52 research outputs found
Helicity of the W Boson in Lepton+Jets ttbar Events
We examine properties of ttbar candidates events in lepton+jets final states
to establish the helicities of the W bosons in t->W+b decays. Our analysis is
based on a direct calculation of a probability that each event corresponds to a
ttbar final state, as a function of the helicity of the W boson. We use the 125
events/pb sample of data collected by the DO experiment during Run I of the
Fermilab Tevatron collider at sqrt{s}=1.8 TeV, and obtain a longitudinal
helicity fraction of F_0=0.56+/-0.31, which is consistent with the prediction
of F_0=0.70 from the standard model
Hard Single Diffraction in pbarp Collisions at root-s = 630 and 1800 GeV
Using the D0 detector, we have studied events produced in proton-antiproton
collisions that contain large forward regions with very little energy
deposition (``rapidity gaps'') and concurrent jet production at center-of-mass
energies of root-s = 630 and 1800 Gev. The fractions of forward and central jet
events associated with such rapidity gaps are measured and compared to
predictions from Monte Carlo models. For hard diffractive candidate events, we
use the calorimeter to extract the fractional momentum loss of the scattered
protons.Comment: 11 pages 4 figures. submitted to PR
Measurement of the Lambda^0_b lifetime in the decay Lambda^0_b -> J/psi Lambda^0 with the D0 Detector
We present measurements of the Lambda^0_b lifetime in the exclusive decay
channel Lambda^0_{b}->J/psi Lambda^0, with J/psi to mu+ mu- and Lambda^0 to p
pi-, the B^0 lifetime in the decay B^0 -> J/psi K^0_S with J/psi to mu+ mu- and
K^0_S to pi+ pi-, and the ratio of these lifetimes. The analysis is based on
approximately 250 pb^{-1} of data recorded with the D0 detector in pp(bar)
collisions at sqrt{s}=1.96 TeV. The Lambda^0_b lifetime is determined to be
tau(Lambda^0_b) = 1.22 +0.22/-0.18 (stat) +/- 0.04 (syst) ps, the B^0 lifetime
tau(B^0) = 1.40 +0.11/-0.10 (stat) +/- 0.03 (syst) ps, and the ratio
tau(Lambda^0_b)/tau(B^0) = 0.87 +0.17/-0.14 (stat) +/- 0.03 (syst). In contrast
with previous measurements using semileptonic decays, this is the first
determination of the Lambda^0_b lifetime based on a fully reconstructed decay
channel.Comment: 7 pages, 4 figures, Submitted to Physical Review Letters, v2: Added
FNAL Pub-numbe
Measurement of the WW production cross section in p anti-p collisions at s**(1/2) = 1.96 TeV
We present a measurement of the W boson pair-production cross section in p
anti-p collisions at a center-of-mass energy of sqrt{s}=1.96 TeV. The data,
collected with the Run II DO detector, correspond to an integrated luminosity
of 224-252 pb^-1 depending on the final state (ee, emu or mumu). We observe 25
candidates with a background expectation of
8.1+/-0.6(stat)+/-0.6(syst)+/-0.5(lum) events. The probability for an upward
fluctuation of the background to produce the observed signal is 2.3x10^-7,
equivalent to 5.2 standard deviations.The measurement yields a cross section of
13.8+4.3/-3.8(stat)+1.2/-0.9(syst)+/-0.9(lum) pb, in agreement with predictions
from the standard model.Comment: submitted to PR
Erratum to Measurement of at 1.96 TeV, published in Phys. Rev. D {71}, 072004 (2005)
A change in estimated integrated luminosity (from 226 pb^{-1}{\sigma (p \bar p \to Z)
\cdot}{(Z \to \tau \tau)}209\pm13(stat.)\pm16(syst.)\pm13(lum) pb
Recommended from our members
Boronated porphyrins in NCT: Results with a new potent tumor localizer
Several chemical methods are available for the solubilization of boronated porphyrins. We have previously reported the tumor localization of nido carboranyl porphyrins in which the icosahedral carborane cages have been opened to give B/sub 9/C/sub 2/ anions. One of these species has shown tumor boron levels of nearly 50 ..mu..g B/g when delivered by week-long subcutaneous infusions. We report here recent in vivo experiments with a new, highly water-soluble porphyrin based on the hematoporphyrin-type of compound in which aqueous solubility is achieved using the two propionic acid side chains of the ''natural'' porphyrin frame. 7 refs
First measurement of
Type I X-ray bursts (XRBs) are the most frequently observed thermonuclear explosions in nature. The 22Mg(α,p)25Al reaction plays a critical role in XRB models. However, experimental information is insufficient to deduce a precise 22Mg(α,p)25Al reaction rate for the respective XRB temperature range. A new measurement of 25Al+p resonant scattring was performed up to the astrophysically interested energy region of 22Mg(α,p)25Al. Several resonances were observed in the excitation functions, and their level properties have been determined based on an R-matrix analysis. In particular, proton widths and spin-parities of four natural-parity resonances above the α threshold of 26Si, which can contribute the reaction rate of 22Mg(α,p)25Al, were first experimentally determined
Two measurements of the
22Na is an important isotope for the study of extinct radioactivity, meanwhile its sufficiently long half life provides the possibility to observe live 22Na in nearby nova explosions. The 22Na(p,γ) 23Mg is one of the key reactions that influence the 22Na abundance in nova ejecta. To study the proton resonant states in 23Mg relevant to the astrophysical 22Na(p,γ) 23Mg reaction rates, two measurements have been carried out at the CRIB separator of University of Tokyo, and the RIBLL secondary beamline in Lanzhou, respectively. The 22Na secondary beam was produced via the 1H(22Ne, 22Na)n charge exchange reaction. Thick-target inverse-kinematics method is applied to obtain the excitation function of 22Na+p elastic scattering. Extended gas target and solid state polyethylene foil were used in the two measurements, respectively, to map the different excitation energy region of the compound nucleus 23Mg. Several new resonant levels are observed and their contribution to the 22Na(p,γ) 23Mg reaction rate is evaluated
- …