Session X10: W, Z, Drell-Yan

Measurement of the differential Drell-Yan cross section with the CMS detector at the LHC

The precision measurement of the differential Drell-Yan cross section $d\sigma/dM$ and the first measurement of the double differential cross section $d^2\sigma/dMdY$ at $\sqrt{s} = 7$~TeV are presented. A dataset of $4.7$~fb$^{-1}$ of pp collisions collected with the CMS detector at the LHC during the year 2011 was used for these measurements. The $d\sigma/dM$ cross section was measured in the dimuon channel in the invariant mass range $15$~GeV to $1.5$~TeV. A substantially improved precision compared to the previous measurements has been achieved. The $d2\sigma/dMdY$ cross section measurement has been performed in the dimuon invariant mass range from $15$~GeV to $1$~TeV covering the dimuon rapidity range from $-2.5$ to $2.5$. Both measurements were found to be in good agreement with theoretical predictions estimated using the NNLO MSTW2008 PDFs.   

Measurement of the Drell-Yan differential cross section dSigma/dM in the electron channel in pp collisions at 7 TeV at CMS

The Drell-Yan differential cross section dSigma/dM is measured in pp collisions at $\sqrt{s}=7$ TeV, from a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 1.1 fb^{-1}$. The cross section measurement in the electron channel, normalized to the measured cross section in the Z region, is reported in the dielectron invariant mass range 15-1500 GeV. The results are found to agree with theoretical predictions.   

FEWZ: A Fully Exclusive Numerical Code for Combined QCD and QED Correction to Drell-Yan Process

The QED correction to hadron collider production of lepton pairs through the Drell-Yan process at next-to-leading order (NLO) is included in the new version of the simulation code FEWZ (Fully Exclusive W and Z Production). We calculate the contributions of the initial/final-state photon radiation (ISR/FSR) as well as the virtual photon correction analytically, and the program is fully differential in the phase space of leptons and additional photonic radiation. It eliminates the need to unfold the FSR effect when comparing experimental data with the theoretical prediction given by the original FEWZ, which only includes the QCD corrections. We demonstrate the code by discussing the effects of photon recombination and different lepton masses. We also study the combined QCD and QED correction to lepton pair production and compare results with experimental data.   

Measurement of $W\gamma$ and $Z\gamma$ production and limits on anomalous gauge couplings using $pp$ collisions at $\sqrt{s}$ = 7 TeV

We describe a study made by the ATLAS collaboration of $W\gamma$ and $Z\gamma$ production from $pp$ collisions at $\sqrt{s}$ = 7 TeV. The analysis is performed on a data sample with an integrated luminosity of 1.0 fb$^{-1}$ collected during 2011 LHC data taking. The measurement uses W and Z bosons identified from leptonic decays (electrons and muons) with an associated high energy isolated photon. Production cross sections for $p+p$ $\to$ $l\nu\gamma$ + X and $p+p$ $\to$ $l^{+}$$l^{-}$$\gamma$ + X are measured in a fiducial phase space well covered by the ATLAS detector acceptance and are studied in several ranges of the transverse energy of the photon. The measured cross sections and production kinematics are compared to Standard Model predictions and used to determine limits on anomalous $W$$W^*$$\gamma$ and $Z$($Z^*$/$\gamma^*$)$\gamma$ couplings.   

Search for excited muons with the ATLAS experiment

A search for excited muons in the decay channel mu* -$>$ mu + gamma with the ATLAS detector is presented. Data from pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 2.05 fb -1 were analyzed. No evidence for signal was found, and 95{\%} C.L. limits in the excited muon mass - compositeness scale phase space were increased.   

Search for high-mass di-tau resonances in pp collisions at $\sqrt{s} = 7$ TeV

Many well motivated scenarios of physics beyond the Standard Model, such as Grand Unified Theories, models with extra spatial dimensions, and Super symmetry (SUSY) suggest the presence of heavy neutral resonances. While these new particles may have different nature and production mechanism, e.g. heavy SUSY Higgs, Z'-boson or Kaluza-Klein excitations, they all share a similar experimental signature which should be observable at the LHC using dilepton final states. We present a direct search for heavy particles decaying into two taus using data from pp collisions recorded by the CMS experiment at the LHC, at center-of-mass energy of 7 TeV, and corresponding to an integrated luminosity of 4.6 fb$^{-1}$. The cross section limit was measured using four channels, Z'$\to \tau \tau \to $e$\tau _{h}$, $\mu \tau _{h}$,e$\mu $, and $\tau _{h}\tau _{h}$, where no significant excess was observed. Using the Sequential Standard Model Z'-boson as a benchmark, we set a 95{\%} confidence-level upper limit on the mass of 1TeV.   

Search for Contact Interactions in the Dimuon Channel in p-p Interactions at $\sqrt{s}=$ 7 TeV

Quark and muon sub-structure is manifest as a deviation from the Standard Model prediction for the invariant mass distribution of opposite-sign dimuon pairs. A search strategy is presented based on a left-handed current model of Contact Interactions. Expected limits are shown as a function of minimum invariant mass. The measured mass distribution is reported based on a data sample corresponding to 5 fb$^{-1}$.   

Signatures of Standard Model Dimuon Sources in the CMS Detector

The response of the CMS detector for standard model sources of pairs of oppositely charged muons is studied using a detailed simulation based on GEANT4. The response is affected by the real-time trigger, geometrical acceptance, reconstruction efficiency, and resolution on invariant mass. The simulated response is compared to the measured distribution of invariant mass using a data sample corresponding to 5 fb-1 of p-p collisions at $\surd $s= 7 TeV.   

Angular Distribution of Muon Pairs Produced by the Drell-Yan Mechanism Compared to an Exotic Model of Contact Interactions for High Energy p-p Collisions

The Pythia Monte Carlo program is used to simulate the angular distributions of oppositely charged pairs of muons porduced in p-p collision at $\sqrt{s}$=7 TeV. The distributions are evaluated in the context of standard model Drell-Yan production and an exotic left-handed current model of quark-lepton interactions. The angular distribution in the rest-frame of the muon pair is characterized by the mean cosine of the angle between the negative muon and the boost direction. We report the dependence of the mean cosine on the invariant mass of the pair and the energy scale parameter of the exotic model.