Stars as Laboratories for Fundamental Physics - MPP Theory Group

418 Chapter 11
per energy interval due to the dominant ν e p reaction in the detectors.
For Kamiokande and IMB an example is shown in Fig. 11.12, based
on Burrows’ (1988) model 55 flux calculation which was tuned to fit
the data. The predicted fluence at Earth per unit energy was shown
in Fig. 11.8 where a distance of 50 kpc was adopted. The solid lines
are for the case when the instantaneous ν e spectra are assumed to be
Maxwell-Boltzmann. Of course, the time-integrated flux is then no
longer thermal as it is a superposition of Maxwell-Boltzmann spectra
at different temperatures. The solid line leads to a total expectation
of 13.1 events at Kamiokande and 6.3 at IMB. The dashed lines correspond
to spectra which are instantaneously pinched (Fig. 11.6) with
a degeneracy parameter η = 2. Again, the time-integrated spectra are
not necessarily pinched. This case leads to 11.6 events at Kamiokande
and 3.9 at IMB.
Fig. 11.12. Expected number of events per energy interval at Kamiokande
and IMB from the SN 1987A ν e flux on the basis of the ν e p → ne + reaction.
The flux prediction is based on Burrows’ (1988) model 55 which was tuned to
fit the SN 1987A data. The distance is taken to be 50 kpc, and the detector
efficiency curves of Fig. 11.8 are used. The dashed lines refer to neutrino
spectra which are instantaneously “pinched” as in Fig. 11.6.
Water Cherenkov detectors, as opposed to scintillation ones, are
imaging devices in that they can resolve the direction of the electron
(positron) because of the directionality of the emitted Cherenkov light.
The main limitation is multiple Coulomb scattering of low-energy e ±
in the medium. A typical path length in water is only a few cm so that
hard collisions are relatively unlikely. The rms angular deviation due