Scenarios for an entry-level Neutrino Factory

1
Scenarios for an entry-level Neutrino Factory

• Mario Campanelli
• Geneva University

2
LSND and its results

• The LSND experiment took data from 1993 to 1997
  at LAMPF, searching for electron appearance in a
  ?? beam. L30 m, 36 MeVltE?lt52.8 MeV
• ??? ?e
• using reaction ?e p-gte n followed by n p-gt d ?
• Excess of 51.020.2-19.5 8.0 events (first run)
• Total oscillation probability (0.31 0.12
  0.05)
• ????e
• Electron from ?e C-gte-X in range 60ltEelt200 MeV
• Excess of 27.7 6.4 events
• Osc. Probability (0.26
  0.10 0.05)

3
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
4
MiniBOONE

• Currently running at Fermilab, using neutrios
  from booster ltEpgt 8 GeV, ltEngt1 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

5
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 ?e in beam (controlled changing
  decay tunnel length)

CC sample (1 nominal year) 6 105 events
6
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.
7
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 NuFact99 A.deRujula)

8
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

22 (disfavored by atmos solar)
31 (disfavored by short-baseline)
31 scheme collapses into 3-family in the weak
mixing limit, it can never be really ruled out,
while 22 not justified if LSND disproved. 32
(hep-ph/0305255) not studied yet.
9
Counting parameters

• Difference anyway irrelevant in oscillation
  experiments

At least 2 masses for CPv
One phase present, but only CP-even possible
Rotations for neutrinos 123 irrelevant
Ordering rotation matrices according to mass
difference is convenient in case degeneracy is
assumed UMSN(22) U14(?14)U13(?13)U24(?24)U23(?2
3,d3)U34(?34,d2)U12(?12,d1) UMSN(31)
U14(?14)U24(?24)U34(?34)U23(?23,d3)U13(?13,
d2)U12(?12,d1)
10
Bounds from data

• Atmospherics and solars strongly disfavor pure
  oscillation into sterile
• Limits to ?e??? transitions (CHOOZ, CDHS etc.)
  set maximal size of gap crossing angles
• In 22, c223sin2(2?24)c424sin2(2?23)lt0.2
• The LSND signal connects actives and steriles
• In 22, 10-3ltc213c224sin2 (2?23)lt10-2
• In 31 schemes, only few zones of parameter space
  marginally allowed, with very small
  active-sterile mixing
• (e.g. c434s214sin2(2?24) ? 2?10-3)

?s, ?µ, ?e, ?t
11
Neutrino Factory and 4-? 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

12
One mass-dominance approximation

• CP is conserved, and only the four angles
  ?13?14?23(22 only)?24 are relevant. We can
  assume, from solar and atmospherics

• ?12 45 ?34 45º ?m21210-4 ?m2343.5?10-3
  (22)
• ?12 22.5 ?13 13 ?34 45º (13) (Fogli Lisi
  Marrone Scioscia)

Donini-Meloni studied sensitivity to gap-crossing
angles in 22 and 31 schemes, for a NF of Eµ20
GeV, 1021 useful muons, 1 ton (1 m3 water!)
detector with eµ0.5, et0.35 placed at 1 km
distance. For simplicity, only negative muon
decays considered. Wrong-sign background assumed
O(10-5).
13
22 scheme

• sin2?13 µ- disappearance

sin2?23 µappearance
sin2?14,sin2?14 t- appearance
14
31 scheme
sin2?14,sin2?14 µ appearance

• sin2?34 t appearance

15
CP violation

• In 3 families, magnitude of effect depends on
  ?m212, while in 4 families on ?m223, so larger,
  can go closer and have small matter effects.
• Here we consider integrated asymmetry,
• ACP(d) (R- -R) / (R- R)
• where RN(la)/N(lß)
• as a function of d, considering known the values
  of the mixing angles

16
CPV sensitivity in 22 schemes
?e???
?????

• ?e???

?e???
17
CP violation sensitivity in 31 schemes
?e??? d20,d390
?e??? d2d315,45, 90

• ?e???

18
Summary on physics

• Obviously, if LSND is confirmed, neutrino physics
  will receive a great boost, due to the relative
  ease to perform measurements.
• t 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.

19
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)

20
NF scheme

• Possible savings

Detector at 10-20 km
21
Pricing

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

22
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

23
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 µs,
Eµ 2 GeV, 100 ton detector 10 meters from machine
24
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 ps
• ps decay within 1st turn
• ms take 200 ms to decay to nes, nms and es
• Debuncher captures 1 x 1011 antiprotons/hour
• 11 pm captured
• 5.2 x 1014 nes 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 ne cross section at 2 GeV
• 16 nes/year from Quasi-elastic and single p
  interactions
• Only useful to calibrate detector response to
  muon and electron neutrino and crosscheck flux
  calculations.

25
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
  t 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