Ricerc@Sapienza

A measurement is reported of the ratio of branching fractions R(J/?)=B(Bc+?J/??+??)/B(Bc+?J/??+??), where the ?+ lepton is identified in the decay mode ?+??+????. This analysis uses a sample of proton-proton collision data corresponding to 3.0 fb-1 of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay Bc+?J/??+?? at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/?)=0.71±0.17(stat)±0.18(syst).

The ratio of branching fractions R(D?-)?B(B0?D?-?+??)/B(B0?D?-?+??) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb-1. The ? lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of b hadrons with high purity.

The ratio of branching fractions R(D?-)?B(B0?D?-?+??)/B(B0?D?-?+??) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb-1. For the first time, R(D?-) is determined using the ?-lepton decays with three charged pions in the final state. The B0?D?-?+?? yield is normalized to that of the B0?D?-?+?-?+ mode, providing a measurement of B(B0?D?-?+??)/B(B0?D?-?+?-?+)=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic.

The production cross-sections of ?(1S), ?(2S) and ?(3S) mesons in proton-proton collisions at s=13 TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb ?1 recorded by the LHCb experiment in 2015. The ? mesons are reconstructed in the decay mode ? ? ? + ? ? . The differential production cross-sections times the dimuon branching fractions are measured as a function of the ? transverse momentum, p T , and rapidity, y, over the range 0 < p T < 30 GeV/c and 2.0 < y < 4.5.

The inclusive Ds± production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of s=7 and 8 TeV. Promptly produced Ds± mesons are used, which decay as Ds± ? ??±, with ? ? K+K?. The measurement is performed in bins of transverse momentum, pT, and rapidity, y, covering the range 2.5 < pT< 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero Ds± production asymmetry is found with a significance of 3.3 standard deviations.[Figure not available: see fulltext.].

The results of a search for new heavy W' bosons decaying to an electron or muon and a neutrino using proton-proton collision data at a centre-of-mass energy of root s = 13 TeV are presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb(-1). As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the W' boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the W' mass.

This paper presents a measurement of the W boson production cross section and the W+/W- cross-section ratio, both in association with jets, in proton-proton collisions at root s = 8 TeV with the ATLAS experiment at the Large Hadron Collider. The measurement is performed in final states containing one electron and missing transverse momentum using data corresponding to an integrated luminosity of 20.2 fb(-1).

The differential cross section for isolated-photon production in pp collisions is measured at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC using an integrated luminosity of 36.1 fb−1. The differential cross section is presented as a function of the photon transverse energy in different regions of photon pseudorapidity. The differential cross section as a function of the absolute value of the photon pseudorapidity is also presented in different regions of photon transverse energy.

The ratio of the cross sections for inclusive isolated-photon production in pp collisions at centre-of-mass energies of 13 and 8 TeV is measured using the ATLAS detector at the LHC. The integrated luminosities of the 13 TeV and 8 TeV datasets are 3.2 fb(-1) and 20.2 fb(-1), respectively. The ratio is measured as a function of the photon transverse energy in different regions of the photon pseudorapidity. The predictions from next-to-leading-order perturbative QCD calculations are compared with the measured ratio.