# Presentation: 531447

## Scenarios for an entry-level Neutrino Factory

- Mario Campanelli
- Geneva University

## LSND and its results

- The LSND experiment took data from 1993 to 1997 at LAMPF, searching for electron appearance in a  beam. L=30 m, 36 MeV<Eν<52.8 MeV
-  e
- using reaction e p->e+ n followed by n p-> d γ
- Excess of 51.0+20.2-19.5 ± 8.0 events (first run)
- Total oscillation probability:      (0.31 ± 0.12 ± 0.05)%
- e
- Electron from e C->e-X in range 60<Ee<200 MeV
- Excess of 27.7 ± 6.4 events
- Osc. Probability:                         (0.26 ± 0.10 ± 0.05)%

## Karmen results

- Karmen (I and II), covering similar parameter space using a pulsed beam did not observe any oscillation.

- A corner of the parameter space is still permitted by the combination of the two experiments due to the slightly different L/E of the two experiments

## MiniBOONE

- Currently running at Fermilab, using neutrios from booster <Ep>= 8 GeV, <En>~1 GeV Main differences wrt LSND:
- 30 times more energy
- 20 times more distance
- Cerenkov light 4 times larger than scintillation
- Neutron capture not used
- Neutrinos instead of                                      (mainly) antineutrinos

## The MiniBOONE philosophy

- The experiment aims at large electron signals if LSND is correct

- Background is also large:
- 600 events from muons
- 600 events from pions
- 1800 events from νe in beam (controlled changing decay tunnel length)

- CC sample (1 nominal year):
- 6 105 events

## After 1021 POT (2 nominal years)

- Build another detector (BOONE) for precision measurements of oscillation parameters

- Run with anti-neutrinos to exclude non-oscillation effects

- So far, 10% taken, running at half the planned rate, but improving. Problems due to radiation issues in the booster tunnel.

## Interpretation of a positive result

- Great excitement! Need to add new pieces to the puzzle
- If signal only in antineutrino mode, lepton flavour and/or CPT violated
- If seen in both modes, we need sterile neutrino(s).
- Normally people tend to:
-  (from NuFact’99 A.deRujula)

## Scenarios with 4 neutrinos

- Sterile neutrinos are like cherries, if you have one you probably have more than one.
- Depending on mass hierarchies, even the simplest case contains several scenarios:

- 3+1 (disfavored by short-baseline)

- 2+2 (disfavored by atmos+ solar)

- 3+1 scheme collapses into 3-family in the weak mixing limit, it can never be really ruled out, while 2+2 not justified if LSND disproved. 3+2     (hep-ph/0305255) not studied yet.

## Counting parameters

- Difference anyway irrelevant in oscillation experiments

- At least 2 masses for CPv

- Rotations for neutrinos 123 irrelevant

- Ordering rotation matrices according to mass difference is convenient in case degeneracy is assumed:
- UMSN(2+2)= U14(θ14)U13(θ13)U24(θ24)U23(θ23,δ3)U34(θ34,δ2)U12(θ12,δ1)
- UMSN(3+1)= U14(θ14)U24(θ24)U34(θ34)U23(θ23,δ3)U13(θ13, δ2)U12(θ12,δ1)

- One phase present, but only CP-even possible

## Bounds from data

- Atmospherics and solars strongly disfavor pure oscillation into sterile
- Limits to νe transitions (CHOOZ, CDHS etc.) set maximal size of gap crossing angles
- In 2+2,    c223sin2(2θ24)+c424sin2(2θ23)<0.2
- The LSND signal connects actives and steriles:
- In 2+2,    10-3<c213c224sin2 (2θ23)<10-2
- In 3+1 schemes, only few zones of parameter space marginally allowed, with very small active-sterile mixing
- (e.g. c434s214sin2(2θ24)  210-3)

-  νs, νμ, νe, ντ

## Neutrino Factory and 4-ν scenarios

- Many simultaneous channels of the NF are a clear benefit to study these complicated scenarios.
- Interest is reciprocal: if LSND is true, larger probabilities mean an entry level NF with reduced fluxes, smaller detectors and shorter baselines

- Several works done:
-  Donini, Gavela, Hernandez, Rigolin hep-ph/9910516
- Barger, Geer, Raja, Whisnant hep-ph/0007181
- Donini, Gavela, Hernandez, Rigolin hep-ph/0007283
- Donini, Meloni hep-ph/0105089
- Donini, Meloni hep-ph/0105163
- Donini, Lusognoli, Meloni hep-ph/0107231

## One mass-dominance approximation

- CP is conserved, and only the four angles θ13θ14θ23(2+2 only)θ24 are relevant. We can assume, from solar and atmospherics:

- θ12= 45°; θ34= 45o; Δm212=10-4 Δm234=3.510-3 (2+2)
- θ12= 22.5°; θ13= 13°; θ34= 45o (1+3) (Fogli Lisi Marrone Scioscia)

- Donini-Meloni studied sensitivity to gap-crossing angles in 2+2 and 3+1 schemes, for a NF of Eμ=20 GeV, 1021 useful muons, 1 ton (1 m3 water!) detector with εμ=0.5, ετ=0.35 placed at 1 km distance. For simplicity, only negative muon decays considered.
- Wrong-sign background assumed O(10-5).

