## D0 Abstracts submitted to ICHEP '06

### QCD hard interaction session:

High PT QCD at D0 (Inclusive jet, Inclusive photon)

The Fermilab Tevatron has been running well and has collected over 1 fb-1 of data. We will present new results in inclusive jet properties from nearly the full data sample, allowing more precise tests of QCD and structure function measurements. In addition we will present inclusive isolated photon measurements, with comparisons to theory.

Heavy flavor QCD (high Pt B tagged jets, W Charm production cross section) at D0

With the multi-decade effort to understand the properties of inclusive jets now well advanced, the more difficult task of studying the properties of exclusive heavy flavor jets has become quite interesting. The theoretical predictions of heavy flavor jets is in some way simpler than the inclusive case and also is sensitive to heavy flavor structure functions (strange, charm and bottom). We present here the fraction of bottom quark jets as a function of jet Pt and dijet mass, ranging from 40 GeV/c and 100 GeV/c2 respectively up to the kinematic limit. In addition a study of charm jet produced with W bosons investigates the structure function of strange quarks.

### QCD soft interaction session:

Diffractive physics (j/psi production, elastic production) at D0

Diffractive physics processes are measured using data collected by the upgraded D0 Detector at the Tevatron $p\bar{p}$ collider. Single diffractive data are selected by demanding pseudorapidity regions with no energy deposits (above threshold) in the detector. Diffractive events in which the beam protons and antiprotons scatter at small angles (~ 1 mrad) are studied using a system of low-angle momentum spectrometers positioned along the Tevatron beamline.

### Electroweak Physics Session

WZ production cross section measurement in p-pbar collisions at the Tevatron

We present a study of the WZ diboson events using data with integrated luminosity of approximately 0.8/fb collected by the D0 experiment at the Tevatron Run II at center-of-mass energy of 1.96 TeV. The signal from processes of WZ -> 3 leptons + neutrino and associated background are studied in detail and WZ production cross section is measured.

Study of Wgamma production in p-pbar collisions at the Tevatron

The coupling parameters for the WWgamma vertex are studied by using final state lepton (electron or muon), neutrino, and photon events that were collected by the Dzero detector at Tevatron Run II at a center-of-mass energy of 1.96 TeV. The analysis is based on ~1/fb of integrated luminosity. Physical features of the WWgamma gauge coupling are discussed. The importance of the Standard Model radiation amplitude zero in the photon-lepton charge signed rapidity difference is detailed.

Zgamma production and limits on anomalous couplings

We present a measurement of the Zgamma production cross section and limits on anomalous ZZgamma and Zgammagamma couplings. The measurement is based on ~1/fb of integrated luminosity collected by the D0 detector at the Tevatron Run II. We also set limits on resonance production in the Zgamma final state.

W production asymmetry measurement in W to munu channel

We present a measurement of the muon charge asymmetry from ppbar -> W -> munu decays. The measurement is based on data collected by D0 experiment at the Tevatron Run II at center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 0.23/fb. The measured charge asymmetry can be used as an additional input to constraint PDFs.

Measurement of Z/gamma* rapidity distribution in p-pbar collisions at the Tevatron

We present a measurement of p-pbar -> Z/gamma* -> e+e- inclusive differential cross section as a function of boson rapidity in a di-electron mass range between 71 to 111 GeV. The data were collected during Run II at the Tevatron collider at center-of-mass energy of 1.96 TeV and correspond to an integrated luminosity of 0.4/fb. At Tevatron Z bosons are produced with rapidities out to +-3. With the D0 detector, the cross section is measured over almost the entire kinematic range.

Measurement of Z/gamma* pT distribution in p-pbar collisions at the Tevatron

The Tevatron has delivered more than 1/fb of p-pbar data with a center-of-mass energy of 1.96 TeV to the D0 experiment. Using events containing two high pT electrons a preliminary measurement of the Z/gamma* cross section and the differential distribution dsigma(Z/gamma* -> e+e-)/dpT(Z) have been obtained. The new result has significantly smaller statistical error than the previous measurement from Run I data. Improved knowledge on the Z transverse momentum spectra, especially at low pT(Z), will reduce the systematic uncertainty in the W mass measurement.

