Nucl.Instrum.Meth.A552:372-398,2005 We describe the design, construction and performance of the upgraded DO muon
system for Run II of the Fermilab Tevatron collider. Significant improvements
have ...been made to the major subsystems of the DO muon detector: trigger
scintillation counters, tracking detectors, and electronics. The Run II central
muon detector has a new scintillation counter system inside the iron toroid and
an improved scintillation counter system outside the iron toroid. In the
forward region, new scintillation counter and tracking systems have been
installed. Extensive shielding has been added in the forward region. A large
fraction of the muon system electronics is also new.
We have searched for a heavy resonance decaying into a Z+jet final state in p-pbar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No ...indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370/pb. We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.
A search for gaugino pair production with a trilepton signature in the framework of R-parity violating supersymmetry via the couplings lambda_121, lambda_122, or lambda_133 is presented. The data, ...corresponding to an integrated luminosity of L~360/pb, were collected from April 2002 to August 2004 with the D0 detector at the Fermilab Tevatron Collider, at a center-of-mass energy of sqrt(s)=1.96 TeV. This analysis considers final states with three charged leptons with the flavor combinations eel, mumul, and eetau (l=e or mu). No evidence for supersymmetry is found and limits at the 95% confidence level are set on the gaugino pair production cross section and lower bounds on the masses of the lightest neutralino and chargino are derived in two supersymmetric models.
We present a new method for modeling the hadronic recoil in W->lnu events produced at hadron colliders. The recoil is chosen from a library of recoils in Z->ll data events and overlaid on a simulated ...W->lnu event. Implementation of this method requires that the data recoil library describe the properties of the measured recoil as a function of the true, rather than the measured, transverse momentum of the boson. We address this issue using a multidimensional Bayesian unfolding technique. We estimate the statistical and systematic uncertainties from this method for the W boson mass and width measurements assuming 1 fb-1 of data from the Fermilab Tevatron. The uncertainties are found to be small and comparable to those of a more traditional parameterized recoil model. For the high precision measurements that will be possible with data from Run II of the Fermilab Tevatron and from the CERN LHC, the method presented in this paper may be advantageous, since it does not require an understanding of the measured recoil from first principles.
We investigate the decay B^+ -> J/psi phi K^+ in a search for the X(4140) state, a narrow threshold resonance in the J/psi phi system. The data sample corresponds to an integrated luminosity of 10.4 ...fb^{-1} of ppbar collisions at sqrt s =1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider. We observe a mass peak with a statistical significance of 3.1 standard deviations and measure its invariant mass to be M=4159.0 +-.3 (stat) +- 6.6 (syst) MeV and its width to be Gamma= 19.9+-12.6 (stat)}^{+1.0}_{-8.0} (syst) MeV. Identifying this mass peak as the X(4140), we measure, for M(J/psi phi) <4.59 GeV, the relative branching fraction B_rel= B(B^+ -> X(4140) K^+)/ B(B^+ ->J/psi phi K^+) to be 21+-8 (stat) +- 4 (syst)%. In addition, the data can accommodate the presence of a second enhancement at a mass of 4328.5+- 12.0 MeV.
Phys.Rev.Lett.88:191801,2002 We present the results of a search for leptoquark (LQ) pairs in (85.2 +- 3.7)
pb^{-1} of p anti-p collider data collected by the D0 experiment at the
Fermilab Tevatron. ...We observe no evidence for leptoquark production and set a
limit on sigma(p anti-p -> LQ anti-LQ -> neutrino neutrino + jets) as a
function of the mass of the leptoquark (m_{LQ}). Assuming the decay LQ ->
neutrino q, we exclude scalar leptoquarks for m_{LQ} < 98 GeV/c^2, and vector
leptoquarks for m_{LQ} < 200 GeV/c^2 and coupling which produces the minimum
cross section, at a 95% confidence level.
Phys.Lett.B525:211-218,2002 The central inclusive jet cross section has been measured using a
successive-combination algorithm for reconstruction of jets. The measurement
uses 87.3 pb^{-1} of data ...collected with the D0 detector at the Fermilab
Tevatron ppbar Collider during 1994-1995. The cross section, reported as a
function of transverse momentum (pT>60 GeV) in the central region of
pseudorapidity (|\eta|<0.5), exhibits reasonable agreement with next-to-leading
order QCD predictions, except at low pT where the agreement is marginal.
We describe a search for evidence of minimal supergravity (mSUGRA) in 92.7 pb^(-1) of data collected with the DØdetector at the Fermilab Tevatron ppbar collider at center of mass energy of 1.8 TeV. ...Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W+jets, misidentified multijet, ttbar, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of mSUGRA model parameters is obtained.
Phys.Rev.D65:052008,2002 The D0 Collaboration has studied for the first time the properties of
hadron-collider jets reconstructed with a successive-combination algorithm
based on relative transverse ...momenta ($k_{\perp}$) of energy clusters. Using
the standard value D = 1.0 of the jet-separation parameter in the $k_{\perp}$
algorithm, we find that the $p_T$ of such jets is higher than the $E_T$ of
matched jets reconstructed with cones of radius R = 0.7, by about 5 (8) GeV at
$p_T \approx 90$ (240) GeV. To examine internal jet structure, the $k_{\perp}$
algorithm is applied within D = 0.5 jets to resolve any subjets. The
multiplicity of subjets in jet samples at $\sqrt{s} = 1800$ GeV and 630 GeV is
extracted separately for gluons ($M_g$) and quarks ($M_q$), and the ratio of
average subjet multiplicities in gluon and quark jets is measured as $(M_{g} -
1) / (M_{q} - 1) = 1.84 \pm 0.15 (stat.) \pm ^{0.22}_{0.18} (sys.)$. This ratio
is in agreement with the expectations from the HERWIG Monte Carlo event
generator and a resummation calculation, and with observations in $e^+e^-$
annihilations, and is close to the naive prediction for the ratio of color
charges of $C_A/C_F = 9/4 = 2.25$.
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