The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (p(T)) at midrapidity (vertical bar ye vertical bar < 0.8) in proton-proton (pp) collisions at a centre-of-mass energy of root s = 13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at root s = 7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: d sigma(c<(c)over bar>)/dy vertical bar(y=0) = 974 +/- 138 (stat.) +/- 140 (syst.) +/- 214(BR) mu b and d sigma(b (b) over bar)/dy vertical bar(y=0) = 79 +/- 14 (stat.) +/- 11 (syst.) +/- 5(BR) mu b using PYTHIA simulations and d sigma(c (c) over bar)/dy vertical bar(y=0) = 1417 +/- 184 (stat.) +/- 204 (syst.) +/- 312(BR) mu b and d sigma(b (b) over bar)/dy vertical bar(y=0) = 48 +/- 14 (stat.) +/- 7 (syst.) +/- 3(BR) mu b for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various p(T) intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of p(T). Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations. (C) 2018 The Author. Published by Elsevier B.V.

. Experimental transition probabilities between states of the ground-state alternating-parity bands of 144 Ba and their theoretical analysis are presented. Lifetimes of states in 144 Ba have been measured using the recoil distance method following spontaneous fission of 252 Cf. The experiment was performed at the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. The experimental data show a significantly larger value of the E 2 transition probability between the negative-parity states compared to the positive-parity ones. It is shown that this effect can be explained by a higher weight of the deformed component in the wave functions of the odd- I states. In the framework of the cluster approach it is explained by a higher weight of the alpha-cluster component in the wave function of the negative-parity states compared to the positive-parity ones. In the framework of the traditional collective model with the quadrupole and octupole degrees of freedom the same effect is explained by a higher value of the quadrupole deformation at the minima of the potential energy as a function of β 20 and β 30 compared to its value at the top of the barrier separating two physically equivalent minima, having opposite signs of the octupole deformation. Additionally, the dependence on parity of the E 2 transition probability is analyzed qualitatively in nuclei with a minimum at β 30 = 0 in the collective potential energy and compared to experimental data for 148 Nd.

Excited nonyrast states of 162Yb were populated through positron/ec decay and studied through off-beam beta-delayed gamma-ray spectroscopy at Yale. New coincidence data provided evidence for a substantial revision of the level scheme and elimination of a previously reported first excited 0+ state. The revised level scheme of 162Yb was compared to pridictions of the X(5) critical point symmetry.

We present a simple method for discerning the evolution from vibrational to rotational structure in nuclei as a function of spin. The prescription is applied to the yrast cascades in the A approximately 110 region and a clear transition from vibrational to rotational motion is found.

Lifetimes of the first 4(+) and 6(+) states in Mo-104 and Mo-106 have been measured using the recoil distance method following spontaneous fission of Cf-252. The experiment was performed at the 88-inch cyclotron of the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. Reduced transition probabilities in the ground state band of Mo-104 are compared with predictions of the critical point symmetry X(5) for phase transitional nuclei between rotational and vibrational shape. While known level energies of Mo-104 are in good agreement with the X(5) predictions, the analysis of the measured B(E2) values favors a rotor interpretation.

Lifetime measurements for the 2+1 levels of 162Er and 162Yb were obtained in β+/ɛ decay at the Yale Moving Tape Collector by fast electronic scintillation timing of β+γ coincidences.

The g factor of the 21+ state in 44Ca has been measured using the transient field technique and Coulomb excitation in inverse kinematics. A positive value of g(21+,44Ca)=+0.12±0.05 was deduced. The result suggests the (fp)4ν configuration competes with excitations of the 40Ca core. A simple model which considers that the wave function for the 21+ state consists of approximately equal admixtures of spherical four valence neutron configurations and a deformed core configuration accounts for the experimentally observed g factor as well as the previously measured quadrupole moment.

The Wright Nuclear Structure Laboratory has recently acquired a gas-filled recoil separator previously used at Berkeley National Laboratory for heavy-element synthesis. The separator will be used to separate reaction recoils from primary beam particles and fission products following target bombardment. Commissioning of the separator has recently been completed, and the structure of 203Rn investigated.

