Lattice calculations of the QCD trace anomaly at temperatures $T<160$ MeV have been shown to match hadron resonance gas model calculations, which include an exponentially rising hadron mass spectrum. In this paper we perform a more detailed comparison of the model calculations to lattice data that confirms the need for an exponentially increasing density of hadronic states. Also, we find that the lattice data is compatible with a hadron density of states that goes as $\rho \left(m\right)\sim m^{-a}\exp (m/T_H)$ at large $m$ with $a>5/2$ (where $T_H\sim 167$ MeV). With this specific subleading contribution to the density of states, heavy resonances are most likely to undergo two-body decay (instead of multiparticle decay), which facilitates their inclusion into hadron transport codes. Moreover, estimates for the shear viscosity and the shear relaxation time coefficient of the hadron resonance model computed within the excluded volume approximation suggest that these transport coefficients are sensitive to the parameters that define the hadron mass spectrum.

We investigate the two-particle interferometry for the particle-emitting sources that undergo the first-order phase transition from the quark-gluon plasma with a finite baryon chemical potential to hadron resonance gas. The effects of source expansion, lifetime, and particle absorption on the transverse interferometry radii $R_{\mathrm{out}}$ and $R_{\mathrm{side}}$ are examined. We find that the emission durations of the particles become large when the system is initially located at the boundary between the mixed phase and the quark-gluon plasma. In this case, the difference between the radii $R_{\mathrm{out}}$ and $R_{\mathrm{side}}$ increases with the transverse momentum of the particle pair significantly. The ratio of $\sqrt{R_{\mathrm{out}}^2-R_{\mathrm{side}}^2}$ to the transverse velocity of the pair is an observable for the enhancement of the emission duration.

The surface tension of quark matter plays a crucial role for the possibility of quark matter nucleation during the formation of compact stellar objects, because it determines the nucleation rate and the associated critical size. However, this quantity is not well known and the theoretical estimates fall within a wide range, ${\gamma }_0\approx 5–300\mathrm{MeV}/{\mathrm{fm}}^2$. We show here that once the equation of state is available one may use a geometrical approach to obtain a numerical value for the surface tension that is consistent with the model approximations adopted. We illustrate this method within the two-flavor linear $\sigma$ model and the Nambu–Jona-Lasinio model with two and three flavors. Treating these models in the mean-field approximation, we find ${\gamma }_0\approx 7–30\mathrm{MeV}/{\mathrm{fm}}^2$. Such a relatively small surface tension would favor the formation of quark stars and may thus have significant astrophysical implications. We also investigate how the surface tension decreases towards zero as the temperature is raised from zero to its critical value.

Starting from a Skyrme interaction we study the properties of the low-energy spectrum of quadrupole excitations in ${}^{90,92}$Zr and ${}^{92,94}$Mo. The coupling between one- and two-phonon terms in the wave functions of excited states are taken into account. We use the finite-rank separable approximation which enables one to perform the QRPA calculations in very large two-quasiparticle spaces. Our results from the SGII Skyrme interaction in connection with the volume pairing interaction are in reasonable agreement with experimental data. In particular, we present the successful description of the $M1$ transition between low-energy quadrupole excitations.

Complete fusion cross sections have been measured using the off-line $\gamma$-ray spectroscopy method for the ${}^6$Li+${}^{90}$Zr system around barrier energies. Statistical and coupled-channel calculations have been performed to investigate the effect of coupling on complete fusion. It is observed that the complete fusion is suppressed by 34 $\pm$ 8$\%$ compared to the coupled channel predictions. The effect of breakup coupling is estimated using the continuum discretized coupled channels (CDCC) method and it is found to reduce the complete fusion probability. Contrary to earlier predictions, a universal behavior of complete fusion suppression factor for the ${}^6$Li projectile with target charge is observed.

Hadron spectra and elliptic flow in high-energy heavy-ion collisions are studied within a (3+1)D ideal hydrodynamic model with fluctuating initial conditions given by the AMPT Monte Carlo model. Results from event-by-event simulations are compared with experimental data at both Relativistic Heavy Ion Collider and Large Hadron Collider energies. Fluctuations in the initial energy density come from not only the number of coherent soft interactions of overlapping nucleons but also incoherent semi-hard parton scatterings in each binary nucleon collision. Mini-jets from semi-hard parton scatterings are assumed to be locally thermalized through a Gaussian smearing and give rise to nonvanishing initial local flow velocities. Fluctuations in the initial flow velocities lead to harder transverse momentum spectra of final hadrons due to nonvanishing initial radial flow velocities. Initial fluctuations in rapidity distributions lead to expanding hot spots in the longitudinal direction and are shown to cause a sizable reduction of final hadron elliptic flow at large transverse momenta.

