47 research outputs found
Status report on TAUOLA, its environment, and its applications
The status of the Monte Carlo programs for the simulation of the tau-lepton
production and decay in high energy accelerator experiments is reviewed. In
particular, the status of the following packages is discussed: (i) TAUOLA for
tau-lepton decay and PHOTOS for radiative corrections in decays, (ii) MC-TESTER
for universal tests of the Monte Carlo programs describing particle decays,
(iii) KORALB, KORALZ, KKMC packages for tau-pair production in e+e- collisions,
and (iv) universal interface of TAUOLA for the decay of tau-leptons produced by
``any'' generator.Comment: Talk at the Seventh International Workshop on Tau Lepton Physics
(TAU02), Santa Cruz, Ca, USA, Sept 2002, 5 pages, LaTeX, 4 eps/ps figure
Production of \uptau τ lepton pairs with high p T jets at the LHC and the TauSpinner reweighting algorithm
The TauSpinner algorithm allows to modify the physics of the Monte Carlo
generated samples due to the changed assumptions of event production dynamics,
without re-generating events. To each event it attributes weights: the spin
effects of tau-lepton production or decay, or the production mechanism are
modified. There is no need to repeat the detector response simulation. We
document the extension to 2 to 4 processes in which the matrix elements for the
parton-parton scattering amplitudes into a tau-lepton pair and two outgoing
partons are used. Tree-level matrix elements for the Standard Model processes,
including the Higgs boson production are used. Automatically generated codes by
MadGraph5 have been adapted. Tests of the matrix elements, reweighting
algorithm and numerical results are presented. For averaged tau lepton
polarisation, we perform comparison of 2 to 2 and 2 to 4 matrix elements used
to calculate the spin weight in pp to tau tau j j events. We show, that for
events with tau-lepton pair close to the Z-boson peak, the tau-lepton
polarisation calculated using 2 to 4 matrix elements is very close to the one
calculated using 2 to 2 Born process only. For the m_(tautau) masses above the
Z-boson peak, the effect from including 2 to 4 matrix elements is also
marginal, however when restricting into subprocesses qq,q bar q to tau tau j j
only, it can lead to a 10% difference on the predicted tau-lepton polarisation.
Choice of electroweak scheme can have significant impact. The modification of
the electroweak or strong interaction can be performed with the re-weighting
technique. TauSpinner v.2.0.0, allows to introduce non-standard couplings for
the Higgs boson and study their effects in the vector-boson-fusion. The
discussion is relegated to forthcoming publications.Comment: 33 pages 7 figure
Coherent Exclusive Exponentiation CEEX: the Case of the Resonant e+ e- Collision
We present the first-order coherent exclusive exponentiation (CEEX) scheme,
with the full control over spin polarization for all fermions. In particular it
is applicable to difficult case of narrow resonances. The resulting spin
amplitudes and the differential distributions are given in a form ready for
their implementation in the Monte Carlo event generator. The initial-final
state interferences are under control. The way is open to the use of the exact
amplitudes for two and more hard photons, using Weyl-spinor techniques, without
giving up the advantages of the exclusive exponentiation, of the
Yennie-Frautschi-Suura type.Comment: 14 page
Initial-Final-State Interference in the Z line-shape
The uncertainty in the determination of the Z line-shape parameters coming
from the precision of the calculation of the Initial-State Radiation and
Initial--Final-State Interference is 2 10**(-4) for the total cross section
sigma zero(had) at the Z peak, 0.15 MeV for the Z mass M Z, and 0.1 MeV for the
Z width Gamma Z. Corrections to Initial--Final-State Interference beyond
\Order{\alpha^1} are discussed.Comment: 10 pages LaTeX including 2 PostScript figure
Probing the CP nature of the Higgs boson at linear colliders with tau spin correlations; the case of mixed scalar--pseudoscalar couplings
The prospects for the measurement of the pseudoscalar admixture in the
h-tau-tau coupling to a Standard Model Higgs boson of 120 GeV mass are
discussed in a quantitative manner e+ e- collisions of 350 GeV centre-of-mass
energy. Specific angular distributions in the h --> tau tau; tau --> rho nu
decay chain can be used to probe mixing angles of scalar--pseudoscalar
h-tau-tau couplings. In the discussion of the feasibility of the method,
assumptions on the properties of a future detector for an e+ e- linear collider
such as TESLA are used. The Standard Model Higgsstrahlung production process is
taken as an example. For the expected performance of a typical Linear Collider
set-up, the sensitivity of a measurement of the scalar--pseudoscalar mixing
angle turned out to be 6 degree. It will be straightforward to apply our
results to estimate the sensitivity of a measurement, in cases another scenario
of the Higgs boson sector (Standard Model or not) is chosen by nature. The
experimental error of the method is expected to be limited by the statistics.Comment: 10 pages, 7 figures, LaTeX. Corrections of published version include
News on PHOTOS Monte Carlo: gamma^* -> pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma)
PHOTOS Monte Carlo is widely used for simulating QED effects in decay of
intermediate particles and resonances. It can be easily connected to other main
process generators. In this paper we consider decaying processes gamma^* ->
pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma) in the framework of
Scalar QED. These two processes are interesting not only for the technical
aspect of PHOTOS Monte Carlo, but also for precision measurement of
alpha_{QED}(M_Z), g-2, as well as pi pi scattering lengths.Comment: 6 pages, 11 figures, proceedings of the PhiPsi09, Oct. 13-16, 2009,
Beijing, Chin
Why do we need higher order fully exclusive Monte Carlo generator for Higgs boson production from heavy quark fusion at LHC?
