Pedrame Bargassa

The D0 experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to D0.

We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in pp collisions at sqrt[s]=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.

We report observation of the electroweak production of single top quarks in pp[over ] collisions at sqrt[s]=1.96 TeV based on 2.3 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(pp[over ]--> tb + X, tqb + X) = 3.94 + or - 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10(-7), corresponding to a 5.0 standard deviation significance for the observation.

We report on a measurement of the inclusive jet cross section in pp[over ] collisions at a center-of-mass energy sqrt[s]=1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0.70 fb;{-1}. The data cover jet transverse momenta from 50 to 600 GeV and jet rapidities in the range -2.4 to 2.4. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.

We present the first measurement of the integrated forward-backward charge asymmetry in top-quark–top-antiquark pair (t¯t) production in proton-antiproton (p¯p) collisions in the lepton+jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming t¯t+X production and decay, a sample of 0.9 fb−1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on t¯t+X production via a Z′ resonance.Received 7 December 2007DOI:https://doi.org/10.1103/PhysRevLett.100.142002©2008 American Physical Society

From an analysis of the flavor-tagged decay Bs0-->J/psiphi we obtain the width difference between the Bs0 light and heavy mass eigenstates, DeltaGammas = 0.19+/-0.07(stat)(-0.01)+0.02(syst) ps(-1), and the CP-violating phase, phi s= -0.57(-0.30)+0.24(stat)(-0.02)+0.08(syst). The allowed 90% CL intervals of DeltaGammas and phi s are 0.06 < DeltaGammas < 0.30 ps(-1) and -1.20 < phi s < 0.06, respectively. The data sample corresponds to an integrated luminosity of 2.8 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron collider.

We report results of a study of the B(s)(0) oscillation frequency using a large sample of B(s)(0) semileptonic decays corresponding to approximately 1 fb(-1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2006. The amplitude method gives a lower limit on the B(s)(0) oscillation frequency at 14.8 ps(-1) at the 95% C.L. At delta m(s) = 19 ps(-1), the amplitude deviates from the hypothesis A= 0(1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, delta m(s), gives a most probable value of 19 ps(-1) and a range of 17 < delta m(s) < 21 ps(-1)at the 90% C.L., assuming Gaussian uncertainties. This is the first direct two-sided bound measured by a single experiment. If delta m(s) lies above 22 ps(-1), then the probability that it would produce a likelihood minimum similar to the one observed in the interval 16-22 ps(-1) is (5.0 +/- 0.3)%.

We report on the first observation of time-reversal symmetry violation through a comparison of the probabilities of K0 transforming into K0 and K0 into K0 as a function of the neutral-kaon eigentime t. The comparison is based on the analysis of the neutral-kaon semileptonic decays recorded in the CPLEAR experiment. There, the strangeness of the neutral kaon at time t=0 was tagged by the kaon charge in the reaction pp→K±π∓K0(K0) at rest, whereas the strangeness of the kaon at the decay time t=τ was tagged by the lepton charge in the final state. An average decay-rate asymmetry〈R(K0t=0→e+π−νt=τ)−R(K0t=0→e−π+νt=τ)R(K0t=0→e+π−νt=τ)+R(K0t=0→e−π+νt=τ)〉=(6.6±1.3stat±1.0syst)×10−3was measured over the interval 1τS<τ<20τS, thus leading to evidence for time-reversal non-invariance.

We present a search for charged Higgs bosons in top quark decays. We analyze the \eplus, \muplus, $ee$, $e\mu$, $\mu\mu$, \etau and \mutau final states from top quark pair production events, using data from about 1${\text{fb}}^{-1}$ of integrated luminosity recorded by the \dzero experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a $\tau$ lepton and a $\tau$ neutrino and a third one where both decays appear. We extract limits on the branching ratio $B(t\to H^+ b)$ for all these models. We use two methods, one where the $t\bar{t}$ production cross section is fixed, and one where the cross section is fitted simultaneously with $B(t\to H^+b)$. Based on the extracted limits, we exclude regions in the charged Higgs boson mass and $\tan \beta$ parameter space for different scenarios of the minimal supersymmetric standard model.

We present a measurement of the shape of the boson rapidity distribution for p¯p→Z/γ∗→e+e−+X events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71<Mee<111 GeV and uses 0.4 fb−1 of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of next-to-next-to-leading order (NNLO) QCD are found to agree well with the data over the full rapidity range.Received 16 February 2007DOI:https://doi.org/10.1103/PhysRevD.76.012003©2007 American Physical Society

A data sample corresponding to an integrated luminosity of 2.1 fb−1 collected by the DØ detector at the Fermilab Tevatron Collider was analyzed to search for squarks and gluinos produced in pp¯ collisions at a center-of-mass energy of 1.96 TeV. No evidence for the production of such particles was observed in topologies involving jets and missing transverse energy, and 95% C.L. lower limits of 379 GeV and 308 GeV were set on the squark and gluino masses, respectively, within the framework of minimal supergravity with tanβ=3, A0=0, and μ<0. The corresponding previous limits are improved by 54 GeV and 67 GeV.

The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron pp[over ] collider. Using a 0.9 fb(-1) dataset, we apply a multivariate analysis to separate signal from background and measure sigma(pp[over ]-->tb+X,tqb+X)=4.9+/-1.4 pb. The probability to measure a cross section at this value or higher in the absence of a signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa matrix element that describes the Wtb coupling and find 0.68<|V(tb)|</=1 at 95% C.L. within the standard model.

We present a measurement of the shape of the $Z/{\ensuremath{\gamma}}^{*}$ boson transverse momentum (${q}_{T}$) distribution in $p\overline{p}\ensuremath{\rightarrow}Z/{\ensuremath{\gamma}}^{*}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}+X$ events at a center-of-mass energy of 1.96 TeV using $0.98\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. The data are found to be consistent with the resummation prediction at low ${q}_{T}$, but above the perturbative QCD calculation in the region of ${q}_{T}&gt;30\text{ }\text{ }\mathrm{GeV}/c$. Using events with ${q}_{T}&lt;30\text{ }\text{ }\mathrm{GeV}/c$, we extract the value of ${g}_{2}$, one of the nonperturbative parameters for the resummation calculation. Data at large boson rapidity $y$ are compared with the prediction of resummation and with alternative models that employ a resummed form factor with modifications in the small Bjorken $x$ region of the proton wave function.

We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psiLambda) = 0.28+/-0.09(stat)(-0.08)(+0.09)(syst).

We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron ppbar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top quark partner that is always produced from strong coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top quark production has been searched for in ever larger datasets. In this analysis, we select events from a 0.9 fb-1 dataset that have an electron or muon and missing transverse energy from the decay of a W boson from the top quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W+jets and ttbar events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top quark production of 4.7 +- 1.3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top quark production.

