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.

Measurements of two- and multi-particle angular correlations in pp collisions at root s = 5, 7, and 13TeV are presented as a function of charged-particle multiplicity. The data, corresponding to integrated luminosities of 1.0 pb(-1) (5 TeV), 6.2 pb(-1) (7 TeV), and 0.7 pb(-1) (13 TeV), were collected using the CMS detector at the LHC. The second-order (v(2)) and third-order (v(3)) azimuthal anisotropy harmonics of unidentified charged particles, as well as v(2) of K-S(0) and Lambda/(Lambda) over bar particles, are extracted from long-range two-particle correlations as functions of particle multiplicity and transverse momentum. For high-multiplicity pp events, a mass ordering is observed for the v(2) values of charged hadrons (mostly pions), K-S(0), and Lambda/(Lambda) over bar, with lighter particle species exhibiting a stronger azimuthal anisotropy signal below pT approximate to GeV/c. For 13 TeV data, the v(2) signals are also extracted from four- and six-particle correlations for the first time in pp collisions, with comparable magnitude to those from two-particle correlations. These observations are similar to those seen in pPb and PbPb collisions, and support the interpretation of a collective origin for the observed long-range correlations in high-multiplicity pp collisions. (C) 2016 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license

Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 fb −1 at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model production, yields an observed (expected) upper limit on the invisible branching fraction of 0.24 (0.23) at the 95% confidence level. The results are also interpreted in the context of Higgs-portal dark matter models. [6,7]. More generally, invisible Higgs boson decays can be realised through interactions between the Higgs boson and dark matter (DM) [8]. In Higgs-portal models [9][10][11][12], the Higgs boson acts as a mediator between SM and DM particles allowing for direct production of DM at the LHC. Furthermore, cosmological models proposing that the Higgs boson played a central role in the evolution of the early universe motivate the study of the relationship between the Higgs boson and DM [13, 14].Direct searches for invisible decays of the Higgs boson increase the sensitivity to the invisible Higgs boson width beyond the indirect constraints. The typical signature at the LHC is a large missing transverse momentum recoiling against a distinctive visible system. Previous searches by the ATLAS and CMS Collaborations have targeted Higgs boson production in association with a vector boson (VH, where V denotes W or Z) [15][16][17] or with jets consistent with a vector boson fusion (VBF, via qq → qqH) topology [17, 18]. A combination of direct searches for invisible Higgs boson decays in qqH and VH production, by the ATLAS Collaboration, yields an upper limit of 0.25 on the Higgs boson invisible branching fraction, B(H → inv), at the 95% confidence level [19]. Additionally, searches by the ATLAS Collaboration for DM in events with missing transverse momentum accompanied by jets have been interpreted in the context of Higgs boson production via gluon fusion and subsequent decay to invisible particles [20].In this paper, results from a combination of searches for invisible decays of the Higgs boson using data collected during 2011, 2012, and 2015 are presented. The searches target the qqH, VH, and ggH production modes. The searches for the VH production mode include searches targeting ZH production, in which the Z boson decays to a pair of leptons (either e + e − or µ + µ − ) or bb, and searches for both the ZH and WH production modes, in which the W or Z boson decays to light-flavour jets. Additional sensitivity is achieved in this analysis by including a search targeting gluon fusion production where the Higgs boson is produced accompanied by a gluon jet (gg → gH). The diagrams for the qqH, VH, and ggH Higgs boson production pr...

Results are presented of a search for heavy stable charged particles produced in proton-proton collisions at ffiffi ffi s p ¼ 13 TeV using a data sample corresponding to an integrated luminosity of 2.5 fb −1 collected in 2015 with the CMS detector at the CERN LHC. The search is conducted using signatures of anomalously high energy deposits in the silicon tracker and long time-of-flight measurements by the muon system. The data are consistent with the expected background, and upper limits are set on the cross sections for production of long-lived gluinos, top squarks, tau sleptons, and leptonlike long-lived fermions. These upper limits are equivalently expressed as lower limits on the masses of new states; the limits for gluinos, ranging up to 1610 GeV, are the most stringent to date. Limits on the cross sections for direct pair production of long-lived tau sleptons are also determined.

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...