Bayesian procedures designed to quantify truncation errors in perturbative calculations of quantum chromodynamics observables are adapted to expansions in effective field theory (EFT). In the Bayesian approach, such truncation errors are derived from degree-of-belief (DOB) intervals for EFT predictions. Computation of these intervals requires specification of prior probability distributions (“priors”) for the expansion coefficients. By encoding expectations about the naturalness of these coefficients, this framework provides a statistical interpretation of the standard EFT procedure where truncation errors are estimated using the order-by-order convergence of the expansion. It also permits exploration of the ways in which such error bars are, and are not, sensitive to assumptions about EFT-coefficient naturalness. We first demonstrate the calculation of Bayesian probability distributions for the EFT truncation error in some representative examples and then focus on the application of chiral EFT to neutron-proton scattering. Epelbaum, Krebs, and Meißner recently articulated explicit rules for estimating truncation errors in such EFT calculations of few-nucleon-system properties. We find that their basic procedure emerges generically from one class of naturalness priors considered and that all such priors result in consistent quantitative predictions for 68% DOB intervals. We then explore several methods by which the convergence properties of the EFT for a set of observables may be used to check the statistical consistency of the EFT expansion parameter.

The improved quantum molecular dynamics (ImQMD) model incorporated with the statistical evaporation model is applied to study the production mechanism of transuranium nuclei in the reaction of ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ at 7.0 MeV/nucleon. The production of primary fragments in the dynamical process is simulated by the ImQMD model, and the decays of them are described by the statistical evaporation model (hivap code). The calculated isotope distributions of the residual fragments and the most probable mass number of fragments are generally in agreement with experimental data. By tracking residual fragments back to their original primary fragments with this approach, we find different mechanisms for the production of the residues: the most probable light uraniumlike residues mainly come from the decay of the most probable primary fragments, while the most probable transuranium residues mainly originate from the decay of more neutron-rich primary fragments rather than from the most probable primary ones. For neutron-rich transuranium isotopes ${}^{254-256}\mathrm{Cf}$, the decay channel of neutron evaporation is suppressed due to the quick drop of the fission barrier height with the increase of neutron number, which leads to the quick drop of the production cross sections for these residues.

Collision centrality as well as the system-size dependencies of the temperatures of the soft ($p_t=0.1-0.5\text{GeV}/c$) and hard ($p_t=0.5-1.2\text{GeV}/c$) components of the experimental transverse momentum distributions of the negative pions produced in ${}^4\mathrm{He}{+}^{12}\mathrm{C}, {}^{12}\mathrm{C}{+}^{12}\mathrm{C}$, and ${}^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$ collisions at $4.2A\text{GeV}/c$ ($\sqrt{s_{NN}}=3.14\mathrm{GeV}$) are analyzed. For the studied collision systems and selected collision centralities, the temperatures are extracted from fitting separately the soft and hard $p_t$ components of the negative pions by one-temperature Hagedorn and one-temperature Boltzmann functions. The extracted temperatures of both the soft and hard components of the $p_t$ distributions of ${\pi }^{-}$ depend on the geometry (size) and degree of overlap of the colliding nuclei in peripheral, semicentral, and central nucleus–nucleus collisions at $\sqrt{s_{NN}}=3.14\mathrm{GeV}$. The gap (differences) between the extracted temperatures in the studied collision systems increases with increasing the degree of overlap of the colliding nuclei, i.e., with an increase in the collision centrality and the corresponding increase in the numbers of participant nucleons and binary collisions. The temperature of the soft $p_t$ component of the negative pions in ${}^{12}\mathrm{C}{+}^{12}\mathrm{C}$ (${}^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$) collisions increases (decreases) with increasing of the collision centrality. The temperature of the hard $p_t$ component of ${\pi }^{-}$ in ${}^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$ (${}^4\mathrm{He}{+}^{12}\mathrm{C}$) collisions increases (decreases) consistently with an increase in the collision centrality. The temperature of the soft $p_t$ component of ${\pi }^{-}$ decreases with an increase in the system size in semicentral and central nucleus–nucleus collisions at $\sqrt{s_{NN}}=3.14\mathrm{GeV}$. In central collisions, the temperature of the hard $p_t$ component increases consistently with an increase in system size. The physical interpretations of the results obtained are given. The quantitative results on temperatures extracted from the $p_t$ spectra of negative pions in nucleus–nucleus collisions at $4.2A\text{GeV}/c$ are compared to those obtained in lower, intermediate, and higher energies in other Joint Institute for Nuclear Research (JINR), Gesellschaft für Schwerionenforschung (GSI), and SPS experiments.

