226 research outputs found
Higher order QCD corrections to the transverse and longitudinal fragmentation functions in electron-positron annihilation
We present the calculation of the order corrections to the
coefficient functions contributing to the longitudinal () and
transverse fragmentation functions () measured in electron-positron
annihilation. The effect of these higher order QCD corrections on the behaviour
of the fragmentation functions and the corresponding longitudinal
() and transverse cross sections ()
are studied. In particular we investigate the dependence of the above
quantities on the mass factorization scale () and the various
parameterizations chosen for the parton fragmentation densities
(; ). Our analysis reveals that the order
\alpha_s^2 contributions to are large whereas these contributions
to are small. From the above fragmentation functions one can also
compute the integrated cross sections and in an
independent way. The sum , corrected up to
order \alphastwo, agrees with the well known result in the literature providing
us with an independent check an our calculations.Comment: 69 pages, latex2e, uses mcite, amsfonts. PostScript version available
at http://rulgm4.leidenuniv.nl/preprints/transfrag.p
Search for the Proton Decay Mode proton to neutrino K+ in Soudan 2
We have searched for the proton decay mode proton to neutrino K+ using the
one-kiloton Soudan 2 high resolution calorimeter. Contained events obtained
from a 3.56 kiloton-year fiducial exposure through June 1997 are examined for
occurrence of a visible K+ track which decays at rest into mu+ nu or pi+ pi0.
We found one candidate event consistent with background, yielding a limit,
tau/B > 4.3 10^{31} years at 90% CL with no background subtraction.Comment: 13 pages, Latex, 3 tables and 3 figures, Accepted by Physics Letters
First Results from the Arcminute Cosmology Bolometer Array Receiver
We review the first science results from the Arcminute Cosmology Bolometer
Array Receiver (ACBAR); a multifrequency millimeter-wave receiver optimized for
observations of the Cosmic Microwave Background (CMB) and the
Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies. ACBAR was installed on
the 2 m Viper telescope at the South Pole in January 2001 and the results
presented here incorporate data through July 2002. We present the power
spectrum of the CMB at 150 GHz over the range \ell = 150 - 3000 measured by
ACBAR as well as estimates for the values of the cosmological parameters within
the context of Lambda-CDM models. We find that the inclusion of Omega_Lambda
greatly improves the fit to the power spectrum. We also observe a slight excess
of small-scale anisotropy at 150 GHz; if interpreted as power from the SZ
effect of unresolved clusters, the measured signal is consistent with CBI and
BIMA within the context of the SZ power spectrum models tested.Comment: To be published in the proceedings of "The Cosmic Microwave
Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and
K.A. Olive). 10 pages, 2 figure
Definition and Calculation of Bottom Quark Cross-Sections in Deep-inelastic Scattering at HERA and Determination of their Uncertainties
The uncertainties involved in the calculation of bottom quark cross-sections
in deep-inelastic scattering at HERA are studied in different phase space
regions. Besides the inclusive bottom quark cross-section, definitions closer
to the detector acceptance requiring at least one high energetic muon from the
semi-leptonic \bquark decay or a jet with high transverse energy are
investigated. For each case the uncertainties due to the choice of the
renormalisation and factorisation scale as well as the \bquark mass are
estimated in the perturbative NLO QCD calculation and furthermore uncertainties
in the fragmenation of the bottom quark to a B-meson and in its semi-leptonic
decay are discussed
Next-to-Leading Order Cross Sections for Tagged Reactions
We extend the phase space slicing method of Giele, Glover and Kosower for
performing next-to-leading order jet cross section calculations in two
important ways: we show how to include fragmentation functions and how to
include massive particles. These extensions allow the application of this
method to not just jet cross sections but also to cross sections in which a
particular final state particle, including a or -meson, is tagged.Comment: 36 pages, Latex Small corrections to text. To appear in Phys. Rev.
Measurement of the Isolated Photon Cross Section in p-pbar Collisions at sqrt{s}=1.96 TeV
The cross section for the inclusive production of isolated photons has been
measured in p anti-p collisions at sqrt{s}=1.96 TeV with the D0 detector at the
Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV
and have pseudorapidity |eta|<0.9. The cross section is compared with the
results from two next-to-leading order perturbative QCD calculations. The
theoretical predictions agree with the measurement within uncertainties.Comment: 7 pages, 5 figures, submitted to Phys.Lett.
Is upper gastrointestinal radiography a cost-effective alternative to a Helicobacter pylori “Test and Treat” strategy for patients with suspected peptic ulcer disease?
Current clinical consensus supports an initial Helicobacter pylori (HP) “test and treat” approach when compared to immediate endoscopy for patients with suspected peptic ulcer disease. Alternative diagnostic approaches that incorporate upper GI radiography (UGI) have not been previously evaluated. We sought to determine the cost effectiveness of UGI compared to a HP test and treat strategy, incorporating recent data addressing the reduced prevalence of HP, lower cost of diagnostic interventions, and reduced attribution of PUD to HP. METHODS : Using decision analysis, three diagnostic and treatment strategies were evaluated: 1) Test and Treat —initial HP serology, treat patients who test positive with HP eradication and antiulcer therapy; 2) Initial UGI series —treat all patients with documented ulcer disease with HP eradication and antiulcer therapy; and 3) Initial UGI series, HP serology if ulcer present — treat ulcer and HP based on diagnostic test results. RESULTS : The estimated cost per ulcer cured for each strategy were as follows: test and treat, 3,690; and UGI with serology, 498; initial UGI, 620. When UGI reimbursement was decreased to less than $50, the UGI strategies yielded a lower cost per patient treated than the test and treat strategy. CONCLUSION : At the current level of reimbursement, UGI should not be considered a cost-effective alternative to the HP test and treat strategy for the initial evaluation of patients with suspected peptic ulcer disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73722/1/j.1572-0241.2000.01837.x.pd
Astronomical Distance Determination in the Space Age: Secondary Distance Indicators
The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations. © 2018, The Author(s)
The mammalian gene function resource: The International Knockout Mouse Consortium
In 2007, the International Knockout Mouse Consortium (IKMC) made the ambitious promise to generate mutations in virtually every protein-coding gene of the mouse genome in a concerted worldwide action. Now, 5 years later, the IKMC members have developed highthroughput gene trapping and, in particular, gene-targeting pipelines and generated more than 17,400 mutant murine embryonic stem (ES) cell clones and more than 1,700 mutant mouse strains, most of them conditional. A common IKMC web portal (www.knockoutmouse.org) has been established, allowing easy access to this unparalleled biological resource. The IKMC materials considerably enhance functional gene annotation of the mammalian genome and will have a major impact on future biomedical research
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