PDF IFIC, Universitat de València/CSIC International Summer ... - Benasque

Mariam Tórtola

IFIC, Universitat de València/CSIC

Neutrino Physics (II)

International Summer Workshop on High Energy Physics 2018 TAE 2018 - Benasque (Spain), Sep 02 - Sep 15

Outline

๏ Historical introduction to neutrino physics

๏ Neutrinos in the Standard Model

๏ Neutrino masses beyond the Standard Model

๏ Neutrino oscillations in vacuum and matter

๏ Three-flavour neutrino oscillations

๏ Beyond three-neutrino flavours: sterile neutrinos

๏ The absolute scale of neutrino mass

๏ Future prospects in neutrino oscillations

๏ Neutrino physics beyond the Standard Model

Three-flavour neutrino

oscillations

θ^12, Δm221 θ^23, Δm231

two-neutrino approximation:

θ^13, Δm231

solar + KamLAND SBL reactor atmospheric + LBL

three-neutrino analysis:

θ^12, Δm221, θ¹³ θ^13, Δm231, θ¹² θ^23, Δm231, θ^13,

Δm221, δ all data samples are connected → a global 3ν analysis is required.

Δm221 << Δm231 P (⇥_↵ ! ⇥ ) = sin² 2 sin²

✓ m²L 4E

◆

Precision measurements of parameters require full 3-nu analysis

Neutrino oscillation analysis methodology

- solar: Homestake, Gallex/GNO, SAGE, Borexino, SNO, Super-K

- atmospheric: Super-K, IceCube, ANTARES

- reactor: KamLAND, Double Chooz, RENO, Daya Bay

- LBL: K2K, MINOS, T2K, NovA

Parameter sensitivity Experimental data

Methodology

The solar neutrino

sector

Solar neutrinos

pp cycle CNO produced in nuclear reactions in the

core of the Sun:

4p→ ⁴He + 2e⁺ + 2ν^e + γ

SSM predictions ν fluxes

ν energy spectra

1

Reaction source Flux (cm⁻²s⁻¹) p p → d e⁺ ν pp 5.97(1 ± 0.006)×10¹⁰ p e⁻ p → d ν pep 1.41(1 ± 0.011)×10⁸

3He p → ⁴He e⁺ ν hep 7.90(1± 0.15)×10³

7Be e⁻ → ⁷Li ν γ ⁷Be 5.07(1 ± 0.06)×10⁹

8B → ⁸Be^∗ e⁺ ν ⁸B 5.94(1 ± 0.11)×10⁶

13N → ¹³C e⁺ ν ¹³N 2.88(1 ± 0.15)×10⁸

15O → ¹⁵N e⁺ ν ¹⁵O 2.15(1 ± ⁰0^..¹⁷16)× 10⁸

17F → ¹⁷O e⁺ ν ¹⁷F 5.82(1 ± ⁰0^..¹⁹17)×10⁶

Radiochemical solar experiments

Homestake (Cl) experiment: 1967-2002

‣ gold mine in Homestake (South Dakota)

‣ 615 tons of perchloro-ethylene (C2Cl4)

‣ detection process (radiochemical)

‣ only 1/3 of SSM prediction detected:

Gallium radiochemical experiments:

50% deficit

Solar neutrinos in Super-Kamiokande

- water cherenkov detector

- sensitive to all neutrino flavors:

ν^x e^- → ν^x e^-

- threshold energy ∼ 4-5 MeV - real-time detector: (E, t)

➡

Super-Kamiokande detects less neutrinos than expected according to the SSM (40%)

The solar neutrino problem

Why the deficit observed is different?

∼30% ∼50% ~40%

➡

All the experiments detect less neutrinos than expected (30-50%)

‣ different type of neutrinos observed

→ radiochemical: ν^e while Super-K: ν^α

‣ different E-range sensitivity:

→ Cl: E > 0.814 MeV

→ Ga: E > 0.233 MeV

→ Super-K: E > 5 MeV

Tutorials

SNO is sensitive to all ν flavors:

The Sudbury Neutrino Observatory, SNO

ν^e flux (CC):

total ν flux (NC):

only 30% of the produced solar neutrinos are detected as ν^e

100% !!

