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تسجيل مستخدم جديدObservation of excited Lambda_b0 baryons
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Using pp collision data corresponding to 1.0 fb-1 integrated luminosity collected by the LHCb detector, two narrow states are observed in the Lambda_b0pi+pi- spectrum with masses 5911.97 +- 0.12(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2 and 5919.77 +- 0.08(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2. The significances of the observations are 5.2 and 10.2 standard deviations, respectively. These states are interpreted as the orbitally-excited Lambda_b0 baryons, Lambda_b*0(5912) and Lambda_b*0(5920).
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Using 980 $fb^-1$ of data collected with the Belle detector operating at the KEKB asymmetric-energy e^+e^- collider, we report a study of the electromagnetic decays of excited {charmed baryons} $Xi_c(2790)$ and $Xi_c(2815)$. A clear signal (8.6 stand
ard deviations) is observed for $Xi_c(2815)^0 to Xi_c^0gamma$, and we measure: $B[Xi_c(2815)^0 to Xi_c^0gamma]/B[Xi_c(2815)^0 to Xi_c(2645)^+pi^- to Xi_c^0pi^+pi^-] = 0.41 pm 0.05 pm 0.03$. We also present evidence (3.8 standard deviations) for the similar decay of the $Xi_c(2790)^0$ and measure: $B[Xi_c(2790)^{0}toXi_c^{0}gamma]/B[Xi_c(2790)^0toXi_c^{prime +}pi^{-}toXi_c^{+}gamma pi^-] = 0.13 pm 0.03 pm 0.02$. The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the $Xi_c(2815)^+$ and $Xi_c(2790)^+$ baryons and set upper limits at the 90% confidence level of: $B[Xi_c(2815)^{+}toXi_c^{+}gamma]/B[Xi_c(2815)^+toXi_c(2645)^0pi^+toXi_c^+pi^-pi^+] < 0.09,$ and $B[Xi_c(2790)^{+}toXi_c^{+}gamma]/B[Xi_c(2790)^+toXi_c^{prime 0}pi^{+}toXi_c^{0}gamma pi^+] < 0.06.$ Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states.
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se 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.
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