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Register a new userObservation of the First Excited State in 23O
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The first excited state in neutron-rich 23O was observed in a (2p1n) knock-out reaction from 26Ne on a beryllium target at a beam energy of 86 MeV/A. The state is unbound with respect to neutron emission and was reconstructed from the invariant mass from the 22O fragment and the neutron. It is unbound by 45(2) keV corresponding to an excitation energy of 2.8(1) MeV. The non-observation of further resonances implies a predominantly direct reaction mechanism of the employed three-nucleon-removal reaction which suggests the assignment of the observed resonance to be the 5/2+ hole state.
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The neutron-deficient nucleus 173Hg has been studied following fusion-evaporation reactions. The observation of gamma rays decaying from excited states are reported for the first time and a tentative level scheme is proposed. The proposed level scheme is discussed within the context of the systematics of neighbouring neutron-deficient Hg nuclei. In addition to the gamma-ray spectroscopy, the alpha decay of this nucleus has been measured yielding superior precision to earlier measurements.
The $^7$H system was populated in the $^2$H($^8$He,$^3$He)$^7$H reaction with a 26 AMeV $^8$He beam. The $^{7}$H missing mass energy spectrum, the $^{3}$H energy and angular distributions in the $^7$H decay frame were reconstructed. The $^7$H missing mass spectrum shows a peak which can be interpreted either as unresolved $5/2^+$ and $3/2^+$ doublet or one of these states at 6.5(5) MeV. The data also provide indications on the $1/2^+$ ground state of $^7$H located at 2.0(5) MeV with quite a low population cross section of $sim 10$ $mu$b/sr within angular range $theta_{text{cm}} simeq 6^{circ} - 30^{circ}$.
The ground state of neutron-rich unbound $^{13}$Li was observed for the first time in a one-proton removal reaction from $^{14}$Be at a beam energy of 53.6 MeV/u. The $^{13}$Li ground state was reconstructed from $^{11}$Li and two neutrons giving a resonance energy of 120$^{+60}_{-80}$ keV. All events involving single and double neutron interactions in the Modular Neutron Array (MoNA) were analyzed, simulated, and fitted self-consistently. The three-body ($^{11}$Li+$n+n$) correlations within Jacobi coordinates showed strong dineutron characteristics. The decay energy spectrum of the intermediate $^{12}$Li system ($^{11}$Li+$n$) was described with an s-wave scattering length of greater than -4 fm, which is a smaller absolute value than reported in a previous measurement.
We report four narrow peaks in the $Xi_b^0K^-$ mass spectrum obtained using $pp$ collisions at center-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$ recorded by the LHCb experiment. Referring to these states by their mass, the mass values are begin{align*} m(Omega_b(6316)^-) &= 6315.64pm0.31pm0.07pm0.50 {rm MeV}, m(Omega_b(6330)^-) &= 6330.30pm0.28pm0.07pm0.50 {rm MeV}, m(Omega_b(6340)^-) &= 6339.71pm0.26pm0.05pm0.50 {rm MeV}, m(Omega_b(6350)^-) &= 6349.88pm0.35pm0.05pm0.50 {rm MeV}, end{align*}where the uncertainties are statistical, systematic and the last is due to the knowledge of the $Xi_b^0$ mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be ${Gamma(Omega_b(6316)^-)<2.8}$ MeV, ${Gamma(Omega_b(6330)^-)<3.1}$ MeV and ${Gamma(Omega_b(6340)^-)<1.5}$ MeV. The natural width of the $Omega_b(6350)^-$ peak is $1.4^{+1.0}_{-0.8}pm0.1$ MeV, which is 2.5$sigma$ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6$sigma$ to 7.2$sigma$. After accounting for the look-elsewhere effect, the significances of the $Omega_b(6316)^-$ and $Omega_b(6330)^-$ peaks are reduced to 2.1$sigma$ and 2.6$sigma$ respectively, while the two higher mass peaks exceed 5$sigma$. The observed peaks are consistent with expectations for excited $Omega_b^-$ resonances.
Two-proton decay of the $^{17}$Ne low-lying states populated in the $^1$H($^{18}$Ne,$d$)$^{17}$Ne transfer reaction was studied. The two-proton width $Gamma_{2p}$ of the $^{17}$Ne first excited $3/2^-$ state at $E^*=1.288$ MeV is of importance for the two-proton radioactivity theory and nuclear-astrophysics applications. A dedicated search for the two-proton emission of this state was performed leading to the new upper limit obtained for the width ratio $Gamma_{2p}/Gamma_{gamma} < 1.6(3) times 10^{-4}$. A novel, combined mass method is suggested and tested capable to improve the resolution of the experiment which is a prime significance for the study of nuclear states with extremely small particle-to-gamma width ratios $Gamma_{mathrm{part}}/Gamma_{gamma}$. The condition $Gamma_{mathrm{part}} ll Gamma_{gamma}$ is quite common for the states of astrophysical interest which makes the proposed approach promising in this field.
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