Neutrino Lectures - Lake Louise

1
Are Our Ancestors Neutrinos?Or How Can a Small
Mass Make a Big Difference

• Michael Shaevitz
• Columbia University
• Neutrinos and the Standard Model (Before 1995)
• Neutrino Masses and Mixing (The Late 90s
  Revolution)
• Many Surprises(Theorists had it all wrong)
• ? New Neutrino Standard Model
• Going Beyond the New Neutrino Standard Model
  (The Next Revolution?)
• Are there more types of neutrinos? CP violation?
• Are neutrinos a key to explaining
  matter-antimatter asymmetry in the Universe?

2
The Big Bang
Dark Matter?
?nm
nSterile?
gCMB
?nSterile?
?nt
gCMB
gCMB
Dark Energy?
?ne
3
The Three Big Questions of Cosmology

• What is the Dark Energy that is causing the
  Universe to accelerate? ? We
  havent got a real clue
• What is the Dark Matter that makes up about 25
  of the Universe? ? We have some
  good candidates but no detection
  (supersymmetric particles, axions, )
• What caused the Universe to be composed of Matter
  and no Anti-Matter? ? Some
  theoretical ideas with experimental input
  Leptogenesis from CP violations with
  neutrinos is a good candidate

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Standard Model of Particle Physics
6
Neutrinos in the Standard Model

• Neutrinos have no electric charge (neutral)
• Neutrinos only interact through the weak force
• Neutrino interaction thru W and Z bosons exchange
  is (V-A)
• Neutrinos are left-handed(Antineutrinos are
  right-handed)
• Neutrinos are massless
• Neutrinos have three types
• Electron ne ? e
• Muon nm ? m
• Tau nt ? t

7
Highlights of Neutrino History
Reines Cowann Detector
Nobel 2002 Observation of neutrinos from
the sun and supernovae
Davis (Solar ns in 1970) and Koshiba (Supernova
ns 1987)
8
Neutrino Interactions

• W exchange gives Charged-Current (CC) events and
  Z exchange gives Neutral-Current (NC) events

In CC events the outgoing lepton determines if
neutrino or antineutrino
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Neutrino Cross Section is Very Small

• Weak interactions are weak because of the massive
  W and Z boson exchange ? s weak
  ? GF2 ? (1/MW or Z)4
• For 100 GeV Neutrinos
• s(ne) 10-40 and s(np) 10-36 cm2
  compared to s(pp) 10-26 cm2
• A neutrino has a good chance of traveling through
  200 earths before interacting at all!
• Mean free path length in Steel 3?109 meters!
  (Need big detectors and lots of ns )

MW 80 GeVMZ 91 GeV
10
Neutrinos in the Standard Model Are
Left-Handed(Helicity and Handedness)

• Handedness (or chirality) is Lorentz-invariant
• Only same as helicity for massless particles.

• Helicity is projection of spin along the
  particles direction
• Frame dependent (if massive)

• If neutrinos have mass then left-handed neutrino
  is
• Mainly left-helicity
• But also small right-helicity component ? m/E

• Neutrinos only interact weakly with a (V-A)
  interaction
• All neutrinos are left-handed
• All antineutrinos are right-handed

Right-handed neutrinos do not interact in the
Standard Model ? ? Sterile
neutrinos
11
Neutrino Interaction Processes
(Deep Inelastic Quark Scattering)
12
Neutrino Sources for Experimentation
Big Bang Neutrinos at 2x10-4 eV ? Probably not
detectable!
13
Neutrino Detectors
ns from sunor atmosphere
Use earthto shield detectorfrom cosmic
rays(mainly muons)
Lower Neutrino Energy ? More depth (10 m 2000
m)
nm make muonsne make electrons
? make light(Use pattern oflight to id type)
ns from accelerator beams(Use earth to
shieldfrom beam muons)
Detector Vat of 1 to 20 kton of
oil, water, or liquid scintillator
with light detectors (PMTs)
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The MiniBooNE Detector

• 12 meter diameter sphere
• Filled with 950,000 liters (900 tons) of very
  pure mineral oil
• Light tight inner region with 1280
  photomultiplier tubes
• Outer veto region with 241 PMTs.
• Oscillation Search Method Look
  for ne events in a pure nm beam

