Final Report Summary - AUGER2FUTURE (Towards a New Giant Detector for Ultra High Energy Cosmic Rays)
Summary description
Cosmic rays are charged particles that are entering constantly the atmosphere of the Earth and can reach tremenduous energies, larger than 1e19 eV. Together with gamma rays and neutrinos they are part of the multi-messenger approach to investigate the highest energy phenomena in the Universe. After a century of experimental toil, the origin, the mass and the acceleration mechanisms still constitute some of the fundamental questions of modern astrophysics. Besides the astrophysical importance, these particles provide a unique way to study fundamental physics, like testing the Lorentz invariance violation and to study particle physics interactions at center of mass energies beyond the ones reached by man-made accelerators.
The Pierre Auger Observatory located in the province of Mendoza, Argentina, and covering a surface of 3000 square kilometers is a state-of-the-art experiment to measure the ultra-high energy cosmic rays. Nevertheless with the current con guration of the detector it is almost impossible to determine the mass composition at the highest energies on an event by event basis. The objective of this project has been to develop and understand new detectors for an upgrade of the Observatory. In the rst period a prototype of new concept of a water-Cherenkov tank, a layered surface detector has been built and its performances have been assessed from data and simulations. This detector has proven to be operating in stable condition and to provide a very good separation of the electromagnetic and muonic part of the air-showers (cascades of secondary particles produced by the interaction of the cosmic rays with the air). This separation helps in the establishment of the cosmic rays mass. The project has been one of the two projects (from five) in the final election, nevertheless the Pierre Auger collaboration has chosen a more non-invading solution: placing scintillators on top of the surface detectors. In the last period of the project we have contributed in determining the performances of an upgrade with
scintillators. This study has shown that the scintillators are well suited to achieve the science goals and has been a major contribution to science case of the Pierre Auger upgrade (AugerPrime).
Work performed
The work performed has been focused on the Auger Upgrade and on the analysis performed to determine the mass of ultra high energy cosmic rays. The fellow has been located at the experiment site, in Malargue, Argentina for two months where in collaboration with the local sta and a group from LPNHE (Paris) has built the first functioning prototype of the Layer Surface Detector, Guapa Guerrera. The work included hardware and local station software developments. Another part has been the co-coordination of the work and management, including material choice and procurement. The fellow has been very active from the incipient phase of the design of the prototype up to deployment in La Pampa and data taking. The design, based on the idea and with the participation of the group in France, separates optically the internal liner of the detector in two horizontal layers. The top layer is mostly sensitive to the electrons, positrons and photons from air-showers, while the bottom part would contain a muon dominated signal. The detector configuration has been implemented in the Geant4 simulations software in order to understand its response. The simulations have been compared with the data from Guapa Guerrera and a good agreement has been found, proving that the detector is performing as one would expect and can be well suited for a future design of cosmic rays detectors.
The Pierre Auger collaboration has decided for another solution for the enhancement of the surface detector: placing scintillators on top of the water-Cherenkov detectors. Given the expected resolutions for these detectors the fellow has calculated the separation power between different astrophysical scenarios, work that has been included in the science case of the Auger upgrade proposal.
The emission of air-showers in the GHz range, via a molecular-bremsstrahlung mechanism has been also part of this proposal. The fellow has participated in shifts for the AMY detector in order to measure the GHz emission using an anachoic chamber at a beam experiment (Frascati, Italy). The data collected will provide the best limits on the GHz emission of air-showers.
The fellow has supervised two undergraduate students and has been in collaboration with one of the PhDs from the group. She has been in the editorial board and wrote part of the paper describing the Pierre Auger Observatory. She participated and gave talks in science popularization events: Semana de la ciencia and CERN 11th International Masterclasses. Meanwhile, being the task leader of the physics task on the energy spectrum she has coordinating the work within the Auger collaboration related to the measurements of the flux of cosmic rays.