Anomalous Trilinear Gauge Coupling limits from WW pair production at the Tevatron

We present limits on anomalous WWgamma and WWZ trilinear gauge couplings obtained using the final states WW->ee, WW->emu, and WW->mumu. The results are based on data collected by the D0 detector during Run II at the Tevatron collider at center-of-mass of 1.96 TeV and correspond to an integrated luminosity of 0.25/fb. Under the assumption that the WWgamma couplings are equal to the WWZ couplings, the combined 95% confidence level coupling limits from all three channels with a form factor scale of Lambda = 2.0 TeV are -0.33 < Delta kappa < 0.46, -0.30 < lambda < 0.31.

W/Z inclusive cross section measurements at Tevatron

We present measurement of inclusive W->enu/munu and Z->e+e-/mu+mu- production cross sections in p-pbar collisions at center-of-mass energy of 1.96 TeV. The data is collected by D0 detector at Tevatron Run II. Indirect measurement of W boson width is extracted using W and Z boson production cross section ratio.

Search for associated W-Higgs production at D0

A search for WH production in pp-bar collisions at a center of mass energy of sqrt(s)=1.96 TeV is presented. Events containing one lepton, missing transverse energy, and one or two b-tagged jets are considered. The analysis is performed separately in the electron and muon channel, with a further subdivision between events having one and two b-tagged jets in the final state. In the single and double b-tagged samples, good agreement between data and the standard model is observed. The combined result of both lepton channels is presented.

Search for associated Z-Higgs production at D0 in the Z->l+l-bb final state

A search for ZH production in pp-bar collisions at a center of mass energy of sqrt(s)=1.96 TeV is presented. Events containing two charged leptons and one or two b-tagged jets are considered. The analysis is performed in the electron and muon channel, with a further subdivision between events having one and two b-tagged jets in the final state. In the single and double b-tagged samples, good agreement between data and the standard model is observed. The combined result of both lepton channels is presented.

Search for associated Z-Higgs production at D0 in the Z->nunubb final state

A search for the standard model Higgs boson produced in association with the Z boson in pp-bar collisions at sqrt(s)=1.96 TeV is presented. We study the channel in which the Z boson decays into two neutrinos. This channel is one of the most sensitive ways to search for light Higgs bosons because of the large Z->nunu and H->bb-bar branching ratios. Search is done in a sample of multijet events with large imbalance in transverse momentum and two b-tagged jets. Limits on the ZH production cross section times the H->bb-bar branching ratio are set based on comparisons of observed and expected number of events in a mass range around the hypothesized Higgs masses.

Search for WH->WWW at D0

We search for associated Higgs boson production in the process pp-bar -> WH -> WWW where two out of three W bosons decay leptonically, producing two like-signed leptons in the dielectron, dimuon and electron-muon final states. We require two like sign isolated leptons (electrons or muons) with p_T >15 GeV plus additional selection cuts. The number of observed like-sign events is in agreement with the standard model expectations. We set upper limits on WH production cross section times the branching ratio of H->WW for various Higgs mass hypotheses.

Search for gg->H->WW at D0

A search for the Higgs boson is presented in H -> WW -> ll' (l, l' = e, µ) decays in pp collisions at a center-of-mass energy of sqrt(s) = 1.96 TeV. Final states containing two oppositely signed leptons (dielectrons, dimuons and electron-muon) have been considered. The data corresponding to an integrated luminosity of the order of 1 fb-1 have been analyzed. No significant excess above the Standard Model background has been observed and upper limits on the gg->H production cross section times the branching ratio for H->WW are presented.

Combined Search for the SM Higgs boson at D0

Upper limits on the cross section for Standard Model Higgs boson production in pp-bar -> H+X at sqrt(s)=1.96 TeV are determined for 100 < m_H < 200 GeV. The contributing processes include associated production (WH->lnubb, ZH->nunubb, and WH->WWW) and gluon fusion (H->WW). Limits for various combinations of the channels are presented.

Measurement of Z+njets at D0

We present a study of events with Z bosons and hadronic jets produced at the Tevatron in pp-bar collisions at a center of mass energy of 1.96 TeV. The data sample consists of Z->ee candidates collected using the D0 detector. We measure ratios of the Z/gamma*(->e+e-)+>=n jet cross sections to the total inclusive Z/gamma*->e+e- cross Z/gamma* + >=1 to 5 jet events. We also make comparisons of kinematic distributions to QCD predictions of matrix-element calculation plus parton shower simulation. Our results are 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.