15
Particle Identification

• Separation of nm from ne events
• Exiting nm events fire the veto
• Stopping nm events have a Michel electron after a
  few msec
• Cerenkov rings from outgoing particles
• Shows up as a ring of hits in the phototubes
  mounted inside the MiniBooNE sphere
• Pattern of phototube hits tells the particle type

Stopping muon event
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Muon Identification Signature m ? e nm
ne after 2msec
Charge (Size)
Time (Color)
17
Neutrino Mass
18
Making Neutrinos Matter

• Standard Model assumes that neutrinos are
  massless
• No symmetry property or theoretical reason for mn
  0
• Neutrinos are partners of the massive charged
  leptons
• Could imply right-handed n s, Majorana n ?n
  or sterile ns
• Neutrino mass hierarchy ?

t m ent nm ne

• Cosmological Consequences
• Neutrinos fill the universe from the Big Bang
  (109 n / m3)? Even a
  small mass (1 eV) will have effects
• Models have hot (n) and cold Dark Matter
• Massive neutrino affect structure formation such
  as galaxies and clusters

19
Neutrino Masses in Cosmology
20
Dirac and Majorana Neutrinos

• Dirac Neutrinos
• Neutrino and Antineutrino are distinct particles
  (like their charged lepton partners)
• Lepton number conserved
• Neutrino ? m-
• Antineutrino ? m
• Dirac Mass Term
• Need to have a right-handed neutrino (Not in
  the Standard Model)
• Mass term like e, m, t

• Majorana Neutrinos
• Neutrinos and Antineutrinos are the same particle
  (This can only happen since neutrinos have no
  charge!)? Only difference is handedness
• Neutrinos are left-handed n ? m-
• Antineutrinos are right-handed n ? m
• Lepton number not conserved
• Neutrino ? Antineutrino with spin flip
• Majorana Mass Term
• New type of mass

Terms in the Lagrangian (Newtons Laws for
Particle physics)
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See Saw Mechanism

• If only the nL exist, then neutrinos only can
  have a Majorana mass
• But if both nL and nR exist then can have both
  Majorana and Dirac mass components
• If postulate that mL0, mDme,m,t ltlt mR very
  heavy (since right-handed )and diagonalize the
  mass matrix
• Explains? why neutrinos have small mass but
  predicts very small mixing

22
Experimental Limits on the Neutrino Mass
Direct decay studies have made steady progress
but limited

• Electron neutrino
• 3H?3He ne e-
• Muon neutrino
• p?mnm decays
• Tau neutrino
• t? (np) nt decays

lt 2 eV
lt 170 keV
lt 18 MeV
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Neutrino Oscillations

• Direct measurements have difficulty probing small
  neutrino masses ? Use neutrino
  oscillations
• If we postulate
• Neutrinos have (different) mass ? Dm2
  m12 m22
• The Weak Eigenstates are a mixture of Mass
  Eigenstates
• Then a pure nm beam at L0, will develop a ne
  component as it travels a distance L.

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Oscillation Formula Parameters
nm Disappearance
ne Appearance
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Oscillation Plots

• If you see an oscillation signal with
• Posc P ? dP then carve out an allowed
  region in (Dm2,sin22q) plane.
• If you see no signal and limit oscillation with
  Posc lt P _at_ 90 CLthen carve out an
  excluded region in the (Dm2,sin22q) plane.

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3-Generation Oscillation Formalism

• But we have 3-generations ne , nm, and nt
  (and maybe even more .. the
  sterile neutrino nss )

• Naively might expect the neutrino and quark
  matrix to look similar

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Situation in mid-1990s Three Experimental
Indications for Neutrino Oscillations
Atmospheric Neutrinos L 15 to 15,000 km E
300 to 2000 MeV
LSND Experiment L 30m E 40 MeV
Solar Neutrinos L 108 km E 0.3 to 3 MeV
Dm2 2 to 8?? 10-5 eV2 ProbOSC 100
Dm2 .3 to 3 eV2 ProbOSC 0.3
Dm2 1 to 7?? 10-3 eV2 ProbOSC 100
30
Solar Neutrino Deficit

• Flux of solar neutrinos detected at the earth is
  much less than expected ? Is it due to neutrino
  oscillations?

