Neutrinos Anna Julia Zsigmond Max-Planck-Institut fr Physik ELFT - - PowerPoint PPT Presentation

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Neutrinos Anna Julia Zsigmond Max-Planck-Institut fr Physik ELFT - - PowerPoint PPT Presentation

Nov 28, 2022 434 likes •884 views

What can we learn about the Universe from Neutrinos Anna Julia Zsigmond Max-Planck-Institut fr Physik ELFT Summer School 3-7. Sept 2018 Questions Nature of neutrinos (Dirac or Majorana) Absolute neutrino mass scale Origin of

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What can we learn about the Universe from

Neutrinos

Anna Julia Zsigmond

Max-Planck-Institut für Physik ELFT Summer School 3-7. Sept 2018

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Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

Some ideas from an experimentalist based on results presented at the Neutrino 2018 conference

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Introduction to neutrino mixing

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  • Standard model originally with massless left-handed neutrinos
  • Adv. High Energy Phys. 2012 (2012) 718259
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Neutrino masses and mixing

  • Two ways to include neutrino masses in the SM
  • Dirac mass term

like all other fermions

  • Majorana mass term
  • nly for neutrinos

new physics scale Λ in coupling ➔ New scale could naturally explain the tiny neutrino masses ➔ Lepton number violation could generate the observed baryon asymmetry

  • f the Universe

➔ What new states are responsible for the new scale?

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Neutrino masses and mixing

  • Neutrino masses imply lepton mixing
  • Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix

where cij = cosθij, sij = sinθij, θij∈[0, π/2], δCP CP violating phase, α1,2 Majorana phases

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SLIDE 6

Neutrino masses and mixing

  • Parameters: 3 mass eigenstates, 3 mixing angles, 1 CP violating Dirac

phase, 2 Majorana phases

  • Mass differences from oscillations

Δm21

2 ≪ |Δm31 2| ≃ |Δm32 2|

  • Two possible mass orderings

normal ordering (NO) m1 < m2 < m3

  • r inverted ordering (IO) m3 < m1 < m2

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arXiv:1307.5487

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SLIDE 7

Neutrino oscillation experiments

Cl Homestake, Gallex, GNO, SAGE, Super-Kamiokande, SNO, KamLAND, Borexino

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  • Phys. Rev. D 83 (2011) 052002
  • Phys. Rev. D 89 (2014) 112007
  • Phys. Rev. Lett. 89 (2002) 011301
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SLIDE 8

Neutrino oscillation experiments

Super-Kamiokande IceCube-DeepCore ANTARES

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  • Phys. Rev. D 71 (2005) 112005
  • Phys. Rev. Lett. 93 (2004) 101801
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Neutrino oscillation experiments

MINOS(+) T2K NOνA

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T2K Run1-8

arXiv:1807.07891

  • M. Sanchez @ Neutrino 2018
  • A. Aurisano @ Neutrino 2018
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SLIDE 10

Neutrino oscillation experiments

Double Chooz Daya Bay RENO

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  • J. P. Ochoa-Ricoux @ Neutrino 2018
  • I. Yu @ Neutrino 2018
  • C. Buck @ Neutrino 2018

RENO Daya Bay

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SLIDE 11

Short baseline reactor neutrinos

3ν oscillation global fits

Long baseline accelerator neutrinos

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Atmospheric neutrinos Solar neutrinos + KamLAND

  • M. Tortóla, Neutrino 2018
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Precision of 3ν oscillation global fits

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Precision 2.4% 1.3% 5.5% 4.7% 4.4% 3.5% 10% 9%

Different group performing global fits: globalfit.astroparticles.es

  • Phys. Lett. B 782 (2018) 633

www.nu-fit.org

JHEP 1701 (2017) 087

Bari

  • Prog. Part. Nucl. Phys. 102 (2018) 48

Reaching very good precision Open questions:

  • Leptonic CP violation
  • Neutrino mass ordering
  • Octant of θ23

Answers within reach ...

  • M. Tortóla, Neutrino 2018
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Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

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Neutrinoless double beta decay

  • The best hope for observing the

Majorana nature of the neutrinos

  • Neutrino accompanied double

beta (2ν2β) decay observed in various isotopes with a lifetime of T2ν2β > 1019 - 1021 years

  • In case of light massive Majorana

neutrino exchange → 0ν2β decay also sensitive to absolute neutrino mass scale

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arXiv:1708.01046

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Search for neutrinoless double beta decay

  • Sensitivity on half-life
  • Background-free regime
  • Challenges

○ Good energy resolution ○ Eliminate all backgrounds ■ Cosmic rays → underground ■ Environmental radioactivity → shielding and active veto ■ Radioactivity in setup material → radio-pure material selection ○ Isotope enrichment 15

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Status of 0ν2β decay searches

