Minutes from March 11 Meeting
Quick Follow-Up from Last Week: Last Week
Mayda showed the NUMI off-axis
beam fluxes for positive and negative horn polarities
(making neutrino or antineutrino beams) and the event rates for neutrinos
were about a factor of 2.5-3 higher than for antineutrinos.
This plot Shows the FLUKA predictions
for electron neutrino and antineutrino
cross sections on an isoscalar
target as a function of energy.
These plots (page 3 especially)
show the cross section
ratios used by Mayda, and also the neutrino flux ratios for the NUMI
off-axis beams. (with two different polarities).
You can see that the production of neutrinos for the
two beams is almost the same, antineutrino production is
only down by about 10% from the neutrino production.
It's only the cross section
we're fighting against here. Cross section tables were used from
the NGS cross section web page Note that the data
(compiled by PDG 1992, appearing in
NUMI note by Hugh Gallagher and Maury Goodman
NuMI-NOTE-SIM-0112 , page 14)
is for muon neutrinos...
and uncertainties in that region are at the 15-20% level...
Plots from Mark Messier:
Performance of a Water Cerenkov
Detector with the NUMI Off-axis beam:
Mark Messier gave a detailed talk about how a SuperK-like detector
might perform in a 2GeV off-axis beam, where he considered not only
the single ring events and the reconstructed energy (like Dave Casper
did in his initial study) but also used information from the
incoming neutrino direction, and a newer pi0 fitter that's being
worked on at SuperK. He said that there was not one single variable
which looked the most useful, so he did a log likelihood analysis
on several variables (listed in the slides above).
It turns out that the biggest problem with the pi0
contamination was from two rings overlapping, not from asymmetric
pi0 decays, which is what the issue is for the JHF to SuperK beam
pi0-induced background. (see pages 16-20 for cool event displays)
After this study was done
Mark got about 2% neutral current acceptance, and from 20 to 30% signal
efficiency. This would correspond to a nc background that was about
twice the intrinsic nue background. Still do to: get more background
statistics and comparisons to understand what phototube granularity has
to do with all of this.
Plots from Fritz DeJongh:
scenario for NUMI upgrades
This scenario involves putting a dipole magnet downstream of
the second horn in the NUMI beamline, and running it at a current
such that 4.5GeV pions get bent by 2 degrees, and then they do
go down the center of the NUMI decay tunnel (so the MINOS detector
would then be in the optimal location, unlike the "off axis" scenario).
Fritz assumed the power coming from a new proton driver. In this case the
protons would get bent by much less, and therefore would hit the
wall of the decay pipe somewhere, not the absorber. This was
seen as one problem with this. The other issue would be tilting the
beamline upstream of the dipole by 2 degrees, but that's not so terrible:
the proton beam itself would only have to hit the target about 3cm
off of where it's currently going. WARNING: For the record, there
was much discussion concerning the "raw" comparison Fritz made
between JHF and the studies that Mayda, Gabriela, and Andre have
been doing: simply scaling the number of events given a choice
of detector mass is not the
right comparison--what you really want to take into account is the
beam shape itself (i.e. how many neutrinos in the peak compared to
the total number of events,) how wide is the peak compared to the
oscillation "frequency", where is the peak compared to the
oscillation frequency, what is the signal efficiency and the neutrino
cross section at the peak energy, etc.).
Last modified: Mon Mar 18 17:06:06 CST 2002