Measurement of Z(->bbbar) production cross-section at D0

A search for Z->bb production and decay has been performed at D0. Candidate events are selected by triggering on muons coming from the semileptonic decay of the b-jets. Signal extraction is challenging due to the huge cross section of generic dijet events. Two slightly different methods of estimating the background from data have been explored. In both approaches, a significant excess of events is observed after background subtraction. Both results are in good agreement with Monte Carlo predictions of the Standard Model.

Single Top Quark Production at the D0 Experiment

We present the results of a search for the electroweak production of single top quarks by the D0 collaboration at the Fermilab Tevatron proton-antiproton collider. We perform independent analyses for two separate production mechanisms, the s-channel and t-channel modes, and search for the channels combined, in the electron+jets and muon+jets final states. We apply loose selection cuts and employ $b$-tagging of jets to improve the signal-background ratio. We then apply advanced multivariate methods to separate the expected signal from the backgrounds to maximize the search sensitivity.

Search for Single Top Quarks Produced via Flavor-Changing Neutral-Current Couplings at the D0 Experiment

The top quark is a good candidate for probing models beyond the Standard Model, since any anomalous coupling would first be observed in the top quark sector because of its unusually large mass, close to the electroweak symmetry-breaking scale. One form of anomalous couplings are the flavor-changing neutral currents, which can give rise to a single top quark in the final state through a gluon exchange, with a $c$ or a $u$ quark in the initial or final state. We search for single top quark production through both the $tcg$ and $tug$ couplings in 230~pb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron proton-antiproton collider, and present limits on the anomalous coupling parameters $\kappa_c/\Lambda$ and $\kappa_u/\Lambda$, where $\Lambda$ defines the scale of the new physics, and $\kappa_c$ ($\kappa_u$) defines the strength of the $tcg$ ($tug$) couplings.

Measurement of the Top Quark Mass at D0 Using Lepton+Jets Events

We report on the measurement of the top quark mass using t-tbar candidates in the lepton+jets final states. For each event, a matrix element probability is calculated as a function of the top mass and the overall jet energy scale. The top mass and jet energy scale are extracted by maximizing a likelihood constructed as the product of the single event probabilities. The overall jet energy scale is constraint by the two hadronic jets forming a W boson. This reduces the large uncertainty due to the jet energy scale.

Measurement of the Top Quark Mass at D0 Using Dilepton Events

We report on the measurement of the top quark mass using t-tbar candidates in the dilepton final states. The kinematics of these events are solved for a range of assumed top quark masses, and the relative likelihood of each solution is assessed. Information from the complete set of events is combined in a maximum likelihood fit to extract the top quark mass and its uncertainty.

Measurement of the W Boson Helicity in Top Quark Decay at D0

We report on a measurement of the fraction of right-handed W bosons in top quark decay. In the Standard Model, this fraction is too small to measure with the current data sample, so a non-zero value would be a clear sign of new physics. The measurement uses t-tbar events in both the lepton+jets and dilepton decay channels, and is based upon the helicity angle theta* between the charged lepton and top quark directions in the W boson rest frame.

### Heavy Quark Physics Session

Measurement of the Branching Fraction for ${B}_{s} \rightarrow {D}_{s1}^{\pm}(2536) \mu \nu {X} \:$ at D0

The orbitally excited charm state ${D}_{s1}^{\pm}(2536)$ has been observed at D0 in the decay channel ${B}_{s} \rightarrow {D}_{s1}^{\pm}(2536) \mu \nu {X} \:$ with ${D}_{s1}^{\pm}(2536) \rightarrow {D}^{* \pm} K^0_S \:$. The ${D}_{s1}^{\pm}(2536)\:$ mass peak is presented with a signal significance of greater than 5.0$\sigma$ and the branching fraction for the semileptonic decay to this state is measured in approximately 1~fb$^{-1}$ of data.

