The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9  fb^{-1}, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26_{-0.26}^{+0.31}.

Dark matter may be discovered through its capture in stars and subsequent annihilation. It is usually assumed that dark matter is captured after a single scattering event in the star, however this assumption breaks down for heavy dark matter, which requires multiple collisions with the star to lose enough kinetic energy to become captured. We analytically compute how multiple scatters alter the capture rate of dark matter and identify the parameter space where the effect is largest. Using these results, we then show how multiscatter capture of dark matter on compact stars can be used to probe heavy m X TeV dark matter with remarkably small dark matter-nucleon scattering cross-sections. As one example, it is demonstrated how measuring the temperature of old neutron stars in the Milky Way's center provides sensitivity to high mass dark matter with dark matter-nucleon scattering cross-sections smaller than the xenon direct detection neutrino floor.

New sets of CMS underlying-event parameters ("tunes") are presented for the pythia8 event generator. These tunes use the NNPDF3.1 parton distribution functions (PDFs) at leading (LO), next-to-leading (NLO), or nextto-next-to-leading (NNLO) orders in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are fit simultaneously to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the event shapes at LEP, global underlying event, soft multiparton interactions, and double-parton scattering contributions. In addition, comparisons are made for observables measured in various specific processes, such as multijet, Drell-Yan, and top quarkantiquark pair production including jet substructure observables. The simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, predictions from pythia8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets.

Properties of the Higgs boson are measured in the H → ZZ → 4 ( = e, µ) decay channel. A data sample of proton-proton collisions at √ s = 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb −1 is used. The signal strength modifier µ, defined as the ratio of the observed Higgs boson rate in the H → ZZ → 4 decay channel to the standard model expectation, is measured to be µ = 1.05 +0.19−0.17 at m H = 125.09 GeV, the combined ATLAS and CMS measurement of the Higgs boson mass. The signal strength modifiers for the individual Higgs boson production modes are also measured. The cross section in the fiducial phase space defined by the requirements on lepton kinematics and event topology is measured to be 2.92−0.24 (syst) fb, which is compatible with the standard model prediction of 2.76 ± 0.14 fb. Differential cross sections are reported as a function of the transverse momentum of the Higgs boson, the number of associated jets, and the transverse momentum of the leading associated jet. The Higgs boson mass is measured to be m H = 125.26 ± 0.21 GeV and the width is constrained using the on-shell invariant mass distribution to be Γ H < 1.10 GeV, at 95% confidence level. The H → ZZ → 4 decay channel ( = e, µ) has a large signal-to-background ratio, and the precise reconstruction of the final-state decay products allows the complete determination of the kinematics of the Higgs boson. This makes it one of the most important channels to measure the properties of the Higgs boson. Measurements performed by the ATLAS and CMS Collaborations using this decay channel with the LHC Run 1 data include the determination of the mass and spin-parity of the boson [14][15][16][17][18], its width [19][20][21], the fiducial cross sections [22, 23], and the tensor structure of its interaction with a pair of neutral gauge bosons [16, 18, 20]. KeywordsIn this paper measurements of properties of the Higgs boson decaying into the fourlepton final state in proton-proton (pp) collisions at √ s = 13 TeV are presented. Events are classified into categories optimized with respect to those used in ref.[14] to provide increased sensitivity to subleading production modes of the Higgs boson such as vector boson fusion (VBF) and associated production with a vector boson (WH, ZH) or top quark pair (ttH). The signal strength modifier, defined as the ratio of the measured Higgs boson rate in the H → ZZ → 4 decay channel to the SM expectation, is measured. The signal strength modifiers for the individual Higgs boson production modes are constrained. In addition, cross section measurements and dedicated measurements of the mass and width of the Higgs boson are performed. This paper is structured as follows: the apparatus and the data samples are described in section 2 and section 3. Section 4 summarizes the event reconstruction and selection. Kinematic discriminants and event categorization are discussed in section 5 and section 6. The background estimation and the signal modelling are reported i...

A combination of the searches for pair-produced vector-like partners of the top and bottom quarks in various decay channels (T→Zt/W b/Ht, B→Z b/Wt/Hb) is performed using 36.1 fb −1 of pp collision data at √ s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the Standard Model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross-section for a range of vector-like quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vector-like quarks decay to Standard Model particles. A singlet T is excluded for masses below 1.31 TeV and a singlet B is excluded for masses below 1.22 TeV. Assuming a weak isospin (T, B) doublet and |V T b | |V t B |, T and B masses below 1.37 TeV are excluded.