It has been shown in recent ALICE@LHC measurements that the odd flow harmonics, in particular, a directed flow $v_1$, occurred to be weak and dominated by random fluctuations. In this work we propose a new method, which makes the measurements more sensitive to the flow patterns showing global collective symmetries. We demonstrate how the longitudinal center of mass rapidity fluctuations can be identified, and then the collective flow analysis can be performed in the event-by-event center of mass frame. Such a method can be very effective in separating the flow patterns originating from random fluctuations, and the flow patterns originating from the global symmetry of the initial state.

The process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ is described in the framework of the extended NJL model in the mean-field approximation. Intermediate vector mesons ${\rho }^0\left(770\right)$, $\omega \left(782\right)$, and ${\rho }^{\prime }\left(1450\right)$ are taken into account. Our results are in satisfactory agreement with experimental data. The prediction for the process $e^{+}{e}^{-}\to \pi {\pi }^{\prime }\left(1300\right)$ is given. Here the main contribution is given by the diagram with intermediate ${\rho }^{\prime }\left(1450\right)$ meson.

A model for low-energy meson-baryon interaction in the strange sector is presented. The interaction is described in terms of separable potentials with multiple partial waves considered. A general solution of the Lippmann-Schwinger equation for the scattering of spin-0 and spin-1/2 particles is derived. Next, the general framework is applied to the $\overline{K}N$ sector in a simple model with only the $S$ and $P$ waves taken into account. The separable potential is designed to match the chiral perturbation theory at the lowest nontrivial order. It is shown that although a simple model with three free parameters works well for the $S$ wave, it fails to reproduce the $P$-wave features of kaon-nucleon physics. Most importantly, the $P$-wave interaction is too weak to express a resonant behavior that could be identified as $\Sigma \left(1385\right)$ resonance.

In multifragmentation of hot nuclear matter, properties of fragments embedded in a soup of nucleonic gas and other fragments should be modified as compared with isolated nuclei. Such modifications are studied within a simple model where only nucleons and one kind of heavy nuclei are considered. The interaction between different species is described with a momentum-dependent two-body potential whose parameters are fitted to reproduce properties of cold isolated nuclei. The internal energy of heavy fragments is parametrized according to a liquid-drop model with density- and temperature-dependent parameters. Calculations are carried out for several subnuclear densities and moderate temperatures, for isospin-symmetric and asymmetric systems. We find that the fragments get stretched due to interactions with the medium and their binding energies decrease with increasing temperature and density of nuclear matter.

We propose a method to separate $\Delta \eta$-dependent and $\Delta \eta$-independent azimuthal correlations using two- and four-particle cumulants between pseudorapidity ($\eta$) bins in symmetric heavy-ion collisions. The $\Delta \eta$-independent correlation may be dominated by harmonic flows, a global correlation resulting from the common collision geometry. The $\Delta \eta$-dependent correlation can be identified as nonflow, particle correlations unrelated to the common geometry. Our method exploits the $\eta$ symmetry of the average harmonic flows and is “data-driven.” We use the ampt and hijing event generators to illustrate our method. We discuss the decomposed $\Delta \eta$-independent and $\Delta \eta$-dependent correlations regarding flow and nonflow in the models.

