1. Based on material presented at various meetings
(last the neutrino town by Alan Bross, Ken Long and others

2. The main messages
the critical elements that are needed for precision measurements of the
neutrino oscillation parameters
why HyperK and DUNE really need this.
how can this be provided by a muon storage ring neutrino beam facility.
what concrete steps are being taken
other synergies

3. Alain Blondel T2K latest results and prospects

4. sin  term is CP violating cos  term is not.
sensitivity to  (precision on  measurement) is driven by
sin  term if  is close to 0 or   rate asymmetry e vse
cos  term if  is close to /2  E shift, common to e ande
different systematics!
Alain Blondel T2K latest results and prospects

5. For  measurement : measure e and e
in proctice
NFAR (e) / NNEAR () which is critically dependent on
the energy reconstruction also affects other parameters (cos, m223 , sin2 23 and sin2 213)
This will be affected by uncertainties on cross-section and efficiency.
In T2K/HyperK as well as NOVA/DUNE we (will) use muon neutrino beams which are
~99% muon neutrino with an (anti) electron neutrino component of (0.3 – 2)%
direct measurement of electron neutrino cross-sections and topologies
and their differences w.r.t. muon neutrino events are difficult to measure
The theoretical difficulty lies in the interplay of the lepton mass effect (106 MeV) with the
-- nuclear physics effects: binding energy Eb = 23 MeV, equiv. Fermi Motion PF = 200 MeV/c)
-- pion production threshold (140 MeV)
 cross-section, selection efficiency and energy recontruction bias are different between
 , e ;  ,e
and should be measured
Parametric model fitting (which is done now) is only as good as the model and errors estimates are problematic.

6. It has been observed since 1998 that muon storage rings would provide well calibrated
neutrino beams
-- well known flux and energy scale (from muon storage ring current and magnets)
-- rigourously equal number of (anti) [muon and anti-electron] (anti) neutrinos (for - [+] )
m- -> e- ne nm and m+ -> e+ ne nm
m polarization controls ne flux:
m+ -X> ne in forward direction
Furthermore the difference between
the fluxes generated by muons of
two different energies is narrow
spectrum near the falling edge
nearly monochromatic beam
ideal for energy resolution and
energy bias measurements

7. NUSTORM
momentum adjustable between 1-6 GeV
-- first flash of muon (anti) neutrinos from the decay of injected pions.
-- then muons from pion decay are stored in the ring.
-- cross-sections to be measured in near detector similar to HyperK or DUNE ND
(water, scintillator and Liq. Argon targets -- also probably iron)
 preferably magnetized for energy reconstruction?
-- require precise instrumentation for number of stored muons and polarization
-- storage time at 6 GeV is 5x144s (fast extraction of short spill required)
-- high field magnets would be highly beneficial by reducing the size of the facility.

9. muons are born longitudinally polarized in pion decay (~18%)
Muon Polarization
muons are born longitudinally polarized in pion decay (~18%)
depolarization is small (Fernow &Gallardo)
effects in electric and magnetic fields is (mostly) described by spin tune:
which is small: at each kick q of a 200 MeV/c muon the polarization
is kicked by n.q = q
in the high energy storage ring polarization precesses. Interestingly
= 0.5 for a beam energy of GeV: at that energy it flips at
each turn.
Alain Blondel NUFACT03

10. muon polarization is too small to be very useful for physics
(AB, Campanelli) but it must be monitored.
In addition it is precious for energy calibration (Raja&Tollestrup, AB)
a muon polarimeter would perform the momentum analysis of the
decay electrons at the end of a straight section.
Because of parity violation in muon decay the ratio of high energy
to low energy electrons is a good polarization monitor.
Alain Blondel NUFACT03

11. # positons with E in [0.6-0.8] Em to number of muons in the ring.
muon polarization
here is the ratio of
# positons with E in [ ] Em
to number of muons in the ring.
 There is no RF in the ring.
spin precession and
depolarization are clearly visible
This is the Fourier Transform
of the muon energy spectrum
(AB)
amplitude=> polarization
frequency => energy
decay => energy spread.
DE/E and sE/E to 10-6
polarization to a few percent.
Alain Blondel NUFACT03

12. preliminary study at CERN

13. possible location at CERN

14. Final comments:
A facility dedicated for direct measurements of the neutrino interaction parameters
that are needed for oscillation experiments
-- neutrino interaction cross-sections
-- neutrino flavour/charge identification
-- neutrino selection efficiencies
-- neutrino energy reconstructions
 clearly spelled out requirement for the future of the long baseline experiments
A muon storage ring seems to be able to provide these answers
It will also be an important step towards muon colliders
first high intensity muon storage ring (development of operation and instrumentation)
search for synergies and complementarities neutrino community, accelerator community, technology (High field magnets etc..)
make the case that this is worth it for HyperK and DUNE (maybe it is too good?)
develop a work program towards the solution
 need to produce a cost estimate, reasonable time scale etc….

15. Neutrino town meeting recommendation

16. submission to European Strategy for Particle Physics

18. RECOMMANDATION:
Extracting the most physics out of DUNE and HyperK will require
ancillary experiments:
CERN should continue improving NA61/SHINE towards
percent level flux determinations;
2) a study should be set-up to evaluate the possible implementation, performance and impact
of a percent-level electron and muon neutrino cross-section measurement facility
(based one.g. ENUBET or NuSTORM) with conclusion in a few years;