Simulations of physics processes occurring in the ATLAS detector is controlled by a number of process switches and physics cuts. The default values set by any atlas#config command corresponds to all Geant Physics processes On. The values of flags are:
DCAY, ANNI, BREM,
COMP, MUNU,
PAIR, PHOT,
PFIS, LOSS,
DRAY, MULS
equal to 1,
RAYL , STRA
equal to 0,
HADR equal to 6.
By default, all tracking cuts (cutgam cutele cuthad cutneu cutmuo ) are set to 100 KeV, while all production cuts ( bcute bcutm dcute dcutm ppcutm) are set to 1 MeV. Default value of tofmax is set to 100 microsec.
This combinations of processes and cuts can always be restored by executing atlas#physics_on macro. Additional parameres supplied with the macro command define new values of tracking cuts (tcut), production cuts (pcut) and choice of the hadronic package.
Another macro useful for debugging purpose or GEANE applications - atlas#physics_off – switches off all GEANT processes apart from decays and non-fluctuating energy losses.
If you are not completely satisfied with default settings for your simulation task, it is possible to change each particular process flag in order to obtain necessary configuration. After running a standard atlas#config macro and before the following gexec, you can input a command line:
process_name flag_value
These commands set the appropriate variable in the /GCKING/ common block as the described in the GEANT3 manual (see except below).
For example, if you use option physics_on and want to study multiple scattering effects, you can get a sample with no scattering at all by typing:
MULS 0
It is also possible to redefine process and cut selection on-flight, after geometry has already been built and even after some events has been simulated – just do not forget to issue gclose all command after you redefine some of the default values. These command forces atlsim to recalculate process cross-section according to your modifications.
Here we describe briefly the meaning of different process flags as they are
understood by GEANT. For more details see the GEANT3
manual .
As a general rule if the variable is set to
Every physical process can be defined using the different data cards available for it. The data record keywords, the flag names and values, and the resulting action are listed below:
Decay in flight. The decaying particle stops. The
variable IDCAY controls this process. See [CONS310, PHYS400].
0 - No decay in flight.
1 - Decay in flight with generation of secondaries. Default setting.
2 - Decay in flight without generation of secondaries.
Multiple scattering. The variable IMULS
controls this process. For more information see [PHYS320 or 325 or 328].
0 - No multiple scattering.
1 - Multiple scattering according to Molière theory. Default setting.
2 - Same as 1. Kept for backward compatibility.
3 - Pure Gaussian scattering according to the Rossi formula.
Nuclear fission induced by a photon. The photon stops.
The variable IPFIS controls this process. See [PHYS240].
0 - No photo-fission. Default setting.
1 - Photo-fission with generation of secondaries.
2 - Photo-fission without generation of secondaries.
Muon-nucleus interactions. The muon is not stopped. The
variable IMUNU controls this process. See [PHYS431] for
more details.
0 - No muon-nucleus interactions.
1 - Muon-nucleus interactions with generation of secondaries. Default
setting.
2 - Muon-nucleus interactions without generation of secondaries.
Continuous energy loss. The variable ILOSS
controls this process.
0 - No continuous energy loss, IDRAY is set to 0.
1 - Continuous energy loss with generation of delta rays above DCUTE
(common/GCUTS/) and restricted Landau fluctuations below DCUTE.
2 - Continuous energy loss without generation of delta rays and full
Landau-Vavilov-Gauss fluctuations. In this case the variable IDRAY
is forced to 0 to avoid double counting of fluctuations. Default setting.
3 - Same as 1, kept for backward compatibility.
4 - Energy loss without fluctuation. The value obtained from the tables
is used directly.
Photoelectric effect. The interacting photon is stopped.
The variable IPHOT controls this process. More info [PHYS230].
0 - No photo-electric effect.
1 - Photo-electric effect with generation of the electron. Default
setting.
2 - Photo-electric effect without generation of the electron.
Compton scattering. The variable ICOMP
controls this process. For additional information see [PHYS220].
0 - No Compton scattering.
1 - Compton scattering with generation of e-. Default
setting.
2 - Compton scattering without generation of e-.
Pair production. The interacting gamma is
stopped. The variable IPAIR controls this process. More info [PHYS210]
0 - No pair production.
1 - Pair production with generation of e-/e+. Default
setting.
2 - Pair production without generation of e-/e+.