The Sun produces ν^e that arrive to the Earth as 1/3 ν^e + 1/3 ν^μ + 1/3 ν^τ

➡ flavor conversion: ν^e → ν^x

The solar neutrino problem

All neutrinos are there!!

Conversion mechanism ? Neutrino oscillations ??

The KamLAND reactor experiment

average distance ∼ 180 km 


→ _Eν/L sensitivity range: Δm2 ∼ 10^-5 eV2

CPT invariance: same oscillation channel as solar ν^e (Δm221 , θ¹²)

reactor experiment:

e + p ! n + e⁺ 55 commercial power reactors

Kamioka Liquid scinitillator Anti-Neutrino Detector

→correct order of magnitude to test solar neutrino oscillations in LMA region

Combined analysis solar + KamLAND

KamLAND confirms solar neutrino oscillations.

Best fit point:


max. mixing excluded at more than 7σ

➡

mismatch between Δm221 from solar and KamLAND

★

0.2 0.3 0.4 0.5

sin²θ

12 2

4 6 8 10 12

∆m2 21 [10-5 eV2 ]

solar KamLAND global

90, 99% C.L.

sin²θ^{12 =} 0.321 + 0.018 Δm221 = 7.56 ± 0.19 x 10^-5 eV²

-0.016

➡

Bound on Δm221 dominated by KamLAND.

➡

_{Bound on θ12} dominated by solar data.

de Salas et al, PLB 782 (2018)

633

The atmospheric neutrino

sector

Atmospheric neutrinos

0 50 100 150 200 250 300 350 400 450

-1 -0.5 0 0.5 1

cosθ

Number of Events

Sub-GeV e-like

0 50 100 150 200 250 300 350 400 450

-1 -0.5 0 0.5 1

cosθ

Number of Events

Sub-GeV µ-like

0 20 40 60 80 100 120 140

-1 -0.5 0 0.5 1

cosθ

Number of Events

Multi-GeV e-like

0 50 100 150 200 250 300 350

-1 -0.5 0 0.5 1

cosθ

Number of Events

Multi-GeV µ-like + PC

0 0.5 1 1.5 2 2.5 3 3.5 4

-1 -0.8 -0.6 -0.4 -0.2 0 cosθ

Flux(10-13 cm-2 s-1 sr-1 ) Upward Through Going µ

0 0.2 0.4 0.6 0.8 1 1.2 1.4

-1 -0.8 -0.6 -0.4 -0.2 0 cosθ

Upward Stopping µ

1998: Evidence ν^μ oscillations at Super-K

2004: oscillatory L/E pattern

P_µµ = 1 sin² 2 ₂₃ sin² m²₃₂ 4

L E_⇥

⇥

Super-K Coll, PRL93, 101801 (2004)

Super-K Coll., PRL 8 (1998) 1562.

oscillation channel ν^{μ →}ν^τ

Neutrino telescopes

IceCube-DeepCore, E

ν

∊ [6-56 GeV]

ANTARES

E

ν

> 20 GeV

Atmospheric neutrino experiments

• IceCube-DeepCore (3 years of data) Aartsen et al, arXiv:1410.7227

• ANTARES (863 days of data) Adrián-Martínez et al, PLB 2012

• Super-Kamiokande (phases I to IV) Wendell et al, PRD81 (2010)

de Salas et al, PLB 782 (2018) 633

GOAL: observation of ν^μ disappearance, ν^e appearance and spectral distortions expected in the case of neutrino oscillations

→ consistent with atmospheric data

→ atm ν oscillations confirmed by laboratory exps

LBL accelerator neutrino experiments

MINOS

T2K

735 km

NovA

Feb2005 - Jun2016

From Jan2010 running in

antineutrino channel From Oct2014

running in

antineutrino channel

Accelerator LBL experiments

all experiments prefer mixing angle close to maximal

• MINOS + T2K (neutrino + antineutrino)

