What can we learn about the Universe from Neutrinos Anna Julia Zsigmond Max-Planck-Institut für Physik ELFT Summer School 3-7. Sept 2018
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 2
Introduction to neutrino mixing Standard model originally with massless left-handed neutrinos ● 3 Adv. High Energy Phys. 2012 (2012) 718259
Neutrino masses and mixing Two ways to include neutrino masses in the SM ● Dirac mass term ● like all other fermions Majorana mass term ● only 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 ➔ of the Universe What new states are responsible for the new scale? ➔ 4
Neutrino masses and mixing Neutrino masses imply lepton mixing ● Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix ● where c ij = cosθ ij , s ij = sinθ ij , θ ij ∈ [0, π/2], δ CP CP violating phase, α 1,2 Majorana phases 5
Neutrino masses and mixing Parameters: 3 mass eigenstates, 3 mixing angles, 1 CP violating Dirac ● phase, 2 Majorana phases Mass differences from oscillations ● 2 ≪ |Δm 31 2 | ≃ |Δm 32 2 | Δm 21 Two possible mass orderings ● normal ordering (NO) m 1 < m 2 < m 3 or inverted ordering (IO) m 3 < m 1 < m 2 6 arXiv:1307.5487
Neutrino oscillation experiments Cl Homestake, Gallex, GNO, SAGE, Super-Kamiokande, SNO, KamLAND, Borexino Phys. Rev. Lett. 89 (2002) 011301 Phys. Rev. D 83 (2011) 052002 Phys. Rev. D 89 (2014) 112007 7
Neutrino oscillation experiments Super-Kamiokande IceCube-DeepCore ANTARES Phys. Rev. Lett. 93 (2004) 101801 Phys. Rev. D 71 (2005) 112005 8
Neutrino oscillation experiments T2K Run1-8 MINOS(+) T2K NOνA A. Aurisano @ Neutrino 2018 arXiv:1807.07891 M. Sanchez @ Neutrino 2018 9
Neutrino oscillation experiments Double Chooz Daya Bay RENO C. Buck @ Neutrino 2018 J. P. Ochoa-Ricoux @ Neutrino 2018 I. Yu @ Neutrino 2018 RENO Daya Bay 10
3ν oscillation global fits Solar Atmospheric neutrinos neutrinos + KamLAND Short Long baseline baseline reactor accelerator neutrinos neutrinos 11 M. Tortóla, Neutrino 2018
Precision of 3ν oscillation global fits Precision Different group performing global fits: 2.4% globalfit.astroparticles.es 1.3% Phys. Lett. B 782 (2018) 633 www.nu-fit.org 5.5% JHEP 1701 (2017) 087 Bari 4.7% Prog. Part. Nucl. Phys. 102 (2018) 48 4.4% Reaching very good precision Open questions: Leptonic CP violation 3.5% ● Neutrino mass ordering ● Octant of θ 23 10% ● Answers within reach ... 9% 12 M. Tortóla, Neutrino 2018
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 ● 13
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 T 2ν2β > 10 19 - 10 21 years In case of light massive Majorana ● neutrino exchange 0ν2β decay also sensitive to → absolute neutrino mass scale 14 arXiv:1708.01046
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
Status of 0ν2β decay searches Isotope T 1/2 sensitivity T 1/2 limit Reference 136 Xe 0.38 × 10 26 0.18 × 10 26 EXO-200 PRL 120 (2018) 072701 136 Xe 0.56 × 10 26 1.07 × 10 26 KamLAND-Zen PRL 117 (2016) 082503 GERDA 76 Ge 1.1 × 10 26 0.9 × 10 26 A. Zsigmond, Neutrino 2018 Majorana 76 Ge 0.48 × 10 26 0.27 × 10 26 V. Giuseppe, Neutrino 2018 CUORE 130 Te 0.07 × 10 26 0.15 × 10 26 PRL 120 (2018) 132501 16
Approaches and experiments 17 A. Giuliani, Neutrino 2018
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 ● 18
Observables related to neutrino mass Oscillations Cosmology Decay kinematics 0ν2β decay m β = ( ∑|U ei | 2 m i 2 m ββ = |∑U ei 2 2 = m i 2 ‒ m j 2 Observable Δm ij M ν = ∑m i ) 1/2 m i | Present Δm 21 2 = 7.6(2)×10 -5 eV 2 < (0.12 - 1) eV < 2 eV < (0.2 - 0.4) eV knowledge |Δm 31 2 | = 2.4(1)×10 -3 eV 2 Future 0.01 - 0.05 eV 0.2 eV 0.01 - 0.05 eV ΛCDM Majorana ν, Model No mass scale Energy with many nuclear matrix dependence information conservation parameters elements, g A 19
Effective Majorana neutrino mass Large uncertainties due to ● nuclear matrix elements and g A Future experiments should ● fully probe the inverted ordering mass region Phys. Rev. D 90 (2014) 033005 20 Phys. Rev. D 96 (2017) 053001
Neutrinos in cosmology Cosmological measurements provide ● Planck constraints on the sum of the neutrino masses CMB temperature and polarisation power ○ spectrum Matter power spectrum ○ Baryon acoustic oscillations ○ ... ○ Current limits ∑m i < 0.1 - 0.7 eV ● depending on the dataset and model assumptions Some indications on preference for ● normal hierarchy Astron. Astrophys. 594 (2016) A13 PDG 2018: Phys. Rev. D 98, 030001 (2018) 21
Direct neutrino mass measurements KATRIN started data taking with tritium this summer ● → Extract effective neutrino mass from spectral shape near to the endpoint of 3 H decay at 18.6 keV ECHo and HOLMES projects measuring electron neutrino mass with 163 Ho ● electron capture decay Project 8 : cyclotron radiation emission spectroscopy on atomic tritium ● 22
Overview of neutrino masses Oscillations set minimum mass ● for at least two neutrinos 2 = 7.6×10 -5 eV 2 Δm sol |Δm atm 2 | = 2.4×10 -3 eV 2 Cosmology sets upper limit for ● the sum of neutrino masses ∑m i < 0.1 - 0.7 eV Direct neutrino mass ● measurements and neutrinoless double beta decay searches set also upper limits m ββ < 0.1 - 0.5 eV 23 Contemp. Phys. 53 (2012) 315
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 ● 24
Neutrino masses Masses of standard model particles between 5.11×10 5 eV and ● 1.72 ×10 11 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? 25
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 ● 26
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
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 ● 28
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 < η SBBN < 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 < η CMB < 6.2 × 10 -10 Agreement gives confidence in ● ΛCDM model 29
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 30
Baryogenesis within the Standard Model 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 31
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