Study of the form factor in semileptonic $\Lambda_b$ decays

We measure the $\Lambda_b$ baryon form factor using the exclusive decay ${\Lambda^0_b \rightarrow \Lambda^+_c \mu^- \bar{\nu}}$ followed by $\Lambda^+_c \rightarrow p^+ K^0_S$ and $K^0_S \rightarrow \pi^+ \pi^-$. The data sample corresponds to an integrated luminosity of approximately 1~fb$^{-1}$, recorded with the D0 detector in $p\bar{p}$ collisions at $\sqrt{s} =1.96$~TeV. We present a preliminary result on the Isgur-Wise slope.

Study of the $B_c$ lifetime via the decay $B_c \rightarrow J/\psi mu \nu X$ The $B_c$ meson is unique as a meson in that it contains two different, yet heavy quarks, resulting in a lifetime that is expected to be shorter than the other $b$ hadrons. Using approximately 1 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron during Run \textrm{II}, the $B_c$ meson in the semileptonic mode $B_c^\pm \rightarrow J/\psi \mu^\pm \nu X$ is studied. Preliminary results on the measured lifetime of this particle are presented.

$\Lambda_b$ lifetime measurement using semileptonic decays at D0

Using approximately 1 fb$^{-1}$ of data collected by the D0 detector in Run II, a sample of over 2000 $\Lambda_b \rightarrow \Lambda_c \mu X (\Lambda_c \rightarrow K_s p)$ decays has been reconstructed. We present preliminary results of a measurement of the $\Lambda_b$ lifetime using this sample.

A precise measurement of the $B^0_s$ lifetime

We report the lifetime measurement of the flavor--specific $B_s^0$ meson decay $B^0_{s}\rightarrow D^-_s \mu^{+}\nu X$, using approximately 400 pb$^ {-1}$ of data collected by the D0 detector during 2002--2004. We have reconstructed 5176 $D^-_s \mu^{+}$ candidate events, from which we have measured the $B^0_s$ lifetime with a combined statistical and systematic uncertainty of less than 16 $\mu$m which is the currently most precise measurement of the $B_s^0$ lifetime.

$B_s$ oscillations

We report results on the determination of the $B_{s}$ oscillation frequency using approximately 1 fb$^{-1}$ of data taken at the D0 experiment during Run IIa at the Tevatron. We search for oscillations in the time dependence of flavor specific $B_s$ decays where the flavor of the $B_s$ at production is determined by studying inclusive properties of the event.

Search for rare flavor-changing and electroweak penguin decays of the $B^0_s$ meson

Using 1 fb$^{-1}$ of data collected with the D0 detector in Run II of the Tevatron, limits are presented for searches for the rare flavor changing neutral current decay $B^0_s \rightarrow \mu^+ \mu^-$, as well as $B^0_s \rightarrow \mu^+ \mu^- \phi$. The former decay mode is particularly sensitive to supersymmetric extensions of the Standard Model. For the latter mode, a measurement of the branching ratio could validate the prediction of the Standard Model.

Measurement of ${\cal B}(B_s \rightarrow D^+_s D^-_s)$

The branching ratio ${\cal B}(B_s \rightarrow D^+_s D^-_s)$ provides an alternative way to estimate the width difference in the $B_s$ system. We report a preliminary result on the measurement of the branching ratio of the decay $B_s \to D^+_s D^-_s$ using 1 fb$^{-1}$ of data collected with the D\O\ detector of the Tevatron.

Study of $B^{**}$ and $B_s^{**}$

Using 1 fb$^{-1}$ of data collected with the D0 detector of the Tevatron, the excited states containing a $b$ quark $B_1$, $B_2^*$ and $B_{s2}^*$ are selected in exclusive decays. A precise measurement of their masses, widths and branching rates is reported.

Measurement of the Lifetime Difference in the $B^0_s$ System

Using approximately 1 fb$^{-1}$ of data collected with the D0 detector of the Tevatron, we present a study of the decay $B^0_s\rightarrow J/\psi\phi$. From a simultaneous fit to the distributions in the candidate mass, proper decay length, and three angles of the decay products, we obtain the average lifetime of the $(B^0_s,\bar{B^0_s})$ system and the width difference between the light and heavy mass eigenstates.

