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 σtimes BF(G -> Z^0 Z^0) < 4 - 6 pb, depending on the graviton mass.
We present a search for neutral supersymmetric Higgs bosons decaying to tau pairs produced in p-pbar collisions at sqrt(s) = 1.96 TeV. The data, corresponding to 310 pb^(-1) integrated luminosity, were collected with the CDF II detector at the Tevatron collider at Fermilab. No significant excess above the standard model backgrounds is observed. We set exclusion limits on the production cross section times branching fraction to tau pairs for Higgs masses in the range from 90 to 250 GeV/c^2.
We have used 19 pb**-1 of data collected with the Collider Detector at Fermilab to search for new particles decaying to dijets. We exclude at 95% confidence level models containing the following new particles: axigluons with mass between 200 and 870 GeV, excited quarks with mass between 80 and 570 GeV, and color octet technirhos with mass between 320 and 480 GeV.
We present the results of a search for Wprime boson decaying to electron-neutrino pairs in pbarp collisions at a center-of-mass energy of 1.96 TeV, using a data sample corresponding to 205 pb^-1 of integrated luminosity collected by the CDF II detector at Fermilab. We observe no evidence for this decay mode and set limits on the production cross section times branching fraction, assuming the neutrinos from Wprime boson decays to be light. If we assume the manifest left-right symmetric model, we exclude a Wprime boson with mass less than 788 GeV/c^2 at the 95% confidence level.
A search for the production of neutral Higgs bosons Phi decaying into tau^+tau^- final states in p-pbar collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of up to 348 pb^-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for Phi b(b) to b-bbar-b(bbar) and are interpreted in the minimal super…
We have searched for a heavy resonance decaying into a Z+jet final state in p-pbar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370/pb. We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.
We present a search for a neutral particle, pair-produced in p-pbar collisions at sqrt(s)=1.96 TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses ~380 pb^-1 of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeV and lifetime of 4x10^-11 s, we exclude values greater than 0.14 pb (95% C.L.). These results are used to limit the interpre…
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.
We present results of searches for technirho, techniomega, and Z' particles, using the decay channels technirho, techniomega, Z' -> e+e-. The search is based on 124.8 pb-1 of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes p pbar -> technirho, techniomega, Z' -> e+e- as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate technirho and techniomega states with masses below about 200 GeV. We exclude a Z' wit…
We report the results of a search for a W' boson produced in p-pbar collisions at a center-of-mass energy of 1.8 TeV using a 106 pb-1 data sample recorded by the Collider Detector at Fermilab. We observe no significant excess of events above background for a W' boson decaying to a top and bottom quark pair, with the top quark subsequently decaying into a semileptonic final state. These data allow us to set limits on the rate of W' boson production and decay. In a model where this boson would mediate interactions involving a massive right-handed neutrino (nu_R) and has Standard Model strength c…
We present a search for Higgs bosons decaying into b-bbar and produced in association with W bosons in p-pbar collisions at sqrt{s}=1.96 TeV. This search uses 320 pb-1 of the dataset accumulated by the upgraded Collider Detector at Fermilab. Events are selected that have a high-transverse momentum electron or muon, missing transverse energy, and two jets, one of which is consistent with a hadronization of a b quark. Both the number of events and the dijet mass distribution are consistent with standard model background expectations, and we set 95% confidence level upper limits on the production…
We report on a search for second generation leptoquarks (LQ) produced in $p\bar{p}$ collisions at sqrt{s} = 1.8 TeV using the D0 detector at Fermilab. Second generation leptoquarks are assumed to be produced in pairs and to decay to either μor νand either a strange or a charm quark (q). Limits are placed on σ(p-pbar -> LQ-LQbar -> μν+ jets) as a function of the mass of the leptoquark. For equal branching ratios to μq and νq, second generation scalar leptoquarks with a mass below 160 GeV/c^2, vector leptoquarks with anomalous minimal vector couplings with a mass below 240 GeV/c^2, and vector le…
A resonance search has been made in the K0s p and K0s pbar invariant-mass spectrum measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The search was performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV for exchanged photon virtuality, Q2, above 1 GeV2. Recent results from fixed-target experiments give evidence for a narrow baryon resonance decaying to K+ n and K0s p, interpreted as a pentaquark. The results presented here support the existence of such state, with a mass of 1521.5+/-1.5(sta…
