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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Search for the rare decay B-0 -> J/psi phi. Chin. Phys. C, 45(4), 043001–14pp.
Abstract: A search for the rare decay B-0 -> J/psi phi, is performed using pp collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). No significant signal of the decay is observed and an upper limit of 1.1 x 10(-7) at 90% confidence level is set on the branching fraction.
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Centelles Chulia, S., Srivastava, R., & Vicente, A. (2021). The inverse seesaw family: Dirac and Majorana. J. High Energy Phys., 03(3), 248–29pp.
Abstract: After developing a general criterion for deciding which neutrino mass models belong to the category of inverse seesaw models, we apply it to obtain the Dirac analogue of the canonical Majorana inverse seesaw model. We then generalize the inverse seesaw model and obtain a class of inverse seesaw mechanisms both for Majorana and Dirac neutrinos. We further show that many of the models have double or multiple suppressions coming from tiny symmetry breaking “mu -parameters”. These models can be tested both in colliders and with the observation of lepton flavour violating processes.
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Barducci, D., Bertuzzo, E., Caputo, A., Hernandez, P., & Mele, B. (2021). The see-saw portal at future Higgs Factories. J. High Energy Phys., 03(3), 117–32pp.
Abstract: We consider an extension of the Standard Model with two right-handed singlet fermions with mass at the electroweak scale that induce neutrino masses, plus a generic new physics sector at a higher scale Lambda. We focus on the effective operators of lowest dimension d = 5, which induce new production and decay modes for the singlet fermions. We assess the sensitivity of future Higgs Factories, such as FCC-ee, CLIC-380, ILC and CEPC, to the coefficients of these operators for various center of mass energies. We show that future lepton colliders can test the cut-off of the theory up to Lambda similar or equal to 500-1000 TeV, surpassing the reach of future indirect measurements of the Higgs and Z boson widths. We also comment on the possibility of determining the underlying model flavor structure should a New Physics signal be observed, and on the impact of higher dimensional d = 6 operators on the experimental signatures.
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Mosbech, M. R., Boehm, C., Hannestad, S., Mena, O., Stadler, J., & Wong, Y. Y. Y. (2021). The full Boltzmann hierarchy for dark matter-massive neutrino interactions. J. Cosmol. Astropart. Phys., 03(3), 066–31pp.
Abstract: The impact of dark matter-neutrino interactions on the measurement of the cosmological parameters has been investigated in the past in the context of massless neutrinos exclusively. Here we revisit the role of a neutrino-dark matter coupling in light of ongoing cosmological tensions by implementing the full Boltzmann hierarchy for three massive neutrinos. Our tightest 95% CL upper limit on the strength of the interactions, parameterized via u(chi) = sigma(0)/sigma(Th) (m(chi)/100GeV)(-1), is u(chi) <= 3.34 . 10(-4), arising from a combination of Planck TTTEEE data, Planck lensing data and SDSS BAO data. This upper bound is, as expected, slightly higher than previous results for interacting massless neutrinos, due to the correction factor associated with neutrino masses. We find that these interactions significantly relax the lower bounds on the value of sigma 8 that is inferred in the context of Lambda CDM from the Planck data, leading to agreement within 1-2 sigma with weak lensing estimates of sigma 8, as those from KiDS1000. However, the presence of these interactions barely affects the value of the Hubble constant H-0.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Study of B-s(0) -> J/psi pi(+)pi-K+K- decays. J. High Energy Phys., 02(2), 024–34pp.
Abstract: The decays B-s(0) -> J/psi pi(+)pi-K+K- are studied using a data set corresponding to an integrated luminosity of 9 fb(-1), collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13TeV. The decays B-s(0) -> J/psi K*(K) over bar *0 and B-s(0) -> chi(c1)(3872)K+K-, where the K+K- pair does not originate from a phi meson, are observed for the first time. Precise measurements of the ratios of branching fractions between intermediate chi(c1)(3872)phi, J/psi K*0 (K) over bar *0, psi(2S)phi and chi(c1)(3872)K+K- states are reported. A structure, denoted as X(4740), is observed in the J/psi phi mass spectrum and, assuming a Breit-Wigner parameterisation, its mass and width are determined to be m(X(4740)) = 4741 +/- 6 +/- 6 MeV/c(2), Gamma(X(4740)) = 53 +/- 15 +/- 11MeV, where the first uncertainty is statistical and the second is systematic. In addition, the most precise single measurement of the mass of the B-s(0) meson is performed and gives a value of m(Bs)(0) = 5366.98 +/- 0.07 +/- 0.13MeV/c(2).
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