Search for Flavor Changing Neutral Current Charm Decays $D\rightarrow \pi^+\mu^+\mu^-$ We study the flavor changing neutral current process $c\rightarrow u \mu^+ \mu^-$ using approximately $1$ fb$^{-1}$ of $p \bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV recorded by the D0 detector operating at the Fermilab Tevatron. We observe the $D_s^+\rightarrow \phi \pi^+ \rightarrow \pi^+ \mu^+\mu^-$ final state and see evidence for $D^+\rightarrow \phi \pi^+ \rightarrow \pi^+ \mu^+\mu^-$. We search for continuum production of $D^+\rightarrow \pi^+\mu^+\mu^-$ in the dimuon invariant mass spectrum away from the $\phi$ resonance. We see no evidence of signal above background in this mode.

$B_d$ mixing measurement using opposite-side flavor tagging

We describe a measurement of the $B_d$ mixing frequency and construction of an opposite-side flavor tagger at the D0 experiment. Various properties associated with the $b$ quark opposite to the reconstructed $B$ hadron were combined together into a single variable with an enhanced tagging power. The algorithm is applied to a large sample of semileptonic $B_d$ decays to determine the initial flavor of the $B_d$ meson. The mixing frequency is extracted from the time dependent asymmetry between mixed and un-mixed data samples.

Measurement of the CP-violation parameter of $B^0$ mixing and decay using 1 fb$^{-1}$ of $p\bar{p}$ data

We measure the dimuon charge asymmetry in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of 1 fb$^{-1}$. Assuming that the asymmetry is due to asymmetric $B^0$ mixing and decay, we extract the CP-violation parameter of $B^0$ mixing and decay $Re(\epsilon_{B^0})/(1 + |\epsilon_{B^0}|^2) = -0.0011 \pm 0.0010 \pm 0.0007$.

$\Lambda_b$ lifetime measurement using fully reconstructed decays at

D0 We report the measurement of the $\Lambda_b$ lifetime in the fully reconstructed decay channel $\Lambda_b\rightarrow J/\psi \Lambda$ using a 1 fb$^{-1}$ data sample at D0. The measurement is also performed on the similar decay channel $B^0\rightarrow J/\psi K_S$ to extract the $B^0$ lifetime and determine the ratio of lifetimes of the $\Lambda_b$ and $B^0$.

Measurement of the CP-violation parameter of $B^0_s$ mixing and decay using 1 fb$^{-1}$ of $p\bar{p}$ data

We measure the charge asymmetry between $B^0_s\rightarrow D^-_s\mu^+ X$ and $\bar{B^0_s}\rightarrow D^+_s\mu^-X$ decays in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of 1 fb$^{-1}$. Assuming that the asymmetry is due to asymmetric $B^0$ mixing and decay, we extract the CP-violation parameter of $B^0_s$ mixing and decay $Re(\epsilon_{B_s})/(1 + |\epsilon_{B_s}|^2)$.

Measurement of the Top Quark Charge at D0

We report on a measurement of the charge of the top quark by resolving the kinematic ambiguity between the standard model scenario of a charge 2/3 quark decaying to W+ b and an exotic scenario of a charge –4/3 quark decaying to W– b. We distinguish between the two scenarios by measuring the charge of the b jet that is kinematically most consistent with arising from the same top quark as the charged lepton.

Measurement of the t-tbar Production Cross Section at D0 Using b Tagging

We report on the measurement of the t-tbar production cross section using candidate events in the lepton+jets final state. The t-tbar signal is discriminated from background processes by the requirement of one or more identified b jets.

Measurement of the t-tbar Production Cross Section at D0 Using Kinematic Information

We report on the measurement of the t-tbar production cross section using candidate events in the lepton+jets final state. The t-tbar signal is discriminated from background processes using kinematic information. Several kinematic variables are combined into a multivariate discriminant to maximize the separation between signal and background.

Measurement of the t-tbar Production Cross Section at D0 Using Dilepton Events

We report on the measurement of the t-tbar production cross section with candidate events in the dilepton final state. The t-tbar signal is discriminated from background processes by requiring two identified leptons and by using kinematic criteria that exploit the presence of neutrinos and energetic jets in t-tbar events.

Measurement of the t-tbar Production Cross Section at D0 Using Lepton + Track Events

We report on the measurement of the t-tbar production cross section with candidate events in the dilepton final state in which only one of the leptons satisfies our usual identification criteria, while the other appears as an isolated charged track. The t-tbar signal is discriminated from background processes by requiring at least one b-tagged jet and by using kinematic criteria that exploit the presence of neutrinos and energetic jets in t-tbar events.

