The CMS muon detector system, muon reconstruction software, and high-level trigger underwent significant changes in 2013-2014 in preparation for running at higher LHC collision energy and instantaneous luminosity. The performance of the modified system is studied using proton-proton collision data at center-of-mass energy √ s = 13 TeV, collected at the LHC in 2015 and 2016. The measured performance parameters, including spatial resolution, efficiency, and timing, are found to meet all design specifications and are well reproduced by simulation. Despite the more challenging running conditions, the modified muon system is found to perform as well as, and in many aspects better than, previously. We dedicate this paper to the memory of Prof. Alberto Benvenuti, whose work was fundamental for the CMS muon detector.
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
The second-order azimuthal anisotropy Fourier harmonics, v 2 , are obtained in p-Pb and PbPb collisions over a wide pseudorapidity (η) range based on correlations among six or more charged particles. The p-Pb data, corresponding to an integrated luminosity of 35 nb −1 , were collected during the 2013 LHC p-Pb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. A sample of semiperipheral PbPb collision data at ffiffiffiffiffiffiffi ffi s NN p ¼ 2.76 TeV, corresponding to an integrated luminosity of 2.5 μb −1 and covering a similar range of particle multiplicities as the p-Pb data, is also analyzed for comparison. The six-and eight-particle cumulant and the Lee-Yang zeros methods are used to extract the v 2 coefficients, extending previous studies of two-and four-particle correlations. For both the p-Pb and PbPb systems, the v 2 values obtained with correlations among more than four particles are consistent with previously published four-particle results. These data support the interpretation of a collective origin for the previously observed long-range (large Δη) correlations in both systems. The ratios of v 2 values corresponding to correlations including different numbers of particles are compared to theoretical predictions that assume a hydrodynamic behavior of a p-Pb system dominated by fluctuations in the positions of participant nucleons. These results provide new insights into the multiparticle dynamics of collision systems with a very small overlapping region. DOI: 10.1103/PhysRevLett.115.012301 PACS numbers: 25.75.Gz Measurements at the CERN LHC have led to the discovery of two-particle azimuthal correlation structures at large relative pseudorapidity (long range) in protonproton (pp) [1] and proton-lead (p-Pb) [2][3][4][5] collisions. Similar long-range structure has also been observed for ffiffiffiffiffiffiffi ffi [6,7]. The results extend previous studies of relativistic heavy-ion collisions, such as for the copper-copper [8], gold-gold [8][9][10][11][12], and lead-lead (PbPb) [13][14][15][16][17][18] systems, where similar long-range, two-particle correlations at small relative azimuthal angle jΔϕj ≈ 0 were first observed. A fundamental question is whether the observed behavior results from correlations exclusively between particle pairs, or if it is a multiparticle, collective effect. It has been suggested that the hydrodynamic collective flow of a strongly interacting and expanding medium [19][20][21] is responsible for these long-range correlations in central and midcentral heavy-ion collisions. The origin of the observed long-range correlations in collision systems with a small overlapping region, such as for pp and p-Pb collisions, is not clear since for these systems the formation of an extended hot medium is not necessarily expected. Various theoretical models have been proposed to interpret the pp [22,23] and p-Pb results, including initial-state gluon saturation without any final state interactions [24,25] and, similar to what is thought to occur in heavi...
The cross section for the diffractive deep-inelastic scattering process ep → eXp is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data analysed cover the range x IP < 0.1 in fractional proton longitudinal momentum loss, 0.08 < |t| < 0.5 GeV −2 in squared four-momentum transfer at the proton vertex, 2 < Q 2 < 50 GeV 2 in photon virtuality and 0.004 < β = x/x IP < 1, where x is the Bjorken scaling variable. For x IP < ∼ 10 −2 , the differential cross section has a dependence of approximately dσ/dt ∝ e 6t , independently of x IP , β and Q 2 within uncertainties. The cross section is also measured triple differentially in x IP , β and Q 2 . The x IP dependence is interpreted in terms of an effective pomeron trajectory with intercept α IP (0) = 1.114±0.018 (stat.)±0.012 (syst.) +0.040 −0.020 (model) and a sub-leading exchange. The data are in good agreement with an H1 measurement for which the event selection is based on a large gap in the rapidity distribution of the final state hadrons, after accounting for proton dissociation contributions in the latter. Within uncertainties, the dependence of the cross section on x and Q 2 can thus be factorised from the dependences on all studied variables which characterise the proton vertex, for both the pomeron and the sub-leading exchange.
A search for a doubly-charged Higgs boson in pp collisions at √ s = 7 TeV is presented. The data correspond to an integrated luminosity of 4.9 fb −1 , collected by the CMS experiment at the LHC. The search is performed using events with three or more isolated charged leptons of any flavor, giving sensitivity to the decays of pair-produced triplet components Φ ++ Φ −− , and Φ ++ Φ − from associated production. No excess is observed compared to the background prediction, and upper limits at the 95 % confidence level are set on the Φ ++ production cross section, under specific assumptions on its branching fractions. Lower bounds on the Φ ++ mass are reported, providing significantly more stringent constraints than previously published limits.
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