Lifetimes of excited states in neutron-rich nuclei, produced in the spontaneous fission of Cf-252, were measured using the recoil distance method. The experiment was performed using the New Yale Plunger Device and the Gammasphere array. In this contribution we present results for Zr-100, Mo-104,Mo-106 and Ba-114. The results for Mo-104 enable us to test if this nucleus is a further empirical realization of the critical point symmetry X(5) of the phase-/shape-transition between spherical and axially deformed nuclei. In Ba-144 we were for the first time able to directly measure the quadrupole and dipole moment of the negative parity octupole band.

Nuclei below the Z = 50 magic shell gap with A∼100 show a wide variety of structural phenomena. These include excellent examples of vibrational collectivity at low-spins, which give way to more rotational-like excitations with increasing angular momentum. In this paper we present recent results from an experiment performed at Yale to study the yrast evolution of states in 98,99 Mo and 101,102 Ru. Although the high-spin data is consistent with predictions from rotational model theories, we propose a simple presciption to distinguish between vibrational and rotational regimes of angular momentum generation. When applied to the nuclei of interest, a clear picture emerges of how these two mechanisms of collective spin generation compete in this region.

The near-yrast structure of the weakly deformed, "transitional," nucleus Ru-101 has been investigated using the fusion-evaporation reaction Zr-96(Be-9,4n)Ru-101 at a beam energy of approximately 44 MeV. The experimental data are compared with theoretical calculations using the cranked Woods-Saxon-Strutinsky method. The yrast positive-parity structures are observed to undergo a backbend, consistent with the crossing of an aligned (nuh(11/2))(2) configuration. The h(11/2)([550]1/2(-)) intruder band configuration is extended to a tentative spin/parity of (47/2(-)) and excitation energy of more than 9 MeV. This structure exhibits properties which can be explained by the rotational alignment of a pair of midshell g(9/2) protons, in contrast to the behavior observed in the heavier N=57, odd-A isotones where the predicted proton crossing is delayed in favor of neutron alignments. The effect of static gamma deformation on the theoretically predicted alignment properties is investigated by means of the cranked shell model. The observed band crossings are found to be consistent with a significant triaxial rigidity, persistent into the medium-spin regime.

The Wright Nuclear Structure Laboratory has recently acquired a gas-filled recoil separator previously used at Berkeley National Laboratory for heavy-element synthesis. The separator will be used to separate reaction recoils from primary beam particles and fission products following target bombardment. Commisioning of the separator has recently been completed, and the structure of Rn-203 investigated.

The near-yrast structure of the weakly deformed, ``transitional,'' nucleus ${}^{101}\mathrm{Ru}$ has been investigated using the fusion-evaporation reaction ${}^{96}\mathrm{Zr}{(}^{9}\mathrm{Be}{,4n)}^{101}\mathrm{Ru}$ at a beam energy of approximately 44 MeV. The experimental data are compared with theoretical calculations using the cranked Woods-Saxon-Strutinsky method. The yrast positive-parity structures are observed to undergo a backbend, consistent with the crossing of an aligned $(\ensuremath{\nu}{h}_{11/2}{)}^{2}$ configuration. The ${h}_{11/2}([550]{\frac{1}{2}}^{\ensuremath{-}})$ intruder band configuration is extended to a tentative spin/parity of $({\frac{47}{2}}^{\ensuremath{-}})$ and excitation energy of more than 9 MeV. This structure exhibits properties which can be explained by the rotational alignment of a pair of midshell ${g}_{9/2}$ protons, in contrast to the behavior observed in the heavier $N=57,$ odd-$A$ isotones where the predicted proton crossing is delayed in favor of neutron alignments. The effect of static \ensuremath{\gamma} deformation on the theoretically predicted alignment properties is investigated by means of the cranked shell model. The observed band crossings are found to be consistent with a significant triaxial rigidity, persistent into the medium-spin regime.