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Motivated by the recent finding of five $Omega_c$ states by the LHCb collaboration, and the successful reproduction of three of them in a recent approach searching for molecular states of meson-baryon with the quantum numbers of $Omega_c$, we extend these ideas and make predictions for the interaction of meson-baryon in the beauty sector, searching for poles in the scattering matrix that correspond to physical states. We find several $Omega_b$ states: two states with masses 6405~MeV and 6465~MeV for $J^P= frac{1}{2}^-$; two more states with masses 6427~MeV and 6665~MeV for $frac{3}{2}^-$; and three states between 6500 and 6820~MeV, degenerate with $J^P=frac{1}{2}^-,,frac{3}{2}^-$, stemming from the interaction of vector-baryon in the beauty sector.
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We observe that four peaks seen in the high energy part of the $Omega_b$ spectrum of the recent LHCb experiment are in remarkable agreement with predictions made for molecular $Omega_b$ states stemming from the meson-baryon interaction, with an approach that applied to the $Omega_c$ states gave rise to three states in good agreement with experiment in masses and widths. While the statistical significance of the peaks prevents us from claims of states at the present time, the agreement found should be an incentive to look at this experiment with increased statistics to give an answer to this suggestive idea.
A method for modelling the prompt production of molecular states using the hadronic rescattering framework of the general-purpose Pythia event generator is introduced. Production cross sections of possible exotic hadronic molecules via hadronic rescattering at the LHC are calculated for the $chi_{c1}(3872)$ resonance, a possible tetraquark state, as well as three possible pentaquark states, $P_c^+(4312)$, $P_c^+(4440)$, and $P_c^+(4457)$. For the $P_c^+$ states, the expected cross section from $Lambda_b$ decays is compared to the hadronic-rescattering production. The $chi_{c1}(3872)$ cross section is compared to the fiducial $chi_{c1}(3872)$ cross-section measurement by LHCb and found to contribute at a level of O(1%). Finally, the expected yields of $P_c^+$ production from hadronic rescattering during Run 3 of LHCb are estimated. The prompt background is found to be significantly larger than the prompt $P_c^+$ signal from hadronic rescattering.
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.
We study the weak decay $Omega_b^- to (Xi_c^+ , K^-) , pi^-$, in view of the narrow $Omega_c$ states recently measured by the LHCb collaboration and later confirmed by the Belle collaboration. The $Omega_c(3050)$ and $Omega_c(3090)$ are described as meson-baryon molecular states, using an extension of the local hidden gauge approach in coupled channels. We investigate the $Xi D$, $Xi_c bar K$ and $Xi_c^prime bar K$ invariant mass distributions making predictions that could be confronted with future experiments, providing useful information that could help determine the quantum numbers and nature of these states.
Electromagnetic transitions from deformed structures based on $alpha$ configurations or on heavier clusters are discussed, drawing the link between multiparticle-multihole excited bands and cluster structures. Enhanced E2 and E1 transitions are reviewed in the light nuclei, $^8$Be, $^{10}$Be, $^{12}$C, $^{16}$O, $^{18}$O and heavier ones like $^{212}$Po. Connections between cluster structures and superdeformed configurations in $^{36}$Ar and $^{40}$Ca are discussed. What the cluster states based on heavier substructures like $^{12}$C and $^{16}$O are concerned, recent results on the resonant radiative capture reaction $^{12}$C($^{16}$O,$gamma$)$^{28}$Si are presented, in particular the strong decay mode involving the feeding of low-lying $^{28}$Si 1$^+$ and 2$^+$ T=1 states by enhanced M1 isovector transitions.
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