Showing papers by "Brad Abbott published in 1998"

The BABAR physics book: Physics at an asymmetric $B$ factory

Abstract: Results of a year-long workshop devoted to a review of the physics opportunities of the BABAR experiment at the PEP-II B Factory, at the Stanford Linear Accelerator Center laboratory are presented.

Measurement of the top quark mass using dilepton events

Abstract: The D0 Collaboration has performed a measurement of the top quark mass m{sub t} based on six candidate events for the process t{ovr t}{r_arrow}bW{sup +}{ovr b}W{sup {minus}} , where the W bosons decay to e{nu} or {mu}{nu} . This sample was collected during an exposure of the D0 detector to an integrated luminosity of 125 pb{sup {minus}1} of {radical}(s)=1.8 TeV p{ovr p} collisions. We obtain m{sub t}=168.4{plus_minus}12.3(stat){plus_minus} 3.6(syst) GeV/c{sup 2} , consistent with the measurement obtained using single-lepton events. Combination of the single-lepton and dilepton results yields m{sub t}=172.0{plus_minus}7.5 GeV/c{sup 2} . {copyright} {ital 1998} {ital The American Physical Society}

Direct measurement of the top quark mass by the DO Collaboration

Abstract: We determine the top quark mass m{sub t} using t{bar t} pairs produced in the DO/ detector by {radical} (s) =1.8thinspTeV p{bar p} collisions in a 125thinsppb{sup {minus}1} exposure at the Fermilab Tevatron. We make a two constraint fit to m{sub t} in t{bar t}{r_arrow}bW{sup +}{bar b}W{sup {minus}} final states with one {ital W} boson decaying to q{bar q} and the other to e{nu} or {mu}{nu}. Likelihood fits to the data yield m{sub t}(l+jets)=173.3{plus_minus}5.6thinsp(stat)thinsp{plus_minus}thinsp5.5thinsp(s st) GeV/c{sup 2}. When this result is combined with an analysis of events in which both {ital W} bosons decay into leptons, we obtain m{sub t}=172.1{plus_minus}5.2thinsp(stat)thinsp{plus_minus}thinsp4.9thinsp(syst) GeV/c{sup 2}. An alternate analysis, using three constraint fits to fixed top quark masses, gives m{sub t}(l+jets)=176.0{plus_minus}7.9thinsp(stat){plus_minus}thinsp4.8thinsp(syst) GeV/c{sup 2}, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented. {copyright} {ital 1998} {ital The American Physical Society}

Search for heavy pointlike dirac monopoles

Abstract: We have searched for central production of a pair of photons with high transverse energies in p{bar p} collisions at {radical}(s)=1.8 TeV using 70 pb{sup {minus}1} of data collected with the D0 detector at the Fermilab Tevatron in 1994{endash}1996. If they exist, virtual heavy pointlike Dirac monopoles could rescatter pairs of nearly real photons into this final state via a box diagram. We observe no excess of events above background, and set lower 95{percent} C.L. limits of 610, 870, or 1580 GeV/c{sup 2} on the mass of a spin 0, 1/2 , or 1 Dirac monopole. {copyright} {ital 1998} {ital The American Physical Society}

Search for first generation scalar leptoquark pairs in pp̅ collisions at √s = 1.8 TeV

Abstract: We have searched for first generation scalar leptoquark (LQ) pairs in the enu+jets channel using ppbar collider data (integrated luminosity= 115 pb^-1) collected by the DZero experiment at the Fermilab Tevatron during 1992-96. The analysis yields no candidate events. We combine the results with those from the ee+jets and nunu+jets channels to obtain 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of beta, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% CL lower limits on the LQ mass of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively.

Measurement of Dijet Angular Distributions and Search for Quark Compositeness

Abstract: We have measured the dijet angular distribution in {radical}(s)=1.8 TeV p {bar p} collisions using the D0 detector. Order {alpha}{sup 3}{sub s} QCD predictions are in good agreement with the data. At 95{percent} confidence limit the data exclude models of quark compositeness in which the contact interaction scale is below 2TeV. {copyright} {ital 1998} {ital The American Physical Society}

Measurement of the Shape of the Transverse Momentum Distribution of W Bosons Produced in pp̄ Collisions at √s = 1.8 TeV

Abstract: The shape of the transverse momentum distribution of W bosons (p_T(W)) produced in pbarp collisions at sqrt(s)= 1.8 TeV is measured with the DO detector at Fermilab. The result is compared to QCD perturbative and resummation calculations over the p_T(W) range from 0-200 GeV/c. The shape of the distribution is consistent with the theoretical prediction.

Search for charge-1/3 third-generation leptoquarks in pp collisions at s =1.8 tev

Abstract: We report on a search for $\mathrm{charge}\ensuremath{-}1/3$ third-generation leptoquarks (LQ) produced in $p\overline{p}$ collisions at $\ensuremath{\surd}s\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ using the $\mathrm{D}0$ 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 $\ensuremath{\sigma}(p\overline{p}\ensuremath{\rightarrow}\mathrm{LQ}\overline{\mathrm{LQ}}){B}^{2}$ as a function of the leptoquark mass ${M}_{\mathrm{LQ}}$. Assuming $B\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, we exclude at the 95% confidence level third-generation scalar leptoquarks with ${M}_{\mathrm{LQ}}l94\mathrm{GeV}{/c}^{2}$, and third-generation vector leptoquarks with ${M}_{\mathrm{LQ}}l216\mathrm{GeV}{/c}^{2}({M}_{\mathrm{LQ}}l148\mathrm{GeV}{/c}^{2}$) assuming Yang-Mills (anomalous) coupling.

