Searches for leptoquark production and compositeness at the Tevatron

Recent searches for leptoquark production and compositeness in p-anti-p collisions at sqrt{s}=1.96 TeV are presented using data samples with integrated luminosities up to 4 fb^{-1} recorded with the D0 and CDF detectors at the Tevatron collider.Comment: Invited talk at European Physical Society Europhysics Conference on High Energy Physics, EPS-HEP 2009, Krakow, Polan

Measurement of the Top Quark Mass in the Dilepton Final State using the Matrix Element Method

The top quark, discovered in 1995 by the CDF and D0 experiments at the Fermilab Tevatron Collider, is the heaviest known fundamental particle. The precise knowledge of its mass yields important constraints on the mass of the yet-unobserved Higgs boson and allows to probe for physics beyond the Standard Model. The first measurement of the top quark mass in the dilepton channel with the Matrix Element method at the D0 experiment is presented. After a short description of the experimental environment and the reconstruction chain from hits in the detector to physical objects, a detailed review of the Matrix Element method is given. The Matrix Element method is based on the likelihood to observe a given event under the assumption of the quantity to be measured, e.g. the mass of the top quark. The method has undergone significant modifications and improvements compared to previous measurements in the lepton+jets channel: the two undetected neutrinos require a new reconstruction scheme for the four-momenta of the final state particles, the small event sample demands the modeling of additional jets in the signal likelihood, and a new likelihood is designed to account for the main source of background containing tauonic Z decay. The Matrix Element method is validated on Monte Carlo simulated events at the generator level. For the measurement, calibration curves are derived from events that are run through the full D0 detector simulation. The analysis makes use of the Run II data set recorded between April 2002 and May 2008 corresponding to an integrated luminosity of 2.8 fb{sup -1}. A total of 107 t{bar t} candidate events with one electron and one muon in the final state are selected. Applying the Matrix Element method to this data set, the top quark mass is measured to be m{sub top}{sup Run IIa} = 170.6 {+-} 6.1(stat.){sub -1.5}{sup +2.1}(syst.)GeV; m{sub top}{sup Run IIb} = 174.1 {+-} 4.4(stat.){sub -1.8}{sup +2.5}(syst.)GeV; m{sub top}{sup comb} = 172.9 {+-} 3.6(stat.) {+-} 2.3(syst.)GeV. Systematic uncertainties are discussed, and the results are interpreted within the Standard Model of particle physics. As the main systematic uncertainty on the top quark mass comes from the knowledge of the absolute jet energy scale, studies for a simultaneous measurement of the top quark mass and the b jet energy scale are presented. The prospects that such a simultaneous determination offer for future measurements of the top quark mass are outlined

Measurement of the Top Quark Mass at D0 Run II with the Matrix Element Method in the Lepton+Jets Final State

The mass of the top quark is a fundamental parameter of the Standard Model. Its precise knowledge yields valuable insights into unresolved phenomena in and beyond the Standard Model. A measurement of the top quark mass with the matrix element method in the lepton+jets final state in D0 Run II is presented. Events are selected requiring an isolated energetic charged lepton (electron or muon), significant missing transverse energy, and exactly four calorimeter jets. For each event, the probabilities to originate from the signal and background processes are calculated based on the measured kinematics, the object resolutions and the respective matrix elements. The jet energy scale is known to be the dominant source of systematic uncertainty. The reference scale for the mass measurement is derived from Monte Carlo events. The matrix element likelihood is defined as a function of both, mtop and jet energy scale JES, where the latter represents a scale factor with respect to the reference scale. The top mass is obtained from a two-dimensional correlated fit, and the likelihood yields both the statistical and jet energy scale uncertainty. Using a dataset of 320 pb-1 of D0 Run II data, the mass of the top quark is measured to be mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV mtop (mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV The jet energy scale measurement in the lepton+jets sample yields JES=1.034 +/- 0.034, suggesting good consistency of the data with the simulation. The measurement forecasts significant improvements to the total top mass uncertainty during Run II before the startup of the LHC, as the data sample will grow by a factor of ten and D0's tracking capabilities will be employed in jet energy reconstruction and flavor identification.Die Masse des Top-Quarks ist ein fundamentaler Parameter des Standard-Modells. Ihre genaue Kenntnis liefert wertvolle Aufschlüsse bezüglich unverstandener Phänomene im Standard-Model und darüber hinaus. Die Messung der Top-Quark-Masse mit der Matrixelement-Methode im Lepton+Jets Zerfallskanal in Run II des D0 Experiments wird präsentiert. Ereignisse werden selektiert, wenn sie ein isoliertes Lepton (Elektron oder Myon), signifikante fehlende transversale Energie und genau vier Kalorimeter-Jets aufweisen. Für jedes Ereignis werden die Wahrscheinlichkeiten berechnet, dass das Ereignis durch den Signal- bzw. Untergrund-Prozess produziert worden ist, basierend auf der gemessenen Kinematik, den Auflösungen der rekonstrierten Objekte und der prozess-spezifischen Matrixelemente. Die Kenntnis der Jet Energie Skala ist die dominierende Quelle systematischer Unsicherheit dieser Messung. Die Referenz-Skala wird in Monte Carlo Ereignissen bestimmt. Die Matrixelement-Likelihood wird definiert als Funktion beider Variablen, mtop und JES, wobei letzterer einen Skalierungs-Faktor bezüglich der Referenzskala beschreibt. Die Topmasse wird mittels eines zweidimensionalen korrelierten Fits bestimmt, wobei der Likelihood sowohl den statistischen Fehler als auch den Fehler durch Jet Energie Skala liefert. Die Methode wird auf einen D0 Run II Datensatz angewandt, der einer integrierten Luminosität von 320 pb-1 entspricht, und die Messung ergibt mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV mtop (mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV Die Messung der Jet Energie Skala im lepton+jets Datensatz ergibt JES=1.034 +/- 0.034, was auf gute Übereinstimmung der Daten mit der Simulation hinweist. Die vorliegende Messung verspricht signifikante Verbesserungen des Gesamtfehlers der Topmasse in Run II noch vor dem Start des LHC, wenn der Datensatz sich verzehnfachen und D0's Spurvermessung in die Rekonstruktion von Jet Energien und die Identifikation von b-Jets einbezogen werden

