4,646 research outputs found
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
Library of SM and anomalous WWgamma couplings for the e+e- -> f \bar{f} n\gamma Monte Carlo programs
A brief description of the library of the Standard Model and anomalous
WWgamma coupling contribution to the matrix element for e+e- -> \nu \bar{\nu}
n\gamma process is given. It can be used with any Monte Carlo program for e+e-
-> f \bar f n\gamma processes. A working example of the application for the
KORALZ version 4.04 is also provided.Comment: 1+5 pages (LaTeX
QED Bremsstrahlung in decays of electroweak bosons
Isolated lepton momenta, in particular their directions are the most
precisely measured quantities in pp collisions at LHC. This offers
opportunities for multitude of precision measurements. It is of practical
importance to verify if precision measurements with lep- tons in the final
state require all theoretical effects evaluated simultaneously or if QED
bremsstrahlung in the final state can be separated without unwanted precision
loss. Results for final state bremsstrahlung in the decays of narrow resonances
are obtained from the Feynman rules of QED in an unambiguous way and can be
controlled with a very high precision. Also for resonances of non-negligible
width, if calculations are appropriately performed, such separation from the
remaining electroweak effects can be expected. Our paper is devoted to
validation that final state QED bremsstrahlung can indeed be separated from the
rest of QCD and electroweak effects, in the production and decay of Z and W
bosons, and to estimation of the resulting systematic error. The quantitative
discussion is based on Monte Carlo programs PHOTOS and SANC, as well as on KKMC
which is used for benchmark results. We show, that for a large classes of W and
Z boson observables as used at LHC, theoretical error on photonic
bremsstrahlung is 0.1 or 0.2%, depending on the program options used. An
overall theoretical error on QED final state radiation, i.e. taking into
account missing corrections due to pair emission and interference with initial
state radiation is estimated respectively at 0.2% or 0.3% again depending on
the program option used.Comment: 1+28 pages, 20 figure
Extra lepton pair emission corrections to Drell-Yan processes in PHOTOS and SANC
In the paper we present results for final state emissions of lepton pairs in
decays of heavy intermediate states such as Z boson. Short presentations of
PHOTOS and SANC algorithms and physics assumptions are given. Numerical
distributions of relevance for LHC observables are shown. They are used in
discussions of systematic errors in the predictions of pair emissions as
implemented in the two programs. Suggestions for the future works are given.
Present results confirm, that for the precision of 0.3% level, in simulation of
final state the pair emissions can be avoided. For the precision of 0.1-0.2%,
the results obtained with the presented programs should be enough. To cross
precision tag of 0.1%, the further work is however required.Comment: 21 pages, 12 figure
Comparison of SANC with KORALZ and PHOTOS
Using the SANC system we study the one-loop electroweak standard model
prediction, including virtual and real photon emissions, for the decays of
on-shell vector and scalar bosons B --> f anti-f (gamma), where B is a vector
boson, Z or W, or a Standard Model Higgs. The complete one-loop corrections and
exact photon emission matrix element are taken into account. For the
phase-space integration, the Monte Carlo technique is used. For Z decay the QED
part of the calculation is first cross-checked with the exact one-loop QED
prediction of KORALZ. For Higgs boson and W decays, a comparison is made with
the approximate QED calculation of PHOTOS Monte Carlo. This provides a useful
element for the evaluation of the theoretical uncertainty of PHOTOS, very
interesting for its application in ongoing LEP2 and future LC and LHC
phenomenology.Comment: Submitted to Acta Physica Polonica. 9 pages, 6 figure
Electron-positron, parton-parton and photon-photon production of -lepton pairs: anomalous magnetic and electric dipole moments spin effects
Anomalous contributions to the electric and magnetic dipole moments of the
lepton from new physics scenarios have brought renewed interest in the
development of new charge-parity violating signatures in pair production
at Belle II energies, and also at higher energies of the Large Hadron Collider
and the Future Circular Collider. In this paper, we discuss the effects of spin
correlations, including transverse degrees of freedom, in the pair
production and decay. These studies include calculating analytical formulas,
obtaining numerical results, and building semi-realistic observables sensitive
to the transverse spin correlations induced by the dipole moments of the
lepton.
The effects of such anomalous contributions to the dipole moments are
introduced on top of precision simulations of ,
and processes,
involving multi-body final states. Respective extensions of the Standard Model
amplitudes and the reweighting algorithms are implemented into the {\tt KKMC}
Monte Carlo, which is used to simulate pair production in
collisions, and the {\tt TauSpinner} program, which is used to reweight events
with pair produced in collisions.Comment: 28 pages, 5 figure
Tau and muon pair production cross-sections in electron-positron annihilations at sqrt{s} = 10.58 GeV
The calculational precision of \ee\to\tautau and \ee\to\mumu production
cross-sections in electron-positron annihilations at \roots = 10.58 \gev are
studied for the \kk Monte Carlo simulation program. We determine
\sigma(\ee\to\tautau) = (0.919 \pm 0.003) \nb and \sigma(\ee\to\mumu) =
(1.147 \pm 0.005) \nb, where the error represents the precision of the
calculation.Comment: 7 pages, 3 tables, 1 figure (published in Physical Review D 77,
054012 (2008)
MiR-181a: a potential biomarker of acute muscle wasting following elective high-risk cardiothoracic surgery
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