Marc M Baarmand

A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set.

The D0 collaboration has performed a measurement of the top quark mass based on six candidate events for the process t tbar -> b W+ bbar W-, 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^-1 of sqrt(s)=1.8 TeV p-pbar collisions. We obtain mt = 168.4 +- 12.3 (stat) +- 3.7 (sys) GeV/c^2, consistent with the measurement obtained using single-lepton events. Combination of the single-lepton and dilepton results yields mt = 172.0 +- 7.5 GeV/c^2.

We determine the top quark mass mt using tt¯ pairs produced in the DØ detector by s=1.8TeV pp¯ collisions in a 125pb−1 exposure at the Fermilab Tevatron. We make a two constraint fit to mt in tt¯→bW+b¯W− final states with one W boson decaying to qq¯ and the other to eν or μν. Likelihood fits to the data yield mt(l+jets)=173.3±5.6(stat)±5.5(syst) GeV/c2. When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain mt=172.1±5.2(stat)±4.9(syst) GeV/c2. An alternate analysis, using three constraint fits to fixed top quark masses, gives mt(l+jets)=176.0±7.9(stat)±4.8(syst) GeV/c2, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented. 14.65.Ha, 13.85.Ni, 13.85.QkReceived 27 January 1998DOI:https://doi.org/10.1103/PhysRevD.58.052001©1998 American Physical Society

We present measurements of the bb production cross section and angular correlations using the DØ detector at the Fermilab Tevatron pp Collider operating at s = 1.8 TeV. The b quark production cross section for |yb|<1.0 and pTb>6 GeV/c is extracted from single muon and dimuon data samples. The results agree in shape with the next-to-leading order QCD calculation of heavy flavor production but are greater than the central values of these predictions. The angular correlations between b and b quarks, measured from the azimuthal opening angle between their decay muons, also agree in shape with the next-to-leading order QCD prediction.

We measure the top quark mass m t using t t pairs produced in the DØ detector by √ s = 1.8 TeV pp collisions in a 125 pb -1 exposure at the Fermilab Tevatron.We make a two constraint fit to m t in t t → bW + bW -final states with one W decaying to q q and the other to eν or µν.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 present a measurement of the inclusive jet cross section in p¯p collisions at √s =1.8 TeV at the Fermilab Tevatron using the Collider Detector at Fermilab. Good agreement is seen with the predictions of recent next-to-leading-order [O(α3s)] QCD predictions. The dependence of the cross section on clustering cone size is reported for the first time. An improved limit on Λc, a term characterizing possible quark substructure, is set at 1.4 TeV (95% C.L.).Received 7 August 1991DOI:https://doi.org/10.1103/PhysRevLett.68.1104©1992 American Physical Society

We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region ( $3\leq|\eta|\leq5$ ), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h≈5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as $\frac{a}{\sqrt{E}}\oplus{b}$ . The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.

We present a search for charged Higgs bosons in decays of pair-produced top quarks using $109.2\ifmmode\pm\else\textpm\fi{}5.8{\mathrm{pb}}^{\ensuremath{-}1}$ of data recorded from $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ by the D0 detector during 1992--1996 at the Fermilab Tevatron. No evidence is found for charged Higgs production, and most parts of the $[{M}_{{H}^{+}},\mathrm{tan}\ensuremath{\beta}]$ parameter space where the decay $t\ensuremath{\rightarrow}{H}^{+}b$ has a branching fraction close to or larger than that for $t\ensuremath{\rightarrow}{W}^{+}b$ are excluded at $95%$ confidence level. Assuming ${m}_{t}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}175\mathrm{GeV}$ and $\ensuremath{\sigma}(p\overline{p}\ensuremath{\rightarrow}t\overline{t})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5.5\mathrm{pb}$, for ${M}_{{H}^{+}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}60\mathrm{GeV}$, we exclude $\mathrm{tan}\ensuremath{\beta}&lt;0.97$ and $\mathrm{tan}\ensuremath{\beta}&gt;40.9$.

We report a measurement of the top quark mass using six candidate events for the process $p\overline{p}\ensuremath{\rightarrow}t\overline{t}+\stackrel{\ensuremath{\rightarrow}}{X}{l}^{+}\ensuremath{\nu}{\mathrm{bl}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}\overline{b}+X$, observed in the D0 experiment at the Fermilab $p\overline{p}$ collider. Using maximum likelihood fits to the dynamics of the decays, we measure a mass for the top quark of ${m}_{t}=168.4\ifmmode\pm\else\textpm\fi{}12.3(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}3.6(\mathrm{syst}) \mathrm{Gev}$. We combine this result with our previous measurement in the $t\overline{t}\ensuremath{\rightarrow}l+\mathrm{jets}$ channel to obtain ${m}_{t}=172.1\ifmmode\pm\else\textpm\fi{}7.1 \mathrm{GeV}$ as the best value of the mass of the top quark measured by D0.

We report a new measurement of the pseudorapidity (eta) and transverse-energy ( E(T)) dependence of the inclusive jet production cross section in pp(macro) collisions at square root of s = 1.8 TeV using 95 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron. The differential cross section d(2)sigma/(dE(T)d eta) is presented up to eta = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.

We report a new measurement of the cross section for the production of isolated photons with transverse energies ( E(gamma)(T)) above 10 GeV and pseudorapidities |eta|<2.5 in p&pmacr; collisions at sqrt[s] = 1.8 TeV. The results are based on a data sample of 107.6 pb(-1) recorded during 1992-1995 with the D0 detector at the Fermilab Tevatron collider. The background, predominantly from jets which fragment to neutral mesons, was estimated using the longitudinal shower shape of photon candidates in the calorimeter. The measured cross section is in good agreement with the next-to-leading order QCD calculation for E(gamma)(T) greater, similar36 GeV.

We present a measurement of the $t\overline{t}$ production cross section in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ by the D0 experiment at the Fermilab Tevatron. The measurement is based on data from an integrated luminosity of approximately $125{\mathrm{pb}}^{\ensuremath{-}1}$ accumulated during the 1992--1996 collider run. We observe 39 $t\overline{t}$ candidate events in the dilepton and $\mathrm{lepton}+\mathrm{jets}$ decay channels with an expected background of $13.7\ifmmode\pm\else\textpm\fi{}2.2$ events. For a top quark mass of $173.3\mathrm{GeV}{/c}^{2}$, we measure the $t\overline{t}$ production cross section to be $5.5\ifmmode\pm\else\textpm\fi{}1.8\mathrm{pb}$.