We combine measurements of the top quark pair production cross section in p¯p collisions in the ℓ+jets, ℓℓ, and τℓ final states (where ℓ is an electron or muon) at a center of mass energy of √s=1.96 TeV in 1 fb−1 of data collected with the D0 detector. For a top quark mass of 170 GeV/c2, we obtain σt¯t=8.18+0.98−0.87 pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined t¯t cross section, consistent with the world average of the top quark mass. In addition, the ratios of t¯t cross sections in different final states are used to set upper limits on the branching fractions B(t→H+b→τ+νb) and B(t→H+b→c¯sb) as a function of the charged Higgs boson mass.Received 31 March 2009DOI:https://doi.org/10.1103/PhysRevD.80.071102©2009 American Physical Society

We present the first measurement of dijet angular distributions in ppbar collisions at sqrt{s}=1.96TeV at the Fermilab Tevatron Collider. The measurement is based on a dataset corresponding to an integrated luminosity of up to 0.7fb-1 collected with the D0 detector. Dijet angular distributions have been measured over a range of dijet masses, from 0.25TeV to above 1.1TeV. The data are in good agreement with the predictions of perturbative QCD and are used to constrain new physics models including quark compositeness, large extra dimensions, and TeV-1 scale extra dimensions. For all models we set the most stringent direct limits to date.

A fully reconstructed Bc-->J/psipi signal is observed with the D0 detector at the Fermilab Tevatron pp[over] collider using 1.3 fb(-1) of integrated luminosity. The signal consists of 54+/-12 candidates with a significance that exceeds 5 standard deviations, and confirms earlier observations of this decay. The measured mass of the Bc meson is 6300+/-14(stat)+/-5(syst) MeV/c2.

The cross section for the inclusive production of isolated photons has been measured in pp¯ collisions at s=1.96TeV with the DØ detector at the Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV and have pseudorapidity |η|<0.9. The cross section is compared with the results from two next-to-leading order perturbative QCD calculations. The theoretical predictions agree with the measurement within uncertainties.

Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the D0 detector in $p\overline{p}$ collisions at a center-of-mass energy $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$. The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of $150\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$. Azimuthal correlations are stronger at larger transverse momenta. These are well described in perturbative QCD at next-to-leading order in the strong coupling constant, except at large azimuthal differences where contributions with low transverse momentum are significant.

We report the observation of the doubly strange b baryon Omegab- in the decay channel Omegab(-)-->J/psiOmega-, with J/psi-->mu+mu(-) and Omega(-)-->LambdaK(-)-->(ppi-)K-, in pp collisions at sqrt[s]=1.96 TeV. Using approximately 1.3 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider, we observe 17.8+/-4.9(stat)+/-0.8(syst) Omegab- signal events at a mass of 6.165+/-0.010(stat)+/-0.013(syst) GeV. The significance of the observed signal is 5.4sigma, corresponding to a probability of 6.7 x 10(-8) of it arising from a background fluctuation.

We present a measurement of the W boson mass in W-->e(nu) decays using 1 fb-1 of data collected with the D0 detector during Run II of the Fermilab Tevatron collider. With a sample of 499830 W-->e(nu) candidate events, we measure M(W)=80.401+/-0.043 GeV. This is the most precise measurement from a single experiment.

We report the direct observation of the excited $L=1$ state ${B}_{s2}^{*}$ in fully reconstructed decays to ${B}^{+}{K}^{\ensuremath{-}}$. The mass of the ${B}_{s2}^{*}$ meson is measured to be $5839.6\ifmmode\pm\else\textpm\fi{}1.1(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.7(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, and its production rate relative to the ${B}^{+}$ meson is measured to be $[1.15\ifmmode\pm\else\textpm\fi{}0.23(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.13(\mathrm{syst})]%$.

We report the results of a search for associated production of charginos and neutralinos using a data set corresponding to an integrated luminosity of 2.3 fb−1 collected with the DØ experiment during Run II of the Tevatron proton–antiproton collider. Final states containing three charged leptons and missing transverse energy are probed for a signal from supersymmetry with four dedicated trilepton event selections. No evidence for a signal is observed, and we set limits on the product of production cross section and leptonic branching fraction. Within minimal supergravity, these limits translate into bounds on m0 and m1/2 that are well beyond existing limits.

We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb−1 of data collected at s=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron pp¯ Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.Received 27 September 2007DOI:https://doi.org/10.1103/PhysRevD.77.011106©2008 American Physical Society

The EPR-type strangeness correlation in the K0K0 system produced in the reaction pp→K0K0 at rest has been tested using the CPLEAR detector. The strangeness was tagged via strong interaction with absorbers away from the creation point. The results are consistent with the QM non-separability of the wave function and exclude a spontaneous wave-function factorisation at creation (CL >99.99%).

A search for pair production of doubly-charged Higgs bosons in the process p pbar to H++H-- to mu+mu+mu-mu- is performed with the D0 Run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive di-muon data collected at an energy of sqrt{s}=1.96 TeV, corresponding to an integrated luminosity of 113 pb-1. In the absence of a signal, 95 % confidence level mass limits of M(H++L)>118.4 GeV/c2 and M(H++R)>98.2 GeV/c2 are set for left-handed and right-handed doubly-charged Higgs bosons, respectively, assuming 100% branching into muon pairs.

We present a measurement of the electron charge asymmetry in pp[over ]-->W+X-->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.

We present new measurements of differential cross sections for Z/γ∗(→μμ)+jet+X production in a 1 fb−1 data sample collected with the DØ detector in pp¯ collisions at s=1.96TeV. Results include the first measurements differential in the Z/γ∗ transverse momentum and rapidity, as well as new measurements differential in the leading jet transverse momentum and rapidity. Next-to-leading order perturbative QCD predictions are compared to the measurements, and reasonable agreement is observed, except in the region of low Z/γ∗ transverse momentum. Predictions from two event generators based on matrix elements and parton showers, and one pure parton shower event generator are also compared to the measurements. These show significant overall normalization differences to the data and have varied success in describing the shape of the distributions.