## 2+2 scheme

-  sin2θ13: μ- disappearance

-  sin2θ23: μ+appearance

- sin2θ14,sin2θ14 : τ- appearance

## 3+1 scheme

-  sin2θ34: τ appearance

- sin2θ14,sin2θ14 : μ+ appearance

## CP violation

- In 3 families, magnitude of effect depends on Δm212, while in 4 families on Δm223, so larger, can go closer and have small matter effects.
- Here we consider integrated asymmetry,
- ACP(δ)= (R- -R+) / (R- +R+)
-  where R±=N(l±α)/N(l±β)
-  as a function of δ, considering known the values of the mixing angles

## CPV sensitivity in 2+2 schemes

- e

- 

- e

- e

## CP violation sensitivity in 3+1 schemes

- e

- e δ2=0,δ3=90°

- e δ2=δ3=15°,45°, 90°

## Summary on physics

- Obviously, if LSND is confirmed, neutrino physics will receive a great boost, due to the relative ease to perform measurements.
-   identification becomes key issue due to complicated parameter space. Simple muon identification gives much worse understanding of oscillation picture.
- To a first approximation, sensitivity scales as N
- Due to the mass governing the effect, the study of CP violation requires detector size and baseline comparable to measuring parameters in a 3-family scenario.
- “simple” parameter measurement in 4 families requires modest effort- detector 2 order of magnitude closer and 4 lighter.

## Entry-level NF?

- We can consider a 100 ton detector, and lower machine power to 21018 μ/y (and 5 years run)
- Beware: due to beam width of ~1m, detector has to be cigar-shaped!
- Aiming to such a low intensity, we can assume:
- No need for a new proton driver (JHF I or even FNAL booster could be sufficient)
- No special radiation-hard targeting
- No need for cooling
- Energy: could be reduced, but not by large amounts (cannot gain like 1/L2 going closer since already embracing all beam with 1 m detector diameter)

## NF scheme

- Possible savings

- Detector at 10-20 km

## Pricing

- Overall, a total saving of about $600M could be envisaged (probably more due to lower cost of other components)

## What if MiniBOONE finds nothing?

- LSND could still be right, and have seen instead of oscillations LFV like +e+l or -e-el.
- It was shown (Bueno, MC, Laveder, Rico, Rubbia hep-ph/0010308) that a low-energy entry-level NF and a 10 ton LAr detector located 100 m from the machine improves limits on these decays, reaching sensitivities relevant to the LSND effect

## An even smaller machine

- A NF with ~1015 μ /y (muons trapped in the CERN AD or FNAL debuncher) has no interest for neutrino oscillations. However, such a machine could be used to measure neutrino cross section at low-energy with precision O(10%), much better than present data

- MC Navas-Concha Rubbia, hep-ph/0107221, 1015 μ’s, Eμ =2 GeV, 100 ton detector 10 meters from machine

## A poor-(wo)man NF?

- It recently came out (B.Fleming) that neutrinos from muons trapped in FNAL debuncher can be seen in MiniBOONE:
- 8 GeV negatives captured ps and s
- s decay within 1st turn
- s take ~200 s to decay to es, s and es
- Debuncher captures 1 x 1011 antiprotons/hour
- 1:1  p: captured
- 5.2 x 1014 es produced by debuncher/year (assumes 100 hr/wk)
- 13% produced off each straight section, the rest in a circle
- 6.24 x 1012 of these hit MiniBooNE
- Folding in the e cross section at ~2 GeV
- 16 es/year from Quasi-elastic and single  interactions
- Only useful to calibrate detector response to muon and electron neutrino and crosscheck flux calculations.

## Conclusions

- After many years of data analysis and checks, LSND effect is still alive and represents arguably the largest “mystery” of experimental neutrino physics
- In case of positive MiniBOONE result, sterile neutrinos will leave their limbo
- The neutrino factory coupled with a detector with τ identification is the best machine to explore them
- Due to larger mass difference scales, physics reach will come with far less effort than in 3 families
- LFV can be explored if no signal at MiniBOONE
- Very low-intensity NF in parasitic mode, cross-sections and calibration studies
- Hope nature prepared a surprise for us, otherwise this talk (and hundreds of papers) would mostly be “sterile”