Nuclear Experiment

The emergence of nuclear collectivity near doubly-magic 132 Sn was explored along the stable, even-even 124−130 Te isotopes. Preliminary measurements of the B(E2; 4 + 1 → 2 + 1 ) transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the g factors of the 4 + 1 states. Isotopically enriched Te targets were excited by 198-205 MeV 58 Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.

We present a new experimental method for measuring inner-shell ionization cross sections of low-charged ions colliding with hydrogen gas target in a storage ring. The method is based on a calibration by the well-known differential cross sections of proton elastic scattering on nuclei. K -shell ionization cross section of 1047(100) barn for the 95 MeV/u 58 Ni 19+ ions colliding with hydrogen atoms was obtained in this work. Compared to the measured ionization cross section, a good agreement is achieved with the prediction by the Relativistic Ionization CODE Modified program (RICODE-M).

Measurements of longitudinal flow decorrelations for charged particles are presented in the pseudorapidity range |η|<1 using a reference detector at 2.1 <| η ref |< 5.1 in Au+Au collisions at s NN − − − − √ = 27 GeV by STAR. The flow decorrelation for v 2 shows a strong centrality dependence, while a weak centrality dependence for v 3 . Results are compared with the results in Au+Au collisions at 200 GeV as a function of η scaled by beam-rapidity, i.e. η/ y beam . No energy dependence is observed for v 2 decorrelation, but clear energy dependence for v 3 decorrelation. These results provide new insights into the longitudinal structure of the initial-state geometry in heavy-ion collisions.

In this work we measured elastic and inelastic angular distributions of the weakly bound 9Be projectile on the 197Au target at several bombarding energies from 84% up to 140% of the Coulomb barrier. The elastic angular distributions were analyzed using a phenomenological Woods-Saxon potential and a double folding Sao Paulo potential and the energy dependence was extracted. Angular distributions from two inelastic peaks were compared with coupled channel calculations using reduced transition probabilities available in the literature. The energy dependence of the two interaction potential models show a similar trend in the region of the Coulomb barrier. Dispersion relation calculation demonstrates the presence of the breakup threshold anomaly proposed for weakly bound systems.

Neutron energy-dependent angular distributions were observed for individual γ -rays from the 0.74 eV p-wave resonance of 139 La+ n to several lower excited states of 140 La. The γ -ray signals were analyzed in a two dimensional histogram of the γ -ray energy, measured with distributed germanium detectors, and neutron energy, determined with the time-of-flight of pulsed neutrons, to identify the neutron energy dependence of the angular distribution for each individual γ -rays. The angular distribution was also found for a photopeak accompanied with a faint p-wave resonance component in the neutron energy spectrum. Our results can be interpreted as interference between s- and p-wave amplitudes which may be used to study discrete symmetries of fundamental interactions.

Above-barrier fusion cross-sections for an isotopic chain of oxygen isotopes with A=16-19 incident on a 12 C target are presented. Experimental data are compared with both static and dynamical microscopic calculations. These calculations are unable to explain the ∼ 37\% increase in the average above-barrier fusion cross-section observed for 19 O as compared to β -stable oxygen isotopes. This result suggests that for neutron-rich nuclei existing time-dependent Hartree-Fock calculations underpredict the role of dynamics at near-barrier energies. High-quality measurement of above-barrier fusion for an isotopic chain of increasingly neutron-rich nuclei provides an effective means to probe this fusion dynamics.

Double beta decay of 136 Xe to excited states of 136 Ba (DBD-ES) has not yet been discovered experimentally yet. The experimental signature of such decays, one or two gamma rays following the beta signals, can be identified more effectively in a gaseous detector with the help of topological signatures. We have investigated key parameters of particle trajectories of DBD-ES with Monte Carlo simulation data of the proposed PandaX-III detector as an example. The background rates can be reduced by about one order of magnitude while keeping more than half of signals with topological analysis. The estimated half-life sensitivity of DBD-ES can be improved by 1.8 times to 4.1 × 10 23 yr (90\% CL). Similarly, the half-life sensitivity of neutrinoless double beta decay of 136 Xe to excited states of 136 Ba can be improved by a factor of 4.8 with topological signatures.