• NOvA (only neutrino data)

Atmospheric parameters

★

0.4 0.45 0.5 0.55 0.6

sin

²

θ

23 2.2

2.3 2.4 2.5 2.6

| ∆ m

2 31

| [10

-3

eV

2

]

★

0.4 0.45 0.5 0.55 0.6

sin

²

θ

23

90,99% C.L. NO IO

LBL only

LBL + atmos

atmospheric parameters are mostly constrained by LBL data

Combined analysis atmospheric + LBL data

de Salas et al, PLB 782 (2018) 633

The reactor mixing

angle θ ¹³

Three on-going reactor experiments

2 cores + 1 ND + 1 FD

6 cores + 4 ND + 4FD 6 cores + 1 ND + 1 FD

Reactor sector

Daya Bay + RENO + Double Chooz

Precision dominated by Daya Bay de Salas et al, PLB 782 (2018) 633

Updated global fit summary

• preference for Normal Ordering with Δ𝞆² (IO-NO) ≈ 11.7

NO

IO

➡ Inverted Ordering disfavoured at 3.4σ

Updated global fit summary

2.4%

1.3%

5.5%

4.7%

3.5%

4.4%

relative 1σ

9%

10%

!!!

Beyond three-neutrino

flavours: sterile neutrinos

‣ according to LEP measurements of invisible Z decay width:

How many neutrinos?

Experimental hints for a 4th sterile neutrino:

→ Nν = 2.984 ± 0.008 (light, active neutrinos)

‣ LSND signal for oscillations with E/L ∼ 1 eV²

‣ MiniBooNE searches for and at similar E/L

⌫

_µ

! ⌫

_e

‣ Reactor antineutrino anomaly: very short baseline disappearance indicated by the reevaluated reactor neutrino fluxes

‣ Gallium anomaly: disappearance during calibration of Gallium solar experiments with radioactive sources (L ∼ 1 m)

⌫

_µ

! ⌫

_e

⌫

_µ

! ⌫

_e

⌫

_e

⌫

_e

What is a sterile neutrino?

‣ sterile neutrino = singlet fermion of the Standard Model

‣ neutrino oscillation anomalies (m ∼ eV)

Motivations: sterile neutrinos can explain...

‣ small neutrino masses (seesaw mechanism, m > TeV-Mpl)

‣ baryon asymmetry of the universe (leptogenesis, m>> 1 GeV)

→ it has no interactions (exceptions: Higgs, mixing and physics BSM)

‣ (part of) the dark matter of the universe (m ∼ keV)

Hints for ν ^μ → ν ^e appearance

LSND Collab., PRD 64 (2001) 112007

⌫

_µ

! ⌫

_e

L ∼ 30m, E ∼ 20-75 MeV

‣ Evidence for oscillations

‣ Excess of ν^e events:

87.9 ± 22.4 ± 6.0 (3.8σ)

The LSND anomaly

LSND Collab., PRD 64 (2001) 112007

⌫

_µ

! ⌫

_e

L ∼ 30m, E ∼ 20-75 MeV

‣ Evidence for oscillations

‣ Excess of ν^e events:

87.9 ± 22.4 ± 6.0 (3.8σ)

‣ Part of the allowed region excluded by other experiments.

‣ Δm2LSND ∼ 0.2-10 eV²

The LSND anomaly

4th sterile neutrino required !!

⌫

_µ

! ⌫

_e

L ∼ 30m, E ∼ 20-75 MeV

LSND Collab., PRD 64 (2001) 112007

‣ Evidence for oscillations

‣ Excess of ν^e events:

87.9 ± 22.4 ± 6.0 (3.8σ)

‣ Part of the allowed region excluded by other experiments.

‣ Δm2LSND ∼ 0.2-10 eV²

→ Δm2LSND ≠ Δm2SOL , Δm2ATM → Δm2LSND ≠ Δm2SOL + Δm2ATM

The LSND anomaly

The MiniBooNE experiment

‣ Designed to test the LSND signal (similar L/E ratio)

‣ Runs in neutrino and antineutrino mode

‣ The neutrino channel results have been changing with time:

Michele Maltoni, Neutrino-2018

Hints for ν ^e disappearance

ν ^e disappearance in reactor experiments

‣ Historically, very-short-baseline reactor experiments (10-100 m) have not observed any disappearance of reactor neutrinos.