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (tt¯) produced in pp¯ collisions at s=1.96 TeV by the Fermilab Tevatron Collider. We use 370 pb−1 of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and b¯-quark jets by using the charge and momenta of tracks within the jet cones. The data are consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQ¯ with |q|=4e/3. We place an upper limit on the fraction of QQ¯ pairs ρ<0.80 at the 90% C.L.Received 18 August 2006DOI:https://doi.org/10.1103/PhysRevLett.98.041801©2007 American Physical Society

This Letter presents the first strong evidence for the resolution of the excited $B$ mesons ${B}_{1}$ and ${B}_{2}^{*}$ as two separate states in fully reconstructed decays to ${B}^{+(*)}{\ensuremath{\pi}}^{\ensuremath{-}}$. The mass of ${B}_{1}$ is measured to be $5720.6\ifmmode\pm\else\textpm\fi{}2.4\ifmmode\pm\else\textpm\fi{}1.4\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and the mass difference $\ensuremath{\Delta}M$ between ${B}_{2}^{*}$ and ${B}_{1}$ is $26.2\ifmmode\pm\else\textpm\fi{}3.1\ifmmode\pm\else\textpm\fi{}0.9\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, giving the mass of the ${B}_{2}^{*}$ as $5746.8\ifmmode\pm\else\textpm\fi{}2.4\ifmmode\pm\else\textpm\fi{}1.7\text{ }\text{ }\mathrm{MeV}/{c}^{2}$. The production rate for ${B}_{1}$ and ${B}_{2}^{*}$ mesons is determined to be a fraction $(13.9\ifmmode\pm\else\textpm\fi{}1.9\ifmmode\pm\else\textpm\fi{}3.2)%$ of the production rate of the ${B}^{+}$ meson.

Using approximately 1.3 fb(-1) of data collected by the D0 detector between 2002 and 2006, we measure the lifetime of the Bc+/- meson in the Bc-/+-->J/psimicro+/-+X final state. A simultaneous unbinned likelihood fit to the J/psi+micro invariant mass and lifetime distributions yields a signal of 881+/-80(stat) candidates and a lifetime measurement of tau(Bc+/-)=0.448(-0.036)(+0.038)(stat)+/-0.032(syst) ps.

We present a search for the pair production of scalar top quarks, t˜, using 995 pb−1 of data collected in pp¯ collisions with the DØ detector at the Fermilab Tevatron Collider at s=1.96TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino (χ˜10), where χ˜10 is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. We find the yield of such events to be consistent with the standard model expectation, and exclude sets of t˜ and χ˜10 masses at the 95% C.L. that substantially extend the domain excluded by previous searches.

From an analysis of the decay B0s→J/ψϕ, we obtain the width difference between the light and heavy mass eigenstates ΔΓ≡(ΓL−ΓH)=0.17±0.09(stat)±0.02(syst) ps−1 and the CP-violating phase ϕs=−0.79±0.56(stat)+0.14−0.01(syst). Under the hypothesis of no CP violation (ϕs≡0), we obtain 1/¯¯¯Γ=¯τ(B0s)=1.52±0.08(stat)+0.01−0.03(syst) ps and ΔΓ=0.12+0.08−0.10(stat)±0.02(syst) ps−1. The data sample corresponds to an integrated luminosity of about 1.1 fb−1 accumulated with the D0 detector at the Fermilab Tevatron collider. This is the first direct measurement of the CP-violating mixing phase in the B0s system.Received 10 January 2007DOI:https://doi.org/10.1103/PhysRevLett.98.121801©2007 American Physical Society

We present a study of the polarization of the Υ(1S) and Υ(2S) states using a 1.3 fb−1 data sample collected by the D0 experiment in 2002–2006 during run II of the Fermilab Tevatron Collider. We measure the polarization parameter α=(σT−2σL)/(σT+2σL), where σT and σL are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum (pΥT) for the Υ(1S) and Υ(2S). Significant pΥT-dependent longitudinal polarization is observed for the Υ(1S). A comparison with theoretical models is presented.Received 18 April 2008DOI:https://doi.org/10.1103/PhysRevLett.101.182004©2008 American Physical Society

We search for long-lived charged massive particles using $1.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected by the D0 detector at the Fermilab Tevatron $p\overline{p}$ Collider. Time-of-flight information is used to search for pair produced long-lived tau sleptons, gauginolike charginos, and Higgsino-like charginos. We find no evidence of a signal and set 95% C.L. cross section upper limits for staus, which vary from 0.31 to 0.04 pb for stau masses between 60 and 300 GeV. We also set lower mass limits of 206 GeV (171 GeV) for pair produced charged gauginos (Higgsinos).

We search for the production of a heavy W′ gauge boson that decays to third generation quarks in 0.9 fb−1 of pp¯ collisions at s=1.96 TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W′ boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W′ bosons, we set lower mass limits of 739 GeV if the W′ boson decays to both leptons and quarks and 768 GeV if the W′ boson decays only to quarks. We also set limits on the coupling of the W′ boson to fermions as a function of its mass.Received 21 March 2008DOI:https://doi.org/10.1103/PhysRevLett.100.211803©2008 American Physical Society

We report on a search for large extra dimensions in a data sample of approximately 1 fb−1 of p¯p collisions at √s=1.96 TeV. We investigate Kaluza-Klein graviton production with a photon and missing transverse energy in the final state. At the 95% C.L. we set limits on the fundamental mass scale MD from 884 to 778 GeV for two to eight extra dimensions.Received 14 March 2008DOI:https://doi.org/10.1103/PhysRevLett.101.011601©2008 American Physical Society

The D0 Collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb−1 of pp¯ collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14−0.80+0.94pb for the t-channel and 1.05±0.81pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.

We report on a first search for production of the lightest neutral $CP$-even Higgs boson ($h$) in the next-to-minimal supersymmetric standard model, where $h$ decays to a pair of neutral pseudoscalar Higgs bosons ($a$), using $4.2\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data recorded with the D0 detector at Fermilab. The $a$ bosons are required to either both decay to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ or one to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and the other to ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$. No significant signal is observed, and we set limits on its production as functions of ${M}_{a}$ and ${M}_{h}$.

We present the results of a search for the flavor-changing neutral current decay B0s→μ+μ− using a data set with integrated luminosity of 240 pb−1 of p¯p collisions at √s=1.96 TeV collected with the D0 detector in run II of the Fermilab Tevatron collider. We find the upper limit on the branching fraction to be B(B0s→μ+μ−)≤5.0×10−7 at the 95% C.L. assuming no contributions from the decay B0d→μ+μ− in the signal region. This limit is the most stringent upper bound on the branching fraction B0s→μ+μ− to date.Received 15 October 2004DOI:https://doi.org/10.1103/PhysRevLett.94.071802©2005 American Physical Society

We present a measurement of the top quark mass with the matrix element method in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the matrix element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty. Using a data set of $0.4\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ taken with the D0 experiment at Run II of the Fermilab Tevatron Collider, the mass of the top quark is measured using topological information to be: ${m}_{\mathrm{top}}^{\ensuremath{\ell}+\mathrm{jets}}(\mathrm{topo})={169.2}_{\ensuremath{-}7.4}^{+5.0}(\mathrm{stat}+JES{)}_{\ensuremath{-}1.4}^{+1.5}(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}$, and when information about identified $b$ jets is included: ${m}_{\mathrm{top}}^{\ensuremath{\ell}+\mathrm{jets}}(b\mathrm{\text{-tag}})={170.3}_{\ensuremath{-}4.5}^{+4.1}(\mathrm{stat}+\phantom{\rule{0ex}{0ex}}JES{)}_{\ensuremath{-}1.8}^{+1.2}(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}$. The measurements yield a jet energy scale consistent with the reference scale.