Centrality dependence of the directed flow of protons in Au+Au collisions at the beam energy of 1.23A GeV collected by the HADES experiment at GSI is presented. Measurements are performed with respect to the spectators plane estimated using the Forward Wall hodoscope. Biases due to non-flow correlations and correlated detector effects are evaluated. The corresponding systematic uncertainties are quantified using estimates of the spectators plane from various forward rapidity regions constructed from groups of Forward Wall channels and protons reconstructed with the HADES tracking system.

New sources of CP violation, beyond the known sources in the standard model (SM), are required to explain the baryon asymmetry of the universe. Measurement of a non-zero permanent electric dipole moment (EDM) for fundamental particles, such as in an electron or a neutron, or in nuclei or atoms, can help us gain a handle on the sources of CP violation, both in SM and beyond. Multiple mechanisms within the SM can generate CP violating EDMs, viz.\ through the CKM matrix in the weak sector or through the QCD θ ¯ parameter in the strong sector. We will estimate the maximum possible EDMs of leptons, certain baryons, select atoms and molecules in the (CKM ⨁ θ ¯ ) framework, assuming that the EDM wholly originates from either of the two SM mechanisms, independently. These estimates have been presented in light of the current experimental upper limits on the EDMs, in the following systems - leptons: e − , μ − , τ − , ν 0 e , ν 0 μ , ν 0 τ , baryons: n 0 , p + , Λ 0 , Σ 0 , Ξ 0 , Λ + c , Ξ + c , atoms: 85 Rb, 133 Cs, 210 Fr, 205 Tl, 199 Hg, 129 Xe, 225 Ra, 223 Rn, and molecules: HfF + , PbO, YbF, ThO, RaF, TlF. Particularly, to drive home the point that EDMs in different systems constrain CP-violating interactions differently, we show that the same measured constraint on the EDM in two different systems may not actually be equally constraining on CP violating parameters, and to emphasize the need to measure a non-zero EDM in multiple systems before understanding the origins of these CP-violating EDMs.

It has been suggested that hydrogen ingestion into the helium shell of massive stars could lead to high 13 C and 15 N excesses when the shock of a core-collapse supernova passes through its helium shell. This prediction questions the origin of extremely high 13 C and 15 N abundances observed in rare presolar SiC grains which is usually attributed to classical novae. In this context 13 N( α ,p) 16 O the reaction plays an important role since it is in competition with 13 N β + -decay to 13 C. The 13 N( α ,p) 16 O reaction rate used in stellar evolution calculations comes from the CF88 compilation with very scarce information on the origin of this rate. The goal of this work is to provide a recommended 13 N( α ,p) 16 O reaction rate, based on available experimental data. Unbound nuclear states in the 17 F compound nucleus were studied using the spectroscopic information of the analog states in 17 O nucleus that were measured at the Alto facility using the 13 C( 7 Li,t) 17 O alpha-transfer reaction, and spectroscopic factors were derived using a DWBA analysis. This spectroscopic information was used to calculate a recommended 13 N( α ,p) 16 O reaction rate with meaningful uncertainty using a Monte Carlo approach. The present 13 N( α ,p) 16 O reaction rate is found to be within a factor of two of the previous evaluation, with a typical uncertainty of a factor 2-3. The source of this uncertainty comes from the three resonances at E c.m. r =221 , 741 and 959 keV. This new error estimation translates to an overall uncertainty in the 13 C production of a factor of 50. The main source of uncertainty on the re-evaluated 13 N( α ,p) 16 O reaction rate currently comes from the uncertain alpha-width of relevant 17 F states.