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Register a new userS-wave nonleptonic hyperon decays and $Xi^-_b to pi^- Lambda_b$
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The decay $Xi^-_b to pi^- Lambda_b$ has recently been observed by the LHCb Collaboration at CERN. In contrast to most weak decays of $b$-flavored baryons, this process involves the decay of the strange quark in $Xi_b$, and thus has features in common with nonleptonic weak decays of hyperons. Thanks to the expected pure S-wave nature of the decay in question in the heavy $b$ quark limit, we find that its amplitude may be related to those for S-wave nonleptonic decays of $Lambda$, $Sigma$, and $Xi$ in a picture inspired by duality. The calculated branching fraction ${cal B}(Xi^-_b to pi^- Lambda_b) = (6.3 pm 4.2) times 10^{-3}$ is consistent with the range allowed in the LHCb analysis. The error is dominated by an assumed 30% uncertainty in the amplitude due to possible U(3) violation. A more optimistic view based on sum rules involving nonleptonic hyperon decay S-wave amplitudes reduces the error on the branching fraction to $2.0 times 10^{-3}$.
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A sensitive search for the rare decays Omega^- to Lambda pi^- and Xi^0 to p pi^- has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |Delta S| = 2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Omega^- to Lambda pi^-)< 2.9 x 10^{-6} and B(Xi^0 to p pi^-)< 8.2 x 10^{-6}, both at 90% confidence level.
We report a new measurement of the decay Omega^- to Xi^- pi^+ pi^- with 76 events and a first observation of the decay Omega^+ to Xi^+ pi^+ pi^- with 24 events, yielding a combined branching ratio (3.74 ^{+0.67}_{-0.56}) times 10^{-4}. This represents a factor 25 increase in statistics over the best previous measurement. No evidence is seen for CP violation, with B(Omega^- to Xi^- pi^+ pi^-)=4.04^{+0.83}_{-0.71} times 10^{-4} and B(Omega^+ to Xi^+ pi^+ pi^-)=3.15^{+1.12}_{-0.89} times 10^{-4}. Contrary to theoretical expectation, we see little evidence for the decays Omega^- to Xi_{1530}^{*0} pi^- and Omega^+ to Xi_{1530}^{*0} pi^+ and place a 90% C.L. upper limit on the combined branching ratio B(Omega^-(Omega^+) to Xi^{*0}_{1530}(Xi^{*0}_{1530}) pi^mp)<7.0 times 10^{-5}.
Using a successful framework for describing S-wave hadronic decays of light hyperons induced by a subprocess $s to u (bar u d)$, we presented recently a model-independent calculation of the amplitude and branching ratio for $Xi^-_b to Lambda_b pi^-$ in agreement with a LHCb measurement. The same quark process contributes to $Xi^0_c to Lambda_c pi^-$, while a second term from the subprocess $cs to cd$ has been related by Voloshin to differences among total decay rates of charmed baryons. We calculate this term and find it to have a magnitude approximately equal to the $s to u (bar u d)$ term. We argue for a negligible relative phase between these two contributions, potentially due to final state interactions. However, we do not know whether they interfere destructively or constructively. For constructive interference one predicts ${cal B}(Xi_c^0 to Lambda_c pi^-) = (1.94 pm 0.70)times 10^{-3}$ and ${cal B}(Xi_c^+ to Lambda_c pi^0) = (3.86 pm 1.35)times 10^{-3}$. For destructive interference, the respective branching fractions are expected to be less than about $10^{-4}$ and $2 times 10^{-4}$.
We report on a theoretical study of the newly observed $Omega(2012)$ resonance in the nonleptonic weak decays of $Omega_c^0 to pi^+ bar{K}Xi^*(1530) (eta Omega) to pi^+ (bar{K}Xi)^-$ and $pi^+ (bar{K}Xipi)^-$ via final-state interactions of the $bar{K}Xi^*(1530)$ and $eta Omega$ pairs. The weak interaction part is assumed to be dominated by the charm quark decay process: $c(ss) to (s + u + bar{d})(ss)$, while the hadronization part takes place between the $sss$ cluster from the weak decay and a quark-antiquark pair with the quantum numbers $J^{PC} = 0^{++}$ of the vacuum, produces a pair of $bar{K}Xi^*(1530)$ and $eta Omega$. Accordingly, the final $bar{K}Xi^*(1530)$ and $eta Omega$ states are in pure isospin $I= 0$ combinations, and the $Omega_c^0 to pi^+ bar{K}Xi^*(1530)(eta Omega) to pi^+ (bar{K}Xi)^-$ decay is an ideal process to study the $Omega(2012)$ resonance. With the final-state interaction described in the chiral unitary approach, up to an arbitrary normalization, the invariant mass distributions of the final state are calculated, assuming that the $Omega(2012)$ resonance with spin-parity $J^P = 3/2^-$ is a dynamically generated state from the coupled channels interactions of the $bar{K}Xi^*(1530)$ and $eta Omega$ in $s$-wave and $bar{K}Xi$ in $d$-wave. We also calculate the ratio, $R^{bar{K}Xipi}_{bar{K}Xi} = {rm Br}[Omega_c^0 to pi^+ Omega(2012)^- to pi^+ (bar{K}Xi pi)^-] / {rm Br}[Omega_c^0 to pi^+ Omega(2012)^- to pi^+ (bar{K}Xi)^-$]. The proposed mechanism can provide valuable information on the nature of the $Omega(2012)$ and can in principle be tested by future experiments.
We report the first observation of the doubly-strange baryon $Xi(1620)^0$ in its decay to $Xi^-pi^+$ via $Xi_c^+ rightarrow Xi^- pi^+ pi^+$ decays based on a $980,{rm fb}^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The mass and width are measured to be 1610.4 $pm$ 6.0 (stat) $^{+5.9}_{-3.5}$ (syst)~MeV$/c^2$ and 59.9 $pm$ 4.8 (stat) $^{+2.8}_{-3.0}$ (syst)~MeV, respectively. We obtain 4.0$sigma$ evidence of the $Xi(1690)^0$ with the same data sample. These results shed light on the structure of hyperon resonances with strangeness $S=-2$.
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