![]() The first two analyses used the most advanced techniques in IceCube searches for neutrino sources. The study involved three analyses that used different and complementary techniques to search for common sources of nearby UHECRs and neutrinos. Three analysis methods were used:ġ) Researchers used muon neutrino tracks in IceCube and ANTARES, which have a good pointing resolution, to look for neutrino sources, i.e., an excess of neutrinos, that are coincident with the arrival directions of specific UHECRs.Ģ) Stacks of a few high-energy neutrinos with a high probability of astrophysical origin were used as markers of possible neutrino sources, which were then used to look for clusters of UHECRs around these neutrinos.ģ) All pairs of UHECRs and these very high energy neutrinos within a certain angle were counted and compared to what we would expect from a random-not a common source-scenario. To get the most out of the data, scientists have searched for correlations using full-sky neutrino and UHECRs data sets obtained by combining data from IceCube and ANTARES, and the Pierre Auger Observatory (Auger) and the Telescope Array (TA), respectively. And, because neutrinos are direct tracers of hadronic interactions of cosmic rays that travel undeflected by magnetic fields, a combined analysis could unveil the location of UHECR sources. ![]() While neutrinos created in coincidence with UHECRs are expected to carry around 3-5% of the original proton energy, which means hundreds of PeV and above for the UHECRs selected in this study, the same sources would also emit lower energy cosmic rays with neutrinos that can be observed by the IceCube and ANTARES detectors. The searches presented in this multi-collaboration paper looked for correlations of nearby extragalactic sources of UHECRs with energies near 50 EeV and above. ![]() For UHECR sources beyond our local universe, intergalactic magnetic fields would scramble the direction of cosmic rays and delay their arrival at Earth, thus losing any correlation with neutrinos produced in the same source. However, at higher energies, UHECRs would escape the local magnetic field and travel to nearby galaxies, with arrival directions at detection that may differ slightly with respect to their initial directions as a result of magnetic field deflections. Measurements of UHECR anisotropy by the Pierre Auger Collaboration indicate that UHECRs with energies above a few EeV are of extragalactic origin, because at lower energies cosmic rays would be trapped by interstellar magnetic fields in their host galaxies. ![]() In fact, the observed intensity is close to the Waxman-Bahcall flux, which sets an upper limit on the neutrino rate expected to escape from UHECR sources after the interaction of primary cosmic ray protons with photons or matter near the source. Second, their intensity is compatible with what scientists expect from a diffuse flux originating from extragalactic populations of sources. First, they are distributed isotropically. There are several hints that point to an extragalactic origin of most high-energy neutrinos in IceCube. Credit: The ANTARES, IceCube, Pierre Auger and Telescope Array collaborations. Sky map of the arrival directions of UHECR events from the Pierre Auger Observatory and the Telescope Array and high-energy neutrinos from IceCube and ANTARES. These results are still intriguing-and again point to the need for further improvements-since they could be explained by an assumption of no common sources of UHECRs and neutrinos, or they could just indicate that we still don’t know enough about them. In contrast to the initial study, the new results, recently submitted to The Astrophysical Journal, looked at more data and used improved analysis techniques to find that the data are consistent with no significant correlation between UHECRs and neutrinos. However, results were not conclusive and identified the need for a more advanced analysis.Īnd this is what an international team of more than 1,000 scientists is now presenting, with a new partnership of the IceCube, Pierre Auger, and Telescope Array collaborations that has grown to include the ANTARES collaboration. The results pointed to a correlation between extragalactic cosmic-ray sources and the highest energy neutrinos in IceCube, with energies between 20 TeV and a few PeVs. Six years ago, a first joint analysis of the IceCube, Pierre Auger, and Telescope Array collaborations looked for correlations between UHECRs and neutrinos. They should produce “hotspots” of high-energy neutrinos if they interact with other particles near their point of origin. UHECRs, which are a mixture of protons and heavy nuclei, are the highest energy particles ever measured. The search for the sources of ultra-high-energy cosmic rays (UHECRs) is not a simple one.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |