Test of Sum Rules in Nucleon Transfer Reactions

The quantitative consistency of nucleon transfer reactions as a probe of the occupancy of valence orbits in nuclei is tested. Neutron-adding, neutron-removal, and proton-adding transfer reactions were measured on the four stable even Ni isotopes, with particular attention to the cross section determinations. The data were analyzed consistently in terms of the distorted wave Born approximation to yield spectroscopic factors. Valence-orbit occupancies were extracted, utilizing the Macfarlane-French sum rules. The deduced occupancies are consistent with the changing number of valence neutrons, as are the vacancies for protons, both at the level of <5%. While there has been some debate regarding the true “observability” of spectroscopic factors, the present results indicate that empirically they yield self-consistent results

Valence nucleon populations in the Ni isotopes

Measurements of neutron-adding, neutron-removing, and proton-adding reactions were carried out for the four stable even Ni isotopes. Particular attention was paid to obtaining precise values of the cross sections at the peaks of the angular distributions. Tests with sum rules for the neutron data indicate that the results are self-consistent at the level of a few tenths of a nucleon. Data on proton-adding reactions were also obtained and analyzed with a slightly different method—while these data are also consistent, the ambiguities are larger. The occupancies of the neutron orbits derived from the data, the proton vacancies, and the energy centroids of the neutron, neutron-hole, and proton single-particle excitations are obtained. The data also provide some estimate about the closure of the 0f7/2 shell. The results are compared to shell-model calculations and may serve as a reference point for future exploration

Evolution of the nuclear spin-orbit splitting explored via the ³²Si<i>(d,p)</i>³³Si reaction using SOLARIS

The spin-orbit splitting between neutron 1p orbitals at 33Si has been deduced using the single-neutron-adding (d,p) reaction in inverse kinematics with a beam of 32Si, a long-lived radioisotope. Reaction products were analyzed by the newly implemented SOLARIS spectrometer at the reaccelerated-beam facility at the National Superconducting Cyclotron Laboratory. The measurements show reasonable agreement with shell-model calculations that incorporate modern cross-shell interactions, but they contradict the prediction of proton density depletion based on relativistic mean-field theory. The evolution of the neutron 1p-shell orbitals is systematically studied using the present and existing data in the isotonic chains of = 17, 19, and 21. In each case, a smooth decrease in the separation of the - orbitals is seen as the respective p-orbitals approach zero binding, suggesting that the finite nuclear potential strongly influences the evolution of nuclear structure in this region

Structure of Fe 70: Single-particle and collective degrees of freedom

Excited states in the neutron-rich Fe70 nucleus were populated in a one-proton removal reaction from Co71 projectiles at 87 MeV/nucleon. A new transition was observed with the γ-ray tracking array GRETINA and shown to feed the previously assigned 41+ state. In comparison to reaction theory calculations with shell-model spectroscopic factors, it is argued that the new γ ray possibly originates from the 61+ state. It is further shown that the Doppler-reconstructed γ-ray spectra are sensitive to the very different lifetimes of the 2+ and 4+ states, enabling their approximate measurement. The emerging structure of Fe70 is discussed in comparison to LNPS-new large-scale shell-model calculations

Intermediate-energy Coulomb excitation of 58,60,62Cr: The onset of collectivity toward N=40

Intermediate-energy Coulomb excitation measurements were performed on the neutron-rich isotopes 58,60,62Cr. The electric quadrupole excitation strengths, B(E2; 01+→21+), of 60,62Cr are determined for the first time. The results quantify the trend of increasing quadrupole collectivity in the Cr isotopes approaching neutron number N=40. The results are confronted with large-scale shell-model calculations in the fpgd shell using the state-of-the-art LNPS effective interaction. Different sets of effective charges are discussed that provide an improved and robust description of the B(E2) values of the neutron-rich Fe and Cr isotopes in this region of rapid shell evolution. The ratio of the neutron and proton transition matrix elements, |Mn/Mp|, is proposed as an effective tool to discriminate between the various choices of effective charges

Search for jet extinction in the inclusive jet-pT spectrum from proton-proton collisions at s=8 TeV

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI.The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7  fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To test this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale

Follow up of GW170817 and its electromagnetic counterpart by Australian-led observing programmes

The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor

Searches for electroweak neutralino and chargino production in channels with Higgs, Z, and W bosons in pp collisions at 8 TeV

Searches for supersymmetry (SUSY) are presented based on the electroweak pair production of neutralinos and charginos, leading to decay channels with Higgs, Z, and W bosons and undetected lightest SUSY particles (LSPs). The data sample corresponds to an integrated luminosity of about 19.5 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV collected in 2012 with the CMS detector at the LHC. The main emphasis is neutralino pair production in which each neutralino decays either to a Higgs boson (h) and an LSP or to a Z boson and an LSP, leading to hh, hZ, and ZZ states with missing transverse energy (E-T(miss)). A second aspect is chargino-neutralino pair production, leading to hW states with E-T(miss). The decays of a Higgs boson to a bottom-quark pair, to a photon pair, and to final states with leptons are considered in conjunction with hadronic and leptonic decay modes of the Z and W bosons. No evidence is found for supersymmetric particles, and 95% confidence level upper limits are evaluated for the respective pair production cross sections and for neutralino and chargino mass values