9,171 research outputs found
Finite Width Effects and Gauge Invariance in Radiative Production and Decay
The naive implementation of finite width effects in processes involving
unstable particles can violate gauge invariance. For the example of radiative
production and decay, , at tree level, it is
demonstrated how gauge invariance is restored by including the imaginary part
of triangle graphs in addition to resumming the imaginary contributions to the
vacuum polarization. Monte Carlo results are presented for the Fermilab
Tevatron.Comment: 10 pages, Revtex, 3 figures submitted separately as uuencoded tarred
postscript files, the complete paper is available at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-878.ps.Z or
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-878.ps.
Radiative corrections to W gamma gamma production at the LHC
Radiative W production at hadron colliders is an important testing ground for
the Standard Model. We consider W gamma gamma production which is sensitive to
the quartic WW gamma gamma coupling. Furthermore the Standard Model amplitude
for this process contains a radiation zero. We present a calculation of the NLO
QCD corrections for W gamma gamma production at the LHC.Comment: 6 pages, talk given at RADCOR 2009 - 9th International Symposium on
Radiative Corrections (Applications of Quantum Field Theory to Phenomenology)
October 25-30 2009, Ascona, Switzerlan
Exclusive meson pair production in peripheral ultrarelativistic heavy ion collisions
The cross sections for exclusive and meson pair
production in peripheral nucleus - nucleus collisions are calculated and
several differential distributions are presented. The calculation of the
elementary cross section is done within the
heavy-quark approximation and in the Brodsky- Lapage formalism with
distribution amplitudes describing recent CLEO data on leptonic decay.
Realistic (Fourier transform of charge density) charge form factors of nuclei
are used to generate photon flux factors. Absorption effects are discussed and
quantified. The cross sections of a few nb are predicted for RHIC and of a few
hundreds of nb for LHC with details depending on the approximation made in
calculating elementary cross sections.Comment: 11 pages, 8 figure
Hadron collider limits on anomalous couplings
A next-to-leading log calculation of the reactions and
is presented including a tri-boson
gauge coupling from non-Standard Model contributions. Two approaches are made
for comparison. The first approach considers the tri-boson coupling
as being uniquely fixed by tree level unitarity at high energies to its
Standard Model form and, consequently, suppresses the non-Standard Model
contributions with form factors. The second approach is to ignore such
considerations and calculate the contributions to non-Standard Model tri-boson
gauge couplings without such suppressions. It is found that at Tevatron
energies, the two approaches do not differ much in quantitative results, while
at Large Hadron Collider (LHC) energies the two approaches give significantly
different predictions for production rates. At the Tevatron and LHC, however,
the sensitivity limits on the anomalous coupling of are too weak to
usefully constrain parameters in effective Lagrangian models.Comment: Revtex 23 pages + 8 figures, UIOWA-94-1
Higher-order QED corrections to W-boson mass determination at hadron colliders
The impact of higher-order final-state photonic corrections on the precise
determination of the W-boson mass at the Tevatron and LHC colliders is
evaluated. In the presence of realistic selection criteria, the shift in the W
mass from a fit to the transverse mass distribution is found to be about 10 MeV
in the channel and almost negligible in the
channel. The calculation, which is implemented in a Monte Carlo event generator
for data analysis, can contribute to reduce the uncertainty associated to the W
mass measurement at future hadron collider experiments.Comment: 9 pages, 2 figures, 1 table, RevTe
Periodicity and Growth in a Lattice Gas with Dynamical Geometry
We study a one-dimensional lattice gas "dynamical geometry model" in which
local reversible interactions of counter-rotating groups of particles on a ring
can create or destroy lattice sites. We exhibit many periodic orbits and and
show that all other solutions have asymptotically growing lattice length in
both directions of time. We explain why the length grows as in all
cases examined. We completely solve the dynamics for small numbers of particles
with arbitrary initial conditions.Comment: 18 pages, LaTe
Is Gold a Hedge or a Safe Haven? An Analysis of Stocks, Bonds and Gold
This paper addresses two questions. First, we investigate whether gold is a hedge against stocks and/or bonds and second, we investigate whether gold is a safe haven for investors if either stocks or bonds fall. A safe haven is defined as a security that loses none of its value in case of a market crash. This is counterpoised against a hedge, defined as a security that does not co-move with stocks or bonds on average. We study constant and time-varying relationships between stocks, bonds and gold in order to investigate the existence of a hedge and a safe haven. The empirical analysis examines US, UK and German stock and bond prices and returns and their relationship with the Gold price. We find that (i) Gold is a hedge against stocks, (ii) Gold is a safe haven in extreme stock market conditions and (iii) Gold is a safe haven for stocks only for 15 trading days after an extreme shock occurred.Safe haven, gold, stock-bond correlation, flight-to-quality
Production of QED pairs at small impact parameter in relativistic heavy ion collisions
The STAR collaboration at RHIC is measuring the production of
electron-positron pairs at small impact parameters, larger than but already
close to the range, where the ions interact strongly with each other. We
calculate the total cross section, as well as, differential distributions of
the pair production process with the electromagnetic excitation of both ions in
a semiclassical approach and within a lowest order QED calculation. We compare
the distribution of electron and positron with the one coming from the cross
section calculation without restriction on impact parameter. Finally we give an
outlook of possible results at the LHC.Comment: 15 pages, 8 figure
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