Introduction to Neutrino Factory Physics

1
Introduction to Neutrino Factory Physics
1st Meeting of the Muon Concertation and
Oversight Committee CERN, Thursday 18 April 2002

• Ken Peach
• Rutherford Appleton Laboratory

2
The Standard Model of Particles and their
Interactions
Quarks
Force Carriers
Leptons

Generations of matter
3
The Standard Model

• The Parameters
• 6 quark masses
• mu , mc, mt
• md, ms, mb
• 3 lepton masses
• me, mm, mt
• 2 vector boson masses
• Mw, MZ
• (mg, mg0)
• 1 Higgs mass
• Mh
• 3 coupling constants
• GF, a, as
• 3 quark mixing angles
• q12, q23, q13
• 1 quark phase
• d

Neutrino masses set to 0!
4
The History of the Neutrino

• 1930s Neutrino proposed
• 1940s ???
• 1950s electron neutrino observed, V-A proposed
• 1960s muon neutrino observed, V-A physics
  neutrino oscillations suggested
• 1970s neutral currents, DIS, structure functions
  solar neutrino deficit
• 1980s sin2qw, more structure functions, charm,
  ...
• 1990s more structure functions,sin2qw, LEP (3
  generations) more solar neutrino deficit
  atmospheric neutrino deficit
• 2000s Tau neutrino discovered, even more solar
  neutrinos accelerator oscillation
  measurements???
• 2010s neutrino factory ???? CP violation???

5
The Solar Neutrino Problem

• Solar Neutrino Problem

6
Solar Neutrino Experiments

• Radio-chemical experiments
• i) Chlorine experiments (Davis et al, Homestake
  mine)
• Next slide
• ii) SAGE (Baksan) GALLEX (Gran Sasso)
• ne 71Ga ?71Ge e- 71Ge ? 71Ga (11.4d)
  Electron Conversion
• Threshold 0.23MeV Sensitive to the main pp
  flux!!!!
• Production rate 0.04/tonne/day!
• Water Cerenkov experiments
• i) Kamiokande and SuperKamiokande
• Electron Scattering (ES) nx e-? nx e-
• ii) SNO
• Reactor experiments
• BUGEY, CHOOZ, PALO VERDE, KAMLAND
• (not solar neutrino experiments as such, but in
  the same energy regime with electron
  antineutrinos.)

7
Homestake mine - Ray Davis
Look for solar neutrinos through the inverse b
reaction ne 37Cl ? 37Ar e-
35 d EC
37Cl 4.9MeV
8
Sudbury Neutrino Observatory (SNO)

• Look for neutrino interactions in water
• SuperKamiokande Electron Scattering
• ES nx e-? nx e-
• SNO
• ES (nx e- ? nx e-)
• CC (ned ? p p e-)

• The ES rates can be directly compared SNO and SK
• SK statistically dominated 20kT vs 1kT, 1000d
  vs 200d
• CC rate only sensitive to electron neutrinos!
• SNO/SSM 0.347 ? 0.029 (ne only)
• SK/SSM 0.459 ? 0.017 (ne 15 nm,t)
• Difference is 0.112 ? 0.034 (3.3 s.d.)
• Solid evidence for active non-electron neutrinos
  from the sun
• SNO advantage
• NC (nxd ? nx p n g)

9
SuperKamiokande
10
Summary of solar neutrino experiments
11
Summary of evidence of a neutrino problem

• Solar Neutrinos
• Electron flux 0.3-0.5 expected from Standard
  Solar Model
• Evidence for an energy dependence of the effect
• Probably ne?nm
• Atmospheric neutrinos
• Muon flux 0.5 expected from production
  mechanism
• Strong evidence for energy and length dependence
• Probably nm?nt
• Accelerator reactor neutrino beams
• Mainly limits
• K2K beginning to see an effect
• LSND ?
• Something happens to neutrinos between creation
  and detection!
• Not a small effect (in general) ? 50 loss!
• Not part of the Standard Model new physics

12
2-flavour oscillations

• 2 flavour eigenstates na,nb, 2 mass eigenstates
  n1,n2

• After a finite time, the neutrino flavour
  balance has changed
• Some wrong flavour component has been
  introduced.
• Note
• 1. If the masses are the same there is no
  oscillation
• 2. If a mass is zero, that neutrino decouples
  from oscillation
• 3. The oscillation is a beating phenomenon
• In the lab frame, the propagation is
• Oscillation depends upon
• Dm2ijm2i-m2j

13
2 flavour oscillation

• 2 flavours (a b) 2 mass eigenstates (i j)

14
Neutrino Oscillation Measurements
Probability that a nb appears as a function of
L from a na produced at L0
Signal
15
Summary of signals
16
Impact of SNO on neutrino oscillations
Lisi
17
Some examples
E (GeV) Dm2 (eV2) lE/1.27Dm2 (km) q (deg) L (km) Prob. na ? na Prob. na ? nb Comment
10-2 10-7 80,000 45 1.5 108 0.5 0.5 Solar vacuum
10-2 10-6 8,000 5 1.5 108 1 0.01 SMA
10-2 10-4 80 45 1.5 108 0.5 0.5 LMA
1 10-4 8,000 10 12,000 1 0.03 e Atmos. ?
1 10-3 800 45 8 1 0.0001 m Atmos. ?
10 10-3 8,000 45 8 1 0 m Atmos. ?
1 10-3 800 45 12,000 0.5 0.5 m Atmos. ?
10 10-3 8,000 45 12,000 0.6 0.4 m Atmos. ?
10-1 1 .08 0.1 0.1 1 10-5 LSND
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3 flavour oscillation

