38 research outputs found
Soft-QCD and UE spectra in pp collisions at very high CM energies (a Snowmass white paper)
We make some educated guesses for the extrapolations of typical
soft-inclusive (minimum-bias, pileup, underlying-event) observables to
proton-proton collisions at center-of-mass energies in the range 13 - 100 TeV.
The numbers should be interpreted with (at least) a 10% uncertainty.Comment: 5 pages. Update (v2) adds numbers for 13 TeV and corrects bug in UE
ET density estimate
QCD (&) Event Generators
Recent developments in QCD phenomenology have spurred on several improved
approaches to Monte Carlo event generation, relative to the post--LEP state of
the art. In this brief review, the emphasis is placed on approaches for 1)
consistently merging fixed--order matrix element calculations with parton
showers, 2) improving the parton shower algorithms themselves, and 3) improving
the description of the underlying event in hadron collisions.Comment: Submitted to proceedings of DIS05, 12 page
A Quick Guide to SUSY Tools
The last decade has seen the emergence of a wide range of automated
calculations for supersymmetric extensions of the Standard Model. This guide
contains a brief summary of these, with the main focus on hadron collider
phenomenology, as well as a brief introduction to the so-called SUSY Les
Houches Accord. See also the Les Houches Web Repository for BSM Tools:
http://www.ippp.dur.ac.uk/montecarlo/BSM/Comment: 6 pages. Prepared for the TeV4LHC Physics Landscapes summary repor
Non-perturbative QCD Effects and the Top Mass at the Tevatron
The modelling of non-perturbative effects is an important part of modern
collider physics simulations. In hadron collisions there is some indication
that the modelling of the interactions of the beam remnants, the underlying
event, may require non-trivial colour reconnection effects to be present. We
recently introduced a universally applicable toy model of such reconnections,
based on hadronising strings. This model, which has one free parameter, has
been implemented in the Pythia event generator. We then considered several
parameter sets (`tunes'), constrained by fits to Tevatron minimum-bias data,
and determined the sensitivity of a simplified top mass analysis to these
effects, in exclusive semi-leptonic top events at the Tevatron. A first attempt
at isolating the genuine non-perturbative effects gave an estimate of order
+-0.5GeV from non-perturbative uncertainties. The results presented here are an
update to the original study and include recent bug fixes of Pythia that
influenced the tunings investigated.Comment: 8 pages, 5 figures, Submitted to the Proceedings of Top2008, 18-24
May 2008, La Biodola, Isola d'Elba, Ital
String Formation Beyond Leading Colour
We present a new model for the hadronisation of multi-parton systems, in
which colour correlations beyond leading are allowed to influence the
formation of confining potentials (strings). The multiplet structure of
is combined with a minimisation of the string potential energy, to decide
between which partons strings should form, allowing also for "baryonic"
configurations (e.g., two colours can combine coherently to form an
anticolour). In collisions, modifications to the leading-colour picture
are small, suppressed by both colour and kinematics factors. But in
collisions, multi-parton interactions increase the number of possible
subleading connections, counteracting their naive suppression.
Moreover, those that reduce the overall string lengths are kinematically
favoured. The model, which we have implemented in the PYTHIA 8 generator, is
capable of reaching agreement not only with the important
\left(n_\mathrm{charged}) distribution but also with measured
rates (and ratios) of kaons and hyperons, in both and collisions.
Nonetheless, the shape of their spectra remains challenging to
explain.Comment: 48 pages, 22 figure
Study of particle production from quark and gluon jets in proton-proton collisions
We investigate whether and how different fragmentation properties of quarks
and gluons affect identified particle spectra. We present a systematic study of
, and production in minimum bias (inelastic, non-diffractive),
two- and three-jet events at RHIC, Tevatron and LHC energies. Through the study
of two- and three-jet events and various jet-production channels we can
directly access the fragmentation properties of quark and gluon jets. We
present MC estimate for the contribution of quark and gluon jets to individual
particle species spectra, that can be compared to experimental results and test
our current knowledge of the physics behind particle production inside jets.Comment: 5 pages, 3 figures, presented at Hot Quarks 201
Tuning Monte Carlo Generators: The Perugia Tunes
We present 9 new tunes of the pT-ordered shower and underlying-event model in
PYTHIA 6.4. These "Perugia" tunes update and supersede the older "S0" family.
The data sets used to constrain the models include hadronic Z0 decays at LEP,
Tevatron minimum-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data
at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In
addition to the central parameter set, called "Perugia 0", we introduce a set
of 8 related "Perugia Variations" that attempt to systematically explore soft,
hard, parton density, and colour structure variations in the theoretical
parameters. Based on these variations, a best-guess prediction of the charged
track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC
is made. Note that these tunes can only be used with PYTHIA 6, not with PYTHIA
8. Note: this report was updated in March 2011 with a new set of variations,
collectively labeled "Perugia 2011", that are optimized for matching
applications and which also take into account some lessons from the early LHC
data. In order not to break the original text, these are described separately
in Appendix B. Note 2: a subsequent "Perugia 2012" update is described in
Appendix C.Comment: 46 page
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
Supersymmetry and Generic BSM Models in PYTHIA 8
We describe the implementation of supersymmetric models in PYTHIA 8,
including production and decay of superparticles and allowing for violation of
flavour, CP, and R-parity. We also present a framework for importing generic
new-physics matrix elements into PYTHIA 8, in a way suitable for use with
automated tools. We emphasize that this possibility should not be viewed as the
only way to implement new-physics models in PYTHIA 8, but merely as an
additional possibility on top of the already existing ones. Finally we address
parton showers in exotic colour topologies, in particular ones involving colour
epsilon tensors and colour sextets.Comment: 20 page
High-precision measurements from LHC to FCC-ee
This document provides a writeup of all contributions to the workshop on
"High precision measurements of : From LHC to FCC-ee" held at CERN,
Oct. 12--13, 2015. The workshop explored in depth the latest developments on
the determination of the QCD coupling from 15 methods where high
precision measurements are (or will be) available. Those include low-energy
observables: (i) lattice QCD, (ii) pion decay factor, (iii) quarkonia and (iv)
decays, (v) soft parton-to-hadron fragmentation functions, as well as
high-energy observables: (vi) global fits of parton distribution functions,
(vii) hard parton-to-hadron fragmentation functions, (viii) jets in p
DIS and -p photoproduction, (ix) photon structure function in
-, (x) event shapes and (xi) jet cross sections in
collisions, (xii) W boson and (xiii) Z boson decays, and (xiv) jets and (xv)
top-quark cross sections in proton-(anti)proton collisions. The current status
of the theoretical and experimental uncertainties associated to each extraction
method, the improvements expected from LHC data in the coming years, and future
perspectives achievable in collisions at the Future Circular Collider
(FCC-ee) with (1--100 ab) integrated luminosities yielding
10 Z bosons and jets, and 10 W bosons and leptons, are
thoroughly reviewed. The current uncertainty of the (preliminary) 2015 strong
coupling world-average value, = 0.1177 0.0013, is about
1\%. Some participants believed this may be reduced by a factor of three in the
near future by including novel high-precision observables, although this
opinion was not universally shared. At the FCC-ee facility, a factor of ten
reduction in the uncertainty should be possible, mostly thanks to
the huge Z and W data samples available.Comment: 135 pages, 56 figures. CERN-PH-TH-2015-299, CoEPP-MN-15-13. This
document is dedicated to the memory of Guido Altarell