We present the results of a search for the production of an excited state of the electron, e*, in proton-antiproton collisions at sqrt(s) = 1.96 TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1 fb^-1. We search for e* in the process ppbar -> e* e, with the e* subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e* production by four-fermion contact interactions and e* decay via electroweak processes, we set 95% C.L. upper limits on the production cross section ranging from 8.9 fb to 27 fb, depending on the mass of the excited electron. Choosing the scale for contact interactions to be Lambda = 1 TeV, excited electron masses below 756 GeV are excluded at the 95% C.L.
We measure the ratio of cross sections, σ(ppbar -> Z + b jet)/σ(ppbar -> Z + jet), for associated production of a Z boson with at least one jet. The ratio is also measured as a function of the jet transverse momentum, jet pseudorapidity, Z boson transverse momentum, and the azimuthal angle between the Z boson and the closest jet for events with at least one b jet. These measurements use data collected by the D0 experiment in Run II of Fermilab's Tevatron ppbar Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of 9.7 fb$^{-1}$. The results are compared …
We present the first measurements of the ratios of cross sections, σ(ppbar -> Z+c jet)/σ(ppbar -> Z+jet) and σ(ppbar -> Z+c jet)/σ(ppbar -> Z+b jet) for the associated production of a Z boson with at least one charm or bottom quark jet. Jets have transverse momentum p_{T}>20 GeV and pseudorapidity |η|<2.5. These cross section ratios are measured differentially as a function of jet and $Z$ boson transverse momenta, based on 9.7 fb^{-1} of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt(s) = 1.96 TeV. The measurements show significant deviations from per…
Reconstructable final state kinematics and charge assignment in the reaction ppbar->ttbar allows tests of discrete strong interaction symmetries at high energy. We define frame dependent forward-backward asymmetries for the outgoing top quark in both the ppbar and ttbar rest frames, correct for experimental distortions, and derive values at the parton-level. Using 1.9/fb of ppbar collisions at sqrt{s}=1.96 TeV recorded with the CDF II detector at the Fermilab Tevatron, we measure forward-backward top quark production asymmetries in the ppbar and ttbar rest frames of A_{FB,pp} = 0.17 +- 0.08 an…
We present a search for exclusive Z boson production in proton-antiproton collisions at sqrt(s) = 1.96 TeV, using the CDF II detector at Fermilab. We observe no exclusive Z->ll candidates and place the first upper limit on the exclusive Z cross section in hadron collisions, sigma(exclu) < 0.96 pb at 95% confidence level. In addition, we observe eight candidate exclusive dilepton events from the quantum electrodynamic process ppbar->gammagamma->p+ll+pbar, and measure the cross section for M(ll) > 40 GeV/c2 and |eta(l)| < 4 to be sigma = 0.24^{+0.13}_{-0.10} pb, which is the first measurement fo…
We report on a search for charge-1/3 third-generation leptoquarks (LQ) produced in ppbar collisions at sqrt(s)=1.96 TeV using the D0 detector at Fermilab. Third generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a b quark with branching fraction B. We place upper limits on sigma(ppbar->LQLQbar)*B^2 as a function of the leptoquark mass M_{LQ}. Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with M_{LQ} < 229 GeV.
Results are presented on a measurement of the ttbar pair production cross section in ppbar collisions at sqrt{s} = 1.8 TeV from nine independent decay channels. The data were collected by the Dzero experiment during the 1992-1996 run of the Fermilab Tevatron Collider. A total of 80 candidate events are observed with an expected background of 38.8 +- 3.3 events. For a top quark mass of 172.1 GeV/c^2, the measured cross section is 5.69 +- 1.21 (stat) +- 1.04 (sys) pb.
We present results of a search in 929 pb-1 of ppbar collisions at 1.96 TeV for the anomalous production of events containing a charged lepton (electron or muon) and a photon, both with high transverse momentum, accompanied by additional signatures, X, including missing transverse energy and additional leptons and photons. We use the same selection criteria as in the previous CDF Run I search, but with an order-magnitude larger data set, a higher ppbar collision energy, and the CDF II detector.
