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:
www.hepl.harvard.edu/~messier/post/NumiCheren.ps
www.hepl.harvard.edu/~messier/post/NumiCheren.pdf
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:
An Agressive scenario for NUMI upgrades
http://home.fnal.gov/~fritzd/files/numi_upgrade.ps
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.).
Deborah Harris
Last modified: Mon Mar 18 17:06:06 CST 2002