Session R12: Electroweak I

Search for $ZZ$ production in $p\overline{p}$ collisions using the D0 Detector

Results are presented from a search for $ZZ$ production at the Fermilab Tevatron collider, with emphasis on the mode $p\overline{p} \rightarrow ZZ \rightarrow v\overline{v}l\overline{l}$ with $l$ a charged lepton. The data sample consists of approximately 2 fb$^{-1}$ of data collected by the D0 experiment during Tevatron Run II.   

Measurement of Di-boson Production in Electron Plus Jets Decays

We present a measurement of the simultaneous production of a W boson in association with a second electroweak boson (W of Z) in proton anti-proton collisions at $\sqrt{s} =$~1.96 TeV. We consider events with one electron, missing transverse energy, and at least two jets. Data used in this analysis consists of 1 fb$^{-1}$ of integrated luminosity collected by the D0 detector at the Tevatron.   

Study of Diboson Physics with the ATLAS Detector at LHC

The talk will present studies of Standard Model diboson productions (WW,WZ,ZZ,W$\gamma$,Z$\gamma$) based on the ATLAS detector at LHC with proton-proton collisions at center-of-mass energy of 14 TeV. Through their leptonic decay channels with electron, muon and photon final states, we estimate SM diboson detection sensitivities in early LHC physics run using full ATLAS detector simulation Monte Carlo data samples. Advanced pattern recognition algorithm - Boosted Decision Trees is applied to improve the diboson signal selection efficiency significantly. The sensitivities of anomalous triple-gauge-boson couplings are also estimated using selected diboson signal.   

Physics with Dimuon Events at the Large Hadron Collider with the CMS Detector

The Large Hadron Collider (LHC), which is scheduled to begin operation in summer 2008, will collide proton beams at a center of mass energy of 14 TeV. The Compact Muon Solenoid (CMS) detector is one of the two general-purpose experiments at the LHC, which will probe the TeV frontier of energies to search for new phenomena. One of the most promising early discoveries can be achieved by checking the dimuon signature. Dimuon events can be explored by CMS with high precision up to very high invariant masses. We present a strategy to measure the inclusive dimuon cross section with the first available data, and discuss possible discovery scenarios of high-mass dimuon resonances by searching for deviations in the invariant mass differential cross section spectrum and the forward-backward asymmetry. These measurements require the development of dedicated methods to determine trigger, reconstruction, and selection efficiencies from data, which are discussed in detail.   

Algebraic Approach to Massive Loop Diagrams

The impending high statistics measurements to be done at the LHC demand precise theoretical predictions involving higher order massive loop calculations, for example in studying the production of heavy quark pairs and heavy quark pairs with extra jets or gauge bosons or Higgs bosons. We investigate the possibility of using algebraic techniques to calculate the loop integrals appearing in 1-loop and 2-loop QCD calculations with massive particles. We test the method proposed on 1-loop integrals and study how to extend it to the case of 2-loop integrals.   

Measurement of the forward-backward charge asymmetry in $Z/\gamma^{*} \rightarrow ee$ events with the $\mbox{D\O}$ detector at the Tevatron

We present a measurement of the forward-backward charge asymmetry for dielectrons produced via an intermediate $Z/\gamma^{*}$ boson with mass between 50 and 600 GeV, using about 1 fb$^{-1}$ of data collected by the $\mbox{D\O}$ detector in $p\bar{p}$ collisons at $\sqrt{s}=1.96$ TeV.   

Toward a 0.5 ppm measurement of $G_F$

The weak coupling constant, $G_F,$ is determined most precisely from the mean life of the positive muon, $\tau_\mu$. Advances in theory have reduced the theoretical uncertainty on $G_F$ as calculated from $\tau_\mu$ to a few tenths of a ppm. The remaining uncertainty on $G_F$ is entirely experimental, and is dominated by the uncertainty on $\tau_\mu$. The MuLan experiment is designed to measure the muon lifetime to a precision of 1 ppm, a twenty-fold improvement over the previous generation of experiments. We report an intermediate result, $\tau_\mu=2.197013(24)$ $\mathrm{\mu s}$ (11 ppm), which is in excellent agreement with the previous world average. The mean life was measured using a pulsed surface muon beam stopped in a ferromagnetic target, surrounded by a symmetric scintillator detector array. The new world average $\tau_\mu=2.197019(21)$ $\mathrm{\mu s}$ determines the Fermi constant $G_F = 1.166371(6) \times 10^{-5}$ $\mathrm{GeV}^{-2}$ (5 ppm). Since the intermediate measurement, the detector was instrumented with waveform digitizers, the muon beam rate and beam extinction were increased, and two data sets were acquired on different targets, each containing over $10^{12}$ muon decays. These data will lead to a new determination of $G_F$ to 0.5 ppm.