‣ 2011: improved calculations of antineutrino fluxes report 3% increase of the neutrino flux

Gariazzo et al, JHEP 2017

‣Mueller et al, arXiv:1101.2663, Huber, arXiv 1106.0687

⇒ SBL reactor experiments show a deficit in the

number of neutrinos detected: R = 0.927 ± 0.023 (3σ effect) -

The Gallium anomaly

⇒ L/E similar to reactor anomaly

→ averaged deficit of ν^e:

(2.9σ)

‣ Calibration of Gallium solar experiments GALLEX and SAGE with intense radioactive νe sources ⁵¹Cr and ³⁷Ar in the process:

e

+

⁷¹

Ga !

⁷¹

Ge + e

→ a reduction in the number of νe is observed

R = 0.84 ± 0.05

‣ L ∼ 1-2 m, E ∼ 0.4-0.8 MeV

‣ oscillations with Δm² ∼ 1 eV² can lead to reduction of the ν^e flux in the detector volume

3σ evidence of SBL ν^e oscillations based on comparisons of measured spectra at different baselines, independent of flux predictions.

Recent indications: NEOS and DANNS

Gariazzo et al, arxiv:1801.06467

10.7 m vs12.7 m

Observation of ratios of reactor antineutrino spectra at two baselines

Interpretation of the anomalies

Δm2sol ∼ 8x10^-5 eV² Δm2atm ∼ 2x10^-3 eV² Δm2LSND ∼ 1 eV²

2+2 neutrino scheme

Maltoni et al, NPB643 (2003), NJP06 (2004)

excluded by solar and

atmospheric data

‣

This scheme requires the presence of sterile

neutrinos either in solar or atmospheric neutrinos

‣

However, solar and atmospheric data show a strong preference for active oscillations

ΔΧ²

Global fit in 3+1 neutrino scheme

‣

3+1 spectra include the 3 active-neutrino scenario as limiting case.

‣

solar & atmos oscillations: mainly active ν + small sterile component

Dentler et al, arXiv:1803.10661

Disagreement between

ν

^e

and

ν

^{μ data}

strong tension between app (LSND/MB) and disapp exp. (CDHS, SK, IceCube,

MINOS/+)

eV-sterile neutrino in Cosmology

‣

In Cosmology, sterile neutrinos with eV masses would contribute to:

Neff = relativistic degrees of freedom.

Σmν = sum of neutrino masses

‣

if the mixing active-sterile neutrino is small, one can relax limits from cosmology

‣

However, for mass & mixing

parameters required to explain the anomalies, ν^s is fully thermalized in the early universe.

Hannestad et al, 1204.5861

→ N

eff

≈ 4

X m_⌫ & 0.05eV +

q

m²₄₁

→ > 1 eV

Bounds from Cosmology

Lattanzi & Gerbino, arxiv:1712.07109

‣

recent limits on the effective number of relativistic dof:

‣

constraints can be avoided by preventing ν^s thermalization in the early universe, but it requires large modifications of cosmological model.

Dasgupta and Kopp, PRL112 (2014) 031803

Example: new interactions in the sterile neutrino sector that suppress their thermalization in the early Universe

-

PLANCK: Neff = 3.15 ± 0.23

-

PLANCK + LSS: Neff = 3.03 ± 0.18

‣

recent limits on the sum of neutrino masses:

Σmν < 0.13 - 0.72 eV < 1 eV !!!! Lattanzi & Gerbino, arxiv:1712.07109

However: these interactions also affect CMB!! Not easy to solve

Forastieri et al, JCAP 1707 (2017) 038

The absolute scale of

neutrino mass

Constraints on neutrino masses

From oscillations: m

_⌫

q

m

²₃₁

+ m

²₂₁

& 0.05 eV

Bounds from cosmology

‣ neutrino masses may affect cosmological observables:

Σ mνi < 0.13- 0.72 eV

→ anisotropies in the CMB spectrum

→ Large Scale Structure formation

→ weak gravitational lensing

‣ Fit ΛCDM model + experimental data (WMAP, PLANCK, HST, LSS,...)

