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Introduction to low-energy ν physics

ν Champagne Workshop Reims, Oct. 19, 2009

Eligio LisiINFN, Bari, Italy

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Low-energy ν: mν< Eν <O(mµ, mπ, fm-1) ~O(100) MeV

(from ASPERA roadmap)

( + Lab neutrinos )

0νββ decay

β decay

Coherent scattering

Broad energy spectrum (down to nonrelativistic neutrinos) Broad physics spectrum (particle, nuclear, geo, astro, cosmo, +technol.) Still many unknowns; potential for decisive new discoveries

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Golden age: high- and low-energy ν oscillations established

2002: Annus Mirabilis for low-energy neutrino physics2002: Best Champagne vintage in the last decade, experts say...20XX: Expect other extraordinary vintages…

19931994

19951996

19971998

19992000

20012002

20032004

20052006

20072008

Atmospheric ν oscillations,Limit fromCHOOZ

Solar and reactor ν oscillations,Nobel 2002 toDavis & Koshiba

Accelerator ν oscillations,Cosmological limitson absolute masses

# ν paperson SPIRES

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(ν1 ν2) sector (ν3)-driven oscillations

hopefully about θ13, at the crossroads of all oscillation searches…

Solar, KamLAND

(Double)CHOOZ,Daya Bay, Reno

Atm., Accelerator

… and crucial gateway to leptonic CP violation, Ue3=sin θ13 exp(-iδCP)

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Outline:In each low-energy neutrino sector,

Important achievements obtained Open issues/New perspectives Cross-disciplinary aspects

→ brief discussion focused on:

(ν1,ν2)-driven oscillations (ν3)-driven oscillations Non-oscillation observables Neutrino interactions

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(ν1,ν2)-driven oscillations

A sector studied for decades;many important achievementsfrom solar and reactor expts.

Current understanding includes… →

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Kinematics (δm2, θ12)… Dynamics (MSW)…

σ~6%σ~2%

Bulk Silicate Earth model…Standard Solar Model…

[figures taken from arXiv:0805.2517, 0905.3549, hep-ph/0506.083, +work in progr.]See talks by Gando, Marti Magro, Orebi Gann, Smirnov, Mantovani, Maricic, …

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Solar, high energy (~MSW):

- +

Reactor (~vacuum): KamLAND

- -_

A possible hint arises from slight tension on θ12 (all solar vs KamLAND),and from different correlations between θ12 and θ13, related to oppositerelative signs in Pee (survival probability):

(ν1,ν2) kinematics, open issue: any room for ν3 ?

[Figure from Fogli et al., arXiv:0806.2649]

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Slight “tension” on θ12 may bereduced for θ13>0 (sin2θ13~0.02):

More solar+KamLAND data can furtherconstrain θ12 (and thus check θ13 hint).

[SNO low-E analysis: Talk by Orebi Gann] [Fogli et al., arXiv:0806.2649, 0905.3549]

θ13 also probed by “high-energy”νμ→νe: Possible hints from slighte-event excess in SK atm., MINOS. Global analysis: sin2θ13~0.02±0.01

In any case, it is important to search for θ13>0 in many different ways, both at low energy (solar+KamLAND, SBL reactors) and at high energy(atmospheric, accelerator). Redundance can only be beneficial, e.g., toreduce degeneracy of θ13>0 with other (non)standard parameters.[Talks by Lindner, Valle, Blondel…]

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(ν1,ν2) solar dynamics: MSW OK, but room for nonstandard effects; e.g.,

FCNC…Friedland, Lunardini, Pena-Garay 2004Guzzo, de Holanda, Peres 2004Valle et al., 2006, 2009

MaVaN…Barger, Huber, Marfatia 2005Gonzalez-Garcia et al., 2006

Long-range…Gonzalez-Garcia et al., 2005

Decoher./fluct…Fogli et al, 2007Balentekin, Yuksel 2003Burgess et al. 2004

Sterile…Cirelli, Marandella, Strumia, Vissani 2004

May induce unexpected “anomalies” in solar (& reactor) ν [Talks by Lindner, Valle]. Near future: Push low-E threshold in SK, SNO [Talks by Marti Magro, Orebi Gann]

Magn. moment…Das, Pulido, Picariello 2009

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Solar ν fluxes: ~OK, but model under scrutiny (metallicity problem)

Recent assessmentby Serenelli et al.,arXiv:0909.2668 [Problem is there,but less severe thanit used to be…]

In principle, new ν flux data may help, if accurate enough[See talk by Nakahata]

[Pena-Garay at PHYSUN 2008] [See Borexino talk by Smirnov]

(Be, B) (Be, CNO)

Cross-disciplinary aspects (problems?): Inversion (fluxes → Z/X) entangled with astrophysical & nuclear inputs (S, Opa., Diff.)Need improved understanding of all these aspects at the same time.

