Periodic Reporting for period 3 - RadNu (Radio detection of the PeV - EeV cosmic-neutrino flux)
Periodo di rendicontazione: 2022-02-01 al 2023-07-31
The RadNu project aims to show the proof-of-principle of the radar detection technique to probe cosmic-neutrino-induced particle cascades. The final goal is to install an in-nature radar detection set-up with the sensitivity to detect 1-10 cosmic neutrinos in the currently unexplored PeV-EeV energy range. The detection of this flux allows us to explore the inner engines and physics of the highest energy environments in our universe. This will be done by the development of cutting-edge radar technologies as well as advanced analysis and reconstruction techniques.
RadNu
In the following, article citations will be numbered following their order in the Publications section. Investigations within the RadNu project are globally separated into its main focus given by the development and providing the proof-of-principle of the Radar detection method to probe high-energy cosmic-neutrino-induced particle cascades in ice, and its secondary focus given by the understanding and detection of the direct radio emission induced by a high-energy cosmic-ray or neutrino induced particle cascade.
Radar detection of high-energy particle cascades and the formation of the Radar Echo Telescope (RET) collaboration:
The RadNu project started with data analysis for the T-576 beam-test experiment performed at the Stanford Linear Accelerator Center. This analysis showed, for the first time in history, a radar reflection from a high-energy particle cascade [1,2,10]. This is a major breakthrough for the RadNu project, providing the prove-of-principle for the radar method to probe high-energy particle cascades, and lead to the formation of the Radar Echo Telescope (RET) collaboration. The collaboration is led by K.D. de Vries and S. Prohira, and consists of members from 9 Universities located in Europe, the U.S. and Taiwan. Webpage: www.radarechotelescope.org.
To show the proof-of-principle of the radar detection technique to probe cosmic-neutrino-induced particle cascades in ice, we first aim to detect high-energy cosmic-ray induced particle cascades penetrating a high-altitude ice layer through the RET-CR experiment. This detection channel is chosen, as detection and reconstruction of the in-air particle cascade using a cosmic-ray surface detector is a well-known process. This surface system will subsequently provide an external trigger for our in-ice radar detector to probe the in-ice continuation of the particle cascade. To model the process of a cosmic-ray induced particle cascade moving into a high-altitude ice layer and its subsequent radar detection, a detailed simulation framework has been developed. This framework was subsequently used to estimate the expected event rate and to optimize the detector layout [14-18]. The RET-CR was successfully installed in May 2023 at Summit Station, Greenland, and operated for several weeks. The detector will be updated and improved based upon this first data-run and a second run will take place in the period of May-August 2024.
Along with the experimental developments, a macroscopic radar reflection model, MARES, has been developed and is available within the collaboration. This allowed us to perform several signal property studies, with initial results presented in [13]. These advancements allowed us to perform preliminary neutrino sensitivity studies for RET-N, providing extremely promising sensitivities that were also shown at ICRC2021 [12].
Direct radio emission from high-energy particle cascades, a (background) signal:
The cosmic-ray or neutrino induced particle cascade will also emit direct radio emission while propagating in air or through the ice. As they pose a possible background/calibration-signal that can be observed by in-ice neutrino radio detectors, understanding these emissions is crucial for RET-CR/N, as well as existing Askaryan radio detectors such as ARA, RNO-G and the future IceCube-Gen2-radio facility. Within the RadNu project, a complete simulation framework was developed to describe the emission from a cosmic-ray particle cascade moving from air into a high-altitude ice-layer. This simulation is currently in use by the above experiments, and written down for publication. Furthermore, multiple collaborative efforts on understanding, detecting, and reconstructing these emissions have been performed within the context of the ARA and RNO-G collaborations, that aim to detect cosmic-neutrinos through the direct Askaryan radio emission from a neutrino-induced particle cascade [3-5,8,9,19,20,22,23].