Bottom-quark production in $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ is studied with $5{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected in 1995 by the D0 detector at the Fermilab Tevatron Collider. The differential production cross section for $b$ jets in the central rapidity region ( $|{y}^{b}|&lt;1$) as a function of jet transverse energy is extracted from a muon-tagged jet sample. Within experimental and theoretical uncertainties, D0 results are found to be higher than, but compatible with, next-to-leading-order QCD predictions.

We report a search for effects of large extra spatial dimensions in pp collisions at a center-of-mass energy of 1.8 TeV with the D0 detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% C.L. on the effective Planck scale between 1.0 and 1.4 TeV for several formalisms and numbers of extra dimensions.

Results are presented from analyses of jet data produced in pp ¯collisions at ͱsϭ630 and 1800 GeV collected with the DØ detector during the 1994 -1995 Fermilab Tevatron Collider run.We discuss the details of detector calibration, and jet selection criteria in measurements of various jet production cross sections at ͱsϭ630 and 1800 GeV.The inclusive jet cross sections, the dijet mass spectrum, the dijet angular distribu- tions, and the ratio of inclusive jet cross sections at ͱsϭ630 and 1800 GeV are compared to next-to-leading- order QCD predictions.The order ␣ s 3 calculations are in good agreement with the data.We also use the data at ͱsϭ1800 GeV to rule out models of quark compositeness with a contact interaction scale less than 2.2 TeV at the 95% confidence level.

We report on measurements on inclusive cross sections times branching fractions into electrons for W and Z bosons produced in pp¯ collisions at s=1.8TeV. From an integrated luminosity of 84.5 pb−1 recorded in 1994–1995 using the DØ detector at the Fermilab Tevatron, we determine σ(pp¯→W+X)×B(W→eν)=2310±10(stat)±50(syst)±100(lum)pb and σ(pp¯→Z+X)×B(Z→ee)=221±3(stat)±4(syst)±10(lum)pb. From these, we derive σ(pp¯→W+X)×B(W→eν)/σ(pp¯→Z+X)×B(Z→ee)=10.43±0.15(stat)±0.20(syst)±0.10(NLO), B(W→eν)=0.1044±0.0015(stat)±0.0020(syst)±0.0017(theory)±0.0010(NLO), and ΓW=2.169±0.031(stat)±0.042(syst)±0.041(theory)±0.022(NLO)GeV. We use the latter to set a 95% confidence level upper limit on the partial decay width of the W boson into nonstandard model final states, ΓWinv, of 0.213 GeV. Combining these results with those from the 1992–1993 data gives σ(pp¯→W+X)×B(W→eν)/σ(pp¯→Z+X)×B(Z→ee)=10.51±0.25, ΓW=2.152±0.066GeV, and a 95% C.L. upper limit on ΓWinv of 0.191 GeV. Using a sample with a luminosity of 505 nb−1 taken at s=630GeV, we measure σ(pp¯→W+X)×B(W→eν)=658±67pb. Received 15 June 1999DOI:https://doi.org/10.1103/PhysRevD.61.072001©2000 American Physical Society

We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU(2)_L gauge group. The data collected with the L3 detector at center-of-mass energies between 130 GeV and 208 GeV are used.The decay channel N_e --> eW is investigated and no evidence is found for a heavy neutrino, N_e, in a mass range between 80 GeV and 205 GeV. Upper limits on the mixing parameter between the heavy and light neutrino are derived.

We present a measurement of the Drell-Yan cross section at high dielectron invariant mass using $120\mathrm{pb}{}^{\ensuremath{-}1}$ of data collected in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ by the D0 Collaboration during 1992--1996. No deviation from standard model expectations is observed. We use the data to set limits on the quark-electron compositeness scale. The $95%$ confidence level lower limits on the compositeness scale vary between 3.3 and 6.1 TeV depending on the assumed form of the effective contact interaction.

The DØ detector is used to study pp̄ collisions at the 1800 and 630 GeV center-of-mass energies available at the Fermilab Tevatron. To measure jets, the detector uses a sampling calorimeter composed of uranium and liquid argon as the passive and active media, respectively. Understanding the jet energy calibration is not only crucial for precision tests of QCD, but also for the measurement of particle masses and the determination of physics backgrounds associated with new phenomena. This paper describes the energy calibration of jets observed with the DØ detector at the two pp̄ center-of-mass energies in the transverse energy and pseudorapidity range ET>8 GeV and |η|<3.

Using the D0 detector at the 1.8 TeV $\overline{p}p$ Fermilab Tevatron collider, we have measured the inclusive dijet mass spectrum in the central pseudorapidity region $|{\ensuremath{\eta}}_{\mathrm{jet}}|&lt;1.0$ for dijet masses greater than $200\mathrm{GeV}{/c}^{2}$. We have also measured the ratio of spectra $\ensuremath{\sigma}(|{\ensuremath{\eta}}_{\mathrm{jet}}|&lt;0.5)/\ensuremath{\sigma}(0.5&lt;|{\ensuremath{\eta}}_{\mathrm{jet}}|&lt;1.0)$. The order ${\ensuremath{\alpha}}_{s}^{3}$ quantum chromodynamics predictions are in good agreement with the data and we rule out models of quark compositeness with a contact interaction scale $&lt;2.4\mathrm{TeV}$ at the $95%$ confidence level.

We have made a precise measurement of the central inclusive jet cross section at sqrt(s) = 1.8 TeV. The measurement is based on an integrated luminosity of 92 pb-1 collected at the Fermilab Tevatron pbar-p Collider with the D-Zero detector. The cross section, reported as a function of jet transverse energy (ET >= 60 GeV) in the pseudorapidity interval |eta| <= 0.5, is in good agreement with predictions from next-to-leading order quantum chromodynamics.

We present a search for electroweak production of single top quarks in ~90 pb^-1 of data collected with the DZero detector at the Fermilab Tevatron collider. Using arrays of neural networks to separate signals from backgrounds, we set upper limits on the cross sections of 17 pb for the s-channel process ppbar->tb+X, and 22 pb for the t-channel process ppbar->tqb+X, both at the 95% confidence level.