Isotope T1/2 sensitivity T1/2 limit Reference EXO-200

136Xe

0.38 × 1026 0.18 × 1026

PRL 120 (2018) 072701

KamLAND-Zen

136Xe

0.56 × 1026 1.07 × 1026

PRL 117 (2016) 082503

GERDA

76Ge

1.1 × 1026 0.9 × 1026

  • A. Zsigmond, Neutrino 2018

Majorana

76Ge

0.48 × 1026 0.27 × 1026

  • V. Giuseppe, Neutrino 2018

CUORE

130Te

0.07 × 1026 0.15 × 1026

PRL 120 (2018) 132501 16

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Approaches and experiments

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  • A. Giuliani, Neutrino 2018
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Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

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Observables related to neutrino mass

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Oscillations Cosmology Decay kinematics 0ν2β decay Observable Δmij

2 = mi 2 ‒ mj 2

Mν = ∑mi mβ = ( ∑|Uei|2 mi

2

)1/2 mββ = |∑Uei

2

mi| Present knowledge

Δm21

2 = 7.6(2)×10-5 eV2

|Δm31

2| = 2.4(1)×10-3 eV2

< (0.12 - 1) eV < 2 eV < (0.2 - 0.4) eV Future 0.01 - 0.05 eV 0.2 eV 0.01 - 0.05 eV Model dependence No mass scale information ΛCDM with many parameters Energy conservation Majorana ν, nuclear matrix elements, gA

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Effective Majorana neutrino mass

  • Large uncertainties due to

nuclear matrix elements and gA

  • Future experiments should

fully probe the inverted

  • rdering mass region

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  • Phys. Rev. D 96 (2017) 053001
  • Phys. Rev. D 90 (2014) 033005
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Neutrinos in cosmology

  • Cosmological measurements provide

constraints on the sum of the neutrino masses

○ CMB temperature and polarisation power spectrum ○ Matter power spectrum ○ Baryon acoustic oscillations ○ ...

  • Current limits ∑mi < 0.1 - 0.7 eV

depending on the dataset and model assumptions

  • Some indications on preference for

normal hierarchy

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  • Astron. Astrophys. 594 (2016) A13

PDG 2018: Phys. Rev. D 98, 030001 (2018)

Planck

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Direct neutrino mass measurements

  • KATRIN started data taking with tritium this summer

→ Extract effective neutrino mass from spectral shape near to the endpoint of 3H decay at 18.6 keV

  • ECHo and HOLMES projects measuring electron neutrino mass with 163Ho

electron capture decay

  • Project 8: cyclotron radiation emission spectroscopy on atomic tritium

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Overview of neutrino masses

  • Oscillations set minimum mass

for at least two neutrinos Δmsol

2 = 7.6×10-5 eV2

|Δmatm

2| = 2.4×10-3 eV2

  • Cosmology sets upper limit for

the sum of neutrino masses ∑mi < 0.1 - 0.7 eV

  • Direct neutrino mass

measurements and neutrinoless double beta decay searches set also upper limits mββ < 0.1 - 0.5 eV

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  • Contemp. Phys. 53 (2012) 315
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Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

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Neutrino masses

  • Masses of standard model particles between 5.11×105 eV and

1.72 ×1011 eV compared to neutrino masses ≲ 10-1 eV

  • Do the neutrinos get their mass from the Higgs mechanism as the others?
  • Or some new scale beyond the standard model is responsible for the

small neutrino masses?

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Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

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Dark matter

  • Numerous indirect evidences for the existence of dark matter

○ Redshift of galaxy clusters ○ Rotational curves of galaxies ○ Gravitational lensing ○ Bullet cluster ○ CMB ○ ...

  • Can neutrinos tell us something about the nature of dark matter?

○ The three active neutrinos have a mass that is too small ○ BUT controversial indications of sterile neutrinos 27

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SLIDE 28

Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

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Baryon asymmetry of the Universe

  • No significant amount of antimatter observed in our Universe
  • Baryon to photon ratio measures the asymmetry
  • Primordial abundances of light elements from Big Bang Nucleosynthesis

→ 5.8 × 10-10 < ηSBBN < 6.6 × 10-10 within ΛCDM and SM

  • Temperature power spectrum of CMB sensitive to equation of state of the

baryon-photon plasma → 6.1 × 10-10 < ηCMB < 6.2 × 10-10

  • Agreement gives confidence in

ΛCDM model

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Sakharov conditions for baryogenesis

Baryon asymmetry has been dynamically created by baryogenesis from a matter-antimatter symmetric initial state. 3 necessary conditions for successful baryogenesis

  • Baryon number violation

→ ΔB ≠ 0 process necessary

  • C and CP violation

→ P(A → Ᾱ) ≠ P(Ᾱ → A) process necessary

  • Deviation from thermal equilibrium

→ in equilibrium the expectation values of all observables are constant → change from B = 0 to B ≠ 0 needs deviation from equilibrium

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  • Baryon number violation

→ Sphalerons at T > 130 GeV, ΔB = ΔL, B−L conserved

  • C and CP violation

→ weak interaction, CKM phase BUT too small

  • Deviation from thermal equilibrium

→ Hubble expansion of the Universe BUT too small

Baryogenesis within the Standard Model

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Baryogenesis beyond the Standard Model