Measurement of the t-tbar Production Cross Section at D0 Using All-Hadronic Events

We report on the measurement of the t-tbar production cross section with candidate events in the all-hadronic final state. The t-tbar signal is discriminated from the QCD multijet background process by requiring identified b-tagged jets and W bosons reconstructed from dijets. A data-derived background sample is normalized to the candidate sample using the dijet mass spectrum in the region below the W mass. The all-hadronic mass spectrum is then fit to derive the t-tbar production cross section.

Measurement of B(t->Wb)/B(t->Wq) at D0

We report on a measurement of the ratio R=B(t->Wb)/B(t->Wq). In the standard model this ratio is > 0.998 at the 95% confidence level. Experimentally, we measure the ratio by fitting the fraction of candidate events that have 0, 1, or 2 b-tagged jets.

### Beyond the Standard model session

Search for Technicolor in the Wbb(c) final state at D0

A search for technicolor in W(->lnu)bQ production, where Q = b, c-quark, at D0 using l + jets events is presented. We select events with b-quark jets by identifying secondary vertices in the jets. We interpret our findings in terms of limits on the production of particles predicted by extended technicolor models and in particular for the production decay chain rho_T -> W(-> e?) + pi_T. In the absence of an excess over standard model background, we compute a 95% C.L. upper limit on the techni-particle production cross section for several techni-rho and techni-pi mass combinations.

Search for Higgs->Z+gamma at D0

We present the results of a search for Higgs boson produced in pp-bar collisions at sqrt(s)=1.96 TeV with the Higgs boson subsequently decaying to Z+gamma. We search for resonances in the Z+gamma invariant mass spectrum. We set limits on the product of cross section times branching fraction as a function of mass between 100 and 1000 GeV.

Search for Susy Higgs in the bbh final state at D0

We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp-bar collisions at sqrt(s)=1.96 TeV, with the Higgs decaying into two bottom quarks. 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 tan beta. 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.

Search for Susy Higgs in the btautau final state at D0

We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp-bar collisions at sqrt(s)=1.96 TeV, with the Higgs boson subsequently decaying into a pair of taus. 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 tan beta. 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.

Search for Susy Higgs in the h->tautau final state at D0

A search for the production of neutral Higgs bosons decaying into a pair of tau lepton final states in pp-bar collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of up to 1 pb-1, have been analyzed. Limits on the production cross section times branching ratio are set. The results are interpreted in the context of minimal supersymmetric standard model.

Search for doubly-charged higgs at D0

A search for pair production of doubly charged Higgs bosons in the process pp-bar -> H++ H--, with each doubly charged Higgs decaying leptonically. The analysis is based on a sample of inclusive dielectron, dimuon and electron+muon data collected at an energy of sqrt(s)=1.96 TeV. In the absence of a signal, 95% confidence level mass limits are set for left-handed and right-handed doubly charged Higgs bosons.

Search for third generation squarks and for generic squarks and gluinos with the D0 detector.

Four searches for squarks and gluinos are reported. They were conducted in 310 - 350 pb-1 of data from ppbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider. A search for generic squarks and gluinos was performed in events with jets and large missing transverse energy. A search for the pair production of scalar bottom quarks was performed in events with two acoplanar b jets. Scalar top quarks were searched in two decay modes: stop into c chi,leading to a final state consisting of two acoplanar charm jets; stop into b l sneutrino, leading to final states containing two leptons with missing transverse energy. No deviation from the standard model expectation was observed in any of these searches, resulting in mass limits for generic squarks, gluinos, top and bottom squarks which are the most constraining to date in supergravity-inspired models with R-parity conservation.

Search for supersymmetry in trilepton final states with the D0 detector.

The D0 experiment at the Fermilab Tevatron p-pbar collider has taken data corresponding to an integrated luminosity of more than 1 fb-1 at a center-of-mass energy of 1.96 TeV. One of the main goals of the D0 experiment is the search for new particles such as Charginos and Neutralinos that are predicted in supersymmetric extensions of the Standard Model. The golden mode at the Tevatron for the search of the associated production of Charginos and Neutralinos is the trilepton channel where the supersymmetric particles decay directly or in cascades into charged leptons and the lightest supersymmetric particle (LSP). Assuming R-parity conservation the LSP, in this case the lightest Neutralino, is stable, leading to final states with three charged leptons and missing transverse energy. Different analyses have been developed taking into account different combinations of electron, muon, and tau final states. In this talk the selection strategy for the different final states (dilepton+track and like-sign dileptons) will be discussed and the latest results will be presented.

