978 research outputs found
Is a Large Intrinsic k_T Needed to Describe Photon + Jet Photoproduction at HERA?
We study the photoproduction of an isolated photon and a jet based on a code
of partonic event generator type which includes the full set of next-to-leading
order corrections. We compare our results to a recent ZEUS analysis in which an
effective k_T of the incoming partons has been determined. We find that no
additional intrinsic k_T is needed to describe the data.Comment: 23 pages LaTeX, 12 figure
Isolated prompt photon photoproduction at NLO
We present a full next-to-leading order code to calculate the photoproduction
of prompt photons. The code is a general purpose program of partonic event
generator type with large flexibility. We study the possibility to constrain
the photon structure functions and comment on isolation issues. A comparison to
ZEUS data is also shown.Comment: 22 pages LaTeX, 15 figure
A NLO calculation of the hadron-jet cross section in photoproduction reactions
We study the photoproduction of large-p_T charged hadrons in e p collisions,
both for the inclusive case and for the case where a jet in the final state is
also measured. Our results are obtained by a NLO generator of partonic events.
We discuss the sensitivity of the cross section to the renormalisation and
factorisation scales, and to various fragmentation function parametrisations.
The possibility to constrain the parton densities in the proton and in the
photon is assessed. Comparisons are made with H1 data for inclusive charged
hadron production.Comment: 28 pages LaTeX, 14 figure
Tools for NLO automation: extension of the golem95C integral library
We present an extension of the program golem95C for the numerical evaluation
of scalar integrals and tensor form factors entering the calculation of
one-loop amplitudes, which supports tensor ranks exceeding the number of
propagators. This extension allows various applications in Beyond the Standard
Model physics and effective theories, for example higher ranks due to
propagators of spin two particles, or due to effective vertices. Complex masses
are also supported. The program is not restricted to the Feynman diagrammatic
approach, as it also contains routines to interface to unitarity-inspired
numerical reconstruction of the integrand at the tensorial level. Therefore it
can serve as a general integral library in automated programs to calculate
one-loop amplitudes.Comment: 17 pages, 1 figure, the program can be downloaded from
http://golem.hepforge.org/95/. arXiv admin note: substantial text overlap
with arXiv:1101.559
Next-to-leading order multi-leg processes for the Large Hadron Collider
In this talk we discuss recent progress concerning precise predictions for
the LHC. We give a status report of three applications of our method to deal
with multi-leg one-loop amplitudes: The interference term of Higgs production
by gluon- and weak boson fusion to order O(alpha^2 alpha_s^3) and the
next-to-leading order corrections to the two processes pp -> ZZ jet and u ubar
-> d dbar s sbar. The latter is a subprocess of the four jet cross section at
the LHC.Comment: 6 pages, 5 figures. Talk given at the 8th international Symposium on
Radiative Corrections (RADCOR), October 1-5 2007, Florence, Ital
A compact representation of the 2 photon 3 gluon amplitude
A compact representation of the loop amplitude gamma gamma ggg -> 0 is
presented. The result has been obtained by using helicity methods and sorting
with respect to an irreducible function basis. We show how to convert spinor
representations into a field strength representation of the amplitude. The
amplitude defines a background contribution for Higgs boson searches at the LHC
in the channel H -> gamma gamma + jet which was earlier extracted indirectly
from the one-loop representation of the 5-gluon amplitude.Comment: 15 pages Latex, 6 eps files included, revised versio
Local disorder and optical properties in V-shaped quantum wires : towards one-dimensional exciton systems
The exciton localization is studied in GaAs/GaAlAs V-shaped quantum wires
(QWRs) by high spatial resolution spectroscopy. Scanning optical imaging of
different generations of samples shows that the localization length has been
enhanced as the growth techniques were improved. In the best samples, excitons
are delocalized in islands of length of the order of 1 micron, and form a
continuum of 1D states in each of them, as evidenced by the sqrt(T) dependence
of the radiative lifetime. On the opposite, in the previous generation of QWRs,
the localization length is typically 50 nm and the QWR behaves as a collection
of quantum boxes. These localization properties are compared to structural
properties and related to the progresses of the growth techniques. The presence
of residual disorder is evidenced in the best samples and explained by the
separation of electrons and holes due to the large in-built piezo-electric
field present in the structure.Comment: 8 figure
Photon - Jet Correlations and Constraints on Fragmentation Functions
We study the production of a large-pT photon in association with a jet in
proton-proton collisions. We examine the sensitivity of the jet rapidity
distribution to the gluon distribution function in the proton. We then assess
the sensitivity of various photon + jet correlation observables to the photon
fragmentation functions. We argue that RHIC data on photon-jet correlations can
be used to constrain the photon fragmentation functions in a region which was
barely accessible in LEP experiments.Comment: 23 pages, 9 figure
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