Experimental Search for Chargino and Neutralino Production in Supersymmetry Models with a Light Gravitino

Abstract: We search for inclusive high $E_T$ diphoton events with large missing transverse energy in $p\bar{p}$ collisions at $\sqrt{s}$=1.8 TeV. Such events are expected from pair production of charginos and neutralinos within the framework of the minimal supersymmetric standard model with a light gravitino. No excess of events is observed. In that model, and assuming gaugino mass unification at the GUT scale, we obtain a 95% CL exclusion region in the supersymmetry parameter space and lower mass bounds of 150 GeV/c$^2$ for the lightest chargino and 75 GeV/c$^2$ for the lightest neutralino.

A Measurement of the W Boson Mass at the Fermilab pp̄ Collider

Abstract: We report a measurement of the W boson mass based on an integrated luminosity of 82 pb −1 from pp collisions at √s = 1.8 TeV recorded in 1994-1995 by the D0 detector at the Fermilab Tevatron. We identify W bosons by their decays to e∨ V and extract the mass by fitting the transverse mass spectrum from 28 323 W boson candidates. A sample of 3563 dielectron events, mostly due to Z→ee decays, constrains models of W boson production and the detector. We measure M W = 80.44±0.10(stat)±0.07(syst) GeV. By combining this measurement with our result form the 1992-1993 data set, we obtain M W = 80.43±0.11 GeV.

Determination of the mass of the W boson using the D detector at the Fermilab Tevatron

Abstract: A measurement of the mass of the W boson is presented which is based on a sample of 5982 W → eνv decays observed in pp collisions at √s=1.8 TeV with the D∅ detector during the 1992-1993 run. From a fit to the transverse mass spectrum, combined with measurements of the Z boson mass, the W boson mass is measured to be MW=80.350±0.140(stat)±0.165(syst)±0.160(scale) GeV/c 2 . Detailed discussions of the determination of the absolute energy scale, the measured efficiencies, and all systematic uncertainties are presented.

Limits on WWγ and WWZ couplings from W boson pair production

Abstract: The results of a search for W boson pair production in pp collisions at √s=1.8TeV with subsequent decay to eμ, ee, and μμ channels are presented. Five candidate events are observed with an expected background of 3.1±0.4 events for an integrated luminosity of approximately 97pb -1 . Limits on the anomalous couplings are obtained from a maximum likelihood fit of the E T spectra of the leptons in the candidate events. Assuming identical WWγ and WWZ couplings, the 95% C.L. limits are -0.62<Δκ<0.77 (λ=0) and -0.53<λ<0.56 (Δκ=0) for a form factor scale Λ=1.5TeV.

Limits on anomalous [Formula Presented] and [Formula Presented] couplings

Abstract: Limits on the anomalous WWγ and WWZ couplings are presented from a simultaneous fit to the data samples of three gauge boson pair final states in pp collisions at √s=1.8TeV: Wγ production with the W boson decaying to eν or μν, W boson pair production with both of the W bosons decaying to eν or μν, and WW or WZ production with one W boson decaying to eν and the other W boson or the Z boson decaying to two jets. Assuming identical WWγ and WWZ couplings, 95% C.L. limits on the anomalous couplings of -0.30<Δκ<0.43 (λ=0) and -0.20<λ<0.20 (Δκ=0) are obtained using a form factor scale Λ=2.0TeV. Limits found under other assumptions on the relationship between the WWγ and WWZ couplings are also presented.

An investigation of uncertainties in the QCD NLO predictions of the inclusive jet cross section in $\mathbf{\bar{p}p}$ collisions at $\sqrt{s} = 1.8$ TeV and 630 GeV

Abstract: Uncertainties in the NLO calculation of the inclusive jet cross section due to the choice of renormalization scale, parton distribution functions and clustering algorithm are explored. These are found to be similar in size to the current experimental uncertainties of the measured inclusive jet cross section at DO and CDF.

Functional characteristics and radiation tolerance of AToM, the front-end chip of BaBar silicon vertex tracker

Abstract: The readout chip designed to process the microstrip signals in the BaBar silicon vertex tracker (SVT), after being realized twice in a radsoft technology has been transferred into the final radhard process. So far the circuit has gone through four different radhard submissions, one aiming at providing a preliminary insight into the characteristics of the radhard chip, the other ones constituting pre-production and production runs. Chips from these submissions have undergone a thorough set of tests addressing functional aspects, noise parameters and effects of radiation on signal and noise behavior. The present paper discusses the results of these tests and describes the final version of the circuit which has been proven to successfully meet the experiment requirements.

Limits on WWγ and WWZ couplings from IV boson pair production

Abstract: The results of a search for W boson pair production in pp collisions at √s=1.8TeV with subsequent decay to eμ, ee, and μμ channels are presented. Five candidate events are observed with an expected background of 3.1±0.4 events for an integrated luminosity of approximately 97pb -1 . Limits on the anomalous couplings are obtained from a maximum likelihood fit of the E T spectra of the leptons in the candidate events. Assuming identical WWγ and WWZ couplings, the 95% C.L. limits are -0.62<Δκ<0.77 (λ=0) and -0.53<λ<0.56 (Δκ=0) for a form factor scale Λ=1.5TeV.

An Investigation of Uncertainties in the QCD NLO Predictions of the Inclusive Jet Cross Section in pbarp Collisions at sqrt(s) = 1.8 TeV and 630 GeV

Abstract: Uncertainties in the NLO calculation of the inclusive jet cross section due to the choice of renormalization scale, parton distribution functions and clustering algorithm are explored. These are found to be similar in size to the current experimental uncertainties of the measured inclusive jet cross section at DZero and CDF.