Geant4 study of the sensitivity of GEM detectors to background particles

Additional plots on RPC sensitivity to background in RPC plots

Plots For Approval

Figure	Caption
	Energy deposited in the drift gap of a GEM chamber crossed by a neutron beam, as a function of the neutron incident energy. This plot proves that the electronic threshold on the induced charge collected by the strips, which corresponds to a cut in the deposited energy as high as ~ 200 eV , would exclude only a small fraction of the events. Indeed, the simulations provide a compatible value for the sensitivity of the detector even with no such threshold. The simulation was performed using GEANT4.10.00.p02 with physics list FTFP_BERT_HP.

Figure

Caption

Energy deposited in the drift gap of a GEM chamber crossed by a neutron beam, as a function of the neutron incident energy. This plot proves that the electronic threshold on the induced charge collected by the strips, which corresponds to a cut in the deposited energy as high as ~ 200 eV , would exclude only a small fraction of the events. Indeed, the simulations provide a compatible value for the sensitivity of the detector even with no such threshold. The simulation was performed using GEANT4.10.00.p02 with physics list FTFP_BERT_HP.

	Energy spectrum of neutrons impinging on the surface of the GE1/1 region. The spectrum was obtained using FOCUS v1.0.0.0. The plot shows that the expected neutron background is mainly made of particles in the energy range between 1 meV and 1 GeV. The number of entries in the plot is 6039.

GE11 neutron spectrum4 FOCUS V1.0.0.0.png

Energy spectrum of neutrons impinging on the surface of the GE1/1 region. The spectrum was obtained using FOCUS v1.0.0.0. The plot shows that the expected neutron background is mainly made of particles in the energy range between 1 meV and 1 GeV. The number of entries in the plot is 6039.

	Energy spectrum of photons impinging on the surface of the GE11 region. The spectrum was obtained using FOCUS v1.0.0.0.The plot shows that the expected photon background is mainly made of particles in the energy range between 0.1 MeV and 10 MeV. The number of entries in the plot is 3597.

GE11 photon spectrum4 FOCUS V1.0.0.0.png

Energy spectrum of photons impinging on the surface of the GE11 region. The spectrum was obtained using FOCUS v1.0.0.0.The plot shows that the expected photon background is mainly made of particles in the energy range between 0.1 MeV and 10 MeV. The number of entries in the plot is 3597.

	Energy spectrum of electrons and positrons impinging on the surface of the GE11 region. The spectrum was obtained using FOCUS v1.0.0.0. The plot shows that the expected electron and positron background is made of particles in the energy range between 0.1 MeV and 10 MeV. The number of entries in the plot is 64.

GE11 charged spectrum4 FOCUS V1.0.0.0.png

Energy spectrum of electrons and positrons impinging on the surface of the GE11 region. The spectrum was obtained using FOCUS v1.0.0.0. The plot shows that the expected electron and positron background is made of particles in the energy range between 0.1 MeV and 10 MeV. The number of entries in the plot is 64.

	In Geant4 different models (physics lists) are available for the simulation of particle interaction with matter. In this plot the behavior of two different Geant4 models (FTFP_BERT_HP and QBBC) is compared to experimental data taken from NIMA 506 (2003) 101. In this work a double gap RPC was exposed to a 252Cf source. Such a source underwent fission events with the emission of gammas and neutrons, which could reach the RPC detector after having passed through different kind of shielding and generate a signal in the detector. A Geant4 simulation was set up to reproduce the experimental setup described in the paper. The plot shows the sensitivity of the double gap RPC to the fission event as a function of the interaction length of shielding that the fission products had to pass through in order to reach the detector. Results obtained with the FTFP_BERT_HP physics list are closer to experimental data and therefore this model has been used for the simulations of the sensitivity of the GEM detectors to background particles. This Physics List is recommended by the Geat4 hadronic group, as it allows to track neutrons down to thermal energies. Geant4 range cuts are set as follows: photons 1 um, electrons 1 nm, positrons 1 um, protons and ions 0 mm. The latter setting is very distant from the default (1 mm), and it is crucial to correctly reproduce the nuclei recoil.