We have searched for the pair production of first generation scalar leptoquarks in the eejj channel using the full data set (123 pb-1) collected with the D0 detector at the Fermilab Tevatron during 1992--1996. We observe no candidates with an expected background of approximately 0.4 events. Comparing the experimental 95% confidence level upper limit to theoretical calculations of the cross section with the assumption of a 100% branching fraction to eq, we set a lower limit on the mass of a first generation scalar leptoquark of 225 GeV/c^2. The results of this analysis rule out the interpretati…
We report on a search for anomalous production of Z boson pairs through a massive resonance decay in data corresponding to 2.5-2.9 fb^-1 of integrated luminosity in p pbar collisions at 1.96 TeV using the CDF II detector at the Fermilab Tevatron. This analysis, with more data and channels where the Z bosons decay to muons or jets, supersedes the 1.1 fb^-1 four-electron channel result previously published by CDF. In order to maintain high efficiency for muons, we use a new forward tracking algorithm and muon identification requirements optimized for these high signal-to-background channels. Pre…
We have used 87 pb^-1 of data collected with the Collider Detector at Fermilab to search for new particles decaying to b bbar. We present model-independent upper limits on the cross section for narrow resonances which excludes the color-octet technirho in the mass interval 350 < M < 440 GeV/c^2. In addition, we exclude topgluons, predicted in models of topcolor-assisted technicolor, of width Gamma = 0.3 M in the mass range 280 < M < 670 GeV/c^2, of width Gamma = 0.5 M in the mass range 340 < M < 640 GeV/c^2, and of width Gamma = 0.7 M in the mass range 375 < M < 560 GeV/c^2.
Data from the Fermilab E835 experiment have been used to study the reaction pbar p -> eta eta pi0 at 5.2 GeV/c. A sample of 22 million six photons events has been analyzed to construct the Dalitz plot containing ~80k eta eta pi0 events. A partial wave analysis of the data has been done. Six f_J-states decaying into eta eta and five a_J-states decaying into eta pi0 are identified in the mass region ~1.3 and 2.4 GeV, and their masses, widths and spins are determined by maximum likelihood analysis of the data. Two f_0 states are identified with the popular candidates for the lightest scalar glueb…
Data on pbar-b annihilation in flight into pizero-pizero-eta are presented for nine beam momenta 600 to 1940 MeV/c. The strongest four intermediate states are found to be f_2(1270)-eta, a_2(1320)-pi, sigma-eta and a_0(980)-pi. Partial wave analysis is performed mainly to look for resonances formed by pbar-p and decaying into pizero-pizero-eta through these intermediate states. There is evidence for the following s-channel I = 0 resonances : two 4^{++} resonances with mass and width (M,Gamma) at (2044, 208) MeV and (2320+-30, 220+-30) MeV; three 2^{++} resonances at (2020+-50, 200+-70) MeV, (22…
With a sample of 232x10^6 Upsilon(4S) --> BBbar events collected with the BaBar detector, we study the decay B+ --> p pbar K+ excluding charmonium decays to ppbar. We measure a branching fraction Br(B+ --> p pbar K+)=(6.7+/-0.5+/-0.4)x10^{-6}. An enhancement at low ppbar mass is observed and the Dalitz plot asymmetry suggests dominance of the penguin amplitude in this B decay. We search for a pentaquark candidate Theta*++ decaying into pK+ in the mass range 1.43 to 2.00 GeV/c2 and set limits on Br(B+ --> Theta*++pbar)xBr(Theta*++ --> pK+) at the 10^{-7} level.
We present the first measurement of the color representation of the hadronically decaying W boson in t-tbar events, from 5.3 fb^-1 of integrated luminosity collected with the D0 experiment. A novel calorimeter-based vectorial variable, "jet pull," is used, sensitive to the color-flow structure of the final state. We find that the fraction of uncolored W bosons is 0.56 +- 0.42(stat+syst), in agreement with the standard model.
The reaction pbar p -> pbar p pi+ pi- has been studied with high statistics at CERN-LEAR with incident pbar momenta from 1.65 to 2.0 GeV/c by the JETSET (PS202) experiment. The aim of this paper is to search for narrow resonances decaying to pbar p. No evidence for such structures is found. In particular, an upper limit for the production of a 2.02 GeV state with a width of Gamma = 20 MeV, having been seen in other hadroproduction experiments, is established. Our results restrict the cross section for such a peak to be below 200 nb at the 95% confidence level.
Data collected by the D0 detector at a p-pbar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider have been used to search for pair production of the lightest supersymmetric partner of the top quark decaying into $b \ell \tildeν$. The search is performed in the $\ell\ell' = eμ$ and $μμ$ final states. No evidence for this process has been found in data samples of approximately 400 pb^-1. The domain in the [$M(\tilde{t}_1),M(\tildeν)$] plane excluded at the 95% C.L. is substantially extended by this search.
