Theoretical Neutrino Physics Hitoshi Murayama (Berkeley) EPS 2003 @ Aachen July 22, 2003.

Theoretical Neutrino Physics

Hitoshi Murayama (Berkeley)

EPS 2003 @ Aachen

July 22, 2003

EPS2003 Hitoshi Murayama 2

Milind Diwan

• “Neutrino physics is so simple. There are no hadronic corrections. We don’t need theorists.”

Why You Need Theoristsin Neutrino Physics

Hitoshi Murayama (Berkeley)

EPS 2003 @ Aachen

July 22, 2003


Outline

• A Little Historical Perspective• Interpretation of Data & Seven Questions

– Solar Neutrino– Interpretation without LSND– Interpretation with LSND– Nature of neutrino mass

• Models of Flavor• Conclusions

A Little Historical Perspective


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


Grand Unification

• electromagnetic, weak, and strong forces have very different strengths

• But their strengths become the same at 1016 GeV if supersymmetry

• A natural candidate energy scale ~1016GeV

m~0.003eV• m~(m2

atm)1/2~0.03eV• m~(m2

LMA)1/2~0.007eV

Neutrino mass may be probing unification!

Interpretation of DataSeven Questions


What we learned since Budapest

• Atmospheric s are lost. P=4.2 10–26 (SK, Hayato)

• converted most likely to (>99%CL)• Solar e is converted to either or (>5) (SNO,

Poon)

• Reactor anti-e are lost (99.95%CL) (KamLAND, Lesko)

• Only the LMA solution left for solar neutrinos• Tiny neutrino mass: the first evidence for

incompleteness of Minimal Standard Model

Solar Neutrino Problem Finally Solved After 35 Years!


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 flavor conversion!

€

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

Dec 2002Expected #events: 86.8±5.6

Background #events: 0.95±0.99Observed #events: 54

No oscillation hypothesisExcluded at 99.95%


No other solution than oscillation

• Neutrino decay– Wrong energy dependence

• Spin-resonant flip– Relies on a large solar magnetic field

• New flavor-changing neutral current– Relies on a high solar matter density

• Violation of the equivalence principle– Relies on the strong solar gravitational potential


March 2002

April 2002 with SNO

Dec 2002with KamLAND

Progress in 2002 on the Solar Neutrino Problem


Solar Neutrino Spectrum

pp7Be

8B


We don’t get enough

We need survival probabilities of

8B: ~1/3

7Be: <1/3

pp: ~2/3

Can we get three numbers correctly with two parameters?


Matter Effect

• CC interaction in the presence of non-relativistic electron

€

L = −GF

2e γμ (1−γ5 )ν eν eγ

μ (1−γ5 )e

= −GF

2e γμ (1−γ5 )eν eγ

μ (1−γ5 )ν e

= − 2GFneν eγ0ν e

• Neutrino Hamiltonian

€

H = common

+Δm2

4E

−cos2θ sin 2θ

sin 2θ cos2θ

⎛

⎝ ⎜

⎞

⎠ ⎟

+ 2GFne1 0

0 0

⎛

⎝ ⎜

⎞

⎠ ⎟

Electron neutrino higher energy in the Sun


Adiabatic

• Use “instantaneous” eigenstates + and –

• For the LMA region, the dynamics is adiabatic: there is no hopping between states

20

Solar Neutrino Astrophysics

• Davis and Bahcall started solar neutrino work because they wanted to probe physics of the sun

• Finally one can fit all solar neutrino data together with KamLAND to measure all major components: pp, 7Be, 8B (Bahcall, Peña-Garay)

Solar luminosity confirmed

• Possible concern: density perturbation (Reggiani)


Loose Ends

• Energy dependence in the solar neutrino survival probability not fully demonstrated– pp, 7Be solar neutrino experiments

• Nobody has seen “oscillation,” i.e., the survival probability dips and comes back up– Atmospheric: MINOS– Solar/reactor: continued KamLAND

• Evidence for “appearance” in atmos still not strong enough (99%CL)– OPERA, ICARUS


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%


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

Interpretation Without LSND


Three-generation Framework

• Standard parameterization of MNS matrix for 3 generations

€

UMNS =

Ue1 Ue2 Ue3

Uμ 1 Uμ 2 Uμ 3

Uτ 1 Uτ 2 Uτ 3

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

=

c12 s12

−s12 c12

1

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

c13 s13e−iδ

1

−s13eiδ c13

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

1

c23 s23

−s23 c23

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

atmospheric???solar


Three-generation

• Solar, reactor, atmospheric and K2K data easily accommodated within three generations

• sin2223 near maximal m2

atm ~ 310–3eV2

• sin2212 large m2

solar ~ 710–5eV2

• sin2213=|Ue3|2< 0.05 from CHOOZ, Palo Verde

• Because of small sin2213, solar (reactor) & atmospheric oscillations almost decouple Gonzalez-Garcia, Peña-Garay

2/dof=136/173


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





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

⎛

⎝ ⎜

⎞

⎠ ⎟


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


Shootout (Lindner)


Seven Questions





Intepretation With LSND


ν μ

ν e?