Background: Realistic nucleon-nucleon interactions induce short-range correlations in nuclei. To solve the many-body problem unitary transformations like the similarity renormalization group (SRG) are often used to soften the interactions.

Purpose: Two-body densities can be used to illustrate how the SRG eliminates short-range correlations in the wave function. The short-range information can however be recovered by transforming the density operators.

Method: The many-body problem is solved for ${}^4\mathrm{He}$ in the no core shell model (NCSM) with SRG transformed $\mathrm{AV}8{}^{\prime }$ and chiral N3LO interactions. The NCSM wave functions are used to calculate two-body densities with bare and SRG transformed density operators in two-body approximation.

Results: The two-body momentum distributions for $\mathrm{AV}8{}^{\prime }$ and N3LO have similar high-momentum components up to relative momenta of about $2.5{\text{fm}}^{-1}$, dominated by tensor correlations, but differ in their behavior at higher relative momenta. The contributions of many-body correlations are small for pairs with vanishing pair momentum but not negligible for the momentum distributions integrated over all pair momenta. Many-body correlations are induced by the strong tensor force and lead to a reshuffling of pairs between different spin-isospin channels.

Conclusions: When using the SRG it is essential to use transformed operators for observables sensitive to short-range physics. Back-to-back pairs with vanishing pair momentum are the best tool to study short-range correlations.

We investigate experimentally the pressure dependence of the production of ultracold neutrons (UCNs) in superfluid helium in the range from saturated vapor pressure to 20 bar. A neutron velocity selector allows the separation of underlying single-phonon and multiphonon processes by varying the incident cold neutron (CN) wavelength in the range from $3.5$ to 10 Å. The predicted pressure dependence of UCN production derived from inelastic neutron scattering data is confirmed for the single-phonon excitation. For multiphonon-based UCN production we found no significant dependence on pressure, whereas calculations from inelastic neutron scattering data predict an increase of 43(6)% at 20 bar relative to saturated vapor pressure. From our data we conclude that applying pressure to superfluid helium does not increase the overall UCN production rate at a typical CN guide.

Background: Stellar electron-capture reactions on medium-heavy nuclei are important for many astrophysical phenomena, including core-collapse and thermonuclear supernovæ and neutron stars. Estimates of electron-capture rates rely on accurate estimates of Gamow-Teller strength distributions, which can be extracted from charge-exchange reactions at intermediate beam energies. Measured Gamow-Teller transition strength distributions for stable pf-shell nuclei are reasonably well reproduced by theoretical calculations in the shell model, except for lower mass nuclei where admixtures from the sd shell can become important.

Purpose: This paper presents a ${\beta }^{+}$ charge-exchange experiment on ${}^{45}\mathrm{Sc}$, one of the lightest pf-shell nuclei. The focus was on Gamow-Teller transitions to final states at low excitation energies, which are particularly important for accurate estimations of electron-capture rates at relatively low stellar densities. The experimental results are compared with various theoretical models.

Method: The double-differential cross section for the ${}^{45}\mathrm{Sc}(t,{}^3\mathrm{He}+\gamma )$ reaction was measured using the NSCL Coupled-Cyclotron Facility at $115\mathrm{MeV}/u$. Gamow-Teller contributions to the excitation-energy spectra were extracted by means of a multipole-decomposition analysis. $\gamma$ rays emitted due to the deexcitation of ${}^{45}\mathrm{Ca}$ were measured using GRETINA to allow for the extraction of Gamow-Teller strengths from very weak transitions at low excitation energies.

Results: Gamow-Teller transition strengths to ${}^{45}\mathrm{Ca}$ were extracted up to an excitation energy of 20 MeV, and that to the first excited state in ${}^{45}\mathrm{Ca}$ at 174 keV was extracted from the $\gamma$-ray measurement, which, even though weak, is important for the astrophysical applications and dominates under certain stellar conditions. Shell-model calculations performed in the pf shell-model space with the GXPF1A, KB3G, and FPD6 interactions did not reproduce the experimental Gamow-Teller strength distribution, and a calculation using the quasiparticle random phase approximation that is often used in astrophysical simulations also could not reproduce the experimental strength distribution.

Conclusions: Theoretical models aimed at describing Gamow-Teller transition strengths from nuclei in the lower pf shell for the purpose of estimating electron-capture rates for astrophysical simulations require further development. The likely cause for the relatively poor performance of the shell-model theory is the influence of intruder configurations from the sd shell. The combination of charge-exchange experiments at intermediate beam energy and high-resolution $\gamma$-ray detection provides a powerful technique to identify weak transitions to low-lying final states that are nearly impossible to identify without the coincidences. Identification of these weak low-lying transitions is important for providing accurate electron-capture rates for astrophysical simulations.

