Cafe neutrino meeting minutes (11/16/09)
Present: E. Benedetto, A. Blondel, F. Dufour, I. Efthymiopoulos, C. Hansen, A. Ioannisyan, G. Prior, E. Wildner

Agenda:

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).

Next meeting:
Tuesday December 1st 10:30 am