Main results
The Layered Surface Detector is a new concept of a water Cherenkov tank that allows us to reconstruct mass sensitive parameters for UHECR with optimal resolution. We have shown that the muon size of the extensive air-showers can be reconstructed with a precision better than 20% above 10 EeV, reaching 10% for energies above 70 EeV. The separation of muonic and electromagnetic lateral distributions on an event by event basis further provides an estimation of the air-shower maximum development with resolutions as low as 30 g/cm2. Guapa Guerrera, one of the prototypes, has proven to have excellent performances in a very good agreement with expectations from Monte-Carlo simulations. After almost two years in the field, the prototype is still working properly. We have shown that the layered surface detectors are very good candidates for any upgrade of existing UHECR observatories or for the construction of new observatories. The results have been published in a peer-reviewed journal.
The chosen solution for the upgrade of the Pierre Auger Observatory has been the installation of scintillator detectors on top of the surface detectors. Even though the performances are not so good as in the case of the layered surface detector, it is a non-invasive solution, i.e. it does not change the current surface detector. The fellow has been co-coordinating the science case work for the upgrade proposal. Given the results from simulations regarding the detector resolution and two realistic astrophysical scenarios that predict di erent fractions of the proton component at the highest energies, we assessed if the science goals of the upgrade of the Observatory can be achieved. The flux suppression of the cosmic rays at the highest energies is related to two effects, energy losses during propagation (for protons and nuclei) and to the maximum injection energy of the sources. Which of these e ects is more important for shaping the upper end of the energy spectrum is still unclear. One of the main goals during the next years will be the measurement of the mass composition of cosmic rays in the suppression region of the energy spectrum (E > 50 EeV). Knowing the energy evolution of the composition will allow us to put further constraints on the sources and also help to understand the physics origin of the flux suppression. A separation between different astrophysical scenarios will be possible with more than 4 standard deviations after 5 years of operation. The search for a proton component in the cosmic ray flux at the highest energies is part of the aims of the composition study. It is of particular importance for understanding whether it will be possible to do particle astronomy, i.e. search for the sources of UHECR by studying the arrival directions of protons. The possible existence of a proton component at the highest energies has also far-reaching implications on the expected neutrino and gamma-ray fluxes. The fellow has played a key-role inside the science study group that has shown that with at least 6 years of operation, the accumulated data will allow to determine if there is a 10% proton component at the highest energies. In November 2015 a memorandum of understanding has been signed between the participating countries for another 10 years of operation of the Observatory and funds start to be allocated for the upgrade of the detector.
Cosmic rays are charged particles that are entering constantly the atmosphere of the Earth and can reach tremenduous energies, larger than 1e19 eV. Together with gamma rays and neutrinos they are part of the multi-messenger approach to investigate the highest energy phenomena in the Universe. After a century of experimental toil, the origin, the mass and the acceleration mechanisms still constitute some of the fundamental questions of modern astrophysics. Besides the astrophysical importance, these particles provide a unique way to study fundamental physics, like testing the Lorentz invariance violation and to study particle physics interactions at center of mass energies beyond the ones reached by man-made accelerators.
The Pierre Auger Observatory located in the province of Mendoza, Argentina, and covering a surface of 3000 square kilometers is a state-of-the-art experiment to measure the ultra-high energy cosmic rays. Nevertheless with the current con guration of the detector it is almost impossible to determine the mass composition at the highest energies on an event by event basis. The objective of this project has been to develop and understand new detectors for an upgrade of the Observatory. In the rst period a prototype of new concept of a water-Cherenkov tank, a layered surface detector has been built and its performances have been assessed from data and simulations. This detector has proven to be operating in stable condition and to provide a very good separation of the electromagnetic and muonic part of the air-showers (cascades of secondary particles produced by the interaction of the cosmic rays with the air). This separation helps in the establishment of the cosmic rays mass. The project has been one of the two projects (from five) in the final election, nevertheless the Pierre Auger collaboration has chosen a more non-invading solution: placing scintillators on top of the surface detectors. In the last period of the project we have contributed in determining the performances of an upgrade with
scintillators. This study has shown that the scintillators are well suited to achieve the science goals and has been a major contribution to science case of the Pierre Auger upgrade (AugerPrime).
