Ricerc@Sapienza

We report the observation of a new structure in the Λ0
bπþπ− spectrum using the full LHCb data set of pp
collisions, corresponding to an integrated luminosity of 9 fb−1, collected at ffiffi
s p ¼ 7, 8, and 13 TeV. A study
of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The
masses and widths of these states are measured to be mΛbð6146Þ0 ¼ 6146.17 0.33 0.22 0.16 MeV;
mΛbð6152Þ0 ¼ 6152.51 0.26 0.22 0.16 MeV; ΓΛbð6146Þ0 ¼ 2.9 1.3 0.3 MeV; ΓΛbð6152Þ0 ¼ 2.1

The ratio of branching fractions of the decays Λ0 → pK−e+e− and Λ0 → pK−μ+μ−, −1, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb−1 recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0.1 < q2 < 6.0 GeV2/c4 and the pK− mass range m(pK−) < 2600 MeV/c2, the ratio of branching fractions is measured to be −1=1.17+0.18−0.16±0.07, where the first uncertainty is statistical and the second systematic.

A search is presented for the lepton flavour violating decay B+ → K+µ−τ+using a sample of proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV,collected with the LHCb detector and corresponding to a total integrated luminosity of9 fb−1. The τ leptons are selected inclusively, primarily via decays with a single chargedparticle. The four-momentum of the τ lepton is determined by using B+ mesons fromB∗0s2 → B+K− decays.

An angular analysis of the B0 → K0ð→ Kþπ−Þμþμ− decay is presented using a dataset corresponding
to an integrated luminosity of 4.7 fb−1 of pp collision data collected with the LHCb experiment. The full
set of CP-averaged observables are determined in bins of the invariant mass squared of the dimuon system.
Contamination from decays with the Kþπ− system in an S-wave configuration is taken into account. The
tension seen between the previous LHCb results and the standard model predictions persists with the new

An analysis of the angular distribution of the decay Λb0 → Λμ+μ− is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately 5 fb−1. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range 15 < q2 < 20 GeV2/c4. The full basis of observables is measured for the first time.

Based on an integrated luminosity of 1.61 fb−1e+e− collision data collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, a search for the P- and CP-violating decay η → π+π− has been performed. Radiative ϕ → ηγ decay is exploited to access the η mesons. No signal is observed in the π+π− invariant mass spectrum, and the upper limit on the branching fraction at 90% confidence level is determined to be ℬ(η → π+π−) < 4.9 × 10−6, which is approximately three times smaller than the previous KLOE result.

A search for B+ ? Ds+K+K? decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb?1, collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be ?(B+?Ds+K+K?)=(7.1±0.5±0.6±0.7)×10?6,where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+?Ds+D¯0. A search is also performed for the pure annihilation decay B+ ? Ds+?.

A search for the lepton-flavour violating decays Bs0 ? e±?? and B0 ? e±?? is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb?1, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the Bs0 ? e±?? decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate.

A search for the decay B-s(0) -> (K) over bar (*0) mu(+) mu(-) is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb(-1) of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations.

A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, t Hq, is presented. The search is based on a dataset of pp collisions at = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb(-1). Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the Hbb and H (+-) decay modes, respectively.