Antonio Di Pilato

For the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both proton and lead dissociation processes are presented. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy per nucleon pair of ${\sqrt{s}}_{\mathrm{NN}}=8.16\mathrm{TeV}$, almost 300 times higher than in previous measurements of diffractive production in proton-nucleus collisions. For lead dissociation processes, which correspond to the pomeron-lead event topology, the epos-lhc generator predictions are a factor of 2 below the data, but the model gives a reasonable description of the rapidity gap spectrum shape. For the pomeron-proton topology, the epos-lhc, qgsjet ii, and hijing predictions are all at least a factor of 5 lower than the data. The latter effect might be explained by a significant contribution of ultraperipheral photoproduction events mimicking the signature of diffractive processes. These data may be of significant help in understanding the high energy limit of quantum chromodynamics and for modeling cosmic ray air showers.

A study of anomalous couplings of the Higgs boson to vector bosons and fermions is presented. The data were recorded by the CMS experiment at a center-of-mass energy of pp collisions at the LHC of 13 TeV and correspond to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. The study uses Higgs boson candidates produced mainly in gluon fusion or electroweak vector boson fusion at the LHC that subsequently decay to a pair of $\tau$ leptons. Matrix-element and machine-learning techniques were employed in a search for anomalous interactions. The results are combined with those from the four-lepton and two-photon decay channels to yield the most stringent constraints on anomalous Higgs boson couplings to date. The pure $CP$-odd scenario of the Higgs boson coupling to gluons is excluded at 2.4 standard deviations. The results are consistent with the standard model predictions.

A search for the direct production of a pair of $\tau$ sleptons, the supersymmetric partners of $\tau$ leptons, is presented. Each $\tau$ slepton is assumed to decay to a $\tau$ lepton and the lightest supersymmetric particle (LSP), which is assumed to be stable and to not interact in the detector, leading to an imbalance in the total reconstructed transverse momentum. The search is carried out in events identified as containing two $\tau$ leptons, each decaying to one or more hadrons and a neutrino, and significant transverse momentum imbalance. In addition to scenarios in which the $\tau$ sleptons decay promptly, the search also addresses scenarios in which the $\tau$ sleptons have sufficiently long lifetimes to give rise to nonprompt $\tau$ leptons. The data were collected in proton-proton collisions at a center-of-mass energy of $13\mathrm{TeV}$ at the CERN LHC with the CMS detector in 2016–2018, and correspond to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. No significant excess is seen with respect to standard model expectations. Upper limits on cross sections for the pair production of $\tau$ sleptons are obtained in the framework of simplified models. In a scenario in which the $\tau$ sleptons are superpartners of left-handed $\tau$ leptons, and each undergoes a prompt decay to a $\tau$ lepton and a nearly massless LSP, $\tau$ slepton masses between 115 and 340 GeV are excluded. In a scenario in which the lifetime of the $\tau$ sleptons corresponds to $c{\tau }_0=0.1\mathrm{mm}$, where ${\tau }_0$ represents the mean proper lifetime of the $\tau$ slepton, masses between 150 and 220 GeV are excluded.

A search is performed for narrow resonances decaying to final states of two jets, with at least one jet originating from a $b$ quark, in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$. The data set corresponds to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ collected with the CMS detector at the LHC. Jets originating from energetic $b$ hadrons are identified through a $b$-tagging algorithm that utilizes a deep neural network or the presence of a muon inside a jet. The invariant mass spectrum of jet pairs is well described by a smooth parametrization and no evidence for the production of new particles is observed. Upper limits on the production cross section are set for excited $b$ quarks and other resonances decaying to dijet final states containing $b$ quarks. These limits exclude at 95% confidence level models of $Z^{\prime }$ bosons with masses from 1.8 TeV to 2.4 TeV and of excited $b$ quarks with masses from 1.8 TeV to 4.0 TeV. This is the most stringent exclusion of excited $b$ quarks to date.

