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Neutrino Oscillations, Proton Decay and Grand Unified Theories

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Title: Neutrino Oscillations, Proton Decay and Grand Unified Theories


1
Neutrino Oscillations,Proton Decayand Grand
Unified Theories
  • D. CasperUniversity of California, Irvine

2
Outline
  • A brief history of neutrinos
  • How neutrinos fit into the Standard Model
  • Grand Unified Theories and proton decay
  • Recent neutrino oscillation discoveries
  • Future prospects for neutrino oscillation and
    proton decay

3
A Desperate Remedy
4
Operation Poltergeist
5
Two Kinds of Neutrinos
  • Reines and Cowans neutrinos produced in
    reaction
  • Observed reaction was
  • Muon decay was known to involve two neutrinos
  • If only one kind of neutrino, the rate for the
    unobserved process much too large
  • Proposal Conserved lepton number and two
    different types of neutrinos(?e and ??)
  • Produce beam with neutrinos from
  • Neutrinos in beam should not produce electrons!

6
Last, but not least
7
Threes Company
  • Number of light neutrinos can be measured!
  • Lifetime (and width) of Z0 vector boson depends
    on number of neutrino species
  • Measured with high precision at LEP
  • N? 3.02 0.04
  • Probably no more families exist

8
Particles of The Standard Model
  • Three families of particles
  • Families behave identically, but have different
    masses
  • Keeping it in the family?
  • Quarks from different families have a small
    mixing do the neutrinos also mix?
  • Each quark comes in three colors
  • The electron and each of its copies has a
    neutrino associated with it
  • Neutrinos must be massless, or the theory must
    have something new added to it.

Quarks
Leptons
9
Forces of The Standard Model
? Z
? Z
? Z
? Z
  • Four known forces hold everything together
  • Gravity the weakest, not included in Standard
    Model
  • Electromagnetism charged particles exchange
    massless photons
  • Strong force holds quarks together, holds
    protons and neutrons together inside nucleus
    particles exchange massless gluons
  • Weak force responsible for radioactivity
    particles exchange W and Z particles

?W?
?W?
?W?
?gluons?
10
Weakly Interacting Neutrinos
  • Neutrinos interact only via the two weakest
    forces
  • Gravity
  • Weak nuclear force
  • W and Z particles extremely massive
  • W mass Kr atom!
  • Force extremely short-ranged
  • This makes the weak force weak
  • Neutrinos pass through light-years of lead as
    easily as light passes through a pane of glass!

11
Mysteries of the Standard Model
  • Why three families of quarks and leptons?
  • Why are do particles have masses?
  • Why are the masses so different?
  • m? lt 10-11 ? mt
  • Are neutrinos the only type of matter without
    mass?
  • Can quarks turn into leptons?
  • Are there really three subatomic forces, or just
    one?

12
Grand Unified Theories
  • Maybe quarks and leptons arent different after
    all?
  • Maybe the three subatomic forces arent different
    either?
  • Maybe a more complete theory can predict particle
    masses?

13
Proton Decay
  • Generic prediction of most Grand Unified Theories
  • Lifetime gt 1033 yr!
  • Requires comparable number of protons
  • Colossal Detectors
  • Proton decay detectors are also excellent
    neutrino detectors (big!)
  • Neutrino interactions are a contamination which
    proved more interesting than the (as yet
    unobserved) signal

14
IMB
  • Worlds first large, ring-imaging water detector
  • Total mass 8000 tons
  • Fiducial mass 3300 tons
  • 2048 Photomultipliers
  • Built to search for proton decay
  • Operated 1983-1990

15
Water Cerenkov Technique
16
The Rise and Fall of SU(5)
  • SU(5) grand-unified theory predicted proton decay
    to e?0 with lifetime 4.5?10291.7 years
  • With only 80 days of data, IMB was able to set a
    limit gt 6.5?1031 years (90CL)
  • SU(5) was ruled out!

17
Nova
18
Atmospheric Neutrinos
  • Products of hadronic showers in atmosphere
  • 21 µe ratio from naive flavor counting
  • Flavor ratio (??/?e) uncertainty 5
  • Neutrinos produced above detector travel 15 km
  • Neutrinos produced below detector travel all the
    way through the Earth (13000 km)

19
Neutrino Interactions
  • Contained (?e , ??)
  • Fully-Contained (FC)
  • Partially-Contained (PC)
  • Upward-Muon (??)
  • Stopping
  • Through-going
  • Difficult to detect ??
  • Not enough energy in most atmospheric neutrinos
    to produce a heavy ? particle

20
The Atmospheric Neutrino Problem
  • Early large water detectors measured significant
    deficit of ?? interactions
  • What happened to these neutrinos?
  • Smaller detectors did not see the effect
  • Needed larger and more sensitive experiments,
    improved checks

21
Neutrino Oscillation
  • Quantum mechanical interference effect
  • Start with one type of neutrino and end up with
    another!
  • Requires
  • Neutrinos have different masses (?m2?0)
  • Neutrino states of definite flavor are mixtures
    of several masses (and vice-versa) (?mixing ?0,
    like quarks mix)
  • Simplest expression (2-flavor)
  • Oscillation probability sin2(2?) sin2(?m2?L/E)

