Nuclear Theory·nucl-th

Tuesday·August 16, 2016

14 papers—4 primary·10 cross-listed

01
Extracting temperature and transverse flow by fitting transverse mass spectra and HBT radii together
Ronghua He🇨🇳 · Jing Qian🇨🇳 · Jianyi Chen🇨🇳 · Qingxin Wu🇨🇳 · Lei Huo🇨🇳
Single particle transverse mass spectra and HBT radii of identical pion and identical kaon are analyzed with a blast-wave parametrization under the assumptions local thermal equilibrium and transverse expansion. Under the assumptions, temperature parameter $T$ and transverse expansion rapidity $ρ$ are sensitive to the shapes of transverse mass $m_{T}$ spectrum and HBT radius $R_{s} (K_{T})$ . Negative and positive correlations between $T$ and $ρ$ are observed by fitting $m_{T}$ spectrum and HBT radius $R_{s} (K_{T})$ , respectively. For a Monte Carlo simulation using the blast-wave function, $T$ and $ρ$ are extracted by fitting $m_{T}$ spectra and HBT radii together utilizing a combined optimization function $χ^{2}$ . With this method, $T$ and $ρ$ of the Monte Carlo sources can be extracted. Using this method for A Multi-Phase Transport model (AMPT) at RHIC energy, the differences of $T$ and $ρ$ between pion and kaon are observed obviously, and the tendencies of $T$ and $ρ$ vs collision energy $s_{NN}$ are similar with the results extracted directly from the AMPT model.
nucl-thMod.Phys.Lett.A(2017)·0 citations
02
Role of ( $α$ ,n) reactions under $r$ -process conditions in neutrino-driven winds revisited
Peter Mohr
Background: The astrophysical $r$ -process occurs in an explosive astrophysical event under extremely neutron-rich conditions, leading to (n, $γ$ )-( $γ$ ,n) equilibrium along isotopic chains which peaks around neutron separation energies of a few MeV. Nuclei with larger $Z$ are usually produced by $β^{-}$ -decay, but under certain conditions also $α$ -induced reactions may become relevant for the production of nuclei with $Z + 2$ . Purpose: The uncertainties of the reaction rates of these $α$ -induced reactions are discussed within the statistical model. As an example, $α$ -induced ( $α$ ,n) and $(α$ , $x$ n) reaction cross sections for the neutron-rich $^{86}$ Se nucleus are studied in detail. Method: In a first step, the relevance of ( $α$ ,n) and $(α$ , $x$ n) reactions is analyzed. Next the uncertainties are determined from a variation of the $α$ -nucleus potential which is the all-dominant parameter for the astrophysical $Z \to Z + 2$ reaction rate. Results: It is found that the $r$ -process flow towards nuclei with larger $Z$ is essentially influenced only by the $α$ -nucleus potential whereas the other ingredients of the statistical model play a very minor role. This finding is based on the fact that the flow towards larger $Z$ depends on the sum over all ( $α$ , $x$ n) cross sections which is practically identical to the total $α$ -induced reaction cross section. Conclusions: $α$ -nucleus potentials play an important role under certain $r$ -process conditions because the flow towards larger $Z$ depends sensitively on the total $α$ -induced reaction cross section. The uncertainty of the reaction rate is about a factor of two to three at higher temperatures and exceeds one order of magnitude at very low temperatures.
nucl-thPRC(2016)·28 citations
03
Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions
V. Vovchenko🇩🇪 · Long-Gang Pang🇩🇪 · H. Niemi🇩🇪 · Iu. A. Karpenko🇺🇦 · M. I. Gorenstein🇺🇦 · L. M. Satarov🇩🇪 · I. N. Mishustin🇩🇪 · B. Kämpfer🇩🇪 · H. Stoecker🇩🇪
Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of $s_{_{NN}} = 2.76$ TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the $p_{T}$ -distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.
nucl-thhep-phPoS(2016)·8 citations
04
From pQCD to neutron stars: matching equations of state to constrain global star properties
Tyler Gorda🇺🇸
The equation of state (EoS) of quantum chromodynamics (QCD) at zero temperature can be calculated in two different perturbative regimes: for small values of the baryon chemical potential $μ$ , one may use chiral perturbation theory (ChEFT); and for large values of $μ$ , one may use perturbative QCD (pQCD). There is, however, a gap for $μ \in (0.97 GeV, 2.6 GeV)$ , where these theories becomes non-perturbative, and where there is currently no known microscopic description of QCD matter. Unfortunately, this interval obscures the values of $μ$ found within the cores of neutron stars (NSs). In this thesis, we argue that thermodynamic matching of the ChEFT and pQCD EoSs is a legitimate way to obtain quantitative constraints on the non-pertubative QCD EoS. Moreover, we argue that this method is effective, verifiable, and systematically improvable. First, we carry out a simplified matching procedure in QCD-like theories that can be simulated on the lattice without a sign problem. Our calculated pressure band serves as a prediction for lattice-QCD practitioners and will allow them to verify or refute the simplified procedure. Second, we apply the state-of-the-art matched EoS of Kurkela et al. (2014) to rotating NSs. This allows us to obtain bounds on observable NS properties, as well as point towards future observations that would more tightly constrain the current state-of-the-art EoS band. Finally, as evidence of the ability to improve the procedure, we carry out calculations in pQCD to improve the zero-temperature pressure. We calculate the full $O (g^{6} ln^{2} g)$ contribution to the pQCD pressure for $n_{f}$ massless quarks, as well as a significant portion of the $O (g^{6} ln g)$ piece and even some of the $O (g^{6})$ piece.
nucl-thastro-ph.HEhep-ph0 citations
05
Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
Jonathan L. Feng🇺🇸 · Bartosz Fornal🇺🇸 · Iftah Galon🇺🇸 · Susan Gardner🇺🇸 · Jordan Smolinsky🇺🇸 · Tim M. P. Tait🇺🇸 · Philip Tanedo🇺🇸
The 6.8 $σ$ anomaly in excited 8Be nuclear decays via internal pair creation is fit well by a new particle interpretation. In a previous analysis, we showed that a 17 MeV protophobic gauge boson provides a particle physics explanation of the anomaly consistent with all existing constraints. Here we begin with a review of the physics of internal pair creation in 8Be decays and the characteristics of the observed anomaly. To develop its particle interpretation, we provide an effective operator analysis for excited 8Be decays to particles with a variety of spins and parities and show that these considerations exclude simple models with scalar particles. We discuss the required couplings for a gauge boson to give the observed signal, highlighting the significant dependence on the precise mass of the boson and isospin mixing and breaking effects. We present anomaly-free extensions of the Standard Model that contain protophobic gauge bosons with the desired couplings to explain the 8Be anomaly. In the first model, the new force carrier is a U(1)B gauge boson that kinetically mixes with the photon; in the second model, it is a U(1)(B-L) gauge boson with a similar kinetic mixing. In both cases, the models predict relatively large charged lepton couplings ~ 0.001 that can resolve the discrepancy in the muon anomalous magnetic moment and are amenable to many experimental probes. The models also contain vectorlike leptons at the weak scale that may be accessible to near future LHC searches.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·254 citations
06
In-Medium Pion Valence Distributions in a Light-Front Model
J. P. B. C de Melo · K. Tsushima · (Laboratório de Fisica Teorica e Computacional - LFTC, Universidade Cruzeiro do Sul) · I. Ahmed · (National Center for Physics, Quaidi-i-Azam University Campus)
Pion valence distributions in nuclear medium and vacuum are studied in a light-front constituent quark model. The in-medium input for studying the pion properties is calculated by the quark-meson coupling model. We find that the in-medium pion valence distribution, as well as the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.
↳ hep-phhep-exhep-latnucl-ex+1PLB(2017)·11 citations
07
Search for doubly-heavy dibaryons in a quark model
J. Vijande🇪🇸 · A. Valcarce🇪🇸 · J.-M. Richard🇫🇷 · P. Sorba🇫🇷
We study the stability of hexaquark systems containing two heavy quarks and four light quarks within a simple quark model. No bound or metastable state is found. The reason stems on a delicate interplay between chromoelectric and chromomagnetic effects. Our calculation provides also information about anticharmed pentaquarks that are seemingly unbound in simple quark models.
↳ hep-phnucl-thPRD(2016)·31 citations
08
Hadronic molecules with a $D ˉ$ meson in a medium
T. F. Caramés🇪🇸 · C. E. Fontoura🇧🇷 · G. Krein🇧🇷 · K. Tsushima🇧🇷 · J. Vijande🇪🇸 · A. Valcarce🇪🇸
We study the effect of a hot and dense medium on the binding energy of hadronic molecules with open-charm mesons. We focus on a recent chiral quark-model-based prediction of a molecular state in the $N D ˉ$ system. We analyze how the two-body thresholds and the hadron-hadron interactions are modified when quark and meson masses and quark-meson couplings change in a function of the temperature and baryon density according to predictions of the Nambu--Jona-Lasinio model. We find that in some cases the molecular binding is enhanced in medium as compared to their free-space binding. We discuss the consequences of our findings for the search for exotic hadrons in high-energy heavy-ion collisions as well as in the forthcoming facilities FAIR or J-PARC.
↳ hep-phnucl-thPRD(2016)·15 citations
09
Impacts of B-factory measurements on determination of fragmentation functions from electron-positron annihilation data
M. Hirai🇯🇵 · H. Kawamura🇯🇵 · S. Kumano🇯🇵 · K. Saito🇯🇵
Fragmentation functions are determined for the pion and kaon by global analyses of charged-hadron production data in electron-positron annihilation. Accurate measurements were reported by the Belle and BaBar collaborations for the fragmentation functions at the center-of-mass energies of 10.52 GeV and 10.54 GeV, respectively, at the KEK and SLAC B factories, whereas other available $e^{+} e^{-}$ measurements were mostly done at higher energies, mainly at the $Z$ mass of 91.2 GeV. There is a possibility that gluon fragmentation functions, as well as quark fragmentation functions, are accurately determined by scaling violation. We report our global analysis of the fragmentation functions especially to show impacts of the B-factory measurements on the fragmentation function determination. Our results indicate that the fragmentation functions are determined more accurately not only by the scaling violation but also by high-statistical nature of the Belle and BaBar data. However, there are some tensions between the Belle and BaBar data in comparison with previous measurements. We also explain how the flavor dependence of quark fragmentation functions and the gluon function are separated by using measurements at different $Q^{2}$ values. In particular, the electric and weak changes are different depending on the quark type, so that a light-quark flavor separation also became possible in principle due to the precise data at both $s ≃ 10.5$ GeV and 91.2 GeV.