Extensive measurements have been made with pions, electrons and muons on four production wedges of the compact muon solenoid (CMS) hadron barrel (HB) calorimeter in the H2 beam line at CERN with particle momenta varying from 20 to 300 GeV/c. The time structure of the events was measured with the full chain of preproduction front-end electronics running at 34 MHz. Moving-wire radioactive source data were also collected for all scintillator layers in the HB. The energy dependent time slewing effect was measured and tuned for optimal performance.

Using data corresponding to an integrated luminosity of $79{\mathrm{pb}}^{\ensuremath{-}1}$, D0 has searched for events containing multiple jets and large missing transverse energy in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$ at the Fermilab Tevatron collider. Observing no significant excess beyond what is expected from the standard model, we set limits on the masses of squarks and gluinos and on the model parameters ${m}_{0}$ and ${m}_{1/2}$, in the framework of the minimal low-energy supergravity models of supersymmetry. For $\mathrm{tan}\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$ and ${A}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$, with $\ensuremath{\mu}&lt;0$, we exclude all models with ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}}&lt;250\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$. For models with equal squark and gluino masses, we exclude $m&lt;260\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$.

We present a measurement of the differential cross section as a function of transverse momentum of the Z boson in ppbar collisions at sqrt{s}=1.8 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider during 1994--1996. We find good agreement between our data and the NNLO resummation prediction and extract values of the non-perturbative parameters for the resummed prediction from a fit to the differential cross section.

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at s=630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.

We present a quasi-model-independent search for the physics responsible for electroweak symmetry breaking.We define final states to be studied, and construct a rule that identifies a set of relevant variables for any particular final state.A new algorithm ͑''SLEUTH''͒ searches for regions of excess in those variables and quantifies the significance of any detected excess.After demonstrating the sensitivity of the method, we apply it to the semi-inclusive channel eX collected in 108 pb Ϫ1 of pp ¯collisions at ͱsϭ1.8 TeV at the DO " experiment during 1992-1996 at the Fermilab Tevatron.We find no evidence of new high p T physics in this sample.

The inclusive cross section for production of isolated photons has been measured in pp macro collisions at square root of s = 630 GeV with the D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E(T)) range from 7-49 GeV and have pseudorapidity absolute value of eta < 2.5. This measurement is combined with the previous D0 result at square root of s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E(T) range.

A measurement of the mass of the W boson is presented based on a sample of 5982 W→eν decays observed in p¯p collisions at √s=1.8TeV with the D0 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/c2.Received 11 July 1996DOI:https://doi.org/10.1103/PhysRevLett.77.3309©1996 American Physical Society

We have searched for the pair production of first generation scalar leptoquarks in the eejj channel using the full data set (123pb−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 of eq, we set a lower limit on the mass of a first generation scalar leptoquark of 225GeV/c2. The results of this analysis rule out the interpretation of the excess of high Q2 events at DESY HERA as leptoquarks which decay exclusively to eq.Received 21 July 1997DOI:https://doi.org/10.1103/PhysRevLett.79.4321©1997 American Physical Society

We have measured the W W gauge boson coupling parameters using p p ! ` + X (`= e; ) events at p s = 1:8 TeV.The data, corresponding to an integrated luminosity of 89:1 pb 1 , were collected using the D detector at the Fermilab Tevatron Collider.The measured cross section times branching ratio for p p ! W + X with p T > 10 GeV/c and R ` > 0:7 is 11:8 +1:7 1:6 2:0 pb, in agreement with the Standard Model prediction.The one degree of freedom 95% con dence level limits on individual CP-conserving parameters are 0:98 < < 1:01 and 0:33 < < 0:31.Similar limits are set on the CP-violating coupling parameters.

We have searched for first generation scalar leptoquark (LQ) pairs in the $e\ensuremath{\nu}+\mathrm{jets}$ channel using $p\overline{p}$ collider data $(\ensuremath{\int}L\mathrm{dt}\ensuremath{\approx}115{\mathrm{pb}}^{\ensuremath{-}1})$ collected by the D0 experiment at the Fermilab Tevatron during 1992--1996. The analysis yields no candidate events. We combine the results with those from the $ee+\mathrm{jets}$ and $\ensuremath{\nu}\ensuremath{\nu}+\mathrm{jets}$ channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and of $\ensuremath{\beta}$, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% C.L. lower limits on the LQ mass of 225, 204, and $79\mathrm{GeV}{/c}^{2}$ for $\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, $\frac{1}{2}$, and 0, respectively.

Final results of the search for the Standard Model Higgs boson are presented for the data collected by the L3 detector at LEP at centre-of-mass energies up to about 209 GeV. These data are compared with the expectations of Standard Model processes for Higgs boson masses up to 120 GeV. A lower limit on the mass of the Standard Model Higgs boson of 112.0 GeV is set at the 95 % confidence level. The most significant high mass candidate is a Hnunu event. It has a reconstructed Higgs mass of 115 GeV and it was recorded at root(s)=206.4 GeV.

A measurement of the cross section for production of single, isolated photons is reported for transverse energies in the range of 10--125 GeV for two regions of pseudorapidity, $|\ensuremath{\eta}|&lt;0.9$ and $1.6&lt;|\ensuremath{\eta}|&lt;2.5$. The data represent $12.9{\mathrm{pb}}^{\ensuremath{-}1}$ of integrated luminosity accumulated in $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ and recorded with the D0 detector at the Fermilab Tevatron Collider. The background, predominantly from jets which fragment to neutral mesons, is estimated using the longitudinal shower shape in the calorimeter. In both pseudorapidity regions the cross section is found to agree with the next-to-leading order QCD prediction for $30\ensuremath{\lesssim}{E}_{T}^{\ensuremath{\gamma}}\ensuremath{\lesssim}80\mathrm{GeV}$.

We present a search for charged Higgs bosons in decays of pair-produced top quarks in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ recorded by the D0 detector at the Fermilab Tevatron collider. With no evidence for signal, we exclude most regions of the ( ${M}_{{H}^{\ifmmode\pm\else\textpm\fi{}}},\mathrm{tan}\ensuremath{\beta}$) parameter space where the decay $t\ensuremath{\rightarrow}{\mathrm{H}}^{+}b$ has a branching fraction $&gt;0.36$ and $B({H}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}\ensuremath{\tau}{\ensuremath{\nu}}_{\ensuremath{\tau}})$ is large.

