Nuclear Theory·nucl-th

Thursday·September 20, 2018

8 papers—4 primary·4 cross-listed

01
Dilepton Radiation in Heavy-Ion Collisions at Small Transverse Momentum
Mariola Klusek-Gawenda🇵🇱 · Ralf Rapp🇺🇸 · Wolfgang Schäfer🇵🇱 · Antoni Szczurek🇵🇱
We study the invariant-mass distributions of dileptons produced in ultrarelativistic heavy-ion collisions at very low pair transverse momenta, $P_{T} \leq 0.15$ GeV. Specifically, we investigate the interplay of thermal radiation with initial photon annihilation processes, $γ γ \to l^{+} l^{-}$ , triggered by the coherent electromagnetic fields of the incoming nuclei. For the thermal radiation, we employ the emission from the QGP and hadronic phases with in-medium vector spectral functions which describes the inclusive excess radiation observed over a wide range of collision energies. For the coherent photon fusion processes, whose spectrum is much softer than for thermal radiation, we employ initial fluxes from the Fourier transform of charge distributions of the colliding nuclei in the equivalent-photon approximation. We first verify that the combination of photon fusion, thermal radiation and final-state hadron decays gives a fair description of the low- $P_{T}$ dilepton mass spectra as recently measured by the STAR collaboration in $s_{N N}$ =200 GeV Au+Au collisions for different centrality classes, including experimental acceptance cuts. The coherent contribution dominates in peripheral collisions, while thermal radiation shows a markedly stronger increase with centrality. We perform similar calculations at lower collision energies ( $s_{N N}$ =17.3 GeV) and compare to the acceptance-corrected dimuon excess spectra measured by the NA60 experiment at the CERN SPS; here, the contribution from photoproduction is subleading. We also provide predictions for the ALICE experiment at the LHC; the pertinent excitation function from SPS to LHC energies reveals a nontrivial interplay of photoproduction and thermal radiation.
nucl-thhep-phPLB(2019)·44 citations
02
A cross-validation check in the covariance analysis of isospin sensitive observables from heavy ion collision
Ilona Bednarek🇵🇱 · Jacek Syska🇵🇱 · Jan Sładkowski🇵🇱
This paper focuses on two problems. The first is related to the consistency checks of the complete correlation coefficients between two groups of variables obtained in Phys. Lett. B 749, 262 (2015). The first group collects parameters that describe properties of nuclear matter referring to the transport model involved. The second one is a group of observables adopted in the heavy ion collision experiments. The second problem concerns the method of determining the values of pure correlations between some variables in heavy ion collision. The application of this method for the analysis of the correlations of the isospin sensitive variables is pointed out.
nucl-thhep-ph0 citations
03
On the width of the $Δ (1232)$ in $N Δ$ and $ΔΔ$ states
Jouni A. Niskanen🇫🇮
Due to the finite kinetic energy in the intermediate $N Δ$ state the (internal) energy available for mesonic decay is decreased and consequently the effective $N Δ$ width is suppressed in $N N$ scattering. The same can happen also in $Δ$ $Δ$ case. Also the $N Δ$ angular momentum suppresses the width as well, while the effect of the initial $N N$ angular momentum is more subtle. The state dependence affects e.g. pion production observables and can also be seen as the origin of T=1 "dibaryons".
nucl-thEPJ Web Conf.(2019)·0 citations
04
Nuclear transition matrix elements for neutrinoless double- $β$ decay within mechanisms involving light Majorana neutrino mass and right-handed current
Yash Kaur Singh🇮🇳 · R. Chandra🇮🇳 · K. Chaturvedi🇮🇳 · Tripti Avasthi🇮🇳 · P.K. Raina🇮🇳 · P.K. Rath🇮🇳
Employing the projected-Hartree-Fock-Bogoliubov (PHFB) model in conjunction with four different parametrizations of pairing plus multipolar effective two body interaction and three different parametrizations of Jastrow short range correlations, nuclear transition matrix elements for the neutrinoless double- $β$ decay of $^{94, 96}$ Zr, $^{100}$ Mo, $^{110}$ Pd, $^{128, 130}$ Te and $^{150}$ Nd isotopes are calculated within mechanisms involving light Majorana neutrino mass and right handed current. Statistically, model specific uncertainties in sets of twelve nuclear transition matrix elements are estimated by calculating the averages along with the standard deviations. For the considered nuclei, \ the most stringent extracted on-axis limits on the effective light Majorana neutrino mass $< m_{ν} >$ , the effective weak coupling of right-handed leptonic current with right-handed hadronic current $< λ >$ , and the effective weak coupling of right-handed leptonic current with left-handed hadronic current $< η >$ \ from the observed limit on half-life $T_{1/2}^{0 ν}$ of $^{130}$ Te isotope are $0.33$ eV, $4.57 \times 1 0^{- 7}$ and $4.72 \times 1 0^{- 9}$ , respectively.