  • Neutrino oscillations and dark matter indicate physics beyond the SM
  • Baryon number violating processes (e.g. proton decay) not observed in

the Universe

  • Two scenarios: direct or baryogenesis through leptogenesis
  • Top-down approach: GUTs and supersymmetric theories constrained by

the baryon asymmetry of the Universe

  • Bottom-up approach: extensions of the SM (minimality and naturalness)
  • One testable scenario discussed today

→ baryogenesis from sterile neutrino oscillations

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Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

One possible solution by extending the SM

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Extension of the Standard Model

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  • Adv. High Energy Phys. 2012 (2012) 718259
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Neutrino minimal Standard Model (νMSM)

  • If MM eigenvalues above the electroweak scale

○ Basis for thermal leptogenesis scenarios ○ CP asymmetry responsible for baryon asymmetry generated during freeze-out and decay

  • f right-handed neutrinos

○ Explains both baryon asymmetry and small neutrino masses at the same time

  • If MM eigenvalues below electroweak scale

○ Asymmetry created during thermal production of sterile neutrinos in the early Universe ○ The initial sterile neutrino abundance deviates from its equilibrium value and chemical equilibrium is not established before sphaleron freeze-out

  • Can explain observed neutrino oscillations, dark matter (DM) and the

baryon asymmetry of the Universe (BAU)

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Heavy sterile neutrinos

  • Mixing with the SM neutrinos suppressed by

small angles θαI = (mDMM

  • 1)αI where mD = λv

with v being the Higgs vacuum expectation value

  • The mass matrix for SM neutrinos is

generated by the seesaw (type I) mechanism leading to the observed neutrino oscillations mν ≃ θMMθT

  • This requires the Yukawa couplings λ to be

tiny for eigenvalues of MM below the electroweak scale

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νMSM and baryon asymmetry of the Universe

  • The measured baryon asymmetry of the Universe can constrain the

parameter space of the model

  • Assuming N1 (lightest) is responsible for dark matter

○ Only two sterile neutrinos participate in baryogenesis ○ N1 mass constrained to 1 keV ≲ M1 ≲ 50 keV ○ Fixes the absolute mass scale of SM neutrinos with the lightest being practically massless ○ CP-violating oscillation between N2,3 can generate lepton asymmetry → translated into baryon asymmetry via sphaleron interactions ○ N2,3 masses in the GeV range, quasi-degenerate (resonant amplification of the CP-violating effects)

  • Assuming all N1,2,3 participate in baryogenesis → no need for mass

degeneracy

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SLIDE 38

Questions

  • Nature of neutrinos (Dirac or Majorana)
  • Absolute neutrino mass scale
  • Origin of tiny neutrino masses
  • Dark matter
  • Baryon asymmetry of the Universe
  • Right-handed neutrinos

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Sterile neutrinos

  • Many further models predict sterile neutrinos (right-handed neutrinos /

heavy neutral leptons / singlet fermions) with a wide range of masses

  • Constraints from cosmology (structure formation, CMB, BBN), neutrino
  • scillations, LHC, meson decays, lepton flavor mixing, etc.
  • Examples

○ MN ~ 109 - 1014 GeV: motivated by GUTs, explains BAU (CP violating decay), problem with fine tuning, no DM, no direct searches ○ MN ~ 102 - 103 GeV: motivated by EW hierarchy, explains BAU (resonant leptogenesis), direct searches at LHC, no DM? ○ MN ~ keV - GeV: explains neutrino masses, oscillations, BAU, DM, direct searches e.g. in beam dump experiments, beta decay, etc. ○ MN ~ eV: motivated by anomalies observed in neutrino oscillation experiments, many further experiments ongoing 39

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Status of eV scale sterile neutrino searches

  • Controversial signal from LSND and MiniBOONE accelerator neutrino
  • scillation experiments: νμ → νe appearance
  • Reactor anomaly: after antineutrino fluxes from reactors have been

reevaluated many experiments see a deficit: νe → νe disappearance

  • NEOS and DANSS short baseline reactor neutrino experiments see also

hints of sterile neutrinos

  • GALLEX and SAGE saw deficit from predicted ν rates from intense 51Cr and

37Ar sources also pointing sterile neutrinos

  • No signal in νμ → νμ disappearance with e.g. atmospheric neutrinos
  • All anomalies individually explained by eV scale sterile neutrinos BUT

severe tension between data samples when combining different channels in global (3+1) analyses

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Status of eV scale sterile neutrino searches

  • Multitude of follow-up experiments at reactors and accelerators taking

data already

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DANSS NEOS STEREO PROSPECT SOLiD MicroBOONE

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Searches for heavy sterile neutrinos

KATRIN → TRISTAN project

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SHiP experiment

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Conclusions

  • Neutrino oscillations entering precision physics era
  • Neutrinoless double beta decay experiments pioneering in

no-background physics

  • Neutrino masses are pushed down by cosmology that will be confirmed

by KATRIN in the near future

  • Minimal extensions of the standard model can explain the tiny neutrino

masses, the baryon asymmetry of the universe as well as dark matter

  • Searches for right-handed / sterile neutrinos in a wide range of masses

with different experimental approaches ongoing / planned

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