Search for R-parity violating supersymmetry with the D0 detector

Searches for R-parity violating supersymmetry are presented. We have searched for gaugino pair production in trilepton final states, and for neutral long-lived particles in final states with two muons, both decaying via non-zero LLE couplings. An other search aims at resonant slepton production via a LQD coupling with a di-muon signature. We analyzed 0.38 fb^-1 of integrated luminosity collected between April 2002 and August 2004 with the D0 detector at the Fermilab Tevatron Collider. The observed numbers of events are in agreement with the standard model expectation, and we calculate 95% confidence level limits on the production cross sections times branching ratio. For gaugino pair production and resonant slepton production, lower bounds on the involved sparticle masses in the framework of minimal supergravity are set. An excluded domain in the plane of the mass and lifetime of a neutral long-lived particle is determined. Previous results obtained in Run I of the Tevatron, at LEP, and at NuTev are significantly extended.

Search for supersymmetry with the D0 detector: GMSB, AMSB and Split

SUSY. This talk covers preliminary D0 results on searches for supersymmetry (SUSY) in final states with photons or long-lived SUSY particles. Such final states arise in various flavors of gauge-mediated or anomaly-mediated SUSY breaking, as well as in "split SUSY", a scenario where all SUSY scalars are very heavy.

Search for large extra dimensions in the monojet topology with the D0 detector

A search for signals of extra spatial dimensions is performed using about 0.8 fb-1 of data from p-pbar collisions at a center-of-mass energy of 1.96 TeV, collected by the DO detector at the Fermilab Tevatron. The topologies analyzed consist of single jets and acoplanar jets with missing E_T. The data show good agreement with the standard model expectations; in absence of evidence for a signal from large extra dimensions, new limits on the fundamental Planck scale have been derived.

Search for leptoquarks with the D0 detector

A search for leptoquarks has been performed in 310 pb-1 of data from ppbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron. The topology analyzed consists of acoplanar jets with missing ET. The data show good agreement with the standard model expectations, and a mass lower limit of 136 GeV has been set at 95% CL for a scalar leptoquark decaying exclusively into a quark and a neutrino.

Search for excited leptons and quarks with the D0 detector

Results of direct searches for quark and lepton substructure with the D0 experiment at the Tevatron proton antiproton collider are presented, using a data sample of about 0.4 fb^-1 at sqrt(s) = 1.96 TeV. We search for an excited state of the muon, mu*, in the process ppbar -> mu* mu, with the mu* subsequently decaying to a muon plus photon. Interpreting the data in the context of a model that describes mu* production by four-fermion contact interactions and mu* decay via electroweak processes, masses below 618 GeV are excluded for a scale for contact interactions of Lambda = 1 TeV. We also search for resonances in the Z+jet channel, where the Z decays into e+e-. Upper limits on the cross section as a function of the resonance mass and width are set. In a specific model of excited quark production mass values m(q*) less than 510 GeV are excluded for Lambda = m(q*).

Search for large extra dimensions and for heavy resonances in dilepton, diphoton and electron + missing ET final states with the D0 detector

The high-mass spectrum of lepton and photon pairs is sensitive to a broad array of new physics. Examples are searches for large spatial extra dimensions in different models in the dielectron, dimuon, and diphoton channels, and Z´ bosons with Standard-Model-like couplings to fermions as well as in a variety of GUT-inspired models. In addition, the electron (or muon) plus missing ET data sample can be searched for a W´ boson. We report on the latest results in searches in the high mass dielectron, dimuon, diphoton, and electron plus missing ET channels obtained by the D0 experiment at the Tevatron, using a data set corresponding to an integrated luminosity of up to 1 fb^-1.

Search for $W^{\prime}$ Bosons in the Top Quark Decay Channel at the D0 Experiment

We present the results of a search for a new heavy boson $W^{\prime}$ in the top quark decay channel using 230~pb$^{-1}$ of data collected with the D0 detector at the Tevatron proton-antiproton collider.