ν ep→ e+n

μ+→ e+νeν μ

p→ π +

π+→ μ+νμ


3.3 Signal

• Excess positron events over calculated BG

P(ν μ → ν e)

=(0.264±0.067±0.045)%


Sterile Neutrino

• LSND, atmospheric and solar neutrino oscillation signalsm2

LSND ~ eV2

m2atm ~ 310–3eV2

m2solar < 10–3eV2

Can’t be accommodated with 3 neutrinos

Need a sterile neutrino

New type of neutrino with no weak interaction

• 3+1 or 2+2 spectrum?


Sterile Neutrino disfavored

• 2+2 spectrum: past fits preferred– Atmospheric mostly

– Solar mostly ea (or vice versa)

– Now solar sterile getting tight due to SNO

Disfavored 1.6 10–6 (Maltoni et al)

• 3+1 spectrum: sin22LSND=4|U4e|2|U4|2

– |U4|2 can’t be big because of CDHS, SK U/D

– |U4e|2 can’t be big because of Bugey

Disfavored 5.6 10–3 (Maltoni et al)


PLSND<0.10% PLSND< 0.20%

P(ν μ → ν e)

=(0.264±0.067±0.045)%

More Sterile Neutrinos?

• Who said there is only one sterile neutrino?

• There could well be one for each generation

• Do more sterile neutrinos help?

• Maybe 3+2 better (Sorel, Conrad, Shaevitz)


WMAP+2dF+Lyman Maltoni, Schwetz, Tortola, Vallehep-ph/0209368

Pierce, HMHannestad

Spergel et al

∑m<0.7eV (95%)


CPT Violation?“A desperate remedy…”

• LSND evidence:anti-neutrinos

• Solar evidence:neutrinos

• If neutrinos and anti-neutrinos have different mass spectra, atmospheric, solar, LSND accommodated without a sterile neutrino

(HM, Yanagida)

Best fit to data before KamLAND (Strumia)


KamLAND impact

• However, now there is an evidence for “solar” oscillation in anti-neutrinos from KamLAND

• Barenboim, Borissov, Lykken: evidence for atmospheric neutrino oscillation is dominantly for neutrinos. Anti-neutrinos suppressed by a factor of 3.

• New CPT violation:


KamLAND impact

• However, now there is an evidence for “solar” oscillation in anti-neutrinos from KamLAND

• Barenboim, Borissov, Lykken: evidence for atmospheric neutrino oscillation is dominantly for neutrinos. Anti-neutrinos suppressed by a factor of 3.

• However fit not good (Gonzalez-Garcia, Maltoni, Schwetz)

• MINOS atmospheric data will settle this

• New CPT violation:


LSND not as oscillation

• Maybe LSND detected anomalous decay of muon (Babu, Pakvasa)

• Lepton-number violation• KARMEN disfavors it

– BR<0.009 (90%) while LSND wants BR=0.019–0.040

• No signal at Mini-BooNE• Predicts Michel parameter =0.74850.75• Current accuracy: =0.7518±0.0026• TWIST experiment at TRIUMF measures Michel

parameter down to a few times 10–4

€

+ → e+ν μ ν e


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


Seesaw Mechanism

• Why is neutrino mass so small?

• Need right-handed neutrinos to generate neutrino mass

νL νR( )mD

mD

⎛

⎝ ⎜

⎞

⎠ ⎟

νL

νR

⎛

⎝ ⎜

⎞

⎠ ⎟ νL νR( )

mD

mD M

⎛

⎝ ⎜

⎞

⎠ ⎟

νL

νR

⎛

⎝ ⎜

⎞

⎠ ⎟ mν =

mD2

M<<mD

To obtain m3~(m2atm)1/2, mD~mt, M3~1015GeV (GUT!)