Super- K (Japan) imageof the sun using neutrinos
31
Standard Solar Model
pep
pp
Sage GallexExps
hep
7Be
8B
Super-K Experimentne e- ? ne e-
32
Solar Neutrino Experiments

• Rate measurement Reaction Obs / Theory
• Homestake (US) ne 37Cl ? 37Ar e- 0.34 ?
  0.03
• SAGE (Russia) ne 71Ga ? 71Ge e- 0.59 ?
  0.06
• GallexGNO (Italy) ne 71Ga ? 71Ge e- 0.58 ?
  0.05
• Super-K (Japan) H2O nx e- ? nx e- 0.46 ?
  0.02
• SNO (Canada) D2O ne d ? p p e- 0.35 ?
  0.03

But how big are the uncertainties incalculating
the neutrino flux?
33
Atmospheric Neutrino Oscillations

• Atmospheric Neutrino Flux
• Experiments measure a deficit in the ratio of
  ratios

cosmic ray showers produce 21 ?m?e
34
The LSND Experiment
Saw an excess of87.9 22.4 6.0 events. With
an oscillation probability of (0.264 0.067
0.045). 3.8 s evidence for oscillation.
Oscillations?
LSND took data from 1993-98 - 49,000 Coulombs
of protons - L 30m and 20 lt Enlt 53 MeV
35
Three Signal Regions(Mid 1990s)
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Theoretical Prejudices before 1995

• Natural scale for Dm2 10 100 eV2 since
  needed to explain dark matter
• Oscillation mixing angles must be small like
  the quark mixing angles
• Solar neutrino oscillations must be small
  mixing angle MSW solutionbecause it is cool
• Atmospheric neutrino anomaly must be other
  physics or experimental problembecause it needs
  such a large mixing angle
• LSND result doesnt fit in so must not be an
  oscillation signal

37
Theoretical Prejudices before 1995
What we know now

• Natural scale for Dm232 10 100 eV2
  Wrongsince needed to explain dark matter
• Oscillation mixing angles must be small
  Wronglike the quark mixing angles
• Solar neutrino oscillations must be Wrong
  small mixing angle MSW solutionbecause it is
  cool
• Atmospheric neutrino anomaly must be
  Wrongother physics or experimental
  problembecause it needs such a large mixing
  angle
• LSND result doesnt fit in so must not
  ????be an oscillation signal

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Neutrino Revolution 1995 - 2003

• Atmospheric neutrino oscillations definitively
  confirmed
• Smoking Gun ? Super-K flux change with zenith
  angle
• Accelerator neutrino confirmation with KEK to
  Super-K exp.
• Value of Dm2 goes down to 2 to 3 10-3 eV2
• Solar Neutrino Oscillations Confirmed and
  Constrained
• SNO experiments sees that total neutrino flux
  correct from sun but just changing flavor
• Kamland experiment using reactor neutrinos
  confirms solar oscillations
• Combination of experiments ? Large Mixing Angle
  Solution

40
Super-Kamiokande (Super-K) Detector

• 22.5 kton of ultra-pure water
• 11,150 20 inch phototubes
• Located in Kamioka mine at a depth of 1000m below
  the surface

41
Atmospheric NeutrinosZenith Angle Dependence of
n Flux

• See variation of nm flux with azimuth or zenith
  angle due to difference in distance from the
  atmosphere

Super-K nm deficit with azimuthBest fit
Dm22.4?10-3eV2 sin22q1.0
No Osc
15 km
With Osc
Super-K AtmosphericOsc. Signal
13,000 km
42
K2K (KEK to Super-K) Oscillation
Experiment(Accelerator Check of Atmospheric Osc.)