We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV utilizing 425 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. We consider the final state of the top quark pair containing one high-pT electron or muon and at least four jets. We exploit specific kinematic features of ttbar events to extract the cross section. For a top quark mass of 175 GeV, we measure sigma_ttbar = 6.4 +1.3-1.2(stat} +/- 0.7(syst)+/- 0.4(lum) pb in good agreement with the standard model prediction.

We search for the production of single top quarks via flavor-changing neutral current couplings of a gluon to the top quark and a charm ($c$) or up ($u$) quark. We analyze 230 pb$^{-1}$ of lepton + jets data from $\ppbar$ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters $\kappacLambda$ and $\kappauLambda$, where $\kappag$ define the strength of $tcg$ and $tug$ couplings, and $\Lambda$ defines the scale of new physics. The limits at 95% C.L. are: $\kappacLambda < 0.15 \rm TeV^{-1}$ and $\kappauLambda < 0.037 \rm TeV^{-1}$.

We report the results of a search for pair production of doubly charged Higgs bosons via pp over-->H++H - - X-->mu+ mu+ mu- mu- X at sqrt s=1.96 TeV. We use a data set corresponding to an integrated luminosity of 1.1 fb(-1) collected from 2002 to 2006 by the D0 detector at the Fermilab Tevatron Collider. In the absence of an excess above the standard model background, lower mass limits of M(H L +/- +/-) >150 GeV/c2 and M(H R+/- +/-) >127 GeV/c2 at 95% C.L. are set, respectively, for left-handed and right-handed doubly charged Higgs bosons assuming a 100% branching ratio into muons.

We present a search for a narrow-width heavy resonance decaying into top quark pairs (X→tt¯) in pp¯ collisions at s=1.96TeV using approximately 0.9fb−1 of data collected with the DØ detector at the Fermilab Tevatron Collider. This analysis considers tt¯ candidate events in the lepton plus jets channel with at least one identified b jet and uses the tt¯ invariant mass distribution to search for evidence of resonant production. We find no evidence for a narrow resonance X decaying to tt¯. Therefore, we set upper limits on σX⋅B(X→tt¯) for different hypothesized resonance masses using a Bayesian approach. For a Topcolor-assisted technicolor model, the existence of a leptophobic Z′ boson with mass MZ′<700GeV and width ΓZ′=0.012MZ′ can be excluded at the 95% C.L.

We present cross section measurements for Z/gamma*+jets+X production, differential in the transverse momenta of the three leading jets. The data sample was collected with the D0 detector at the Fermilab Tevatron proton anti-proton collider at a center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 1 fb-1. Leading and next-to-leading order perturbative QCD predictions are compared with the measurements, and agreement is found within the theoretical and experimental uncertainties. We also make comparisons with the predictions of four event generators. Two parton-shower-based generators show significant shape and normalization differences with respect to the data. In contrast, two generators combining tree-level matrix elements with a parton shower give a reasonable description of the the shapes observed in data, but the predicted normalizations show significant differences with respect to the data, reflecting large scale uncertainties. For specific choices of scales, the normalizations for either generator can be made to agree with the measurements.

This Letter describes the search for a new heavy charged gauge boson W' decaying into an electron and a neutrino. The data were collected with the D0 detector at the Fermilab Tevatron pp[over] Collider at sqrt[s]=1.96 TeV, and correspond to an integrated luminosity of about 1 fb(-1). Lacking any significant excess in the data in comparison with known processes, an upper limit is set on sigma_(W') x B(W')-->e nu), and a W' boson with mass below 1.00 TeV can be excluded at the 95% C.L., assuming standard-model-like couplings to fermions. This result significantly improves upon previous limits and is the most stringent to date.

We present results from a study of p¯p→Wγ+X events utilizing data corresponding to 0.7 fb−1 of integrated luminosity at √s=1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We set limits on anomalous WWγ couplings at the 95% C.L. The one-dimensional 95% C.L. limits are 0.49<κγ<1.51 and −0.12<λγ<0.13. We make the first study of the charge-signed rapidity difference between the lepton and the photon and find it to be indicative of the standard model radiation-amplitude zero in the Wγ system.Received 1 March 2008DOI:https://doi.org/10.1103/PhysRevLett.100.241805©2008 American Physical Society

First measurements of the differential cross sections d;{3}sigma/(dp_{T};{gamma}dy;{gamma}dy;{jet}) for the inclusive production of a photon in association with a heavy quark (b, c) jet are presented, covering photon transverse momenta 30<p_{T};{gamma}<150 GeV, photon rapidities |y;{gamma}|<1.0, jet rapidities |y;{jet}|<0.8, and jet transverse momenta p_{T};{jet}>15 GeV. The results are based on an integrated luminosity of 1 fb;{-1} in pp[over ] collisions at sqrt[s]=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.

We measure the mass of the top quark using top-quark pair candidate events in the lepton+jets channel from data corresponding to 1 fb−1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider. We use a likelihood technique that reduces the jet energy scale uncertainty by combining an in situ jet energy calibration with the independent constraint on the jet energy scale (JES) from the calibration derived using photon+jets and dijet samples. We find the mass of the top quark to be 171.5±1.8(stat.+JES)±1.1(syst.) GeV.Received 14 July 2008DOI:https://doi.org/10.1103/PhysRevLett.101.182001©2008 American Physical Society

We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a bb pair, using 3.6 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.

We measure the t¯t production cross section in p¯p collisions at √s=1.96 TeV in the lepton+jets channel. Two complementary methods discriminate between signal and background: b tagging and a kinematic likelihood discriminant. Based on 0.9 fb−1 of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure σt¯t=7.62±0.85 pb, assuming the current world average mt=172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top-quark mass of 170±7 GeV.Received 19 March 2008DOI:https://doi.org/10.1103/PhysRevLett.100.192004©2008 American Physical Society

We have improved by two orders of magnitude the limit currently available for the CPT violation parameter Re(δ). To this purpose we have analyzed the full sample of neutral-kaon decays to eπν recorded in the CPLEAR experiment, where the strangeness of the neutral kaons was tagged at production and decay time. An appropriate function of the measured decay rates, including information from the analysis of π+π− decay channel, gives directly Re(δ). The result Re(δ)=(3.0±3.3stat±0.6syst)×10−4 is compatible with zero. Values for the parameters Im(δ), Re(x−) and Im(x+) were also obtained.