We have measured the W boson mass using the DØ detector and a data sample of 82 pb−1 from the Fermilab Tevatron collider. This measurement uses W→eν decays, where the electron is close to a boundary of a central electromagnetic calorimeter module. Such “edge” electrons have not been used in any previous DØ analysis, and represent a 14% increase in the W boson sample size. For these electrons, new response and resolution parameters are determined, and revised backgrounds and underlying event energy flow measurements are made. When the current measurement is combined with previous DØ W boson mass measurements, we obtain MW=80.483±0.084 GeV. The 8% improvement from the previous DØ measurement is primarily due to the improved determination of the response parameters for non-edge electrons using the sample of Z bosons with non-edge and edge electrons.Received 10 April 2002DOI:https://doi.org/10.1103/PhysRevD.66.012001©2002 American Physical Society

The response of the CMS barrel calorimeter (electromagnetic plus hadronic) to hadrons, electrons and muons over a wide momentum range from 2 to 350 GeV/c has been measured. To our knowledge, this is the widest range of momenta in which any calorimeter system has been studied. These tests, carried out at the H2 beam-line at CERN, provide a wealth of information, especially at low energies. The analysis of the differences in calorimeter response to charged pions, kaons, protons and antiprotons and a detailed discussion of the underlying phenomena are presented. We also show techniques that apply corrections to the signals from the considerably different electromagnetic (EB) and hadronic (HB) barrel calorimeters in reconstructing the energies of hadrons. Above 5 GeV/c, these corrections improve the energy resolution of the combined system where the stochastic term equals 84.7±1.6% and the constant term is 7.4±0.8%. The corrected mean response remains constant within 1.3% rms.

We have searched for central production of a pair of photons with high transverse energies in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ using $70{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected with the D0 detector at the Fermilab Tevatron in 1994--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 $95%$ C.L. limits of 610, 870, or $1580\mathrm{GeV}{/c}^{2}$ on the mass of a spin 0, $1/2$, or 1 Dirac monopole.

The D0 collaboration has performed a study of spin correlation in $t\overline{t}$ production for the process $t\overline{t}\ensuremath{\rightarrow}{\mathrm{bW}}^{+}\overline{b}{W}^{\ensuremath{-}}$, where the $W$ bosons decay to $e\ensuremath{\nu}$ or $\ensuremath{\mu}\ensuremath{\nu}$. A sample of six events was collected during an exposure of the D0 detector to an integrated luminosity of approximately $125{\mathrm{pb}}^{\ensuremath{-}1}$ of $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ $p\overline{p}$ collisions. The standard model (SM) predicts that the short lifetime of the top quark ensures the transmission of any spin information at production to the $t\overline{t}$ decay products. The degree of spin correlation is characterized by a correlation coefficient $\ensuremath{\kappa}$. We find that $\ensuremath{\kappa}&gt;\ensuremath{-}0.25$ at the $68%$ confidence level, in agreement with the SM prediction of $\ensuremath{\kappa}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.88$.

We have measured the dijet angular distribution in $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}p\overline{p}$ collisions using the D0 detector. Order ${\ensuremath{\alpha}}_{s}^{3}$ QCD predictions are in good agreement with the data. At 95% confidence limit the data exclude models of quark compositeness in which the contact interaction scale is below 2 TeV.

This paper presents the first measurement of inclusive J͞c production cross section in the forward pseudorapidity region 2.5 # jh J͞c j # 3.7 in pp collisions at p s 1.8 TeV.The results are based on 9.8 pb 21 of data collected using the D0 detector at the Fermilab Tevatron Collider.The inclusive J͞c cross section for transverse momenta between 1 and 16 GeV͞c is compared with theoretical models of charmonium production.[S0031-9007(98)08183-6

We have measured the $\mathrm{ZZ}\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}\ensuremath{\gamma}$ couplings by studying $13.1{\mathrm{pb}}^{\ensuremath{-}1}$ of $p\overline{p}\ensuremath{\rightarrow}{E}_{t}\ensuremath{\gamma}+X$ data at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ with the D\O{} detector at the Fermilab Tevatron Collider. This is the first study of hadronic $Z\ensuremath{\gamma}$ production in the neutrino decay channel. Combining this measurement with our previous results using $Z\ensuremath{\rightarrow}\mathrm{ee}$ and $\ensuremath{\mu}\ensuremath{\mu}$ yields the most stringent 95% C.L. limits to date on anomalous couplings: $|{h}_{30}^{Z}|&lt;0.4$, $|{h}_{40}^{Z}|&lt;0.06$ ( $\ensuremath{\Lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}750\mathrm{GeV}$).

This Letter describes a measurement of the muon cross section originating from $b$-quark decay in the forward rapidity range $2.4&lt;|{y}^{\ensuremath{\mu}}|&lt;3.2$ in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$. The data used in this analysis were collected by the D0 experiment at the Fermilab Tevatron. We find that next-to-leading-order QCD calculations underestimate $b$-quark production by a factor of 4 in the forward rapidity region.

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron. Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X exclusive final states are systematically analyzed for hints of physics beyond the standard model. Simultaneous sensitivity to a variety of models predicting new phenomena at the electroweak scale is demonstrated by testing the method on a particular signature in each set of final states. No evidence of new high p_T physics is observed in the course of this search, and we find that 89% of an ensemble of hypothetical similar experimental runs would have produced a final state with a candidate signal more interesting than the most interesting observed in these data.

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p(T) physics in approximately 100 pb(-1) of pp collisions at square root of (s) = 1.8 TeV collected by the D0 experiment during 1992-1996 at the Fermilab Tevatron. We systematically analyze many exclusive final states and demonstrate sensitivity to a variety of models predicting new phenomena at the electroweak scale. No evidence of new high p(T) physics is observed.

We present a search for electroweak production of single top quarks in the electronϩjets and muonϩjets decay channels.The measurements use Ϸ90 pb Ϫ1 of data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with the DO " detector between 1992 and 1995.We use events that include a tagging muon, implying the presence of a b jet, to set an upper limit at the 95% confidence level on the cross section for the s-channel process pp ¯→tbϩX of 39 pb.The upper limit for the t-channel process pp ¯→tqbϩX is 58 pb.

