# April 16 Minutes

### Matter Effects Discussion

Andrea Romanino lead a discussion about matter effects in the
case that LSND is confirmed. If this is the case, then the
resonance energy corresponding to the largest mass difference
is 1-3TeV*(delta m^2 LSND/1eV^2), so matter effects would
be invisible. The only matter effects that might appear are
in transitions between nu_e and nu sterile.
The other matter effect that would arise would be that between
nu_e and nu_mu, but with an energy 0.1->0.3GeV (delta m^2 solar/10^-4eV^2).
But since that transition is already expected to be at a large
angle (theta_12 might be almost maximal), the matter effects would only
serve to make the theta-12 effective a little smaller, not magnify it.
However, if LSND is confirmed and we do think there is a sterile neutrino,
then there is actually less of an imperative to measure the sign of
the second largest mass splitting, since half the models predict one sign,
and half the models predict the other sign.

### Super-MINOS studies

We also talked about Larry Wai's superbeam study, using a
fine-grained version of the MINOS detector, the NUMI-Medium Energy
Beam, and 10kton-years, going towards SLAC. Bob Bernstein looked
at the precision one would achieve with 10kton years and a baseline
of 2800km--one could presumably get about a 2% measurement of
sin^2 2 theta_23, so one might be able to say we had large as opposed
to maximal mixing. Romanino and Barenboim pointed out that it would
be important theoretically to be able to distinguish between large
and maximal mixing.

### Other business

We didn't have time to discuss the outline that Debbie started putting
together about the detector R&D report that is due in May, a link to
the very very preliminary outline can be found
here.

Deborah Harris
Last modified: Fri Apr 20 15:22:52 CDT 2001