We present results from a search for anomalous WW and WZ production in ppbar collisions at sqrt(s) = 1.8 TeV. We used ppbar->evjjX events observed during the 1992-1993 run of the Fermilab Tevatron collider, corresponding to an integrated luminosity of 13.7 +- 0.7 pb^-1. A fit to the transverse momentum spectrum of the W boson yields direct limits on the CP-conserving anomalous WWgamma and WWZ coupling parameters of -0.9 < delta kappa < 1.1 (with lambda = 0) and -0.6 < lambda < 0.7 (with delta kappa = 0) at the 95% confidence level, for a form factor scale Lambda = 1.5 TeV, assuming that the WW…
We present a measurement of the inclusive jet cross section in ppbar interactions at sqrt{s}=1.96 TeV using 385 pb^{-1} of data collected with the CDF II detector at the Fermilab Tevatron. The results are obtained using an improved cone-based jet algorithm (Midpoint). The data cover the jet transverse momentum range from 61 to 620 GeV/c, extending the reach by almost 150 GeV/c compared with previous measurements at the Tevatron. The results are in good agreement with next-to-leading order perturbative QCD predictions using the CTEQ6.1M parton distribution functions.
We have measured the differential cross section for the inclusive production of psi(2S) mesons decaying to mu^{+} mu^{-1} that were produced in prompt or B-decay processes from ppbar collisions at 1.96 TeV. These measurements have been made using a data set from an integrated luminosity of 1.1 fb^{-1} collected by the CDF II detector at Fermilab. For events with transverse momentum p_{T} (psi(2S)) > 2 GeV/c and rapidity |y(psi(2S))| < 0.6 we measure the integrated inclusive cross section sigma(ppbar -> psi(2S)X) Br(psi(2S) -> mu^{+} mu^{-}) to be 3.29 +- 0.04(stat.) +- 0.32(syst.) nb.
A search for leptoquarks has been performed in 310 pb-1 of data from ppbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider. The topology analyzed consists of acoplanar jets with missing transverse energy. The data show good agreement with standard model expectations, and a lower mass limit of 136 GeV has been set at the 95% C.L. for a scalar leptoquark decaying exclusively into a quark and a neutrino.
We present measurements of production cross sections of single top quarks in $\ppbar$ collisions at $\sqrt{s}=1.96\;\rm TeV$ in a data sample corresponding to an integrated luminosity of $5.4\;\rm fb^{-1}$ collected by the D0 detector at the Fermilab Tevatron Collider. We select events with an isolated electron or muon, an imbalance in transverse energy, and two, three, or four jets, with one or two of them containing a bottom hadron. We obtain an inclusive cross section of $σ({\ppbar}{\rargap}tb+X, tqb+X) = 3.43\pm^{0.73}_{0.74}\;\rm pb$ and use it to extract the CKM matrix element $0.79 < |V…
Using 5.4 fb-1 of integrated luminosity from ppbar collisions at sqrt(s)=1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider, we search for decays of the lightest Kaluza-Klein mode of the graviton in the Randall-Sundrum model to ee and gammagamma. We set 95% C.L. lower limits on the mass of the lightest graviton between 560 GeV and 1050 GeV for values of the coupling k/Mbar_pl between 0.01 and 0.1.
Using 1 fb-1 of data from ppbar collisions at sqrt(s)=1.96 TeV at the Fermilab Tevatron collider collected by the D0 detector, we search for decays of Kaluza-Klein excitations of the graviton in the Randall-Sundrum model of extra dimensions to e+e- and diphotons. We set 95% confidence level upper limits on the production cross section times branching fraction which translate into lower limits on the mass of the lightest excitation between 300 and 900 GeV for values of the coupling k/M(Planck) between 0.01 and 0.1.
The central inclusive jet cross section has been measured using a successive-combination algorithm for reconstruction of jets. The measurement uses 87.3 pb^{-1} of data collected with the D0 detector at the Fermilab Tevatron ppbar Collider during 1994-1995. The cross section, reported as a function of transverse momentum (pT>60 GeV) in the central region of pseudorapidity (|η|<0.5), exhibits reasonable agreement with next-to-leading order QCD predictions, except at low pT where the agreement is marginal.
