It took me one month of being back at work to really get back into the swing of things. The first month was not terribly productive, but now I feel I am back to where I was before I took parental leave.
The last few weeks have been very exciting for me from a physics perspective as SNO's hep neutrino working group (of which I am one of the members) is currently considering doing a search for the Diffuse Supernova Neutrino Background (DSNB); DSNB is sometimes called SRN = Supernova Relic Neutrinos. Doing a search for DSNB fits in very nicely with our current plans for doing a search for hep solar neutrinos.
What is DSNB? They are the neutrinos that have been produced by all the supernovae that have exploded since stars started exploding. It is estimated that approximately one star explodes somewhere in the Universe every second. Vast numbers of neutrinos are created when a supernova occurs, so since the the birth of the Universe, an incredibly huge number of neutrinos have contributed to the DSNB.
Previous experiments have searched for these elusive neutrinos, but no experiment has detected them yet. We plan to use SNO's great sensitivity to neutrinos to try to detect the DSNB. The hardest part of seeing the DSNB is that most of the DSNB neutrino signal is swamped by neutrinos from the Sun, which is much closer to us than any of the other stars in the Universe. The DSNB neutrinos can have greater energies than solar neutrinos though, so we look for DSNB by looking for high energy neutrinos; that's 20 -> 30 MeV for the physicists out there.
It is not likely that we will be successful: most models of the DSNB predict very few neutrinos at these high energies. Also, we have to contend with the background from atmospheric neutrinos (neutrinos produced in the upper atmosphere after collisions between cosmic rays and molecules of gas in our upper atmosphere). It is likely that the atmospheric neutrino background, which has higher energies than the solar neutrino background, will also swamp the DSNB signal.
Despite this pessimistic outlook, it is still worthwhile to search for the DSNB. Maybe most of the models are wrong and we can detect these ancient neutrinos. If we do, that would be a very exciting discovery. In principle, these neutrinos carry information about how supernovae work and how the Universe has evolved since stars started to explode.
We hope to have some preliminary results before this World Year of Physics is over! Stay tuned.
