Observation of long-range, near-side angular correlations in proton-proton collisions at the LHC

This is the pre-print version of the Published Article, which can be accessed from the link below - Copyright @ 2010 Springer VerlagResults on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (eta) and azimuthal angle (phi). Short-range correlations in Delta(eta), which are studied in minimum bias events, are characterized using a simple "independent cluster" parametrization in order to quantify their strength (cluster size) and their extent in eta (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 inverse nb data set at 7 TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate transverse momentum of 1-3 GeV/c, 2.0< |Delta(eta)| <4.8 and Delta(phi) near 0. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in pp or p p-bar collisions

Observation of long-range, near-side angular correlations in proton-proton collisions at the LHC

Results on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (eta) and azimuthal angle (phi). Short-range correlations in Delta(eta), which are studied in minimum bias events, are characterized using a simple "independent cluster" parametrization in order to quantify their strength (cluster size) and their extent in eta (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 nb(-1) data set at 7TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate p(T) of 1-3 GeV/c, 2.

Search for third-generation scalar leptoquarks and heavy right-handed neutrinos in final states with two tau leptons and two jets in proton-proton collisions at sqrt(s)=13 TeV

A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying τ lepton, and at least two jets, using a s=13 TeV pp collision data sample corresponding to an integrated luminosity of 12.9 fb-1collected with the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction. A limit is set at 95% confidence level on the product of the leptoquark pair production cross section and β2, where β is the branching fraction of leptoquark decay to a τ lepton and a bottom quark. Assuming β = 1, third-generation leptoquarks with masses below 850 GeV are excluded at 95% confidence level. An additional search based on the same event topology involves heavy right-handed neutrinos, NR, and right-handed W bosons, WR, arising in a left-right symmetric extension of the standard model. In this search, WRbosons are assumed to decay to a tau lepton and NRfollowed by the decay of the NRto a tau lepton and an off-shell WRboson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, WRboson masses below 2.9 TeV are excluded at 95% confidence level. These results improve on the limits from previous searches for third-generation leptoquarks and heavy right-handed neutrinos with τ leptons in the final state.[Figure not available: see fulltext.]

Search for third-generation scalar leptoquarks and heavy right-handed neutrinos in final states with two tau leptons and two jets in proton-proton collisions at √s=13 TeV

A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying τ lepton, and at least two jets, using a s√=13s=13 TeV pp collision data sample corresponding to an integrated luminosity of 12.9 fb-1 collected with the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction. A limit is set at 95% confidence level on the product of the leptoquark pair production cross section and β2, where β is the branching fraction of leptoquark decay to a τ lepton and a bottom quark. Assuming β = 1, third-generation leptoquarks with masses below 850 GeV are excluded at 95% confidence level. An additional search based on the same event topology involves heavy right-handed neutrinos, NR, and right-handed W bosons, WR, arising in a left-right symmetric extension of the standard model. In this search, WR bosons are assumed to decay to a tau lepton and NR followed by the decay of the NR to a tau lepton and an off-shell WR boson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, WR boson masses below 2.9 TeV are excluded at 95% confidence level. These results improve on the limits from previous searches for third-generation leptoquarks and heavy right-handed neutrinos with τ leptons in the final state