Lattanzi & Gerbino, arxiv:1712.07109

Tritium beta decay experiments

‣ β-decay spectrum close to the endpoint is very sensitive to neutrino mass:

m( _e)² = X

i

|U_ei|²m( _i)² effective neutrino mass:

K(T) =

"

(Q T )

XN

i=1

|U_ei|² q

(Q T)² m²_i ⇥(Q T m_i)

#^1/2

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Mainz and Troitsk Experiments

m

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< 2.2 eV (95% C.L.)

The KATRIN experiment

(KArlsruhe TRItium Neutrino experiment)

Inauguration 11 June 2018

sensitivity (90%CL) mν < 0.2 eV

discovery potential mν = 0.35 eV (5σ)

Neutrinoless double beta decay

‣2νββ: rare process in the SM with t1/2∼ 10²¹ years

‣0νββ: possible for massive Majorana neutrinos.

→ violates Lepton Number

→ rate depends on mν, unknown phases and nuclear mass matrix elements

→ t1/2∼ 10²⁶-10²⁷years

→ good separation 2νββ from 0νββ

→ low bg 0νββ peak region test ν nature

(A,Z) →(A,Z+2) + e^- + e^-

→ not observed yet

0⌫

= G

^0⌫

| M

^0⌫

|

²

< m >

²

< m >= | X

i

U

_ei²

m

_i

|

mββ < 120-270 meV GERDA II

→ degenerate region explored

Bounds from 0 νββ decay experiments

< m >= | X

i

U

_ei²

m

_i

|

Lattanzi & Gerbino, arxiv:1712.07109

At 90% CL:

mββ < 61-165 meV KL-Zen

mββ < 147-398 meV EXO-200 mββ < 140-400 meV CUORE

→ next generation: full IH region mlight < 1 eV

mlight < 0.2 eV

3σ discovery sensitivity 20 meV

Future prospects in

neutrino oscillations

Prospects for precision

∼1% precision on ∆m232

θ23

sin2

0.4 0.5 0.6

322 mΔ

2.2 2.4 2.6 2.8 3

−3

×10

POT by 2014 , 90% C.L POT, 90% C.L 7.8x1021

POT w/improvement, 90% C.L 20x1021

Stat. only Systematics

T2K-II

Abe et al, 1609.04111

∼1-3% precision on sin²θ²³

JUNO

DayaBay

An et al, 1507.05613 (6 years)

∼0.6% precision on ∆m221

∼0.7% precision on sin²θ12

< 3% precision in sin²2θ¹³ and ∆m2ee by

2020

(2026)

Cao and Luk, 1605.01502

Prospects for CP violation

T2K-II

‣ by 2024:

> 2σ sensitivity on CP violation at max CP violation

NOνA

21) Protons-on-Target (x10

0 5 10 15 20

=0 CPδ to exclude sin2 χΔ

0 5 10 15

w/ eff. stat. improvements (no sys. errors) w/ eff. stat. & sys. improvements

w/ eff. stat. improvements & 2016 sys. errors

90% C.L.

99% C.L.

C.L.

3σ

‣ by 2026 (20×10²¹ POT):

> 3σ sensitivity on CP violation

→ > 5σ sensitivity for some fraction of δ^CP

Prospects for CP violation

‣ for sensitivities above 3σ from a single experiment: DUNE, Hyper-K

ORCA _NOνA

• by 2020: 3σ sensitivity (NO and δ=3π/2)

• by 2024: 3σ sensitivity for 30/50% of δ

• by 2023: 3σ determination of MO

JUNO

3σ sensitivity on mass ordering after 6 years

(similar results for PINGU)

Reactor experiment with L=50 km upgraded ANTARES exp.

