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
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
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
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.
Last modified: Fri Jan 25 16:42:50 CST 2002