6 research outputs found
Non-Global Logarithms in Filtered Jet Algorithms
We analytically and numerically study the effect of perturbative gluons
emission on the "Filtering analysis", which is part of a subjet analysis
procedure proposed two years ago to possibly identify a low-mass Higgs boson
decaying into b\bar{b} at the LHC. This leads us to examine the non-global
structure of the resulting perturbative series in the leading single-log
large-N_c approximation, including all-orders numerical results, simple
analytical approximations to them and comments on the structure of their series
expansion. We then use these results to semi-analytically optimize the
parameters of the Filtering analysis so as to suppress as much as possible the
effect of underlying event and pile-up on the Higgs mass peak reconstruction
while keeping the major part of the perturbative radiation from the b\bar{b}
dipole.Comment: 47 pages, 25 figures, 1 figure and a few comments added, version
accepted for publication in JHE
The mass area of jets
We introduce a new characteristic of jets called mass area. It is defined so
as to measure the susceptibility of the jet's mass to contamination from soft
background. The mass area is a close relative of the recently introduced
catchment area of jets. We define it also in two variants: passive and active.
As a preparatory step, we generalise the results for passive and active areas
of two-particle jets to the case where the two constituent particles have
arbitrary transverse momenta. As a main part of our study, we use the mass area
to analyse a range of modern jet algorithms acting on simple one and
two-particle systems. We find a whole variety of behaviours of passive and
active mass areas depending on the algorithm, relative hardness of particles or
their separation. We also study mass areas of jets from Monte Carlo simulations
as well as give an example of how the concept of mass area can be used to
correct jets for contamination from pileup. Our results show that the
information provided by the mass area can be very useful in a range of
jet-based analyses.Comment: 36 pages, 12 figures; v2: improved quality of two plots, added entry
in acknowledgments, nicer form of formulae in appendix A; v3: added section
with MC study and pileup correction, version accepted by JHE
Non-global Structure of the O({\alpha}_s^2) Dijet Soft Function
High energy scattering processes involving jets generically involve matrix
elements of light- like Wilson lines, known as soft functions. These describe
the structure of soft contributions to observables and encode color and
kinematic correlations between jets. We compute the dijet soft function to
O({\alpha}_s^2) as a function of the two jet invariant masses, focusing on
terms not determined by its renormalization group evolution that have a
non-separable dependence on these masses. Our results include non-global single
and double logarithms, and analytic results for the full set of non-logarithmic
contributions as well. Using a recent result for the thrust constant, we
present the complete O({\alpha}_s^2) soft function for dijet production in both
position and momentum space.Comment: 55 pages, 8 figures. v2: extended discussion of double logs in the
hard regime. v3: minor typos corrected, version published in JHEP. v4: typos
in Eq. (3.33), (3.39), (3.43) corrected; this does not affect the main
result, numerical results, or conclusion
Jet Shapes and Jet Algorithms in SCET
Jet shapes are weighted sums over the four-momenta of the constituents of a
jet and reveal details of its internal structure, potentially allowing
discrimination of its partonic origin. In this work we make predictions for
quark and gluon jet shape distributions in N-jet final states in e+e-
collisions, defined with a cone or recombination algorithm, where we measure
some jet shape observable on a subset of these jets. Using the framework of
Soft-Collinear Effective Theory, we prove a factorization theorem for jet shape
distributions and demonstrate the consistent renormalization-group running of
the functions in the factorization theorem for any number of measured and
unmeasured jets, any number of quark and gluon jets, and any angular size R of
the jets, as long as R is much smaller than the angular separation between
jets. We calculate the jet and soft functions for angularity jet shapes \tau_a
to one-loop order (O(alpha_s)) and resum a subset of the large logarithms of
\tau_a needed for next-to-leading logarithmic (NLL) accuracy for both cone and
kT-type jets. We compare our predictions for the resummed \tau_a distribution
of a quark or a gluon jet produced in a 3-jet final state in e+e- annihilation
to the output of a Monte Carlo event generator and find that the dependence on
a and R is very similar.Comment: 62 pages plus 21 pages of Appendices, 13 figures, uses JHEP3.cls. v2:
corrections to finite parts of NLO jet functions, minor changes to plots,
clarified discussion of power corrections. v3: Journal version. Introductory
sections significantly reorganized for clarity, classification of logarithmic
accuracy clarified, results for non-Mercedes-Benz configurations adde
The Communication and Risk Management of Volcanic Ballistic Hazards
Tourists, hikers, mountaineers, locals and volcanologists frequently visit
and reside on and around active volcanoes, where ballistic projectiles are a
lethal hazard. The projectiles of lava or solid rock, ranging from a few
centimetres to several metres in diameter, are erupted with high kinetic,
and sometimes thermal, energy. Impacts from projectiles are amongst the
most frequent causes of fatal volcanic incidents and the cause of hundreds
of thousands of dollars of damage to buildings, infrastructure and property
worldwide. Despite this, the assessment of risk and communication of
ballistic hazard has received surprisingly little study. Here, we review the
research to date on ballistic distributions, impacts, hazard and risk
assessments and maps, and methods of communicating and managing
ballistic risk including how these change with a changing risk environment.
The review suggests future improvements to the communication and
management of ballistic hazard