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Amazing to note that the same ν detectors might probe “trace metals” both in the interior of the Sun (Z/X) and of the Earth (U,Th) …

CNO U,Th

Borexino KamLANDSNO+

Chondrule

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Earth models: fundamental open issues may be constrained by geo-ν

[McDonoughNUTECH’09]

Near future: New data from KamLAND, first data from Borexino [Talks by Gando, Smirnov]

Far Future: More large-volume detectors [Talks by Virtue, Maricic]

Goal: disentangle interesting sources (global, deep) from “uninteresting” ones (local, surface). Thus:

Place at least one detector on the mantle (e.g., HanoHano) [Marrodan]

Build accurate local models (together with Earth scientists) [Mantovani]

Exploit directionality of inverse beta decay process

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Reactor

Directional effects… θ13 limits at Δm2 scale…

Celebrated CHOOZ results…

[In the following: Δm2 = (Δm312 +Δm32

2)/2 ]

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(ν3)-driven oscillations: Δm2 scale

SK-I+II+III [Shiozawa@Erice’09] ⊕ MINOS’09: [Holin]

Δm2 ~(2.3±0.1)x10-3 eV2

[subjective estimate]

→ δm2 ~ 0.8 σ(Δm2)

Better to account for both mass2 differences in precision analyses

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E.g., consider the full 3ν survival probability for reactor neutrinos(upper/lower Δm2 sign for normal/inverted hierarchy), assuming θ13>0:

“slow osc.”(long baseline)

“fast osc.”(short baseline)

Fast oscillations not invariant under hierarchy swap, iff[Fogli, EL & Palazzo hep-ph/0105080]

A reactor experiment at intermediate baseline (few tens of km), sensitivein principle to both slow and fast terms, might then distinguish hierarchy[Petcov & Piai hep-ph/0112074; Choubey, Petcov and Piai, hep-ph/0306017]. See talk by Huber

… Very difficult! Revisit after DoubleChooz, DayaBay, Reno experience [Batygov, Dye, Learned 0810.0580; Zahn et al., 0901.2976]

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All in one slide…Double CHOOZDaya Bay, Reno

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Double CHOOZ, Daya Bay, Reno, can provide a direct and clean measurement of (or limits on) θ13, being essentially sensitive to

Ue3 Ue3* = sin2θ13

Next-generation accelerator experiments will also be sensitiveto other mixing parameters, e.g., via

Uµ3 Ue3* = sinθ23 cosθ13 sinθ13 exp(iδCP)

Discovery of θ13>0 in next-generation experiments would open a window on leptonic CP violation, and on the very origin of matter in our universe…

In that case…

[Talks by Bongrand, Link, Kim]

[Talks by Blondel, Lindner]

4

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Leptonic CP violation & Majorana neutrinos would make it plausiblethat νR at a new, high-energy scale mR may induce: [See Abada talk]

- Matter-antimatter asymmetry (via leptogenesis, νR→ l+≠ νR→ l-)- Small Majorana ν masses (via see-saw mechanism, mν~mD

2/mR)

Possible mR range very large…for mD ~ me … mtop:mR from TeV to GUT scale,models from LR-sym to SO(10)

[adapted from Mohapatra @Erice 2009]

Further data will at least constrain the phase space of successful theories

[~Like wine tasting: educated guesses from taste/scent may not trace theoriginal grapes with certainty… but provide a pleasant experience anyway!]

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… This leads us towards: Absolute ν mass issues.Three probes: (mβ, mββ, Σ). In first approximation:

1) Single β decay: m2i ≠ 0 alters the spectrum tail. Sensitive to: [Drexlin]

2) Double 0νββ decay: Iff m2i ≠ 0 and ν=anti-ν (Majorana).

Sensitive to the “effective Majorana mass” (and phases): [Schoenert]

3) Cosmology: m2i ≠ 0 alters large scale structure formation within

standard cosmology constrained by CMB + other data. Measures:

… and maybe the hierarchy? Neutrinos with different masses become non-relativistic at different redshifts… [Pastor, Melchiorri]

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Oscillation data constrain regions of the non-oscillation parameter space (mβ, mββ, Σ) for both hierarchies (degenerate in the “large” mass limit)

Nor

mal

Inve

rted

Deg

ener

ate

Spread due to unknown Majorana phases

[arXiv:0805.2517]

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Let’s entertain the possibility that the “true” masses are just around the corner… For instance, that neutrinos are Majorana, with nearly degenerate mass values as high as:

m1~m2~m3~0.2 eV .