We present evidence for dilepton events from t tbar production with one electron or muon and one hadronically decaying tau lepton from the decay t tbar -> (l nu_l) (tau nu_tau) b bbar, (l=e, mu), using the Collider Detector at Fermilab (CDF). In a 109 pb^-1 data sample of p pbar collisions at sqrt(s) = 1.8 TeV we expect ~1 signal event and a total background of ~2 events; we observe 4 candidate events (2 e tau and 2 mu tau). Three of these events have jets identified as b candidates, compared to an estimated background of 0.28+-0.02 events.
A study of the decay B+->ppbarK+ is performed using 81fb-1 of data collected at the Upsilon(4S) with the BaBar detector at PEP-II. The branching fraction of B+->ppbarK+ is measured to be (6.7+/-0.9+/-0.6)x10^-6. An upper limit on the branching fraction of B+->Theta*++pbar, where Theta*++ is a narrow state decaying to pK+, is set to be 1.5x10^-7 for 1.43<m(Theta*++)<1.85GeV/c^2 at 90% confidence level. All results are preliminary.
We present a search for excited and exotic electrons (e*) decaying to an electron and a photon, both with high transverse momentum. We use 202/pb of data collected in p-pbar collisions at sqrt(s) = 1.96 TeV with the CDF II detector. No signal above Standard Model expectation is seen for associated ee* production. We discuss the e* sensitivity in the parameter space of the excited electron mass M(e*) and the compositeness energy scale Lambda. In the contact interaction model, we exclude 132 < M(e*) < 879 GeV/c^2 for Lambda = M(e*) at 95% confidence level (C.L.). In the gauge-mediated model, we …
We propose to investigate various charmonium states using their common decay channel to p pbar at LHC. Having the branching ratios for charmonium decaying into the p pbar final state measured or calculated, we propose to measure the charmonium production rate for both hadroproduction including soft-diffraction and inclusive production from b-hadron decays. We discuss the theoretical impacts in QCD of measuring different charmonium production rates and also the experimental prospects at LHCb, in particular, those for yet unmeasured eta_c and h_c.
We report on a search for the supersymmetric partner of the top quark (scalar top) decaying into a charm quark and a neutralino in p-pbar collisions at sqrt(s)=1.96 TeV. The data sample, collected by the CDFII detector at the Fermilab Tevatron, corresponds to an integrated luminosity of 2.6 fb-1. Candidate events are selected by requiring two or more jets and a large imbalance in the transverse momentum. To enhance the analysis sensitivity, at least one of the jets is required to be identified as originating from a charm quark using an algorithm specifically designed for this analysis. The sel…
We have studied tbar-t production using multijet final states in pbar-p collisions at a center-of-mass energy of 1.8 TeV, with an integrated luminosity of 110.3 pb(-1). Each of the top quarks with these final states decays exclusively to a bottom quark and a W boson, with the W bosons decaying into quark-antiquark pairs. The analysis has been optimized using neural networks to achieve the smallest expected fractional uncertainty on the tbar-t production cross section, and yields a cross section of 7.1 +/- 2.8(stat.) +/- 1.5(syst.) pb, assuming a top quark mass of 172.1 GeV/c^(2). Combining thi…
We present the results of a search for a new heavy top-like quark, tprime, decaying to a W boson and another quark using the CDF II Detector in Run II of the Tevatron ppbar collider. New top-like quarks are predicted in a number of models of new physics. Using a data sample corresponding to 2.8 fb-1 of integrated luminosity we fit the observed spectrum of total transverse energy and reconstructed quark mass to a combination of background plus signal. We see no evidence for tprime production, so use this result to set limits on the tprime tprimebar production cross section times the branching r…
We search for evidence of resonant top quark pair production in 955 pb-1 of p-pbar collisions at sqrt(s)=1.96 TeV recorded with the CDF II detector at the Fermilab Tevatron. For fully reconstructed candidate t-tbar events triggered on leptons with large transverse momentum and containing at least one identified b-quark jet, we compare the invariant mass spectrum of t-tbar pairs to the expected superposition of standard model t-tbar, non-t-tbar backgrounds, and a simple resonance model based on a sequential Z' boson. We establish upper limits for sigma(p-pbar to Z') times Br(Z' to t-tbar) in th…
We present a search for a Higgs boson decaying into a pair of photons based on 9.6 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the non-resonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. …
Long-lived, heavy particles are predicted in a number of models beyond the standard model of particle physics. We present the first direct search for such particles' decays, occurring up to 100 hours after their production and not synchronized with an accelerator bunch crossing. We apply the analysis to the gluino (~g), predicted in split supersymmetry, which after hadronization can become charged and lose enough momentum through ionization to come to rest in dense particle detectors. Approximately 410 pb^-1 of p-pbar collisions at 1.96 TeV collected with the D0 detector during Run II of the F…
An analysis of data on pbar-p -> eta-eta-pizero-pizero is presented at pbar beam momenta 600 to 1940 MeV/c. There is evidence for an I = 1, J^PC = 2^-+ resonance in eta-eta-pizero with mass M = 1880 +- 20 MeV and width 255 +- 45 MeV, decaying strongly a2(1320)-eta; it is too strong to be explained as the high mass tail of π_2(1670) -> a2(1320)-eta. There is tentative evidence also for weak decays to f_0(1500)π. It makes a natural partner to the eta 2(1860).