The ttbar spin correlation at production is a fundamental prediction of QCD and a potentially incisive test of new physics coupled to top quarks. We measure the ttbar spin state in ppbar collisions at sqrt(s) = 1.96 TeV using 1001 candidate events in the lepton plus jets decay channel reconstructed in the CDF II detector. In the helicity basis, for a top-quark mass of 172.5 GeV/c^2, we find a spin correlation coefficient kappa = 0.60 +/- 0.50 (stat) +/- 0.16 (syst), consistent with the QCD prediction, kappa ~= 0.40.
We present a measurement of the $\ttbar$ differential cross section with respect to the $\ttbar$ invariant mass, dSigma/dMttbar, in $\ppbar$ collisions at $\sqrt{s}=1.96$ TeV using an integrated luminosity of $2.7\invfb$ collected by the CDF II experiment. The $\ttbar$ invariant mass spectrum is sensitive to a variety of exotic particles decaying into $\ttbar$ pairs. The result is consistent with the standard model expectation, as modeled by \texttt{PYTHIA} with \texttt{CTEQ5L} parton distribution functions.
We present a search for anomalous triple gauge couplings (ATGC) in WW and WZ boson production. The boson pairs are produced in ppbar collisions at sqrt{s}=1.96 TeV, and the data sample corresponds to 350 pb-1 of integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. In this search one W decays to leptons, and the other boson (W or Z) decays hadronically. Combining with a previously published CDF measurement of Wgamma boson production yields ATGC limits of -0.18 < lambda < 0.17 and -0.46 < Delta kappa < 0.39 at the 95% confidence level, using a cut-off scale Lambda=1…
We present a measurement of ppbar->Zgamma->ll+gamma (l = e, mu) production with a data sample corresponding to an integrated luminosity of 6.2 fb^{-1} collected by the D0 detector at the Fermilab Tevatron ppbar Collider. The results of the electron and muon channels are combined, and we measure the total production cross section and the differential cross section dsigma/dp_T^gamma, where p_T^gamma is the momentum of the photon in the plane transverse to the beamline. The results obtained are consistent with the standard model predictions from next-to-leading order calculations. We use the tran…
We present a search for tau sneutrino production using the Tevatron ppbar collision data collected with the CDF II detector and corresponding to an integrated luminosity of 1 fb^-1. We focus on the scenarios predicted by the R-parity violating (RPV) supersymmetric models in which tau sneutrinos decay to two charged leptons of different flavor. With the data consistent with the standard model expectations, we set the upper limits on sigma(ppbar -> tau sneutrino)*BR(tau sneutrino ->emu,mutau,etau) and use these results to constrain the RPV couplings as a function of tau sneutrino mass.
We measure the ttbar production cross section in ppbar collisions at sqrt{s}=1.96 TeV in the lepton+jets channel. Two complementary methods discriminate between signal and background, b-tagging and a kinematic likelihood discriminant. Based on 0.9 fb-1 of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure sigma_ttbar=7.62+/-0.85 pb, assuming the current world average m_t=172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top quark mass of 170+/-7 GeV.
A measurement of the $\ttbar$ production cross section in $\ppbar$ collisions at $\sqrt{\rm s}$ = 1.96 TeV using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II Detector. The result in a data sample corresponding to an integrated luminosity 2.8 fb$^{-1}$ is: $σ_{\ttbar}$ = 6.27 $\pm$ 0.73(stat) $\pm$ 0.63(syst) $\pm$ 0.39(lum) pb. for an assumed top mass of 175 GeV/$c^{2}$.
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.