↳ hep-phhep-exnucl-exnucl-thPTEP(2016)·23 citations
10
Precise Determination of the U-235 Reactor Antineutrino Cross Section per Fission
Carlo Giunti🇮🇹
We investigate which among the reactor antineutrino fluxes from the decays of the fission products of $^{235} U$ , $^{238} U$ , $^{239} Pu$ , and $^{241} Pu$ may be responsible for the reactor antineutrino anomaly if the anomaly is due to a miscalculation of the antineutrino fluxes. We find that it is very likely that at least the calculation of the $^{235} U$ flux must be revised. From the fit of the data we obtain the precise determination $σ_{f, 235} = (6.33 \pm 0.08) \times 1 0^{- 43} cm^{2} / fission$ of the $^{235} U$ cross section per fission, which is more precise than the calculated value and differs from it by $2.2 σ$ . The cross sections per fission of the other fluxes have large uncertainties and in practice their values are undetermined by the fit.
↳ hep-phhep-exnucl-exnucl-thPLB(2017)·41 citations
11
Sound Attenuation in Quark Matter Due to Pairing Fluctuations
Boris Kerbikov🇷🇺
The sound wave in dense quark matter is subject to strong absorption due to diquark field fluctuations above T critical. The result is another facet of Mandelshtam-Leontovich slow relaxation time theory.
↳ hep-phnucl-thEPJ Web Conf.(2016)·3 citations
12
Finite Temperature QCD Sum Rules: a Review
Alejandro Ayala🇲🇽 · C. A. Dominguez🇿🇦 · M. Loewe🇿🇦
The method of QCD sum rules at finite temperature is reviewed, with emphasis on recent results. These include predictions for the survival of charmonium and bottonium states, at and beyond the critical temperature for de-confinement, as later confirmed by lattice QCD simulations. Also included are determinations in the light-quark vector and axial-vector channels, allowing to analyse the Weinberg sum rules, and predict the dimuon spectrum in heavy ion collisions in the region of the rho-meson. Also in this sector, the determination of the temperature behaviour of the up-down quark mass, together with the pion decay constant, will be described. Finally, an extension of the QCD sum rule method to incorporate finite baryon chemical potential is reviewed.
↳ hep-phhep-latnucl-thAdv.High Energy Phys.(2017)·38 citations
13
High-precision quadrupole moment reveals significant intruder component in 33Al20 ground state
H. Heylen🇧🇪 · M. De Rydt🇧🇪 · G. Neyens🇧🇪 · M.L. Bissell🇧🇪 · L. Caceres🇫🇷 · R. Chevrier🇫🇷 · J.M. Daugas🇫🇷 · Y. Ichikawa🇯🇵 · Y. Ishibashi🇯🇵 · O. Kamalou🇫🇷 · T.J. Mertzimekis🇬🇷 · P. Morel🇫🇷 and 9 other authors
The electric quadrupole moment of the 33Al20 ground state, located at the border of the island of inversion, was obtained using continuous-beam beta-detected nuclear quadrupole resonance (beta-NQR). From the measured quadrupole coupling constant Q = 2.31(4) MHz in an alpha-Al2O3 crystal, a precise value for the electric quadrupole moment is extracted: Qs= 141(3) mb. A comparison with large-scale shell model calculations shows that 33Al has at least 50% intruder configurations in the ground state wave function, favoring the excitation of two neutrons across the N = 20 shell gap. 33Al therefore clearly marks the gradual transition north of the deformed Na and Mg nuclei towards the normal Z>14 isotopes.
↳ nucl-exnucl-thPRC(2016)·18 citations
14
Hadronic matter at the edge: A survey of some theoretical approaches to the physics of the QCD phase diagram
Alejandro Ayala🇲🇽
In the past few years a wealth of high quality data has made possible to test current theoretical ideas about the properties of hadrons subject to extreme conditions of density and temperature. The relativistic heavy-ion program carried out at the CERN-SPS and under development at the BNL-RHIC and CERN-LHC has provided results that probe the evolution of collisions of hadronic matter at high energies from the initially large density to the late dilute stages. In addition, QCD on the lattice has produced results complementing these findings with first principles calculations for observables in a regime where perturbative techniques cannot describe the nature of strongly coupled systems. This work aims to review some recent developments that make use of field theoretical methods to describe the physics of hadrons at finite temperature and density. I concentrate on two of the main topics that have been explored in the last few years: (1) The search for the structure of the phase diagram and (2) analytical signals linked to the chiral symmetry restoration/deconfinement.
↳ hep-phhep-latnucl-thJ.Phys.Conf.Ser.(2016)·3 citations

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