Selected Publications by D. Stuart

• "Background Modeling in New Physics Searches Using Forward Events at LHC."
  Victor Pavlunin and David Stuart. PhysRevD78:035012 (hep-ex:0806.2338).
  

  We present a method to measure dominant Standard Model backgrounds using data containing high rapidity objects in pp collisions at the Large Hadron Collider (LHC). The method is developed for analyses of early LHC data when robustness against imperfections of background modeling and detector simulation can be a key to the discovery of new physics at LHC.

• "Search for New Heavy Particles Decaying to Z0 Z0 ---> eeee in p - anti-p Collisions at s**(1/2) = 1.96-TeV."
  T. Aaltonen et al. PhysRevD78:012008 (hep-ex:0801.1129)
  

  We report the results of a search for the anomalous production of a massive particle decaying to four electrons via two Z^0 bosons in 1.1 fb^{-1} of p-pbar collisions at sqrt(s)=1.96 TeV collected by the CDF II detector at Fermilab. We employ optimized electron identification criteria to maximize acceptance and efficiency. We estimate the backgrounds in the invariant mass range 500 - 1000 GeV/c^2 to be 0.028 +/- 0.009 (stat) +/- 0.011 (syst) events. We observe zero events in this search region. Assuming a Randall-Sundrum graviton production model, we set 95% CL limits on \sigma times BF(G -> Z^0 Z^0) < 4 - 6 pb, depending on the graviton mass.

• "Search for New Particles Leading to Z+jets Final States in p anti-p Collisions at s**(1/2) = 1.96-TeV."
  T. Aaltonen et al. Phys.Rev.D76:072006,2007
  

  We present the results of a search for new particles that lead to a \Z boson plus jets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using the Collider Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 \ifb\ collected using \Z boson decays to $ee$ and $\mu\mu$ is used. We describe a completely data-based method to predict the dominant background from standard-model \Z+jet events. This method can be similarly applied to other analyses requiring background predictions in multi-jet environments, as shown when validating the method by predicting the background from $W$+jets in \ttbar production. No significant excess above the background prediction is observed, and a limit is set using a fourth generation quark model to quantify the acceptance. Assuming $BR(b' \to b\Z) = 100%$ and using a leading-order calculation of the $b'$ cross section, $b'$ quark masses below 268 $\gev/c^2$ are excluded at 95% confidence level.

• "Search for new high mass particles decaying to lepton pairs in p anti-p collisions at s**(1/2) = 1.96-TeV."
  A. Abulencia et al. Phys.Rev.Lett.95:252001,2005
  

  A search for new particles (X) that decay to electron or muon pairs has been performed using approximately 200 pb**(-1) of pbarp collision data at sqrt(s)=1.96 TeV collected by the CDF II experiment at the Fermilab Tevatron. Limits on sigma(ppbar -> X)*BR(X -> ll) are presented as a function of dilepton invariant mass m(ll) > 150 GeV/c**2, for different spin hypotheses (0, 1, or 2). The limits are approximately 25 fb for m(ll) > 600 GeV/c**2. Lower mass bounds for X from representative models beyond the Standard Model including heavy neutral gauge bosons are presented.

• "Measurement of the forward-backward charge asymmetry from W ---> e nu production in p anti-p collisions at s**(1/2) = 1.96 TeV."
  D. Acosta et al., Phys.Rev.D71:051104,2005
  

  We report a measurement of the forward-backward charge asymmetry of electrons from W boson decays in p anti-p collisions at s**(1/2) = 1.96 TeV using a data sample of 170 pb-1 collected by the Collider Detector at Fermilab. The asymmetry is measured as a function of electron rapidity and transverse energy and provides new input on the momentum fraction dependence of the u and d quark parton distribution within the proton.

• "Search for long lived charged massive particles in anti-p p collisions at s**1/2 = 1.8-TeV."
  D. Acosta et al., Phys.Rev.Lett.90:131801,2003
  

  We report a search for production of long-lived charged massive particles in a data sample of 90 pb^{-1} of \sqrt{s} = 1.8 TeV p anti-p collisions recorded by the Collider Detector at Fermilab (CDF). The search uses the muon-like penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data is found to agree with background expectations, and cross section limits of \cal{O} (1) pb are derived using two reference models, a stable quark and a stable scalar lepton.