We report on a search for Bs->mu+mu- and Bd->mu+mu- decays in ppbar collisions at sqrt(s)=1.96 TeV using 171 pb-1 of data collected by the CDF II experiment at the Fermilab Tevatron Collider. The decay rates of these rare processes are sensitive to contributions from physics beyond the Standard Model. One event survives all our selection requirements,consistent with the background expectation. We derive branching ratio limits of BR(Bs->mu+mu-) < 5.8 x 10^-7 and BR(Bd->mu+mu-) < 1.5 x 10^-7 at 90% confidence level.
We report on a study of color coherence effects in ppbar collisions at a center of mass energy sqrt(s)=1.8 TeV. The data were collected with the D0 detector during the 1992-1993 run of the Fermilab Tevatron Collider. We observe the presence of initial-to-final state color interference with the spatial correlations between soft and hard jets in multijet events in the central and in forward pseudorapidity regions. The results are compared to Monte Carlo simulations with different color coherence implementations and to the predictions of O(alpha_s^3) QCD calculations.
We report the results of a study of color coherence effects in ppbar collisions based on data collected by the D0 detector during the 1994-1995 run of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8 TeV. Initial-to-final state color interference effects are studied by examining particle distribution patterns in events with a W boson and at least one jet. The data are compared to Monte Carlo simulations with different color coherence implementations and to an analytic modified-leading-logarithm perturbative calculation based on the local parton-hadron duality hypothesis…
We report a set of measurements of inclusive invariant transverse momentum differential cross sections of lambda, cascade and omega hyperons reconstructed in the central region with pseudorapidity within 1 and transverse momentum up to 10 GeV/c Events are collected with a minimum-bias trigger in ppbar collisions at a center-of-mass energy of 1.96 TeV using the CDF II detector at the Tevatron Collider. As transverse momentum increases, the slopes of the differential cross sections are similar not only to each other but also to those of mesons, which could indicate a universality of the particle…
We present combined searches for the Low Mass Standard Model Higgs boson at a center-of-mass energy of $\sqrt{s}=$1.96 TeV, using up to 5 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. The major contributing processes are associated production ($WH\to lνbb$, $ZH\toννbb$, $ZH\to ll bb$). The significant improvements across the full mass range resulting from the larger data sets and improved analyses as well as future prospects are discussed.
We present a search for first generation leptoquark with 110pb^1 of data collected with the CDF detector. We set 95% C.L. cross section limits as a function of the leptoquark mass.
We report a measurement of the ttbar production cross section using the CDF-II detector at the Fermilab Tevatron. The analysis is performed using 311 pb-1 of ppbar collisions at sqrt(s)=1.96 TeV. The data consist of events selected with six or more hadronic jets with additional kinematic requirements. At least one of these jets must be identified as a b-quark jet by the reconstruction of a secondary vertex. The cross section is measured to be sigma(tbart)=7.5+-2.1(stat.)+3.3-2.2(syst.)+0.5-0.4(lumi.) pb, which is consistent with the standard model prediction.
We present a search for the rare radiative decay \wpigamma\ using data corresponding to an integrated luminosity of 4.3 \invfb\ of proton-antiproton collisions at a center of mass energy of 1.96 TeV collected by the CDF experiment at Fermilab. As no statistically significant signal is observed, we set a 95% confidence level upper limit on the relative branching fraction \bratio\ at $6.4\times 10^{-5}$, a factor of 10 improvement over the previous limit.
We present the first direct measurement of the $W$ production charge asymmetry as a function of the $W$ boson rapidity $\yW$ in $\ppbar$ collisions at $\sqrt{s} = 1.96$ $\TeV$. We use a sample of $\wenu$ events in data from 1 $\ifb$ of integrated luminosity collected using the CDF II detector. In the region $|\yW| <$ 3.0, this measurement is capable of constraining the ratio of up and down quark momentum distributions in the proton more directly than in previous measurements of the asymmetry that are a function of the charged-lepton pseudorapidity.
Inclusive jet cross sections in Z/gamma^* events, with Z/gamma^* decaying into an electron-positron pair, are measured as a function of jet transverse momentum and jet multiplicity in ppbar collisions at sqrt{s} = 1.96 TeV with the upgraded Collider Detector at Fermilab in Run II, based on an integrated luminosity of 1.7 fb^-1. The measurements cover the rapidity region | yjet | < 2.1 and the transverse momentum range ptjet > 30 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.
