Cafe neutrino meeting minutes (11/16/09)
Present: E. Benedetto, A. Blondel, F. Dufour, I. Efthymiopoulos, C. Hansen, A. Ioannisyan, G. Prior, E. Wildner
Outcome of the GSI meeting (E. Benedetto): .pdf
Visit was to discuss the production ring issue. Agenda and talks posted on the beta-beams
website. Presentation of GSI facility by C. Dimipoulo. Presentation of
A. Khoukaz on production of cluster-jet beams. The gas is precooled and
condensates into clusters of molecules. In principle any shape of the
gas beam can be produced by changing the skimmers/collimator shape.
Beta-beams need a wedge shape. But the density seen by the particle
beam crossing should be the same. The order of the wedge is few cm, an
order 3-4 of magnitude bigger than what is used at GSI. Not trivial to
achieve. Density from GSI is order of 1014 atoms per cm2. But from C. Rubbia paper we have 1019
order. Need to calculate what is needed and relative to what
(transverse to the target or beam). Numbers will be checked.
Concerning the vacuum does not seem to have issues. GSI is interesting
by hosting an experiment either at GSI or COSY. At GSI there is almost
all kind of ions that can be sent in the experimental storage ring.
COSY has protons and deuterium ions and is a little high in energy in
comparison to what beta-beams would need. Idea is to demonstrate the
principle of gas beam and wedge but not with the beta-beams ions.
Stochastic cooling is taking a long time and probably electron cooling
is too long too, so ionisation cooling would be interesting. Can we
make not a geometrical wedge with the correct density but have a
density profile instead that fill the same density condition than an
geometrical wedge ? Problems with the gas collector. Need to look into
the collection system. Temperature pressure conditions are 20 K, 18
bar. Will discuss with S. Maury who has experience with gas jets. At
GSI they are interested by completing a full cycle of stochastic,
electron and ionisation cooling. Beta-beams could find some synergy
there. Side question for neutrino-factories, what other possible metal
beside Hg ? There is Bi but hot too. No pratical applications for 6He ions outside the interest of beta-beams. 8Li is one of the ions that could be done the same way than He is done (spallation). And maybe 8B. Christian H. is also looking at some other possibilities for the ions.
Beta-beams duty factors (E. Wildner): .pdf
High-Q issue is if we send the ions to a longer baseline, the flux at
the detector is smaller. Merit factor can be written as M = γ/Q. If Q
increases, M decreases and the flux in the detector need to be
increased.Would need to produce five times more ions.
Duty factor is the ratio of signal over noise. For noise suppression,
need to let the neutrino through in very short intervals and involve
throwing away half of the ions produced. The bunch is shorten and the
beam is squeezed at maximum but the limitation comes from the bucket
which cannot take anymore. The ions will hit the collimators.
Detector geometry issue, Water Cherenkov (WC) do not do well at high
energy. There is no written up performance of LAr at 2 GeV and it is
needed. SPS for CNGS is doing now 4.1013 so 5.1013 does not seem unreasonable but 7.1013
is not in what can be done right now. About efficiencies, if we take a
WC at low energy 500 MeV in water, reconstruction with 100% efficiency.
For higher energies the pions production obliges to put a cut on the
mininum energy for the reconstruction which limits the efficiency to
70%, that is probably the number quoted as 6 times more efficiency for
LAr in comparison with WC. Example of a super-beam 100 MeV-2 GeV if the
LAr detector is three times smaller than the WC it comes about the same
efficiency with a detector sitting 1000 km away. How does this compare
with for beta-beams energies. LAr does not do as well for muon
neutrinos, need to be examined. Question whether or not we need high-Q
ions is also on the table for the SPC recommendations.
Physics reach as fonction of the duty factor(C. Hansen): .pdf
Study done by E. Fernandez-Martinez. Simulated the atmospheric background. Put a cut in the beam direction. The detector suppression
factor is equal to the decay ring duty cycle (DC). In FP6 DC was 0.45%
for 6He and 18Ne
achieved fluxes. Assumes a WC detector to Gran-Sasso, previous study
was for a baseline to Frejus. Looked at different cases with different
years number for each ions. Sensitivity for mass hierarchy is not
great. 1014/20 intensity is already a limit according to the
RF specialists. Need to start with a reasonable duty factor value and
use this one for further study for the time being. Comparison with the
physics reach for T2KK (paper draft).
Tuesday December 1st 10:30 am