821 research outputs found
From QCD at high energy to statistical physics and back
In these proceedings, we shall first recall the evolution equations arising
when increasing the rapidity within the perturbative QCD regime. We
shall then summarise the main properties on their asymptotic solutions and
discuss the physical picture emerging from our analysis.Comment: 4 pages, talk presented at the DIS2006 meeting, April 19-24, Tsukuba,
Japa
SoftKiller, a particle-level pileup removal method
Existing widely-used pileup removal approaches correct the momenta of
individual jets. In this article we introduce an event-level, particle-based
pileup correction procedure, SoftKiller. It removes the softest particles in an
event, up to a transverse momentum threshold that is determined dynamically on
an event-by-event basis. In simulations, this simple procedure appears to be
reasonably robust and brings superior jet resolution performance compared to
existing jet-based approaches. It is also nearly two orders of magnitude faster
than methods based on jet areas.Comment: 26 pages, 16 figures (2 appendices with further checks added
On the use of charged-track information to subtract neutral pileup
The use of charged pileup tracks in a jet to predict the neutral pileup
component in that same jet could potentially lead to improved pileup removal
techniques, provided there is a strong local correlation between charged and
neutral pileup. In Monte Carlo simulation we find that the correlation is
however moderate, a feature that we attribute to characteristics of the
underlying non-perturbative dynamics. Consequently,
`neutral-proportional-to-charge' (NpC) pileup mitigation approaches do not
outperform existing, area-based, pileup removal methods. This finding contrasts
with the arguments made in favour of a new method, "jet cleansing", in part
based on the NpC approach. We identify the critical differences between the
performances of linear cleansing and trimmed NpC as being due to the former's
rejection of subjets that have no charged tracks from the leading vertex, a
procedure that we name "zeroing". Zeroing, an extreme version of the
"charged-track trimming" proposed by ATLAS, can be combined with a range of
pileup-mitigation methods, and appears to have both benefits and drawbacks. We
show how the latter can be straightforwardly alleviated. We also discuss the
limited potential for improvement that can be obtained by linear combinations
of the NpC and area-subtraction methods.Comment: 27 pages, 10 figures; v2 adapts the discussion of cleansing to the
trimming parameter choice clarified in v2 of the cleansing paper
(arXiv:1309.4777) and identifies and analyses the origin of differences with
Np
Testing the Gaussian Approximation to the JIMWLK Equation
In processes involving small-x partons, like in deep inelastic scattering and
in hadronic collisions at high energy, the final state can be expressed in
terms of correlators of Wilson lines. We study such high-point correlators
evolving according to the JIMWLK equation and we confirm the results of
previous numerical and analytic work, by using an independent method, that the
solution to the JIMWLK equation can be very well approximated by an appropriate
Gaussian wavefunction. We explore both fixed and running coupling evolution,
where in the latter the scale is set according to various prescriptions. As a
byproduct, we also numerically confirm to high accuracy the validity of the law
governing the behavior of the S-matrix close to the unitarity limit, the
Levin-Tuchin formula. We furthermore outline how to calculate correlators with
open color indices.Comment: 25 pages, 11 figures. v2: minor corrections, one equation added,
updated to match published versio
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