We present a calculation of the cross section for the process p pbar -> Zt' -> t tbar, the production of a Topcolor Z' with subsequent decay to top quark pairs in proton anti-proton collisions at 1.8 TeV. Variations of the cross section with varying assumptions about the model, the resonance width, the parton distributions and the renormalization scale are presented.
We combine the results of searches for the standard model Higgs boson based on the full CDF Run II data set obtained from sqrt(s) = 1.96 TeV p-pbar collisions at the Fermilab Tevatron corresponding to an integrated luminosity of 9.45/fb. The searches are conducted for Higgs bosons that are produced in association with a W or Z boson, have masses in the range 90-150 GeV/c^2, and decay into bb pairs. An excess of data is present that is inconsistent with the background prediction at the level of 2.5 standard deviations (the most significant local excess is 2.7 standard deviations).
Recent results on light hadron spectroscopy are reported, with special emphasis on the evidence for a narrow baryonic state decaying to Ks p and Ks pbar, compatible with the pentaquark state theta^+ observed by fixed target experiments. The data were collected with the ZEUS detector at HERA using an integrated luminosity of 121 pb^-1. The analyses were performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV. Evidence for a narrow resonance in the Ks p and Ks pbar invariant mass spectrum is obtained, with mass 1521.5 \pm 1.5(…
We present the results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into b bbar using the data sample collected with the D0 detector in p pbar collisions at sqrt{s}=1.96 TeV at the Fermilab Tevatron Collider. We derive 95% CL upper limits on the Higgs boson cross section relative to the standard model prediction in the mass range 100 GeV <= M_H <= 150 GeV, and we exclude Higgs bosons with masses smaller than 102 GeV at the 95% CL. In the mass range 120 GeV <= M_H <= 145 GeV the data exhibit an excess above the backgr…
We present the results of a search for standard model Higgs boson production with decay to WW*, identified through the leptonic final states e+ e- nubar nu ,e mu nubar nu and mu+ mu- nubbar nu. This search uses 360 pb-1 of data collected from p pbar collisions at sqrt{s} = 1.96 TeV by the upgraded Collider Detector at Fermilab (CDF II). We observe no signal excess and set 95% confidence level upper limits on the production cross section times branching ratio for the Higgs boson to WW* or any new scalar particle with similar decay products. These upper limits range from 5.5 to 3.2 pb for Higgs …
We present a search for the standard model Higgs boson produced in association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data collected with the CDF II detector at the Tevatron corresponding to an integrated luminosity of 9.45 fb-1. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a neutrino, we set 95% credibility level upper limits on the WH production cross section times the H->bb branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) t…
Limits on the anomalous WWgamma and WWZ couplings are presented from a simultaneous fit to the data samples of three gauge boson pair final states in pbar-p collisions at sqrt(s)=1.8 TeV: Wgamma production with the W boson decaying to enu or munu, W boson pair production with both of the W bosons decaying to enu or munu, and WW or WZ production with one W boson decaying to enu and the other W boson or the Z boson decaying to two jets. Assuming identical WWgamma and WWZ couplings, 95 % C.L. limits on the anomalous couplings of -0.30<Delta kappa<0.43 (lambda = 0) and -0.20<lambda<0.20 (Delta kap…
Several searches for long-lived particles have been performed using data from p-pbar collisions from Run II at the Tevatron. In most cases, new analysis techniques have been developed to carry out each search and/or estimate the backgrounds. These searches expand the discovery potential of the CDF and D0 experiments to new physics that may have been missed by traditional search techniques. This review discusses searches for (1) neutral, long-lived particles decaying to muons, (2) massive, neutral, long-lived particles decaying to a photon and missing energy, (3) stopped gluinos, and (4) charge…
We combine searches by the CDF and D0 Collaborations for the associated production of a Higgs boson with a W or Z boson and subsequent decay of the Higgs boson to a bottom-antibottom quark pair. The data, originating from Fermilab Tevatron p-pbar collisions at sqrt{s}=1.96 TeV, correspond to integrated luminosities of up to 9.7 fb^-1. The searches are conducted for a Higgs boson with mass in the range 100-150 GeV/c^2. We observe an excess of events in the data compared with the background predictions, which is most significant in the mass range between 120 and 135 GeV/c^2. The largest local si…
