Neutrino Mass Experiments Patrick Decowski decowski@nikhef.nl - PowerPoint PPT Presentation

Neutrino Mass Experiments Patrick Decowski decowski@nikhef.nl

Measuring Neutrino Mass 0 νββ β decay / EC Cosmology Observable Relies on Λ CDM Majorana Kinematics

Direct Measurement Using Weak Decays Wish List for Direct Measurements • low end-point → relatively large spectrum deformation • short life → small source amount / less scattering in source • (super) allowed transition → matrix element reliably calculable • simple molecular → molecular states calculable • high isotopic purity • source stability • established procurement � Only two isotopes of choice: Beta Decay (Tritium) Electron Capture (Holmium) � He � � � � � ��� Ho � � � � ��� D�� � � � � H � � � E 0 = 18.6 keV Q EC = 2.8 keV � 1/2 = 12.3 y � 1/2 = 4570 y super-allowed [Slide S. Enomoto]

Neutrino Mass Measurements with Weak Decays KATRIN Beta Decay (Tritium) � He � � � � � Electron Spectrum � H � � � (E 0 = 18.6 keV) beta electron Electron Capture (Holmium) Dy = Dysprosium ��� Ho � � � � ��� D�� � � � De-excitation Spectrum (Q EC = 2.8 keV) � � X-ray Auger electron No capture from K and L [Slide S. Enomoto]

6 Electron Spectroscopy with Electro-Static Filter electron tritium U counter source electro-static retarding potential e e eU Problem: only small fraction of electrons reach this → guiding magnetic field [Slide S. Enomoto]

7 Electron Spectroscopy with Electro-Static Filter electron guiding tritium U counter magnetic-field source electro-static retarding potential eU E parallel / E transversal depends on Problem: only E parallel is measured initial emission angle → adiabatic collimation [Slide S. Enomoto]

8 Electron Spectroscopy with Electro-Static Filter electron guiding tritium U counter magnetic-field source electro-static retarding potential eU reduce magnetic field adiabatically E � � � � const ⇒ magnetic moment conserves: ⇒ collimation B [Slide S. Enomoto]

9 MAC-E (Magnetic-Adiabatic-Collimation Electro-static) Filter Adiabatic Transmission (constant magnetic moment) � � � � � � const Energy resolution is electron determined by B-Ratio counter �� � � �min �ma� Retarding eU Potential B min B max Adiabatic Transmission (or blocking) [Slide S. Enomoto]

11 KATRIN Experiment KArlsruhe TRItium Neutrino Experiment • located at Karlsruhe Institute of Technology, Karlsruhe, Germany • design sensitivity: m( � e ) < 0.2 eV (90%CL, 3 years) Injection Calibration 10 － 14 mbar l/s 1.8 mbar l/s E-Gun Tritium Retention Electron Counter (electrons guided by B) (~10 mHz) 10 11 Bq Gaseous Tritium Source 0.9 eV Resolution MAC-E Filter

KATRIN 70m

Results − 1.1 eV 2 Best-fit: m 2 ( ν e ) = − 1.0 +0.9 KATRIN upper limit on neutrino mass: m ν < 1.1 eV (90% CL) [1 σ fluctuation to negative result] Only 4 weeks of data! By 2024: m ν < 0.2 eV (90% CL) or = 0.35 eV (5 σ ) arXiv:1909.06048

Neutrinoless Double Beta Decay

Double beta decay Isotopes 9 136 53 I � 136 Pr 8 � A=136 59 + � 7 6 5 (A,Z+1) 4 136 La 136 Ce (A,Z) 57 136 � 55 Cs 58 136 � Xe 3 + ββ even-even 54 � (A,Z+2) �� 2 1 136 Ba (MeV) 56 A second-order process only detectable if first-order beta decay is energetically forbidden

Neutrinoless Double Beta Decay e - e - But what if ν is Majorana? ν i ν i M ν 6 = 0 U ei U ei | ∆ L | W - W - = 2 Nuclear Process > > (A, Z) (A, Z+2)

