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

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

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