333 research outputs found
Another determination of the quark condensate from an overlap action
I use the technique of Hernandez, et al (hep-lat/0106011) to convert a recent
calculation of the lattice-regulated quark condensate from an overlap action to
a continuum-regulated number. I find Sigma(MSbar)(mu = 2 GeV) = (282(6)
MeV)-cubed times (a-inverse/1766 MeV)-cubed from a calculation with the Wilson
gauge action at beta=5.9.Comment: 3 pages, Revtex, 1 postscript figure. References added. COLO-HEP-47
Short distance current correlators: Comparing lattice simulations to the instanton liquid
Point to point correlators of currents are computed in quenched QCD using a
chiral lattice fermion action, the overlap action. I compare correlators made
of exact quark propagators with correlators restricted to low (less than 500
MeV) eigenvalue eigenmodes of the Dirac operator. In many cases they show
qualitative resemblence (typically at small values of the quark mass and
distances larger than 0.4 fm) and they differ qualitatively at larger quark
masses or at very short distance. Lattice results are in qualitative agreement
(and in the difference of vector and axial vector channels, quantitative
agreement) with the expectations of instanton liquid models. The scalar channel
shows the effects of a quenched finite volume zero mode artifact, a negative
correlator.Comment: 18 pages, Revtex, 11 postscript figures. Some changes. Version to
appear in Phys. Rev.
One loop matching coefficients for a variant overlap action--and some of its simpler relatives
I present one-loop perturbative calculations of matching coefficients between
matrix elements in continuum regulated QCD and lattice QCD with overlap
fermions, with emphasis a recently-proposed variant discretization of the
overlap. These fermions have extended (``fat link'') gauge connections. The
scale for evaluation of the running coupling constant (in the context of the
Lepage-Mackenzie fixing scheme) is also given.
A variety of results (for additive mass renormalization, local currents, and
some non-penguin four-fermion operators) for naive, Wilson, clover, and overlap
actions are shown.Comment: 17 pages, Revtex, 11 postscript figures. COLO-HEP-48
Kaon B Parameter in Quenched QCD
I calculate the kaon B-parameter with a lattice simulation in quenched
approximation. The lattice simulation uses an action possessing exact lattice
chiral symmetry, an overlap action. Computations are performed at two lattice
spacings, about 0.13 and 0.09 fm (parameterized by Wilson gauge action
couplings beta=5.9 and 6.1) with nearly the same physical volumes and quark
masses. I describe particular potential difficulties which arise due to the use
of such a lattice action in finite volume. My results are consistent with other
recent lattice determinations using domain-wall fermions.Comment: 23 pages, Revtex, 16 postscript figure
Topological susceptibility with the improved Asqtad action
As a test of the chiral properties of the improved Asqtad (staggered fermion)
action, we have been measuring the topological susceptibility as a function of
quark masses for 2 + 1 dynamical flavors. We report preliminary results, which
show reasonable agreement with leading order chiral perturbation theory for
lattice spacing less than 0.1 fm. The total topological charge, however, shows
strong persistence over Monte Carlo time.Comment: Lattice2002(algor
Squaring the circle: a priority-setting method for evidence-based service development, reconciling research with multiple stakeholder views.
BACKGROUND: This study demonstrates a technique to aid the implementation of research findings through an example of improving services and self-management in longer-term depression. In common with other long-term conditions, policy in this field requires innovation to be undertaken in the context of a whole system of care, be cost-effective, evidence-based and to comply with national clinical guidelines. At the same time, successful service development must be acceptable to clinicians and service users and choices must be made within limited resources. This paper describes a novel way of resolving these competing requirements by reconciling different sources and types of evidence and systematically engaging multiple stakeholder views.
METHODS: The study combined results from mathematical modelling of the care pathway, research evidence on effective interventions and findings from qualitative research with service users in a series of workshops to define, refine and select candidate service improvements. A final consensus-generating workshop used structured discussion and anonymised electronic voting. This was followed by an email survey to all stakeholders, to achieve a pre-defined criterion of consensus for six suggestions for implementation.
RESULTS: An initial list of over 20 ideas was grouped into four main areas. At the final workshop, each idea was presented in person, visually and in writing to 40 people, who assigned themselves to one or more of five stakeholder groups: i) service users and carers, ii) clinicians, iii) managers, iv) commissioners and v) researchers. Many belonged to more than one group. After two rounds of voting, consensus was reached on seven ideas and one runner up. The survey then confirmed the top six ideas to be tested in practice.
CONCLUSIONS: The method recruited and retained people with diverse experience and views within a health community and took account of a full range of evidence. It enabled a diverse group of stakeholders to travel together in a direction that converged with the messages coming out of the research and successfully yielded priorities for service improvement that met competing requirements
Observation of Hadronic W Decays in t-tbar Events with the Collider Detector at Fermilab
We observe hadronic W decays in t-tbar -> W (-> l nu) + >= 4 jet events using
a 109 pb-1 data sample of p-pbar collisions at sqrt{s} = 1.8 TeV collected with
the Collider Detector at Fermilab (CDF). A peak in the dijet invariant mass
distribution is obtained that is consistent with W decay and inconsistent with
the background prediction by 3.3 standard deviations. From this peak we measure
the W mass to be 77.2 +- 4.6 (stat+syst) GeV/c^2. This result demonstrates the
presence of two W bosons in t-tbar candidates in the W (-> l nu) + >= 4 jet
channel.Comment: 20 pages, 4 figures, submitted to PR
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
Measurement of the Associated Production Cross Section in Collisions at TeV
We present the first measurement of associated direct photon + muon
production in hadronic collisions, from a sample of 1.8 TeV
collisions recorded with the Collider Detector at Fermilab. Quantum
chromodynamics (QCD) predicts that these events are primarily from the Compton
scattering process , with the final state charm quark producing
a muon. Hence this measurement is sensitive to the charm quark content of the
proton. The measured cross section of is compared to a
leading-order QCD parton shower model as well as a next-to-leading-order QCD
calculation.Comment: 12 pages, 4 figures Added more detailed description of muon
background estimat
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