Prospects for early discoveries at the LHC with dileptons, jets and no missing energy with the ATLAS detector

This article describes the search for leptoquark pair production and for the decay of a right-handed $W$ in the cascade decay $W_R -> l N_l -> lqlq$ in final states containing two leptons, additional jets and no missing transverse energy. Both final states with two electrons and two muons are studied. With a center of mass energy of $sqrt{s} = 14$ TeV leptoquarks up to 500-600 GeV and the studied scenarios of left-right symmetric models (LRSM) can be discovered with about $100 pb^{-1}

Supersymmetric virtual effects in heavy quark pair production at LHC

We consider the production of heavy ($b,t$) quark pairs at proton colliders in the theoretical framework of the MSSM. Under the assumption of a "moderately" light SUSY scenario, we first compute the leading logarithmic MSSM contributions at one loop for the elementary processes of production from a quark and from a gluon pair in the 1 TeV c.m. energy region. We show that in the initial gluon pair case (dominant in the chosen situation at LHC energies) the electroweak and the strong SUSY contributions concur to produce an enhanced effect whose relative value in the cross sections could reach the twenty percent size for large $\tan\beta$ values in the realistic proton-proton LHC process.Comment: 19 pages and 8 figures; version to appear in Phys. Rev.

Bose-Einstein Correlations of Three Charged Pions in Hadronic Z^0 Decays

Bose-Einstein Correlations (BEC) of three identical charged pions were studied in 4 x 10^6 hadronic Z^0 decays recorded with the OPAL detector at LEP. The genuine three-pion correlations, corrected for the Coulomb effect, were separated from the known two-pion correlations by a new subtraction procedure. A significant genuine three-pion BEC enhancement near threshold was observed having an emitter source radius of r_3 = 0.580 +/- 0.004 (stat.) +/- 0.029 (syst.) fm and a strength of \lambda_3 = 0.504 +/- 0.010 (stat.) +/- 0.041 (syst.). The Coulomb correction was found to increase the \lambda_3 value by \~9% and to reduce r_3 by ~6%. The measured \lambda_3 corresponds to a value of 0.707 +/- 0.014 (stat.) +/- 0.078 (syst.) when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed.Comment: 19 pages, LaTeX, 5 eps figures included, accepted by Eur. Phys. J.

Determination of alpha_s using Jet Rates at LEP with the OPAL detector

Hadronic events produced in e+e- collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed jets. The data were collected between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure alpha(s) in the LEP energy range by fitting an expression in which order alpah_2s calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass energies, the value of alpha_s (Mz) was determined to be alpha(s)(Mz)=0.1177+-0.0006(stat.)+-0.0012$(expt.)+-0.0010(had.)+-0.0032(theo.) \.Comment: 40 pages, 17 figures, Submitted to Euro. Phys. J.

Measurement of the W boson mass

We present a measurement of the W boson mass in W -> ev decays using 1 fb^-1 of data collected with the D0 detector during Run II of the Fermilab Tevatron collider. With a sample of 499830 W -> ev candidate events, we measure M_W = 80.401 +- 0.043 GeV. This is the most precise measurement from a single experiment.Comment: As published in PR

Measurement of the lifetime of the B_c meson in the semileptonic decay channel

Using approximately 1.3 fb-1 of data collected by the D0 detector between 2002 and 2006, we measure the lifetime of the B_c meson in the B_c -> J/psi mu nu X final state. A simultaneous unbinned likelihood fit to the J/\psi+mu invariant mass and lifetime distributions yields a signal of 881 +/- 80 (stat) candidates and a lifetime measurement of \tau(B_c) = 0.448 +0.038 -0.036 (stat) +/- 0.032 (syst) ps.Comment: 7 pages, 2 figures, submitted to Phys. Rev. Let

Measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at sqrt{s}=1.96 TeV

We present a measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.Comment: 7 pages, 3 figures, Fermilab-Pub-08/249-E, submitted to Phys. Rev. Let

A search for the standard model Higgs boson in the missing energy and acoplanar b-jet topology at sqrt(s) = 1.96 TeV

We report a search for the standard model Higgs boson in the missing energy and acoplanar b-jet topology, using an integrated luminosity of 0.93 inverse femtobarn recorded by the D0 detector at the Fermilab Tevatron Collider. The analysis includes signal contributions from pp->ZH->nu nu b b, as well as from WH production in which the charged lepton from the W boson decay is undetected. Neural networks are used to separate signal from background. In the absence of a signal, we set limits on the cross section of pp->VH times the branching ratio of H->bb at the 95% C.L. of 2.6 - 2.3 pb, for Higgs boson masses in the range 105 - 135 GeV, where V=W,Z. The corresponding expected limits range from 2.8 pb - 2.0 pb.Comment: Submitted to Phys. Rev. Letter

Observation of ZZ production in ppbar collisions at sqrt(s) = 1.96 TeV

We present an observation for ZZ -> l+l-l'+l'- (l, l' = e or mu) production in ppbar collisions at a center-of-mass energy of sqrt(s) = 1.96 TeV. Using 1.7 fb-1 of data collected by the D0 experiment at the Fermilab Tevatron Collider, we observe three candidate events with an expected background of 0.14 +0.03 -0.02 events. The significance of this observation is 5.3 standard deviations. The combination of D0 results in this channel, as well as in ZZ -> l+l-nunubar, yields a significance of 5.7 standard deviations and a combined cross section of sigma(ZZ) = 1.60 +/- 0.63 (stat.) +0.16 -0.17 (syst.) pb.Comment: 7 pages, 1 figure, 2 tables Modified slightly following review proces

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging

We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($\sigma_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $\sigma_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let