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Register a new userObservation of an excited $B_c^+$ state
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Using $pp$ collision data corresponding to an integrated luminosity of $8.5,mathrm{fb}^{-1}$ recorded by the LHCb experiment at centre-of-mass energies of $sqrt{s} = 7$, $8$ and $13mathrm{,Tekern -0.1em V}$, the observation of an excited $B_c^+$ state in the $B_c^+pi^+pi^-$ invariant-mass spectrum is reported. The observed peak has a mass of $6841.2 pm 0.6 {,rm (stat),} pm 0.1 {,rm (syst),} pm 0.8,(B_c^+) mathrm{,MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $B_c^+$ mass. It is consistent with expectations of the $B_c^{*}(2^{3}S_{1})^+$ state reconstructed without the low-energy photon from the $B_c^{*}(1^{3}S_{1})^+ to B_c^+ gamma$ decay following $B_c^{*}(2^{3}S_{1})^+ to B_c^{*}(1^{3}S_{1})^+ pi^+ pi^-$. A second state is seen with a global (local) statistical significance of $2.2,sigma$ ($3.2,sigma$) and a mass of $6872.1 pm 1.3 {,rm (stat),} pm 0.1 {,rm (syst),} pm 0.8,(B_c^+) mathrm{,MeV}/c^2$, and is consistent with the $B_c(2^{1}S_{0})^+$ state. These mass measurements are the most precise to date.
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A search is performed in the invariant mass spectrum of the $B_c^{+}pi^{+}pi^{-}$ system for the excited $B_c^{+}$ states $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ using a data sample of $pp$ collisions collected by the LHCb experiment at the centre-of-mass energy of $sqrt{s} = 8 ,{mathrm{TeV}}$, corresponding to an integrated luminosity of $2 ,{mathrm{fb^{-1}}}$. No evidence is seen for either state. Upper limits on the ratios of the production cross-sections of the $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ states times the branching fractions of ${B_c(2^{1}S_{0})^+} to {B_c^{+}pi^{+}pi^{-}}$ and ${B_c(2^{3}S_{1})^+} to {B_c^{*+}pi^{+}pi^{-}}$ over the production cross-section of the $B_c^{+}$ state are given as a function of their masses. They are found to be between 0.02 and 0.14 at $95%$ confidence level for $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ in the mass ranges $[6830, 6890] ,{mathrm{MeV}}/c^{2}$ and $[6795,6890] ,{mathrm{MeV}}/c^{2}$, respectively.
Using data recorded with the Belle detector, we observe a new excited hyperon, an $Omega^{*-}$ candidate decaying into $Xi^0K^-$ and $Xi^-K^0_S$ with a mass of $2012.4pm0.7 {rm (stat)pm 0.6 (rm syst)} {rm MeV}/c^2$ and a width of $Gamma=6.4^{+2.5}_{-2.0} {rm(stat)}pm1.6 {rm(syst)} {rm MeV}$. The $Omega^{*-}$ is seen primarily in $Upsilon(1S), Upsilon(2S)$, and $Upsilon(3S)$ decays.
A baryonic decay of the $B_c^+$ meson, $B_c^+to J/psi poverline{p}pi^+$, is observed for the first time, with a significance of $7.3$ standard deviations, in $pp$ collision data collected with the LHCb detector and corresponding to an integrated luminosity of $3.0$ fb$^{-1}$ taken at center-of-mass energies of $7$ and $8$ $mathrm{TeV}$. With the $B_c^+to J/psi pi^+$ decay as normalization channel, the ratio of branching fractions is measured to be begin{equation*} frac{mathcal{B}(B_c^+to J/psi poverline{p}pi^+)}{mathcal{B}(B_c^+to J/psi pi^+)} = 0.143^{,+,0.039}_{,-,0.034},(mathrm{stat})pm0.013,(mathrm{syst}). end{equation*} The mass of the $B_c^+$ meson is determined as $M(B_c^+)=6274.0pm1.8,(mathrm{stat})pm0.4,(mathrm{syst}),mathrm{MeV}/c^2$, using the $B_c^+to J/psi poverline{p}pi^+$ channel.
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 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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