of jet energy around the jet axis. The effect of varying the boundary between different generators is studied and a theoretically motivated criterion for the location of this boundary is proposed. The importance of such an approach with coupled generators to the modeling of jet quenching is discussed.
nucl-thhep-phnucl-exPRC(2017)·110 citations
03
Nuclear Fission: from more phenomenology and adjusted parameters to more fundamental theory and increased predictive power
A. Bulgac · S. Jin · P. Magierski · K. Roche · N. Schunck · I. Stetcu
Two major recent developments in theory and computational resources created the favorable conditions for achieving a microscopic description of nuclear fission almost eighty years after its discovery in 1939 by Hahn and Strassmann (1930). The first major development was in theory, the extension of the Time-Dependent Density Functional Theory (TDDFT) to superfluid fermion systems. The second development was in computing, the emergence of powerful enough supercomputers capable of solving the complex systems of equations describing the time evolution in three dimensions without any restrictions of hundreds of strongly interacting nucleons. Even though the available nuclear energy density functionals (NEDFs) are phenomenological still, their accuracy is improving steadily and the prospects of being able to perform calculations of the nuclear fission dynamics and to predict many properties of the fission fragments, otherwise not possible to extract from experiments, are within reach, all without making recourse anymore to uncontrollable assumptions and simplified phenomenological models.
nucl-thEPJ Web Conf.(2017)·3 citations
04
Charge asymmetry in elastic scattering of massive leptons on protons
O. Koshchii🇺🇸 · A. Afanasev🇺🇸
The charge asymmetry due to higher-order QED corrections in elastic lepton-proton scattering is estimated without employing the ultrarelativistic approximation. Our calculation is performed by generalizing the soft-photon approximation approach suggested by Tsai. Corresponding loop integrals that take a form of Passarino-Veltman scalar three-point functions are calculated analytically without neglecting the mass of the lepton. Our results provide model-independent charge asymmetry predictions for scattering of unpolarized and massive leptons on proton targets. These predictions can be used in corresponding experiments to determine the contribution coming from model-dependent hard two-photon exchange processes.
nucl-thhep-phPRD(2017)·31 citations
05
Alpha Cluster Formation and Decay in Quartetting Wave Function Approach
Chang Xu🇨🇳 · G. Ropke🇩🇪 · P. Schuck🇫🇷 · Zhongzhou Ren🇨🇳 · Y. Funaki🇯🇵 · H. Horiuchi🇯🇵 · A. Tohsaki🇯🇵 · T. Yamada · Bo Zhou🇯🇵
We present a microscopic calculation of alpha-cluster formation in heavy nuclei by using the quartetting wave function approach. The interaction of the quartet with the core nucleus is taken in local density approximation. The alpha-cluster formation is found to be particularly sensitive to the interplay of the mean field felt by the alpha-cluster and the Pauli blocking as a consequence of antisymmetrization. The striking feature of alpha-cluster formation probability across the major shell closures of 82 protons and 126 neutrons is reproduced. The shell (or subshell) effects on the alpha-cluster formation in superheavy nuclei are also analyzed.
nucl-thPRC(2017)·75 citations
06
Nucleon-anti-nucleon intruder state of Dirac equation for nucleon in deep scalar potential well
T.T.S. Kuo · T.K. Kuo · E. Osnes · S. Shu
We solve the Dirac radial equation for a nucleon in a scalar Woods-Saxon potential well of depth $V_{0}$ and radius $r_{0}$ . A sequence of values for the depth and radius are considered. For shallow potentials with $- 1000 M e V ≲ V_{0} < 0$ the wave functions for the positive-energy states $Ψ_{+} (r)$ are dominated by their nucleon component $g (r)$ . But for deeper potentials with $V_{0} ≲ - 1500 M e V$ the $Ψ_{+} (r)$ s begin to have dominant anti-nucleon component $f (r)$ . In particular, a special intruder state enters with wave function $Ψ_{1/2} (r)$ and energy $E_{1/2}$ . We have considered several $r_{0}$ values between 2 and 8 fm. For $V_{0} ≲ - 2000 M e V$ and the above $r_{0}$ values, $Ψ_{1/2}$ is the only bound positive-energy state and has its $g (r)$ closely equal to $- f (r)$ , both having a narrow wave-packet shape centered around $r_{0}$ . The $E_{1/2}$ of this state is practically independent of $V_{0}$ for the above $V_{0}$ range and obeys closely the relation $E_{1/2} = \frac{ℏ c}{r _{0}}$ .
