Search for the standard model Higgs boson produced in association with W and Z bosons in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the rapidity and transverse momentum distributions of Z bosons in pp collisions at root(s)=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Jet production rates in association with W and Z bosons in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for a narrow, spin-2 resonance decaying to a pair of Z bosons in the qq̄ℓ+ℓ- final state

Results are presented from a search for a narrow, spin-2 resonance decaying into a pair of Z bosons, with one Z-boson decaying into leptons (e+e- or μ+μ-) and the other into jets. An example of such a resonance is the Kaluza-Klein graviton, GKK, predicted in Randall-Sundrum models. The analysis is based on a 4.9 fb-1 sample of proton-proton collisions at a center-of-mass energy of 7 TeV, collected with the CMS detector at the LHC. Kinematic and topological properties including decay angular distributions are used to discriminate between signal and background. No evidence for a resonance is observed, and upper limits on the production cross sections times branching fractions are set. In two models that predict Z-boson spin correlations in graviton decays, graviton masses are excluded lower than a value which varies between 610 and 945 GeV, depending on the model and the strength of the graviton couplings. © 2012 CERN.

Search for anomalous production of highly boosted Z bosons decaying to mu(+)mu(-) in proton-proton collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for top-squark pairs decaying into Higgs or Z bosons in pp collisions at root s=8 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Study of final-state radiation in decays of Z bosons produced in pp collisions at 7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Zweischleifenkorrekturen zum leptonischen Zerfall des Z-Bosons

Im Rahmen der vorliegenden Dissertation wurde, basierend auf der Parallel-/Orthogonalraum-Methode, eine neue Methode zur Berechnung von allgemeinen massiven Zweischleifen-Dreipunkt-Tensorintegralen mit planarer und gedrehter reduzierter planarer Topologie entwickelt. Die Ausarbeitung und Implementation einer Tensorreduktion fuer Integrale, welche eine allgemeine Tensorstruktur im Minkowski-Raum besitzen koennen, wurde durchgefuehrt. Die Entwicklung und Implementation eines Algorithmus zur semi-analytischen Berechnung der schwierigsten Integrale, die nach der Tensorreduktion verbleiben, konnte vollendet werden. (Fuer die anderen Basisintegrale koennen wohlbekannte Methoden verwendet werden.) Die Implementation ist bezueglich der UV-endlichen Anteile der Masterintegrale, die auch nach Tensorreduktion noch die zuvor erwaehnten Topologien besitzen, abgeschlossen. Die numerischen Integrationen haben sich als stabil erwiesen. Fuer die verbleibenden Teile des Projektes koennen wohlbekannte Methoden verwendet werden. In weiten Teilen muessen lediglich noch Links zu existierenden Programmen geschrieben werden. Fuer diejenigen wenigen verbleibenden speziellen Topologien, welche noch zu implementieren sind, sind (wohlbekannte) Methoden zu implementieren. Die Computerprogramme, die im Rahmen dieses Projektes entstanden, werden auch fuer allgemeinere Prozesse in das xloops-Projekt einfliessen. Deswegen wurde sie soweit moeglich fuer allgemeine Prozesse entwickelt und implementiert. Der oben erwaehnte Algorithmus wurde insbesondere fuer die Evaluation der fermionischen NNLO-Korrekturen zum leptonischen schwachen Mischungswinkel sowie zu aehnlichen Prozessen entwickelt. Im Rahmen der vorliegenden Dissertation wurde ein Grossteil der fuer die fermionischen NNLO-Korrekturen zu den effektiven Kopplungskonstanten des Z-Zerfalls (und damit fuer den schachen Mischungswinkel) notwendigen Arbeit durchgefuehrt.

