ABSTRACT
We report the first direct observation of neutrino interactions at a particle collider experiment. Neutrino candidate events are identified in a 13.6 TeV center-of-mass energy pp collision dataset of 35.4 fb^{-1} using the active electronic components of the FASER detector at the Large Hadron Collider. The candidates are required to have a track propagating through the entire length of the FASER detector and be consistent with a muon neutrino charged-current interaction. We infer 153_{-13}^{+12} neutrino interactions with a significance of 16 standard deviations above the background-only hypothesis. These events are consistent with the characteristics expected from neutrino interactions in terms of secondary particle production and spatial distribution, and they imply the observation of both neutrinos and anti-neutrinos with an incident neutrino energy of significantly above 200 GeV.
ABSTRACT
We perform the first global fit to inclusive BâX_{s}γ measurements using a model-independent treatment of the nonperturbative b-quark distribution function, with next-to-next-to-leading logarithmic resummation and O(α_{s}^{2}) fixed-order contributions. The normalization of the BâX_{s}γ decay rate, given by |C_{7}^{incl}V_{tb}V_{ts}^{*}|^{2}, is sensitive to physics beyond the standard model (SM). We determine |C_{7}^{incl}V_{tb}V_{ts}^{*}|=(14.77±0.51_{fit}±0.59_{theory}±0.08_{param})×10^{-3}, in good agreement with the SM prediction, and the b-quark mass m_{b}^{1S}=(4.750±0.027_{fit}±0.033_{theory}±0.003_{param}) GeV. Our results suggest that the uncertainties in the extracted BâX_{s}γ rate have been underestimated by up to a factor of 2, leaving more room for beyond-SM contributions.
ABSTRACT
The heavy quark effective theory makes model independent predictions for semileptonic Λ_{b}âΛ_{c} decays in terms of a small set of parameters. No subleading Isgur-Wise function occurs at order Λ_{QCD}/m_{c,b}, and only two subsubleading functions enter at order Λ_{QCD}^{2}/m_{c}^{2}. These features allow us to fit the form factors and decay rates calculated up to order Λ_{QCD}^{2}/m_{c}^{2} to LHCb data and lattice QCD calculations. We derive a significantly more precise standard model prediction for the ratio B(Λ_{b}âΛ_{c}τν[over ¯])/B(Λ_{b}âΛ_{c}µν[over ¯]) than prior results, and find the expansion in Λ_{QCD}/m_{c} well behaved, addressing a long-standing question. Our results allow more precise and reliable calculations of Λ_{b}âΛ_{c}âν[over ¯] rates, and are systematically improvable with better data on the µ (or e) modes.