10,569 research outputs found
An Introduction to PYTHIA 8.2
The PYTHIA program is a standard tool for the generation of events in
high-energy collisions, comprising a coherent set of physics models for the
evolution from a few-body hard process to a complex multiparticle final state.
It contains a library of hard processes, models for initial- and final-state
parton showers, matching and merging methods between hard processes and parton
showers, multiparton interactions, beam remnants, string fragmentation and
particle decays. It also has a set of utilities and several interfaces to
external programs. PYTHIA 8.2 is the second main release after the complete
rewrite from Fortran to C++, and now has reached such a maturity that it offers
a complete replacement for most applications, notably for LHC physics studies.
The many new features should allow an improved description of data.Comment: 45 page
Light in the beam dump -- ALP production from decay photons in proton beam-dumps
The exploration of long-lived particles in the MeV-GeV region is a formidable
task but it may provide us a unique access to dark sectors. Fixed-target
facilities with sufficiently energetic and intense proton beams are an ideal
tool for this challenge. In this work we show that the production rate of
Axion-Like-Particles (ALPs) coupled pre-dominantly to photons receives a
significant contribution from daughter-photons of secondary and
mesons created in the proton shower. We carefully compare the PYTHIA simulated
spectra of such secondaries to experimental literature, compute the ALP flux
from the Primakoff conversion of these photons, and finally revisit existing
limits on ALPs and update the prospects for a set of existing and future
searches. Our results show that taking this production mechanism into account
significantly enhances the sensitivity compared to previous studies based on
coherent ALP production in primary proton-nucleus interactions.Comment: 24 pages, 13 figures, v2 matches version published in JHEP, v3 adds
appendix with corrections of some figures of the main text, conclusions
unchange
QCD-aware partonic jet clustering for truth-jet flavour labelling
We present an algorithm for deriving partonic flavour labels to be applied to
truth particle jets in Monte Carlo event simulations. The inputs to this
approach are final pre-hadronization partons, to remove dependence on
unphysical details such as the order of matrix element calculation and shower
generator frame recoil treatment. These are clustered using standard jet
algorithms, modified to restrict the allowed pseudojet combinations to those in
which tracked flavour labels are consistent with QCD and QED Feynman rules. The
resulting algorithm is shown to be portable between the major families of
shower generators, and largely insensitive to many possible systematic
variations: it hence offers significant advantages over existing ad hoc
labelling schemes. However, it is shown that contamination from multi-parton
scattering simulations can disrupt the labelling results. Suggestions are made
for further extension to incorporate more detailed QCD splitting function
kinematics, robustness improvements, and potential uses for truth-level physics
object definitions and tagging
Study on space-time structure of Higgs boson decay using HBT correlation Method in ee collision at =250 GeV
The space-time structure of the Higgs boson decay are carefully studied with
the HBT correlation method using ee collision events produced through
Monte Carlo generator PYTHIA 8.2 at =250GeV. The Higgs boson jets
(Higgs-jets) are identified by H-tag tracing. The measurement of the Higgs
boson radius and decay lifetime are derived from HBT correlation of its decay
final state pions inside Higgs-jets in the ee collisions events with an
upper bound of fm and fs. This result is consistent with CMS data.Comment: 7 pages,3 figure
Bottom Production
We review the prospects for bottom production physics at the LHC.Comment: 74 pages, Latex, 71 figures, to appear in the Report of the ``1999
CERN Workshop on SM physics (and more) at the LHC'', P. Nason, G. Ridolfi, O.
Schneider G.F. Tartarelli, P. Vikas (conveners
Vincia for Hadron Colliders
We present the first public implementation of antenna-based QCD initial- and
final-state showers. The shower kernels are antenna functions, which
capture not only the collinear dynamics but also the leading soft (coherent)
singularities of QCD matrix elements. We define the evolution measure to be
inversely proportional to the leading poles, hence gluon emissions are evolved
in a measure inversely proportional to the eikonal, while processes
that only contain a single pole (e.g., ) are evolved in
virtuality. Non-ordered emissions are allowed, suppressed by an additional
power of . Recoils and kinematics are governed by exact on-shell phase-space factorisations. This first implementation is limited to massless
QCD partons and colourless resonances. Tree-level matrix-element corrections
are included for QCD up to (4 jets), and for
Drell-Yan and Higgs production up to ( + 3
jets). The resulting algorithm has been made publicly available in Vincia 2.0
Recent Pythia 8 developments: Hard diffraction, Colour reconnection and collisions
An overview of recent developments in \pythia~8 is given. First the new hard
diffraction model, which is implemented as a part of the multiparton
interactions (MPI) framework, is discussed. Then the new colour reconnection
model, which includes beyond leading colour effects that can become important
when MPI are present, is briefly reviewed. As a last topic an introduction is
given to our implementation of photon-photon collisions. In particular photon
PDFs, required modifications for the initial state radiation algorithm and beam
remnant handling with photon beams is discussed.Comment: Contribution to proceedings of 7th International Workshop on Multiple
Partonic Interactions at the LHC, 23 - 27 November 2015, Miramare, Trieste,
Ital
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