Page MenuHomeHEPForge
Files F19251396

Tauola_README.txt
No OneTemporary
Actions

Size
5 KB
Referenced Files
None
Subscribers
None

Tauola_README.txt
View Options

The TAUOLA external event generator can be used to decay tau particles.
The syntax for decay.dec files is
Decay tau-
<BF> TAUOLA <modeInt>;
Enddecay
where <BF> is the relative branching fraction (0 to 1) and modeInt is the
integer value specifying what TAUOLA decay is to be generated.
Note that the daughter particle types of the mode are not specified within
the "Decay" command - the mode integer will generate the correct daughters for you.
Alised tau particles can use the TAUOLA model, but the generated daughters cannot
be aliased particles; there is no simple way to ensure that the order of any
daughter particle definitions will match the order of the particles generated by
TAUOLA, especially for the modes with many pions in the final state.
Allowed TAUOLA decay mode integers are (from the TAUOLA documentation):
0 All TAUOLA modes (1 to 22 below)
1 tau- -> e- anti-nu_e nu_tau
2 tau- -> mu- anti-nu_mu nu_tau
3 tau- -> pi- nu_tau
4 tau- -> rho- nu_tau
5 tau- -> a_1- nu_tau
6 tau- -> K- nu_tau
7 tau- -> K*- nu_tau
8 tau- -> 2pi- pi+ pi0 nu_tau
9 tau- -> 3pi0 pi- nu_tau
10 tau- -> 2pi- pi+ 2pi0 nu_tau
11 tau- -> 3pi- 2pi+ nu_tau
12 tau- -> 3pi- 2pi+ pi0 nu_tau
13 tau- -> 2pi- pi+ 3pi0 nu_tau
14 tau- -> K- K+ pi- nu_tau
15 tau- -> K0 anti-K0 pi- nu_tau
16 tau- -> K- anti-K0 pi0 nu_tau
17 tau- -> 2pi0 K- nu_tau
18 tau- -> pi- pi+ K- nu_tau
19 tau- -> pi- pi0 K0 nu_tau
20 tau- -> eta pi- pi0 nu_tau
21 tau- -> pi- pi0 gamma nu_tau
22 tau- -> K- K0 nu_tau
For example, to generate tau- -> 3pi0 pi- nu_tau (40%) and
tau- -> mu- anti-nu_mu nu_tau (60%), use
Decay Mytau-
0.4 TAUOLA 9;
0.6 TAUOLA 2;
Enddecay
CDecay Mytau+
To ensure decay mode consistency, any tau particle decay definition (normal or alised)
using TAUOLA should use it for all sub-modes, i.e do not mix TAUOLA and other
decay models, such as phase space (PHSP), within the same "Decay" definition.
An example which is NOT allowed is:
Decay Mytau+
0.4 TAUOLA 9;
0.5 TAUOLA 2;
0.1 e+ nu_e anti-nu_tau PHSP; # Decay model is not TAUOLA.
Enddecay
If this is detected, the program will stop and ask you to correct the decay definition(s).
The reason for this limitation is due to the fact that TAUOLA decays any tau particles
by considering the kinematics of its parent particle and the rest of the daughters, one of
which is the tau particle itself and other tau particles (charged or neutrino) that
are there in order to conserve tau lepton number. We let TAUOLA decay _all_ tau particle
types within the decay tree. EvtGen is then prevented from decaying the other tau
particle(s), since TAUOLA has already done that. If other physics models are used for the
other tau particle(s), then the correlated decay kinematics generated by TAUOLA will be
lost, leading to unphysical results.
If a particle decay contains at least two tau particles, and one of these uses TAUOLA
decay modes, then all other tau particles should use the same TAUOLA decay definitions to
ensure consistency:
Alias MyB0 B0
Alias Myanti-B0 anti-B0
ChargeConj Myanti-B0 MyB0
Alias Mytau+ tau+
Alias Mytau- tau-
ChargeConj Mytau- Mytau+
Decay MyB0
1.0 Mytau+ Mytau- PHSP;
Enddecay
CDecay Myanti-B0
Decay Mytau+
0.4 TAUOLA 9;
0.6 TAUOLA 2;
Enddecay
CDecay Mytau-
You should not define two or more (via aliases) tau decays with different TAUOLA
sub-mode branching fractions. Also tau- and tau+ particles must have the same decay
modes/branching fractions. These limitions are due to the fact that the core code
of TAUOLA is FORTRAN, and changing the TAUOLA mode parameters for one tau particle will
affect it for all other tau particles as well. So, EvtGen will only initialise
TAUOLA modes when it counters the first tau-type particle in the "evt.pdl" file that
has a TAUOLA decay mode defined for it. So, for example, if TAUOLA decays are
defined for "tau-", which corresponds to the first tau particle in the evt.pdl file, then
other TAUOLA decay definitions will be ignored, and the modes defined for tau- will also
be used for tau+ etc.. It is important to make sure the decay file uses the TAUOLA
mode definitions correctly to ensure consistency in decay tree results/information:
1) Decide what tau modes you want from TAUOLA.
2) Define the allowed decay modes for the tau- and tau+ particle, using only TAUOLA modes.
It is possible to keep the decay.dec generic (non-TAUOLA) decay modes for tau- and tau+, and
create aliased tau ("signal") particles such as Mytau- and Mytau+ to only use TAUOLA modes:
Alias Mytau- tau-
Alias Mytau+ tau+
ChargeConj Mytau+ Mytau-
Decay Mytau-
0.4 TAUOLA 9;
0.6 TAUOLA 2;
Enddecay
CDecay Mytau+
3) Make sure the TAUOLA modes for tau+ match those for tau- (easily done by using "CDecay").
4) Do not create other (alised) tau particles using TAUOLA modes. These settings will be ignored.
The PHOTOS generator can be used with the TAUOLA code, although the only way at present to
have this enabled is to set the "yesPhotos" global option in the decay.dec file. This means
that PHOTOS will be turned on for ALL decays. More work is needed to change the decay table
reading code (EvtGenBase/EvtDecayTable) to enable/disable PHOTOS for TAUOLA decays only.

File Metadata

Mime Type
text/plain
Expires
Tue, Sep 30, 5:51 AM (1 d, 13 h)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
6253771
Default Alt Text
Tauola_README.txt (5 KB)

Event Timeline

HEPForge.org · .