Work performed
The work performed has been focused on the Auger Upgrade and on the analysis performed to determine the mass of ultra high energy cosmic rays. The fellow has been located at the experiment site, in Malargue, Argentina for two months where in collaboration with the local sta and a group from LPNHE (Paris) has built the first functioning prototype of the Layer Surface Detector, Guapa Guerrera. The work included hardware and local station software developments. Another part has been the co-coordination of the work and management, including material choice and procurement. The fellow has been very active from the incipient phase of the design of the prototype up to deployment in La Pampa and data taking. The design, based on the idea and with the participation of the group in France, separates optically the internal liner of the detector in two horizontal layers. The top layer is mostly sensitive to the electrons, positrons and photons from air-showers, while the bottom part would contain a muon dominated signal. The detector configuration has been implemented in the Geant4 simulations software in order to understand its response. The simulations have been compared with the data from Guapa Guerrera and a good agreement has been found, proving that the detector is performing as one would expect and can be well suited for a future design of cosmic rays detectors.
The Pierre Auger collaboration has decided for another solution for the enhancement of the surface detector: placing scintillators on top of the water-Cherenkov detectors. Given the expected resolutions for these detectors the fellow has calculated the separation power between different astrophysical scenarios, work that has been included in the science case of the Auger upgrade proposal.
The emission of air-showers in the GHz range, via a molecular-bremsstrahlung mechanism has been also part of this proposal. The fellow has participated in shifts for the AMY detector in order to measure the GHz emission using an anachoic chamber at a beam experiment (Frascati, Italy). The data collected will provide the best limits on the GHz emission of air-showers.
The fellow has supervised two undergraduate students and has been in collaboration with one of the PhDs from the group. She has been in the editorial board and wrote part of the paper describing the Pierre Auger Observatory. She participated and gave talks in science popularization events: Semana de la ciencia and CERN 11th International Masterclasses. Meanwhile, being the task leader of the physics task on the energy spectrum she has coordinating the work within the Auger collaboration related to the measurements of the flux of cosmic rays.
Main results
The Layered Surface Detector is a new concept of a water Cherenkov tank that allows us to reconstruct mass sensitive parameters for UHECR with optimal resolution. We have shown that the muon size of the extensive air-showers can be reconstructed with a precision better than 20% above 10 EeV, reaching 10% for energies above 70 EeV. The separation of muonic and electromagnetic lateral distributions on an event by event basis further provides an estimation of the air-shower maximum development with resolutions as low as 30 g/cm2. Guapa Guerrera, one of the prototypes, has proven to have excellent performances in a very good agreement with expectations from Monte-Carlo simulations. After almost two years in the field, the prototype is still working properly. We have shown that the layered surface detectors are very good candidates for any upgrade of existing UHECR observatories or for the construction of new observatories. The results have been published in a peer-reviewed journal.
The chosen solution for the upgrade of the Pierre Auger Observatory has been the installation of scintillator detectors on top of the surface detectors. Even though the performances are not so good as in the case of the layered surface detector, it is a non-invasive solution, i.e. it does not change the current surface detector. The fellow has been co-coordinating the science case work for the upgrade proposal. Given the results from simulations regarding the detector resolution and two realistic astrophysical scenarios that predict di erent fractions of the proton component at the highest energies, we assessed if the science goals of the upgrade of the Observatory can be achieved. The flux suppression of the cosmic rays at the highest energies is related to two effects, energy losses during propagation (for protons and nuclei) and to the maximum injection energy of the sources. Which of these e ects is more important for shaping the upper end of the energy spectrum is still unclear. One of the main goals during the next years will be the measurement of the mass composition of cosmic rays in the suppression region of the energy spectrum (E > 50 EeV). Knowing the energy evolution of the composition will allow us to put further constraints on the sources and also help to understand the physics origin of the flux suppression. A separation between different astrophysical scenarios will be possible with more than 4 standard deviations after 5 years of operation. The search for a proton component in the cosmic ray flux at the highest energies is part of the aims of the composition study. It is of particular importance for understanding whether it will be possible to do particle astronomy, i.e. search for the sources of UHECR by studying the arrival directions of protons. The possible existence of a proton component at the highest energies has also far-reaching implications on the expected neutrino and gamma-ray fluxes. The fellow has played a key-role inside the science study group that has shown that with at least 6 years of operation, the accumulated data will allow to determine if there is a 10% proton component at the highest energies. In November 2015 a memorandum of understanding has been signed between the participating countries for another 10 years of operation of the Observatory and funds start to be allocated for the upgrade of the detector.