nucl-thIJMPE(2017)·0 citations
07
Low density nuclear matter with light clusters in a generalized nonlinear relativistic mean-field model
Zhao-Wen Zhang · Lie-Wen Chen
We systematically investigate the thermodynamic properties of homogeneous nuclear matter with light clusters at low densities and finite temperatures using a generalized nonlinear relativistic mean-field (gNL-RMF) model, in which light clusters up to $α$ ( $1 \leq A \leq 4$ ) are included as explicit degrees of freedom and treated as point-like particles with their interactions described by meson exchanges and the medium effects on the cluster binding energies are described by density- and temperature-dependent energy shifts with the parameters obtained by fitting the experimental cluster Mott densities. We find that the composition of low density nuclear matter with light clusters is essentially determined by the density- and temperature-dependence of the cluster binding energy shifts. Compared with the values of the conventional (second-order) symmetry energy, symmetry free energy and symmetry entropy, their fourth-order values are found to be significant at low densities ( $ρ \sim 1 0^{- 3}$ fm $^{- 3}$ ) and low temperatures ( $T ≲ 3$ MeV), indicating the invalidity of the empirical parabolic law for the isospin asymmetry dependence of these nuclear matter properties. Our results indicate that in the density region of $ρ ≳ 0.02$ fm $^{- 3}$ , the clustering effects become insignificant and the nuclear matter is dominated by nucleon degree of freedom. In addition, we compare the gNL-RMF model predictions with the corresponding experimental data on the symmetry energy and symmetry free energy at low densities and finite temperatures extracted from heavy-ion collisions, and reasonable agreement is found.
nucl-thastro-ph.SRnucl-exPRC(2017)·18 citations
08
Relativistic fluid dynamics with spin
Wojciech Florkowski🇵🇱 · Bengt Friman🇩🇪 · Amaresh Jaiswal🇩🇪 · Enrico Speranza🇩🇪
Using the conservation laws for charge, energy, momentum, and angular momentum, we derive hydrodynamic equations for the charge density, local temperature, and fluid velocity, as well as for the spin tensor, starting from local equilibrium distribution functions for particles and antiparticles with spin 1/2. The resulting set of differential equations extend the standard picture of perfect-fluid hydrodynamics with a conserved entropy current in a minimal way. This framework can be used in space-time analyzes of the evolution of spin and polarization in various physical systems including high-energy nuclear collisions. We demonstrate that a stationary vortex, which exhibits vorticity-spin alignment, corresponds to a special solution of the spin-hydrodynamical equations.
nucl-thhep-phnucl-exPRC(2018)·321 citations
09
Fierz-complete NJL model study: fixed points and phase structure at finite temperature and density
Jens Braun🇩🇪 · Marc Leonhardt🇩🇪 · Martin Pospiech🇩🇪
Nambu-Jona-Lasinio-type models are frequently employed as low-energy models in various research fields. With respect to the theory of the strong interaction, this class of models is indeed often used to analyze the structure of the phase diagram at finite temperature and quark chemical potential. The predictions from such models for the phase structure at finite quark chemical potential are of particular interest as this regime is difficult to access with lattice Monte Carlo approaches. In this work, we consider a Fierz-complete version of a Nambu-Jona-Lasinio model. By studying its renormalization group flow, we analyze in detail how Fierz-incomplete approximations affect the predictive power of such model studies. In particular, we investigate the curvature of the phase boundary at small chemical potential, the critical value of the chemical potential above which no spontaneous symmetry breaking occurs, and the possible interpretation of the underlying dynamics in terms of difermion-type degrees of freedom. We find that the inclusion of four-fermion channels other than the conventional scalar-pseudoscalar channel is not only important at large chemical potential but also leaves a significant imprint on the dynamics at small chemical potential as measured by the curvature of the finite-temperature phase boundary.
↳ hep-phnucl-thPRD(2017)·70 citations
10
Critical assessment of nuclear sensitivity metrics for the r-process
Zachary Shand · Rachid Ouyed · Nico Koning · Iris Dillmann · Reiner Krücken · Prashanth Jaikumar
Any simulation of the r-process is affected by uncertainties in our present knowledge of nuclear physics quantities and astrophysical conditions. It is common to quantify the impact of these uncertainties through a global sensitivity metric, which is then used to identify specific nuclides that would be most worthwhile to measure experimentally. Using descriptive statistics, we assess a set of metrics used in previous sensitivity studies, as well as a new logarithmic measure. For certain neutron-rich nuclides lying near the r-process path for the typical hot-wind scenario, we find opposing conclusions on their relative sensitivity implied by different metrics, although they all generally agree which ones are the most sensitive nuclei. The underlying reason is that sensitivity metrics which simply sum over variations in the r-process distribution depend on the scaling used in the baseline, which often varies between simulations. We show that normalization of the abundances causes changes in the reported sensitivity factors and recommend reporting a minimized F statistic in addition to a scale estimation for rough calibration to be used when comparing tables of sensitivity factors from different studies.
↳ astro-ph.HEnucl-th1 citation
11
Formation of hadrons at chemical freeze-out
David Blaschke🇵🇱 · Jakub Jankowski🇵🇱 · Michal Naskret🇵🇱
We use a kinetic condition to predict the chemical freeze-out parameters for hadronic species produced in heavy ion collisions. The resulting freeze-out lines for different hadrons lie close to one another in the temperature and baryochemical potential plane, defining a universal, narrow region. The chemical freeze-out is driven by the localization of hadrons due to the chiral symmetry breaking and confining aspects of the QCD transition.
