11 Detector Simulation
497
The most common particles produced by hadronic interactions are nucleons,
pions and kaons. The diversity of particles and interactions make modeling a
great challenge. Specialised codes including HETC [61], GHEISHA, CALOR [18],
FLUKA, and SHIELD [62] were developed for HEP and other application areas
in the 1970s and 1980s. Few models and codes from other application domains
have been available which cover a substantial part of the energy range (above
the 1–2 GeV used in spallation applications) and the full set of particles needed
for HEP. One exception is the MCNPX tool, an extension of the MCNP code
for neutron/gamma radiation transport and reactor simulation. MCNPX hadronic
models are shared with MARS.
Interactions are divided into elastic and inelastic, which produce new particles in
the final state. The smaller cross-sections for inelastic interactions of hadrons with
nucleons compared to EM interactions, and the growing multiplicity and variety of
particles emitted in interactions above a few GeV, result in significantly different
structure for hadronic showers.
The modeling approach depends on several factors: the availability of detailed
experimental measurements; the complexity of final states of reactions for a
particular combination of incident particle, energy and target; and the availability
and suitability of theoretical or phenomenological descriptions. In many application
domains there is a requirement for conservation of energy, momentum and quantum
number in each interaction, and for the coincidence or correlation between the
products of an interaction; in selected cases conservation of energy only as an
average over different interactions may suffice. A small number of interaction
models, including GHEISHA, and most low-energy neutron interactions sampling
methods treat particle interactions only in the average, and do not conserve energy
and momentum.
For many applications full energy conservation of individual interactions and
the treatment of the correlations of particle tracks is required in order to obtain
reliable results. For example, the estimation of the energy resolution of hadronic
calorimeters is strongly affected by these factors.
In many cases a phenomenological model is supplemented by fits of model
parameters with available data. In a few cases (evaluated) data libraries are
used directly—typically for low-energy neutron transport. Another approach is to
use parameterizations, either directly of data or indirectly for the parameters of
simplified models, as in GHEISHA.
11.3.7 Models of Interactions at Low Energies
At the lowest energies, the largest hadronic cross section belongs to the elastic
interaction, which is a coherent interaction of a hadron projectile with the full
nucleus. Hadronic cross sections, including those for elastic scattering, are typically
parameterized from data.
497
The most common particles produced by hadronic interactions are nucleons,
pions and kaons. The diversity of particles and interactions make modeling a
great challenge. Specialised codes including HETC [61], GHEISHA, CALOR [18],
FLUKA, and SHIELD [62] were developed for HEP and other application areas
in the 1970s and 1980s. Few models and codes from other application domains
have been available which cover a substantial part of the energy range (above
the 1–2 GeV used in spallation applications) and the full set of particles needed
for HEP. One exception is the MCNPX tool, an extension of the MCNP code
for neutron/gamma radiation transport and reactor simulation. MCNPX hadronic
models are shared with MARS.
Interactions are divided into elastic and inelastic, which produce new particles in
the final state. The smaller cross-sections for inelastic interactions of hadrons with
nucleons compared to EM interactions, and the growing multiplicity and variety of
particles emitted in interactions above a few GeV, result in significantly different
structure for hadronic showers.
The modeling approach depends on several factors: the availability of detailed
experimental measurements; the complexity of final states of reactions for a
particular combination of incident particle, energy and target; and the availability
and suitability of theoretical or phenomenological descriptions. In many application
domains there is a requirement for conservation of energy, momentum and quantum
number in each interaction, and for the coincidence or correlation between the
products of an interaction; in selected cases conservation of energy only as an
average over different interactions may suffice. A small number of interaction
models, including GHEISHA, and most low-energy neutron interactions sampling
methods treat particle interactions only in the average, and do not conserve energy
and momentum.
For many applications full energy conservation of individual interactions and
the treatment of the correlations of particle tracks is required in order to obtain
reliable results. For example, the estimation of the energy resolution of hadronic
calorimeters is strongly affected by these factors.
In many cases a phenomenological model is supplemented by fits of model
parameters with available data. In a few cases (evaluated) data libraries are
used directly—typically for low-energy neutron transport. Another approach is to
use parameterizations, either directly of data or indirectly for the parameters of
simplified models, as in GHEISHA.
11.3.7 Models of Interactions at Low Energies
At the lowest energies, the largest hadronic cross section belongs to the elastic
interaction, which is a coherent interaction of a hadron projectile with the full
nucleus. Hadronic cross sections, including those for elastic scattering, are typically
parameterized from data.