6,400 research outputs found
Information and treatment of unknown correlations in the combination of measurements using the BLUE method
We discuss the effect of large positive correlations in the combinations of
several measurements of a single physical quantity using the Best Linear
Unbiased Estimate (BLUE) method. We suggest a new approach for comparing the
relative weights of the different measurements in their contributions to the
combined knowledge about the unknown parameter, using the well-established
concept of Fisher information. We argue, in particular, that one We discuss the
effect of large positive correlations in the combinations of several
measurements of a single physical quantity using the Best Linear Unbiased
Estimate (BLUE) method. We suggest a new approach for comparing the relative
weights of the different measurements in their contributions to the combined
knowledge about the unknown parameter, using the well-established concept of
Fisher information. We argue, in particular, that one contribution to
information comes from the collective interplay of the measurements through
their correlations and that this contribution cannot be attributed to any of
the individual measurements alone. We show that negative coefficients in the
BLUE weighted average invariably indicate the presence of a regime of high
correlations, where the effect of further increasing some of these correlations
is that of reducing the error on the combined estimate. In these regimes, we
stress that assuming fully correlated systematic uncertainties is not a truly
conservative choice, and that the correlations provided as input to BLUE
combinations need to be assessed with extreme care instead. In situations where
the precise evaluation of these correlations is impractical, or even
impossible, we provide tools to help experimental physicists perform more
conservative combinations
Generalized Mukai conjecture for special Fano varieties
Let X be a Fano variety of dimension n, pseudoindex i_X and Picard number
\rho_X. A generalization of a conjecture of Mukai says that \rho_X(i_X-1)\le n.
We prove that the conjecture holds if: a) X has pseudoindex i_X \ge
\frac{n+3}{3} and either has a fiber type extremal contraction or does not have
small extremal contractions b) X has dimension five.Comment: 19 page
Top mass at the LHC
With about 10 millions top-pair events per year at low luminosity, the LHC will be a top factory. Among all precision measurements that will be performed in the top quark sector, the determination of its mass is probably the most important and will help in constraining the Standard Model. A brief review of the direct and indirect measurements of the top quark mass will be given, with indications about the potential of ATLAS and CMS in different luminosity scenario
W mass from fully leptonic and mixed decays at LEP
This article describes the determination of the W boson mass through the mixed hadronic-leptonic and fully leptonic channels at LEP. The results are preliminary and refer to the data collected up to 1998. The combined LEP W mass value for (mixed)-leptonic events is m/sub w /=(80.310+or-0.060) GeV/c/sup 2/. This value, combined with the result from the hadronic channel, gives m/sub w/=(80.339+or-0.055) Ge V/c/sup 2/. (4 refs)
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