We report a new measurement of the $t\overline{t}$ production cross section in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV using events with one charged lepton (electron or muon), missing transverse energy, and jets. Using $425\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected using the D0 detector at the Fermilab Tevatron Collider, and enhancing the $t\overline{t}$ content of the sample by tagging $b$ jets with a secondary vertex tagging algorithm, the $t\overline{t}$ production cross section is measured to be ${\ensuremath{\sigma}}_{p\overline{p}\ensuremath{\rightarrow}t\overline{t}+X}=6.6\ifmmode\pm\else\textpm\fi{}0.9(\mathrm{stat}+\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.4(\mathrm{lum})\text{ }\text{ }\mathrm{pb}$. This cross section is the most precise D0 measurement to date for $t\overline{t}$ production and is in good agreement with standard model expectations.

We present measurements of the inclusive production cross sections of the Gamma(1S) bottomonium state in pp collisions at (square root)s = 1.96 TeV. Using the Gamma(1S) --> mu(+)mu(-) decay mode for a data sample of 159 +/- 10 pb(-1) collected by the D0 detector at the Fermilab Tevatron collider, we determine the differential cross sections as a function of the Gamma(1S) transverse momentum for three ranges of the Gamma(1S) rapidity: 0 < y(Gamma) < or = 0.6, 0.6 < y(Gamma) < or = 1.2, and 1.2 < y(Gamma) < or = 1.8.

We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp collisions, using 260 pb-1 of data collected with the D0 detector in Run II of the Fermilab Tevatron Collider. The cross sections for these processes are enhanced in many extensions of the standard model (SM), such as in its minimal supersymmetric extension at large tanbeta. The results of our analysis agree with expectations from the SM, and we use our measurements to set upper limits on the production of neutral Higgs bosons in the mass range of 90 to 150 GeV.

We measure the dimuon charge asymmetry $A$ in $p\overline{p}$ collisions at a center of mass energy $\sqrt{s}=1960\text{ }\text{ }\mathrm{GeV}$. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately $1.0\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. Assuming that the asymmetry $A$ is due to asymmetric ${B}^{0}\ensuremath{\leftrightarrow}{\overline{B}}^{0}$ mixing and decay, we extract the $CP$-violation parameter of ${B}^{0}$ mixing and decay: $\frac{\ensuremath{\mathfrak{R}}({ϵ}_{{B}^{0}})}{1+|{ϵ}_{{B}^{0}}{|}^{2}}=\frac{{A}_{{B}^{0}}}{4}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.0023\ifmmode\pm\else\textpm\fi{}0.0011(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.0008(\mathrm{syst}).$${A}_{{B}^{0}}$ is the dimuon charge asymmetry from decays of ${B}^{0}{\overline{B}}^{0}$ pairs. The general case, with $CP$ violation in both ${B}^{0}$ and ${B}_{s}^{0}$ systems, is also considered. Finally we obtain the forward-backward asymmetry that quantifies the tendency of ${\ensuremath{\mu}}^{+}$ to go in the proton direction and ${\ensuremath{\mu}}^{\ensuremath{-}}$ to go in the antiproton direction. The results are consistent with the standard model and constrain new physics.

We present the first simultaneous measurement of the ratio of branching fractions, R=B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(tt[over]) in the lepton plus jets channel using 0.9 fb(-1) of pp[over] collision data at sqrt(s)=1.96 TeV collected with the D0 detector. We extract R and sigma(tt[over]) by analyzing samples of events with 0, 1, and > or =2 identified b jets. We measure R=0.97(+0.09)/(-0.08)(stat+syst) and sigma(tt[over])=8.18(+0.09)(-0.84)(stat+syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.

We describe a search for production of a charged Higgs boson, qq[over ];{'}-->H;{+}, reconstructed in the tb[over ] final state in the mass range 180< or =M_{H;{+}}< or =300 GeV. The search was undertaken at the Fermilab Tevatron collider with a center-of-mass energy sqrt[s]=1.96 TeV and uses 0.9 fb;{-1} of data collected with the D0 detector. We find no evidence for charged Higgs boson production and set upper limits on the production cross section in the types I, II, and III two-Higgs-doublet models (2HDMs). An excluded region in the (M_{H;{+}}, tanbeta) plane for type I 2HDM is presented.

We present a study of events with Z bosons and associated jets produced at the Fermilab Tevatron collider in pp¯ collisions at a center of mass energy of 1.96 TeV. The data sample consists of nearly 14 000 Z/γ∗→e+e− candidates corresponding to an integrated luminosity of 0.4 fb−1 collected with the DØ detector. Ratios of the Z/γ∗+⩾n jet cross sections to the total inclusive Z/γ∗ cross section have been measured for n=1–4 jets, and found to be in good agreement with a next-to-leading order QCD calculation and with a tree-level QCD prediction with parton shower simulation and hadronization.

We present a search for the production of neutral Higgs bosons ϕ decaying into τ+τ− final states in p¯p collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated luminosity of approximately 1 fb−1, were collected by the D0 experiment at the Fermilab Tevatron Collider. Limits on the production cross section times branching ratio are set. The results are interpreted in the minimal supersymmetric standard model yielding limits that are the most stringent to date at hadron colliders.Received 16 May 2008DOI:https://doi.org/10.1103/PhysRevLett.101.071804©2008 American Physical Society

We provide the most precise measurement of the WW production cross section in pp collisions to date at a center of mass energy of 1.96 TeV, and set limits on the associated trilinear gauge couplings. The WW-->lnul'nu (l, l' = e, mu) decay channels are analyzed in 1 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. The measured cross section is sigma(pp --> WW) = 11.5+/-2.1(stat+syst)+/-0.7(lumi) pb. One- and two-dimensional 95% C.L. limits on trilinear gauge couplings are provided.

We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1 fb(-1) sample of candidate tt events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron pp Collider. We reconstruct the angle theta(*) between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting costheta(*) distribution finds that the fraction of longitudinal W bosons f(0)=0.425+/-0.166(stat)+/-0.102(syst) and the fraction of right-handed W bosons f(+)=0.119+/-0.090(stat)+/-0.053(syst), which is consistent at the 30% C.L. with the standard model.

We present a measurement of the fraction of inclusive W+jets events produced with net charm quantum number ±1, denoted W+c-jet, in pp¯ collisions at s=1.96 TeV using approximately 1 fb−1 of data collected by the DØ detector at the Fermilab Tevatron Collider. We identify the W+jets events via the leptonic W boson decays. Candidate W+c-jet events are selected by requiring a jet containing a muon in association with a reconstructed W boson and exploiting the charge correlation between this muon and W boson decay lepton to perform a nearly model-independent background subtraction. We measure the fraction of W+c-jet events in the inclusive W+jets sample for jet pT>20 GeV and pseudorapidity |η|<2.5 to be 0.074±0.019(stat.)±0.0140.012(syst.), in agreement with theoretical predictions. The probability that background fluctuations could produce the observed fraction of W+c-jet events is estimated to be 2.5×10−4, which corresponds to a 3.5σ statistical significance.

