I'd appreciate it if I could get a little help on this one, I'm confused about how this is done. I know there are numerous papers out there about how to do this based on the SN1987A event that was detected with KII and IMB. The problem in my textbook asks me to make a rough estimate of the neutrino mass based on a simplified version of the data: Assume that the neutrinos were generated and left the core in a period of one second. A large fraction of the twenty neutrinos detected 160,000 years later were all observed in a period of 2 seconds, with a mean energy of 8MeV. That's the problem. Here's what (I think) I've figured out: If the neutrinos were produced INSTANTLY, the difference in their arrival times at the detectors on earth would allow me to calculate their mass based on the time-energy uncertainty relation, and the energy of the neutrinos as they arrive. Because the neutrinos in this problem are produced over a period of a second, I can only give an upper limit. The main thing stopping me from actually doing this is that I don't know how to account for the time it takes to produce the neutrinos. My second problem is that I don't know how to account for the time that it takes to produce the neutrinos. Any help would be appreciated.