Observation of Z decays to four leptons with the CMS detector at the LHC

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Performance of the CMS Level-1 trigger during commissioning with cosmic ray muons and LHC beams

The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-taking runs in 2008, and to estimate the level of detector noise. This paper describes the trigger components used, the algorithms that were executed, and the trigger synchronisation. Using data from extended cosmic ray runs, the muon, electron/photon, and jet triggers have been validated, and their performance evaluated. Efficiencies were found to be high, resolutions were found to be good, and rates as expected. © 2010 IOP Publishing Ltd and SISSA.

Performance of the CMS hadron calorimeter with cosmic ray muons and LHC beam data

The CMS Hadron Calorimeter in the barrel, endcap and forward regions is fully commissioned. Cosmic ray data were taken with and without magnetic field at the surface hall and after installation in the experimental hall, hundred meters underground. Various measurements were also performed during the few days of beam in the LHC in September 2008. Calibration parameters were extracted, and the energy response of the HCAL determined from test beam data has been checked. © 2010 IOP Publishing Ltd and SISSA.

Performance of CMS hadron calorimeter timing and synchronization using test beam, cosmic ray, and LHC beam data

This paper discusses the design and performance of the time measurement technique and of the synchronization systems of the CMS hadron calorimeter. Time measurement performance results are presented from test beam data taken in the years 2004 and 2006. For hadronic showers of energy greater than 100 GeV, the timing resolution is measured to be about 1.2 ns. Time synchronization and out-of-time background rejection results are presented from the Cosmic Run At Four Tesla and LHC beam runs taken in the Autumn of 2008. The inter-channel synchronization is measured to be within 2 ns. © 2010 IOP Publishing Ltd and SISSA.

Measurement of the underlying event activity at the LHC with √s = 7 TeV and comparison with √s = 0:9 TeV

A measurement of the underlying activity in events with a jet of transverse momentum in the several GeV region is performed in proton-proton collisions at √ s = 0:9 and 7TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |η|<2 and transverse momentum pT >0:5 GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-pT sum of the particles in the transverse region is observed with increasing pT of the leading trackjet, followed by a much slower rise above a few GeV/c. For track-jet pT larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centreof- mass energy increase from 0:9 to 7TeV. Predictions of several QCD-inspired models as implemented in pythia are compared to the data.

Search for third-generation leptoquarks and scalar bottom quarks in pp collisions at √s=7Tev

Results are presented from a search for third-generation leptoquarks and scalar bottom quarks in a sample of proton-proton collisions at √s=7Tev collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.7 fb-1. A scenario where the new particles are pair produced and each decays to a b quark plus a tau neutrino or neutralino is considered. The number of observed events is found to be in agreement with the standard model prediction. Upper limits are set at 95% confidence level on the production cross sections. Leptoquarks with masses below ~450 GeV are excluded. Upper limits in the mass plane of the scalar quark and neutralino are set such that scalar bottom quark masses up to 410 GeV are excluded for neutralino masses of 50 GeV. © 2012 CERN for the benefit of CMS collaboration.

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at s=7TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0fb-1 of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at s=7TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W'→tb, leading to a final state signature with a single electron or muon, missing transverse energy, and jets, at least one of which is identified as a b-jet. A W' boson that couples to the right-handed (left-handed) chiral projections of the fermions with the same coupling constants as the W is excluded for masses below 1.85 (1.51) TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge couplings for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits. © 2012 CERN.

Measurement of differential top-quark-pair production cross sections in pp collisions at √s = 7TeV

Normalised differential top-quark-pair production cross sections are measured in pp collisions at a centre-of-mass energy of 7 TeVat the LHC with the CMS detector using data recorded in 2011 corresponding to an integrated luminosity of 5. 0 fb-1. The measurements are performed in the lepton+jets decay channels (e+jets and μ+jets) and the dilepton decay channels (e+}e-, μ+μ-, and μ±e∓). The tt̄ differential cross section is measured as a function of kinematic properties of the final-state charged leptons and jets associated to b quarks, as well as those of the top quarks and the tt̄ system. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision. No significant deviations from the standard model are observed. © 2013 CERN for the benefit of the CMS collaboration.

Search for exotic resonances in diboson final states with the CMS detector at the LHC

The results of searches for new resonances decaying to a pair of massive vector bosons (WW, WZ, ZZ) are presented. All searches are performed using 5.0 fb-1 of proton-proton collisions, at TeV of center of mass energy, collected by the Compact Muon Solenoid detector at the Large Hadron Collider. No significant excess compared to the standard model background expectation is observed, and upper limits at 95% confidence level are set on the production cross section times the branching fraction of hypothetical particles decaying to a pair of vector bosons. The results are interpreted in the context of several benchmark models, such as the Randall-Sundrum gravitons, the Sequential Standard Model W′, and Technicolor. Graviton resonances in the Randall-Sundrum model with masses smaller than 940 GeV/c2, for coupling parameter k/MPl = 0.05 are excluded. Bulk (ADPS) Randall-Sundrum gravitons with masses smaller than 610 GeV/c2 are excluded, for k/MPl = 0.05. Sequential Standard Model W′ with masses smaller than 1143 GeV/c2 are excluded, as well as ρTC in the 167-687 GeV/c2 mass range, in Low Scale Technicolor models with M(πTC) = 3/4 M(ρTC) - 25 GeV/c2. © 2013 IOP Publishing Ltd.

Identification of b-quark jets with the CMS experiment

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for supersymmetry in events with b jets and missing transverse momentum at the LHC

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Alignment of the CMS tracker with LHC and cosmic ray data

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of jet multiplicity distributions in t(t)over-bar production in pp collisions at root s=7TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Constraints on parton distribution functions and extraction of the strong coupling constant from the inclusive jet cross section in pp collisions at root s=7TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Sensitivity of the Top quark mass measurement with the CMS experiment at LHC using t-tbar multijet simulated events

This thesis comes after a strong contribution on the realization of the CMS computing system, which can be seen as a relevant part of the experiment itself. A physics analysis completes the road from Monte Carlo production and analysis tools realization to the final physics study which is the actual goal of the experiment. The topic of physics work of this thesis is the study of tt events fully hadronic decay in the CMS experiment. A multi-jet trigger has been provided to fix a reasonable starting point, reducing the multi-jet sample to the nominal trigger rate. An offline selection has been provided to reduce the S/B ratio. The b-tag is applied to provide a further S/B improvement. The selection is applied to the background sample and to the samples generated at different top quark masses. The top quark mass candidate is reconstructed for all those samples using a kinematic fitter. The resulting distributions are used to build p.d.f.’s, interpolating them with a continuous arbitrary curve. These curves are used to perform the top mass measurement through a likelihood comparison