Neutrinos are Majorana

, 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• m3Ue3

2<<m3 and we can typically ignore m3 • <me>=m1cos212+eim2sin212

– possible cancellation due to unknown Majorana phase

• Fortunately, they cannot cancel exactly because the maximal angle 12 excluded by SNO: cos212–sin212=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


WMAP again

• WMAP constraint:– m<0.23eV each (95%CL)

• Puts upper limit on the effective neutrino mass in the neutrinoless double beta decay (Pierce, HM)

– |<me>|=|imiUei2|<imi |Uei

2|<0.23eV

– Heidelberg-Moscow: |<me>|=0.11–0.56 eV

– Reanalysis by Vogel: |<me>|=0.4–1.3 eV

Models of Flavor


Typical Theorists’ View ca. 1990

• Solar neutrino solution must be small angle MSW solution because it’s cute

• Natural scale for m223 ~ 10–100 eV2

because it is cosmologically interesting• Angle 23 must be of the order of Vcb

• Atmospheric neutrino anomaly must go away because it needs a large angle

Wrong!

Wrong!

Wrong!

Wrong!


Surprises

• Prejudice from quarks, charged leptons:– Mixing angles are small

– Masses are hierarchical

• In LMA, all mixing except Ue3 large

– Two mass splittings not very different

– Atmospheric mixing maximal

– Any new symmetry or structure behind it?€

e μ τ( )

big big medium?

big big big

big big big

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

ν e

ν μ

ν τ

⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

Δmsolar2

Δmatm2 ~0.01– 0.2


Question of Flavor

• What distinguishes different generations?– Same gauge quantum numbers, yet different

• Hierarchy with small mixings:

Need some ordered structure

• Probably a hidden flavor quantum number

Need flavor symmetry– Flavor symmetry must allow top Yukawa

– Other Yukawas forbidden

– Small symmetry breaking generates small Yukawas

• Try to find underlying symmetries from data (bottom-up)– Repeat Heisenberg, Gell-Mann–Okubo


Different Flavor Symmetries

Altarelli-Feruglio-Masina hep-ph/0210342

Hall, HM, Weiner

Sato, YanagidaVissani

Barbieri et al


Lack of symmetry explains data

• Suppose there is no symmetry behind the neutrino masses and mixings (“anarchy”)

• Random 3 by 3 matrix• MNS matrix

distributed to the group invariant measure (Haba, HM)

3-D Kolmogorov–Smirnov test(de Gouvêa, HM)

P=68%


Lower Bound on 13

• Anarchy predicts flat distribution in cos413

• 1D PKS= 2(1–cos413)~sin2213 for small 13

• Lower bounds:– sin2213>0.05 (95%CL)

– sin2213>0.01 (99%CL)


Critical Measurements

• sin2 223=1.000.01?– Determines a need for a new symmetry to enforce the maximal

mixing

• sin2 213<0.01?– Determines if the flavor quantum number of electron is different

from , • Normal or inverted hierarchy?

– Most symmetries predict the normal hierarchy

• CP Violation?– Plausibility test of leptogenesis


Dynamics behind flavor symmetry?

• Once flavor symmetry structure identified (e.g., Gell-Man–Okubo), what is dynamics? (e.g., QCD)

• Supersymmetry:–Anomalous U(1) gauge symmetry with Green-Schwarz mechanism

• Large Extra Dimensions:–Fat brane with physically separated left- and right-handed particles

• Technicolor:–New broken gauge symmetries at 100TeV scale


Large 23 and quarks

• Large mixing between and

• Make it SU(5) GUT

• Then a large mixing between sR and bR

• Mixing among right-handed fields drop out from CKM matrix

• But mixing among superpartners physical

• O(1) effects on bs transition possible evading ebs constraints

(Chang, Masiero, HM)

• Expect CP violation in neutrino sector especially if leptogenesis (Rodejohann)


Consequences in B physics

• Addt’l contrib to ms

• CP violation in Bs mixing (BsJ/ )

• Addt’l CP violation in penguin bs

(Bd Ks)

Very reasonable place for new physics to show up!

EPS2003 Hitoshi Murayama 63Harnik, Larson, HM, Pierce

also

Uli

Nie

rste

in H

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Fla

vour

ses

sion

RR-dom case


Conclusions

• Enormous progress in neutrino data– Solar neutrino problem solved!

• Still some loose ends– Many forthcoming experiments

• Three-generation oscillation very reasonable• LSND still unclear• Cosmological constraints beginning to be interesting• Next key: 13

– Long-baseline or reactor

• Neutrinos not stand alone– Need info from high-energy frontier, quark sector to address the origin

of masses and mixing

Do We Need Theorists?

Theoretical Neutrino Physics Hitoshi Murayama (Berkeley) EPS 2003 @ Aachen July 22, 2003.

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Transcript of Theoretical Neutrino Physics Hitoshi Murayama (Berkeley) EPS 2003 @ Aachen July 22, 2003.