Universidad Iberoamericana Ciudad de México

About: Universidad Iberoamericana Ciudad de México is a education organization based out in Mexico City, Mexico. It is known for research contribution in the topics: Large Hadron Collider & Standard Model. The organization has 2259 authors who have published 3981 publications receiving 109298 citations.

Search for physics beyond the standard model in events with two leptons of same sign, missing transverse momentum, and jets in proton–proton collisions at √s=13TeV

Abstract: A data sample of events from proton-proton collisions with two isolated same-sign leptons, missing transverse momentum, and jets is studied in a search for signatures of new physics phenomena by the CMS Collaboration at the LHC. The data correspond to an integrated luminosity of 35.9 inverse femtobarns, and a center-of-mass energy of 13 TeV. The properties of the events are consistent with expectations from standard model processes, and no excess yield is observed. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos, squarks, and same-sign top quarks, as well as top-quark associated production of a heavy scalar or pseudoscalar boson decaying to top quarks, and on the standard model production of events with four top quarks. The observed lower mass limits are as high as 1500 GeV for gluinos, 830 GeV for bottom squarks. The excluded mass range for heavy (pseudo)scalar bosons is 350-360 (350-410) GeV. Additionally, model-independent limits in several topological regions are provided, allowing for further interpretations of the results.

Measurement of the weak mixing angle using the forward-backward asymmetry of Drell-Yan events in pp collisions at 8 TeV.

Abstract: A measurement is presented of the effective leptonic weak mixing angle ( $\sin ^2\theta ^{\ell \text {eff}}$ ) using the forward–backward asymmetry of Drell–Yan lepton pairs ( $\mu \mu $ and $\mathrm {e}$ $\mathrm {e}$ ) produced in proton–proton collisions at $\sqrt{s}=8\,\text {TeV} $ at the CMS experiment of the LHC. The data correspond to integrated luminosities of 18.8 and $19.6{{\,\text {fb}^{-1}}} $ in the dimuon and dielectron channels, respectively, containing 8.2 million dimuon and 4.9 million dielectron events. With more events and new analysis techniques, including constraints obtained on the parton distribution functions from the measured forward–backward asymmetry, the statistical and systematic uncertainties are significantly reduced relative to previous CMS measurements. The extracted value of $\sin ^2\theta ^{\ell \text {eff}}$ from the combined dilepton data is $\sin ^2\theta ^{\ell \text {eff}} =0.23101\pm 0.00036\,\text {(stat)} \pm 0.00018\,\text {(syst)} \pm 0.00016\,\text {(theo)} \pm 0.00031\,\text {(parton distributions in proton)}=0.23101 \pm 0.00053$ .

Measurements of tt¯differential cross sections in proton-proton collisions at √s=13 TeV using events containing two leptons

Abstract: Measurements of differential top quark pair $ \mathrm{t}\overline{\mathrm{t}} $ cross sections using events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV containing two oppositely charged leptons are presented. The data were recorded by the CMS experiment at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb$^{−1}$. The differential cross sections are presented as functions of kinematic observables of the top quarks and their decay products, the $ \mathrm{t}\overline{\mathrm{t}} $ system, and the total number of jets in the event. The differential cross sections are defined both with particle-level objects in a fiducial phase space close to that of the detector acceptance and with parton-level top quarks in the full phase space. All results are compared with standard model predictions from Monte Carlo simulations with next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD) at matrix-element level interfaced to parton-shower simulations. Where possible, parton-level results are compared to calculations with beyond-NLO precision in QCD. Significant disagreement is observed between data and all predictions for several observables. The measurements are used to constrain the top quark chromomagnetic dipole moment in an effective field theory framework at NLO in QCD and to extract $ \mathrm{t}\overline{\mathrm{t}} $ and leptonic charge asymmetries.

Search for Leptoquarks Coupled to Third-Generation Quarks in Proton-Proton Collisions at s =13 TeV

Abstract: Three of the most significant measured deviations from standard model predictions, the enhanced decay rate for B→D(*)τν, hints of lepton universality violation in B→K(*)ll decays, and the anomalous magnetic moment of the muon, can be explained by the existence of leptoquarks (LQs) with large couplings to third-generation quarks and masses at the TeV scale. The existence of these states can be probed at the LHC in high energy proton-proton collisions. A novel search is presented for pair production of LQs coupled to a top quark and a muon using data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb-1, recorded by the CMS experiment. No deviation from the standard model prediction has been observed and scalar LQs decaying exclusively into tμ are excluded up to masses of 1420 GeV. The results of this search are combined with those from previous searches for LQ decays into tτ and bν, which excluded scalar LQs below masses of 900 and 1080 GeV. Vector LQs are excluded up to masses of 1190 GeV for all possible combinations of branching fractions to tμ, tτ and bν. With this analysis, all relevant couplings of LQs with an electric charge of -1/3 to third-generation quarks are probed for the first time.

Measurement of differential and integrated fiducial cross sections for Higgs boson production in the four-lepton decay channel in pp collisions at √s=7 and 8 TeV

Abstract: Differential and integrated fiducial cross sections for the production of four leptons via the H to 4l decays (l = e, mu) are measured in pp collisions at sqrt(s) = 7 and 8 TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 inverse-femtobarns at 7 TeV, and 19.7 inverse-femtobarns at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z to 4l cross section, and its ratio to the H to 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. The integrated H to 4l fiducial cross section is measured to be 0.56 +0.67-0.44 (stat) +0.21-0.06 (syst) fb at 7 TeV, and 1.11 +0.41-0.35 (stat) +0.14-0.10 (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.