We study the nuclear symmetry energy $S\left(\rho \right)$ and related quantities of nuclear physics and nuclear astrophysics predicted generically by relativistic mean-field (RMF) and Skyrme-Hartree-Fock (SHF) models. We establish a simple prescription for preparing equivalent RMF and SHF parametrizations starting from a minimal set of empirical constraints on symmetric nuclear matter, nuclear binding energy, and charge radii, enforcing equivalence of their Lorenz effective masses, and then using the pure neutron matter (PNM) equation of state obtained from ab initio calculations to optimize the pure isovector parameters in the RMF and SHF models. We find that the resulting RMF and SHF parametrizations give broadly consistent predictions of the symmetry energy $J$ and its slope parameter $L$ at saturation density within a tight range of $\lesssim 2$ and $\lesssim 6$ MeV, respectively, but that clear model dependence shows up in the predictions of higher-order symmetry energy parameters, leading to important differences in (a) the slope of the correlation between $J$ and $L$ from the confidence ellipse, (b) the isospin-dependent part of the incompressibility of nuclear matter $K_{\tau }$, (c) the symmetry energy at suprasaturation densities, and (d) the predicted neutron star radii. The model dependence can lead to about 1–2 km difference in predictions of the neutron star radius given identical predicted values of $J$ and $L$ and symmetric nuclear matter (SNM) saturation properties. Allowing the full freedom in the effective masses in both models leads to constraints of $30\lesssim J\lesssim 31.5$ MeV, $35\lesssim L\lesssim 60$ MeV, and $-330\lesssim K_{\tau }\lesssim -216$ MeV for the RMF model as a whole and $30\lesssim J\lesssim 33$ MeV, $28\lesssim L\lesssim 65$ MeV, and $-420\lesssim K_{\tau }\lesssim -325$ MeV for the SHF model as a whole. Notably, given PNM constraints, these results place RMF and SHF models as a whole at odds with some constraints on $K_{\tau }$ inferred from giant monopole resonance and neutron skin experimental results.

The energy spectra of light charged particles and intermediate mass fragments from ${}^{112}\mathrm{Sn}+{}^{112}\mathrm{Sn}$ and ${}^{124}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions at an incident energy of $E/A=50$ MeV have been measured with a large array of silicon strip detectors. We used charged-particle multiplicities detected in an array with nearly 4$\pi$ coverage to select data from the central collision events. We study isospin observables analogous to ratios of neutron and proton spectra, including double ratios and yield ratios of triton/${}^3$He and of asymmetries constructed from fragments with $Z=3$–8. Using the energy spectra, we can construct these observables as functions of kinetic energy. Most of the fragment asymmetry observables have a large sensitivity to sequential decays.

For the study of the $\Sigma$ resonances, we analyze the differential cross sections and $\Lambda$ polarizations for the reactions $K^{-}n\to {\pi }^{-}\Lambda$ and $K^{-}p\to {\pi }^0\Lambda$ with an effective Lagrangian approach. Data of an early experiment and the recent Crystal Ball experiment at BNL are included in the analysis with the c.m. energy from 1550 to 1676 MeV. Our results clearly support the existence of a $\Sigma$ resonance with $J^P={\frac{1}{2}}^{+}$, mass near 1633 MeV, and width about 120 MeV, which confirms the three-star $\Sigma \left(1660\right){\frac{1}{2}}^{+}$ in PDG. Meanwhile, our results do not support the existence of the two-star $\Sigma \left(1620\right){\frac{1}{2}}^{-}$ in PDG. The analysis results for the parameters of the relevant $\Sigma$ resonances and couplings are presented.

We compute the three-body structure of the lowest resonances of ${}^{12}$Be considered as two neutrons around an inert ${}^{10}$Be core. This is an extension of the bound-state calculations of ${}^{12}$Be into the continuum spectrum. We investigate the lowest resonances of angular momenta and parities, $0^{\pm }$, $1^{-}$, and $2^{+}$. Surprisingly enough, they all are naturally occurring in the three-body model. We calculate bulk structure dominated by small-distance properties as well as decays determined by the asymptotic large-distance structure. Both $0^{+}$ and $2^{+}$ have two-body ${}^{10}$Be-neutron $d$-wave structure, while $1^{-}$ has an even mixture of $p$ and $d$ waves. The corresponding relative neutron-neutron partial waves are distributed among $s$, $p$, and $d$ waves. The branching ratios show different mixtures of one-neutron emission, three-body direct, and sequential decays. We argue for spin and parities $0^{+}$, $1^{-}$, and $2^{+}$ for the resonances at $0.89$, $2.03$, and $5.13$, respectively. The computed structures are in agreement with existing reaction measurements.

Background: Heavy-flavor production in $p$ + $p$ collisions is a good test of perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from $p$ + $p$ results, quantified with the nuclear-modification factor ($R_{AA}$), provides information on both cold- and hot-nuclear-matter effects. Midrapidity heavy-flavor $R_{AA}$ measurements at the Relativistic Heavy Ion Collider have challenged parton-energy-loss models and resulted in upper limits on the viscosity-entropy ratio that are near the quantum lower bound. Such measurements have not been made in the forward-rapidity region.

