156,707 research outputs found
Observation of Single Top Quark Production at D0
This paper presents the observation of the electroweak production of single
top quarks in the D0 detector at the Fermilab Tevatron Collider at a
center-of-mass energy of 1.96 TeV. Events containing an isolated electron or
muon and missing transverse energy, together with jets originating from the
fragmentation of b quarks are used to measure a cross section for single top
quark production of sigma(ppbar -> tb + X, tqb + X) = 3.94 +- 0.88 pb. The
probability to measure a cross section at this value or higher in the absence
of signal is 2.5X10^-7, corresponding to a 5.0 standard deviation significance.Comment: 4 pages, 2 figures; Proceedings paper of SUSY 2009 conference,
Boston, MA, USA, June 2009 (to be published in AIP Conf.Proc.
Propensity Score Analysis with Matching Weights
The propensity score analysis is one of the most widely used methods for
studying the causal treatment effect in observational studies. This paper
studies treatment effect estimation with the method of matching weights. This
method resembles propensity score matching but offers a number of new features
including efficient estimation, rigorous variance calculation, simple
asymptotics, statistical tests of balance, clearly identified target population
with optimal sampling property, and no need for choosing matching algorithm and
caliper size. In addition, we propose the mirror histogram as a useful tool for
graphically displaying balance. The method also shares some features of the
inverse probability weighting methods, but the computation remains stable when
the propensity scores approach 0 or 1. An augmented version of the matching
weight estimator is developed that has the double robust property, i.e., the
estimator is consistent if either the outcome model or the propensity score
model is correct. In the numerical studies, the proposed methods demonstrated
better performance than many widely used propensity score analysis methods such
as stratification by quintiles, matching with propensity scores, and inverse
probability weighting
- …