A Search for Resonant t-tbar Production at D0

We report on a search for a massive particle that decays to t-tbar. The search is performed using t-tbar candidates in the lepton+jets channel. A constrained kinematic fit, with top quark mass fixed, is used to evaluate the t-bar invariant mass for each candidate. We then search for deviations from the t-tbar mass distribution predicted by QCD.

### Grid Computing

Grid Computing for D0

The DO experiment is a pioneer in Grid computing for large scale production activities manipulating collider data samples. In 2005, the collaboration undertook a full reconstruction of 1 Billion raw data events using SAMGrid. This effort took six months, 3.0 THz of cpu distributed at 12 sites and the distribution of 200 TB of data to the sites and 50 TB of output back to the primary storage at FNAL, and the use of proxy servers to distribute calibration constants. This effort enabled D0 to run a secondary level reprocessing on a data set of 1.5 Billion events at using 3.2 THz at 7 sites in 5 weeks in February 2006. In addition, D0 generates Monte Carlo events on the grid, producing of 150 M full Geant/fully reconstructed events in the past six months. As part of these efforts, SAMGrid has moved to a fully interoperating mode with LCG and OSG middleware for job brokering and resource selection.

### R & D for future accelerators, detectors & new facilities

Development of the replacement Analog Front End boards with timing (AFEII-t) for the fiber tracker detectors at Dzero.

The Dzero experiment operates a Fiber Tracker with about 77K channels read out using Visible Light Photon Counters. In addition, the Central and Forward Preshower detectors use the same technology and electronics which brings the total number of channels to approximately 100k. As the instantaneous luminosity of the Tevatron grows, the limitations of the original electronics can become a serious problem. Therefore Dzero developed a replacement front-end readout board, the AFEII-t, which is backwards compatible with the existing system, but offers powerful tools for improving operations at the highest instantaneous luminosity and removes the limitations of the current electronics. AFEII-t uses modern FPGA based design in combination with a custom mixed signal ASIC developed at Fermilab (the TriP-t chip) to provide backward compatibility while reducing noise, improving efficiency and giving a fine timing measurement (~1ns) which can be used to improve pattern recognition. We describe the design, development and testing of this electronics.

Upgrades to D0 for Triggering at High Luminosity

With increasing Tevatron luminosity, efficient triggers that meet the bandwidth limitations of the experiment's data acquisition system become more and more difficult to construct. To meet these challenges, the D0 experiment has significantly enhanced the capability of its three-level trigger system. The major components of this upgrade are (1) a completely re-designed level-1 calorimeter trigger that uses novel architecture and algorithms to maintain acceptable background rejection while preserving or even improving signal efficiency at the highest luminosities foreseen (2) an upgrade to the central track trigger which uses a new generation of FPGA's for finer granularity track finding at level 1 to reduce the combinatoric backgrounds from multiple interactions, (3) a new system to match tracks with calorimeter objects at level 1, (4) an increase of processing power and algorithm improvements at level 2, and (5) the incorporation of the new silicon layer-0 detector into the silicon track trigger at level 2. We describe interesting features of the trigger upgrades and give highlights from their first few months of operation.

Design and Performance of the Layer 0 Detector for D0

We describe a new inner layer silicon strip detector installed in the D0 experiment at Fermilab in April of 2006. It is designed to provide a low mass, high resolution, radiation hard, inner layer for the D0 Silicon Microstrip Tracker (D0SMT). Layer 0 should improve impact parameter resolution for low Pt tracks by a factor of two and b-tagging efficiency in top decay by 15%. The detector consists of 48 silicon strip sensors mounted on six facets on a 1.68 m long, 1.6 cm. radius carbon fiber support structure. It was installed through the inner aperture of the existing D0 Silicon Microstrip Tracker. Sensors near the interaction point, with longer analog cables, are 7cm long, while the four sensors at the ends of the facets are 12 cm long; resulting in approximately balanced capacitive loads. Sensors on the inner facets have 71 micron pitch, while those in the outer facets have 81 micron pitch. This combination provides 98.4% geometrical coverage while keeping the device compact. A variety of techniques were utilized to minimize coherent noise in the readout system. Our initial tests indicate very low levels of coherent noise, below 10% of the random noise. We describe the design of the detector and discuss its performance at the Tevatron.