LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). A measurement of ΔΓs. J. High Energy Phys., 05(5), 253–21pp.
Abstract: Using a dataset corresponding to 9 fb(-1) of integrated luminosity collected with the LHCb detector between 2011 and 2018 in proton-proton collisions, the decay-time distributions of the decay modes B-s(0) -> J/psi eta' and B-s(0) -> J/psi pi(+) pi(-) are studied. The decay-width difference between the light and heavy mass eigenstates of the B-s(0) meson is measured to be Delta Gamma(s)= 0.087 +/- 0.012 +/- 0.009 ps(-1), where the first uncertainty is statistical and the second systematic.
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Ardu, M., & Marcano, X. (2024). Completing the one-loop νSMEFT renormalization group evolution. J. High Energy Phys., 10(10), 212–23pp.
Abstract: In this work we consider the Standard Model Effective Field Theory extended with right-handed neutrinos, the nu SMEFT, and calculate the full set of one-loop anomalous dimensions that are proportional to Yukawa couplings. These contributions are particularly relevant when symmetry-protected low scale seesaw models are embeded in the SMEFT, since large neutrino Yukawa couplings are expected. By combining our results with the already available gauge anomalous dimensions, we provide the complete set of one-loop renormalization group evolution equations for the dimension six nu SMEFT. As a possible phenomenological implication of our results, we discuss the sensitivity of lepton flavor-violating observables to nu SMEFT operators, focusing on the more sensitive μ-> e transitions.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Amplitude analysis of the radiative decay Bs0 → K+K-γ. J. High Energy Phys., 08(8), 093–39pp.
Abstract: A search for radiative decay of B-s(0) mesons to orbitally excited K+K- states is performed using proton proton collisions recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The dikaon spectrum in the mass range m(KK) < 2400 MeV/c(2) is dominated by the phi(1020) resonance that accounts for almost 70% of the decay rate. Considering the possible contributions of f(2)(1270), f(2)'(1525) and f(2)(2010) meson states, the overall tensor contribution to the amplitude is measured to be F-{f2} = 16.8 +/- 0.5 (stat.) +/- 0.7 (syst.)%, mostly dominated by the f2 '(1525) state. Several statistically equivalent solutions are obtained for the detailed resonant structure depending on whether the smaller amplitudes interfere destructively or constructively with the dominant amplitude. The preferred solution that corresponds to the lowest values of the fit fractions along with constructive interference leads to the relative branching ratio measurement B(B-s(0) -> f(2)'gamma)/B(B-s(0) -> phi gamma) = 19.4(-0.8)(+0.9)(stat.)(-0.5)(+1.4) (syst.) +/- 0.5(B)%, where the last uncertainty is due to the ratio of measured branching fractions to the K+K- final state. This result represents the first observation of the radiative B-s(0) -> f(2)'(1525)gamma decay, which is the second radiative transition observed in the B-s(0) sector.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). First observation of the Λb0→ D+D-Λ decay. J. High Energy Phys., 07(7), 140–22pp.
Abstract: The Lambda(0)(b) -> D+D-Lambda decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb(-1). Using the B-0 -> (D+D-KS0) decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be R = sigma(Lambda b0)/sigma(B0) x B(Lambda(0)(b) -> D+D-Lambda)/B(B-0 -> (D+D-KS0))=0.179 +/- 0.022 +/- 0.014, where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B(B-0 -> (D+D-KS0)), and the cross-section ratio, sigma Lambda(b0)/sigma(B0), previously measured by LHCb are used to derive the branching fraction of the Lambda(0)(b)-> D+D-Lambda decay B(Lambda(0)(b) -> D+D-Lambda) = (1.24 +/- 0.15 +/- 0.10 +/- 0.28 +/- 0.11)x10(-4), where the third and fourth contributions are due to uncertainties of B(B-0 -> (D+D-KS0)) and sigma(Lambda b0)/sigma(B0), respectively. Inspection of the D+Lambda and D+D- invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Lambda(0)(b) -> D*+D-Lambda decay is also observed for the first time as a partially reconstructed component in the D+D-Lambda invariant mass spectrum.
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Fernandez Navarro, M., King, S. F., & Vicente, A. (2024). Minimal complete tri-hypercharge theories of flavour. J. High Energy Phys., 07(7), 147–36pp.
Abstract: The tri-hypercharge proposal introduces a separate gauged weak hypercharge assigned to each fermion family as the origin of flavour. This is arguably one of the simplest setups for building “gauge non-universal theories of flavour” or “flavour deconstructed theories”. In this paper we propose and study two minimal but ultraviolet complete and renormalisable tri-hypercharge models. We show that both models, which differ only by the heavy messengers that complete the effective theory, are able to explain the observed patterns of fermion masses and mixings (including neutrinos) with all fundamental coefficients being of O(1). In fact, both models translate the complicated flavour structure of the Standard Model into three simple physical scales above electroweak symmetry breaking, completely correlated with each other, that carry meaningful phenomenology. In particular, the heavy messenger sector determines the origin and size of fermion mixing, which controls the size and nature of the flavour-violating currents mediated by the two heavy Z ' gauge bosons of the theory. The phenomenological implications of the two minimal models are compared. In both models the lightest Z ' remains discoverable in dilepton searches at the LHC Run 3.
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