Ricerc@Sapienza

We consider an extension of the Standard Model with two singlet leptons, with masses in the electroweak range, that induce neutrino masses via the see-saw mechanism, plus a generic new physics sector at a higher scale, Λ. We apply the minimal flavor violation (MFV) principle to the corresponding Effective Field Theory (νSMEFT) valid at energy scales E ≪ Λ. We identify the irreducible sources of lepton flavor and lepton number violation at the renormalizable level, and apply the MFV ansätz to derive the scaling of the Wilson coefficients of the νSMEFT operators up to dimension six.

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 search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in pp collisions at s = 13 TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb−1, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of c- or b-quarks. The observed yield in each channel is consistent with the Standard Model background expectation.

In this paper, a new technique for reconstructing and identifying hadronically decaying tau (+)tau (-) pairs with a large Lorentz boost, referred to as the di-tau tagger, is developed and used for the first time in the ATLAS experiment at the Large Hadron Collider. A benchmark di-tau tagging selection is employed in the search for resonant Higgs boson pair production, where one Higgs boson decays into a boosted bb pair and the other into a boosted tau (+)tau (-) pair, with two hadronically decaying tau -leptons in the final state.

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.

A search is performed for a spin-0 boson, ϕ, produced in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, using prompt ϕ → μ+μ− decays and a data sample corresponding to an integrated luminosity of approximately 3.0 fb−1 collected with the LHCb detector. No evidence is found for a signal in the mass range from 5.5 to 15 GeV. Upper limits are placed on the product of the production cross-section and the branching fraction into the dimuon final state.

A search for resonances in the mass range 12–70 GeV produced in association with a b quark jet and a second jet, and decaying to a muon pair, is reported. The analysis is based on data from proton-proton collisions at center-of-mass energies of 8 and 13 TeV, collected with the CMS detector at the LHC and corresponding to integrated luminosities of 19.7 and 35.9 fb−1, respectively. The search is carried out in two mutually exclusive event categories.

Asymptotically safe extensions of the Standard Model have been searched for by adding vector-like fermions charged under the Standard Model gauge group and having Yukawa-like interactions with new scalar fields. Here we study the corresponding renormalization group β-functions to next and next-to-next to leading order in the perturbative expansion, varying the number of extra fermions and the representations they carry. We test the fixed points of the β-functions against various criteria of perturbativity to single out those that are potentially viable.

We study models that interpolate between an elementary and a composite Higgs boson. Such models, arising in theories with new vector-like fermions with electroweak quantum numbers and charged under a confining gauge interaction, are entirely compatible with current data, with only weak bounds from flavor, CP-violation and precision tests. After classifying the models from the point of view of symmetries, we study their collider phenomenology at LHC.

We discuss the measurements of the anomalous triple gauge couplings at Large Hadron Collider focusing on the contribution of the O 3W and O 3W˜ operators. These deviations were known to be particularly hard to measure due to their suppressed interference with the SM amplitudes in the inclusive processes, leading to approximate flat directions in the space of these Wilson coefficients.