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.

2018 JINST 13 P05011 8.5 Measurement of the data-to-simulation scale factors as a function of the discriminator value 76 8.6 Comparison of the measured data-to-simulation scale factors 79 9 Measurement of the tagging efficiency for boosted topologies 82 9.1 Comparison of data with simulation 82 9.2 Efficiency for subjets 83 9.2.1 Misidentification probability 83 9.2.2 Measurement of the b tagging efficiency 84 9.3 Efficiency of the double-b tagger 86 9.3.1 Measurement of the double-b tagging efficiency 86 9.3.2 Measurement of the misidentification probability for top quarks 87

This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing detector signals consistent with an electron, photon, muon, τ lepton, jet, or missing transverse energy. A programmable menu of up to 128 object-based algorithms is used to select events for subsequent processing. The trigger thresholds are adjusted to the LHC instantaneous luminosity during data taking in order to restrict the output rate to 100 kHz, the upper limit imposed by the CMS readout electronics. The second level, implemented in software, further refines the purity of the output stream, selecting an average rate of 400 Hz for offline event storage. The objectives, strategy and performance of the trigger system during the LHC Run 1 are described.

Measurements of two- and four-particle angular correlations for charged particles emitted in pPb collisions are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 31 inverse nanobarns, were collected during the 2013 LHC pPb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. The results are compared to 2.76 TeV semi-peripheral PbPb collision data, collected during the 2011 PbPb run, covering a similar range of particle multiplicities. The observed correlations are characterized by the near-side (abs(Delta(phi)~0) associated pair yields and the azimuthal anisotropy Fourier harmonics (v[n]). The second-order (v[2]) and third-order (v[3]) anisotropy harmonics are extracted using the two-particle azimuthal correlation technique. A four-particle correlation method is also applied to obtain the value of v[2] and further explore the multi-particle nature of the correlations. Both associated pair yields and anisotropy harmonics are studied as a function of particle multiplicity and transverse momentum. The associated pair yields, the four-particle v[2], and the v[3] become apparent at about the same multiplicity. A remarkable similarity in the v[3] signal as a function of multiplicity is observed between the pPb and PbPb systems. Predictions based on the color glass condensate and hydrodynamic models are compared to the experimental results

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