Prospects for mass ordering

Neutrino physics beyond the Standard Model

‣ Non-standard neutrino interactions

‣ Non-unitary neutrino mixing

Non-Standard Interactions (NSI)

• NSI appear in models of neutrino masses

• NSI may affect oscillation parameters ,

• Information about the size of NSI could be very useful for neutrino model building

f ^f’

ν

α

ν

β

sensitivity reach of upcoming experiments (degeneracies and ambiguities)

precision measurements at current experiments

NSI: Notation

L

^{CC NSI}

= 2 p

2G

_F

✏

^{f f}_↵ ^0X

(¯ ⌫

_↵ ^µ

P

_L

` ) ¯ f

⁰ _µ

P

_X

f

may affect neutrino production and detection

✏

^s_↵ (source)

✏

^d_↵ (detector)

L

^{NC NSI}

= 2 p

2G

_F

✏

^{f X}_↵

(¯ ⌫

_↵ ^µ

P

_L

⌫ ) ¯ f

_µ

P

_X

f

→ NSI violate lepton flavor (FC-NSI)

✏

_↵↵

✏ 6 = 0

_→ NSI violate LF universality (NU-NSI)

✏

_↵

6 = 0

mainly affecting neutrino propagation in matter:

✏

^m_↵

(but also detection, e.g., Super-K and Borexino)

NSI in the solar sector

Gonzalez-Garcia et al, JHEP 2013 Miranda et al, JHEP 2006

A degenerate solution appears, with θ

¹²

> π/4

Standard solution without NSI

Gouvea and Kelly, NPB 2016

NSI at future LBL experiments

( θ

23

- 𝜖

^ττ

) degeneracy in DUNE

Coloma, JHEP 2016

•Most models of neutrino masses -> extra heavy states Ex: type I seesaw, inverse seesaw

• NxN mixing matrix with:

N(N-1)/2 mixing angles and (N-1)(N-2)/2 Dirac CP phases

Non-unitary light neutrino mixing

✓ 0 M

_D

M

_D^T

M

_R

◆

⁰

@ 0 M_D 0 M_D^T 0 M

0 M^T µ

1 A

→ (3x3) light neutrino mixing matrix U is non-unitary in general

→ if U is non-unitary: 9 more parameters are needed to describe

mixing: 6 new moduli + 3 new phases.

NU neutrino oscillations in DUNE

The new phases will modify the standard oscillation picture in LBL experiments, such as DUNE

→ (δ, 𝜙) degeneracies in

P

μe for E≳ 3 GeV spoil sensitivity to δ

Escrihuela et al, NJP 2017

CP violation searches in DUNE

> 5σ sensitivity for some fraction of δ^CP

E. Worcester, DUNE Collaboration

DUNE CP sensitivity with NU

Escrihuela et al, NJP 2017

The sensitivity to CP violation might be significantly spoiled in the presence of NU

Summary (I)

‣

Neutrinos play an important role in many physical and astrophysical scenarios

‣

Important discoveries on neutrino physics along last century have provided the first evidence for physics beyond the Standard Model

‣

Extensions of the SM can explain the smallness of neutrino mass, although the flavor structure is not well understood yet

‣

Neutrino oscillations are well stablished with observations in several experiments, with natural and artificial sources.

‣

Oscillation parameters are measured quite accurately (≲ 6%) by the combination of different experiments.

‣

First indications for normal mass ordering and maximal CP violation.

Summary (II)

‣

there are several indications for sterile neutrinos at eV scale.

‣

signal from ν^e disappearance at reactor and Gallium experiments are consistent, and not in disagreement with other data samples

‣

hint from ν^μ → ν^e appearance in LSND and MiniBooNE are in

disagreement with negative signals in ν^μ disappearance experiments.

‣

consistent picture of eV-sterile neutrinos in tension with cosmology

‣

new physics beyond the SM may affect significantly the standard picture of neutrino oscillations.

‣

the absolute scale of neutrino mass is bounded from cosmological and laboratory measurements, below 1 eV.