70 research outputs found
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
Next-to-Leading order Higgs + 2 jet production via gluon fusion
We present phenomenological results for the production of a Higgs boson in
association with two jets at the LHC. The calculation is performed in the limit
of large top mass and is accurate to next-to-leading order in the strong
coupling, i.e. Comment: 13 pages, 6 figures; v2: references added, modified acknowledgments,
final version as published in JHE
Inclusive Jet Production, Parton Distributions, and the Search for New Physics
Jet production at the Tevatron probes some of the smallest distance scales
currently accessible. A gluon distribution that is enhanced at large x compared
to previous determinations provides a better description of the Run 1b jet data
from both CDF and D0. However, considerable uncertainty still remains regarding
the gluon distribution at high x. In this paper, we examine the effects of this
uncertainty, and of the remaining uncertainties in the NLO QCD theory, on jet
cross section comparisons to Run 1b data. We also calculate the range of
contributions still possible from any new physics. Predictions are also made
for the expanded kinematic range expected for the ongoing Run 2 at the Tevatron
and for the LHC.Comment: 50 pages, 31 figures, RevTe
Next-to-leading order QCD corrections to W+W- production via vector-boson fusion
Vector-boson fusion processes constitute an important class of reactions at
hadron colliders, both for signals and backgrounds of new physics in the
electroweak interactions.
We consider what is commonly referred to as W+W- production via vector-boson
fusion (with subsequent leptonic decay of the Ws), or, more precisely, e+ nu_e
mu- nubar_mu + 2 jets production in proton-proton scattering, with all resonant
and non-resonant Feynman diagrams and spin correlations of the final-state
leptons included, in the phase-space regions which are dominated by t-channel
electroweak-boson exchange.
We compute the next-to-leading order QCD corrections to this process, at
order alpha^6 alpha_s.
The QCD corrections are modest, changing total cross sections by less than
10%. Remaining scale uncertainties are below 2%. A fully-flexible
next-to-leading order partonic Monte Carlo program allows to demonstrate these
features for cross sections within typical vector-boson-fusion acceptance cuts.
Modest corrections are also found for distributions.Comment: 29 pages, 14 figure
QCD radiative corrections to prompt diphoton production in association with a jet at hadron colliders
We compute the next-to-leading order corrections in to prompt
diphoton production in association with a jet at hadron colliders. We use a
next-to-leading order general-purpose partonic Monte Carlo event generator that
allows the computation of a rate differential in the produced photons and
hadrons.Comment: 17 pages, 6 figures, JHEP3 documen
Dominant next-to-leading order QCD corrections to Higgs plus three jet production in vector-boson fusion
We present the calculation of the dominant next to leading order QCD
corrections to Higgs boson production in association with three jets via vector
boson fusion in the form of a NLO parton-level Monte Carlo program. QCD
corrections to integrated cross sections are modest, while the shapes of some
kinematical distributions change appreciably at NLO. Scale uncertainties are
shown to be reduced at NLO for the total cross section and for distributions.
We consider a central jet veto at the LHC and analyze the veto probability for
typical vector boson fusion cuts. Scale uncertainties of the veto probability
are sufficiently small at NLO for precise Higgs coupling measurements at the
LHC.Comment: 40 pages, 17 figures, 2 tables, published versio
Accurate QCD predictions for heavy-quark jets at the Tevatron and LHC
Heavy-quark jets are important in many of today's collider studies and
searches, yet predictions for them are subject to much larger uncertainties
than for light jets. This is because of strong enhancements in higher orders
from large logarithms, ln(p_t/m_Q). We propose a new definition of heavy-quark
jets, which is free of final-state logarithms to all orders and such that all
initial-state collinear logarithms can be resummed into the heavy-quark parton
distributions. Heavy-jet spectra can then be calculated in the massless
approximation, which is simpler than a massive calculation and reduces the
theoretical uncertainties by a factor of three. This provides the first ever
accurate predictions for inclusive b- and c-jets, and the latter have
significant discriminatory power for the intrinsic charm content of the proton.
The techniques introduced here could be used to obtain heavy-flavour jet
results from existing massless next-to-leading order calculations for a wide
range of processes. We also discuss the experimental applicability of our
flavoured jet definition.Comment: 22 pages, 7 figure
The anti-k_t jet clustering algorithm
The k_t and Cambridge/Aachen inclusive jet finding algorithms for
hadron-hadron collisions can be seen as belonging to a broader class of
sequential recombination jet algorithms, parametrised by the power of the
energy scale in the distance measure. We examine some properties of a new
member of this class, for which the power is negative. This ``anti-k_t''
algorithm essentially behaves like an idealised cone algorithm, in that jets
with only soft fragmentation are conical, active and passive areas are equal,
the area anomalous dimensions are zero, the non-global logarithms are those of
a rigid boundary and the Milan factor is universal. None of these properties
hold for existing sequential recombination algorithms, nor for cone algorithms
with split--merge steps, such as SISCone. They are however the identifying
characteristics of the collinear unsafe plain ``iterative cone'' algorithm, for
which the anti-k_t algorithm provides a natural, fast, infrared and collinear
safe replacement.Comment: 12 pages, 5 figures. Small changes made for publication. Version
published in JHE
PYTHIA 6.4 Physics and Manual
The PYTHIA program can be used to generate high-energy-physics `events', i.e.
sets of outgoing particles produced in the interactions between two incoming
particles. The objective is to provide as accurate as possible a representation
of event properties in a wide range of reactions, within and beyond the
Standard Model, with emphasis on those where strong interactions play a role,
directly or indirectly, and therefore multihadronic final states are produced.
The physics is then not understood well enough to give an exact description;
instead the program has to be based on a combination of analytical results and
various QCD-based models. This physics input is summarized here, for areas such
as hard subprocesses, initial- and final-state parton showers, underlying
events and beam remnants, fragmentation and decays, and much more. Furthermore,
extensive information is provided on all program elements: subroutines and
functions, switches and parameters, and particle and process data. This should
allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further
information may be found on the PYTHIA web page:
http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly
deleted section heading for "Physics Processes" reinserted, affecting section
numbering. Minor updates to take into account referee comments and new colour
reconnection option
Construction and response of a highly granular scintillator-based electromagnetic calorimeter
A highly granular electromagnetic calorimeter with scintillator strip readout is being developed for future linear collider experiments. A prototype of 21.5 푋0 depth and 180 × 180 mm2 transverse dimensions was constructed, consisting of 2160 individually read out 10 × 45 × 3 mm3 scintillator strips. This prototype was tested using electrons of 2–32 GeV at the Fermilab Test Beam Facility in 2009. Deviations from linear energy response were less than 1.1%, and the intrinsic energy resolution was determined to be (12.5±0.1(stat.)±0.4(syst.))%∕√퐸[GeV]⊕(1.2± 0.1(stat.)+0.6−0.7(syst.))%, where the uncertainties correspond to statistical and systematic sources, respectively
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