We report on a search for large extra spatial dimensions in the dielectron and diphoton channels using a data sample of 1.05 fb−1 of pp¯ collisions at a center-of-mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. The invariant mass spectrum of the data agrees well with the prediction of the standard model. We find the most restrictive 95% C.L. lower limits on the effective Planck scale between 2.1 and 1.3 TeV for 2 to 7 extra dimensions.Received 18 September 2008DOI:https://doi.org/10.1103/PhysRevLett.102.051601©2009 American Physical Society

We present the first measurements at a hadron collider of differential cross sections for Z/γ∗+jet+X production in Δϕ(Z,jet), |Δy(Z,jet)| and |yboost(Z+jet)|. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.

Abstract As part of its HL-LHC upgrade program, the CMS collaboration is developing a High Granularity Calorimeter (CE) to replace the existing endcap calorimeters. The CE is a sampling calorimeter with unprecedented transverse and longitudinal readout for both electromagnetic (CE-E) and hadronic (CE-H) compartments. The calorimeter will be built with ∼30,000 hexagonal silicon modules. Prototype modules have been constructed with 6-inch hexagonal silicon sensors with cell areas of 1.1 cm 2 , and the SKIROC2-CMS readout ASIC. Beam tests of different sampling configurations were conducted with the prototype modules at DESY and CERN in 2017 and 2018. This paper describes the construction and commissioning of the CE calorimeter prototype, the silicon modules used in the construction, their basic performance, and the methods used for their calibration.

Abstract The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly read out by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data.

Data from the CPLEAR experiment, together with the most recent world averages for some of the neutral-kaon parameters, were constrained with the Bell–Steinberger (or unitarity) relation, allowing the T-violation parameter Re(ϵ) and the CPT-violation parameter Im(δ) of the neutral-kaon mixing matrix to be determined with an increased accuracy: Re(ϵ)=(164.9±2.5)×10−5, Im(δ)=(2.4±5.0)×10−5. Moreover, the constraint allows the CPT-violation parameter for the neutral-kaon semileptonic decays, Re(y), to be determined for the first time. The ΔS≠ΔQ parameters Re(x−) and Im(x+) are given with an increased accuracy. The quantity Re(y+x−), which enters the T-violation CPLEAR asymmetry previously published, is determined to be (−0.2±0.3)×10−3. The value obtained for Re(δ) is in agreement with the one resulting from a previous unconstrained fit and has a slightly smaller error.

We present a search for electroweak production of single top quarks in the s-channel and t-channel using neural networks for signal–background separation. We have analyzed 230 pb−1 of data collected with the DØ detector at the Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no evidence for a single top quark signal. The resulting 95% confidence level upper limits on the single top quark production cross sections are 6.4 pb in the s-channel and 5.0 pb in the t-channel.

LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.

The results of a search for squarks and gluinos using data from pp¯ collisions recorded at a center-of-mass energy of 1.96 TeV by the DØ detector at the Fermilab Tevatron Collider are reported. The topologies analyzed consist of acoplanar-jet and multijet events with large missing transverse energy. No evidence for the production of squarks or gluinos was found in a data sample of 310 pb−1. Lower limits of 325 and 241 GeV were derived at the 95% C.L. on the squark and gluino masses, respectively, within the framework of minimal supergravity with tanβ=3, A0=0, and μ<0.

We present a measurement of the top quark pair (tt¯) production cross section (σtt¯) in pp¯ collisions at a center-of-mass energy of 1.96 TeV using 230 pb−1 of data collected by the DØ detector at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), large missing transverse energy, and at least four jets, and extract the tt¯ content of the sample based on the kinematic characteristics of the events. For a top quark mass of 175 GeV, we measure σtt¯=6.7−1.3+1.4(stat)−1.1+1.6(syst)±0.4(lumi)pb, in good agreement with the standard model prediction.

We present a measurement of the top quark pair (tt¯) production cross section (σtt¯) in pp¯ collisions at s=1.96TeV using 230 pb−1 of data collected by the DØ experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the tt¯ purity of the selected sample. For a top quark mass of 175 GeV, we measure σtt¯=8.6−1.5+1.6(stat.+syst.)±0.6(lumi.)pb, in agreement with the standard model expectation.

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 h 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 pp collisions at square root(s) = 1.96 TeV collected with the D0 detector during Run II of the Fermilab Tevatron collider are analyzed in search of such "stopped gluinos" decaying into a gluon and a neutralino (chi(1)(0)). Limits are placed on the (gluino cross section) x (probability to stop) x [BR(g --> g chi(1)(0))] as a function of the gluino and chi(1)(0) masses, for gluino lifetimes from 30 micros-100 h.

We present a measurement of the forward-backward charge asymmetry (${A}_{FB}$) in $p\overline{p}\ensuremath{\rightarrow}Z/{\ensuremath{\gamma}}^{*}+X\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}+X$ events at a center-of-mass energy of 1.96 TeV using $1.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. ${A}_{FB}$ is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the ${A}_{FB}$ measurement to extract the effective weak mixing angle ${sin}^{2}{\ensuremath{\theta}}_{W}^{\mathrm{eff}}=0.2326\ifmmode\pm\else\textpm\fi{}0.0018(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.0006(\mathrm{syst})$.

We present a search for a narrow resonance in the inclusive diphoton final state using approximately 2.7 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron pp Collider. We observe good agreement between the data and the background prediction, and set the first 95% C.L. upper limits on the production cross section times the branching ratio for decay into a pair of photons for resonance masses between 100 and 150 GeV. This search is also interpreted in the context of several models of electroweak symmetry breaking with a Higgs boson decaying into two photons.

The process pp¯→γ+jet+X is studied using 1.0 fb−1 of data collected by the D0 detector at the Fermilab Tevatron pp¯ collider at a center-of-mass energy s=1.96TeV. Photons are reconstructed in the central rapidity region |yγ|<1.0 with transverse momenta in the range 30<pTγ<400GeV while jets are reconstructed in either the central |yjet|<0.8 or forward 1.5<|yjet|<2.5 rapidity intervals with pTjet>15GeV. The differential cross section d3σ/dpTγdyγdyjet is measured as a function of pTγ in four regions, differing by the relative orientations of the photon and the jet in rapidity. Ratios between the differential cross sections in each region are also presented. Next-to-leading order QCD predictions using different parameterizations of parton distribution functions and theoretical scale choices are compared to the data. The predictions do not simultaneously describe the measured normalization and pTγ dependence of the cross section in the four measured regions.

