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Tauola_README.md
- This file was moved from Tauola_README.txt.
# Tauola README | |||||
The TAUOLA external event generator can be used to decay tau particles. | The TAUOLA external event generator can be used to decay tau particles. | ||||
The syntax for decay.dec files is | The syntax for decay.dec files is | ||||
``` | |||||
Decay tau- | Decay tau- | ||||
<BF> TAUOLA <modeInt>; | <BF> TAUOLA <modeInt>; | ||||
Enddecay | Enddecay | ||||
``` | |||||
where <BF> is the relative branching fraction (0 to 1) and modeInt is the | where `<BF>` is the relative branching fraction (0 to 1) and `modeInt` is the | ||||
integer value specifying what TAUOLA decay is to be generated. | integer value specifying what TAUOLA decay is to be generated. | ||||
Note that the daughter particle types of the mode are not specified within | 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. | 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 | 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 | 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 | daughter particle definitions will match the order of the particles generated by | ||||
TAUOLA, especially for the modes with many pions in the final state. | TAUOLA, especially for the modes with many pions in the final state. | ||||
Show All 20 Lines | |||||
18 tau- -> pi- pi+ K- nu_tau | 18 tau- -> pi- pi+ K- nu_tau | ||||
19 tau- -> pi- pi0 K0 nu_tau | 19 tau- -> pi- pi0 K0 nu_tau | ||||
20 tau- -> eta pi- pi0 nu_tau | 20 tau- -> eta pi- pi0 nu_tau | ||||
21 tau- -> pi- pi0 gamma nu_tau | 21 tau- -> pi- pi0 gamma nu_tau | ||||
22 tau- -> K- K0 nu_tau | 22 tau- -> K- K0 nu_tau | ||||
For example, to generate tau- -> 3pi0 pi- nu_tau (40%) and | For example, to generate tau- -> 3pi0 pi- nu_tau (40%) and | ||||
tau- -> mu- anti-nu_mu nu_tau (60%), use | tau- -> mu- anti-nu_mu nu_tau (60%), use | ||||
``` | |||||
Decay Mytau- | Decay Mytau- | ||||
0.4 TAUOLA 9; | 0.4 TAUOLA 9; | ||||
0.6 TAUOLA 2; | 0.6 TAUOLA 2; | ||||
Enddecay | Enddecay | ||||
CDecay Mytau+ | CDecay Mytau+ | ||||
``` | |||||
To ensure decay mode consistency, any tau particle decay definition (normal or alised) | 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 | 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. | decay models, such as phase space (PHSP), within the same "Decay" definition. | ||||
An example which is NOT allowed is: | An example which is NOT allowed is: | ||||
``` | |||||
Decay Mytau+ | Decay Mytau+ | ||||
0.4 TAUOLA 9; | 0.4 TAUOLA 9; | ||||
0.5 TAUOLA 2; | 0.5 TAUOLA 2; | ||||
0.1 e+ nu_e anti-nu_tau PHSP; # Decay model is not TAUOLA. | 0.1 e+ nu_e anti-nu_tau PHSP; # Decay model is not TAUOLA. | ||||
Enddecay | Enddecay | ||||
``` | |||||
If this is detected, the program will stop and ask you to correct the decay definition(s). | 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 | 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 | 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 | 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 | 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 | 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 | 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 | other tau particle(s), then the correlated decay kinematics generated by TAUOLA will be | ||||
lost, leading to unphysical results. | lost, leading to unphysical results. | ||||
If a particle decay contains at least two tau particles, and one of these uses TAUOLA | 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 | decay modes, then all other tau particles should use the same TAUOLA decay definitions to | ||||
ensure consistency: | ensure consistency: | ||||
``` | |||||
Alias MyB0 B0 | Alias MyB0 B0 | ||||
Alias Myanti-B0 anti-B0 | Alias Myanti-B0 anti-B0 | ||||
ChargeConj Myanti-B0 MyB0 | ChargeConj Myanti-B0 MyB0 | ||||
Alias Mytau+ tau+ | Alias Mytau+ tau+ | ||||
Alias Mytau- tau- | Alias Mytau- tau- | ||||
ChargeConj Mytau- Mytau+ | ChargeConj Mytau- Mytau+ | ||||
Decay MyB0 | Decay MyB0 | ||||
1.0 Mytau+ Mytau- PHSP; | 1.0 Mytau+ Mytau- PHSP; | ||||
Enddecay | Enddecay | ||||
CDecay Myanti-B0 | CDecay Myanti-B0 | ||||
Decay Mytau+ | Decay Mytau+ | ||||
0.4 TAUOLA 9; | 0.4 TAUOLA 9; | ||||
0.6 TAUOLA 2; | 0.6 TAUOLA 2; | ||||
Enddecay | Enddecay | ||||
CDecay Mytau- | CDecay Mytau- | ||||
``` | |||||
You should not define two or more (via aliases) tau decays with different TAUOLA | 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 | 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 | 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 | 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 | 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 | 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 | 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 | 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 | 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 | 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: | mode definitions correctly to ensure consistency in decay tree results/information: | ||||
1) Decide what tau modes you want from TAUOLA. | 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. | 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 | 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: | create aliased tau ("signal") particles such as Mytau- and Mytau+ to only use TAUOLA modes: | ||||
``` | |||||
Alias Mytau- tau- | Alias Mytau- tau- | ||||
Alias Mytau+ tau+ | Alias Mytau+ tau+ | ||||
ChargeConj Mytau+ Mytau- | ChargeConj Mytau+ Mytau- | ||||
Decay Mytau- | Decay Mytau- | ||||
0.4 TAUOLA 9; | 0.4 TAUOLA 9; | ||||
0.6 TAUOLA 2; | 0.6 TAUOLA 2; | ||||
Enddecay | Enddecay | ||||
CDecay Mytau+ | CDecay Mytau+ | ||||
``` | |||||
3) Make sure the TAUOLA modes for tau+ match those for tau- (easily done by using "CDecay"). | 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. | 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 | 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 | 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 | 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. | reading code (EvtGenBase/EvtDecayTable) to enable/disable PHOTOS for TAUOLA decays only. |