• Low energy, ?E?gt1.4 GeV, beam sent from KEK to
  SuperK (250 km)
• See large deficit of neutrinos (50)
• Confirm Atmospheric oscillations using an
  accelerator neutrino beam

43
Sudbury Neutrino Observatory (SNO)(Detector that
can see all active solar neutrinos)
1000 tons D2O(12m Inner Vessel)in Canadian
nickel mineat 2000m depth
44
SNO Physics

• First measurement of the total flux of 8Be
  neutrinosftotal(8Be) 5.21 0.47 106 cm-2s-1
• Agrees well with solar modelsftotal(8Be)
  5.05 1.00 106 cm-2s-1

? Solar Oscillations not totally to sterile
neutrinos
45
Kamland Reactor Exp.(Probes for ?ne Osc. In the
Solar Region)

• Uses?ne from all the reactors in Japan
• 85 of signal events from
• Closest 60 GW of power
• Distance range 140km to 344 km
• KamLAND is a 1 kton liquid scintillator detector
• 2000 photomultiplier tubes
• Began data taking in Sept., 2001.

46
Kamland and New Global Results

• First Results
• Kamland 54 events observed, 86?6 expected
• ? Osc. Probability 0.39 ? 0.09
• Reproduced results for solar neutrinos with a
  terrestrial neutrino source !!!

• Global fit with all solar data (Kamland, SNO,
  Super-K )
• Dm2Solar ? 7.1 ? 1.0 x 10-5 eV2
  

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Current Knowledge of Oscillation Parameters
48
Too Many n-Oscillation Signals

• With the three known neutrinos ne nm nt ?
  Cannot explain three different Dm2 values.
• Explanation could be experimental or theoretical
  (or both)
• Experimental ideas
• Not all of the three signals are neutrino
  oscillations
• Unknown uncertainties give false signals
• Theoretical ideas
• Neutrinos and antineutrinos have different masses
  
• More than three types of neutrinos extra
  sterile neutrino types

? Important next step is to test LSND signal !!!
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Booster Neutrino Experiment(MiniBooNE)
Use protons from the 8 GeV booster ? Neutrino
Beam ltEngt 1 GeV
MiniBooNE designed to check LSND signal by
searching for ne appearance in a nm beam at
Fermilab.
12m sphere filled withmineral oil and
PMTslocated 500m from source
Oscillation Search Method Look for ne events in a
pure nm beam
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MiniBooNE Collaboration
Y. Liu, I. Stancu Alabama S. Koutsoliotas
Bucknell E. Hawker, R.A. Johnson, J.L. Raaf
Cincinnati T. Hart, R.H. Nelson, E.D. Zimmerman
Colorado A. Aguilar-Arevalo, L.Bugel, L.
Coney, J.M. Conrad, J. Formaggio, J. Link, J.
Monroe, K. McConnel, D. Schmitz, M.H.
Shaevitz, M. Sorel, L. Wang, G.P. Zeller
Columbia D. Smith Embry Riddle
L.Bartoszek, C. Bhat, S J. Brice, B.C. Brown,
D.A. Finley, B.T. Fleming, R. Ford,
F.G.Garcia, P. Kasper, T. Kobilarcik, I.
Kourbanis, A. Malensek, W. Marsh, P. Martin,
F. Mills, C. Moore, P. Nienaber, E. Prebys,
A.D. Russell, P. Spentzouris, R. Stefanski,
T. Williams Fermilab D. C. Cox, A. Green, H.-O.
Meyer, R. Tayloe Indiana G.T. Garvey, C.
Green, W.C. Louis, G.McGregor, S.McKenney,
G.B. Mills, V. Sandberg, B. Sapp, R.
Schirato, R. Van de Water, D.H. White Los
Alamos R. Imlay, W. Metcalf, M. Sung, M.O.
Wascko Louisiana State J. Cao, Y. Liu,
B.P. Roe, H. Yang Michigan A.O. Bazarko,
P.D. Meyers, R.B. Patterson, F.C. Shoemaker,
H.A.Tanaka Princeton
MiniBooNE consists of about 70 scientists from 12
institutions.
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MiniBooNE Neutrino Beam

• Variable decay pipe length
• (2 absorbers _at_ 50m and 25m)

8 GeV Proton Beam Transport
p ? m n
One magnetic Horn, with Be target
Detector
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(Examples of Two MiniBooNE Data Events)
Charged Currentnm n ? m- pwith outgoing
muon (1 ring)
Neutral Currentnm n ? nm p0 pwith
outgoing p0 ? gg (2 rings)
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MiniBooNE Sensitivity to LSND
With two years of running MiniBooNE will
completely include or exclude the entire LSND
signal region at the 5s level.