nucl-thIJMPE(2019)·1 citation
05
A new parametrization for the scalar pion form factors
Stefan Ropertz🇩🇪 · Christoph Hanhart🇩🇪 · Bastian Kubis🇩🇪
We derive a new parametrization for the scalar pion form factors that allows us to analyze data over a large energy range via the inclusion of resonances, and at the same time to ensure consistency with the high-accuracy dispersive representations available at low energies. As an application the formalism is used to extract resonance properties of excited scalar mesons from data for $B ˉ_{s}^{0} \to J / ψ π π$ . In particular we find for the pole positions of $f_{0} (1500)$ and $f_{0} (2020)$ $1465 \pm 18 - i (50 \pm 9) MeV$ and $1910 \pm 50 - i (199 \pm 40) MeV$ , respectively. In addition, from their residues we calculate the respective branching ratios into $π π$ to be $(58 \pm 31) %$ and $(1.3 \pm 1.8) %$ .
↳ hep-phhep-exnucl-thEPJC(2018)·90 citations
06
Flavor symmetry breaking in the $Δ$ sea
J. J. Ethier🇳🇱 · W. Melnitchouk🇺🇸 · Fernanda Steffens🇩🇪 · A. W. Thomas🇦🇺
The discovery of a sizeable asymmetry in the $u ˉ$ and $d ˉ$ distributions in the proton was one of the more consequential experimental findings in hadron physics last century. Although widely believed to be related to the fundamental role of chiral symmetry in QCD, a definitive verification of this hypothesis has remained elusive. We propose a novel test of the role of chiral symmetry in generating the sea flavor asymmetry by comparing the $d ˉ - u ˉ$ content in the proton with that in the $Δ^{+}$ baryon, where a significant enhancement is expected around the opening of the $N π$ decay channel. Recent developments in lattice QCD suggest a promising way to test this prediction in the near future.
↳ hep-phhep-latnucl-thPRD(2019)·4 citations
07
Quasiparticle properties of nonequilibrium gluon plasma
Jarkko Peuron🇫🇮
We apply classical gluodynamics to early stages of ultrarelativistic heavy-ion collisions. We start by going through the space-time evolution of ultrarelativistic heavy-ion collisions in the color glass condensate framework and the basics of real-time gluodynamics on the lattice in the temporal gauge. We study the plasmon mass scale in three- and two-dimensional systems by comparing three different methods to measure the mass scale. The methods are a formula which can be derived from Hard Thermal Loop effective theory at leading order (HTL), the effective dispersion relation (DR) and measurement of the plasma oscillation frequency triggered by the introduction of a uniform electric field (UE) into the system. We observe that in both systems the plasmon mass scale decreases like a power law after an occupation number dependent initial transient time. In both cases the UE and HTL methods are in rough agreement, and in the three-dimensional case the two agree in the continuum limit. As a second way to study the quasiparticle properties, we derive, implement and test an algorithm which can be used to simulate linearized fluctuations on top of the classical background. The algorithm is derived by requiring conservation of Gauss' law and gauge invariance. We then apply the algorithm to spectral properties of overoccupied gluodynamics using linear response theory. We establish the existence of transverse and longitudinal quasiparticles by extracting their spectral functions. We also extract the dispersion relation, effective mass, plasmon mass and damping rate of the quasiparticles. Our results are consistent with the HTL effective theory, but we also observe effects beyond leading order HTL.
↳ hep-lathep-phnucl-th1 citation
08
Constraining the relativistic mean-field model equations of state with gravitational wave observations
Rana Nandi🇮🇳 · Prasanta Char🇮🇹 · Subrata Pal🇮🇳
The first detection of gravitational waves from the binary neutron star merger event GW170817 has started to provide important new constraints on the nuclear equation of state at high density. The tidal deformability bound of GW170817 combined with the observed two solar mass neutron star poses a serious challenge to theoretical formulations of realistic equations of state. We analyze a fully comprehensive set of relativistic nuclear mean-field theories by confronting them with the observational bounds and the measured neutron-skin thickness. We find that only a few models can withstand these bounds which predict a stiff overall equation of state but with a soft neutron-proton symmetry energy. Two possible indications are proposed: Circumstantial evidence of hadron-quark phase transition inside the star and new parametrizations that are consistent with ground state properties of finite nuclei and observational bounds. Based on extensive analysis of these sets, an upper limit on the radius of a $1.4 M_{⊙}$ neutron star of $R_{1.4} ≲ 12.9$ km is deduced.
↳ astro-ph.HEnucl-thPRC(2019)·69 citations

Affiliations

first authorsco-authorsvia INSPIRE