Bremsstrahlung. The interacting particle e+,
e-, mu+, mu- is not stopped. The
variable IBREM controls this process. More details in [PHYS340].
0 - No bremsstrahlung.
1 - bremsstrahlung with generation of gamma. Default setting.
2 - bremsstrahlung without generation of gamma.
Rayleigh effect. The interacting gamma is not
stopped. The variable IRAYL controls this process. See [PHYS250] for
details.
0 - No Rayleigh effect. Default setting.
1 - Rayleigh effect.
delta ray production. The variable IDRAY
controls this process. See [PHYS430]
0 - No delta rays production.
1 - delta rays production with generation of . Default setting.
2 - delta rays production without generation of .
Positron annihilation. The e+ is
stopped. The variable IANNI controls this process. For reference see [PHYS350].
0 - No positron annihilation.
1 - Positron annihilation with generation of photons. Default setting.
2 - Positron annihilation without generation of photons.
Hadronic interactions. The particle is stopped in case
of inelastic interaction, while in case of elastic interaction it is not
stopped. To simulate the interactions of hadrons with the nuclei of the matter
traversed, four alternatives are provided:
1.The generator of the FLUKA hadron shower MonteCarlo and the
interface routines to GEANT. See [PHYS520] for
more information.
2.The generator of the GHEISHA hadron shower MonteCarlo and the
interface routines to GEANT. See [PHYS510] for
more details.
3.The generator of the MICAP hadron shower MonteCarlo and the
interface routines to GEANT.
4.The generator of the GCALOR hadron shower MonteCarlo and the
interface routines to GEANT.
The variable IHADR controls this process.
0 - No hadronic interactions.
1 - Hadronic interactions with generation of secondaries using GHEISHA
package.
2 – same as 1.
3 – same as 1.
4 - Hadronic interactions are simulated using FLUKA package.
5 - Hadronic interactions are simulated using MICAP package.
6 - Hadronic interactions are simulated using GCALOR package.
Light ABSorption. This process is an absorption of light
photons (particle type 7) in dielectric materials. It is turned on by default
when the generation of Cerenkov light is requested (data record CKOV).
For more information see [PHYS260].
This process controlled by ILABS.
0 - No absorption of photons.
1 - Absorption of photons with possible detection.
This flag turns on the collision sampling method to
simulate energy loss in thin materials, particularly gases. For more
information see [PHYS334].
The control variable is ISTRA .
0 - Collision sampling is switched off. Default setting.
1 - Collision sampling is activated.
Synchrotron radiation in magnetic field. Defined by
variable ISYNC. See [PHYS360].
0 - The synchrotron radiation is not simulated. Default setting.
1 - Synchrotron photons are generated, at the end of the tracking step.
2 - Photons are not generated, the energy is deposited locally.
3 - Synchrotron photons are generated, distributed along the curved path
of the particle.
Physics
cuts
Besides of physics settings described in the previous section, user can specify the value of each available physics cut by means of CUTS command. The usage of this command is:
CUTS [cutgam cutele cuthad cutneu cutmuo bcute bcutm dcute dcutm ppcutm tofmax gcuts]
If no parameter is given, the list of the current cuts is printed. The meanings of the parameters listed above are:
cutgam - "cut for gammas". The default GEANT
value is 0.001, ATLAS
default is 0.0001.
cutele - "cut for electrons". The
default GEANT value is 0.001, ATLAS default is 0.0001.
cuthad - "cut for charged hadrons". The default GEANT
value is 0.01, ATLAS default is
0.0001.
cutneu - "cut for neutral hadrons". The default GEANT
value is 0.01, ATLAS default is
0.0001.
cutmuo - "cut for muons". The default GEANT
value is 0.01, ATLAS default is
0.0001.
bcute - "cut for electron brems". The
default GEANT value is -1,
ATLAS default is 0.001.
bcutm - "cut for muon brems". The default GEANT
value is -1, ATLAS default is
0.001.
dcute - "cut for electron
delta-rays". The default GEANT value is -1, ATLAS default is 0.001.
dcutm - "cut for muon delta-rays". The
default GEANT value is -1,
ATLAS default is 0.001.
ppcutm- "cut for e+e- pairs by muons". The default GEANT
value is 0.01, ATLAS default is
0.002.
tofmax - "time of flight cut". The default GEANT
value is 1.E+10, ATLAS default
is 1.E-7.
gcuts - "5 user words". Default is 0.