This study reports the first measurement of the azimuthal decorrelation between jets with pseudorapidity separation up to five units. The data were accumulated using the DØdetector during the 1992--1993 collider run of the Fermilab Tevatron at $\sqrt{s}=$ 1.8 TeV. These results are compared to next--to--leading order (NLO) QCD predictions and to two leading--log approximations (LLA) where the leading--log terms are resummed to all orders in $α_{\scriptscriptstyle S}$. The final state jets as predicted by NLO QCD show less azimuthal decorrelation than the data. The parton showering LLA Monte Carlo {\small HERWIG} describes the data well; an analytical LLA prediction based on BFKL resummation shows more decorrelation than the data.

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 search for inclusive high ${E}_{T}$ diphoton events with large missing transverse energy in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$. 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% C.L. exclusion region in the supersymmetry parameter space and lower mass bounds of $150\mathrm{GeV}{/c}^{2}$ for the lightest chargino and $77\mathrm{GeV}{/c}^{2}$ for the lightest neutralino.

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

We present a measurement of the W boson mass using data collected by the DØ experiment at the Fermilab Tevatron during 1994–1995. We identify W bosons by their decays to eν final states where the electron is detected in a forward calorimeter. We extract the W boson mass MW by fitting the transverse mass and transverse electron and neutrino momentum spectra from a sample of 11 089 −→Weν decay candidates. We use a sample of 1687 dielectron events, mostly due to →Zee decays, to constrain our model of the detector response. Using the forward calorimeter data, we measure MW=80.691±0.227GeV. Combining the forward calorimeter measurements with our previously published central calorimeter results, we obtain MW=80.482±0.091GeV. Received 23 August 1999DOI:https://doi.org/10.1103/PhysRevD.62.092006©2000 American Physical Society

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 DØ detector at the Fermilab Tevatron pp 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.

We present a measurement of t t production in pp collisions at √ s = 1.8 TeV from 110 pb -1 of data collected in the all-jets decay channel with the DØ detector at Fermilab.A neural network analysis yields a cross section of 7.1 ± 2.8 (stat.)± 1.5 (syst.)pb, at a top quark mass (mt) of 172.1 GeV/c 2 .Using previous DØ measurements from dilepton and single lepton channels, the combined DØ result for the t t production cross section is 5.9 ± 1.2 (stat.)± 1.1 (syst.)pb for mt = 172.1 GeV/c 2 .

We report a measurement of the W boson mass based on an integrated luminosity of 82pb−1 from p¯p collisions at √s=1.8TeV recorded in 1994–1995 by the D0 detector at the Fermilab Tevatron. We identify W bosons by their decays to eν 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 MW=80.44±0.10(stat)±0.07(syst)GeV. By combining this measurement with our result form the 1992–1993 data set, we obtain MW=80.43±0.11GeV.Received 23 December 1997DOI:https://doi.org/10.1103/PhysRevLett.80.3008©1998 American Physical Society

We report a measurement of the W boson mass based on an integrated luminosity of 82 pb(-1) from p&pmacr; collisions at sqrt[s] = 1.8 TeV recorded in 1994-1995 by the D0 detector at the Fermilab Tevatron. We identify W bosons by their decays to enu, where the electron is detected in the forward calorimeters. We extract the mass by fitting the transverse mass and the electron and neutrino transverse momentum spectra of 11 089 W boson candidates. We measure M(W) = 80.691+/-0.227 GeV. By combining this measurement with our previously published central calorimeter results from data taken in 1992-1993 and 1994-1995, we obtain M(W) = 80.482+/-0.091 GeV.

We present a study of Z +gamma + X production in p-bar p collisions at sqrt{S}=1.8 TeV from 97 (87) pb^{-1} of data collected in the eegamma (mumugamma) decay channel with the D0 detector at Fermilab. The event yield and kinematic characteristics are consistent with the Standard Model predictions. We obtain limits on anomalous ZZgamma and Zgammagamma couplings for form factor scales Lambda = 500 GeV and Lambda = 750 GeV. Combining this analysis with our previous results yields 95% CL limits |h{Z}_{30}| < 0.36, |h{Z}_{40}| < 0.05, |h{gamma}_{30}| < 0.37, and |h{gamma}_{40}| < 0.05 for a form factor scale Lambda=750 GeV.

We have studied t t ¯production using multijet final states in pp ¯collisions at a center-of-mass energy of 1.8 TeV, with an integrated luminosity of 110.3 pb Ϫ1 .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 t t ¯production cross section, and yields a cross section of 7.1Ϯ2.8͑stat͒Ϯ1.5͑syst͒ pb, assuming a top quark mass of 172.1 GeV/c 2 .Combining this result with previous DO " measurements, where one or both of the W bosons decay leptonically, gives a t t ¯production cross section of 5.9Ϯ1.2(stat)Ϯ1.1 (syst) pb.͓S0556-2821͑99͒03607-3͔

A search for new physics has been carried out in the channel p¯p→γγ+ET, as expected in various supersymmetric models. We require two photons with transverse energy EγT>12GeV and pseudorapidity |ηγ|<1.1. The distribution of missing transverse energy ( ET) is consistent with background and no events have ET>25GeV. We set limits on production cross sections for selectron, sneutrino, and neutralino pairs, decaying into photons, which range from about 400 fb to 1 pb depending on the sparticle masses. A general limit of 185 fb (95% C.L.) is set on σ(p¯p→γγET+X), where EγT>12GeV, |ηγ|<1.1, and ET>25GeV.Received 12 December 1996DOI:https://doi.org/10.1103/PhysRevLett.78.2070©1997 American Physical Society

Inclusive dijet production at large pseudorapidity intervals (Deltaeta) between the two jets has been suggested as a regime for observing Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics. We have measured the dijet cross section for large Deltaeta in pp collisions at sqrt[s]=1800 and 630 GeV using the D0 detector. The partonic cross section increases strongly with the size of Deltaeta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of alphaBFKL(20 GeV)=1.65+/-0.07.

The shape of the transverse momentum distribution of W bosons ( pTW) produced in pp¯ collisions at s=1.8 TeV is measured with the D0 detector at Fermilab. The result is compared with QCD perturbative and resummation calculations over the pTW range from 0 to 200GeV/c. The shape of the distribution is consistent with the theoretical prediction.Received 3 March 1998DOI:https://doi.org/10.1103/PhysRevLett.80.5498©1998 American Physical Society

We have searched for second-generation leptoquark (LQ) pairs in the &mgr;&mgr;+jets channel using 94+/-5 pb(-1) of &pmacr;p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the &mgr;nu+jets and nunu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c(2) for beta = 1(1 / 2) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of beta.

