S. Donato

During its second run of operation (Run 2), started in 2015, the LHC will deliver a peak instantaneous luminosity that may reach 2 · 10 34 cm -2 s -1 with an average pileup of about 55, far larger than the design value. Under these conditions, the online event selection is a very challenging task. In CMS, it is realized by a two-level trigger system: the Level-1 (L1) Trigger, implemented in custom-designed electronics, and the High Level Trigger (HLT), a streamlined version of the offine reconstruction software running on a computer farm. In order to face this challenge, the L1 trigger has been through a major upgrade compared to Run 1, whereby all electronic boards of the system have been replaced, allowing more sophisticated algorithms to be run online. Its last stage, the global trigger, is now able to perform complex selections and to compute high-level quantities, like invariant masses. Likewise, the algorithms that run in the HLT have been greatly improved; in particular, new approaches for the online track reconstruction lead to a drastic reduction of the computing time, and to much improved performances. This document will describe the performance of the upgraded trigger system in Run 2.

respectively. A 95% confidence level upper limit of 1.79 (0.89) times SM Higgs boson cross section has been observed (expected) at a Higgs boson mass of 125 GeV. An excess of events is observed above the expected background with a local significance of 2.2 standard deviations, which is consistent with the expectation from the production of the SM Higgs boson. The signal strength corresponding to this excess, relative to that of the SM Higgs boson, is 0.97 ± 0.48.

The discovery of the Higgs boson has been an important success of the LHC Run 1.This document presents the combination of the ATLAS and CMS measurements of the Higgs boson production and decay rates and of the Higgs boson coupling with vector bosons and fermions.The analysis uses the LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb -1 at √ s = 7 TeV and 20 fb -1 at √ s = 8 TeV.The Higgs boson production and decay rates measured by the two experiments have been combined using different parameterizations.The total Higgs boson cross-section has been measured to be 1.09 ± 0.11 the Standard Model prediction.The combination of the ATLAS and CMS results gives observed significances for the vector boson fusion production process and for the H → ττ decay of 5.4 and 5.5 standard deviations, respectively.The data are consistent with the Standard Model predictions for all parameterizations considered.

A search for the Standard Model (SM) Higgs boson decaying into two b jets using associated production with a Z boson decaying into a pair of neutrinos is presented at LHCP. The CMS pp collisions data-samples of 4.7/fb of at the center-of-mass energy of 7 TeV and 19.0 /fb at the energy of 8 TeV have been analyzed. The techniques employed to discriminate signal from background are explained. An upper limit of 2.3 times the SM Higgs cross section at 95% of confidence level has been observed. The signal strength for mH = 125 GeV is 1.0 ± 0.8 times the SM prediction.

The discovery of the Standard Model Higgs boson performed by the CMS and ATLAS collaborations during the LHC Run 1 has been an important success. This document is a short review of the search for the Higgs boson performed by the CMS collaboration during the LHC Run 1 and Run 2. In the first part, after a brief description of the Higgs boson production and decay channels, the Run-1 results are presented emphasizing the possible hints of New Physics. The main part of this document is devoted to the search for the Higgs boson with the 13-TeV data collected by the CMS experiment in 2015 and 2016, including the Standard Model searches as well as the Beyond Standard Model searches, such as the search for additional Higgs bosons and for resonant and non-resonant double Higgs boson production.

A search is presented for narrow resonances decaying to dijet final states in proton–proton collisions at s√=13TeV using data corresponding to an integrated luminosity of 12.9 $fb{−1}$. The dijet mass spectrum is well described by a smooth parameterization and no significant evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet scalars below 3.0 TeV, W′ bosons below 2.7 TeV, Z′ bosons below 2.1 TeV and between 2.3 and 2.6 TeV, and RS gravitons below 1.9 TeV. These extend previous limits in the dijet channel. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter are excluded below 2.0 TeV. The first limits in the dijet channel on dark matter mediators are presented as functions of dark matter mass and are compared to the exclusions of dark matter in direct detection experiments.

The CMS experiment has a sophisticated two-level triggering system composed of the Level-1, instrumented by custom-design hardware boards, and the High Level Trigger, a streamlined version of the offline reconstruction software running on a computer farm (more than 30k CPU cores). In 2017, the LHC delivered proton-proton collisions at a centre-of-mass energy of 13TeV with a peak instantaneous luminosity larger than 2 · 10^34 cm−2 s−1, more than twice the peak luminosity reached during Run1 and far larger than the design value. The CMS Level-1 triggerwas upgraded during the end-of-the year technical stop between 2015 and 2016 in order to improve its performance at high luminosity and at large number of simultaneous inelastic collisions per crossing (pile-up). All the electronic boards have been replaced and the upgraded electronics tested and commissioned with data. Smarter, more sophisticated, and innovative algorithms are now the core of the first decision layer of CMS: the upgraded trigger system implements pattern recognition and MVA (Boosted Decision Tree) regression techniques in the trigger boards for pT assignment, pile-up subtraction, and isolation requirements for electrons and tau leptons. In addition, the new global trigger is capable of evaluating complex selection algorithms such as those involving the invariant mass of trigger objects. The High Level Trigger features a trade-off between the offline complexity of the algorithms and the available computing power, and be-tween the selection efficiency the maximum sustainable output rate. The trigger selections used in Run-2 will be presented, ranging from simpler single-object selections to more sophisticated algorithms combining different objects and applying analysis-level reconstruction and selection.This document describes the design and performance of the Phase I trigger and how it influences the path towards the Phase II upgrade necessary for the LHC run at a center-of mass energy of 14 TeV with luminosity of 5 − 7 · 10^34 cm−2 s−1 , corresponding to 140–200 pile-up events. The addition of the tracker information at Level-1 and the enhanced computing resources at HLT will maintain the trigger efficiency at a similar level as the present one.

We present a search for the standard model Higgs boson decaying into b quarks and produced in association with a pair of top quarks decaying in the all-jet final state.This search is performed on the full 13-TeV dataset of proton-proton collisions collected by the CMS experiment at the LHC in 2016.To separate the t tH signal from the irreducible t t + b b background, this analysis takes advantage of a matrix element method.A data-driven method has been used to estimate the large multijet background.

The cross sections for the production of $t\overline{t}b\overline{b}$ and $t\overline{t}jj$ events and their ratio $\sigma_{t\overline{t}b\overline{b}} / \sigma_{t\overline{t}jj}$ are measured using data corresponding to an integrated luminosity of 2.3 $fb^{−1}$collected in pp collisions at $\sqrt{s}$ = 13TeV with the CMS detector at the LHC. Events with two leptons (e or μ) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is $0.022 \pm 0.003(stat) \pm 0.006(syst)$, the cross section $\sigma_{t\overline{t}b\overline{b}}$ is $4.0 \pm 0.6(stat) \pm 1.3(syst)pb$ and $\sigma_{t\overline{t}jj}$ is $184 \pm 6(stat) \pm 33(syst)pb$. The measurements are compared with the standard model expectations obtained from a powheg simulation at next-to-leading-order interfaced with pythia.