1,979 research outputs found
Search for the Top Quark at D0 using Multivariate Methods
We report on the search for the top quark in proton-antiproton collisions at
the Fermilab Tevatron in the di-lepton and lepton+jets channels using
multivariate methods. An H-matrix analysis of the e-mu data corresponding to an
integrated luminosity of about 13.5 pb-1 yields one event with a likelihood to
be a top event (assuming top mass of 180 GeV/c**2) that is 10 times more than
WW and 18 times more than Z -> tau tau. A neural network analysis of e+jets
channel with about 48 pb-1 of data shows an excess of events in the signal
region and yields a cross-section for top-antitop production of 6.7 +/-
2.3(stat.) pb, assuming a top mass of 200 GeV/c**2. A PDE analysis of e+jets
data gives results consistent with the above.Comment: 12 pages, http://d0wop.fnal.gov/d0pubs/ppbar95/pushpa.ps Replaced
because the first submission was problemati
Quantum Boltzman equation study for the Kondo breakdown quantum critical point
We develop the quantum Boltzman equation approach for the Kondo breakdown
quantum critical point, involved with two bands for conduction electrons and
localized fermions. Particularly, the role of vertex corrections in transport
is addressed, crucial for non-Fermi liquid transport of temperature linear
dependence. Only one band of spinons may be considered for scattering with
gauge fluctuations, and their associated vertex corrections are introduced in
the usual way, where divergence of self-energy corrections is cancelled by that
of vertex corrections, giving rise to the physically meaningful result in the
gauge invariant expression for conductivity. On the other hand, two bands
should be taken into account for scattering with hybridization excitations,
giving rise to coupled quantum Boltzman equations. We find that vertex
corrections associated with hybridization fluctuations turn out to be
irrelevant due to heavy mass of spinons in the so called decoupling limit,
consistent with the diagrammatic approach showing the non-Fermi liquid
transport
V_cs from D_s to {\phi}l{\nu} semileptonic decay and full lattice QCD
We determine the complete set of axial and vector form factors for the Ds to
{\phi}l{\nu} decay from full lattice QCD for the first time. The valence quarks
are implemented using the Highly Improved Staggered Quark action and we
normalise the appropriate axial and vector currents fully nonperturbatively.
The q^2 and angular distributions we obtain for the differential rate agree
well with those from the BaBar experiment and, from the total branching
fraction, we obtain Vcs = 1.017(63), in good agreement with that from D to
Kl{\nu} semileptonic decay. We also find the mass and decay constant of the
{\phi} meson in good agreement with experiment, showing that its decay to
K{\bar{K}} (which we do not include here) has at most a small effect. We
include an Appendix on nonperturbative renormalisation of the complete set of
staggered vector and axial vector bilinears needed for this calculation.Comment: 19 pages, 13 figure
VERITAS Observations of Extragalactic Non-Blazars
During the 2007/2008 season, VERITAS was used for observations at E>200 GeV
of several extragalactic non-blazar objects such as galaxy clusters, starburst
and interacting galaxies, dwarf galaxies, and nearby galaxies. In these
proceedings, we present preliminary results from our observations of dwarf
galaxies and M87. Results from observation of other non-blazar sources are
presented in separate papers in the proceedings.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
VERITAS Distant Laser Calibration and Atmospheric Monitoring
As a calibrated laser pulse propagates through the atmosphere, the intensity
of the Rayleigh scattered light arriving at the VERITAS telescopes can be
calculated precisely. This allows for absolute calibration of imaging
atmospheric Cherenkov telescopes (IACT) to be simple and straightforward. In
these proceedings, we present the comparison between laser data and simulation
to estimate the light collection efficiencies of the VERITAS telescopes, and
the analysis of multiple laser data sets taken in different months for
atmospheric monitoring purpose.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Nonperturbative comparison of clover and highly improved staggered quarks in lattice QCD and the properties of the ϕ meson
We compare correlators for pseudoscalar and vector mesons made from valence strange quarks using the
clover quark and highly improved staggered quark (HISQ) formalisms in full lattice QCD. We use fully
nonperturbative methods to normalize vector and axial vector current operators made from HISQ quarks,
clover quarks and from combining HISQ and clover fields. This allows us to test expectations for the
renormalization factors based on perturbative QCD, with implications for the error budget of lattice QCD
calculations of the matrix elements of clover-staggered b-light weak currents, as well as further HISQ
calculations of the hadronic vacuum polarization.We also compare the approach to the (same) continuum limit
in clover and HISQ formalisms for the mass and decay constant of the ϕ meson. Our final results for these
parameters, using single-meson correlators and allowing an uncertainty for the neglect of quark-line
disconnected diagrams are: Mϕ ¼ 1.023ð6Þ GeV and fϕ ¼ 0.238ð3Þ GeV in good agreement with experiment.
The results come from calculations in the HISQ formalism using gluon fields that include the effect of u,
d, s and c quarks in the sea with three lattice spacing values and mu=d values going down to the physical point
Validation of a modified clinical risk score to predict cancer-specific survival for stage II colon cancer
Many patients with stage II colon cancer will die of their disease despite curative surgery. Therefore, identification of patients at high risk of poor outcome after surgery for stage II colon cancer is desirable. This study aims to validate a clinical risk score to predict cancer-specific survival in patients undergoing surgery for stage II colon cancer. Patients undergoing surgery for stage II colon cancer in 16 hospitals in the West of Scotland between 2001 and 2004 were identified from a prospectively maintained regional clinical audit database. Overall and cancer-specific survival rates up to 5 years were calculated. A total of 871 patients were included. At 5 years, cancer-specific survival was 81.9% and overall survival was 65.6%. On multivariate analysis, age ≥75 years (hazard ratio (HR) 2.11, 95% confidence intervals (CI) 1.57–2.85; P<0.001) and emergency presentation (HR 1.97, 95% CI 1.43–2.70; P<0.001) were independently associated with cancer-specific survival. Age and mode of presentation HRs were added to form a clinical risk score of 0–2. The cancer-specific survival at 5 years for patients with a cumulative score 0 was 88.7%, 1 was 78.2% and 2 was 65.9%. These results validate a modified simple clinical risk score for patients undergoing surgery for stage II colon cancer. The combination of these two universally documented clinical factors provides a solid foundation for the examination of the impact of additional clinicopathological and treatment factors on overall and cancer-specific survival
The pseudoscalar meson electromagnetic form factor at high Q2 from full lattice QCD
We give an accurate determination of the vector (electromagnetic) form factor, F(Q^2), for a light pseudoscalar meson up to squared momentum transfer Q^2 values of 6 GeV^2 for the first time from full lattice QCD, including u, d, s and c quarks in the sea at multiple values of the lattice spacing. Our results show good control of lattice discretisation and sea quark mass effects. We study a pseudoscalar meson made of valence s quarks but the qualitative picture obtained applies also to the \pi meson, relevant to upcoming experiments at Jefferson Lab. We find that Q^2F(Q^2) becomes flat in the region between Q^2 of 2 GeV^2 and 6 GeV^2, with a value well above that of the asymptotic perturbative QCD expectation, but well below that of the vector-meson dominance pole form appropriate to low Q^2 values. Our calculations show that we can reach higher Q^2 values in future to shed further light on where the perturbative QCD result emerges
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