Periodic Report Summary 2 - HE NEUTRINO ICECUBE (High energy neutrino astronomy with IceCube: towards the detection of neutrinos from Gamma Ray Bursts (GRBs))
The aim of this project was to shed light on the origin of high-energy cosmic rays, which has remained unclear for an entire century after their discovery. These electrically charged particles cannot be traced back to their origin, because they get deflected in magnetic fields. The acceleration of electrically charged cosmic rays is expected to coincide with the production of high-energy neutrinos. These neutrinos are electrically neutral and propagate virtually undisturbed directly from their sources to the Earth. Hence, they allow us to trace back to the origin and the detection of high-energy astrophysical neutrinos would ultimately answer the question of the origin of the cosmic rays as well. However, due to the undisturbed propagation of the neutrinos, their detection is a challenge as well. The IceCube detector at the geographic South Pole used the Antarctic ice shield for the detection of the neutrinos. This extremely transparent material allows us to detect the traces of any high-energy neutrino interaction by photomultiplier tubes over the volume of a cubic kilometre. The operation of a detector of this scale, its construction and the analysis of the data collected requires a large international collaboration, as it is the case with the project. This project contributed in all these aspects to the success of the project.
While no sources of high-energy neutrinos have been detected by the project so far, the obtained upper limits already put significant constraints on the origin of cosmic rays.
Among the very few candidates for the emission of cosmic rays are Gamma ray bursts (GRBs) and Active galactic nuclei (AGN), as these are the only known objects which provide the extreme conditions needed to accelerate particles to the observed energies. The results obtained so far put severe constraints on the expected neutrino emission from GRBs, i.e. they are unlikely the dominant source of cosmic rays if the otherwise favoured fireball model describes them correctly. The limits obtained on AGN or other persistent sources are less constraining, because their emission is not at a known time, making it more challenging to distinguish astrophysical neutrinos from background produced in the atmosphere of the Earth.
While no sources of high-energy neutrinos have been detected by the project so far, the obtained upper limits already put significant constraints on the origin of cosmic rays.
Among the very few candidates for the emission of cosmic rays are Gamma ray bursts (GRBs) and Active galactic nuclei (AGN), as these are the only known objects which provide the extreme conditions needed to accelerate particles to the observed energies. The results obtained so far put severe constraints on the expected neutrino emission from GRBs, i.e. they are unlikely the dominant source of cosmic rays if the otherwise favoured fireball model describes them correctly. The limits obtained on AGN or other persistent sources are less constraining, because their emission is not at a known time, making it more challenging to distinguish astrophysical neutrinos from background produced in the atmosphere of the Earth.