A search for signals of new physics has been carried out in the channel p pbar -> gamma gamma + ETmiss. This signature is expected in various recently proposed supersymmetric (SUSY) models. We observe 842 events with two photons having transverse momentum ET(g) > 12 GeV and pseudorapidity |eta(g)| < 1.1. Of these, none have missing transverse energy (ETmiss) in excess of 25 GeV. The distribution of ETmiss is consistent with that of the expected background. We therefore set limits on production cross sections for selectron, sneutrino and neutralino pairs, decaying into photons. The limits range…
A search for the production of neutral Higgs bosons decaying into tau anti-tau final states is presented in p-pbar collisions at a center-of-mass energy of 1.96 TeV. The integrated luminosity used for the study is about 2.2 fb^-1, collected by the DO Experiment at the Fermilab Tevatron Collider. No significant excess is observed over the background expectation. The results are interpreted in the Minimal Supersymmetric Standard Model (MSSM) and regions in the mA, tan(beta) parameter space for two MSSM benchmark scenarios are excluded.
We present properties of weakly decaying bottom baryons, Xi_b and Omega_b, using 4.2 fb^-1 of data from p-pbar collisions at sqrt{s}=1.96 TeV, and recorded with the Collider Detector at Fermilab. We report the observation of the Omega_b through the decay chain Omega_b -> J/psi Omega^-, where J/psi -> mu^+ mu^-, Omega^- -> Lambda K^-, and Lambda -> p pi^-. Significance of the observed signal is estimated to be 5.5 Gaussian standard deviations. The Omega_b mass and lifetime are measured to be 6054.4 +- 6.8 (stat.) +- 0.9 (syst.) MeV/c^2 and 1.13^{+0.53}_{-0.40}(stat.) +- 0.02(syst.) ps, respecti…
We present a search for neutral Higgs bosons decaying into b-bbar, produced in association with b quarks in p-pbar collisions. This process could be observable in supersymmetric models with high values of tan(beta). The event sample corresponds to 2.6/fb of integrated luminosity collected with the CDF II detector at the Fermilab Tevatron collider. We search for an enhancement in the mass of the two lead jets in events with three jets identified as coming from b quarks using a displaced vertex algorithm. A data-driven procedure is used to estimate the dijet mass spectrum of the non-resonant mul…
We present the results of a search for the production of new particles decaying into two jets in pbarp collisions at sqrt{s} = 1.8 TeV, using the DZero 1992-1995 data set corresponding to 109 pb^-1. We exclude at the 95% confidence level the production of excited quarks (q*) with masses below 775 GeV/c^2, the most restictive limit to date. We also exclude standard-model-like W' (Z') bosons with masses between 300 and 800 GeV/c^2 (400 and 640 GeV/c^2). A W' boson with mass $<$ 300 GeV/c^2 has been excluded by previous measurements, and our lower limit is therefore the most stringent to date.
We measure the top quark mass m_t using t tbar pairs produced in the D0 detector by root(s) = 1.8 TeV p pbar collisions in a 125 pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in t tbar --> b W^+ bbar W^- final states with one W decaying to q qbar and the other to e nu or mu nu. Events are binned in fit mass versus a measure of probability for events to be signal rather than background. Likelihood fits to the data yield m_t = 173.3 +- 5.6 (stat) +- 6.2 (syst) GeV/c^2.
We report on a search for pair production of a fourth generation charge -1/3 quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron using an integrated luminosity of 93 pb^-1. Both quarks are assumed to decay via flavor changing neutral currents (FCNC). The search uses the signatures gamma + 3 jets + mu-tag and 2 gamma + 2 jets. We see no significant excess of events over the expected background. We place an upper limit on the production cross section times branching fraction that is well below theoretical expectations for a b' quark decaying exclusively via FCNC for b' …
We present the results of a search for the production of an excited state of the muon, mu*, in proton antiproton collisions at sqrt s = 1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb^-1. We search for mu* in the process p pbar -> mu* mu, with the mu* subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes mu* production by four-fermion contact interactions and m…
