Neutrino mass and mixing parameters - a short review -

Eligio LisiINFN, Bari, Italy

Rencontres de Moriond March 2005

Special thanks to: G.L. Fogli, A. Marrone, A. Melchiorri, A. Mirizzi, D. Montanino, A.M. Rotunno, A. Palazzo

1

Outline:

• Overview of 3 mass-mixing parameters• Constraints from oscillation searches• Constraints from non-oscillation searches• Combining oscill. & non-oscill. observables• Beyond the standard 3 scenario (LSND)• Conclusions

2

Organizers’ request: “Talk should be a short introduction aimed at PhD students in experimental (non-neutrino) particle physics” I shall skip all refs. or details for experts/theorists, with apologies to colleagues (for more info, see Proceedings or ask me)

3 mixing

Neutrinos mix (as quarks do):

The standard rotation ordering of the CKM matrix for quarks happens to be useful also for neutrinos:

… but with very different angles:

Only if s2130 one can hope to probe the CP-violating

phase (“holy grail” of future oscillation experiments see Kayser’s talk)

3

3 massmass2 2 spectrumspectrum and flavor content (ee )

+m2

m22 21

3

3

-m2

Abs. scale Normal hierarchy Inverted hierarchy mass2 splittings

Absolute mass scale unknown [but < O(eV)] Hierarchy [sign(∆m2)] unknowne content of 3 unknown [but < few%]

(“solar” splitting)(“atmospheric” splitting)

4

3 oscillations Flavor is not conserved as neutrinos propagate

Oscill. phase:

Two macroscopic oscillation lengths governed by m2 and m2, with amplitudes governed by ij. Leading expt. sensitivities:

(m2, 23, 13)

(m2, 12, 13)

(m2, 13)

Atmospheric , K2K long baseline accelerator (a)

Solar , KamLAND long baseline reactor (b)

CHOOZ short-baseline reactor (a,b)

(a) (1,2) difference weakly probed (b) (,) difference not probed

5

Constraints on (m2, 23, 13) from SK + K2K + CHOOZ

See talks by Sulak (SK) and Mariani (K2K)

6

Super-Kamiokande atmospheric

For 13~0 and m2~0, a very simple formula fits all SK data (+ MACRO & Soudan2)

1st oscillation dip still visibledespite large L & E smearing

Strong constraints on the parameters (m2, 23)

7

Atmospheric oscillation evidence robust & confirmed with lab- in K2K Many interesting details depend on theoretical input & subleading effects

Contours at 1, 2, 3 (1 dof). Note linear scale for m2 and sin223, with 2nd octant of 23 unfolded

8

At the m2 scale of SK+K2K, nonobservation of ee in the CHOOZ reactor experiment sets strong upper bounds on 13

SK+K2K+CHOOZ

Growing literature & interest in subleading effects due to 13, m2, sign(m2), But need very significant error reduction to probe them

A challenge for future high-statistics experiments

9

Constraints on (m2, 12, 13) from solar + KamLAND

See talks by Sulak (SK), Berger (kamLAND), Miknaitis (new SNO data)

10

Solar ee,, vs atmospheric : matter (MSW) effect

Atmospheric and feel backgroundfermions in the same way (through NC);no relative phase change (~ vacuum-like)

But e , in addition to NC, have CC interac.with background electrons (density Ne).Energy difference: V = 2 GF Ne

Solar analysis must account for MSW effects in the Sun and in the Earth (Earth matter effects negligible for KamLAND reactor neutrinos)Solar+KamLAND combination provide evidence for Vsun (not yet for Vearth)

11

, ,

fermion

Z

W

e e

e e

Dramatic reduction of the (m2,12) param. space in 2001-2003(note change of scales)

Cl+Ga+SK (2001)

+SNO-I (2001-2002) +KamLAND-I (2002) +SNO-II (2003)

Direct proof of solar e, in SNO through comparison of

12

(+ confirmation of solar model)

… in 2004 (KamLAND-II with revised background): unique Large Mixing Angle solution, and another change of scale…

+ evidence for oscillatory effectsin KamLAND reactor L/E spectrum

What about MSW effects?

