Papers by Valentina Avila
The results of a search for pair production of a heavy, top-like quark, t , in the decay mode t t... more The results of a search for pair production of a heavy, top-like quark, t , in the decay mode t t → bW + bW − → b + ν b − ν are presented. The search is performed with a data sample corresponding to an integrated luminosity of 5.0 fb −1 in pp collisions at a center-of-mass energy of 7 TeV, collected by the CMS experiment at the LHC. The observed number of events agrees with the expectation from standard model processes, and no evidence of t t production is found. Upper limits on the production cross section as a function of t mass are presented, and t masses below 557 GeV/c 2 are excluded at the 95% confidence level.
Measurement of the underlying event activity in pp collisions at √ s = 0.9 and 7 TeV with the nov... more Measurement of the underlying event activity in pp collisions at √ s = 0.9 and 7 TeV with the novel jet-area/median approach The CMS Collaboration *
Forward-backward asymmetry of Drell-Yan lepton pairs in pp collisions at √ s = 7 TeV
Inclusive and differential measurements of the tt charge asymmetry in proton-proton collisions at... more Inclusive and differential measurements of the tt charge asymmetry in proton-proton collisions at √ s = 7 TeV
Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb −1 of i... more Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb −1 of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at √ s = 7 TeV. 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 lepton (e, µ), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W boson that couples to fermions with the same coupling constant as the W but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W gauge coupling for a set of left-and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.
The CMS muon system has been aligned using cosmic-ray muons collected in 2008 and beam-halo muons... more 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.
A measurement is presented of W-boson production in PbPb collisions carried out at a nucleon-nucl... more A measurement is presented of W-boson production in PbPb collisions carried out at a nucleon-nucleon (NN) centre-of-mass energy √ s NN of 2.76 TeV at the LHC using the CMS detector. In data corresponding to an integrated luminosity of 7.3 µb −1 , the number of W → µν µ decays is extracted in the region of muon pseudorapidity |η µ | < 2.1 and transverse momentum p µ T > 25 GeV/c. Yields of muons found per unit of pseudorapidity correspond to (159 ± 10(stat.) ± 12( syst.)) × 10 −8 W + and (154 ± 10(stat.) ± 12(syst.)) × 10 −8 W − bosons per minimum-bias PbPb collision. The dependence of W production on the centrality of PbPb collisions is consistent with a scaling of the yield by the number of incoherent NN collisions. The yield of W bosons is also studied in a sample of pp interactions at √ s = 2.76 TeV corresponding to an integrated luminosity of 231 nb −1 . The individual W + and W − yields in PbPb and pp collisions are found to agree, once the neutron and proton content in Pb nuclei is taken into account. Likewise, the difference observed in the dependence of the positive and negative muon production on pseudorapidity is consistent with next-toleading-order perturbative QCD calculations.
The resolution and the linearity of time measurements made with the CMS electromagnetic calorimet... more The resolution and the linearity of time measurements made with the CMS electromagnetic calorimeter are studied with samples of data from test beam electrons, cosmic rays, and beam-produced muons. The resulting time resolution measured by lead tungstate crystals is better than 100 ps for energy deposits larger than 10 GeV. Crystal-to-crystal synchronization with a precision of 500 ps is performed using muons produced with the first LHC beams in 2008.
The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-takin... more 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.
A search is presented for physics beyond the standard model (BSM) in final states with a pair of ... more A search is presented for physics beyond the standard model (BSM) in final states with a pair of opposite-sign isolated leptons accompanied by jets and missing transverse energy. The search uses LHC data recorded at a center-of-mass energy √ s = 7 TeV with the CMS detector, corresponding to an integrated luminosity of approximately 5 fb −1 . Two complementary search strategies are employed. The first probes models with a specific dilepton production mechanism that leads to a characteristic kinematic edge in the dilepton mass distribution. The second strategy probes models of dilepton production with heavy, colored objects that decay to final states including invisible particles, leading to very large hadronic activity and missing transverse energy. No evidence for an event yield in excess of the standard model expectations is found. Upper limits on the BSM contributions to the signal regions are deduced from the results, which are used to exclude a region of the parameter space of the constrained minimal supersymmetric extension of the standard model. Additional information related to detector efficiencies and response is provided to allow testing specific models of BSM physics not considered in this paper. T and hadronic energy, while the counting experiments do not as-2 3 Event Selection sume a specific dilepton production mechanism and are also sensitive to BSM scenarios that produce lepton pairs with uncorrelated flavor.
Este proyecto se adelanta como un primer acercamiento arqueológico a un área que antes no había s... more Este proyecto se adelanta como un primer acercamiento arqueológico a un área que antes no había sido estudiada, y que resulta de gran interés para establecer las relaciones prehispánicas que pudieron darse entre los habitantes de la costa pacífica y los de la cordillera occidental, por ser el río Dagua, una ruta natural de acceso que facilita la comunicación entre estas dos grandes regiones. Los trabajos se iniciaron en el bajo río Pepitas, que desemboca en el Dagua en la mitad de su curso al océano Pacífico. En una zona conocida como Vega Grande, localizada a tres horas a pie de la desembocadura del Pepitas en el Dagua, se realizó un reconocimiento arqueológico sistemático ... de un transecto que atraviesa la vega del río a 500 mts. sobre el nivel del mar, y remonta las cumbres contiguas, hasta alcanzar aproximadamente los 900 metros sobre el nivel del mar IGAC,1980. En esta franja de terreno se documentaron 94 plataformas artificiales en ladera o tambos, elaborados por sus habitantes prehispámcos. Estas plataformas dan razón de la densidad de población del sitio, a la vez que nos muestra la influencia del hombre precolombino en el paisaje y manejo de un medio ambiente determinado. A lo largo de este transecto se escogieron dos sitios para ser excavados de manera parcial: El Paraíso II, situado a 700 metros sobre el nivel del mar, y El Puente, situado a 500 metros sobre el nivel del mar, a orillas del Pepitas.
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Papers by Valentina Avila