• Neutrinos are created as flavour eigenstates
• electron ne , muon nm , tau nt
• but these are not the mass eigenstates
• n1 , n2 , n3
• The flavour eigenstates are a mix of the mass
  eigenstates

U is the Maki-Nakagawa-Sakata Matrix
Prog.Theor.Phys.28 870 (1962).
19
Neutrino Mixing
20
CP-violation

• Ignore sub-leading effects in the CP-even
  transitions

21
Neutrino Mixing what do we know?
absolute mass scale ? Less than few eV
(electron neutrino)
22

• Oscillation phenomenology (CP/T violating)

L/E
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CP-violation and T-violation

• Fundamentally equivalent via CPT Theorem
• But different systematically practically
• CP violation
• Compare neutrino with antineutrino oscillations
• T-violation
• Compare oscillation of (say) electron to muon
  neutrino with muon to electron
  neutrino
• Both experiments difficult
• Flux normalisation
• Matter effects in the earth
• Backgrounds (especially in electron channel)
• Redundancy (in principle)

24
CP-violation what L/E?

• Flux/m2/muon decay at a distance L (m) from muons
  of energy E (gm10E, E in GeV) (10E/L)2/p.
• e.g. Em50GeV, L1000km gives 8 ? 10-8
  n/m2/m-decay
• Significance independent of sinq13
• independent of L
• Effect ? sin2(Dm231L/4E) ? L2 but flux ? L-2
• ? E
• Effect ? sin2(Dm231L/4E) ? E-2 but flux ? E2
  but snp ? E
• Need sin(Dm231L/4E) maximal (p/2)

Em GeV Dm2 eV2 lE/1.27Dm2 km Sin term _at_ 3300 km n Flux/m2 _at_ 3300km/1021 m Comment
20 4 10-3 3,300 1 1012 m Atmos.
20 10-4 160,000 0.04 1012 LMA
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Number of Events?

• CC cross-section f ? 0.67 ? 10-38 cm2 ? En
  (GeV)
• f1 for neutrinos and 0.5 for anti-neutrinos
• Flux 10-4 (Em/L)2/p (L in km, E in GeV)

Em20 GeV, L3300km, Nm1021, MD50kT gives
lt6,000 events
c2s2lt0.01
(sind 1) 20 effect ? ?1200 events
CPV
26
a complicated business

• (Richter hep-ph/0008222)

a 2?2 GFneEn 7.6 10-5 r E Where is the
electron density r is the density (g/cm3) E
is the neutrino energy (GeV)
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Matter v. CP-violation effects
28
nt appearance
29
Basic features of a neutrino factory

• High intensity proton source
• 2-50GeV, 100-1Hz
• High power target
• 4MW (liquid metal, moving solid, )
• Pion capture decay channel, muon capture
• solenoid
• Cooling
• phase rotation, ionisation
• Acceleration
• Storage
• Aim gt1020 muon decays/year
• Em 20-50 GeV
• All are a technical challenge

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What can you do with a neutrino factory?

• (almost) complete study of neutrino mixing
• ne, nm ? nx disappearance
• ne ? nm appearance
• ne, nm ? nt appearance
• and
• m? m- charge conjugate

Note a Neutrino Factory is the only way to
create pure high energy flavour-tagged electron
neutrino beams!
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The Neutrino Factory

• CPV gt 1020 muon decays
• Conventional n beams
• p,m K decay
• Some flavour selectivity
• Contamination
• Fluxes 1017-1018 n
• Reactor n beams
• Pure ne
• Huge Fluxes
• Very low energy (MeV)
• Super Conventional n beams
• p, ( some m) decay
• Flavour selectivity (nm)
• Low Contamination at Elt200MeV
• Fluxes 1018-1019 n?
• The Neutrino Factory

32
CP reach of a neutrino factory
40 kT detector 50GeV muons 1021 useful decays 2
(3) baselines
Gomez-Cadenas
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Challenges

• Machine
• proton source
• target
• pion and muon capture
• muon cooling
• (RLAs)
• muon storage ring
• RADIATION!

• Detector
• technology ( mass)
• magnetic field
• electron charge identification
• tau identification
• cost
• cost
• cost

34
Scientific Challenges

• Theory
• What gives neutrinos mass?
• Why three generations?
• What determines the mixing angles?
• Why are left- right-handed neutrinos so
  different?
• Are they Majorana particles?
• If so, why? If not, why not?
• Is CP/T violation in the neutrino sector a factor
  in the baryon asymmetry of the universe?

• Phenomenology
• What is the impact of Beyond the Standard Model
  on the MNS phenomenology?
• How can absolute neutrino masses be inferred or
  measured?
• What constraints on the MNS matrix? Are there
  loopholes?
• How to show whether Majorana neutrinos? How to
  measure Majorana phases?
• Other implications of finite neutrino masses
  mixing?

35
Summary Conclusions

• A neutrino factory provides the best opportunity
  to study in detail the neutrino sector
• CP physics
• oscillation physics
• new physics?
• (not discussed) A neutrino factory has an
  exciting and extensive programme of conventional
  neutrino physics
• (not discussed) The proton source could provide
  new opportunities for rare decay and precision
  measurements of particle properties
• (not discussed) A neutrino factory is an
  essential first step towards a muon collider
• Technical challenges abound (machine detectors)
• A neutrino factory is needed somewhere at some
  time
• soon?
• Crucial low energy experiments
• Neutrinoless double beta decay
• Neutrino absolute mass measurement
• Cosmological and Astrophysical observations