(Muon Ionization Cooling Experiment)

1
the MICE experiment

• (Muon Ionization Cooling Experiment)

A Neutrino Factory (NF) is a device conceived to
produce a large amount of neutrinos (nm ,ne) in a
very clean way, due to the underlying physical
process of their generation. These
characteristics make the NF a really powerful
tool to investigate the ultimate properties of
the leptonic sector (q13 mixing angle and the
measurement of a leptonic CP violation effect).
To reach these goals we need to store
1021 muons/yr. A possible design for a NF
foresees to store 20 GeV muons in a ring where
they decay along the straight sections (m ? nm
ne e) generating the neutrinos suitable for the
physics where the phenomenon of neutrino
oscillation is exploited to study the properties
of neutrinos with great precision. Since the
mechanism of neutrino oscillation is used in the
downstream detector the optimal baseline is of
the order of few 1000 km. A schematic view of the
NF is shown in fig. 1 Muons are tertiary beams
and are produced with a high emittance therefore
they need to be cooled before acceleration. The
cooling must also be fast, given the short
lifetime of the muon (t 2 ms) this fact puts
conventional systems (e.g. stochastic cooling)
out of the game. Ionization Cooling,
instead, appears to be the only practical
technique. The principle (illustrated in fig.2)
is quite simple layers of an absorber material
and RF sections are alternated. The absorber
causes an energy loss by ionization of the
charged particle crossing the medium, the RF
cavity accelerates the muon in the forward
direction. The cooling effect is somewhat spoiled
by the multiple scattering always present when
going trhough a material. At the proper initial
emittance the overall effect is a reduction in
the transverse emittance. The mechanism is well
known to work , theoretically. The goal of MICE
is to prove the feasibility of this principle by
building a portion of a cooling channel and
measuring its performances MICE will be built at
the Rutherford Laboratory (UK) in 6 steps,
starting from a very basic configuration to a
final layout displayed in the cartoon of fig. 3
and on fig.4. It is an international collaboration
involving institutions from UK, Europe, United
States, Japan and China.
Fig. 1 a possible layout of the Neutrino Factory
Fig. 2 principle of muon cooling and theoretical
formula with the effects of cooling and multiple
scattering
Optmizing the matching coil currents
Fig. 3 emittance reduction in MICE
emittance variation vs initial e
BZ along axis (T)
b (m)
Transmission of the channel
downstream
SPE (m rad)
MICE steps and phases
? low Z absorber material ? tight focus (low b
function) ? H2 is best absorber material
PHASE I
Emittance vs amplitude
PHASE II
Poster session, CERN accelerator school 2006,
Zakopane
m.apollonio_at_physics.ox.ac.uk