New sets of parameter tunes for two of the colour reconnection models, quantum chromodynamics-inspired and gluon-move, implemented in the pythia 8 event generator, are obtained based on the default CMS pythia 8 underlying-event tune, CP5. Measurements sensitive to the underlying event performed by the CMS experiment at centre-of-mass energies $$\sqrt{s}=7$$s = 7 and 13 $$\,\text {Te\hspace{-.08em}V}$$Te V , and by the CDF experiment at 1.96 $$\,\text {Te\hspace{-.08em}V}$$Te V are used to constrain the parameters of colour reconnection models and multiple-parton interactions simultaneously. The new colour reconnection tunes are compared with various measurements at 1.96, 7, 8, and 13 $$\,\text {Te\hspace{-.08em}V}$$Te V including measurements of the underlying-event, strange-particle multiplicities, jet substructure observables, jet shapes, and colour flow in top quark pair ( $${{\text {t}} {}{\bar{\text {t}}}}$$t t ¯ ) events. The new tunes are also used to estimate the uncertainty related to colour reconnection modelling in the top quark mass measurement using the decay products of $${{\text {t}} {}{\bar{\text {t}}}}$$t t ¯ events in the semileptonic channel at 13 $$\,\text {Te\hspace{-.08em}V}$$Te V .

A search is reported for pairs of light Higgs bosons ( $${\textrm{H}} _1$$H 1 ) produced in supersymmetric cascade decays in final states with small missing transverse momentum. A data set of LHC $$\hbox {pp}$$pp collisions collected with the CMS detector at $$\sqrt{s}=13\,\text {TeV} $$s = 13 TeV and corresponding to an integrated luminosity of 138 $$\,\text {fb}^{-1}$$fb - 1 is used. The search targets events where both $${\textrm{H}} _1$$H 1 bosons decay into "Equation missing" pairs that are reconstructed as large-radius jets using substructure techniques. No evidence is found for an excess of events beyond the background expectations of the standard model (SM). Results from the search are interpreted in the next-to-minimal supersymmetric extension of the SM, where a “singlino” of small mass leads to squark and gluino cascade decays that can predominantly end in a highly Lorentz-boosted singlet-like $${\textrm{H}} _1$$H 1 and a singlino-like neutralino of small transverse momentum. Upper limits are set on the product of the squark or gluino pair production cross section and the square of the "Equation missing" branching fraction of the $${\textrm{H}} _1$$H 1 in a benchmark model containing almost mass-degenerate gluinos and light-flavour squarks. Under the assumption of an SM-like "Equation missing" branching fraction, $${\textrm{H}} _1$$H 1 bosons with masses in the range 40–120 $$\,\text {GeV}$$GeV arising from the decays of squarks or gluinos with a mass of 1200–2500 $$\,\text {GeV}$$GeV are excluded at 95% confidence level.

Measurements of Higgs boson production, where the Higgs boson decays into a pair of $$\uptau $$τ leptons, are presented, using a sample of proton-proton collisions collected with the CMS experiment at a center-of-mass energy of "Equation missing", corresponding to an integrated luminosity of 138 $$\,\text {fb}^{-1}$$fb - 1 . Three analyses are presented. Two are targeting Higgs boson production via gluon fusion and vector boson fusion: a neural network based analysis and an analysis based on an event categorization optimized on the ratio of signal over background events. These are complemented by an analysis targeting vector boson associated Higgs boson production. Results are presented in the form of signal strengths relative to the standard model predictions and products of cross sections and branching fraction to $$\uptau $$τ leptons, in up to 16 different kinematic regions. For the simultaneous measurements of the neural network based analysis and the analysis targeting vector boson associated Higgs boson production signal strengths are found to be $$0.82\pm 0.11$$0.82 ± 0.11 for inclusive Higgs boson production, $$0.67\pm 0.19$$0.67 ± 0.19 ( $$0.81\pm 0.17$$0.81 ± 0.17 ) for the production mainly via gluon fusion (vector boson fusion), and $$1.79\pm 0.45$$1.79 ± 0.45 for vector boson associated Higgs boson production.