We present a measurement of the top quark pair production cross section in pp¯ collisions at s=1.96TeV using approximately 1 fb−1 collected with the DØ detector. We consider decay channels containing two high pT charged leptons where one lepton is identified as an electron or a muon while the other lepton can be an electron, a muon or a hadronically decaying τ lepton. For a mass of the top quark of 170 GeV, the measured cross section is 7.5−1.0+1.0(stat)−0.6+0.7(syst)−0.5+0.6(lumi)pb. Using ℓτ events only, we measure: σtt¯×B(tt¯→ℓτbb¯)=0.13−0.08+0.09(stat)−0.06+0.06(syst)−0.02+0.02(lumi)pb. Comparing the measured cross section as a function of the mass of the top quark with a partial next-to-next-to leading order Quantum Chromodynamics theoretical prediction, we extract a mass of the top quark of 171.5−8.8+9.9GeV, in agreement with direct measurements.

In a data sample of approximately 1.3 fb;{-1} collected with the D0 detector between 2002 and 2006, the orbitally excited charm state D_{s1};{+/-}(2536) has been observed with a measured mass of 2535.7+/-0.6(stat)+/-0.5(syst) MeV/c;{2} via the decay mode B_{s};{0}-->D_{s1};{-}(2536)mu;{+}nu_{mu}X. A first measurement is made of the branching ratio product Br(b[over ]-->D_{s1};{-}(2536)mu;{+}nu_{mu}X)xBr(D_{s1};{-}-->D;{*-}K_{S};{0}). Assuming that D_{s1};{-}(2536) production in semileptonic decay is entirely from B_{s};{0}, an extraction of the semileptonic branching ratio Br(B_{s};{0}-->D_{s1};{-}(2536)mu;{+}nu_{mu}X) is made.

We combine the D0 measurement of the width difference between the light and heavy B0s mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B0s→J/ψϕ decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B0s lifetime, we obtain ΔΓs≡(ΓL−ΓH)=0.13±0.09 ps−1 and |ϕs|=0.70+0.39−0.47 or ΔΓs=−0.13±0.09 ps−1 and |ϕs|=2.44+0.47−0.39. The data sample corresponds to an integrated luminosity of 1.1 fb−1 accumulated with the D0 detector at the Fermilab Tevatron Collider.Received 21 February 2007DOI:https://doi.org/10.1103/PhysRevD.76.057101©2007 American Physical Society

We present a search for charged Higgs bosons in decays of top quarks, in the mass range $80 < m_{H^{\pm} < 155$ GeV, assuming the subsequent decay $H^{+} \to \tau^{+} \nu_\tau$ (and its charge conjugate). Using 0.9 fb$^{-1}$ of lepton+jets data collected with the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider, operating at a center of mass energy $\sqrt{s}=1.96$ TeV, we find no evidence for a $H^{\pm}$ signal. Hence, we exclude branching ratios $B(t \to H^+b) > 0.24$ for $m_{H^{\pm}=80$ GeV, and $B(t \to H^+b) > 0.19$ for $m_{H^{\pm}=155$ GeV, at the 95% C.L.

We present a study of micro micro micro micro, eeee, and micro micro ee events using 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron pp[over ] Collider at square root s=1.96 TeV. Requiring the lepton pair masses to be greater than 30 GeV, we observe one event, consistent with the expected background of 0.13+/-0.03 events and with the predicted standard model ZZ and Zgamma* production of 1.71+/-0.15 events. We set an upper limit on the ZZ and Zgamma* cross section of 4.4 pb at the 95% C.L. We also derive limits on anomalous neutral trilinear ZZZ and ZZgamma* gauge couplings. The one-parameter 95% C.L. coupling limits with a form-factor scale Lambda=1.2 TeV are -0.28<f(40)(Z)<0.28, -0.31<f(50)(Z)<0.29, -0.26<f(40)(gamma)<0.26, and -0.30<f(50)(gamma)<0.28.

We report results of a search for supersymmetry (SUSY) with gauge-mediated symmetry breaking in di-photon events collected by the D0 experiment at the Fermilab Tevatron Collider in 2002–2006. In 1.1 fb−1 of data, we find no significant excess beyond the background expected from the standard model and set the most stringent lower limits to date for a standard benchmark model on the lightest neutralino and chargino masses of 125 GeV and 229 GeV, respectively, at 95% confidence.

We have performed a search for $CP$ violation in a sample of ${B}_{s}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{D}_{s}^{\ensuremath{-}}X$ decays corresponding to $5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of proton-antiproton collisions collected by the D0 detector in Run II at the Fermilab Tevatron Collider. New physics in ${B}_{s}^{0}$ mixing could contribute a significant $CP$ violating weak phase, which would be observed as a difference in the decay-time distribution for ${B}_{s}^{0}\ensuremath{\rightarrow}{\overline{B}}_{s}^{0}$ oscillated states versus that for ${\overline{B}}_{s}^{0}\ensuremath{\rightarrow}{B}_{s}^{0}$. A fit to the decay-time distributions of the ${B}_{s}^{0}/{\overline{B}}_{s}^{0}$ candidates yields the flavor-specific asymmetry ${a}_{\mathrm{fs}}^{s}=[\ensuremath{-}1.7\ifmmode\pm\else\textpm\fi{}9.1(\mathrm{stat}{)}_{\ensuremath{-}1.5}^{+1.4}(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which excludes $CP$ violation due to new physics within the experimental sensitivity.

We have searched for third generation leptoquarks (${\mathrm{LQ}}_{3}$) using $1.05\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the D0 detector at the Fermilab Tevatron Collider operating at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$. We set a 95% C.L. lower limit of 210 GeV on the mass of a scalar ${\mathrm{LQ}}_{3}$ state decaying solely to a $b$ quark and a $\ensuremath{\tau}$ lepton.

To investigate the fundamental nature of matter and its interactions, particles are accelerated to very high energies and collided inside detectors, producing a multitude of other particles that are scattered in all directions. As charged particles traverse the detector, they leave signals of their passage. The problem of track reconstruction is to recover the original trajectories from these signals. This challenging data analysis task will become even more demanding as the luminosity of future accelerators increases, leading to collision events with a more complex structure. We identify four fundamental routines present in every local tracking method and analyse how they scale in the context of a standard tracking algorithm. We show that for some of these routines we can reach a lower computational complexity with quantum search algorithms. Although the found quantum speedups are mild, this constitutes, to the best of our knowledge, the first rigorous evidence of a quantum advantage for a high-energy physics data processing task.

We report the first direct search for the Kaluza-Klein (KK) modes of Randall-Sundrum gravitons using dielectron, dimuon, and diphoton events observed with the D0 detector operating at the Fermilab Tevatron pp(-) Collider at sqrt[s]=1.96 TeV. No evidence for resonant production of gravitons has been found in the data corresponding to an integrated luminosity of approximately equal to 260 pb(-1). Lower limits on the mass of the first KK mode at the 95% C.L. have been set between 250 and 785 GeV, depending on its coupling to standard model particles.

