Search for physics beyond the standard model in events with τ leptons, jets, and large transverse momentum imbalance in pp collisions at √s = 7 TeV

A search for physics beyond the standard model is performed with events having one or more hadronically decaying τ leptons, highly energetic jets, and large transverse momentum imbalance. The data sample corresponds to an integrated luminosity of 4.98 fb-1 of proton-proton collisions at √ = 7 TeV collected with the CMS detector at the LHC in 2011. The number of observed events is consistent with predictions for standard model processes. Lower limits on the mass of the gluino in supersymmetric models are determined. © 2013 CERN for the benefit of the CMS collaboration.

Observation of a new boson with mass near 125 GeV in pp collisions at √=7 and 8 TeV

A detailed description is reported of the analysis used by the CMS Collaboration in the search for the standard model Higgs boson in pp collisions at the LHC, which led to the observation of a new boson. The data sample corresponds to integrated luminosities up to 5.1 fb-1 at √=7 TeV, and up to 5.3 fb-1 at √ s=8 TeV. The results for five Higgs boson decay modes γγ, ZZ, WW, ττ, and bb, which show a combined local significance of 5 standard deviations near 125 GeV, are reviewed. A fit to the invariant mass of the two high resolution channels, γγ and ZZ → 4ℓ, gives a mass estimate of 125.3 ± 0.4 (stat.) ± 0.5 (syst.) GeV. The measurements are interpreted in the context of the standard model Lagrangian for the scalar Higgs field interacting with fermions and vector bosons. The measured values of the corresponding couplings are compared to the standard model predictions. The hypothesis of custodial symmetry is tested through the measurement of the ratio of the couplings to the W and Z bosons. All the results are consistent, within their uncertainties, with the expectations for a standard model Higgs boson. [Figure not available: see fulltext.] © 2013 CERN for the benefit of the CMS collaboration.

Searches for long-lived charged particles in pp collisions at □ =7 and 8 TeV

Abstract: Results of searches for heavy stable charged particles produced in pp collisions at □ = 7 and 8 TeV are presented corresponding to an integrated luminosity of 5.0 fb-1 and 18.8 fb-1, respectively. Data collected with the CMS detector are used to study the momentum, energy deposition, and time-of-flight of signal candidates. Leptons with an electric charge between e/3 and 8e, as well as bound states that can undergo charge exchange with the detector material, are studied. Analysis results are presented for various combinations of signatures in the inner tracker only, inner tracker and muon detector, and muon detector only. Detector signatures utilized are long time-of-flight to the outer muon system and anomalously high (or low) energy deposition in the inner tracker. The data are consistent with the expected background, and upper limits are set on the production cross section of long-lived gluinos, scalar top quarks, and scalar τ leptons, as well as pair produced long-lived leptons. Corresponding lower mass limits, ranging up to 1322 GeV/c 2 for gluinos, are the most stringent to date. [Figure not available: see fulltext.] © 2013 Cern for the benefit of the CMS collaboration.

Study of exclusive two-photon production of W+W- in pp collisions at √s=7 TeV and constraints on anomalous quartic gauge couplings

A search for exclusive or quasi-exclusive W+W- production by photon-photon interactions, pp → p(*)W +W-p(*), at √s=7 TeV is reported using data collected by the CMS detector with an integrated luminosity of 5.05 fb-1. Events are selected by requiring a μ ±e∓ vertex with no additional associated charged tracks and dilepton transverse momentum p T(μ ±e∓) > 30 GeV. Two events passing all selection requirements are observed in the data, compared to a standard model expectation of 2.2 ± 0.4 signal events with 0.84 ± 0.15 background. The tail of the dilepton p T distribution is studied for deviations from the standard model. No events are observed with p T > 100 GeV. Model-independent upper limits are computed and compared to predictions involving anomalous quartic gauge couplings. The limits on the parameters α0,C W/λ2 with a dipole form factor and an energy cutoff Λcutoff = 500 GeV are of the order of 10-4. © 2013 CERN for the benefit of the CMS collaboration.