First measurements of the differential cross sections for the inclusive production of a photon in association with a heavy quark (c, b) jet are presented, covering photon transverse momenta 30-150 GeV, photon rapidities | y_gamma| < 1.0, jet rapidities |y_jet| < 0.8, and jet transverse momenta pT_jet > 15 GeV. The results are based on an integrated luminosity of 1 fb^-1 in ppbar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.
We describe a search for evidence of minimal supergravity (mSUGRA) in 92.7 pb^(-1) of data collected with the DØdetector at the Fermilab Tevatron ppbar collider at center of mass energy of 1.8 TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W+jets, misidentified multijet, ttbar, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of mSUGRA model parameters is obtained.
A search for direct production of scalar bottom quarks (sb) is performed with 310 pb-1 of data collected by the DO experiment in ppbar collisions at sqrt(s)=1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos chi0_1, with chi0_1 assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m_sb,m_chi0_1) mass plane, improving significantly upon the results from Run I of the Tevatron.
We present a measurement of the W+W- production cross section using 184/pb of ppbar collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W+W- -> l+l-vvbar, where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0+2.2-0.8 events. The resulting W+W- production cross section measurement of sigma(ppbar -> W+W-) = 14.6 +5.8 -5.1 (stat) +1.8 -3.0 (syst) +-0.9 (lum) pb agrees well with the Standard Model expectation.
Inclusive jet cross sections in Z/γ^* events, with Z/γ^* decaying into an electron-positron pair, are measured as a function of jet transverse momentum and jet multiplicity in ppbar collisions at sqrt{s} = 1.96 TeV with the upgraded Collider Detector at Fermilab in Run II, based on an integrated luminosity of 2.5 fb-1. The measurements cover the rapidity region |yjet | < 2.1 and the transverse momentum range ptjet > 30 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.
We present the first observation of the Zgamma to nunugamma process at the Tevatron at 5.1 standard deviations significance, based on 3.6 fb-1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron ppbar Collider at sqrt{s} = 1.96 TeV. The measured Zgamma cross section multiplied by the branching fraction of Z to nunu is 32 +- 9 (stat.+syst.) +- 2 (lumi.) fb for the photon ET > 90 GeV. It is in agreement with the standard model prediction of 39 +- 4 fb. We set the most restrictive limits on anomalous trilinear Zgammagamma and ZZgamma gauge boson couplings at a hadron …
We report the results of a search for a charged Higgs boson in the decays of top quarks produced in \ppbar collisions at a center-of-mass energy of 1.96 TeV. We use a data sample corresponding to an integrated luminosity of 193/pb collected by the upgraded Collider Detector at Fermilab. No evidence for charged Higgs production is found, allowing 95% C.L. upper limits to be placed on BR(t->H^+b) for different charged Higgs decay scenarios. In addition, we present in the MSSM (mH,tan beta) plane the first exclusion regions with radiative and Yukawa coupling corrections.
We present a search for hypothetical vector-like quarks in ppbar collisions at sqrt(s) = 1.96 TeV. The data were collected by the D0 detector at the Fermilab Tevatron Collider and correspond to an integrated luminosity of 5.4 fb^(-1). We select events with a final state composed of a W or Z boson and a jet consistent with a heavy object decay. We observe no significant excess in comparison to the background prediction and set limits on production cross sections for vector-like quarks decaying to W+jet and Z+jet. These are the most stringent mass limits for electroweak single vector-like quark …
We present a measurement of the top quark pair (ttbar) production cross section in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb-1 of data collected by the DO detector at the Fermilab Tevatron Collider. We select events in the dilepton final states ee, emu and mumu based on kinematical properties consistent with ttbar events. For a top quark mass of 175 GeV, we measure a top pair production cross section sigma(ttbar) = 8.6 +3.2-2.7 (stat) +/-1.1 (syst) +/-0.6 (lumi) pb, in good agreement with the standard model prediction.