13

Exercise: (1) Change MSW potential “by hand,” V aMSWV (2) Reanalyze all data with (m2,12,aMSW) free (3) Project (m2,12) away and check if aMSW~1

(… a way of “measuring” GF through solar neutrino oscillations …)

Results: with 2004 data, aMSW~1 confirmed within factor of ~2and aMSW~0 excluded Evidence for MSW effects in the Sun

But: expected subleading effect in the Earth (day-night difference) still below experimental uncertainties.

14

2005 (last week): new data + detailed analysis from SNO

2004 2005

Solar

Solar+KL

Previous resultsbasically confirmed

Slightly higher ratioCC/NC ~ P(ee)

Slight shift (<1 upwards)of allowed range for 12

15

3 analysis of 2004 solar+KamLAND data (13 free)

Solar and KamLAND data also prefer 13~0 (nontrivial consistency with SK+CHOOZ)

Bounds on (m2,12) notsignificantly altered forunconstrained 13

16

“Grand Total” from global analysis of oscillation data

17

Marginalized 2 curves for each parameter (2004) 18

Numerical ±2 ranges (95% CL for 1dof), 2004 data:19

Note: Precise values for 12 and 23 relevant for model building (see talk by Tanimoto)

Probing absolute masses through non-oscillation searches

20

Three main tools (m, m, ):

1) decay: m2i 0 can affect spectrum endpoint. Sensitive to

the “effective electron neutrino mass”: (most direct method)

2) 02 decay: Can occur if m2i 0 and =. Sensitive to the

“effective Majorana mass” (and phases): (several talks this afternoon)

3) Cosmology: m2i 0 can affect large scale structures in (standard)

cosmology constrained by CMB+other data. Probes: (see talk by Pastor)

21

Even without non-oscillation data, the (m, m, ) parameter space is constrained by previous oscillation results:

Significant covariances

Partial overlap betweenthe two hierarchies

Large m spread due tounknown Majorana phases

22

But we do have information from non-oscillation experiments:

1) decay: no signal so far. Mainz & Troitsk expts: m < O(eV)

2) 02 decay, no signal in all experiment, except in the most sensitive one (Heidelberg-Moscow). Rather debated claim. Claim accepted: m in sub-eV range (with large uncertainties) Claim rejected: m < O(eV).

3) Cosmology. Upper bounds: < eV/sub-eV range, depending on several inputs and priors. E.g.,

23

02 claim rejected 02 claim accepted

Cosmological bound dominates, but does not probe hierarchy yet

Tension with cosmological bound (no combination possible at face value)But: too early to draw definite conclusions

24

E.g., if 02 claim accepted & cosmological bounds relaxed:

Combination of all data(osc+nonosc.) possible

Complete overlap ofthe two hierarchies(degenerate spectrumwith “large” masses)

High discovery potential in future (m, m, ) searches

25

Beyond three-neutrino mixing: LSND

Many theoretical reasons to go beyond the standard 3 scenarioA purely experimental reason: the puzzling LSND oscillation claim M2~O(eV2) with very small mixing?

Solutions invented so far (new sterile states, newinteractions or properties)seem rather “ad hoc” and/or in poor agreementwith world neutrino dataIf MiniBoone (talk by McGregor)confirms LSND this year,many ideas will be revised, and the neutrino session of Moriond 2006 will be fun!

26

27

ConclusionsNeutrino mass & mixing: established factDetermination of (m2,12) and (m2,23) Upper bounds on 13 Oscillation-induced spectral distortionsDirect evidence for solar flavor changeEvidence for matter effects in the SunUpper bounds on masses in (sub)eV range…………

Determination of 13Leptonic CP violationAbsolute m from -decay and cosmologyTest of 02 claim and of Dirac/Majorana Matter effects in the EarthNormal vs inverted hierarchyBeyond the standard 3 scenarioDeeper theoretical understanding …………

Great progressin recent years …

… and great challenges for the future!