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Penalva, N., Hernandez, E., & Nieves, J. (2020). (B)over-bar(c) ->eta(c),(B)over-bar(c) -> J/psi and (B)over-bar -> D-(*()) semileptonic decays including new physics. Phys. Rev. D, 102(9), 096016–27pp.
Abstract: We apply the general formalism derived by Penalva et al. [Phys. Rev. D 101, 113004 (2020)] to the semileptonic decay of pseudoscalar mesons containing a b quark. While present (B) over bar -> D-(*()) data give the strongest evidence in favor of lepton flavor universality violation, the observables that are normally considered are not able to distinguish between different new physics (NP) scenarios. In the above reference we discussed the relevant role that the various contributions to the double differential decay widths d(2)Gamma (d omega d cos theta(l)) and d(2)Gamma (d omega dE(l)) could play to this end. Here omega is the product of the two hadron fourvelocities, theta(l) is the angle made by the final lepton and final hadron three-momenta in the center of mass of the final two-lepton system, and E-l is the final charged lepton energy in the laboratory system. The formalism was applied by Penalva et al. to the analysis of the Lambda(b) -> Lambda(c) semileptonic decay, showing the new observables were able to tell apart different NP scenarios. Here we analyze the (B) over barc -> eta(c)tau(nu) over bar (tau), (B) over barc -> J/psi tau(nu) over bar (tau), (B) over bar -> D tau(nu) over bar (tau) and (B) over bar -> D*tau(nu) over bar (tau) , semileptonic decays. We find that, as a general rule, the (B) over barc -> J/psi observables, even including (tau) polarization, are less optimal for distinguishing between NP scenarios than those obtained from (B) over barc -> eta(c) decays, or those presented by Penalva et al. for the related Lambda(b) -> Lambda(c) semileptonic decay. Finally, we show that (B) over bar -> D and (B) over barc -> eta(c) , and (B) over bar -> D* and (B) over barc -> J/psi decay observables exhibit similar behaviors.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). First branching fraction measurement of the suppressed decay Xi(0)(c) -> pi(-) Lambda(+)(c). Phys. Rev. D, 102(7), 071101–11pp.
Abstract: The Xi(0)(c) baryon is unstable and usually decays into charmless final states by the c -> sud transition. It can, however, also disintegrate into a pi(-) meson and a Lambda(+)(c) baryon via s quark decay or via cs -> dc weak scattering. The interplay between the latter two processes governs the size of the branching fraction B(Xi(0)(c) -> pi(-) Lambda(+)(c)), first measured here to be (0.55 +/- 0.02 +/- 0.18)%, where the first uncertainty is statistical and second systematic. This result is compatible with the larger of the theoretical predictions that connect models of hyperon decays using partially conserved axial currents and SU(3) symmetry with those involving the heavy-quark expansion and heavy-quark symmetry. In addition, the branching fraction of the normalization channel, B(Xi(+)(c) -> pK(-) pi(+)) = (1.135 +/- 0.002 +/- 0.387)% is measured.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). First observation of the decay Lambda(0)(b) -> eta(c) (1S)pK(-). Phys. Rev. D, 102(11), 112012–12pp.
Abstract: The decay Lambda(0)(b) -> eta(c) (1S)pK(- )is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of 5.5 fb I, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the Lambda(0)(b) -> J/psi pK(-) decay as a normalization mode, to be B(Lambda(0)(b) -> eta(c) (1S)pK(-)) = (1.06 +/- 0.16 +/- 0.06(-019)(+0.22)) x 10(-4), where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the eta(c)(1S)p mass spectrum is performed to search for the P-c(4312)(+) pentaquark state. No evidence is B(Lambda(0)(b) -> P-c(4312)K-+(-))xB(P-c(4312)(+)-> eta(c)(1S)p)/B(Lambda(0)(b) -> eta(c) (1S)pK(-)) < 0.24( ) observed and an upper limit of < 0.24 is obtained at the 95% confidence level.
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Arbelaez, C., Cepedello, R., Fonseca, R. M., & Hirsch, M. (2020). (g-2) anomalies and neutrino mass. Phys. Rev. D, 102(7), 075005–14pp.
Abstract: Motivated by the experimentally observed deviations from standard model predictions, we calculate the anomalous magnetic moments a(alpha) = (g – 2)(alpha) for a = e, μin a neutrino mass model originally proposed by Babu, Nandi, and Tavartkiladze (BNT). We discuss two variants of the model: the original model, and a minimally extended version with an additional hypercharge-zero triplet scalar. While the original BNT model can explain a(mu), only the variant with the triplet scalar can explain both experimental anomalies. The heavy fermions of the model can be produced at the high-luminosity LHC, and in the part of parameter space where the model explains the experimental anomalies it predicts certain specific decay patterns for the exotic fermions.
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Han, C., Lopez-Ibañez, M. L., Melis, A., Vives, O., & Yang, J. M. (2021). Anomaly-free leptophilic axionlike particle and its flavor violating tests. Phys. Rev. D, 103(3), 035028–7pp.
Abstract: Motivated by the recent Xenon1T result, we study a leptophilic flavor-dependent anomaly-free axionlike particle (ALP) and its effects on charged-lepton flavor violation. We present two representative models. The first one considers that the ALP origins from the flavon that generates the charged-lepton masses. The second model assumes a larger flavor symmetry such that more general mixings in the charged-lepton are possible, while maintaining flavor-dependent ALP couplings. We find that a keV ALP explaining the Xenon1T result is still viable for lepton flavor violation and stellar cooling astrophysical limits. On the other hand, if the Xenon1T result is confirmed, future charged-lepton flavor violation measurements can be complementary to probe such a possibility.
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