status of neutrino science
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Status of Neutrino Science
Hitoshi Murayama
LBNLnu
April 11, 2003
LBNLnu Hitoshi Murayama 2
Two Main Directions
• Neutrino Properties– Neutrino Masses– Neutrino Mixings– Nature of Neutrinos
• Neutrino as a Probe– Parton Distribution Function– Precision Electroweak Physics– Neutrino Astrophysics
LBNLnu Hitoshi Murayama 3
Outline
• Introduction
• Current Status of Neutrino Oscillation
• Main Scientific Questions
• Majorana vs Dirac
• The last mixing angle and CP violation
• Conclusion
Current Status of Neutrino Oscillation
LBNLnu Hitoshi Murayama 5
Rare Effects from High-Energies
• Effects of physics beyond the SM as effective operators
• Can be classified systematically (Weinberg)
LBNLnu Hitoshi Murayama 6
Unique Role of Neutrino Mass
• Lowest order effect of physics at short distances
• Tiny effect (m/E)2~(eV/GeV)2=10–18!
• Interferometry (i.e., Michaelson-Morley)!– Need coherent source
– Need interference (i.e., large mixing angles)
– Need long baseline
Nature was kind to provide all of them!
• “neutrino interferometry” (a.k.a. neutrino oscillation) a unique tool to study physics at very high scales
LBNLnu Hitoshi Murayama 7
MNS matrix
• Standard parameterization of Maki-Nakagawa-Sakata matrix for 3 generations
UMNS=
Ue1 Ue2 Ue3
Uμ1 Uμ2 Uμ3
Uτ1 Uτ2 Uτ3
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
=
1
c23 s23
−s23 c23
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
c13 s13e−iδ
1
−s13eiδ c13
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
c12 s12
−s12 c12
1
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
atmospheric ??? solar
LBNLnu Hitoshi Murayama 8
What we learned in 2001–2
• Atmospheric is lost (>10), converted most likely to (>99%CL) (SK, MACRO, SOUDAN-II)
• Solar e is converted to either or (>5) (SNO)
• Reactor anti-e are lost (99.95%CL) (KamLAND)
• Only the LMA solution left for solar neutrinos• Tiny neutrino mass: the first evidence for
incompleteness of Minimal Standard Model
LBNLnu Hitoshi Murayama 9
SNO Result
• Only e produced in the Sun• Wrong Neutrinos are
coming from the Sun!• Somehow some of e were
converted to on their way from the Sun’s core to the detector neutrino oscillation!
€
ΦCC =1.76 ± 0.05 ± 0.09 ⋅106 cm−2 sec−1
€
ΦNC = 5.09 −0.43+0.44 −0.43
+0.46 ⋅106 cm−2 sec−1
LBNLnu Hitoshi Murayama 10
KamLAND result
• First terrestrial expt relevant to solar neutrino problem
• KamLAND will exclude or verify LMA definitively
Dec 2002Expected #events: 86.8±5.6
Background #events: 0.95±0.99Observed #events: 54
No oscillation hypothesisExcluded at 99.95%
LBNLnu Hitoshi Murayama 11
Summary of Neutrino Oscillation
Before SNO and KamLAND
Dec 2002with SNO and KamLAND
LBNLnu Hitoshi Murayama 12
Three-generation
• Solar, reactor & atmospheric oscillations easily accommodated within three generations
• sin2223 near maximal, m2atm ~ 310–3eV2
• sin2212 large, m2solar ~ 5–2010–5eV2
• sin2213=|Ue3|2< 0.05 from CHOOZ, Palo Verde
• Because of small sin2213, solar (reactor) & atmospheric oscillations almost decouple
LBNLnu Hitoshi Murayama 13
Seven Questions
• Dirac or Majorana? • Absolute mass scale?
• How small is 13?
• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?
LBNLnu Hitoshi Murayama 14
Seven Questions
• Dirac or Majorana? • Absolute mass scale?
• How small is 13?
• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?
LBNLnu Hitoshi Murayama 15
Extended Standard Model
• Massive Neutrinos Minimal SM incomplete• How exactly do we extend it?• Abandon either
– Minimality: introduce new unobserved light degrees of freedom (right-handed neutrinos)
– Lepton number: abandon distinction between neutrinos and anti-neutrinos and hence matter and anti-matter
• Dirac or Majorana neutrino• Without knowing which, we don’t know how to
extend the Standard Model
LBNLnu Hitoshi Murayama 16
Theoretical Bias:Seesaw Mechanism
• Why is neutrino mass so small?
