242 research outputs found

### Symmetry of Anomalous Dimension Matrices for Colour Evolution of Hard Scattering Processes

In a recent paper, Dokshitzer and Marchesini rederived the anomalous
dimension matrix for colour evolution of $gg \to gg$ scattering, first derived
by Kidonakis, Oderda and Sterman. They noted a weird symmetry that it possesses
under interchange of internal (colour group) and external (scattering angle)
degrees of freedom and speculated that this may be related to an embedding into
a context that correlates internal and external variables such as string
theory.
In this short note, I point out another symmetry possessed by all the colour
evolution anomalous dimension matrices calculated to date. It is more prosaic,
but equally unexpected, and may also point to the fact that colour evolution
might be understood in some deeper theoretical framework. To my knowledge it
has not been pointed out elsewhere, or anticipated by any of the authors
calculating these matrices. It is simply that, in a suitably chosen colour
basis, they are complex symmetric matrices.Comment: 3 page

### Gaps between Jets in the High Energy Limit

We use perturbative QCD to calculate the parton level cross section for the
production of two jets that are far apart in rapidity, subject to a limitation
on the total transverse momentum Q0 in the interjet region. We specifically
address the question of how to combine the approach which sums all leading
logarithms in Q/Q0 (where Q is the jet transverse momentum) with the BFKL
approach, in which leading logarithms of the scattering energy are summed. This
paper constitutes progress towards the simultaneous summation of all important
logarithms. Using an "all orders" matching, we are able to obtain results for
the cross section which correctly reproduce the two approaches in the
appropriate limits.Comment: 29 pages, 9 figures, minor corrections to text and improved figure

### Aspects of power corrections in hadron-hadron collisions

The program of understanding inverse-power law corrections to event shapes
and energy flow observables in e+ e- annihilation to two jets and DIS (1+1)
jets has been a significant success of QCD phenomenology over the last decade.
The important extension of this program to similar observables in hadron
collisions is not straightforward, being obscured by both conceptual and
technical issues. In this paper we shed light on some of these issues by
providing an estimate of power corrections to the inter-jet E_t flow
distribution in hadron collisions using the techniques that were employed in
the e+ e- annihilation and DIS cases.Comment: 15 pages, 1 figure, uses JHEP3.cl

### Super-leading logarithms in non-global observables in QCD: Fixed order calculation

Super-leading logarithmic terms have previously been observed in non-global
QCD observables. In this paper we re-calculate the first super-leading
contribution to the `gaps between jets' cross-section using a diagrammatic
fixed order approach. We calculate for the first time the super-leading
contribution at fifth order in alpha_s.Comment: 18 pages, 7 figure

### The resummation of inter-jet energy flow for gaps-between-jets processes at HERA

We calculate resummed perturbative predictions for gaps-between-jets
processes and compare to HERA data. Our calculation of this non-global
observable needs to include the effects of primary gluon emission (global
logarithms) and secondary gluon emission (non-global logarithms) to be correct
at the leading logarithm (LL) level. We include primary emission by calculating
anomalous dimension matrices for the geometry of the specific event definitions
and estimate the effect of non-global logarithms in the large $N_c$ limit. The
resulting predictions for energy flow observables are consistent with
experimental data.Comment: 31 pages, 4 figures, 2 table

### Diffractive Dijet Production

We explore the diffractive interaction of a proton with an anti-proton which
results in centrally produced dijets. This process has been recently studied at
the Tevatron. We make predictions within an Ingelman-Schlein approach and
compare them to the recent data presented by the CDF collaboration. Earlier
calculations resulted in theoretical cross-sections which are much larger than
those observed by CDF. We find that, after consideration of hadronisation
effects and the parton shower, and using parton density functions extracted
from diffractive deep inelastic scattering at HERA, it is possible to explain
the CDF data. We need to assume a gap survival probability of around 10% and
this is in good agreement with the value predicted by theory. We also find that
the non-diffractive contribution to the process is probably significant in the
kinematical region probed by the Tevatron.Comment: 12 pages, 6 figures, 3 table

### Constraints on Galileon-induced precessions from solar system orbital motions

We use latest data from solar system planetary orbital motions to put
constraints on some Galileon-induced precessional effects. Due to the
Vainshtein mechanism, the Galileon-type spherically symmetric field of a
monopole induces a small, screened correction proprtional to \sqrt{r} to its
usual r^-1 Newtonian potential which causes a secular precession of the
pericenter of a test particle. In the case of our solar system, latest data
from Mars allow to constrain the magnitude of such an interaction down to
\alpha <= 0.3 level. Another Galileon-type effect which might impact solar
system dynamics is due to an unscreened constant gradient induced by the
peculiar motion of the Galaxy. The magnitude of such an effect, depending on
the different gravitational binding energies of the Sun and the planets, is \xi
<= 0.004 from the latest bounds on the supplementary perihelion precession of
Saturn.Comment: LaTex2e, 11 pages, 1 table, no figures, 35 references. To appear in
Journal of Cosmology and Astroparticle Physics (JCAP

### On large angle multiple gluon radiation

Jet shape observables which involve measurements restricted to a part of
phase space are sensitive to multiplication of soft gluon with large relative
angles and give rise to specific single logarithmically enhanced (SL) terms
(non-global logs). We consider associated distributions in two variables which
combine measurement of a jet shape V in the whole phase space (global) and that
of the transverse energy flow away from the jet direction, Eout (non-global).
We show that associated distributions factorize into the global distribution in
V and a factor that takes into account SL contributions from multi-gluon
``hedgehog'' configurations in all orders. The latter is the same that
describes the single-variable Eout distribution, but evaluated at a rescaled
energy VQ.Comment: 16 page

### Jet vetoing at the LHC

We study the effect of a veto on additional jets in the rapidity region
between a pair of high transverse momentum jets at the LHC. We aim to sum the
most important logarithms in the ratio of the jet transverse momentum to the
veto scale and to that end we attempt to assess the significance of the
super-leading logarithms that appear at high orders in the perturbative
expansion. We also compare our results to those of HERWIG++, in an attempt to
ascertain the accuracy of the angular ordered parton shower. We find that there
are large corrections that arise for large enough jet transverse momenta as a
consequence of Coulomb gluon exchanges.Comment: 25 page

### Results of the EUROTeV Post Collision Line Design (PCDL) Task

This paper is the deliverable of the EUROTeV Post Collision Line Design (PCDL) task and gives an overview of the published results

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