G4 physics list validation 252cftest3.png

In Geant4 different models (physics lists) are available for the simulation of particle interaction with matter. In this plot the behavior of two different Geant4 models (FTFP_BERT_HP and QBBC) is compared to experimental data taken from NIMA 506 (2003) 101. In this work a double gap RPC was exposed to a 252Cf source. Such a source underwent fission events with the emission of gammas and neutrons, which could reach the RPC detector after having passed through different kind of shielding and generate a signal in the detector. A Geant4 simulation was set up to reproduce the experimental setup described in the paper. The plot shows the sensitivity of the double gap RPC to the fission event as a function of the interaction length of shielding that the fission products had to pass through in order to reach the detector. Results obtained with the FTFP_BERT_HP physics list are closer to experimental data and therefore this model has been used for the simulations of the sensitivity of the GEM detectors to background particles. This Physics List is recommended by the Geat4 hadronic group, as it allows to track neutrons down to thermal energies. Geant4 range cuts are set as follows: photons 1 um, electrons 1 nm, positrons 1 um, protons and ions 0 mm. The latter setting is very distant from the default (1 mm), and it is crucial to correctly reproduce the nuclei recoil.

	Neutron interaction in a GEM chamber: When a neutron enters a GEM chamber, it can interact with the materials inside the detector, producing secondary particles which can reach the gas gaps and can give rise to a background signal. This histogram shows the frequency of processes that generate particles inside the drift and the first transfer gap of the chamber, as a function of the energy of the incident neutron. Processes are named using the Geant4 convention. For a neutron energy in the range between 10 meV and 1 keV the incident neutron interacts mainly via neutron capture on hydrogen and other heavier nuclei, with the emission of gamma rays that in turn undergo compton scattering and pair production (“conv”). The intermediate energy range is dominated by neutron elastic scattering on hydrogen nuclei. For neutron energy greater than a few MeV the dominant interaction processes are neutron induced nuclear reactions (“NeutronInelastic”), leading to the fragmentation of the target nucleus and the production of nuclear fragments. The neutron energy range considered for this simulation matches the one of the background photons in CMS cavern according to FOCUS simulations. The simulation was performed using GEANT4.9.6.p02 and the physics list FTFP_BERT_HP.

Neutron interaction in a GEM chamber: When a neutron enters a GEM chamber, it can interact with the materials inside the detector, producing secondary particles which can reach the gas gaps and can give rise to a background signal. This histogram shows the frequency of processes that generate particles inside the drift and the first transfer gap of the chamber, as a function of the energy of the incident neutron. Processes are named using the Geant4 convention. For a neutron energy in the range between 10 meV and 1 keV the incident neutron interacts mainly via neutron capture on hydrogen and other heavier nuclei, with the emission of gamma rays that in turn undergo compton scattering and pair production (“conv”). The intermediate energy range is dominated by neutron elastic scattering on hydrogen nuclei. For neutron energy greater than a few MeV the dominant interaction processes are neutron induced nuclear reactions (“NeutronInelastic”), leading to the fragmentation of the target nucleus and the production of nuclear fragments. The neutron energy range considered for this simulation matches the one of the background photons in CMS cavern according to FOCUS simulations. The simulation was performed using GEANT4.9.6.p02 and the physics list FTFP_BERT_HP.

	Photon interaction in a GEM chamber: When a photon enters a GEM chamber, it can interact with the materials inside the detector, producing secondary particles which can reach the gas gaps and can give rise to a background signal. This histogram shows the frequency of processes that generate particles inside the drift and the first transfer gap of the chamber, as a function of the energy of the incident photon. Processes are named using the Geant4 convention. For energies up to 0.3 MeV the incident photon interacts mainly via photoelectric effect (“phot”) . The intermediate energy range is dominated by compton scattering. For photon energy greater than about 13 MeV the dominant interaction process is pair production. The photon energy range considered for this simulation matches the one of the background photons in CMS cavern according to FOCUS simulations. The simulation was performed using GEANT4.9.6.p02 and the physics list FTFP_BERT_HP.