22
Checking the Result
  • A number of incorrect discoveries of neutrino
    oscillation made over the years
  • Atmospheric neutrino problem was treated with
    (appropriate) skepticism
  • Less exotic explanations were explored
  • Incorrect calculation of expected flux?
  • Many comparisons of calculations failed to find
    any mistake
  • Systematic problem with particle ID?
  • Beam tests of water detector particle ID
    performed at KEK lab in Japan proved that water
    detectors can discriminate e and ?
  • Conclusive confirmation required with higher
    statistics, improved sensitivity

23
Super-Kamiokande
  • Total Mass 50 kt
  • Fiducial Mass 22.5 kt
  • Active Volume
  • 33.8 m diameter
  • 36.2 m height
  • Veto Region gt 2.5m
  • 11,146 ? 50 cm PMTs
  • 1,885 ? 20 cm PMTs

24
Evidence for Oscillation
  • SuperK also sees deficit of ?? interactions
  • Also clear angular (L) and energy (E) effects
  • Finally a smoking gun!
  • All data fits ??? ?? oscillation perfectly
  • Surprise
  • Maximal mixing between neutrino flavors

25
Checking the Result (Again)
  • Look for expected East/West modulation of
    atmospheric flux
  • Due to earths B field
  • Independent of oscillation
  • Fit the data to a function of sin2(L?En)
  • Best fit at -1 (?L/E)

26
The Solar Neutrino Problem
  • Homestake experiment first to measure neutrinos
    from Sun, finds huge deficit (factor of 3!)
  • Anomaly confirmed by SAGE, GALLEX, Kamiokande
    experiments

27
SuperK Solar Neutrinos
  • Real-time measurement allows many tests for signs
    of oscillation
  • Day/Night variation
  • Spectral distortions
  • Seasonal variation
  • Allowed oscillation parameter space is shrinking
  • SMA is disfavored by SK data

28
SNO
  • Water detector with a difference
  • Heavy water
  • Able to measure charged current (?e) and neutral
    current (?x)
  • Can determine (finally!) whether solar neutrinos
    are oscillating or not

29
Resolving the Solar Neutrino Problem
  • In July, 2000 SNO published their first results
  • Measured the rate of ?D charged-current
    scattering (only ?e)
  • Compare with SuperK precision measurement of ?e
    scattering (?x)
  • Significant difference between flux of ?e and ?x
    implies non-zero ?? ?? flux from the Sun
    oscillation!
  • Combined flux of all neutrinos agrees well with
    solar model

30
SuperK p?e?0
  • Require 2-3 showering rings, 0 ??e
  • ?0 mass cut if 3 rings
  • Overall Detection Efficiency 43
  • No candidates (0.2 background expected)
  • ?/? gt 5.7 1033 yrs (90 CL)

31
16O?15N ?K, K? ??
No candidates
16O
p
Present limit for ?K?/?gt2?1033 years
32
Status of Proton Decay
33
The K2K Experiment
34
K2K Results
  • 56 events observed at Super-K, vs. 806 expected
  • Energy spectrum of observed events consistent
    with oscillation
  • Appears completely consistent with SuperK
  • More data next year

35
2nd Generation LongBaseline (MINOS,CNGS)
  • 730 km baselines
  • MINOS
  • Factor 500 more events than K2K (at 3? distance)
  • Disappearance and appearance (?e, ??) experiments
  • CNGS
  • Higher-energy beam from CERN to look for ??
    appearance at Gran Sasso
  • Only a handful of signal events expected

36
JHF/SuperK Experiment
  • Approved
  • 50 GeV PS
  • 0.77 MW
  • (K2K is 0.005 MW)
  • Proposed
  • Neutrino beamline to Kamioka
  • Upgrade to 4 MW
  • Outlook
  • Completion of PS in 2006

37
Neutrino Factory
  • The Ultimate Neutrino Beam
  • Produce an intense beam of high-energy muons
  • Allow to decay in a storage ring pointed at a
    distant detector
  • Perfectly known beam
  • Technically very challenging!

38
UNO (and Hyper-Kamiokande)
  • Fiducial Mass 450 kton
  • 20 ? Super-Kamiokande
  • Sensitive to proton decay up to 1035 yr lifetime
  • Able to study leptonic CP violation (with
    neutrino beam)
  • Hyper-Kamiokande
  • 1 Mton Japanese version

39
A World-Wide Neutrino Web?
  • Enormous interest in future long-baseline
    oscillation experiments world-wide!
  • Some theoretical indications that proton decay
    may be within reach

40
Solving the Mysteries
  • Why three families of quarks and leptons?
  • Quark and lepton family mixing seems very
    different
  • Only beginning to measure lepton mixings in
    detail
  • Why are do particles have masses?
  • Why are the masses so different?
  • m? lt 10-11 ? mt
  • Are neutrinos the only type of matter without
    mass?
  • It now seems clear that neutrinos have (very
    tiny) masses
  • Can quarks turn into leptons?
  • Are there really three subatomic forces, or just
    one?
  • Mixing between families, and the small neutrino
    masses may tell us a lot about a Grand Unified
    Theory
  • Observation of proton decay would be direct
    evidence for it!
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