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),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 pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

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 WWgamma and WWZ coupling parameters are equal.

Evidence of anomalous WW and WZ production was sought in pbar{p} collisions at a center-of-mass energy of sqrt(s) = 1.8 TeV. The final states $WW (WZ) to mu-nu-jet-jet + X, WZ to mu-nu-e-e + X and WZ to e-nu-e-e + X were studied using a data sample corresponding to an integrated luminosity of approximately 90 pb-1. No evidence of anomalous diboson production was found. Limits were set on anomalous WWgamma and WWZ couplings and were combined with our previous results. The combined 95% confidence level anomalous coupling limits for Lambda=2 TeV are -0.25 LE Delta-kappa LE 0.39 (lambda=0) and -0.18 LE lambda LE 0.19 (Delta \kappa = 0), assuming the WWgamma couplings are equal to the WWZ couplings.

We present limits on anomalous $\mathrm{WWZ}$ and $\mathrm{WW}\ensuremath{\gamma}$ couplings from a search for $\mathrm{WW}$ and $\mathrm{WZ}$ production in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$. We use $p\overline{p}\ensuremath{\rightarrow}e\ensuremath{\nu}\mathrm{jjX}$ events recorded with the D0 detector at the Fermilab Tevatron Collider during the 1992--1995 run. The data sample corresponds to an integrated luminosity of $96.0\ifmmode\pm\else\textpm\fi{}5.1{\mathrm{pb}}^{\ensuremath{-}1}$. Assuming identical $\mathrm{WWZ}$ and $\mathrm{WW}\ensuremath{\gamma}$ coupling parameters, the 95% C.L. limits on the $\mathrm{CP}$-conserving couplings are $\ensuremath{-}0.33&lt;\ensuremath{\lambda}&lt;0.36$ $(\ensuremath{\Delta}\ensuremath{\kappa}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)$ and $\ensuremath{-}0.43&lt;\ensuremath{\Delta}\ensuremath{\kappa}&lt;0.59$ $(\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)$, for a form factor scale $\ensuremath{\Lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.0\mathrm{TeV}$. Limits based on other assumptions are also presented.

We have searched for a heavy neutral gauge boson, Z′, using the decay channel Z′ → ee. The data were collected with the DØ detector at the Fermilab Tevatron during the 1992–1993 pp collider run at s=1.8 TeV from an integrated luminosity of 15±1 pb−1. Limits are set on the cross section times brancing ratio for the process pp → Z′ → ee as a function of the Z′ mass. We exclude the existence of a Z′ of mass less than 490 GeV/c2, assuming a Z′ with the same coupling strengths to quarks and leptons as the standard model Z boson.

We report on a search for pair production of a fourth generation charge −1/3 quark ( b′) in pp¯ collisions at s=1.8 TeV by the DØ experiment at the Fermilab Tevatron using an integrated luminosity of 93 pb−1. Both b′ quarks are assumed to decay via flavor changing neutral currents (FCNC). The search uses the signatures γ+3 jets +μ-tag and 2γ+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′ decaying exclusively via FCNC for b′ masses up to mZ+mb.Received 26 November 1996DOI:https://doi.org/10.1103/PhysRevLett.78.3818©1997 American Physical Society

We report a measurement of the differential cross section for W boson production as a function of its transverse momentum in proton–antiproton collisions at s=1.8 TeV. The data were collected by the DØ experiment at the Fermilab Tevatron Collider during 1994–1995 and correspond to an integrated luminosity of 85 pb−1. The results are in good agreement with quantum chromodynamics over the entire range of transverse momentum.

In this note the CMS discovery potential for the light charged Higgs boson in the minimal supersymmetric standard model framework is presented. Different Higgs boson production mechanisms were studied to cover the mass range . The analysis is based on the CMS full simulation and reconstruction. Systematic uncertainties on the background determination are included. It is shown that the systematic uncertainties reduce the observability of H± mainly at low tan β. Finally the 5σ discovery contour for an integrated luminosity of 30 fb−1 is presented.

We report on a search for R-parity violating supersymmetry in p-pbar collisions at sqrt(s) = 1.8 TeV using the D0 detector at Fermilab. Events with at least two electrons and four or more jets were studied. We observe 2 events in 99 +- 4.4 pb-1 of data, consistent with the expected background of 1.8 +- 0.4 events. This result is interpreted within the framework of minimal low-energy supergravity supersymmetry models. Squarks with mass below 243 GeV/c^2 and gluinos with mass below 227 GeV/c^2 are excluded at the 95% confidence level (C. L.) for A_0=0, mu &lt; 0$, tan beta=2 and a finite value for R-parity violating Yukawa coupling lambda'_1jk (j=1, 2 and k=1, 2, 3). For equal squark and gluino masses, the corresponding mass limit is 277 GeV/c^2.

The gauge boson pair production processes Wg, WW, WZ, and Zg were studied using pbarp collisions corresponding to an integrated luminosity of ~14 pb-1 at a center-of-mass energy of sqrt(s) = 1.8 TeV. Analysis of Wg prod with subsequent W boson decay to lv (l=e,mu) is reported, including a fit to the pT spectrum of the photons which leads to limits on anomalous WWg couplings. A search for WW prod with subsequent decay to l-lbar-v-vbar (l=e,mu) is presented leading to an upper limit on the WW prod cross section and limits on anomalous WWg and WWZ couplings. A search for high pT W bosons in WW and WZ prod is described, where one W boson decays to an ev and the second W boson or the Z boson decays to two jets. A maximum likelihood fit to the pT spectrum of W bosons resulted in limits on anomalous WWg and WWZ couplings. A combined fit to the three data sets which provided the tightest limits on anomalous WWg and WWZ couplings is also described. Limits on anomalous ZZg and Zgg couplings are presented from an analysis of the photon ET spectrum in Zg events in the decay channels (ee, mu-mu, and v-vbar) of the Z boson.

We report on a search for bottom squarks $(\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{b})$ produced in $p\overline{p}$ collisions at $\sqrt{s}=1.8 \mathrm{TeV}$ using the D\O{} detector at Fermilab. Bottom squarks are assumed to be produced in pairs and to decay to the lightest supersymmetric particle (LSP) and a b quark with a branching fraction of 100%. The LSP is assumed to be the lightest neutralino and stable. We set limits on the production cross section as a function of $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{b}$ mass and LSP mass.

