3,037 research outputs found
Poincare's Recurrence Theorem and the Unitarity of the S matrix
A scattering process can be described by suitably closing the system and
considering the first return map from the entrance onto itself. This scattering
map may be singular and discontinuous, but it will be measure preserving as a
consequence of the recurrence theorem applied to any region of a simpler map.
In the case of a billiard this is the Birkhoff map. The semiclassical
quantization of the Birkhoff map can be subdivided into an entrance and a
repeller. The construction of a scattering operator then follows in exact
analogy to the classical process. Generically, the approximate unitarity of the
semiclassical Birkhoff map is inherited by the S-matrix, even for highly
resonant scattering where direct quantization of the scattering map breaks
down.Comment: 4 latex pages, 5 ps figure
Green function approach for scattering quantum walks
In this work a Green function approach for scattering quantum walks is
developed. The exact formula has the form of a sum over paths and always can be
cast into a closed analytic expression for arbitrary topologies and position
dependent quantum amplitudes. By introducing the step and path operators, it is
shown how to extract any information about the system from the Green function.
The method relevant features are demonstrated by discussing in details an
example, a general diamond-shaped graph.Comment: 13 pages, 6 figures, this article was selected by APS for Virtual
Journal of Quantum Information, Vol 11, Iss 11 (2011
Semiclassical properties and chaos degree for the quantum baker's map
We study the chaotic behaviour and the quantum-classical correspondence for
the baker's map. Correspondence between quantum and classical expectation
values is investigated and it is numerically shown that it is lost at the
logarithmic timescale. The quantum chaos degree is computed and it is
demonstrated that it describes the chaotic features of the model. The
correspondence between classical and quantum chaos degrees is considered.Comment: 30 pages, 4 figures, accepted for publication in J. Math. Phy
The classical limit for a class of quantum baker's maps
We show that the class of quantum baker's maps defined by Schack and Caves
have the proper classical limit provided the number of momentum bits approaches
infinity. This is done by deriving a semi-classical approximation to the
coherent-state propagator.Comment: 18 pages, 5 figure
Classical limit in terms of symbolic dynamics for the quantum baker's map
We derive a simple closed form for the matrix elements of the quantum baker's
map that shows that the map is an approximate shift in a symbolic
representation based on discrete phase space. We use this result to give a
formal proof that the quantum baker's map approaches a classical Bernoulli
shift in the limit of a small effective Plank's constant.Comment: 12 pages, LaTex, typos correcte
Differential Production Cross Section of Z Bosons as a Function of Transverse Momentum at sqrt{s}=1.8 TeV
We present a measurement of the transverse momentum distribution of Z bosons
produced in ppbar collisions at sqrt{s}=1.8 TeV using data collected by the D0
experiment at the Fermilab Tevatron Collider during 1994--1996. We find good
agreement between our data and a current resummation calculation. We also use
our data to extract values of the non-perturbative parameters for a particular
version of the resummation formalism, obtaining significantly more precise
values than previous determinations.Comment: 10 pages, 2 figures, submitted to Phys. Rev. Letters v2 has margin
error correcte
Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up
Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated
Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic Calorimeter
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2010 IOPEnsuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered
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
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