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A bstract A search is presented for additional scalar (H) or pseudoscalar (A) Higgs bosons decaying to a top quark pair in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set analyzed corresponds to an integrated luminosity of 35.9 fb − 1 collected by the CMS experiment at the LHC. Final states with one or two charged leptons are considered. The invariant mass of the reconstructed top quark pair system and variables that are sensitive to the spin of the particles decaying into the top quark pair are used to search for signatures of the H or A bosons. The interference with the standard model top quark pair background is taken into account. A moderate signal-like deviation compatible with an A boson with a mass of 400 GeV is observed with a global significance of 1.9 standard deviations. New stringent constraints are reported on the strength of the coupling of the hypothetical bosons to the top quark, with the mass of the bosons ranging from 400 to 750 GeV and their total relative width from 0.5 to 25%. The results of the search are also interpreted in a minimal supersymmetric standard model scenario. Values of m A from 400 to 700 GeV are probed, and a region with values of tan β below 1.0 to 1.5, depending on m A , is excluded at 95% confidence level.

A bstract A search for the K + → π + X decay, where X is a long-lived feebly interacting particle, is performed through an interpretation of the K + → π + ν ν ¯ analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV /c 2 and 154–260 MeV /c 2 , and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR( K + → π + X ), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.

Results are presented from a search for particle dark matter (DM), extra dimensions, and unparticles using events containing a jet and an imbalance in transverse momentum. The data were collected by the CMS detector in proton–proton collisions at the LHC and correspond to an integrated luminosity of 19.7 fb -1 at a centre-of-mass energy of 8 TeV . The number of observed events is found to be consistent with the standard model prediction. Limits are placed on the DM-nucleon scattering cross section as a function of the DM particle mass for spin-dependent and spin-independent interactions. Limits are also placed on the scale parameter M D in the Arkani-Hamed, Dimopoulos, and Dvali (ADD) model of large extra dimensions, and on the unparticle model parameter Λ U . The constraints on ADD models and unparticles are the most stringent limits in this channel and those on the DM-nucleon scattering cross section are an improvement over previous collider results.

A bstract The NA62 experiment at CERN, designed to study the ultra-rare decay K + → π + ν ν ¯ , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ + μ − pairs is reported, based on a sample of 1 . 4 × 10 17 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV /c 2 .

A bstract A measurement of the K + → π + ν ν ¯ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement of B K + → π + ν ν ¯ = 13.0 − 3.0 + 3.3 × 10 − 11 is reported. With 51 signal candidates observed and an expected background of 18 − 2 + 3 events, B K + → π + ν ν ¯ becomes the smallest branching ratio measured with a signal significance above 5 σ .

The differential cross section and charge asymmetry for inclusive p p → W ± + X → μ ± ν + X production at s = 8 TeV are measured as a function of muon pseudorapidity. The data sample corresponds to an integrated luminosity of 18.8 fb - 1 recorded with the CMS detector at the LHC. These results provide important constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10 - 3 to 10 - 1 .

A bstract Pair production of Y(1S) mesons is observed at the LHC in proton-proton collisions at s = 8 TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb −1 . Both Y(1S) candidates are fully reconstructed via their decays to μ + μ − . The fiducial acceptance region is defined by an absolute Y(1S) rapidity smaller than 2.0. The fiducial cross section for the production of Y(1S) pairs, assuming that both mesons decay isotropically, is measured to be 68.8±12.7 (stat)±7.4 (syst)±2.8 ( ℬ ) pb, where the third uncertainty comes from the uncertainty in the branching fraction of Y(1S) decays to μ + μ − . Assuming instead that the Y(1S) mesons are produced with different polarizations leads to variations in the measured cross section in the range from −38% to +36%.

A bstract A search for a charged Higgs boson is performed with a data sample corresponding to an integrated luminosity of 19.7 ± 0.5 fb −1 collected with the CMS detector in proton-proton collisions at s = 8 ,TeV. The charged Higgs boson is searched for in top quark decays for m H ± < m t − m b , and in the direct production pp → t(b)H ± for m H ± > m t − m b . The H ± → τ ± ν τ and H ± → tb decay modes in the final states τ h +jets, μτ h , ℓ +jets, and ℓℓ ’ ( ℓ =e, μ ) are considered in the search. No signal is observed and 95% confidence level upper limits are set on the charged Higgs boson production. A model-independent upper limit on the product branching fraction ℬ t → H ± b ℬ H ± → τ ± ν τ = 1.2 − 0.15 % is obtained in the mass range m H ± = 80–160 GeV, while the upper limit on the cross section times branching fraction σ pp → t b H ± ℬ H ± → τ ± ν τ = 0.38 − 0.025 pb is set in the mass range m H + = 180–600 GeV. Here, σ (pp → t(b)H ± ) stands for the cross section sum σ pp → t ¯ b H + + σ pp → t b ¯ H − . Assuming ℬ H ± → t b = 1 , an upper limit on σ (pp → t(b)H ± ) of 2.0–0.13 pb is set for m H ± = 180–600 GeV. The combination of all considered decay modes and final states is used to set exclusion limits in the m H ±−tan β parameter space in different MSSM benchmark scenarios.

The nuclear modification factor R AA and the azimuthal anisotropy coefficient v 2 of prompt and nonprompt (i.e. those from decays of b hadrons) J / ψ mesons, measured from PbPb and pp collisions at s NN = 2.76 TeV at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta p T > 6.5 GeV / c and rapidity | y | < 2.4 , extending down to p T = 3 GeV / c in the 1.6 < | y | < 2.4 range. The v 2 of prompt J / ψ is found to be nonzero, but with no strong dependence on centrality, rapidity, or p T over the full kinematic range studied. The measured v 2 of nonprompt J / ψ is consistent with zero. The R AA of prompt J / ψ exhibits a suppression that increases from peripheral to central collisions but does not vary strongly as a function of either y or p T in the fiducial range. The nonprompt J / ψ R AA shows a suppression which becomes stronger as rapidity or p T increases. The v 2 and R AA of open and hidden charm, and of open charm and beauty, are compared.

Normalized double-differential cross sections for top quark pair ( t t ¯ ) production are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7 fb - 1 . The measurement is performed in the dilepton e ± μ ∓ final state. The t t ¯ cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and t t ¯ system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured t t ¯ cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.