Photon interaction in a GEM chamber: When a photon enters a GEM chamber, it can interact with the materials inside the detector, producing secondary particles which can reach the gas gaps and can give rise to a background signal. This histogram shows the frequency of processes that generate particles inside the drift and the first transfer gap of the chamber, as a function of the energy of the incident photon. Processes are named using the Geant4 convention. For energies up to 0.3 MeV the incident photon interacts mainly via photoelectric effect (“phot”) . The intermediate energy range is dominated by compton scattering. For photon energy greater than about 13 MeV the dominant interaction process is pair production. The photon energy range considered for this simulation matches the one of the background photons in CMS cavern according to FOCUS simulations. The simulation was performed using GEANT4.9.6.p02 and the physics list FTFP_BERT_HP.

	Sensitivity of a GEM chamber to neutrons, photons, electrons and positrons as a function of the incident particle energy . The sensitivity has been evaluated in the energy ranges of the background particles , according to energy spectra provided by CMS FOCUS v.1.0.0.0 simulations. In the simulations the incident particles were fired on the detector with angular distributions compatible with the ones expected in the GE1/1 region, according to FOCUS v1.0.0.0. Averaging these sensitivity curves over the GE1/1 energy spectra we get the mean values of background sensitivity: neutrons 0.08%+0.01, photons 0.97%+0.08%, charged particles 27%+7%. Such values were obtained for the following energy ranges: 1 meV – 1 GeV for neutrons, 0.01 MeV – 100 MeV for photons, 0.1 MeV – 100 MeV. The simulation was performed using GEANT4.9.6.p02 with physics list FTFP_BERT_HP.

Sensitivity of a GEM chamber to neutrons, photons, electrons and positrons as a function of the incident particle energy . The sensitivity has been evaluated in the energy ranges of the background particles , according to energy spectra provided by CMS FOCUS v.1.0.0.0 simulations. In the simulations the incident particles were fired on the detector with angular distributions compatible with the ones expected in the GE1/1 region, according to FOCUS v1.0.0.0. Averaging these sensitivity curves over the GE1/1 energy spectra we get the mean values of background sensitivity: neutrons 0.08%+0.01, photons 0.97%+0.08%, charged particles 27%+7%. Such values were obtained for the following energy ranges: 1 meV – 1 GeV for neutrons, 0.01 MeV – 100 MeV for photons, 0.1 MeV – 100 MeV. The simulation was performed using GEANT4.9.6.p02 with physics list FTFP_BERT_HP.

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
png	Energy_in_drift_gap_G4_GEM_neutron2.png	r1	manage	247.6 K	2014-09-11 - 12:25	UnknownUser
png	G4_physics_list_validation_252cftest3.png	r1	manage	115.3 K	2014-09-19 - 16:08	UnknownUser
png	G4process_GEM_neutron2.png	r1	manage	172.8 K	2014-09-11 - 12:25	UnknownUser
png	G4process_GEM_photon2.png	r1	manage	181.6 K	2014-09-11 - 12:25	UnknownUser
png	GE11_charged_spectrum4_FOCUS_V1.0.0.0.png	r1	manage	83.4 K	2014-09-19 - 16:08	UnknownUser
png	GE11_neutron_spectrum4_FOCUS_V1.0.0.0.png	r1	manage	89.2 K	2014-09-19 - 16:08	UnknownUser
png	GE11_photon_spectrum4_FOCUS_V1.0.0.0.png	r1	manage	89.7 K	2014-09-19 - 16:08	UnknownUser
png	GE11_sensitivity2.png	r1	manage	121.1 K	2014-09-11 - 12:25	UnknownUser

Topic revision: r5 - 2014-09-19 - unknown

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