Minutes from January 24 2002 Meeting

Report from NNN02 Workshop at CERN

Maury Goodman talked about the situation at CERN right now--things seem sort of up in the air right now, due to the LHC crisis. However, on the bright side, half of the CNGS decay pipe region has already been excavated, as well as the regions leading up to and including the target and horn areas.

Maury also went over some of the new ideas which are percolating through the JHF group--they expect to submit the proposal this spring, and hope to get approval in December. They have selected a spot for HyperK, one which is 10km away from where SuperK is now. (this would be 2 degrees apart). They plan to build a trapezoidal decay "pipe" (narrow upstream, flaring out to a wide area at the downstream end) and fill it with helium (to minimize multiple scattering without worrying about vacuum windows). Then they can use the same beamline to make both on or off-axis beams to either SuperK or HyperK.

Debbie then gave a quick overview of the betabeam concept, using slides from Piero Zucchelli's Talk on Beta Beams(power point file) which were shown at NNN02. Remember the Beta beam idea is where you create a beam of radioactive ions which decay, (i.e. just like the muon storage ring, only heavier). One nice thing is that the beam is really really pure (beam backgrounds at the 10^-4 level) and is ONLY nu_e or nubar_e. There are a few big differences though between the betabeams and muon storage ring beams: for one thing, the neutrinos in beta decay don't carry off a large fraction of the ion energy, so it's hard to get a very energetic neutrino beam. Another difference is that the lifetimes of these ions are on the order of seconds, so you have very different issues associated with storing the ions, and putting them in bunches in the ring. Because the energies of the beta beams will be low (hundreds of MeV) there would be big backgrounds due to atmospheric neutrinos if the beam were DC--some duty factor is needed. In the slides provided there was a proposal for both a neutrino and an antineutrino beam. One very nice thing about this idea is that it is a very sensible way of "taking advantage of the water cerenkov" technology since you don't need a magnetic field.

The next big news from NNN02 came from Dave Casper's Talk on Water Cerenkov vs Beamlines (power point file) --you can see he's been busy looking at the water cerenkov capabilities for the beta beam. But also (pages 16 and later) you can see he's also calculated what the signal efficiency and background rejection are for the NUMI 10km off-axis beam, and the dipole beam at 3GeV that Fritz came up with for the Homestake experiment. This talk shows the visible energy spectrum for both beams, where the events were required to be single ring electron-like events. Unfortunately the nc background is still at the per cent level, which is not very different from a MINOS-type detector. What's worse is that the efficiency is about 24% from the single-ring cut. This was a very preliminary look at things, though, they may improve.

Finally, we discussed plots Debbie showed at NNN02 at CERN concerning capabilities of different experiments for the numi off-axis beam. What these show is the sin^2(2theta_13) reach of different detectors versus beamline, assuming various signal efficiencies and background rejection capabilities, and assuming the NUMI off-axis beam rates (70 events/kton/year at 730km, and 0.5% nue background under the numu peak). The bottom line (second to last page) is that roughly speaking, a 20kton fine-grained detector which eliminates the nc background does only slightly better than a 50kton water cerenkov (with 1.5% systematic error), and is comparable also to a 4.8kton liquid argon detector. The systematic error matters more for the 50kton water cerenkov than for the other detectors, it turns out--so reducing the systematic error on the other technologies wouldn't help. There was some discussion about how much error was systematic and how much statistical-- it's still mostly (80%) statistical for the masses assumed in the plots. Also, there was some discussion about why the water cerenkov looked different between two different slides--it turns out the horizontal axes on the two different slides are different, which unfortunately caused some confusion. What is marked on the slides IS what is plotted.

Report from Beam Design Group

Mikhail Kostin reported from the Beam design group--from their preliminary work on this the most difficult thing about this new beamline will be designing a target that can take the beam power. This file shows the energy density for several different target materials considered--both solid and liquid. He assumed a 1mm beam sigma--the "rule of thumb" is that you do the best with a target that is 2.5 times as wide as the beam--so he assumed a 5mmx5mm target which was 2 interaction lengths long. This table gives the energy depositions for different materials, the change in temperature, and the melting temperature.

The mercury target would survive, as would the Indium target. However, a sodium or lithium target would be tough because the jet would have to be very very long to get 2 interaction lengths. Doug Michael asked about the tradeoffs between just making the proton spot size larger to get a lower energy density, and making the target less long.

Kirk McDonald agreed to give a talk in 4 weeks about the targeting experiments that has has done for neutrino factory R&D. He also recommended we contact Thieberger about the work he's done on INVAR.


Deborah Harris
Last modified: Fri Jan 25 16:42:50 CST 2002