Electroweak physics at the Tevatron

Recent measurements of processes involving the electroweak bosons, Z and W, performed at the Fermilab Tevatron Collider are summarized. The large integrated luminosities collected by both the D0 and CDF Collaborations enable precise measurements of differential single boson production cross sections, the determination of the W mass with unprecedented precision, and the observation of diboson production including ZZ.Comment: 6+1 pages, plenary talk at Physics at LHC 2008, Split, Croatia (for the D0 and CDF Collaborations

The XMM-BCS galaxy cluster survey: I. The X-ray selected cluster catalog from the initial 6 deg2^2

The XMM-Newton - Blanco Cosmology Survey project (XMM-BCS) is a coordinated X-ray, optical and mid-infrared cluster survey in a field also covered by Sunyaev-Zel dovich effect (SZE) surveys by the South Pole Telescope and the Atacama Cosmology Telescope. The aim of the project is to study the cluster population in a 14 deg{sup 2} field (center: {alpha} {approx} 23:29:18.4, {delta} {approx} -54:40:33.6). The uniform multi-wavelength coverage will also allow us for the first time to comprehensively compare the selection function of the different cluster detection approaches in a single test field and perform a cross-calibration of cluster scaling relations. In this work, we present a catalog of 46 X-ray selected clusters from the initial 6 deg{sup 2} survey core.We describe the XMM-BCS source detection pipeline and derive physical properties of the clusters. We provide photometric redshift estimates derived from the BCS imaging data and spectroscopic redshift measurements for a low redshift subset of the clusters. The photometric redshift estimates are found to be unbiased and in good agreement with the spectroscopic values. Our multi-wavelength approach gives us a comprehensive look at the cluster and group population up to redshifts z {approx} 1. The median redshift of the sample is 0.47 and the median mass M{sub 500} {approx} 1 x 10{sup 14} M{sub {circle_dot}} ({approx} 2 keV). From the sample, we derive the cluster log N - log S using an approximation to the survey selection function and find it in good agreement with previous studies. We compare optical mass estimates from the Southern Cosmology Survey available for part of our cluster sample with our estimates derived from the X-ray luminosity. Weak lensing masses available for a subset of the cluster sample are in agreement with our estimates. Optical masses based on cluster richness and total optical luminosity are found to be significantly higher than the X-ray values. The present results illustrate the excellent potential of medium-deep, X-ray surveys to deliver cluster samples for cosmological modelling. In combination with available multi-wavelength data in optical, near-infrared and SZE, this will allow us to probe the dependence of the selection functions on relevant cluster observables and provide thus an important input for upcoming large-area multi-wavelength cluster surveys

NLO merging in tt+jets

In this talk the application of the recently introduced methods to merge NLO calculations of successive jet multiplicities to the production of top pairs in association with jets will be discussed, in particular a fresh look is taken at the top quark forward-backward asymmetries. Emphasis will be put on the achieved theoretical accuracy and the associated perturbative and non-perturbative error estimates.Comment: 6 pages, 3 figures, proceedings contribution for EPS 2013, Stockholm, 17-24 Jul

QCD Radiation in the Production of High s-hat Final States

In the production of very heavy final states - high Mandelstam s-hat - extra QCD radiation can play a significant role. By comparing several different parton shower approximations to results obtained with fixed-order perturbation theory, we quantify the degree to which these approaches agree (or disagree), focussing on initial state radiation above pT = 50 GeV, for top pair production at the Tevatron and at the LHC, and for SUSY pair production at the LHC. Special attention is paid to ambiguities associated with the choice of the maximum value of the ordering variable in parton shower models.Comment: Invited talk at 2005 International Linear Collider Physics and Detector Workshop and Second ILC Accelerator Workshop, Snowmass, CO (Snowmass05), 5 pages, LaTeX, 3 eps figure

Report of the 2005 Snowmass Top/QCD Working Group

This report discusses several topics in both top quark physics and QCD at an International Linear Collider (ILC). Issues such as measurements at the $t\bar{t}$ threshold, including both theoretical and machine requirements, and the determination of electroweak top quark couplings, are reviewed. New results concerning the potential of a 500 GeV $e^+e^-$ collider for measuring $Wtb$ couplings and the top quark Yukawa coupling are presented. The status of higher order QCD corrections to jet production cross sections, heavy quark form factors, and longitudinal gauge boson scattering, needed for percent-level studies at the ILC, are reviewed. A new study of the measurement of the hadronic structure of the photon at a $\gamma\gamma$ collider is presented. The effects on top quark properties from several models of new physics, including composite models, Little Higgs theories, and CPT violation, are studied.Comment: 39 pages, many figs; typos fixed and refs added. Contributed to the 2005 International Linear Collider Physics and Detector Workshop and 2nd ILC Accelerator Workshop, Snowmass, Colorado, 14-27 Aug 200