In this paper we argue that having available higher order fully exclusive
Monte Carlo generator for Higgs boson production from heavy quark fusion will
be mandatory for data analysis at LHC. The H to tau tau channel, a key for
early discovery of the Higgs boson in the MSSM scenario, is discussed. With
simplified example and for mH = 120 GeV we show, that depending on choice among
presently available approaches, used for simulation of Higgs boson production
from b bbar H Yukawa coupling, final acceptance for the signal events being
reconstructed inside mass window may differ by a factor of 3. The spread is
even larger (up to a factor of 10) for other production mechanisms (promising
for some regions of the MSSM parameter space). The complete analysis, which
necessarily will add stringent requirements for background rejection (such as
identification of b-jet or veto on b-jet) and which will require statistical
combination of samples selected with different selection criteria may only
enhance the uncertainty.Comment: 14 pages, 22 figure
MC-TESTER: 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. Our test consists of two steps. Different
Monte Carlo programs are run; events with decays of a chosen particle are
searched, decay trees are analysed and appropriate information is stored. Then,
at the analysis step, a list of all found decay modes is defined and branching
ratios are calculated for both runs. Histograms of all scalar Lorentz-invariant
masses constructed from the decay products are plotted and compared for each
decay mode found in both runs. For each plot a measure of the difference of the
distributions is calculated and its maximal value over all histograms for each
decay channel is printed in a summary table. As an example of MC-TESTER
application, we include a test with the tau lepton decay Monte Carlo
generators, TAUOLA and PYTHIA. The HEPEVT (or LUJETS) common block is used as
exclusive source of information on the generated events.Comment: Version as published in Computer Physics Communications, 157(2004) 1,
pp 39-6
Measuring the Higgs boson's parity using tau --> rho nu
We present a very promising method for a measurement of the Higgs boson
parity using the H/A -> tau^+ tau^- --> rho^+ nu rho^- nu --> pi^+ pi^0 nu pi^-
pi^0 nu decay chain. The method is both model independent and independent of
the Higgs production mechanism. Angular distributions of the tau decay products
which are sensitive to the Higgs boson parity are defined and are found to be
measurable using typical properties of a future detector for an e^+ e^- linear
collider. The prospects for the measurement of the parity of a Higgs boson with
a mass of 120 GeV are quantified for the case of e^+ e^- collisons of 500 GeV
center of mass energy with an integrated luminosity of 500 fb^-1. The Standard
Model Higgsstrahlung production process is used as an example.Comment: 10 pages, 4 figures, LaTeX, version of Phys. Lett.
Coherent Exclusive Exponentiation for Precision Monte Carlo Calculations
In this contribution we give a short overview of the new Coherent Exclusive
Exponentiation (CEEX) which is implemented in the new \KK MC event generator
for the process , with
validity for center of mass energies from lepton threshold to 1TeV, that
is for LEP1, LEP2, SLC, future Linear Colliders, -factories etc. In
CEEX effects due to photon emission from initial beams and outgoing fermions
are calculated in QED up to second-order, including all interference effects.
Electroweak corrections are included in first-order, at the amplitude level.
Beams can be polarized longitudinally and transversely, and all spin
correlations are incorporated in an exact manner. We describe briefly the
essence of CEEX as compared with older exclusive variants of the exponentiation
(EEX) and present samples of the numerical results, concentrating on the
question of the technical and physical precision for the total cross section
and for the charge asymmetry. New results on the interference between initial
and final state photon emission at LEP2 energies are also shown.Comment: new paper, not replacement for hep-ph/000635