Alignment of the CMS Muon System with Cosmic-Ray and Beam-Halo Muons

Abstract The CMS muon system has been aligned using cosmic-ray muons collected in 2008 and beam-halo muons from the 2008 LHC circulating beam tests. After alignment, the resolution of the most sensitive coordinate is 80 microns for the relative positions of superlayers in the same barrel chamber and 270 microns for the relative positions of endcap chambers in the same ring structure. The resolution on the position of the central barrel chambers relative to the tracker is comprised between two extreme estimates, 200 and 700 microns, provided by two complementary studies. With minor modifications, the alignment procedures can be applied using muons from LHC collisions, leading to additional significant improvements. * See Appendix A for the list of collaboration members arXiv:0911.4022v2 [physics.ins-det] 8 Feb 2010 FERMILAB-PUB-10-163-CMS Introduction The primary goal of the Compact Muon Solenoid (CMS) experiment [1] is to explore particle physics at the TeV energy scale exploiting the proton-proton collisions delivered by the Large Hadron Collider (LHC) The muon system consists of hundreds of independent tracking chambers mounted within the CMS magnetic field return yoke. Three technologies are employed: Drift Tube (DT) chambers on the five modular wheels of the barrel section, Cathode Strip Chambers (CSC) on the six endcap disks (illustrated in Figs. 1 and 2) and Resistive Plate Chambers (RPC) throughout. The DTs and CSCs are sufficiently precise to contribute to the momentum resolution of highmomentum muons (several hundred GeV/c) assuming that these chambers are well-aligned relative to the CMS tracker, a one-meter radius silicon strip and pixel detector. Between the tracker and the muon system are electromagnetic and hadronic calorimeters (ECAL and HCAL, respectively) for particle identification and energy measurement, as well as the solenoid coil for producing an operating magnetic field strength of 3.8 T in which to measure charged-particle momenta (all shown in The CMS collaboration is developing multiple techniques to align the DT and CSC chambers and their internal layers. Photogrammetry and in-situ measurement devices [3] provide realtime monitoring of potential chamber movements on short timescales and measurements of degrees of freedom to which tracks are only weakly sensitive. Track-based alignment, the subject of this paper, optimizes component positions for a given set of tracks, directly relating the active elements of the detectors traversed by the charged particles in a shared coordinate frame. Methods using tracks are employed both to align nearby components relative to one another and to align all muon chambers relative to the tracker. A challenge to track-based alignment in the CMS muon system is the presence of large quantities of material between the chambers. As a central design feature of the detector, 20-60 cm layers of steel are sandwiched between the chambers to concentrate the magnetic field and absorb beam-produced hadrons. Consequently, uncertainties in track trajectories become significant as muons propagate through the material, making it necessary to develop alignment procedures that are insensitive to scattering, even though typical deviations in the muon trajectories (3-8 mm) are large compared to the intrinsic spatial resolution (100-300 µm). Two types of approaches are presented in this paper: the relative alignment of nearby structures, which avoids extrapolation of tracks through material but does not relate distant coordinate frames to each other, and the alignment using tracks reconstructed in the tracker, which allows for a more sophisticated treatment of propagation effects by simplifying the interdependence of alignment parameters. This paper begins with a brief overview of the geometry of the muon system and conventions to be used thereafter (Section 2), followed by presentations of three alignment procedures: (a) internal alignment of layers within DT chambers using a combination of locally fitted track segments and survey measurements (Section 3); (b) alignment of groups of overlapping CSC chambers relative to one another, using only (c) alignment of each chamber relative to the tracker, using the tracks from the tracker, propagated to the muon system with a detailed map of the magnetic field and material distribution of CMS (Section 5). Procedure (c), above, completes the alignment, relating all local coordinate frames to a shared frame. Its performance is greatly improved by supplying internally aligned chambers from procedure (a), such that only rigid-body transformations of whole chambers need to be considered. Procedures (b) and (c) both align CSC chambers relative to one another, but in different ways: (b) does not need many tracks, only about 1000 per chamber, to achieve high precision, and (c) additionally links the chambers to the tracker. With the first LHC collisions, groups of CSCs will be interaligned using (b) and these rigidbody groups will be aligned relative to the tracker with (c). As more data become available, comparisons of results from (b) and (c) yield highly sensitive tests of systematic errors in (c). Although the ideal tracks for these procedures are muons from LHC collisions, this paper focuses on application of the procedures using currently available data, namely cosmic rays (a and c) and beam-halo muons from circulating LHC beam tests in September 2008 (b). In particular, (c) requires a magnetic field to select high-quality, high-momentum muons and concurrent operation of the tracker and muon systems. The CMS Collaboration conducted a monthlong data-taking exercise known as the Cosmic Run At Four Tesla (CRAFT) during OctoberNovember 2008, with the goal of commissioning the experiment for extended operation The formalism and results of each procedure are presented together. Details of the data transfer and the computing model which were used to implement these procedures are described in Ref. Geometry of the Muon System and Definitions Muon chambers are independent, modular track detectors, each containing 6-12 measurement layers, sufficient to determine the position and direction of a passing muon from the intersections of its trajectory with the layer planes (&quot;hits&quot;). The DT layers are oriented nearly perpendicular to lines radially projected from the beamline, and CSC layers are perpendicular to lines parallel with the beamline. Hits are initially expressed in a local coordinate frame (x, y, z) defined by the layers: z = 0 is the plane of the layer and x is the more precisely measured (or the only measured) of the two plane coordinates. On CSC layers, the most precise measurement is given by cathode strips, which fan radially from the beamline A semi-local coordinate system for the entire chamber is defined with x, y, and z axes nominally parallel to the layers&apos; axes, but with a single origin. Within this common frame, the positions of hits from different layers can be related to each other and combined by a linear fit into segments with position (x,ȳ) and direction ( dx dz , dy dz ). The nominal x direction of every chamber is perpendicular to the beamline and radial projections from the beamline

Measurements of inclusive W and Z cross sections in pp collisions at √s = 7 TeV The CMS collaboration

Measurements of inclusive W and Z boson production cross sections in pp collisions at √s = 7 TeV are presented, based on 2.9 pb-1 of data recorded by the CMS detector at the LHC. The measurements, performed in the electron and muon decay channels, are combined to give σ(pp → WX) × B(W → l?) = 9.95 ± 0.07 (stat.) ± 0.28 (syst.) ± 1.09 (lumi.) nb and σ(pp → ZX) × B(Z → l +l-) = 0.931 ± 0.026 (stat.) ± 0.023 (syst.) ± 0.102 (lumi.) nb, where l stands for either e or μ. Theoretical predictions, calculated at the next-to-next-to-leading order in QCD using recent parton distribution functions, are in agreement with the measured cross sections. Ratios of cross sections, which incur an experimental systematic uncertainty of less than 4%, are also reported