471 research outputs found
EFFECTS OF HANDLE AND BLOCK CONFIGURATION ON SWIM START PERFORMANCE
The purpose of this study was to quantify differences in swimming track start performances using side handle and front handle grip techniques and using an inclined platform at the rear of the starting platform. An instrumented starting block system was designed to allow front grip and side grip starting techniques and inclusion of a rear incline. Thirty male and 20 female junior elite swimmers completed three starts in each of four start block configurations: (1) Flat (traditional) block, front handle grip; (2) Flat (traditional) block, side handle grip; (3) Incline (new) block, front handle grip; (4) Incline (new) block, side handle grip. Force and video data were used to quantify parameters related to starting performance. Results indicated that use of side handles had a substantial impact on start performance while the effects of the rear incline were less pronounced. Compared to using a front grip technique, use of the side handles increased horizontal velocity at takeoff up to 18%, resulted in a more horizontal takeoff angle by up to 2°, increased contribution to horizontal impulse from arms up to 12%, increased peak horizontal power up to 28%, decreased time to 6 m by 4% and increased velocity at 6 m by 2.5%. These advantages were achieved at a cost of an 8% increase in propulsion time. Based on this study, we recommend swimmers develop familiarity with the use of side handles when performing a track start and to use this technique if handles are available on a starting block
Measurement of the B0_s semileptonic branching ratio to an orbitally excited D_s** state, Br(B0_s -> Ds1(2536) mu nu)
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 via
the decay mode B0_s -> D_s1(2536) mu nu X. A first measurement is made of the
branching ratio product Br(b(bar) -> D_s1(2536) mu nu X).Br(D_s1(2536)->D*
K0_S). Assuming that D_s1(2536) production in semileptonic decay is entirely
from B0_s, an extraction of the semileptonic branching ratio Br(B0_s ->
D_s1(2536) mu nu X) is made.Comment: 7 pages, 2 figures, LaTeX, version with minor changes as accepted by
Phys. Rev. Let
Search for single vector-like quarks in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for hypothetical vector-like quarks in ppbar collisions
at sqrt(s) = 1.96 TeV. The data were collected by the D0 detector at the
Fermilab Tevatron Collider and correspond to an integrated luminosity of 5.4
fb^(-1). We select events with a final state composed of a W or Z boson and a
jet consistent with a heavy object decay. We observe no significant excess in
comparison to the background prediction and set limits on production cross
sections for vector-like quarks decaying to W+jet and Z+jet. These are the most
stringent mass limits for electroweak single vector-like quark production at
hadron colliders.Comment: submitted to Phys. Rev. Let
Search for new fermions ("quirks") at the Fermilab Tevatron Collider
We report results of a search for particles with anomalously high ionization
in events with a high transverse energy jet and large missing transverse energy
in fb of integrated luminosity collected by the D0 experiment at
the Fermilab Tevatron collider. Production of such particles
(quirks) is expected in scenarios with extra QCD-like {\it SU(N)} sectors, and
this study is the first dedicated search for such signatures. We find no
evidence of a signal and set a lower mass limit of 107 ~GeV for the mass of a
charged quirk with strong dynamics scale in the range from 10 keV to
1 MeV.Comment: submitted to Phys. Rev. Letter
Simultaneous measurement of the ratio B(t->Wb)/B(t->Wq) and the top quark pair production cross section with the D0 detector at sqrt(s)=1.96 TeV
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_ttbar in the lepton plus jets channel
using 0.9 fb-1 of ppbar collision data at sqrt(s)=1.96 TeV collected with the
D0 detector. We extract R and sigma_ttbar by analyzing samples of events with
0, 1 and >= 2 identified b jets. We measure R = 0.97 +0.09-0.08 (stat+syst) and
sigma_ttbar = 8.18 +0.90-0.84 (stat+syst)} +/-0.50 (lumi) pb, in agreement with
the standard model prediction.Comment: submitted to Phys.Rev.Letter
Measurements of differential cross sections of Z/gamma*+jets+X events in proton anti-proton collisions at sqrt{s}=1.96 TeV
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.Comment: Published in PLB. 11 pages, 3 figure
Measurement of the t-channel single top quark production cross section
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 ppbar
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 +0.94 -0.80 pb for
the t-channel and 1.05 +-0.81 pb 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.Comment: 7 pages, 6 figure
Measurement of the top quark pair production cross section in the lepton+jets channel in proton-antiproton collisions at =1.96 TeV
We present a measurement of the inclusive top quark pair production cross
section in \ppbar collisions at (\sqrt{s}=1.96) TeV utilizing data
corresponding to an integrated luminosity of \lumi\ collected with the D0
detector at the Fermilab Tevatron Collider. We consider final states containing
one high- isolated electron or muon and at least two jets, and we
perform three analyses: one exploiting specific kinematic features of \ttbar
events, the second using -jet identification, and the third using both
techniques to separate \ttbar\ signal from background. In the third case, we
determine simultaneously the cross section and the ratio of the
production rates of +heavy flavor jets and +light flavor jets, which
reduces the impact of the systematic uncertainties related to the background
estimation. Assuming a top quark mass of 172.5 GeV, we obtain
pb. This result agrees with
predictions of the standard model.Comment: 19 pages, 6 figures, submitted to Phys. Rev.
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 trilinear gauge boson couplings from WW + WZ to lnu jj events in pp-bar collisions at sqrt{s}=1.96 TeV
We present a direct measurement of trilinear gauge boson couplings at gammaWW
and ZWW vertices in WW and WZ events produced in pp-bar collisions at
sqrt{s}=1.96 TeV. We consider events with one electron or muon, missing
transverse energy, and at least two jets. The data were collected using the D0
detector and correspond to 1.1/fb of integrated luminosity. Considering two
different relations between the couplings at the gammaWW and ZWW vertices, we
measure these couplings at 68% C.L. to be kappa_{gamma}=1.07^{+0.26}_{-0.29},
lambda =0.00^{+0.06}_{-0.06} and g_{1}^{Z}=1.04^{+0.09}_{-0.09} in a scenario
respecting SU(2)_L x U(1)_Y gauge symmetry and kappa =1.04^{+0.11}_{-0.11} and
lambda=0.00^{+0.06}_{-0.06} in an "equal couplings" scenario.Comment: 14 pages, 7 figures, published in Phys. Rev. D, updated to published
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