channeling/ch2/README.md

0001 \page Examplech2 Example ch2
0002
0003 \author Alexei Sytov, Gianfranco Paternò - INFN Ferrara Division (Italy) \n
0004  sytov@fe.infn.it, paterno@fe.infn.it
0005
0006 ## INTRODUCTION
0007 Example ch2 is an enhanced version of ch1, providing the user with the full functionality of
0008 both the G4ChannelingFastSimModel and G4BaierKatkov, with parameters set up via a macro,
0009 in order to simulate the physics of channeling and channeling radiation/coherent bremsstrahlung.
0010
0011 The example can be exploited for a wide range of cases to study coherent effects in
0012 a straight, bent or periodically bent crystal (crystalline undulator). Channeling
0013 physics in ch2 is active for protons, ions, muons, pions, electrons and their antiparticles.
0014 Any other charged particle can also be activated.
0015
0016 The example contains also other setups for specific applications.
0017
0018 ## DESCRIPTION
0019 The setup of the example ch2 in run.mac is identical to ch1. As ch1, this example includes a bent crystal
0020 and a detector positioned behind it. Like ch1, it is based on the experiments on
0021 channeling [1] and channeling radiation [2] in a bent crystal, carried out at
0022 Mainz Mikrotron MAMI with 855 MeV electrons. The experimental validation of
0023 G4ChannelingFastSimModel is described in [3].
0024
0025 However, since ch2 parameters are fully set up in the macro run.mac, this example
0026 is quite flexible and can be easily adapted for entirely different cases.
0027
0028 In addition more specific macros were created to supply users with the setups related to the applications.
0029 These macros partially exploit the model defaults to simplify the example. They include:
0030 -# run_Bent_Crystal_Deflection_Radiation.mac - reduced version (some commands setting defaults deleted) of run.mac but with an identical setup.
0031 -# run_Bent_Crystal_HE_Deflection.mac - an example of particle deflection in a bent crystal at high energies.
0032 -# run_Positron_Source.mac - a simplified example of a positron source within a single W target.
0033 -# run_Radiation.mac - an example of a radiation source in a straight crystal.
0034
0035 A description of all the available options is provided in run.mac and partially in other macros.
0036 It includes crystal and detector geometry, activation flags for
0037 G4ChannelingFastSimModel and G4BaierKatkov and various options.
0038
0039 The example also provides detailed descriptions of various options for
0040 G4ChannelingFastSimModel and G4BaierKatkov, which can adjust model parameters
0041 depending on the specific case (see DetectorConstruction::ConstructSDandField()).
0042
0043 The front surface of the crystal is placed at z=0 (with z as the beam direction),
0044 while the front position of the detector can be set up via run.mac.
0045
0046 The output is recorded into the file results.root as a set of root ntuples.
0047 These ntuples include:
0048 -# crystal: particles recorded at the crystal entrance,
0049 -# detector_primaries: primaries recorded at the detector entrance AND passed through the crystal.
0050 -# detector_photons: photons recorded at the detector entrance produced by primaries passed through the crystal.
0051 -# detector_sedondaries: secondaries recorded at the detector entrance produced by primaries passed through the crystal.
0052 -# missed_crystal: all the particles missed the crystal, however, entering the detector, if any.
0053
0054 The format of every ntuple includes the following 10 variables (columns):
0055
0056 - "eventID", "volume", "x", "y", "angle_x", "angle_y", "Ekin", "particle", "particleID", "parentID"
0057
0058 The variables represent:
0059 -# the event number within the run (column 0),
0060 -# the volume, either the crystal or the detector (column 1),
0061 -# the coordinate (x,y) and the angles (x'=dx/dz, y'=dy/dz) of the impinging particles (columns 2-6),
0062 -# the kinetic energy of the particle (column 7),
0063 -# the particle name (column 8),
0064 -# the particle ID (column 9),
0065 -# the parent ID of the particle (column 10).
0066
0067 For convenience for detector_primaries were added four more variables:
0068 -# the incoming angle x at the crystal entrance,
0069 -# the deflection angle x (the difference between the angle at the detector and the incoming angle),
0070 -# the incoming angle y at the crystal entrance,
0071 -# the deflection angle y (the difference between the angle at the detector and the incoming angle).
0072
0073 These four variables are especially useful for the studies of deflection of primary particles.
0074
0075 To visualize these data, one should either open results.root using root TBrowser or use the python script analysis_ch2.py or its identical version in the jupyter notebook format analysis_ch2.ipynb.
0076
0077 The output data also includes the spectrum of photons using the data produced inside the Baier-Katkov method.
0078 This spectrum requires nearly 2 order on magnitude less data, then the collection of gamma produced in Geant4 as secondaries.
0079 It is very useful especially if the goal is to produce only the spectrum of radiation. This spectrum is normalized on the
0080 total radiation emission probability, which is an equivalent to 1/Nprimaries dN_photon/dE_photon normalization.
0081
0082 Moreover, it is possible to set up a round virtual collimator - an angular selection of photons in the Baier-Katkov method.
0083 This is extremely useful for coherent bremsstrahlung simulation.
0084
0085 CAUTION: though the Baier-Katkov spectrum should identically coincide with the spectrum by secondary photons, sometimes
0086 it may be less accurate, since it is updated only after every setNSmallTrajectorySteps (see run.mac). Moreover,
0087 the virtual collimator does not take into account the transverse positions of particles. Therefore, it is recommended
0088 to use the Baier-Katkov spectrum at low statistics for preliminary researches and optimization while the secondaries produced at
0089 high statistics as a final result.
0090
0091 CAUTION: the angular center of virtual collimator coincides with the global z direction.
0092
0093 The spectrum is produced as a text file, containing the photon energies in the first column and the corresponding spectrum value in the second one.
0094 Note, the bins are not equidistant, they are sampled according to the bremsstrahlung spectrum, with the bin size proportional to 1/E_photon.
0095
0096 ## REFERENCES
0097
0098 -# A. Mazzolari et al. <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.135503">Phys. Rev. Lett. 112, 135503 (2014).</a>
0099 -# L. Bandiera et al. <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.025504">Phys. Rev. Lett. 115, 025504 (2015).</a>
0100 -# A. Sytov et al. <a href="https://link.springer.com/article/10.1007/s40042-023-00834-6"> Journal of the Korean Physical Society 83, 132–139 (2023).</a>