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تسجيل مستخدم جديدTriple product asymmmetries in $Lambda_b$ and $Xi_b$ decays
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The LHCb experiment is capable of studying four-body decays of the $b$-flavored baryons $Lambda_b$ and $Xi_b^0$ to charmless final states consisting of charged pions, kaons, and baryons. We remark on the search in such modes for CP-violating triple product asymmetries and for CP rate asymmetries relative to decays involving charmed baryons.
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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 $2 times 10^{-4}$.
A search for $CP$ violation in charmless four-body decays of $Lambda_b$ and $Xi_b^0$ baryons with a proton and three charged mesons in the final state is performed. To cancel out production and detection charge-asymmetry effects, the search is carrie
d out by measuring the difference between the $CP$ asymmetries in a charmless decay and in a decay with an intermediate charmed baryon with the same particles in the final state. The data sample used was recorded in 2011 and 2012 with the LHCb detector and corresponds to an integrated luminosity of $3 {rm fb}^{-1}$. A total of 18 $CP$ asymmetries are considered, either accounting for the full phase space of the decays or exploring specific regions of the decay kinematics. No significant $CP$-violation effect is observed in any of the measurements.
Inclusive semileptonic decays of beauty baryons are studied using the heavy quark expansion to ${cal O}(1/m_b^3)$, at leading order in $alpha_s$. The case of a polarized decaying baryon is examined, with reference to $Lambda_b$. An extension of the S
tandard Model effective Hamiltonian inducing $b to U ell {bar u}_ ell$ transitions ($U=u,,c$ and $ell=e,,mu,,tau$) is considered, which comprises the full set of D=6 semileptonic operators with left-handed neutrinos. The effects of the new operators in several observables are described.
A search for charmless four-body decays of $Lambda_{b}^{0}$ and $Xi_{b}^{0}$ baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb expe
riment and corresponds to an integrated luminosity of 3 fb$^{-1}$. Six decay modes are observed, among which $Lambda_{b}^{0} to pK^{-}pi^{+}pi^{-}$, $Lambda_{b}^{0} to pK^{-}K^{+}K^{-}$, $Xi_{b}^{0} to pK^{-}pi^{+}pi^{-}$ and $Xi_{b}^{0} to pK^{-} pi^{+}K^{-}$ are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the $Xi_{b}^{0}$ baryon) are determined relative to the $Lambda_{b}^{0} to Lambda_{c}^{+}pi^{-}$ decay.
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