5,256 research outputs found
The colour evolution of the process q q -> q q g
We calculate the soft anomalous dimension matrix for a five-parton process,
qq -> qqg. Considering different bases we unveil some interesting properties of
this matrix.Comment: 11 pages; calculation extended to general 5-parton kinematic
THE STRUCTURE FUNCTION F_2^{\gamma}(x,Q^2) AT LEP2
The unique nature of the photon can be investigated in hitherto unexplored
kinematic regions at LEP2. We discuss the theoretical significance of deep
inelastic measurements and present a prescription that allows a theoretically
and experimentally sensible separation of the so-called `anomalous' and
`hadronic' components of the target photon. We perform preliminary studies
regarding the ability to reconstruct the CM energy (and hence
) and the usefulness of the easier to measure electron structure function.Comment: 6 pages Latex + 5 figures in a uuencoded fil
Breakdown of QCD coherence ?
We reconsider the calculation of a non-global QCD observable and find the
possible breakdown of QCD coherence. This breakdown arises as a result of wide
angle soft gluon emission developing a sensitivity to emission at small angles
and it leads to the appearance of super-leading logarithms. We use the `gaps
between jets' cross-section as a concrete example and illustrate that the new
logarithms are intimately connected with the presence of Coulomb gluon
contributions. Numerical estimates of their potential phenomenological
significance are presented.Comment: 7 pages, 3 figures; proceedings of Workshop on Diffraction in
High-Energy Physics - DIFFRACTION 2006, Sep. 5-10 2006, Adamantas, Milos
island, Greec
Rapidity Gaps Between Jets
An excess of events with a rapidity gap between jets, over what would be
expected from non-diffractive processes, has been observed at HERA. A process
based on a perturbative QCD calculation of colour singlet exchange has been
added to HERWIG. With this addition, HERWIG is able to describe the number of
events with a gap between jets over the number without a gap. This gap fraction
is predicted to rise at large rapidity intervals between jets which would only
be visible if the detector coverage were increased.Comment: 5 pages including 3 figures. To appear in the conference proceedings
of the Workshop "Future Physics at HERA
Soft interactions in Herwig++
We describe the recent developments to extend the multi-parton interaction
model of underlying events in Herwig++ into the soft, non-perturbative, regime.
This allows the program to describe also minimum bias collisions in which there
is no hard interaction, for the first time. It is publicly available from
versions 2.3 onwards and describes the Tevatron underlying event and minimum
bias data. The extrapolations to the LHC nevertheless suffer considerable
ambiguity, as we discuss.Comment: 10 pages, talk given by Manuel Bahr at First International Workshop
on Multiple Partonic Interactions at the LHC, "MPI@LHC'08", Perugia, Italy,
October 27-31 200
Symmetry of anomalous dimension matrices explained
In a previous paper, one of us pointed out that the anomalous dimension
matrices for all physical processes that have been calculated to date are
complex symmetric, if stated in an orthonormal basis. In this paper we prove
this fact and show that it is only true in a subset of all possible orthonormal
bases, but that this subset is the natural one to use for physical
calculations.Comment: 4 page
Resummed Cross Section for Jet Production at Hadron Colliders
We study the resummation of large logarithmic perturbative corrections to the
single-inclusive jet cross section at hadron colliders. The corrections we
address arise near the threshold for the partonic reaction, when the incoming
partons have just enough energy to produce the high-transverse-momentum final
state. The structure of the resulting logarithmic corrections is known to
depend crucially on the treatment of the invariant mass of the produced jet at
threshold. We allow the jet to have a non-vanishing mass at threshold, which
most closely corresponds to the situation in experiment. Matching our results
to available semi-analytical next-to-leading-order calculations, we derive
resummed results valid to next-to-leading logarithmic accuracy. We present
numerical results for the resummation effects at Tevatron and RHIC energies.Comment: 10 figures include
Recommended from our members
Patterns of contribution to citizen science biodiversity projects increase understanding of volunteersâ recording behaviour
The often opportunistic nature of biological recording via citizen science leads to taxonomic, spatial and temporal biases which add uncertainty to biodiversity estimates. However, such biases may also give valuable insight into volunteersâ recording behaviour. Using Greater London as a case-study we examined the composition of three citizen science datasets â from Greenspace Information for Greater London CIC, iSpot and iRecord - with respect to recorder contribution and spatial and taxonomic biases, i.e. when, where and what volunteers record. We found most volunteers contributed few records and were active for just one day. Each dataset had its own taxonomic and spatial signature suggesting that volunteersâ personal recording preferences may attract them towards particular schemes. There were also patterns across datasets: speciesâ abundance and ease of identification were positively associated with number of records, as was plant height. We found clear hotspots of recording activity, the 10 most popular sites containing open water. We note that biases are accrued as part of the recording process (e.g. speciesâ detectability) as well as from volunteer preferences. An increased understanding of volunteer behaviour gained from analysing the composition of records could thus enhance the fit between volunteersâ interests and the needs of scientific projects
Non-global logarithms in inter-jet energy flow with kt clustering requirement
Recent work in inter-jet energy flow has identified a class of leading
logarithms previously not considered in the literature. These so-called
non-global logarithms have been shown to have significant numerical impact on
gaps-between-jets calculations at the energies of current particle colliders.
Here we calculate, at fixed order and to all orders, the effect of applying
clustering to the gluonic final state responsible for these logarithms for a
trivial colour flow 2 jet system. Such a clustering algorithm has already been
used for experimental measurements at HERA. We find that the impact of the
non-global logarithms is reduced, but not removed, when clustering is demanded,
a result which is of considerable interest for energy flow observable
calculations.Comment: 13 pages, 4 figure
Herwig++ 2.0 Release Note
A new release of the Monte Carlo program Herwig++ (version 2.0) is now
available. This is the first version of the program which can be used for
hadron-hadron physics and includes the full simulation of both initial- and
final-state QCD radiation.Comment: Source code and additional information available at
http://hepforge.cedar.ac.uk/herwig
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