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Register a new userObservation of a new $Xi_b^-$ resonance
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From samples of $pp$ collision data collected by the LHCb experiment at $sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $Lambda_b^0K^-$ and $Xi_b^0pi^-$ invariant mass spectra is observed. In the quark model, radially and orbitally excited $Xi_b^-$ resonances with quark content $bds$ are expected. Referring to this peak as $Xi_b(6227)^-$, the mass and natural width are measured to be $m_{Xi_{b}(6227)^-}=6226.9pm2.0pm0.3pm0.2$ MeV/$c^2$ and $Gamma_{Xi_b(6227)^-}=18.1pm5.4pm1.8$ MeV/$c^2$, where the first uncertainty is statistical, the second is systematic, and the third, on $m_{Xi_b(6227)^-}$, is due to the knowledge of the $Lambda_b^0$ baryon mass. Relative production rates of the ${Xi_b(6227)^-toLambda_b^0K^-}$ and ${Xi_b(6227)^-toXi_b^0pi^-}$ decays are also reported.
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Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5 fb$^{-1}$, the observation of a new excited $Xi_b^0$ resonance decaying to the $Xi_b^-pi^+$ final state is presented. The state, referred to as $Xi_b(6227)^0$, has a measured mass and natural width of $m(Xi_b(6227)^0) = 6227.1^{,+1.4}_{,-1.5}pm0.5$ MeV, $Gamma(Xi_b(6227)^0) = 18.6^{,+5.0}_{,-4.1}pm1.4$ MeV, where the uncertainties are statistical and systematic. The production rate of the $Xi_b(6227)^0$ state relative to that of the $Xi_b^-$ baryon in the kinematic region $2<eta<5$ and $p_{rm T}<30$ GeV is measured to be $frac{f_{Xi_b(6227)^0}}{f_{Xi_b^-}}{mathcal{B}}(Xi_b(6227)^0toXi_b^-pi^+) = 0.045pm0.008pm0.004$, where ${mathcal{B}}(Xi_b(6227)^0toXi_b^-pi^+)$ is the branching fraction of the decay, and $f_{Xi_b(6227)^0}$ and $f_{Xi_b^-}$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed $Xi_b(6227)^-$ state, along with the mass of the $Xi_b^-$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.
Two structures are observed close to the kinematic threshold in the $Xi_b^0 pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = frac{1}{2}^+$ and $J^P=frac{3}{2}^+$ states, denoted $Xi_b^{prime -}$ and $Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(Xi_b^{prime -}) - m(Xi_b^0) - m(pi^{-}) = 3.653 pm 0.018 pm 0.006$ MeV$/c^2$, $m(Xi_b^{*-}) - m(Xi_b^0) - m(pi^{-}) = 23.96 pm 0.12 pm 0.06$ MeV$/c^2$, $Gamma(Xi_b^{*-}) = 1.65 pm 0.31 pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $Gamma(Xi_b^{prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.
Decays of the $Xi_b^-$ and $Omega_b^-$ baryons to the charmless final states $p h^{-}h^{prime -}$, where $h^{(prime)}$ denotes a kaon or pion, are searched for with the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at centre-of-mass energies $sqrt{s} = 7$ and $8 TeV$, corresponding to an integrated luminosity of $3 {rm fb}^{-1}$. The decay $Xi_b^- to p K^-K^-$ is observed with a significance of $8.7$ standard deviations, and evidence at the level of $3.4$ standard deviations is found for the $Xi_b^- to p K^-pi^-$ decay. Results are reported, relative to the $B^-to K^+K^-K^-$ normalisation channel, for the products of branching fractions and $b$-hadron production fractions. The branching fractions of $Xi_b^- to p K^-pi^-$ and $Xi_b^- to p pi^-pi^-$ relative to $Xi_b^- to p K^-K^-$ decays are also measured.
We report on a high-statistics measurement of the basic double pionic fusion reaction $pn to dpi^0pi^0$ over the energy region of the so-called ABC effect, a pronounced low-mass enhancement in the $pipi$-invariant mass spectrum. The measurements were performed with the WASA detector setup at COSY. The data reveal the ABC effect to be associated with a Lorentzian shaped energy dependence in the integral cross section. The observables are consistent with a resonance with $I(J^P) =0(3^+)$ in both $pn$ and $DeltaDelta$ systems. Necessary further tests of the resonance interpretation are discussed.
We report the observation of a new $D_{sJ}$ meson produced in $B^{+} to bar{D}^{0} D_{sJ} to bar{D}^{0} D^{0} K^{+}$. This state has a mass of $M=2708 pm 9 ^{+11}_{-10} rm{MeV}/{it c}^{2}$, a width $Gamma = 108 pm 23 ^{+36}_{-31} ~rm{MeV}/ {it c}^{2}$ and a $1^{-}$ spin-parity. The results are based on an analysis of 449 million $Bbar{B}$ events collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider.
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