LHCb

Abstract:

We review the most precise tests of the CKM model of flavour physics performed by the LHCb collaboration during 2021. These include world best measurements of both time-dependent and time-independent CP violation in charm decays, the first observation of a nonzero mass difference of the neutral charm-meson eigenstates, and the most precise determination to date of the mass difference between the B0s eigenstates. A new simultaneous combination of measurements of the CKM angle γ and of charm decays allows to improve the precision on the decay-width difference of the neutral charm-meson eigenstates by a factor of 2 with respect to the combination of charm results only.

Abstract:

Two related searches for phenomena beyond the standard model (BSM) are performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton–proton collisions at a center-of-mass energy of 13TeV, collected by the CMS experiment at the LHC in 2016–2018 and corresponding to an integrated luminosity of 137fb⁻¹. The first search is inclusive, based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of jets identified as originating from bottom quarks, and the value of the kinematic variable M_(T2) for events with at least two jets. For events with exactly one jet, the transverse momentum of the jet is used instead. The second search looks in addition for disappearing tracks produced by BSM long-lived charged particles that decay within the volume of the tracking detector. No excess event yield is observed above the predicted standard model background. This is used to constrain a range of BSM models that predict the following: the pair production of gluinos and squarks in the context of supersymmetry models conserving R-parity, with or without intermediate long-lived charginos produced in the decay chain; the resonant production of a colored scalar state decaying to a massive Dirac fermion and a quark; or the pair production of scalar and vector leptoquarks each decaying to a neutrino and a top, bottom, or light-flavor quark. In most of the cases, the results obtained are the most stringent constraints to date

Abstract:

A search for the hadronic decays of the hc meson to the final states (Formula Presented.) via the process (Formula Presented.)is performed using (4.48 ± 0.03) × 108 (3686) events collected with the BESIII detector. The decay channel hc !(Formula Presented.) is observed for the first time with a significance greater than (Formula Presented.) and a branching fraction of (6.41 ± 1.74 ± 0.53 ± 1.00) × 10−4, where the uncertainties are statistical, systematic, and that from the branching fraction of (Formula Presented.). Strong evidence for the decay hc ! (Formula Presented.) is found with a significance of 4.9(Formula Presented.) and a branching fraction of (3.84 ± 0.83 ± 0.69 ± 0.58) × 10−3. The significances include systematic uncertainties. No clear signal of the decay hc ! (Formula Presented.) is found, and an upper limit of 6.59 × 10−4 on its branching fraction is set at the 90% confidence level