A: The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic τ decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8 TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions. 3 Reconstruction of the particle-flow elements 9 3.1 Charged-particle tracks and vertices 9 3.1.

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...

The spectra of charged particles produced within the pseudorapidity window |η| < 1 at √ s NN = 5.02 TeV are measured using 404 µb −1 of PbPb and 27.4 pb −1 of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < p T < 400 GeV in pp and 0.7 < p T < 400 GeV in PbPb collisions. The corresponding nuclear modification factor, R AA , is measured in bins of collision centrality. The R AA in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the p T region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest p T measured, and approaches unity in the vicinity of p T = 200 GeV. The R AA is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS collaboration to construct the pPb nuclear modification factor, R pA , up to 120 GeV. For p T > 20 GeV, R pA exhibits weak momentum dependence and shows a moderate enhancement above unity. The CMS collaboration 241 IntroductionThe charged-particle transverse momentum (p T ) spectrum is an important tool for studying parton energy loss in the dense QCD medium, known as the quark gluon plasma (QGP), that is produced in high energy nucleus-nucleus (AA) collisions [1,2]. In such collisions, high-p T particles, which originate from parton fragmentation, are sensitive to the amount of energy loss that the partons experience traversing the medium. By comparing highp T particle yields in AA collisions to predictions of theoretical models, insight into the fundamental properties of the QGP can be gained. Over the years, a number of results have been made available by experiments at SPS [3,4], at RHIC [5][6][7][8], and at the CERN LHC [9][10][11]. The modification of high-p T particle production is typically quantified using the ratio of the charged-particle p T spectrum in AA collisions to that of pp collisions, scaled by the average number of binary nucleon-nucleon collisions, N coll . This quantity is known as the nuclear modification factor, R AA , and can also be formulated as function of p T as R AA (p T ) = dN AA /dp T N coll dN pp /dp T = dN AA /dp T T AA dσ pp /dp T , ( 1) where N AA and N pp are the charged-particle yields in AA collisions and pp collisions, and σ pp is the charged-particle cross section in pp collisions. The ratio of N coll with the total inelastic pp cross section, defined as T AA = N coll /σ pp inel , is known as the nuclear overlap function and can be calculated from a Glauber model of the nuclear collision geometry [12]. In this work we adopt natural units, such that c = 1.-1 - JHEP04(2017)039The factor of 5 suppression observed in the R AA of charged hadrons and neutral pions at RHIC [5][6][7][8] was an indication of strong medium effects on particle production in the final state. However, the RHIC measurements were limited to a p T range below 25 GeV and a collision energy...

Charge-dependent azimuthal particle correlations with respect to the second-order event plane in p-Pb and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been studied with the CMS experiment at the LHC. The measurement is performed with a three-particle correlation technique, using two particles with the same or opposite charge within the pseudorapidity range jηj < 2.4, and a third particle measured in the hadron forward calorimeters (4.4 < jηj < 5). The observed differences between the same and opposite sign correlations, as functions of multiplicity and η gap between the two charged particles, are of similar magnitude in p-Pb and PbPb collisions at the same multiplicities. These results pose a challenge for the interpretation of charge-dependent azimuthal correlations in heavy ion collisions in terms of the chiral magnetic effect.

The first observation of electroweak production of same-sign W boson pairs in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of 35.9    fb^{-1} collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. Events are selected by requiring exactly two leptons (electrons or muons) of the same charge, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass. The observed significance of the signal is 5.5 standard deviations, where a significance of 5.7 standard deviations is expected based on the standard model. The ratio of measured event yields to that expected from the standard model at leading order is 0.90±0.22. A cross section measurement in a fiducial region is reported. Bounds are given on the structure of quartic vector boson interactions in the framework of dimension-8 effective field theory operators and on the production of doubly charged Higgs bosons.