• Expected events
• 500,000 nm CC quasi-elastic
• 500 extra nes if LSND correct

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MiniBooNE Run Plan

• At the current time have collected 2.5x1020
  protons on target
• Plan is to open the box when analysis has been
  substantiated and experiment has collected 1x1021
  p.o.t. ? Current estimate is sometime in
  2005
• Which then leads to the question of the next
  step
• If MiniBooNE sees no indications of oscillations
  with nm ? Need to run with?nm since LSND
  signal was?nm??ne
• If MiniBooNE sees an oscillation signal ?
  Then

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Possible New Surprises

• Sterile Neutrinos
• Are they light enough that we can see them?
• They would give a whole new spectrum of mass
  states and mixings
• ? MiniBooNE and follow-ups are key
• Probing for CP violation
• CP violation comes about when a process has a
  different rate for particles and anti-particles
• Need to measure last mixing angle
  ? q13
• Then look at ?n versus n oscillations to measure
  d
• ? New long baseline and reactor experiments are
  key

58
Experimental Program with Sterile Neutrinos

• If sterile neutrinos then many mixing angles,
  CP phases, and Dm2 to include

• Measure number of extra masses Dm142, Dm152

• Measure mixings Could be many small
  angles

• Compare nm and?nm oscillations ? CP and CPT
  violations

59
Methods to Measure sin22?13

• Appearance nm?ne (Offaxis Exps.)
• Use fairly pure, accelerator produced nm beam
  with a detector at long distance (300 km - 900
  km) from the source
• Look for the appearance of ne events
• Use near detector to measure background ne's
  (beam and misid)

• Disappearance?ne??ne (Reactor Exp)
• Use a set of reactors as a source of ?ne's with a
  detector at few km
• Look for a non- 1/r2 behavior of the ne rate
• Use near detector to measure the un-oscillated
  flux

Byron, Illinois
Sites being considered at Illinois, China,
Japan, and France
overburden
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Neutrino vs. Quark Mixingsare very different
d gives CP violation(Has been measuredfor
quark mixing)
Why?

• The Third Big Cosmology Question
• - How did the Universe become dominated by
  matter over antimatter?
• If there are sterile neutrinos and CP violating
  processes in the neutrino mixing, then
  Leptogenesis may be the explanation

61
Matter-Antimatter Asymmetry (?B ? 0)from
Leptogenesis

• Hard to generate a baryon asymmetry (?B ? 0)
  using quark matrix CP violation
• Generate ?L ? 0 in the early universe from CP (or
  CPT) violation in heavy neutrino N3 vs.
  decays (only needs to be at the 10-6 level)
• B-L processes then convert neutrino excess to
  baryon excess.
• Sign and magnitude correct to generate baryon
  asymmetry in the universe with mN gt 109 GeV and
  mn lt 0.2 eV

n Mixing
n Mixing
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Summary

• Neutrinos have mass and flavor mixing
• Observed masses and differences are much smaller
  than charged lepton partners ??
• Mixings are very large ?? near 100 ??
• But expect small mixings if mn is from the
  See-Saw
• If all indications true, need to add more
  neutrinos (sterile, heavy?)
• Neutrinos may have an important role in producing
  the baryon-antibaryon asymmetry in the universe
• Need CP violation in the neutrino mixing
• Need sterile neutrinos (also needed for
  See-Saw)
• Are we on the verge of a next neutrino
  revolution?
• Many studies of modest size and cost ongoing or
  planned great time for young physicists to
  make their mark.

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Maybe it was the n?s !
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11 Key Questions about the Universe

• What is dark matter?
• What are the masses of the neutrinos, and how
  have they shaped the evolution of the universe?
• Are there additional spacetime dimensions?
• What is the nature of the dark energy?
• Are protons unstable?
• How did the Universe begin?
• Did Einstein have the last word on gravity?
• How do cosmic accelerators work and what are
  they accelerating?
• Are there new states of matter at exceedingly
  high density and temperature?
• Is a new theory of matter and light needed at
  the highest energies?
• How were the elements from iron to uranium
  made?