Then we might reasonably hope to observe, in the next few years,all three nonoscillation signals, e.g.,

In which case…

Current nonoscillation data provide important (sub)eV upper bounds in these planes. How would positive signals look like?[Talks by Schoenert, Drexlin, Melchiorri]

(at Katrin limits…)

(⊂ Klapdor’s claim)

(within Planck sensit.)

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…The absolute neutrino mass would be reconstructed within ~25%uncertainty, and one Majorana phase (φ2) might be constrained… (another handle on leptonic CP violation)

exp(iφ2) = +1exp(iφ2) = -1(disfavored)

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Can 0νββ nuclear matrix elements be computed with the required accuracy?

Still large (co)variances within each model (e.g., QRPA)…

Barea and Iachello, PRC 79, 044301 (2009) Faessler, Fogli et al. [arXiv:0810.5733]

…but significant recent progress towards convergence of models

Reduction of uncertainties and of their correlations will requirean intensive cross-disciplinary effort (nuclear+particle), in orderto make the best use of upcoming data from different nuclei.

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Multi-isotope data might discriminate (some) 0νββ mechanisms

u e e u

W Wν

Standard

u e e u

W W

N Heavy ν

u e e u

Kaluza-Klein(KK±1 Brane:a=10±1/GeV)

W Wν(n)

u e e u

WR,L

νL,R

RHC λ,η λ=RH had, η=LH had

WR,L

e u u e

u u

g SUSY g

~ ~

~~

p e e p

π

SUSY π

πSUSY

[Gehman & Elliott 2007; Deppisch & Pas 2007; Fogli, EL, Rotunno 2009]

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… Finally: back to standard model interactions!

νe

ν ν

ν ν

ν ν

νe

e e

(Z,A) (Z,A)

CC

NC

NC

νe-e scattering: observed in absorption modeand in interference mode (MSW via δm2 osc.)

ν-ν scattering: not yet observed[but potentially very relevant in SN physics]Nonlinear flavor evolution! [Talk by Raffelt]

ν coherent scattering: not yet observed[but potentially relevant for the whole field!][Talk by Wong]

The first two diagrams may provide handles to the mass hierarchy problem [Huber] via interference with ±Δm2-driven oscillation phases

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Pushing detector technologies to lower and lower energies …

Low-energy spectraof SN neutrinos…[talk by Scholberg]

Low-energy recoilsof nuclei…[talk by Wong]

[Several talks on new detector concepts and technological applications]

[arXiv:0808.0807]

Collar@NUTECH’09

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CONCLUSIONS

Revolutionary results in recent years have establishedν oscillations and a new framework in neutrino physics

We are in the process of learning more on “standard”neutrino kinematics and dynamics via low-energy neutrinos(especially concerning the unknown mixing angle θ13)

Progress involves fundamental physics, cross-disciplinaryaspects, new detector concepts, technological applications

There is great potential for important new discoveries,including signals of “nonstandard” physics

A bright future for low-energy ν physics !

Thank you…

…for your attention!

Back-up slides

Oscillation parameters in (1,2) sector:

Dominated by KamLAND(reactors)

Dominated by solar(especially by SNO)

σ~6%σ~2%

Oscillation parameters in (2,3) sector:

Dominated by MINOS(accelerator) Dominated by SuperK(atmospheric)

σ~5%σ~12%

Note: δm2/Δm2 ~3%, comparable to σ(Δm2) ~5%

(1,3) sector: the smallest mixing angle

Robust upper limit,dominated by the famous CHOOZ expt with reactor neutrinos… Will be improved by

Double-CHOOZ + …in the near future

However, some datasets may suggest two hints of lower limits…

~1σ from sector (2,3) - “old”~1σ from sector (1,2) - “new” ~90% CL total:

sin2θ13 = 0.016 ± 0.010

Near-future improvements on θ12 (from TAUP’09)

Final results from SNO low-energy threshold analysis (LETA) imminent. Preliminary results seem to suggest a preference for relatively low values of θ12

in the SNO-LETA → Possibleimplications for θ13

Low-E analysis also in progress in SK →

SK & SNO expected to probe theexpected LMA spectrum upturn at low energy.