Electron capture decay of ${}^{229}\mathrm{U}$ is investigated by measuring the $\gamma$-ray and conversion electron spectra of mass-separated and unseparated ${}^{229}\mathrm{U}$ sources with high-resolution germanium and silicon detectors, respectively. Gamma-gamma coincidence measurements are also performed using germanium detectors. These studies provide level energies and level ordering in ${}^{229}\mathrm{Pa}$. Single-particle assignments are given to these levels which are in agreement with the systematics in this region and also with theory. In a previous study, we report the observation of a 5/$2^{\pm }$ parity doublet in the ${}^{229}\mathrm{Pa}$ ground state, which is a signature of octupole deformation. The present analysis of the data still shows a splitting of $60\pm 50$ eV, but with this large uncertainty the existence of the doublet is not certain.

The nuclear root-mean-square charge radii and nuclear density distributions have been calculated in the framework of relativistic self-consistent mean-field models based on density-dependent meson-exchange relativistic energy density functional for even isotopes of Ti $\left(A=44-56\right)$. The calculations agree well with available laser spectroscopic measurements for ${}^{44,46,48,50}\mathrm{Ti}$, and results for neutron-rich isotopes are reported. The semimicroscopic proton optical potentials for ${}^{44-56}\mathrm{Ti}$ have been derived by folding the target matter density with the extended Jeukenne-Lejeune-Mahaux energy- and density-dependent internucleon interaction and are used to calculate the differential elastic scattering and reaction cross sections at 65 MeV. The calculated differential cross sections reproduce the corresponding experimental values for stable even isotopes, and predictions are presented for ${}^{44,52,54,56}\mathrm{Ti}$. The calculations reveal a prominent kink at the $N=28$ shell closure observed in the variation of reaction cross sections, consistent with mean-square charge radii systematics in the Ti isotopic chain.

The agreement between the fragments' internal and kinetic temperatures with the breakup temperature is investigated using a statistical multifragmentation model, which makes no a priori assumption on the relationship between them. We thus examine the conditions for obtaining such agreement and find that, in the framework of our model, this holds only in a relatively narrow range of excitation energy. The role played by the qualitative shape of the fragments' state densities is also examined. Our results suggest that the internal temperature of the light fragments may be affected by this quantity, whose behavior may lead to constant internal temperatures over a wide excitation energy range. It thus suggests that the nuclear thermometry may provide valuable information on the nuclear state density.

The likely presence of $\mathrm{\Lambda }$ baryons in dense hadronic matter tends to soften the equation of state to an extent that the observed heaviest neutron stars are difficult to explain. We analyze this “hyperon problem” with a phenomenological approach. First, we review what can be learned about the interaction of $\mathrm{\Lambda }$ particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on nonstrange dense matter, including its uncertainties, to conclude that the interaction between $\mathrm{\Lambda }$'s and dense matter has to become repulsive at densities below three times the nuclear saturation density.

This paper reports on the first cross section measurement of the ${}^{72}\mathrm{Ge}\left(p,\gamma \right){}^{73}\mathrm{As}$ reaction. The proton capture reaction on ${}^{72}\mathrm{Ge}$ is relevant to the astrophysical $p$-process and was identified in a sensitivity study as one of the important reactions required to estimate the abundances of the light $p$ nuclei. The $\gamma$-summing technique was employed using the summing NaI(Tl) detector (SuN) from the National Superconducting Cyclotron Laboratory. The experiment was performed at the University of Notre Dame using a 1.8–3.6 MeV proton beam. In order to test the predictive power of different theoretical calculations in the region, experimental values were compared to the results given by the nuclear reaction code talys1.6. The theoretical uncertainties in the cross section arising from different combinations of nuclear level densities, $\gamma$-ray strength functions, and optical model potentials were reduced to 10–18% by the experimental data. The recommended reaction rates from the standard astrophysical libraries, BRUSLIB and REACLIB, are found to be in good agreement with the experimental results.