We determine the strong coupling constant alphas and its energy dependence from the pT dependence of the inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < pT < 145 GeV. Using perturbative QCD calculations to order O(alphas^3) combined with O(alphas^4) contributions from threshold corrections, we obtain alphas(MZ) = 0.1161 +0.0041 -0.0048. This is the most precise result obtained at a hadron-hadron collider.
We report a search for diphoton events with large missing transverse energy produced in ppbar collisions at sqrt(s)=1.96 TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider, and correspond to 6.3 fb-1 of integrated luminosity. The observed missing transverse energy distribution is well described by the standard model prediction, and 95% C.L. limits are derived on two realizations of theories beyond the standard model. In a gauge mediated supersymmetry breaking scenario, the breaking scale Lambda is excluded for Lambda < 124 TeV. In a universal extra dimension mo…
We present the first search for pair production of isolated jets of charged leptons in association with a large imbalance in transverse energy in ppbar collisions using 5.8 fb^-1 of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider. No excess is observed above Standard Model background, and the result is used to set upper limits on the production cross section of pairs of supersymmetric chargino and neutralino particles as a function of "dark-photon" mass, where the dark photon is produced in the decay of the lightest supersymmetric particle.
We report on a search for pair production of first-generation scalar leptoquarks (LQ) in ppbar collisions at sqrt(s)=1.96 TeV using an integrated luminosity of 252pb-1 collected at the Fermilab Tevatron collider by the D0 detector. We observe no evidence for LQ production in the topologies arising from LQLQbar->eqeq and LQLQbar->eqnuq, and derive 95% C.L. lower limits on the LQ mass as a function of beta, where beta is the branching fraction for LQ->eq. The limits are 241 and 218 GeV/c2 for beta=1 and 0.5, respectively. These results are combined with those obtained by D0 at sqrt(s)=1.8 TeV, w…
We present a preliminary measurement of the central inclusive jet cross section using a successive combination algorithm based on relative transverse momenta (kT) for jet reconstruction. We analyze a 87.3 pb-1 data sample collected by the D0 detector at the Fermilab Tevatron ppbar Collider during 1994-1995. The cross section, reported as a function of transverse momentum (pT > 60 GeV) in the central region of pseudo-rapidity (|eta| < 0.5), is in reasonable agreement with next-to-leading order QCD predictions. This is the first jet production measurement in a hadron collider using a successive …
We present the first search for supersymmetry (SUSY) in Zgamma final states with large missing transverse energy using data corresponding to an integrated luminosity of 6.2 fb-1 collected with the D0 experiment in ppbar collisions at sqrt(s)=1.96 TeV. This signature is predicted in gauge-mediated SUSY-breaking models, where the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP) and is produced in pairs, possibly through decay from heavier supersymmetric particles. The NLSP can decay either to a Z boson or a photon and an associated gravitino that escapes detection. We e…
The strong coupling constant alpha_s and its dependence on the momentum scale is determined from the p_T dependence of the inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV measured with the D0 experiment. The jet transverse momentum range of 50 < p_T < 145 GeV contributes to the determination. Using perturbative QCD caclulations to order O(alpha_s^3) combined with resummed threshold corrections to order O(alpha_s^4) an alpha_s(M_Z)=0.1161^{+0.0041}_{-0.0048} is obtained. This is the most precise result from a hadron-hadron collider.
A direct measurement of the total decay width of the W boson G_W is presented using 350 pb-1 of data from ppbar collisions at sqrt(s) = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. The width is determined by normalizing predicted signal and background distributions to 230185 W candidates decaying to enu and munu in the transverse-mass region 50 < M_T < 90 GeV and then fitting the predicted shape to 6055 events in the high-M_T region, 90 < M_T < 200 GeV. The result is G_W = 2032 +/- 45 (stat.) +/- 57 (syst.) MeV, consistent with the standard model expectation.
We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV utilizing 425 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. We consider the final state of the top quark pair containing one high-pT electron or muon and at least four jets. We exploit specific kinematic features of ttbar events to extract the cross section. For a top quark mass of 175 GeV, we measure sigma_ttbar = 6.4 +1.3-1.2(stat} +/- 0.7(syst)+/- 0.4(lum) pb in good agreement with the standard model prediction.