Scale-invariant resonance tagging in multijet events and new physics in Higgs pair production

We study resonant pair production of heavy particles in fully hadronic final states by means of jet substructure techniques. We propose a new resonance tagging strategy that smoothly interpolates between the highly boosted and fully resolved regimes, leading to uniform signal efficiencies and background rejection rates across a broad range of masses. Our method makes it possible to efficiently replace independent experimental searches, based on different final state topologies, with a single common analysis. As a case study, we apply our technique to pair production of Higgs bosons decaying into b\overline{b} pairs in generic New Physics scenarios. We adopt as benchmark models radion and massive KK graviton production in warped extra dimensions. We find that despite the overwhelming QCD background, the 4b final state has enough sensitivity to provide a complementary handle in searches for enhanced Higgs pair production at the LHC. © 2013 SISSA.

Measurement of the λb 0 lifetime in pp collisions at √s=7 TeV

A measurement of the λb 0 lifetime using the decay λb 0-1, was recorded with the CMS experiment at the Large Hadron Collider using triggers that selected dimuon events in the J/ψ mass region. The λb 0 lifetime is measured to be 1.503 ± 0.052 (stat.) ± 0.031 (syst.) ps. [Figure not available: see fulltext.] © 2013 Cern for the benefit of the CMS collaboration.

Search for microscopic black holes in pp collisions at √s=8 TeV

A search for microscopic black holes and string balls is presented, based on a data sample of pp collisions at √s=8 TeV recorded by the CMS experiment at the Large Hadron Collider and corresponding to an integrated luminosity of 12 fb-1. No excess of events with energetic multiparticle final states, typical of black hole production or of similar new physics processes, is observed. Given the agreement of the observations with the expected standard model background, which is dominated by QCD multijet production, 95% confidence level limits are set on the production of semiclassical or quantum black holes, or of string balls, corresponding to the exclusions of masses below 4.3 to 6.2 TeV, depending on model assumptions. In addition, model-independent limits are set on new physics processes resulting in energetic multiparticle final states. [Figure not available: see fulltext.] © 2013 CERN for the benefit of the CMS collaboration.

Search in leptonic channels for heavy resonances decaying to long-lived neutral particles

A search is performed for heavy resonances decaying to two long-lived massive neutral particles, each decaying to leptons. The experimental signature is a distinctive topology consisting of a pair of oppositely charged leptons originating at a separated secondary vertex. Events were collected by the CMS detector at the LHC during pp collisions at √s = 7 TeV, and selected from data samples corresponding to 4.1 (5.1) fb-1 of integrated luminosity in the electron (muon) channel. No significant excess is observed above standard model expectations, and an upper limit is set with 95% confidence level on the production cross section times the branching fraction to leptons, as a function of the long-lived massive neutral particle lifetime. Copyright CERN.

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.

Estudo de Monte Carlo da produção de nova ressonância neutra decaindo em dois bósons vetoriais no experimento CMS

Pós-graduação em Física - IFT

Femtoscopia em colisões próton-próton no detector CMS do Large Hadron Collider

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Busca por ressonâncias de grávitons em modelos com dimensões extras no LHC

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Quebra da simetria de sabor na interação de mésons charmosos com o núcleon

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for narrow resonances and quantum black holes in inclusive and b-tagged dijet mass spectra from pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the ZZ production cross section and search for anomalous couplings in 2l2l' final states in pp collisions at root s=7 TeV

A measurement is presented of the ZZ production cross section in the ZZ -> 2l2l' decay mode with l = e, mu and l' = e, mu, tau in proton-proton collisions at root s = 7 TeV with the CMS experiment at the LHC. Results are based on data corresponding to an integrated luminosity of 5.0 fb(-1). The measured cross section sigma(pp -> ZZ) = 6.24(-080)(+0.86) (stat.)(-0.32)(+0.41) (syst.) +/- 0.14 (lumi.) pb is consistent with the standard model predictions. The following limits on ZZZ and ZZ-gamma anomalous trilinear gauge couplings are set at 95% confidence level: -0.011 < f(4)(Z) < 0.012, -0.012 < f(5)(Z) < 0.012, -0.013 < f(4)(gamma) < 0.015, and -0.014 < f(5)(gamma) < 0.014.