• Need right-handed neutrinos to generate neutrino mass
νL νR( )mD
mD
⎛
⎝ ⎜
⎞
⎠ ⎟ νLνR
⎛
⎝ ⎜
⎞
⎠ ⎟ νL νR( )
mD
mD M
⎛
⎝ ⎜
⎞
⎠ ⎟ νLνR
⎛
⎝ ⎜
⎞
⎠ ⎟ mν =
mD2
M<<mD
To obtain m3~(m2atm)1/2, mD~mt, M3~1015GeV (GUT!)
Majorana Neutrinos
, but R SM neutral
LBNLnu Hitoshi Murayama 17
Neutrinoless Double-beta Decay
• The only known practical approach to discriminate Majorana vs Dirac neutrinos
0: nn ppe–e– with no neutrinos• Matrix element <me>=imiUei
2
• Current limit |<me>| ≤ about 1eV• m3~(m2
23)1/2≈0.05eV looks a promising goal• However, m3Ue3
2<<m3 and we can ignore m3 • Fortunately, Ue1
2 and Ue22 cannot cancel exactly because
the maximal angle excluded by SNO: Ue12–
Ue22=cos2212>0.07 (1)
LBNLnu Hitoshi Murayama 18
Three Types of Mass Spectrum
• Degenerate– All three around >0.1eV with small splittings– Possible even after WMAP+2dF: m<0.23eV– May be confirmed by KATRIN, cosmology– |<me>|=|imiUei
2|>m cos2212>0.07m
• Inverted– m3~0, m1~m2~(m2
23)1/2≈0.05eV– May be confirmed by long-baseline experiment with matter effect– |<me>|=|imiUei
2|>(m223)1/2 cos2212>0.0035eV
• Normal– m1~m2~0, m3~(m2
23)1/2≈0.05eV– |<me>|=|imiUei
2| may be zero even if Majorana
LBNLnu Hitoshi Murayama 19
Seven Questions
• Dirac or Majorana? • Absolute mass scale?
• How small is 13?
• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?
LBNLnu Hitoshi Murayama 20
Now that LMA is confirmed...
• Dream case for neutrino oscillation physics!• m2
solar within reach of long-baseline expts• Even CP violation may be probable
– neutrino superbeam– muon-storage ring neutrino factory
• Possible only if:– m12
2, s12 large enough (LMA)– 13 large enough
€
P(ν μ → ν e ) − P(ν μ → ν e ) = −16s12c12s13c132 s23c23
sinδ sinΔm12
2
4EL
⎛
⎝ ⎜
⎞
⎠ ⎟sin
Δm132
4EL
⎛
⎝ ⎜
⎞
⎠ ⎟sin
Δm232
4EL
⎛
⎝ ⎜
⎞
⎠ ⎟
LBNLnu Hitoshi Murayama 21
Shootout (Lindner)
LBNLnu Hitoshi Murayama 22
LBNLnu Hitoshi Murayama 23
LBNLnu Hitoshi Murayama 24
13 decides the future
• The value of 13 crucial for the future of neutrino oscillation physics
• Determines the required facility/parameters/baseline/energy
• Two paths to determine 13
– Long-baseline accelerator neutrino oscillation– Reactor neutrino experiment with two detectors
LBNLnu Hitoshi Murayama 25
Seven Questions
• Dirac or Majorana? • Absolute mass scale?
• How small is 13?
• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?
LBNLnu Hitoshi Murayama 26
Verify Oscillation
• Even atmospheric neutrino data do not show “oscillation” yet MINOS, J-PARC
m223, 23, mass
hierarchy and 13
• KamLAND data is consistent with overall suppression continued running
m212
LBNLnu Hitoshi Murayama 27
Low-Energy Solar Neutrinos
• Solar neutrino data suggest energy-dependent survival probability tests MSW effect
12
Helps interpretation of CP violation, double beta decay data
7%1%
20%
LBNLnu Hitoshi Murayama 28
Seven Questions
• Dirac or Majorana? • Absolute mass scale?
• How small is 13?
• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?
LBNLnu Hitoshi Murayama 29
If LSND right,All hell breaks loose
• Sterile neutrinos are strongly constrained by the combination of all existing data and WMAP+2dF
• CPT violation is strongly constrained by SNO+KamLAND
• If LSND correct, all previous measurements need to be re-examined by a collection of short-, medium- and long-baseline experiments. Possibly mini-muon-storage ring.
LBNLnu Hitoshi Murayama 30
Seven Questions
• Dirac or Majorana? • Absolute mass scale?
• How small is 13?
• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?
Specific recommendations to attack these questions in the context of LBNL
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