20 research outputs found
PHOTOS Interface in C++; Technical and Physics Documentation
For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of
particles and resonances has been available with an interface to the C++ HepMC
event record. The main purpose of the present paper is to document the
technical aspects of the PHOTOS Monte Carlo installation and present version
use. A multitude of test results and examples are distributed together with the
program code.
The PHOTOS C++ physics precision is better than its FORTRAN predecessor and
more convenient steering options are also available. An algorithm for the event
record interface necessary for process dependent photon emission kernel is
implemented. It is used in Z and W decays for kernels of complete first order
matrix elements of the decays. Additional emission of final state lepton pairs
is also available.
Physics assumptions used in the program and properties of the solution are
reviewed. In particular, it is explained how the second order matrix elements
were used in design and validation of the program iteration procedure. Also, it
is explained that the phase space parametrization used in the program is exact.Comment: Updated version; for the program as of April 201
MC generator TAUOLA: implementation of Resonance Chiral Theory for two and three meson modes. Comparison with experiment
We present a partial upgrade of the Monte Carlo event generator TAUOLA with
the two and three hadron decay modes using the theoretical models based on
Resonance Chiral Theory. These modes account for 88% of total hadronic width of
the tau meson. First results of the model parameters have been obtained using
BaBar data for three pion mode.Comment: 5 pages, 1 figure, contribution to the Proceedings of the QCD@Work12
Conferenc
Application of TauSpinner for studies on tau-lepton polarization and spin correlations in Z, W and H decays at LHC
The tau-lepton plays an important role in the physics program at LHC. Its
spin can be used for separation of signal from background or in measuring
properties of New Particles decaying to tau leptons.
The TauSpinner package represents a tool to modify tau spin effects in any
sample containing tau leptons. Generated events, featuring taus produced from
intermediate state W, Z, H bosons can be used as an input. The information on
the polarization and spin correlations is reconstructed from the kinematics of
the tau lepton(s) (nutau in case of W-mediated processes) and tau decay
products. By weights, attributed on the event-by-event basis, it enables
numerical evaluation and/or modification of the spin effects.
We review distributions to monitor spin effects in leptonic and hadronic tau
decays with up to three pions, to provide benchmarks for validation of spin
content of the event sample and to visualize the tau lepton spin polarization
and correlation effects. The demonstration examples for use of TauSpinner
libraries, are documented. New validation methods of such an approach are
provided. Other topics, like TauSpinner systematic errors or sensitivity of
experimental distributions to spin, are addressed in part only.
This approach is of interest for implementation of spin effects in embedded
tau lepton samples, where Z to mu mu events from data of muons are replaced by
simulated tau leptons. Embedding is used at LHC for estimating Z to tau tau
background to H to tau tau signatures.Comment: 1+41 pages, 5 figures in main text, multitude of figures in
appendice
Theoretical inputs and errors in the new hadronic currents in TAUOLA
The new hadronic currents implemented in the TAUOLA library are obtained in
the unified and consistent framework of Resonance Chiral Theory: a Lagrangian
approach in which the resonances exchanged in the hadronic tau decays are
active degrees of freedom included in a way that reproduces the low-energy
results of Chiral Perturbation Theory. The short-distance QCD constraints on
the imaginary part of the spin-one correlators yield relations among the
couplings that render the theory predictive.
In this communication, the obtaining of the two- and three-meson form factors
is sketched. One of the criticisms to our framework is that the error may be as
large as 1/3, since it is a realization of the large-N_C limit of QCD in a
meson theory. A number of arguments are given which disfavor that claim
pointing to smaller errors, which would explain the phenomenological success of
our description in these decays. Finally, other minor sources of error and
current improvements of the code are discussed.Comment: 5 pages, no figures, contribution to the Proceedings of the
QCD@Work12 Conferenc
TauSpinner: a tool for simulating CP effects in H to tau tau decays at LHC
In this paper, we discuss application of the TauSpinner package as a
simulation tool for measuring the CP state of the newly discovered Higgs boson
using the transverse spin correlations in the H to tau tau decay channel. We
discuss application for its main background Z/gamma* to tau tau as well. The
TauSpinner package allows one to add, with the help of weights, transverse spin
correlations corresponding to any mixture of scalar/pseudoscalar state, on
already existing events using information from the kinematics of outgoing tau
leptons and their decay products only. This procedure can be used when
polarimetric vectors of the taus decays and density matrix for tau-pair
production are not stored with the event sample.
We concentrate on the well-defined effects for the Higgs (or Higgs-like
scalar) decays, which are physically separated from the production processes.
TauSpinner also allows to reintroduce (or remove) spin correlations to events
from Drell-Yan Z/gamma* to tau tau process, the main background for the Higgs
parity observables, again with the help of weights only.
