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تسجيل مستخدم جديد$Lambda_b to pi^- (D_s^-) Lambda_c(2595),~pi^- (D_s^-) Lambda_c(2625)$ decays and $DN,~D^*N$ molecular components
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From the perspective that the $Lambda_c(2595)$ and $Lambda_c(2625)$ are dynamically generated resonances from the $DN,~D^*N$ interaction and coupled channels, we have evaluated the rates for $Lambda_b to pi^- Lambda_c(2595)$ and $Lambda_b to pi^- Lambda_c(2625)$ up to a global unknown factor that allows us to calculate the ratio of rates and compare with experiment, where good agreement is found. Similarly, we can also make predictions for the ratio of rates of the, yet unknown, decays of $Lambda_b to D_s^- Lambda_c(2595)$ and $Lambda_b to D_s^- Lambda_c(2625)$ and make estimates for their individual branching fractions.
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We study the implications for $Lambda_b to Lambda_c^*ellbar{ u}_ell$ and $Lambda_b to Lambda_c^*pi^-$ $[Lambda_c^*=Lambda_c(2595)$ and $Lambda_c(2625)]$ decays that can be deduced from heavy quark spin symmetry (HQSS). Identifying the odd parity $Lam
bda_c(2595)$ and $Lambda_c(2625)$ resonances as HQSS partners, with total angular momentum--parity $j_q^P=1^-$ for the light degrees of freedom, we find that the ratios $Gamma(Lambda_brightarrowLambda_c(2595)pi^-)/Gamma(Lambda_brightarrowLambda_c(2625)pi^-)$ and $Gamma(Lambda_brightarrow Lambda_c(2595) ell bar{ u}_ell)/ Gamma(Lambda_brightarrowLambda_c(2625) ell bar{ u}_ell)$ agree, within errors, with the experimental values given in the Review of Particle Physics. We discuss how future, and more precise, measurements of the above branching fractions could be used to shed light into the inner HQSS structure of the narrow $Lambda_c(2595)$ odd-parity resonance. Namely, we show that such studies would constrain the existence of a sizable $j^P_q=0^-$ component in its wave-function, and/or of a two-pole pattern, in analogy to the case of the similar $Lambda(1405)$ resonance in the strange sector, as suggested by most of the approaches that describe the $Lambda_c(2595)$ as a hadron molecule. We also investigate the lepton flavor universality ratios $R[Lambda_c^*] = {cal B}(Lambda_b to Lambda_c^* tau,bar u_tau)/{cal B}(Lambda_b to Lambda_c^* mu,bar u_mu)$, and discuss how $R[Lambda_c(2595)]$ may be affected by a new source of potentially large systematic errors if there are two $Lambda_c(2595)$ poles.
We evaluate the partial decay widths for the semileptonic $Lambda_b to bar u_l l Lambda_c(2595)$ and $Lambda_b to bar u_l l Lambda_c(2625)$ decays from the perspective that these two $Lambda^*_c$ resonances are dynamically generated from the $DN$ a
nd $D^*N$ interaction with coupled channels. We find that the ratio of the rates obtained for these two reactions is compatible with present experimental data and is very sensitive to the $D^* N$ coupling, which becomes essential to obtain agreement with experiment. Together with the results obtained for the $Lambda_b to pi^- Lambda^*_c$ reactions, it gives strong support to the molecular picture of the two $Lambda^*_c$ resonances and the important role of the $D^*N$ component neglected in prior studies of the $Lambda_c(2595)$ from the molecular perspective.
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 $2 times 10^{-4}$.
Using 567 $pb^{-1}$ of data collected with the BESIII detector at a center-of-mass energy of $sqrt{s}=$ 4.599 $GeV$, near the $Lambda_{c}^{+}Lambda_{c}^{-}$ threshold, we study the singly Cabibbo-suppressed decays $Lambda_c^{+}to ppi^{+}pi^{-}$ and $
Lambda_c^{+}to pK^{+}K^{-}$. By normalizing with respect to the Cabibbo-favored decay $Lambda_c^{+}to pK^{-}pi^{+}$, we obtain ratios of branching fractions: $frac{mathcal{B}(Lambda_c^{+}to ppi^{+}pi^{-})}{mathcal{B}(Lambda_c^{+}to pK^{-}pi^{+})}$ = $(6.70 pm 0.48 pm 0.25)%$, $frac{mathcal{B}(Lambda_c^{+}to pphi)}{mathcal{B}(Lambda_c^{+}to pK^{-}pi^{+})}$ = $(1.81 pm 0.33 pm 0.13)%$, and $frac{mathcal{B}(Lambda_c^{+}to pK^{+}K^{-}_{text{non-}phi})}{mathcal{B}(Lambda_c^{+}to pK^{-}pi^{+})}$ = $(9.36 pm 2.22 pm 0.71)times10^{-3}$, where the uncertainties are statistical and systematic, respectively. The absolute branching fractions are also presented. Among these measurements, the decay $Lambda_c^{+}to ppi^{+}pi^{-}$ is observed for the first time, and the precision of the branching fraction for $Lambda_c^{+}to pK^{+}K^{-}_{text{non-}phi}$ and $Lambda_c^{+}to pphi$ is significantly improved.
The decay $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ is observed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $sqrt{s}=$ 7 and 8 TeV, corresponding to an integrated luminosity of 3 $fb^{-1}$. The ratio o
f branching fractions between $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ and $Lambda_b^0 to Lambda_c^+ pi^-$ decays is measured to be begin{equation*} frac{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ pi^-)} = 0.0540 pm 0.0023 pm 0.0032. end{equation*} Two resonant structures are observed in the $ Lambda_c^+ pi^-$ mass spectrum of the ${Lambda_b^0 to Lambda_c^+ poverline{p} pi^-}$ decays, corresponding to the $Sigma_c(2455)^0$ and $Sigma_c^{*}(2520)^0$ states. The ratios of branching fractions with respect to the decay $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ are begin{align*} frac{mathcal{B}(Lambda_b^0 to Sigma_c^0 poverline{p})timesmathcal{B}(Sigma_c^0to Lambda_c^+ pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)} = 0.089pm0.015pm0.006, frac{mathcal{B}(Lambda_b^0 to Sigma_c^{*0} poverline{p})timesmathcal{B}(Sigma_c^{*0}to Lambda_c^+ pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)} = 0.119pm0.020pm0.014. end{align*} In all of the above results, the first uncertainty is statistical and the second is systematic. The phase space is also examined for the presence of dibaryon resonances. No evidence for such resonances is found.
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