We describe a general search for resonances decaying to a neutral e-mu final state in ppbar collisions at a center-of-mass energy of 1.96 TeV. Using a data sample representing 344 pb^-1 of integrated luminosity recorded by the CDF-II experiment, we compare Standard Model predictions with the number of observed events for invariant masses between 50 and 800 GeV/c^2. Finding no significant excess (5 events observed vs. 7.7 +/- 0.8 expected for e-mu invariant masses > 100 GeV/c^2), we set limits on sneutrino and Z' masses as functions of lepton family number violating couplings.
We present a measurement of the Zγproduction cross section and limits on anomalous ZZγand Zγγcouplings for form-factor scales of Lambda = 750 and 1000 GeV. The measurement is based on 138 (152) candidate events in the eeγ(μμγ) final state using 320 (290) pb^{-1} of ppbar collisions at \sqrt{s} = 1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h_{10,30}^{Z}|<0.23, |h_{20,40}^{Z}|<0.020, |h_{10,30}^γ|<0.23, and |h_{20,40}^γ|<0.019 for Lambda = 1000 GeV.
A data sample corresponding to an integrated luminosity of 2.1 fb-1 collected by the D0 detector at the Fermilab Tevatron Collider was analyzed to search for squarks and gluinos produced in ppbar collisions at a center-of-mass energy of 1.96 TeV. No evidence for the production of such particles was observed in topologies involving jets and missing transverse energy, and 95% C.L. lower limits of 379 GeV and 308 GeV were set on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan(beta)=3, A0=0, and mu<0. The corresponding previous limits are improved …
We report a search for a narrow ttbar resonance that decays into a lepton+jets final state based on an integrated luminosity of 5.3/fb of proton-antiproton collisions at sqrt{s}=1.96 TeV collected by the D0 Collaboration at the Fermilab Tevatron Collider. We set upper limits on the production cross section of such a resonance multiplied by its branching fraction to ttbar which we compare to predictions for a leptophobic topcolor Z' boson. We exclude such a resonance at the 95% confidence level for masses below 835 GeV.
The recent results on various Beyond the Standard Model (BSM) Higgs boson searches performed by the DZERO experiment at the Tevatron are presented here. In particular, the Higgs bosons in supersymmetric models and fermiophobic scenario have been investigated. No significant excess over the Standard Model (SM) expectations have been observed and accordingly limits have been established on the corresponding model parameters.
We present the first direct experimental bound on the total decay width of the top quark using 955pb^-1 of the Tevatron's ppbar collisions recorded by the Collider Detector at Fermilab. We identify 253 top-antitop pair candidate events. The distribution of reconstructed top quark mass from these events is fitted to templates representing different values of the top quark width. Using a confidence interval based on likelihood ratio ordering, we extract an upper limit at 95% C.L. of Gamma_t <13.1 GeV for an assumed top quark mass of 175 GeV/c^2.
We report on a search for Standard Model t-channel and s-channel single top quark production in ppbar collisions at a center of mass energy of 1.96 TeV. We use a data sample corresponding to 162 pb^{-1} recorded by the upgraded Collider Detector at Fermilab. We find no significant evidence for electroweak top quark production and set upper limits at the 95% confidence level on the production cross section, consistent with the Standard Model: 10.1 pb for the t-channel, 13.6 pb for the s-channel and 17.8 pb for the combined cross section of t- and s-channel.
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 (sy…
The results of a search for squarks and gluinos using data from ppbar collisions recorded at a center-of-mass energy of 1.96 TeV by the D0 detector at the Fermilab Tevatron Collider are reported. The topologies analyzed consist of acoplanar-jet and multijet events with large missing transverse energy. No evidence for the production of squarks or gluinos was found in a data sample of 310 pb-1. Lower limits of 325 and 241 GeV were derived at the 95% C.L. on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan(beta)=3, A0=0, and mu<0.