Production of Z bosons in proton-proton collisions at root out s = 10 TeV: Expectations for early measurements at the ATLAS experiment

The production of the Z boson in proton-proton collisions at the LHC serves as a standard candle at the ATLAS experiment during early data-taking. The decay of the Z into an electron-positron pair gives a clean signature in the detector that allows for calibration and performance studies. The cross-section of ~ 1 nb allows first LHC measurements of parton density functions. In this thesis, simulations of 10 TeV collisions at the ATLAS detector are studied. The challenges for an experimental measurement of the cross-section with an integrated luminositiy of 100 pb−1 are discussed. In preparation for the cross-section determination, the single-electron efficiencies are determined via a simulation based method and in a test of a data-driven ansatz. The two methods show a very good agreement and differ by ~ 3% at most. The ingredients of an inclusive and a differential Z production cross-section measurement at ATLAS are discussed and their possible contributions to systematic uncertainties are presented. For a combined sample of signal and background the expected uncertainty on the inclusive cross-section for an integrated luminosity of 100 pb−1 is determined to 1.5% (stat) +/- 4.2% (syst) +/- 10% (lumi). The possibilities for single-differential cross-section measurements in rapidity and transverse momentum of the Z boson, which are important quantities because of the impact on parton density functions and the capability to check for non-pertubative effects in pQCD, are outlined. The issues of an efficiency correction based on electron efficiencies as function of the electron’s transverse momentum and pseudorapidity are studied. A possible alternative is demonstrated by expanding the two-dimensional efficiencies with the additional dimension of the invariant mass of the two leptons of the Z decay.

Measurement of Zγ production in pp̅ collisions at √s=1.96 TeV

The production rate and kinematics of photons produced in association with Z bosons are studied using 2/fb of p\bar{p} collision data collected at the Collider Detector at Fermilab. The cross section for p\bar{p} -> l^+ l^- gamma + X (where the leptons l are either muons or electrons with dilepton mass M_{ll} > 40 GeV/c^2, and where the photon has transverse energy Et_{gamma} > 7 GeV and is well separated from the leptons) is 4.6 +/- 0.2 (stat) +/- 0.3 (syst) +/- 0.3 (lum) pb, which is consistent with standard model expectations. We use the photon Et distribution from Z-gamma events where the Z has decayed to mu^+ mu^-, e^+ e^-, or nu\bar{nu} to set limits on anomalous (non-standard-model) trilinear couplings between photons and Z bosons.

Signals of additional Z ` boson in e(+)e(-) -> W+W- at the ILC with polarized beams

We consider the possibility of fingerprinting the presence of heavy additional Z' bosons that arise naturally in extensions of the standard model such as E-6 models and left-right symmetric models, through their mixing with the standard model Z boson. By considering a class of observables including total cross sections, energy distributions and angular distributions of decay leptons we find significant deviation from the standard model predictions for these quantities with right-handed electrons and left-handed positrons at root s= 800GeV. The deviations being less pronounced at smaller centre of mass energies as the models are already tightly constrained. Our work suggests that the ILC should have a strong beam polarization physics program particularly with these configurations. On the other hand, a forward backward asymmetry and lepton fraction in the backward direction are more sensitive to new physics with realistic polarization due to interesting interplay with the neutrino t-channel diagram. This process complements the study of fermion pair production processes that have been considered for discrimination between these models.

Measurement of the ratios of the Z/gamma*+ >= n jet production cross sections to the total inclusive Z/gamma* cross section in p(p)over-bar collisions at root s=1.96 TeV

We present a study of events with Z bosons and associated jets produced at the Fermilab Tevatron collider in p p collisions at a center of mass energy of 1.96 TeV The data sample consists of nearly 14000 Z/gamma* -> e(+)e(-) candidates corresponding to an integrated luminosity of 0.4 fb(-1) collected with the D circle divide detector. Ratios of the Z/gamma*+ >= n jet cross sections to the total inclusive Z/gamma* cross section have been measured for n = 1-4 jets, and found to be in good agreement with a next-to-leading order QCD calculation and with a tree-level QCD prediction with parton shower simulation and hadronization. Published by Elsevier B.V

Measurement of the normalized Z/gamma* -> mu(+)mu(-) transverse momentum distribution in p(p)over-bar collisions at root s=1.96 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Study of Z Boson Production in PbPb Collisions at root s(NN)=2.76 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Forward energy flow, central charged-particle multiplicities, and pseudorapidity gaps in W and Z boson events from pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)