Purpose: Determine transverse-momentum ($p_T$) spectra and the corresponding $R_{AA}$ for muons from heavy-flavor meson decay in $p$ + $p$ and Cu $+$ Cu collisions at $\sqrt{s_{NN}}=200$ GeV and $y=1.65$.

Method: Results are obtained using the semileptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the $p_T$ spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted.

Results: The charm-production cross section in $p$ + $p$ collisions at $\sqrt{s}=200$ GeV, integrated over $p_T$ and in the rapidity range $1.4<y<1.9$, is found to be $d{\sigma }_{c\overline{c}}/dy=0.139\pm 0.029{\left(\mathrm{stat}\right)}_{-0.058}^{+0.051}\left(\mathrm{syst}\right)$ mb. This result is consistent with a perturbative fixed-order-plus-next-to-leading-log calculation within scale uncertainties and is also consistent with expectations based on the corresponding midrapidity charm-production cross section measured by PHENIX. The $R_{AA}$ for heavy-flavor muons in Cu $+$ Cu collisions is measured in three centrality bins for $1<p_T<4$ GeV/$c$. Suppression relative to binary-collision scaling ($R_{AA}<1$) increases with centrality.

Conclusions: Within experimental and theoretical uncertainties, the measured charm yield in $p$ + $p$ collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu $+$ Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.

Contributions of perturbative pions around a nontrivial fixed point are studied by utilizing dibaryon fields. We calculate ${}^1{S}_0$ and ${}^3{S}_1$ phase shifts for the $np$ scattering at low energies up to one-pion-exchange contributions. We also calculate effective range parameters, $v_2$, $v_3$, and $v_4$, in the higher order of the effective range expansion, and obtain corrections of the effective range to the expressions previously reported by Cohen and Hansen. After the scattering length and the effective range are renormalized, we study the role of renormalization scale parameter $\mu$ and we discuss the range of validity of the theory.

The recently proposed symmetry-conserving energy density functional approach [G. Hupin, D. Lacroix, and M. Bender, Phys. Rev. C 84, 014309 (2011)] is applied to perform variation after projection onto the good particle number using the Skyrme interaction, including density-dependent terms. We propose a simplification to reduce the numerical effort to perform the variation. We present a systematic study of the Kr and Sn isotopic chains. This approach leads to nonzero pairing in magic nuclei and a global enhancement of the pairing gap compared to the original theory, which breaks particle number symmetry.

Background: Recent years have seen a renewed interest in the Oklo phenomenon, particularly in relation to the study of time variation of the fine structure constant $\alpha$. The neutron fluence is one of the crucial parameters for Oklo reactors. Several approaches to its determination were elaborated in the past.

Purpose: We consider whether it is possible to use the present isotopic ${}^{138}$La$-{}^{139}$La data for RZ10 as an additional indicator of neutron fluences in the active cores of the reactors.

Results: We calculate the dependence of the Oklo ${}^{138}$La abundance on neutron fluence and elemental lanthanum concentration.

Conclusion: The neutron fluence in RZ10 can be deduced from lanthanum isotopic data, but requires reliable data on the primordial elemental abundance. Conversely, if the fluence is known, the isotope ratio provides information on the primordial lanthanum abundance that is not otherwise easily determined.

Background: The eikonal approximation is commonly used to calculate heavy-ion elastic scattering. However, the full evaluation has only been done (without the use of Monte Carlo techniques or additional approximations) for $\alpha -\alpha$ scattering.

Purpose: Develop, improve, and test the Monte Carlo eikonal method for elastic scattering over a wide range of nuclei, energies, and angles.

Method: Monte Carlo evaluation is used to calculate heavy-ion elastic scattering for heavy nuclei including the center-of-mass correction introduced in this paper and the Coulomb interaction in terms of a partial-wave expansion. A technique for the efficient expansion of the Glauber amplitude in partial waves is developed.

Results: Angular distributions are presented for a number of nuclear pairs over a wide energy range using nucleon-nucleon scattering parameters taken from phase-shift analyses and densities from independent sources. We present the first calculations of the Glauber amplitude, without further approximation, and with realistic densities for nuclei heavier than helium. These densities respect the center-of-mass constraints. The Coulomb interaction is included in these calculations.

Conclusion: The center-of-mass and Coulomb corrections are essential. Angular distributions can be predicted only up to certain critical angles which vary with the nuclear pairs and the energy, but we point out that all critical angles correspond to a momentum transfer near 1 fm${}^{-1}$.