Ricerc@Sapienza

This paper presents a search for new heavy particles decaying into a pair of top quarks using 139 fb−1 of proton-proton collision data recorded at a centre-of-mass energy of s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search is performed using events consistent with pair production of high-transverse-momentum top quarks and their subsequent decays into the fully hadronic final states.

A time-dependent analysis of the B0s→ϕγ decay rate is performed to determine the CP -violating observables Sϕγ and Cϕγ and the mixing-induced observable AΔϕγ. The measurement is based on a sample of pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3  fb−1 at center-of-mass energies of 7 and 8 TeV. The measured values are Sϕγ=0.4±0.30±0.11, Cϕγ=0.11±0.29±0.11, and AΔϕγ=−0.67+0.37−0.41±0.17, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables S and C in radiative B0s decays.

A new baryon state is observed in the Λ0b+− mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies √ = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The mass and natural width of the new state are measured to be

A measurement of the branching fraction of the decay B0s→K0SK0S is performed using proton–proton collision data corresponding to an integrated luminosity of 5  fb−1 collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be B(B0s→K0SK0S)=[8.3±1.6(stat)±0.9(syst)±0.8(norm)±0.3(fs/fd)]×10−6, where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode B0→ϕK0S and the ratio of hadronization fractions fs/fd.

The Cabibbo-suppressed semileptonic decay +→⎯⎯⎯+ is observed for the first time using a sample of pp collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7 fb−1 at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The differential branching fraction is measured as a function of the ⎯⎯⎯ invariant mass using the decay mode B+→ J/ψK+ for normalisation. The total branching fraction is measured to be

(+→⎯⎯⎯+)=(5.27+0.23−0.24±0.21±0.15)×10−6,

The ratio of the B0s and B+ fragmentation fractions fs and fu is studied with B0s→J/ψϕ and B+→J/ψK+ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of B-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio fs/fu is observed to depend on the B-meson transverse momentum with a significance of 6.0σ.

We report four narrow peaks in the Ξ0bK− mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  fb−1 recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Ωb(6316)−]=6315.64±0.31±0.07±0.50  MeV, m[Ωb(6330)−]=6330.30±0.28±0.07±0.50  MeV, m[Ωb(6340)−]=6339.71±0.26±0.05±0.50  MeV, m[Ωb(6350)−]=6349.88±0.35±0.05±0.50  MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξ0b mass.

Using a data sample corresponding to an integrated luminosity of 2.0 fb−1, collected by the LHCb experiment, the production of the (1) state in proton–proton collisions at a centre-of-mass energy of √=13 TeV is studied in the rapidity range 2.0<<4.5 and in the transverse momentum range 6.5<T<14.0GeV. The cross-section for prompt production of (1) mesons relative to that of the / meson is measured using the ⎯⎯⎯ decay mode and is found to be (1)//=1.69±0.15±0.10±0.18.

The ϒ(1S)μ+μ− invariant-mass distribution is investigated for a possible exotic meson state composed of two b quarks and two b¯ quarks, Xbb¯bb¯. The analysis is based on a data sample of pp collisions recorded with the LHCb detector at centre-of-mass energies s=7, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb−1. No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the Xbb¯bb¯ state.

The prompt production of Λ c+ baryons is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58 nb −1 recorded at a nucleon-nucleon centre-of-mass energy of sNN=5.02 TeV. Measurements of the differential cross-section and the forwardbackward production ratio are reported for Λ c+ baryons with transverse momenta in the range 2 < p T < 10 GeV/c and rapidities in the ranges 1.5 < y ∗ < 4.0 and −4.5 < y ∗ < −2.5 in the nucleon-nucleon centre-of-mass system.