We present the results of a search for the effects of large extra spatial dimensions in pp collisions at sqrt[s] = 1.96 TeV in events containing a pair of energetic muons. The data correspond to 246 pb(-1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. Good agreement with the expected background was found, yielding no evidence for large extra dimensions. We set 95% C.L. lower limits on the fundamental Planck scale between 0.85 and 1.27 TeV within several formalisms. These are the most stringent limits achieved in the dimuon channel to date.

A search for direct production of scalar bottom quarks (b) is performed with 310 pb(-1) of data collected by the D0 experiment in pp collisions at square root s = 1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (chi(1)0), with chi(1)0 assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m(b), m(chi(1)0)) mass plane, improving significantly upon the results from run I of the Tevatron.

We report on a measurement of the ${B}_{d}^{0}$ mixing frequency and the calibration of an opposite-side flavor tagger in the D0 experiment. Various properties associated with the $b$ quark on the opposite side of the reconstructed $B$ meson are combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance is tested with data, using a large sample of reconstructed semileptonic $B\ensuremath{\rightarrow}\ensuremath{\mu}{D}^{0}X$ and $B\ensuremath{\rightarrow}\ensuremath{\mu}{D}^{*}X$ decays, corresponding to an integrated luminosity of approximately $1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The events are divided into groups depending on the value of the combined tagging variable, and an independent analysis is performed in each group. Combining the results of these analyses, the overall effective tagging power is found to be $\ensuremath{\epsilon}{\mathcal{D}}^{2}=(2.48\ifmmode\pm\else\textpm\fi{}{0.21}_{\ensuremath{-}0.06}^{+0.08})%$. The measured ${B}_{d}^{0}$ mixing frequency $\ensuremath{\Delta}{m}_{d}=0.506\ifmmode\pm\else\textpm\fi{}0.020(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.016(\mathrm{syst})\text{ }\text{ }{\mathrm{ps}}^{\ensuremath{-}1}$ is in good agreement with the world average value.

A search for the production of neutral Higgs bosons $\ensuremath{\Phi}$ decaying into ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ final states in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of approximately $325\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$, 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 $\ensuremath{\Phi}b(\overline{b})\ensuremath{\rightarrow}b\overline{b}b(\overline{b})$ and are interpreted in the minimal supersymmetric standard model.

A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from pp¯ collisions at s=1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between tt¯ signal and background from other physics processes and to improve the assignment of the observed jets to the quarks in the tt¯ hypothesis. We extract a multiplicative jet energy scale (JES) factor in situ, greatly reducing the systematic effect related to the jet energy measurement. In a data sample with an integrated luminosity of 425 pb−1, we observe 230 candidate events, with an estimated background of 123 events, and measure mt=173.7±4.4(stat+JES)−2.0+2.1(syst) GeV. This result represents the first application of the ideogram technique to the measurement of the top quark mass in lepton+jets events.2 MoreReceived 11 February 2007DOI:https://doi.org/10.1103/PhysRevD.75.092001©2007 American Physical Society

In 0.9 fb(-1) of pp[over] collisions, the D0 Collaboration presented evidence for single top quark production in events with an isolated lepton, missing transverse momentum, and two to four jets. We examine these data to study the Lorentz structure of the Wtb coupling. The standard model predicts a left-handed vector coupling at the Wtb vertex. The most general lowest dimension, CP-conserving Lagrangian admits right-handed vector and left- or right-handed tensor couplings as well. We find that the data prefer the left-handed vector coupling and set upper limits on the anomalous couplings. These are the first direct constraints on a general Wtb interaction and the first direct limits on left- and right-handed tensor couplings.

We present a measurement of the $t\overline{t}$ pair production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ utilizing approximately $425\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected with the D0 detector. We consider decay channels containing two high ${p}_{T}$ charged leptons (either $e$ or $\ensuremath{\mu}$) from leptonic decays of both top-daughter $W$ bosons. These were gathered using four sets of selection criteria, three of which required that a pair of fully identified leptons (i.e., $e\ensuremath{\mu}$, $ee$, or $\ensuremath{\mu}\ensuremath{\mu}$) be found. The fourth approach imposed less restrictive criteria on one of the lepton candidates and required that at least one hadronic jet in each event be tagged as containing a $b$ quark. For a top quark mass of 175 GeV, the measured cross section is $7.4\ifmmode\pm\else\textpm\fi{}1.4(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.0(\mathrm{syst})\text{ }\text{ }\mathrm{pb}$ and for the current Tevatron average top quark mass of 170.9 GeV, the resulting value of the cross section is $7.8\ifmmode\pm\else\textpm\fi{}1.8(\mathrm{stat}+\mathrm{syst})\text{ }\text{ }\mathrm{pb}$.

We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs σ(pp¯→Z+X)Br(Z→τ+τ−) in pp¯ collisions at s=1.96TeV. The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos, and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb−1 collected with the DØ detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain σ⋅Br=240±8(stat)±12(sys)±15(lum)pb, which is consistent with the standard model prediction.

We report on a search for the pair production of second generation scalar leptoquarks (LQ) in pp¯ collisions at the center of mass energy s=1.96TeV using a data set corresponding to an integrated luminosity of 1.0fb−1 collected with the DØ experiment at the Fermilab Tevatron Collider. Topologies arising from the LQLQ¯→μqνq and LQLQ¯→μqμq decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction β for the decay LQ→μq. These are interpreted as lower limits on the leptoquark mass as a function of β. For β=1(0.5), scalar second generation leptoquarks with masses up to 316 GeV (270 GeV) are excluded.

We search for a new light gauge boson, a dark photon, with the D0 experiment. In the model we consider, supersymmetric partners are pair produced and cascade to lightest neutralinos that can decay into the hidden sector state plus either a photon or a dark photon. The dark photon decays through its mixing with a photon into fermion pairs. We therefore investigate a previously unexplored final state that contains a photon, two spatially close leptons, and large missing transverse energy. We do not observe any evidence for dark photons and set a limit on their production.

A search for pair production of first-generation leptoquarks (LQ) is performed with data collected by the DØ experiment in pp¯ collisions at s=1.96TeV at the Fermilab Tevatron Collider. In a sample of data corresponding to ∼1fb−1 the search has been performed on the final states with two electrons and two jets or one electron, two jets and missing transverse energy. We find our data consistent with standard model expectations. The results are combined with those found in a previous analysis of events with two jets and missing transverse energy to obtain scalar LQ mass limits. We set 95% C.L. lower limits on a scalar LQ mass of 299 GeV, 284 GeV and 216 GeV for β=1, β=0.5 and β=0.02 respectively, where β is the LQ branching ratio in the eq channel. This improves the results obtained with a lower luminosity sample from Run II of the Tevatron. Lower limits on vector LQ masses with different couplings from 357 GeV to 464 GeV for β=0.5 are also set using this analysis.