The study of the ${}^2\mathrm{H}(d,p){}^3\mathrm{H}$ reaction is very important for the nucleosynthesis in both the standard Big Bang and stellar evolution, as well as for the future fusion reactor's planning of energy production. The ${}^2\mathrm{H}(d,p){}^3\mathrm{H}$ bare nucleus astrophysical $S\left(E\right)$ factor has been measured indirectly at energies from about 400 keV down to several keV by means of the Trojan-horse method applied to the quasifree process ${}^2\mathrm{H}({}^6\mathrm{Li},pt){}^4\mathrm{He}$ induced at a lithium beam energy of 9.5 MeV, which is closer to the zero-quasifree-energy point. An accurate analysis leads to the determination of the $S_{\text{bare}}\left(0\right)=56.7\pm 2.0$ keV b and of the corresponding electron screening potential $U_e=13.2\pm 4.3$ eV. In addition, this work gives an updated test for the Trojan-horse nucleus invariance by comparing with previous indirect investigations using the ${}^3\mathrm{He}=(d+p)$ breakup.

We construct a theoretical framework to describe the evolution of heavy flavors produced in relativistic heavy-ion collisions. The in-medium energy loss of heavy quarks is described using our modified Langevin equation that incorporates both quasielastic scatterings and the medium-induced gluon radiation. The space-time profiles of the fireball are described by a (2+1)-dimensional hydrodynamics simulation. A hybrid model of fragmentation and coalescence is utilized for heavy quark hadronization, after which the produced heavy mesons together with the soft hadrons produced from the bulk quark-gluon plasma (QGP) are fed into the hadron cascade ultrarelativistic quantum molecular dynamics (UrQMD) model to simulate the subsequent hadronic interactions. We find that the medium-induced gluon radiation contributes significantly to heavy quark energy loss at high $p_{\mathrm{T}}$; heavy-light quark coalescence enhances heavy meson production at intermediate $p_{\mathrm{T}}$; and scatterings inside the hadron gas further suppress the $D$ meson $R_{\mathrm{AA}}$ at large $p_{\mathrm{T}}$ and enhance its $v_2$. Our calculations provide good descriptions of heavy meson suppression and elliptic flow observed at both the Large Hadron Collider and the Relativistic Heavy-Ion Collider.

We estimate the modification of quarkonia yields due to different processes in the medium produced in PbPb collisions at LHC energy. The quarkonia and heavy flavor cross sections calculated up to next-to-leading order (NLO) are used in the study. Shadowing corrections are obtained with the NLO EPS09 parametrization. A kinetic model is employed which incorporates quarkonia suppression inside a QGP, suppression due to hadronic comovers, and regeneration from charm pairs. The quarkonia dissociation cross section due to gluon collisions has been considered and the regeneration rate has been obtained using the principle of detailed balance. The modification in quarkonia yields due to collisions with hadronic comovers has been estimated assuming that the comovers are pions. The manifestations of these effects on the nuclear modification factors for both $J/\psi$ and $\mathrm{{\rm Y}}$ in different kinematic regions has been demonstrated for PbPb collisions at $\sqrt{s_{{}_{NN}}}=2.76$ TeV in comparison with the measurements. Both the suppression and regeneration due to a deconfined medium strongly affect the low and intermediate $p_T$ range. The large observed suppression of $J/\psi$ at $p_T>10\text{GeV}/c$ exceeds the estimates of suppression by gluon dissociation.

In the hot and dense hadronic sources formed in high-energy heavy-ion collisions, the particle interactions in medium might lead to a squeezed back-to-back correlation (BBC) of boson-antiboson pairs. We calculate the BBC functions of $\varphi \varphi$ for sources evolving hydrodynamically in $\left(2+1\right)$ dimensions and with longitudinal boost invariance. The BBC functions for hydrodynamic sources exhibit oscillations as a function of the particle momentum because the temporal distributions of hydrodynamic sources have sharp falls to 0 at large evolving times. The dependences of the BBC functions on the directions of the particle momentum are investigated. For transverse anisotropic sources, the BBC functions are minimum when the azimuthal angles of the particles reach 0. The BBC functions increase with decreasing absolute value of the particle pseudorapidity. The oscillations and the dependences on the particle azimuthal angle and pseudorapidity are the significant signatures for detecting the BBC in high-energy heavy-ion collisions.

We investigate possible non-Markovian effects in fission dynamics of highly excited nuclei by using the generalized Langevin approach for a single nuclear shape parameter. We estimate the effective friction and stiffness coefficients of the non-Markovian dynamics for different values of the correlation time of the random force in the Langevin equation of motion. We discuss the found nonmonotonic dependence of the fission rate on the correlation time. We also show how to extend the Kramers theory of fission rate in the case of non-Markovian thermal diffusion over barrier.

