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Register a new userIdentification of a long lived $beta$ decaying isomer in $^{150}$Pm
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The decay of odd-odd $^{150}$Pm has been studied by populating the nucleus with the $^{150}$Nd(p,n)$^{150}$Pm reaction at E$_{beam}$ = 8.0 MeV using 97$%$ enriched $^{150}$Nd target. The presence of an isomeric state with $beta$ decay half life of 2.2(1) h could be identified in $^{150}$Pm by following the half lives of the observed $gamma$ transitions. The decay of the isomer to the excited levels of $^{150}$Sm has been confirmed by observing the $gamma - gamma$ coincidence with the VENUS array of six Compton suppressed Clover HPGe detectors. The $beta$ decay end-point energies corresponding to the decay from the $^{150g}$Pm and $^{150m}$Pm have been measured using a $beta-gamma$ coincidence setup of two thin window Planar HPGe detectors and four Clover HPGe detectors of the VENUS array. The systematics of the similar isomeric states in neighboring nuclei has been studied to understand the underlying structure of these states. Shell model calculation has been performed by using OXBASH code which indicates the presence of a 5$^-$ isomeric state at very low excitation in the nucleus. The calculation also suggests hindered electromagnetic decay of this isomer and supports the possibility of its $beta$ decay to the excited levels of $^{150}$Sm.
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We report on the investigation of the population mechanism for the 454-KeV level in 71Cu. This level was identified for the first time in a recent Coulomb excitation measurement with a radioactive beam of 71Cu. The selective nature of the Coulomb-excitation process as well as nuclear-structure considerations constrain the possible spin values for the newly observed state to Ipi=1/2-. A re-examination of the data set obtained in a beta-decay study at the LISOL separator revealed that this state is also populated in the decay of 71Ni, most probably by direct feeding from a newly identified 1/2- beta-decaying isomer having a T1/2=2.34(25) s. In this paper we investigate the proposed scenario by reanalyzing the beta-gamma and gamma-gamma coincidences obtained in the beta-decay study at LISOL.
Long-lived particles decaying to $e^pm mu^mp u$, with masses between 7 and $50$ GeV/c$^2$ and lifetimes between 2 and $50$ ps, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using $5.4$ fb$^{-1}$ of $pp$ collisions collected with the LHCb detector at a centre-of-mass energy of $sqrt{s} = 13$ TeV. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of $125$ GeV/c$^2$, and the charged current production from an on-shell $W$ boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.
Collinear laser spectroscopy has been performed on the $^{79}_{30}$Zn$_{49}$ isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred milliseconds half-life was confirmed, and the nuclear spins and moments of the ground and isomeric states in $^{79}$Zn as well as the isomer shift were measured. From the observed hyperfine structures, spins $I = 9/2$ and $I = 1/2$ are firmly assigned to the ground and isomeric states. The magnetic moment $mu$ ($^{79}$Zn) = $-$1.1866(10) $mu_{rm{N}}$, confirms the spin-parity $9/2^{+}$ with a $ u g_{9/2}^{-1}$ shell-model configuration, in excellent agreement with the prediction from large scale shell-model theories. The magnetic moment $mu$ ($^{79m}$Zn) = $-$1.0180(12) $mu_{rm{N}}$ supports a positive parity for the isomer, with a wave function dominated by a 2h-1p neutron excitation across the $N = 50$ shell gap. The large isomer shift reveals an increase of the intruder isomer mean square charge radius with respect to that of the ground state: $delta langle r^{2}_{c}rangle^{79,79m}$ = +0.204(6) fm$^{2}$, providing first evidence of shape coexistence.
The close similarity between the shell structures in the 132Sn and 208Pb regions is a well known phenomenon. Thus, using the correspondence between the high-j orbits located above the Z=50 and Z=82 shell gaps, we discuss the evolutions of the fully aligned states with one broken proton pair in the N=82 and N=126 isotones. A long-lived isomeric state was discovered in 217Pa more than thirty years ago and despite two other experiments giving new experimental results, the discussions on its main properties (spin, parity, configuration) remained inconclusive. Then, using the comparison with the I^pi=17/2^+ isomeric state recently measured in 139La, the isomeric state of 217Pa is assigned as the fully aligned state of the (pi h_{9/2})^2(pi f_{7/2})^1 configuration.
A search is presented for long-lived particles with a mass between 25 and 50 GeV$/c^2$ and a lifetime between 1 and 200 ps in a sample of proton-proton collisions at a centre-of-mass energy of $sqrt{s}=7$ TeV, corresponding to an integrated luminosity of 0.62 fb$^{-1}$, collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a Standard Model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.
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