We report on a search for charge−1/3 third-generation leptoquarks (LQ) produced in p¯p collisions at √s=1.8TeV 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 σ(p¯p→LQ¯LQ)B2 as a function of the leptoquark mass MLQ. Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with MLQ<94GeV/c2, and third-generation vector leptoquarks with MLQ<216GeV/c2(MLQ<148GeV/c2) assuming Yang-Mills (anomalous) coupling.Received 10 March 1998DOI:https://doi.org/10.1103/PhysRevLett.81.38©1998 American Physical Society

A measurement of the mass of the W boson is presented which is based on a sample of 5982 −→Weν decays observed in p¯p 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/c2. Detailed discussions of the determination of the absolute energy scale, the measured efficiencies, and all systematic uncertainties are presented.Received 15 October 1997DOI:https://doi.org/10.1103/PhysRevD.58.012002©1998 American Physical Society

Based on 85 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ data of $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{TeV}$ collected using the D\O{} detector at Fermilab during the 1994--1995 run of the Tevatron, we present a direct measurement of the total decay width of the W boson ${\ensuremath{\Gamma}}_{W}.$ The width is determined from the transverse mass spectrum in the $\stackrel{\ensuremath{\rightarrow}}{W}e+{\ensuremath{\nu}}_{e}$ decay channel and found to be ${\ensuremath{\Gamma}}_{W}{=2.23}_{\ensuremath{-}0.14}^{+0.15}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.10(\mathrm{syst})\mathrm{GeV},$ consistent with the expectation from the standard model.

Mg -1Mq -1 = 1.84 ± 0.15 (stat.)± 0.22 0.18 (sys.).This ratio is

Using the D0 detector, we have studied events produced in proton-antiproton collisions that contain large forward regions with very little energy deposition (``rapidity gaps'') and concurrent jet production at center-of-mass energies of root-s = 630 and 1800 Gev. The fractions of forward and central jet events associated with such rapidity gaps are measured and compared to predictions from Monte Carlo models. For hard diffractive candidate events, we use the calorimeter to extract the fractional momentum loss of the scattered protons.

The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that is not contained by the barrel (HCAL HB) and electromagnetic (ECAL EB) calorimeters. Due to space limitation the barrel calorimeters do not contain completely the hadronic shower and an outer calorimeter (HO) was designed, constructed and inserted in the muon system of CMS to measure the energy leakage. Testing and calibration of the HO was carried out in a 300 GeV/c test beam that improved the linearity and resolution. HO will provide a net improvement in missing E T measurements at LHC energies. Information from HO will also be used for the muon trigger in CMS.

We report on a search for the trilepton decay signature from the associated production of supersymmetric gaugino pairs, ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}$, within the context of minimal supersymmetric models that conserve $R$ parity. This search uses $95{\mathrm{pb}}^{\ensuremath{-}1}$ of $p\overline{p}$ data taken at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ with the D0 detector. No evidence of a trilepton signature has been found, and a limit on the product of cross section times branching fraction to trileptons is given as a function of ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ mass.

Limits on anomalous WW␥ and WWZ couplings are presented from a study of WW/WZ→e j j events produced in pp ¯collisions at ͱsϭ1.8 TeV.Results from the analysis of data collected using the DO " detector during the 1993-1995 Tevatron collider run at Fermilab are combined with those of an earlier study from the 1992-1993 run.A fit to the transverse momentum spectrum of the W boson yields direct limits on anomalous WW␥ and WWZ couplings.With the assumption that the WW␥ and WWZ couplings are equal, we obtain Ϫ0.34ϽϽ0.36͑with ⌬ϭ0) and Ϫ0.43Ͻ⌬Ͻ0.59͑with ϭ0) at the 95% confidence level for a formfactor scale ⌳ϭ2.0 TeV.

Bose-Einstein correlations of both neutral and like-sign charged pion pairs are measured in a sample of 2 million hadronic Z decays collected with the L3 detector at LEP. The analysis is performed in the four-momentum difference range 300 MeV < Q < 2 GeV. The radius of the neutral pion source is found to be smaller than that of charged pions. This result is in qualitative agreement with the string fragmentation model.

We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of pp events corresponding to 108.3 pb(-1) of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, t-->b chi+1 and t-->blnu, no evidence for signal is found. We derive cross-section limits as a function of stop ( t ), chargino ( chi+1), and sneutrino ( nu) masses.

DO has measured the inclusive production cross section of W and Z bosons in a sample of 13 pb$^{-1}$ of data collected at the Fermilab Tevatron. The cross sections, multiplied by their leptonic branching fractions, for production in pbar-p collisions at sqrt{s}=1.8 TeV are sigma_W*B(W-&gt;e nu) = 2.36+-0.02+-0.08+-0.13 nb, sigma_W*B(W-&gt;mu nu) = 2.09+-0.06+-0.22+-0.11 nb, sigma_Z*B(Z-&gt;e+ e-) = 0.218+-0.008+-0.008+-0.012 nb, and sigma_Z*B(Z-&gt;mu+ mu-) = 0.178+-0.022+-0.021+-0.009 nb, where the first uncertainty is statistical and the second systematic; the third reflects the uncertainty in the integrated luminosity. For the combined electron and muon analyses, we find sigma_W*B(W-&gt;l mu)/sigma_Z*B(Z-&gt;l+ l-) = 10.90+-0.52. Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain Gamma(W) = 2.044+-0.097 GeV.

We report on a study of color coherence effects in pp collisions at a center of mass energy s = 1.8 TeV. The data were collected with the DØ 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(αs3) QCD calculations.

We search for new physics using events with one high transverse energy photon, two or more jets, and an apparent imbalance in transverse energy, in p¯p collisions at the Fermilab Tevatron at √s=1.8TeV. Such events are predicted for production of supersymmetric particles in some models. No excess is observed beyond expected background. For the parameter space of the minimal supersymmetric standard model with branching fraction B(˜χ02→γ˜χ01)=1 and m˜χ02−m˜χ01>20GeV, we obtain a 95% confidence level lower mass limit of 310 GeV for equal mass squarks and gluinos. The results are also interpreted in models with low energy gauge mediated supersymmetry breaking.Received 14 August 1998DOI:https://doi.org/10.1103/PhysRevLett.82.29©1999 American Physical Society

We report on a measurement of sigma(pp-->W+X)B(W-->taunu) in pp collisions at sqrt[s]=1.8 TeV at the Fermilab Tevatron. The measurement is based on an integrated luminosity (lum) of 18 pb-1 of data collected with the D0 detector during 1994-1995. We find that sigma(pp-->W+X)B(W-->taunu)=2.22+/-0.09 (stat)+/-0. 10 (syst)+/-0.10 (lum) nb. Lepton universality predicts that the ratio of the tau and electron electroweak charged current couplings to the W boson, gWtau/gWe, be unity. We find gWtau/gWe=0.980+/-0.031, in agreement with lepton universality.