From the literature, we recall well-established observables, developed for
measuring the CP of the Higgs, and use them as benchmarks for illustrating
applications of the TauSpinner package. We also include a description of the
code and prepared testing examples.Comment: 1+18 pages,4 figure
Resonance Chiral Lagrangian Currents and Experimental Data for
In this paper we document the modifications introduced to the previous
version of the Resonance Chiral Lagrangian current ({\it Phys.Rev.} {\bf D86}
(2012) 113008) of the decay
which enable the one dimensional distributions measured by the BaBar
collaboration to be well modeled. The main change required to model the data is
the addition of the resonance. Systematic errors, theoretical and
experimental ones, limitations due to fits of one dimensional distributions
only, and resulting difficulties and statistical/systematic errors for fitted
parameters are addressed. The current and fitting environment is ready for
comparisons with the fully exclusive experimental data. The present result for
is encouraging for work on
other decay modes and Resonance Chiral Lagrangian based currents.Comment: 16 pages, 2 figure
TauSpinner program for studies on spin effect in tau production at the LHC
Final states involving tau leptons are important components of searches for
new particles at the Large Hadron Collider (LHC). A proper treatment of tau
spin effects in the Monte Carlo (MC) simulations is important for understanding
the detector acceptance as well as for the measurements of tau polarization and
tau spin correlations. In this note we present a TauSpinner package designed to
simulate the spin effects. It relies on the availability of the four-momenta of
the taus and their decay products in the analyzed data. The flavor and the
four-momentum of the boson decaying to the tau-tau+ or tau+- nu pair need to be
known. In the Z/gamma* case the initial state quark configuration is attributed
from the intermediate boson kinematics, and the parton distribution functions
(PDF's). TauSpinner is the first algorithm suitable for emulation of tau spin
effects in tau-embedded samples. It is also the first tool that offers the user
the flexibility to simulate a desired spin effect at the analysis level. An
algorithm to attribute tau helicity states to a previously generated sample is
also provided.Comment: 13 pages, 6 figures New feature, an algorithm to attribute tau
helicity states introduced in v
PHOTOS Interface in C++: Technical and Physics Documentation
For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of particles and resonances has been available with an interface to the C++ HepMC event record. The main purpose of the present paper is to document the technical aspects of the PHOTOS Monte Carlo installation and present version use. A multitude of test results and examples are distributed together with the program code. The PHOTOS C++ physics precision is better than its FORTRAN predecessor and more convenient steering options are also available. An algorithm for the event record interface necessary for process dependent photon emission kernel is implemented. It is used in Z and W decays for kernels of complete first order matrix elements of the decays. Additional emission of final state lepton pairs is also available. Physics assumptions used in the program and properties of the solution are reviewed. In particular, it is explained how the second order matrix elements were used in design and validation of the program iteration procedure. Also, it is explained that the phase space parametrization used in the program is exact.For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of particles and resonances has been available with an interface to the C++ HepMC event record. The main purpose of the present paper is to document the technical aspects of the PHOTOS Monte Carlo installation and present version use. A multitude of test results and examples are distributed together with the program code. The PHOTOS C++ physics precision is better than its FORTRAN predecessor and more convenient steering options are also available. An algorithm for the event record interface necessary for process dependent photon emission kernel is implemented. It is used in Z and W decays for kernels of complete first order matrix elements of the decays. Additional emission of final state lepton pairs is also available. Physics assumptions used in the program and properties of the solution are reviewed. In particular, it is explained how the second order matrix elements were used in design and validation of the program iteration procedure. Also, it is explained that the phase space parametrization used in the program is exact.For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of particles and resonances has been available with an interface to the C++ HepMC event record. The main purpose of the present paper is to document the technical aspects of the PHOTOS Monte Carlo installation and present version use. A multitude of test results and examples are distributed together with the program code
Documentation of TauSpinner algorithms: program for simulating spin effects in \uptau τ -lepton production at LHC
Abstract \uptau τ -leptons produced in pp collisions allow to measure Standard Model parameters and offer probes for New Physics. The TauSpinner program can be used to modify spin (or production matrix elements) effects in any \uptau τ sample. It relies on the kinematics of outgoing particles: \uptau τ lepton(s) (also \upnu _\uptau ντ in case of W-mediated processes, optionally also four-moments of accompanying hard jets) and \uptau τ decay products. No other information is required from the event record. With calculated spin (or production/decay matrix element) weights, attributed on the event-by-event basis, modifications to the spin/decay/production features, is possible without the need for regenerating events. With TauSpinner algorithms, the experimental techniques developed over years since LEP 1 times are already used and extended for LHC applications. The purpose of the present publication is to systematically document physics basis of the program, and to overview its application domain and systematic errors
MC-TESTER v. 1.23: a universal tool for comparisons of Monte Carlo predictions for particle decays in high energy physics
Theoretical predictions in high energy physics are routinely provided in the form of Monte Carlo generators. Comparisons of predictions from different programs and/or different initialization set-ups are often necessary. MC-TESTER can be used for such tests of decays of intermediate states (particles or resonances) in a semi-automated way. Since 2002 new functionalities were introduced into the package. In particular, it works now with the HepMC event record, the standard of C++ programs. The complete set-up for benchmarking the interface, such as between tau-lepton production and decay, including QED bremsstrahlung effects is shown. The example is chosen to illustrate the new options introduced into the program and novel ways of its use. From the technical perspective, our paper documents program updates and supplements previous documentation. As in the past, our test consists of two steps. Distinct Monte Carlo programs are run separately; events with decays of a chosen particle are searched, and information is stored by MC-TESTER. Then, at the analysis step, information from the pair of such runs may be compared and represented in a form of tables and plots