Minutes from December 7 Meeting
Attendees: Steve Geer, Nikolai Mokhov, Mikhail Kostin, Valeri Balbekov,
Debbie Harris, Craig Moore, Fritz DeJongh, Bob Bernstein, Ray Stefanski
(and possibly others...)
Topic 1: New Proton Driver Study
The first piece of news from this meeting is that there will be a new
proton driver study
which will have two prongs--one studying the
machine itself, and one studying the physics. The beam study will be
headed by Steve Holmes, and the physics study will be headed by Mike
Shaevitz. The physics study will cover neutrinos, kaons, and other
physics, and hopefully this group will get very busy working on the details of
the neturino section.
The beam study is motivated (among other things) by
an Idea from Bill Foster on an 8GeV Linac based on TESLA R&D. The
goal for the machine study is that they would like to figure out a way
to make a 2MW proton source. (2MW at 120GeV). So there are a few
ways superbeams could be made--either using the 2MW source at 120GeV,
or using the 2/n source at 120/n GeV, or finally, using the 8GeV protons
If we're aiming for a 3GeV neutrino beam 8GeV is probably too
low an energy, on the other hand we wouldn't have to worry about kaon
production (Ray Stefanski underscored this!). Also, if we are aiming
for a 1GeV neutrino beam because of "second peak" running then 8GeV
might be enough proton energy. Since it's expected we're in the
background-dominated regime we're not only concerned with getting the
highest flux of neutrinos, it has to be a very clean beam. In other
words, the figure of merit might be sqrt(background)/signal, or
0.xx*background/signal, assuming an xx% uncertainty on background prediction.
Neutrino Beamline Design Team--new blood!
So, this meeting was the first one
(in a series) that we will have with Nikolai
Mokhov and Mikhail Kostin, who will be working on possible beamline designs
for a superbeam from Fermilab to Homestake. The first superbeam study this
group did was a very broad study, making general assumptions, and looking
at a variety of detectors and baselines, assuming the NUMI or JHF fluxes,
and assuming "variable" background levels. So now we would like to
do a more detailed study where we pick one baseline, one detector,
and come up with the best beamline design (and presumably we should look
at running on the peak but also the "next peak").
Then we can see how excursions from this "baseline" will affect the
physics. (excursions meaning other detectors, modifications in the beamline
Nikolai and Mikhail will be looking at issues such as: designing a target
station that can take a 2MW proton power, because it is generally expected
that graphite targets wouldn't survive above 1MW or so. Liquid metal
jets might work, and are being studied for neutrino factories already.
In fact, the environment for a superbeam liquid metal jet target would be
less daunting than one for a neutrino factory, since for a neutrino factory
the target has to be in the middle of a solenoid which has to collect
hte low energy pions. For a superbeam the target can be more upstream of
the first focusing device. Nikolai pointed out that for a 4MW source
(which is what's assumed for a neutrino factory) a 20m/s jet velocity
has to be obtained. Already folks have achieved 2-3 m/s jet velocity.
Possible "tricks" that have been considered for cleaning up the beams
are beam stops (to eliminate the high energy tails), a dipole in the
beamline (to eliminate the neutral kaon-based contamination) or "going
off axis"). Certainly all of these will be considered...
Fritz DeJongh is going to be
attending the NNN01 workshop in Louisiana next week, and hopefully will
get the water cerenkov community in on this at the ground level. Our basline
assumption about the detector will be water cerenkov, with an assumption
of a few hundred ktons mass, probably.
The time scale for this study is to have something quantitative
by next april, when there will be a workshop at Fermilab on
intense proton sources.
Update on Study Group Activities
Fritz DeJongh talked about what we've been studying so far in our group
with the pbeam (fast monte carlo used by NUMI) simulations--and showed
how putting a dipole in the beam gives a nice sharp high energy cutoff
in the neutrino event energy distribution, which is more important than a
sharp low energy cutoff. Also, Fritz showed slides on the off-axis
concept, and how given 120geV protons, for perfect focusing the
best signal rate occurs (assuming no background, so again maybe not the right
figure of merit) at about 3GeV. (for a 725m decay pipe).
Slides from this meeting which Fritz will also show in Louisiana are
located here. (This file shows the
whole talk, not all of which got shown at the December 7 meeting).
What to shoot for in neutrino beamline design:
An idea for a quick study that could be done would be the following:
one can parameterize a "general neutrino beam" as a gaussian peak
followed by a high energy tail. The two parameters describing this
general beam could be A) the fractional width of the peak of the event
energy distribution for cc events (w) and B) the height or
integrated contents of the tail (t). What would be useful for Nikolai
and Mikhail would be to know what w and t to shoot for: below some w you're
losing event rate, above some w you're not at the peak any more. Also,
the nc background is a function of both w and t. As was remarked above,
though, the figure of merit could be sqrt(background)/signal or it could
be 0.xx*background/signal if you're in systematics dominated land.
Last modified: Thu Feb 7 12:47:04 CST 2002