Radio signal propagation:
One of the major uncertainties in our radar and radio signal predictions is the propagation of radio-waves in the Antarctic ice. Due to its non-uniform density profile, radio waves will be bent, refracted or reflected on their path to our detector. Investigating these non-linear propagation modes lead to the application of so-called parabolic equation (PE) solvers to this problem. In [6], within the RET collaboration, we indeed show that standard ray-propagators are insufficient to provide a full description of the expected and observed radio emission.
In the following, article citations will be numbered following their order in the Publications section. Investigations within the RadNu project are globally separated into its main focus given by the development and providing the proof-of-principle of the Radar detection method to probe high-energy cosmic-neutrino-induced particle cascades in ice, and its secondary focus given by the understanding and detection of the direct radio emission induced by a high-energy cosmic-ray or neutrino induced particle cascade.
Radar detection of high-energy particle cascades and the formation of the Radar Echo Telescope (RET) collaboration:
The RadNu project started with data analysis for the T-576 beam-test experiment performed at the Stanford Linear Accelerator Center. This analysis showed, for the first time in history, a radar reflection from a high-energy particle cascade [1,2,10]. This is a major breakthrough for the RadNu project, providing the prove-of-principle for the radar method to probe high-energy particle cascades, and lead to the formation of the Radar Echo Telescope (RET) collaboration. The collaboration is led by K.D. de Vries and S. Prohira, and consists of members from 9 Universities located in Europe, the U.S. and Taiwan. Webpage: www.radarechotelescope.org.
To show the proof-of-principle of the radar detection technique to probe cosmic-neutrino-induced particle cascades in ice, we first aim to detect high-energy cosmic-ray induced particle cascades penetrating a high-altitude ice layer through the RET-CR experiment. This detection channel is chosen, as detection and reconstruction of the in-air particle cascade using a cosmic-ray surface detector is a well-known process. This surface system will subsequently provide an external trigger for our in-ice radar detector to probe the in-ice continuation of the particle cascade. To model the process of a cosmic-ray induced particle cascade moving into a high-altitude ice layer and its subsequent radar detection, a detailed simulation framework has been developed. This framework was subsequently used to estimate the expected event rate and to optimize the detector layout [14-18]. The RET-CR was successfully installed in May 2023 at Summit Station, Greenland, and operated for several weeks. The detector will be updated and improved based upon this first data-run and a second run will take place in the period of May-August 2024.
Along with the experimental developments, a macroscopic radar reflection model, MARES, has been developed and is available within the collaboration. This allowed us to perform several signal property studies, with initial results presented in [13]. These advancements allowed us to perform preliminary neutrino sensitivity studies for RET-N, providing extremely promising sensitivities that were also shown at ICRC2021 [12].
Direct radio emission from high-energy particle cascades, a (background) signal:
The cosmic-ray or neutrino induced particle cascade will also emit direct radio emission while propagating in air or through the ice. As they pose a possible background/calibration-signal that can be observed by in-ice neutrino radio detectors, understanding these emissions is crucial for RET-CR/N, as well as existing Askaryan radio detectors such as ARA, RNO-G and the future IceCube-Gen2-radio facility. Within the RadNu project, a complete simulation framework was developed to describe the emission from a cosmic-ray particle cascade moving from air into a high-altitude ice-layer. This simulation is currently in use by the above experiments, and written down for publication. Furthermore, multiple collaborative efforts on understanding, detecting, and reconstructing these emissions have been performed within the context of the ARA and RNO-G collaborations, that aim to detect cosmic-neutrinos through the direct Askaryan radio emission from a neutrino-induced particle cascade [3-5,8,9,19,20,22,23].
Radio signal propagation:
One of the major uncertainties in our radar and radio signal predictions is the propagation of radio-waves in the Antarctic ice. Due to its non-uniform density profile, radio waves will be bent, refracted or reflected on their path to our detector. Investigating these non-linear propagation modes lead to the application of so-called parabolic equation (PE) solvers to this problem. In [6], within the RET collaboration, we indeed show that standard ray-propagators are insufficient to provide a full description of the expected and observed radio emission.
