Status of Neutrino Science

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


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


Rare Effects from High-Energies

• Effects of physics beyond the SM as effective operators

• Can be classified systematically (Weinberg)


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


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


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


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


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%


Summary of Neutrino Oscillation

Before SNO and KamLAND

Dec 2002with SNO and KamLAND


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


Seven Questions

• Dirac or Majorana? • Absolute mass scale?

• How small is 13?

• CP Violation?• Mass hierarchy?• Verify Oscillation?• LSND? Sterile neutrino(s)? CPT violation?


Seven Questions





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


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


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)


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


Seven Questions





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

⎛

⎝ ⎜

⎞

⎠ ⎟


Shootout (Lindner)




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


Seven Questions





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


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%


Seven Questions





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.


Seven Questions




Specific recommendations to attack these questions in the context of LBNL

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Status of Neutrino Science

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