• "Charged jet evolution and the underlying event in proton - anti-proton collisions at 1.8-TeV."
  T. Affolder et al., Phys.Rev.D65:092002,2002
  

  The growth and development of "charged particle jets" produced in proton-antiproton collisions at 1.8 TeV are studied over a transverse momentum range from 0.5 GeV/c to 50 GeV/c. A variety of leading (highest transverse momentum) charged jet observables are compared with the QCD Monte Carlo models herwig, isajet, and pythia. The models describe fairly well the multiplicity distribution of charged particles within the leading charged jet, the size of the leading charged jet, the radial distribution of charged particles and transverse momentum around the leading charged jet direction, and the momentum distribution of charged particles within the leading charged jet. The direction of the leading "charged particle jet" in each event is used to define three regions of eta-phi space. The "toward" region contains the leading "charged particle jet," while the "away" region, on the average, contains the away-side jet. The "transverse" region is perpendicular to the plane of the hard 2-to-2 scattering and is very sensitive to the "underlying event" component of the QCD Monte Carlo models. Herwig, isajet, and pythia with their default parameters do not describe correctly all the properties of the "transverse" region.

• "Forward - backward charge asymmetry of quark pairs produced at the KEK TRISTAN e+ e- collider."
  D. Stuart et al. Phys.Rev.D49:3098-3105,1994
  

  We report on a measurement of the forward-backward charge asymmetry in e⁺e^---->q qbar at KEK TRISTAN, where the asymmetry is near maximum. We sum over all flavors and measure the asymmetry by determining the charge of the quark jets. In addition we exploit flavor dependencies in the jet charge determination to enhance the contributions of certain flavors. This provides a check on the asymmetries of individual flavors. The measurement agrees with the standard model expectations.

• "Some studies of the applications of CsI photocathodes in gaseous detectors."
  G. Charpak, I. Gaudean, Y. Giomataris, V. Peskov, D. Scigocki, F. Sauli, D. Stuart. Nucl.Instrum.Meth.A333:391-398,1993
  

  Cesium-iodide photocathodes have been investigated in combination with gaseous detectors. The quantum efficiency of a semi-transparent CsI photocathode has been measured in the UV range and found to be 10% at 140 nm. We report experimental results obtained with such photocathodes coupled to BaF2 and KMgF3 scintillators and read out by parallel-plate gaseous detectors.

• "Measurement of the forward-backward charge asymmetry in electron-positron annihilation into a quark-antiquark pair: A test of electroweak interference."
  D. Stuart. UMI-93-13526, Dec 1992. PhD Thesis
  

  The forward-backward asymmetry of quarks produced in e⁺e^- annihilations, summed over all flavors, is measured at sqrt(s) between 50 and 64 GeV. The asymmetry is found to agree with the electroweak standard model.

• "Investigation of operation of a parallel plate avalanche chamber with a CsI photocathode under high gain conditions."
  G. Charpak, P. Fonte, V. Peskov, F. Sauli, D. Seigocki, D. Stuart. Nucl.Instrum.Meth.A307:63-68,1991
  

  We report results of a systematic study of the operational characteristics of a single-step parallel-plate avalanche chamber with CsI photocathode under high-gain conditions at room temperature and 1 atm pressure. Different mixtures of He and Ar with hydrocarbons were tested, as well as with ethylferrocene vapor which are known to form an adsorbed photosensitive layer on the CsI photocathode. The chamber can reach high gains, up to 106, has a very good time resolution (500 ps FWHM), and an energy resolution of 8.2% FWHM for 3 × 103 primary photoelectrons with a quantum efficiency of the CsI photocathode of about 20% at 193 nm. Photon feedback, caused by avalanche emission with wavelength longer than 200 nm, was observed for large total charge and found to be nearly independent of the concentration of quencher in the range 7 to 70 Torr. Breakdown appears at a total charge of 1010 electrons and is always of the slow type. There is good proportionality up to the breakdown limit.

• "Forward - backward charge asymmetry in e+ e- ---> hadron jets."
  D. Stuart et al. Phys.Rev.Lett.64:983,1990
  

  The forward-backward asymmetry of quarks produced in e⁺e^- annihilations, summed over all flavors, is measured at sqrt(s) between 50 and 60.8 GeV. Methods of determining the charge direction of jet pairs are discussed. The asymmetry is found to agree with the five-flavor standard model.