Background: A new type of asymmetric fission was observed in $\beta$-delayed fission of ${}^{180}\mathrm{Tl}$ [Phys. Rev. Lett. 105, 252502 (2010)] as symmetric mass distribution would be expected based on conventional shell effects leading to the formation of $N=50$ fragments. Following this observation, theoretical calculations were carried out which predict asymmetric mass distribution for several mercury isotopes around mass region of $\sim 180$ at low and moderate excitation energies [Moller, Randrup, and Sierk, Phys. Rev. C 85, 024306 (2012); Andreev, Adamian, and Antonenko, Phys. Rev. C 86, 044315 (2012)]. Studies on fission fragment mass distribution are required in this mass region to investigate this newly observed phenomenon.

Purpose: The fission fragment mass distributions have been measured in ${}^{35}\mathrm{Cl}+{}^{144,154}\mathrm{Sm}$ reactions at $E_{\mathrm{lab}}=152.5,156.1,\mathrm{and}163.7\mathrm{MeV}$ populating compound nuclei in the mass region of ∼180 with variable excitation energy and neutron number to investigate the nature of mass distribution.

Method: The fission fragment mass distribution has been obtained by measuring the “time of flight (TOF)” of fragments with respect to the beam pulse using two multiwire proportional counters placed at ${\theta }_{\mathrm{lab}}=\pm 65.5^{\circ }$ with respect to the beam direction. From the TOF of fragments, their velocities were determined, which were used to obtain mass distribution taking the compound nucleus as the fissioning system.

Results: For both systems, mass distributions, although, appear to be symmetric, could not be fitted well by a single Gaussian. The deviation from a single Gaussian fit is more pronounced for the ${}^{35}\mathrm{Cl}+{}^{144}\mathrm{Sm}$ reaction. A clear flat top mass distribution has been observed for the ${}^{35}\mathrm{Cl}+{}^{144}\mathrm{Sm}$ reaction at the lowest beam energy. The mass distribution is very similar to that observed in the ${}^{40}\mathrm{Ca}+{}^{142}\mathrm{Nd}$ reaction, which populated a similar compound nucleus, but for the pronounced dip in the symmetric region [Phys. Rev. C 91, 064605 (2015)].

Conclusions: The present study shows that the mass distribution deviates from that expected on the basis of a pure liquid drop model in the mass region of ∼180, indicating a contribution from asymmetric fission. The contribution from asymmetric fission is more pronounced for the ${}^{35}\mathrm{Cl}+{}^{144}\mathrm{Sm}$ reaction as evident from the large deviation of the fission fragment mass distribution from the single Gaussian fit. This is consistent with the observation of an asymmetric component in the ${}^{40}\mathrm{Ca}+{}^{142}\mathrm{Nd}$ reaction in a recent study [Phys. Rev. C 91, 064605 (2015)]. The contribution from asymmetric component is also consistent with the theoretical predictions by Moller et al. [Phys. Rev. C 85, 024306 (2012)], although the magnitude of the effect appears to be smaller.

We study the effects of a finite chemical potential on the occurrence of cavitation in a quark gluon plasma (QGP). We solve the evolution equations of second-order viscous relativistic hydrodynamics using two equations of state. The first one was derived in lattice QCD and represents QGP at zero chemical potential and it was previously used in the study of cavitation. The second equation of state also comes from lattice QCD and is a recent parametrization of the QGP at finite chemical potential. We conclude that at finite chemical potential, cavitation in the QGP occurs earlier than at zero chemical potential. We also consider transport coefficients from a holographic model of a nonconformal QGP at zero chemical potential. In this case cavitation does not occur.

The microscopic coupled-channel (MCC) calculations for proton $+{}^{12}\mathrm{C}$ inelastic scattering are performed in the energy range of $E_p=29.95$ to 65 MeV. The nuclear interactions for the proton-${}^{12}\mathrm{C}$ system are constructed from the folding model, which employs the internal wave function of ${}^{12}\mathrm{C}$, obtained from the $3\alpha$ resonating group method ($3\alpha$ RGM), and an effective nucleon-nucleon interaction of the density-dependent Michigan three-range Yukawa (DDM3Y). The MCC calculation with the $3\alpha$ RGM + DDM3Y nicely reproduces all of the differential cross sections for elastic and inelastic scattering in the angular range of ${\theta }_{\mathrm{c}.\mathrm{m}.}=30$ to ${120}^{\circ }$. The channel-coupling effect is analyzed by comparing the full MCC calculation with the calculation of the distorted wave Born approximation (DWBA). The effect of the spin-orbit interaction, obtained in a simplified manner with the folding procedure, is also discussed.