Weak hint for θ13 > 0 from atmospheric + LBL + Chooz data (Bari group, 2006), at the level of ~1 sigma. Results as presented by E.L. at Erice ISNP’05:

“Old” θ13 hint from atmospheric data - remarks

Slight preference (<1σ) for s13≠0 and δ=π (over δ=0)driven by atmospheric electron neutrino data

Very tiny difference at s13=0 (entirely due to δm2>0)

“

”

Three selected examples in sub- and multi-GeV SK electron samples

δm2 off, θ13 on

δm2 on, θ13 off

δm2 on, θ13 on

Dashed: central valuesSolid: +system. shifts( )

Effects often smallerthan stat+syst errorsin each bin; need globalfits to large datasets

We attributed the preference for θ13>0 to “solar term” interference effects(δm2 on & θ13 on), which seem to help the fit of sub-GeV e-like data in SK-I.

[Hint is NOT killed by adding K2K and MINOS disappearance data.]

But, other analyses found weaker or no atmospheric hint (Note: not all ofthem include solar terms). Such “old’’ hint seems to be still fragile.

The “last word” can only beexpected from the Super-Kcollaboration, since their atm.data analysis is becoming toodifficult to be reproduced atthe needed level of accuracy(hundreds of bins, dozens ofsystematics).

A possible independent hint of θ13>0 (at 90% C.L.) seems to come fromthe recent, preliminary MINOS results in appearance channel νμ->νe

Combining all data (with some optimism), the grand total is:

sin2θ13 ≈ 0.02 ± 0.01 (all data, circa 2009)

which is an encouraging 2σ hint, testable in the next few years.(N.B.: MINOS, SK, SNO, KamLAND can still provide further improvements )

Previous comparison in terms of observable half-lives is preferableto the more popular comparison in terms of unobservable Majoranamass, where covariance info is lost (although patterns are similar).

Here, correlations among different NME actually help!

Statis. approach: Compare a null hypothesis with mock data. Set 95% C.L. as threshold for discrimination. Use 4 nuclei for simplicity: 76Ge, 82Se, 130Te, 136Xe.

Null hypothesis: Standard case with light Majorana neutrino exchange, assuming 76Ge half-life of 1026 y (just to set a scale). Attach previously estimated theoretical covariances.

Mock data: Assume data centered at theoretical predictions for nonstandard mechanisms, rescaled to match benchmark value of T(76Ge)= 1026 y. Attach 25% expt. error.

Application : Testing nonstandard mechanisms for 0νββ decay

Results: two nonstandard mechanisms can be distinguished at >95 % CL

Discrimination would be insignificant if correlations were ignored.

benc

hmar

k

MASS HIERARCHY: NORMAL vs INVERTED

The ambiguity related to hierarchy, namely, sign(±Δm2), can beaddressed (in principle), via interference of Δm2-driven oscillationswith oscillations driven by some quantity Q having a known sign.

Barring states/interactions, the only known options are:

Q = Electron density (MSW effect in Earth or SNe)

Q = Neutrino density (Collective effects in SNe)

Q = δm2 (High-resolution oscill. patterns)

In addition, nonoscillation data provide another handle.

In any case, the name of the game is: high accuracy!

νν

νν

νe

νe

Oscillation probes. In vacuum, να→νβ oscillation amplitudes between νi and νj are proportional to |UαiUαjUβiUβj|, while

their phases are proportional to m2i-m

2j.

E.g., for αβ=μτ and ij=23:

+Δm2

δm2m2ν

ν2ν1

ν3

ν3

-Δm2

Abs.scale Normal hierarchy… OR… Inverted hierarchy mass2 splittings

Same amplitude, but role of largest and next-to largest phases interchanged in different hierarchies (distinguishable in principle)

Cosmology: Updated limits (2008) on the sum of ν massesfrom various data sets (assuming the “flat ΛCDM model”):

Case 1: “conservative” (only CMB data, dominated by WMAP 5y) Case 5: “aggressive” (all relevant cosmological data)

Upper limits in the range Σ < 0.6-1.2 eV have gained large consensus.

[Cosmologists envisage a brighter future, with sensitivities at the level of ~0.1 eV and, perhaps, to the hierarchy. But, will particle physicists be ready to accept a cosmological claim for Σ > 0 ?]

Cosmo-“conservative” Cosmo-“aggressive”

Single β decay Tritium experiments:

Mainz + Troitsk: mβ < 2 eV

KATRIN: improvement of O(10)

Some possible outcomes fromKATRIN (±1σ, [eV]):

mβ = 0 ±0.12 (<0.2 at 90% CL)

mβ = 0.30±0.10 (3σ, evidence)

mβ = 0.35±0.07 (5σ, discovery)

Clearly, new ideas are neededto go below ~0.2 eV. MARE ?