The results of a search for W boson pair production in pp collisions at √ s = 1.8 TeV 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 97 pb -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 W W γ and W W Z couplings, the 95% C.L. limits are -0.62 < ∆κ < 0.77 (λ = 0) and -0.53 < λ < 0.56 (∆κ = 0) for a form factor scale Λ = 1.5 TeV.

The D0 Collaboration has measured the inclusive jet cross section in barpp collisions at square root of s = 630 GeV. The results for pseudorapidities (eta)<0.5 are combined with our previous results at square root of s = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute magnitude, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

We describe a search for the pair production of first-generation scalar and vector leptoquarks in the eejj and enujj channels by the D0 Collaboration. The data are from the 1992--1996 ppbar run at sqrt{s} = 1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the eejj and enujj channels are combined with those from a previous D0 analysis of the nunujj channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of beta, the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 GeV/c^2 are set on the mass for beta=1, 1/2, and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings.

We have searched for the flavor-changing neutral current decay b→Xsμ+μ− in pp̄ collisions at s=1.8 TeV with the DØ detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B(b→Xsμ+μ−) < 3.2×10−4. We argue that this limit is more stringent than the best published limit on this decay rate.

We report on a search for second generation leptoquarks (LQ) produced in p¯p collisions at √s=1.8TeV using the D0 detector at Fermilab. Second generation leptoquarks are assumed to be produced in pairs and to decay to either μ or ν and either a strange or a charm quark (q). Limits are placed on σ(p¯p→LQ¯LQ→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 160GeV/c2, vector leptoquarks with anomalous minimal vector couplings with a mass below 240GeV/c2, and vector leptoquarks with Yang-Mills couplings with a mass below 290GeV/c2, are excluded at the 95% confidence level.Received 23 April 1999DOI:https://doi.org/10.1103/PhysRevLett.83.2896©1999 American Physical Society

We describe QUAERO, a method that (i) enables the automatic optimization of searches for physics beyond the standard model, and (ii) provides a mechanism for making high energy collider data generally available. We apply QUAERO to searches for standard model WW, ZZ, and t t macro production, to searches for these objects produced through a new heavy resonance, and to the first direct search for W'-->WZ. Through this interface, we make three data sets collected by the D0 experiment at square root of [s] = 1.8 TeV publicly available.

We report on a search for supersymmetry using the DØ detector. The 1994–1996 data sample of √s=1.8 TeV p¯p collisions was analyzed for events containing two leptons (e or μ), two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with A0=0 and μ<0, various thresholds were employed to optimize the search. No events were found beyond expectation from the background. We set a lower limit at the 95% C.L. of 255 GeV/c2 for equal mass squarks and gluinos for tanβ=2, and present exclusion contours in the (m0,m1/2) plane for tanβ=2–6.Received 9 February 2000DOI:https://doi.org/10.1103/PhysRevD.63.091102©2001 American Physical Society

We report on a study of the ratio of inclusive three-jet to inclusive two-jet production cross sections as a function of total transverse energy in p&pmacr; collisions at a center-of-mass energy sqrt[s] = 1.8 TeV, using data collected with the D0 detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are used to deduce preferred renormalization scales in perturbative O(alpha(3)(s)) QCD calculations in modeling soft-jet emission.

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 p¯p 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.Received 19 March 1998DOI:https://doi.org/10.1103/PhysRevD.58.031102©1998 American Physical Society

This report describes the first search for top squark pair production in the channel ${t}_{1}t{\overline{\ifmmode \tilde{}\else \~{}\fi{}}}_{1}\ensuremath{\rightarrow}b\overline{b}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{+}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{ee}$+jets+${E}_{T}$ using $74.9\ifmmode\pm\else\textpm\fi{}8.9$ pb${}^{\ensuremath{-}1}$ of data collected using the D\O{} detector. A 95% confidence level upper limit on $\ensuremath{\sigma}\ensuremath{\cdot}B$ is presented. The limit is above the theoretical expectation for $\ensuremath{\sigma}\ensuremath{\cdot}B$ for this process, but does show the sensitivity of the current D\O{} data set to a particular topology for new physics.

The reactions e+e−→e+e− π 0 X and e+e−→e+e−KS 0 X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Inclusive differential cross sections are measured as a function of the particle transverse momentum p t and the pseudo-rapidity. For p t ⩽1.5 GeV, the π 0 and KS 0 differential cross sections are described by an exponential, typical of soft hadronic processes. For p t ⩾1.5 GeV, the cross sections show the presence of perturbative QCD processes, described by a power-law. The data are compared to Monte Carlo predictions and to NLO QCD calculations.

We present the results of a search for leptoquark (LQ) pairs in (85.2+/-3.7) pb(-1) of pp* collider data collected by the D0 experiment at the Fermilab Tevatron. We observe no evidence for leptoquark production and set a limit on sigma(pp*-->LQLQ-->nunu+jets) as a function of the mass of the leptoquark (m(LQ)). Assuming the decay LQ-->nuq, we exclude scalar leptoquarks for m(LQ) < 98 GeV/c(2), and vector leptoquarks for m(LQ) < 200 GeV/c(2) and coupling which produces the minimum cross section, at a 95% confidence level.

A simple network of comparators applied to the strip signals of a cathode strip chamber allows quick hit localization to within a halfstrip width, or ± a quarter-strip. A six-plane chamber with 6.4 mm wide strips was tested in a high-energy muon beam. The chamber was placed behind a 30 cm thick iron block. We show that patterns of hits localized to within a halfstrip allowed us to identify 300 GeV/c muon tracks with 99% probability and 0.7 mm spatial resolution in the presence of bremsstrahlung radiation. This technique of finding muon tracks will be used in the cathode strip chambers of the CMS Endcap Muon System.