Post on 09-Feb-2016
description
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
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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
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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)
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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)
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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
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Constraints on (m2, 23, 13) from SK + K2K + CHOOZ
See talks by Sulak (SK) and Mariani (K2K)
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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)
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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
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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
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Constraints on (m2, 12, 13) from solar + KamLAND
See talks by Sulak (SK), Berger (kamLAND), Miknaitis (new SNO data)
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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)
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, ,
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
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(+ 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?
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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.
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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
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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
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“Grand Total” from global analysis of oscillation data
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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
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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)
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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
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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.,
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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
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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
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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!
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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!