8,446 research outputs found
Measurement of the W Mass at LEP2
The mass of the W boson has been measured by the LEP collaborations from the
data recorded during the LEP2 programme at e+ e- centre of mass energies from
161 to 209 GeV, giving the result : mw = 80.450 +/- 0.039 GeV/c^2. This paper
discusses the measurements of the W Mass from direct reconstruction of the
invariant mass of the WW decay products, particular emphasis is placed on the
evaluation of systematic errors. Results on the direct measurement of the W
width are also presented.Comment: Contribution to XXXVIIth Moriond Electroweak Conference, March 2002.
6 pages, 3 figures This version with typos correcte
Alignment procedure of the LHCb Vertex Detector
LHCb is one of the four main experiments of the Large Hadron Collider (LHC)
project, which will start at CERN in 2008. The experiment is primarily
dedicated to B-Physics and hence requires precise vertex reconstruction. The
silicon vertex locator (VELO) has a single hit precision of better than 10
micron and is used both off-line and in the trigger. These requirements place
strict constraints on its alignment. Additional challenges for the alignment
arise from the detector being retracted between each fill of the LHC and from
its unique circular disc r/phi strip geometry. This paper describes the track
based software alignment procedure developed for the VELO. The procedure is
primarily based on a non-iterative method using a matrix inversion technique.
The procedure is demonstrated with simulated events to be fast, robust and to
achieve a suitable alignment precision.Comment: accepted for publication in NIM
LHCb VELO software alignment, Part III: the alignment of the relative sensor positions
The LHCb Vertex Locator contains 42 silicon sensor modules. Each module has
two silicon sensors. A method for determining the relative alignment of the
silicon sensors within each module from data is presented. The software
implementation details are discussed. Monte-Carlo simulation studies are
described that demonstrate an alignment precision of 1.3 micron is obtained in
the sensor plane
Finiteness in N=1 SYM Theories
I present a criterion for all-order finiteness in N=1 SYM theories. Three
applications are given; they yield all-order finite N=1 SYM models with global
symmetries of the superpotential.Comment: 3 pages, plain LaTex, no figure
Multi-item Vickrey-Dutch auctions
Descending price auctions are adopted for goods that must be sold quickly and in private values environments, for instance in flower, fish, and tobacco auctions. In this paper, we introduce ex post efficient descending auctions for two environments: multiple non-identical items and buyers with unit-demand valuations; and multiple identical items and buyers with non-increasing marginal values. Our auctions are designed using the notion of universal competitive equilibrium (UCE) prices and they terminate with UCE prices, from which the Vickrey payments can be determined. For the unit-demand setting, our auction maintains linear and anonymous prices. For the homogeneous items setting, our auction maintains a single price and adopts Ausubel's notion of "clinching" to compute the final payments dynamically. The auctions support truthful bidding in an ex post Nash equilibrium and terminate with an ex post efficient allocation. In simulation, we illustrate the speed and elicitation advantages of these auctions over their ascending price counterparts.
Simplicity-Expressiveness Tradeoffs in Mechanism Design
A fundamental result in mechanism design theory, the so-called revelation
principle, asserts that for many questions concerning the existence of
mechanisms with a given outcome one can restrict attention to truthful direct
revelation-mechanisms. In practice, however, many mechanism use a restricted
message space. This motivates the study of the tradeoffs involved in choosing
simplified mechanisms, which can sometimes bring benefits in precluding bad or
promoting good equilibria, and other times impose costs on welfare and revenue.
We study the simplicity-expressiveness tradeoff in two representative settings,
sponsored search auctions and combinatorial auctions, each being a canonical
example for complete information and incomplete information analysis,
respectively. We observe that the amount of information available to the agents
plays an important role for the tradeoff between simplicity and expressiveness
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