The first ever detection of a radar scatter from a high-energy particle cascade
During the SLAC T-576 experiment the first ever radar signal from a high-energy particle cascade was detected, showing the proof-of-principle of the radar method in to probe high-energy particle cascades in a laboratory environment. This result got a broad attention in the media (see www.radarechotelescope.org).
Coherent transition radiation: implications for the anomalous ANITA events
Studies were performed to predict the background signal from coherent transition radiation, expected not only in a beam test experiment like the one performed at SLAC, but also in the natural process of a cosmic-ray-induced air shower hitting a large altitude ice sheet. The results of our calculations showed that the transition radiation from cosmic-ray air showers moving from air to ice could form an explanation for two so-far unexplained events detected by the ANITA neutrino detector.
Simulating radar reflections and radio emission from cosmic-ray and neutrino-induced particle cascades penetrating a high-altitude ice layer
A full simulation chain is set up for the RET-CR experiment, combining the in-air particle simulation using the CORSIKA air-shower simulation code, of which its output is used in the GEANT4 simulation code to simulate the in-ice propagation of the cosmic-ray-induced particle cascade. The direct radio emission from this process is implemented within these codes and its outputs are also directly tied to the RadioScatter radar simulation code. This simulation allowed us to optimize the RET-CR detector layout. These simulations are currently in use within the RET-CR, ARA, and RNO-G collaborations.
Within the RadNu project, a deterministic, macroscopic model for the radar scatter off of a high-energy particle cascade was developed. This model, dubbed MARES, is finished and in use within the RET collaboration and will be made public in the near future.
Installation of the first ever in-ice particle radar detector RET-CR
The final goal of the RadNu project was to install an in-nature radar particle detector. This was achieved by the installation of the RET-CR detector in May 2023. Currently, first data is being analyzed, and a second data-run is foreseen from May-August 2024 during the Summit Station, Greenland summer season.
During the SLAC T-576 experiment the first ever radar signal from a high-energy particle cascade was detected, showing the proof-of-principle of the radar method in to probe high-energy particle cascades in a laboratory environment. This result got a broad attention in the media (see www.radarechotelescope.org).
Coherent transition radiation: implications for the anomalous ANITA events
Studies were performed to predict the background signal from coherent transition radiation, expected not only in a beam test experiment like the one performed at SLAC, but also in the natural process of a cosmic-ray-induced air shower hitting a large altitude ice sheet. The results of our calculations showed that the transition radiation from cosmic-ray air showers moving from air to ice could form an explanation for two so-far unexplained events detected by the ANITA neutrino detector.
Simulating radar reflections and radio emission from cosmic-ray and neutrino-induced particle cascades penetrating a high-altitude ice layer
A full simulation chain is set up for the RET-CR experiment, combining the in-air particle simulation using the CORSIKA air-shower simulation code, of which its output is used in the GEANT4 simulation code to simulate the in-ice propagation of the cosmic-ray-induced particle cascade. The direct radio emission from this process is implemented within these codes and its outputs are also directly tied to the RadioScatter radar simulation code. This simulation allowed us to optimize the RET-CR detector layout. These simulations are currently in use within the RET-CR, ARA, and RNO-G collaborations.
Within the RadNu project, a deterministic, macroscopic model for the radar scatter off of a high-energy particle cascade was developed. This model, dubbed MARES, is finished and in use within the RET collaboration and will be made public in the near future.
Installation of the first ever in-ice particle radar detector RET-CR
The final goal of the RadNu project was to install an in-nature radar particle detector. This was achieved by the installation of the RET-CR detector in May 2023. Currently, first data is being analyzed, and a second data-run is foreseen from May-August 2024 during the Summit Station, Greenland summer season.