1. BEAMS FOR OSCILLATION SEARCHES

1.1 What is the range of useful energies for

1.1.1 ν_τ appearance searches

1.1.2 μ⁺/μ^- appearance searches

1.1.2 disappearance searches

1.2 Is the beam polarization relevant for oscillation searches?

1.3 Is the conventional neutrino beam produced by hadrons (input to muon accumulator) better suited for τ appearance searches?

1.3.1 Intensity issue

1.3.2 Beam composition

1.3.3 Limitations of a hadron beam (ν_e-->ν_τ)

1.3.4 Practical aspects (does it make sense to build TWO beams?)

2. POSITIVE AND/OR NEGATIVE MUONS?

2.1 Neutrinos vs antineutrinos. Is it easier to separate μ⁺ or μ^- from the background?

3. DETECTORS

τ appearance searches

Appearance Wrong Sign Muon searches

Disappearance searches

In optimizing the sensitivity in each of these measurements, we should clarify the following questions:

- Do we need several detectors for the different measurements ?

- what is the level of irreducible background that can be achieved with each technique ?

This is important because for a given intensity of the beam the level of irreducible background fixes the desirable distance between source and detector. Conversely, for given distance, the i.b. determines the maximum intensity that makes sense to hope for.

- Should we have detectors at different long base lines ?

Atmospheric neutrinos

Also we should think of after-superK atmospheric neutrinos detectors. In particular we should explore the possibility of a universal detector which can do disappearance and atmospheric neutrino searches.

We should also think of near detectors for non oscillation physics.

3.1 DETECTOR FOR TAU APPEARANCE SEARCHES

One important advantage of this beam is that we can search for ν_μ -> ν_τ as well as ν_e -> ν_τ transitions, which contain different information about the neutrino mixing matrix. We should think of detectors that are able to search for both transitions.

Tau appearance experiments at the neutrino factory must improve considerably the sensitivities to taus of NUMI/LNGS experiments. We should aim at least to the canonical one order of magnitude improvement (in the number of observed taus, assuming that this number is not zero).

Tau appearance experiments will have to deal with very large intensities, resulting in (at least) 10⁴ CC per kiloton/year. Thus, Tau appearance detectors must deal with a background which will be (at least) one order of magnitude larger than the background expected in the "present generation" LBL experiments.


We should study how well the different techniques of detecting taus can do:

3.1.1 Detectors based on Vertex criteria (tau kink)

3.1.2 Detectors based on Kinematical criteria

3.1.3 Hybrid detectors?

3.2 DETECTORS FOR WRONG SIGN MUONS SEARCHES

In addition to its unprecedent intensity, a NU factory presents the advantage that it contains only two flavours of opposite charge conjugation. This allows to have appearance chanels other than tau production: ie. the production of wrong-sign muons. This measurement would be extremely sensitive to the angle of the mixing matrix theta_13 (in a three family mixing notation). Furthermore if this angle is not too small, the measurement of wrong sign muons could give the most sensitive measurement of Δm².

We should think of the detector requirements for a precise mu+/mu- separation. This will require large mass magnetized detectors. We should aim at rejecting background at the level of 10^-4 or 10^-5.

3.3 DETECTORS FOR DISAPPEARANCE MEASUREMENTS

The clean and well defined neutrino spectrum of the NU factory opens the possibility of very sensitive disappearance measurements of the two flavours in the beam. These measurements are sensitive to a different combination of the mixing angles than the appearance measurements and so add very valuable information.

We should think of detector requirements for counting muons and electrons.


3.4 'NEAR' DETECTOR CONSIDERATIONS

In a facility like a NU factory it seems desirable to consider one or more than one near detectors, with the goal of performing a precise measurement of interaction cross sections as well as the intrinsic backgrounds to the oscillation searches.

Such detector(s) would also be of interest for a program of precision non-oscillation neutrino physics.
The questions to discuss:

- What are the near detector requirements ?

- How many detectors are needed ?