Poster Excerpt 4: Appearance of Rare Physics Phenomena in the Opera Experiment
(The excerpt below is from the poster of Marco Roda, from the Opera collaboration)
The tau neutrino is very difficult to be detected. Since it is a neutrino, it requires huge and homogeneous detectors in order to maximize the luminosity of your experiment. Then, since its interaction produces a tau particle, you also need a tracker with a spatial resolution at the micrometer level. Once you have obtained that, you can reject your background in an extremely efficient way. So efficient that, in 2000, just 4 events were enough to claim the discovery of the tau neutrino particle.
The OPERA experiment has been designed to detect the presence of tau neutrinos in the CNGS neutrino beam, 700 km far away from the production site, the CERN.
Recently a new interesting event has been discovered in OPERA with a very peculiar topology: instead of one quickly decaying particle, it has two!
The figure shows the structure of the recorded events. There is a longer decaying track (4) which decays after 1 mm in only one charged track (6) and in photons which create an electromagnetic shower after 2 mm. The second decaying particle has a very short path before it goes into 2 tracks (1 and 3).
This kind of event was supposed to be so rare that it was not taken into account in the experiment proposal. That’s why a new dedicated analysis has to be prepared. The possible interpretations are all intriguing and on top of them there is a never observed process: tau neutrino charged current interaction with charm production.
At present the analysis is still blind, since we want to apply the analysis only when a complete strategy will be defined. What is already clear is that the interesting signals can be efficiently separated from the possible backgrounds.