Inference on fission timescale from neutron multiplicity measurement in18O+184W

The pre-scission and post-scission neutron multiplicities are measured for the 18O + 184W reaction in the excitation energy range of 67.23−76.37 MeV. Langevin dynamical calculations are performed to infer the energy dependence of fission decay time in compliance with the measured neutron multiplicities. Different models for nuclear dissipation are employed for this purpose. Fission process is usually expected to be faster at a higher beam energy. However, we found an enhancement in the average fission time as the incident beam energy increases. It happens because a higher excitation energy helps more neutrons to evaporate that eventually stabilizes the system against fission. The competition between fission and neutron evaporation delicately depends on the available excitation energy and it is explained here with the help of the partial fission yields contributed by the different isotopes of the primary compound nucleus.

Soft gluon fields and anomalous magnetic moment of muon

An impact of nonperturbatively treated soft gluon modes on the value of anomalous magnetic moment of muon a_µ is studied within the mean-field approach to QCD vacuum and hadronization. It is shown that radial excitations of vector mesons strongly enhance contribution of hadronic vacuum polarization to a_µ, doubling the contribution of one-meson processes compared to the result for ground state mesons. The mean field also strongly influences the hadronic light-by-light scattering contribution due to the Wilson line in quark propagators.

A study on the isolated photon production in nuclear collisions at the CERN-LHC energies

An analysis of prompt photon production in high energy nuclear collisions at the LHC is performed within the parton saturation picture taking into account the updated phenomenological color dipole models. Comparison between $\langle N_{coll}\rangle$ scaling for hard scattering in heavy-ion collisions and the $N_{part}$-scaling based on geometric scaling arguments has been done. The predictions are parameter free in the first case whereas a dependence on the constant of proportionality $\kappa$ between the number of participants and the nuclear saturation scale appears in the second case. This parameter has been analyzed in the prompt photon spectrum at small transverse momentum even though no fitting procedure was performed. Results are confronted with the measurements made by the ALICE, ATLAS, and CMS experiments in terms of photon transverse momentum at different rapidity bins. We show that the prompt photon production exhibits distinct scalings in $AA$ events associated to geometrical properties of the collision and can be properly addressed in the color dipole formalism. Based on the $N_{part}$-scaling, an analytical parametrization for the invariant cross section is provided and employed to predict the $x_T$-scaling in measurements. For $\kappa$ of order of unit the theoretical scaling curve correctly describes data in the range $x_T\leq 5\times 10^{-2}$.

Nuclear level densities away from line of β-stability

The variation of total nuclear level densities (NLDs) and level density parameters with proton number Z are studied around the β-stable isotope, Z0, for a given mass number. We perform our analysis for a mass range A=40 to 180 using the NLDs from popularly used databases obtained with the single-particle energies from two different microsopic mass-models. These NLDs which include microscopic structural effects such as collective enhancement, pairing and shell corrections, do not exhibit inverted parabolic trend with a strong peak at Z0 as predicted earlier. We also compute the NLDs using the single-particle energies from macroscopic-microscopic mass-model. Once the collective and pairing effects are ignored, the inverted parabolic trends of NLDs and the corresponding level density parameters become somewhat visible. Nevertheless, the factor that governs the (Z-Z0) dependence of the level density parameter, leading to the inverted parabolic trend, is found to be smaller by an order of magnitude. We further find that the (Z-Z0) dependence of NLDs is quite sensitive to the shell effects.

Production of unknown neutron-rich transuranium isotopes 245−249Np, 248−251Pu, 248−254Am, and 252−254Cm in multinucleon transfer reactions

The production cross sections of unknown neutron-rich transuranium isotopes of elements Np, Pu, Am and Cm are investigated in multinucleon transfer reactions based on the dinuclear system model with GEMINI code. The influence of the incident energy on the production of neutron-rich transuranium nuclei in actinideactinide collisions is studied. The calculation results show that the final isotopic production cross sections are larger at 1.06-1.10 Vcont than at other energies. Considering the high fissility of transuranium nuclides, 1.06 Vcont is chosen as the optimal incident energy. The N/Z ratio equilibration mechanism in the nucleon transfer process is also studied in this work. The larger difference of N/Z ratio between projectile and target corresponds to larger neutron diffusion during the nucleon exchange process. The 238U beam with high N/Z ratio and neutron-rich actinide targets are good selections to produce neutron-rich transuranium nuclides. The production cross sections of unknown neutron-rich transuranium isotopes 245-249Np, 248-251Pu, 248-254Am, and 252-254Cm are predicted in 238U-induced actinide-based (249Bk, 249Cf, and 252Cf) multinucleon transfer reactions. It is found that a large number of these unknown neutron-rich transuranium nuclei could be generated at the level of nb to µb in the reactions 238U+249Bk and 238U+252Cf. Our research indicates that the reaction 238U+249Bk is a suitable projectile-target combination in the current experimental conditions and the reaction 238U+252Cf could be a promising candidate to produce unknown neutron-rich transuranium nuclides in case that the 252Cf target were to be achieved in the future.

The time substructure of jets and boosted object tagging

We propose the study of the time substructure of jets, motivated by the fact that the next generation of detectors at particle colliders will resolve the time scale over which jet constituents arrive. This effect is directly related to the fragmentation and hadronization process, which transforms partons into massive hadrons with a distribution of velocities. We review the basic predictions for the velocity distribution of jet hadrons, and suggest an application for this information in the context of boosted object tagging. By noting that the velocity distribution is determined by the properties of the color string which ends on the parton that initiates the jet, we observe that jets originating from boosted color singlets, such as Standard Model electroweak bosons, will exhibit velocity distributions that are boosted relative to QCD jets of similar jet energy. We find that by performing a simple cut on the corresponding distribution of charged hadron arrival times at the detector, we can discriminate against QCD jets that would otherwise give a false positive under a traditional spatial substructure based boosted object tagger.

The Ξ-nuclear potential constrained by recent Ξ– hypernuclei experiments

The $\Xi$-nuclear potential is investigated in the quark mean-field (QMF) model based on recent results of the $\Xi^-+^{14}\rm{N}$ ($_{\Xi^-}^{15}\rm{C}$) system. The experimental data on the binding energy of $1p$-state $\Xi^-$ hyperon in $_{\Xi^-}^{15}\rm{C}$ hypernuclei in KISO, IBUKI, E07-T011, E176-14-03-35 events are merged as $B_{\Xi^-}(1p)=1.14\pm0.11$ MeV. With this constraint, the coupling strengths between the $\omega$ vector meson and $\Xi$ hyperon are fixed in three QMF parameter sets. At the same time, the $\Xi^-$ binding energy of $1s$ state in $_{\Xi^-}^{15}\rm{C}$ is predicted as $B_{\Xi^-}(1s)=5.66\pm0.38$ MeV with the same interactions, completely consistent with the data from the KINKA and IRRAWADDY events. Finally, the $\Xi$-nuclear potential is calculated in the symmetric nuclear matter in the framework of QMF models. It is $U_{\Xi }=-11.96\pm 0.85$ MeV at nuclear saturation density, which will be essential to determine the onset density of $\Xi$ hyperon in neutron star.

Self-consistent description of the halo nature of 31Ne with continuum and pairing correlations

Using a Glauber model with our relativistic fully microscopic structure model input, we give a full description of the halo nature of $^{31}$Ne that includes a self-consistent use of pairing and continuum contributions that makes predictions consistent with reaction cross section measurements. Our predictions of total reaction and one-neutron removal cross sections of $^{31}$Ne on a Carbon target were significantly enhanced compared with those of neighboring Neon isotopes, agreeing with measurements at 240 MeV/nucleon and consistent with a single neutron halo. Furthermore, our calculations of the inclusive longitudinal momentum distribution of the $^{30}$Ne and valence neutron residues from the $^{31}$Ne breakup reaction indicate a dilute density distribution in coordinate space, another halo signature.

Continuous and discrete symmetries of renormalization group equations for neutrino oscillations in matter

Three-flavor neutrino oscillations in matter can be described by three effective neutrino masses mi (for i = 1, 2, 3) and the effective mixing matrix Vαi (for α = e, µ, τ and i = 1, 2, 3). When the matter parameter a ≡ 2√2GFNeE is taken as an independent variable, a complete set of first-order ordinary differential equations for m2 i and |Vαi|2have been derived in the previous works. In the present paper, we point out that such a system of differential equations possesses both the continuous symmetries characterized by one-parameter Lie groups and the discrete symmetry associated with the permutations of three neutrino mass eigenstates. The implications of these symmetries for solving the differential equations and looking for differential invariants are discussed.

Hard gluon evolution in the last stage of the bottom-up thermalization

The study of how fast thermalization in heavy ion collisions occurs has been one of the central topics in the heavy ion community. In the weak coupling picture this thermalization occurs from “the bottom up”: high energy partons, formed early in the collision, radiate low energy gluons which then proceed to equilibrate among themselves, forming a thermal bath that brings the high energy sector to equilibrium. In this scheme we apply a model on parton energy loss to discuss the effects of medium expansion on the thermalization problem and estimate the average transverse momentum diffusivity for thermalization in a Bjorken expanding medium.