1,122 research outputs found
Self-Consistency and Calibration of Cluster Number Count Surveys for Dark Energy
Cluster number counts offer sensitive probes of the dark energy if and only
if the_evolution_ of the cluster mass versus observable relation(s) is well
calibrated. We investigate the potential for internal calibration by demanding
consistency in the counts as a function of the observable. In the context of a
constant dark energy equation of state, known initial fluctuation amplitude
expected from the CMB, universal underlying mass function, and an idealized
selection, we find that the ambiguity from the normalization of the
mass-observable relationships, or an extrapolation of external mass-observable
determinations from higher masses, can be largely eliminated with a
sufficiently deep survey, even allowing for an arbitrary evolution. More
generally, number counts as a function of both the redshift and the observable
enable strong consistency tests on assumptions made in modelling the
mass-observable relations and cosmology.Comment: 4 pages, 3 figures, submitted to PRD rapid communication
Search for right-handed W bosons in top quark decay
We present a measurement of the fraction f+ of right-handed W bosons produced
in top quark decays, based on a candidate sample of events in the
lepton+jets decay mode. These data correspond to an integrated luminosity of
230pb^-1, collected by the DO detector at the Fermilab Tevatron
Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the
kinematics of the and decay products, which allows for the
measurement of the leptonic decay angle for each event. By comparing
the distribution from the data with those for the expected
background and signal for various values of f+, we find
f+=0.00+-0.13(stat)+-0.07(syst). This measurement is consistent with the
standard model prediction of f+=3.6x10^-4.Comment: Submitted to Physical Review D Rapid Communications 7 pages, 3
figure
Measurement of the Lifetime Difference in the B_s^0 System
We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd
fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/-
0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0)
=1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width
difference between the heavy and light mass eigenstates, Delta Gamma/Gamma =
(Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst).
With the additional constraint from the world average of the B_s^0$lifetime
measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps
and Delta Gamma/\Gamma = 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and
B^0 lifetimes we obtain tau(B_s^0)/tau(B^0)} = 0.91 +/- 0.09 (stat) +/- 0.003
(syst).Comment: submitted to Phys. Rev. Lett. FERMILAB-PUB-05-324-
Measurement of Semileptonic Branching Fractions of B Mesons to Narrow D** States
Using the data accumulated in 2002-2004 with the DO detector in
proton-antiproton collisions at the Fermilab Tevatron collider with
centre-of-mass energy 1.96 TeV, the branching fractions of the decays B ->
\bar{D}_1^0(2420) \mu^+ \nu_\mu X and B -> \bar{D}_2^{*0}(2460) \mu^+ \nu_\mu X
and their ratio have been measured: BR(\bar{b}->B) \cdot BR(B-> \bar{D}_1^0
\mu^+ \nu_\mu X) \cdot BR(\bar{D}_1^0 -> D*- pi+) =
(0.087+-0.007(stat)+-0.014(syst))%; BR(\bar{b}->B)\cdot BR(B->D_2^{*0} \mu^+
\nu_\mu X) \cdot BR(\bar{D}_2^{*0} -> D*- \pi^+) =
(0.035+-0.007(stat)+-0.008(syst))%; and (BR(B -> \bar{D}_2^{*0} \mu^+ \nu_\mu
X)BR(D2*0->D*- pi+)) / (BR(B -> \bar{D}_1^{0} \mu^+ \nu_\mu X)\cdot
BR(\bar{D}_1^{0}->D*- \pi^+)) = 0.39+-0.09(stat)+-0.12(syst), where the charge
conjugated states are always implied.Comment: submitted to Phys. Rev. Let
Search for Large Extra Spatial Dimensions in Dimuon Production with the D0 Detector
We present the results of a search for the effects of large extra spatial
dimensions in collisions at 1.96 TeV in events
containing a pair of energetic muons. The data correspond to 246 \ipb 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 TeV and 1.27 TeV within several
formalisms. These are the most stringent limits achieved in the dimuon channel
to date.Comment: 8 pages, 3 figures, 1 table. Published in Phys. Rev. Lett. Minor
changes in v2 to match the published versio
Search for R-parity violating supersymmetry via the LLE couplings lambda_{121}, lambda_{122} or lambda_{133} in ppbar collisions at sqrt(s)=1.96 TeV
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.Comment: 9 pages, 4 figures (fig2 includes 3 subfigures
Measurement of the ppbar to ttbar production cross section at sqrt(s)=1.96 TeV in the fully hadronic decay channel
A measurement of the top quark pair production cross section in proton
anti-proton collisions at an interaction energy of sqrt(s)=1.96 TeV is
presented. This analysis uses 405 pb-1 of data collected with the D0 detector
at the Fermilab Tevatron Collider. Fully hadronic ttbar decays with final
states of six or more jets are separated from the multijet background using
secondary vertex tagging and a neural network. The ttbar cross section is
measured as sigma(ttbar)=4.5 -1.9 +2.0 (stat) -1.1 +1.4 (syst) +/- 0.3 (lumi)
pb for a top quark mass of m(t) = 175 GeV/c^2.Comment: 10 pages, 10 figures, submitted to Phys. Rev.
Measurement of the Lifetime Using Semileptonic Decays
We report a measurement of the lifetime in the semileptonic decay
channel (and its charge conjugate), using
approximately 0.4 fb of data collected with the D0 detector during 2002
-- 2004. We have reconstructed 5176 signal events, where the
is identified via the decay , followed by . Using these events, we have measured the lifetime to be
. This is the most precise measurement of the lifetime to date.Comment: To appear in Phys. Rev. Lett., 7 pages, 2 figure
Search for Neutral Higgs Bosons Decaying to Tau Pairs in p-pbar Collisions at sqrt(s) = 1.96 TeV
A search for the production of neutral Higgs bosons Phi decaying into
tau^+tau^- final states in p-pbar collisions at a center-of-mass energy of 1.96
TeV is presented. The data, corresponding to an integrated luminosity of up to
348 pb^-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 Phi b(b) to b-bbar-b(bbar) and are interpreted in the minimal
supersymmetric standard model.Comment: Version accpeted by Phys. Rev. Lett. (minor changes
A search for W bb and W Higgs production in ppbar collisions at sqrt(s)=1.96 TeV
We present a search for W b \bar{b} production in p \bar{p} collisions at
sqrt{s}=1.96 TeV in events containing one electron, an imbalance in transverse
momentum, and two b-tagged jets. Using 174 pb-1 of integrated luminosity
accumulated by the D0 experiment at the Fermilab Tevatron collider, and the
standard-model description of such events, we set a 95% C.L. upper limit on W b
\bar{b}WH--$135
GeV.Comment: 7 pages, 4 figures, 1 table, submitted to Physical Review Letter
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