↳ hep-phnucl-th8 citations
12
Theory of the n=2 levels in muonic helium-3 ions
Beatrice Franke (1 and 2)🇩🇪 · Julian J. Krauth (1 and 3)🇩🇪 · Aldo Antognini (4 and 5)🇨🇭 · Marc Diepold (1)🇩🇪 · Franz Kottmann (4)🇨🇭 · Randolf Pohl (3 and 1) ((1) Max-Planck-Institut für Quantenoptik, Garching, Germany, (2) Triumf, Vancouver, Canada, (3) Johannes Gutenberg-Universität Mainz, Quantum, Institut für Physik and Exzellenzcluster PRISMA, Mainz, Deutschland, (4) Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland, (5) Paul Scherrer Institute, Villigen, Switzerland)🇩🇪
The present knowledge of Lamb shift, fine-, and hyperfine structure of the 2S and 2P states in muonic helium-3 ions is reviewed in anticipation of the results of a first measurement of several $2S \to 2P$ transition frequencies in the muonic helium-3 ion, $μ^{3} H e^{+}$ . This ion is the bound state of a single negative muon $μ^{-}$ and a bare helium-3 nucleus (helion), $^{3} H e^{++}$ . A term-by-term comparison of all available sources, including new, updated, and so far unpublished calculations, reveals reliable values and uncertainties of the QED and nuclear structure-dependent contributions to the Lamb shift and the hyperfine splitting. These values are essential for the determination of the helion rms charge radius and the nuclear structure effects to the hyperfine splitting in $μ^{3} H e^{+}$ . With this review we continue our series of theory summaries in light muonic atoms; see Antognini et al., Ann. Phys. 331, 127 (2013), Krauth et al., Ann.Phys. 366, 168 (2016), and Diepold et al., ArXiv 1606.05231 (2016).
↳ physics.atom-phnucl-thEur.Phys.J.D(2017)·29 citations
13
Radiative decay of heavy neutrinos at MiniBooNE and MicroBooNE
Luis Alvarez-Ruso🇪🇸 · Eduardo Saul-Sala🇪🇸
The MiniBooNE experiment reported results from the analysis of $ν_{e}$ and $ν_{e}$ appearance searches, which showed an excess of signal-like events at low reconstructed neutrino energies with respect to the expected background. A proposed explanation for this anomaly is based on the existence of a heavy ( $\sim 50$ ~MeV) sterile neutrino. These $ν_{h}$ would be produced by $ν_{μ}$ electromagnetic and neutral current interactions. A fraction of them decays radiatively inside the detector. The emitted photon is misidentified as an electron or positron in MiniBooNE. We have investigated the $ν_{h}$ production by coherent and incoherent electroweak interactions at the MiniBooNE and MicroBooNE targets, CH $_{2}$ and Ar, respectively. Studying the $ν_{h}$ propagation inside the detector, we obtain the energy and angular distributions of emitted photons for a choice of model parameters. The distinctive shape and total number of photon events from this mechanism at MicroBooNE makes its experimental investigation possible.
↳ hep-phhep-exnucl-th14 citations
14
Are there near-threshold Coulomb-like Baryonia?
Li-Sheng Geng🇨🇳 · Jun-Xu Lu🇨🇳 · Manuel Pavon Valderrama🇨🇳 · Xiu-Lei Ren🇨🇳
The $Λ_{c} (2590) Σ_{c}$ system can exchange a pion near the mass-shell. Owing to the opposite intrinsic parity of the $Λ_{c} (2590)$ and $Σ_{c}$ , the pion is exchanged in S-wave. This gives rise to a Coulomb-like force that might be able to bind the system. If one takes into account that the pion is not exactly on the mass shell, there is a shallow S-wave state, which we generically call the $Y_{cc} (5045)$ and $Y_{c c ˉ} (5045)$ for the $Λ_{c} (2590) Σ_{c}$ and $Λ_{c} (2590) Σ ˉ_{c}$ systems respectively. For the baryon-antibaryon case this Coulomb-like force is independent of spin: the $Y_{c c ˉ} (5045)$ baryonia will appear either in the spin $S = 0$ or $S = 1$ configurations with G-parities $G = (- 1)^{L + S + 1}$ . For the baryon-baryon case the Coulomb-like force is attractive in the spin $S = 0$ configuration, for which a doubly charmed molecule is expected to form near the threshold. This type of spectrum might be very well realized in other molecular states composed of two opposite parity hadrons with the same spin and a mass difference close to that of a pseudo-Goldstone boson, of which a few examples include the $Λ (1405) N$ , $Λ (1520) Σ^{*}$ , $Ξ (1690) Σ$ , $D_{s 0}^{*} (2317) D$ and $D_{s 1}^{*} (2460) D^{*}$ molecules.
↳ hep-phhep-exnucl-thPRD(2018)·6 citations

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