Candidate 0 ν 2 β Nuclei [Candidates with Q>2 MeV] Candidate Q[MeV] %Abund Candidates are even-even nuclei 4.271 0.187 48 Ca → 48 Ti 76 Ge → 76 Se 2.04 7.8 2.995 9.2 82 Se → 82 Kr 96 Zr → 96 Mo 3.35 2.8 (A,Z+1) 100 Mo → 100 Ru 3.034 9.6 (A,Z) 2.013 11.8 110 Pd → 110 Cd ββ even-even 116 Cd → 116 Sn 2.802 7.5 (A,Z+2) 2.228 5.64 124 Sn → 124 Te 2.53 34.5 130 Te → 130 Xe 136 Xe → 136 Ba 2.479 8.9 3.367 5.6 150 Nd → 150 Sm Natural abundance of 0 ν 2 β candidates is low → enrichment necessary

Detecting 0 ν 2 β Decay With energy resolution Without energy resolution 2 ν 2 β 2 ν 2 β : ( A , Z ) → ( A , Z + 2) + 2 e − + 2 ν e 0 ν 2 β : ( A , Z ) → ( A , Z + 2) + 2 e − 0 ν 2 β � E e /Q • General approach: detect the two final-state electrons • Signature: Two simultaneous electrons with summed energy Q ββ , the Q-value for the ββ decay in the isotope of study

2 ν 2 β has been measured 1 / 2 ) − 1 = G 2 ν ( Q, Z ) | M 2 ν | 2 ( T 2 ν Isotope T 1/22 ν [yr] 48 Ca 4.2±1.0 x 10 19 Phase Space Nuclear factor Matrix Element 76 Ge 1.5±0.1 x 10 21 82 Se 0.92±0.07 x 10 20 • Conserves lepton number 96 Zr 2.0±0.3 x 10 19 100 Mo 7.1±0.4 x 10 18 • Does not discriminate between Dirac and Majorana 116 Cd 3.0±0.2 x 10 19 neutrinos 128 Te 2.5±0.3 x 10 24 • Not sensitive to neutrino mass scale 130 Te 0.9±0.1 x 10 21 136 Xe 2.165±0.054 x 10 21 • Nevertheless: slow process! 150 Nd 7.8±0.8 x 10 18 238 U 2.0±0.6 x 10 21 [2 ν 2EC on 124 Xe: 1.8 x 10 22 yr]

What mass does 0 ν 2 β measure? 1 / 2 ) − 1 = G 0 ν ( Q, Z ) | M 0 ν | 2 � m ββ ⇥ 2 ( T 0 ν Phase Space factor: Nuclear Matrix Element: Interesting physics Calculable Hard to calculate Effective Majorana mass: � � 3 � � X U 2 h m ββ i = ei m i � � [coherent sum] � � � � i =1 Where U ei elements from the Lepton Mixing Matrix

Nuclear Matrix Elements 1 / 2 ) − 1 = G 0 ν ( Q, Z ) | M 0 ν | 2 � m ββ ⇥ 2 ( T 0 ν • Model dependence: spread of 2-3x for each isotope • No significant preference for particular isotope 76 Ge 136 Xe

E ff ective Majorana Mass S. Elliot, Mod. Phys. Lett. A 27, 1230009 (2012) θ 13 non-zero KKDC claim in 76 Ge Next-generation of 0 ν 2 β expt: few 100kg Future 0 ν 2 β expt: ton-scale KATRIN θ 12 = 33.58 0 θ 12 = 33.58 δ δ Normal Inverted θ 13 = 0 0 θ 13 = 8.33 δ δ

Experimental sensitivity 1 / 2 ∝ ✏ a No experimental T 0 ν AMt background: Detector Isotopic Mass Fraction Detector Running Efficiency Time � 1 / 2 ∝ � a Mt With experimental T 0 ν background: A b ∆ E Detector Atomic Resolution Mass Background Rate

Backgrounds • The signal level of the experiments is few cnts/(ton-year) • Background control critical For any rare event expt: log(sensitivity) • Typical backgrounds involved BG free: ~t • Contamination from U and Th decay-chain isotopes BG: ~t 1/2 Systematics • Compton-scattered ɣ rays, β and α particles • Cosmogenic muon induced backgrounds log(exposure) =mass x time • Activation of shielding, source material etc. 0 ν 2 β experiments are ultra-clean and conducted deep under ground

Q-val and Background Natural radioactivity ( 40 K, 60 Co, 234m Pa, external 214 Bi and 208 Tl…) 214 Bi and Radon 208 Tl (2.6 MeV γ line) and Thorium γ from (n, γ ) reactions Surface or bulk contamination in α emitters Cosmogenic production 150 Nd 100 Mo 130 Te 76 Ge 96 Zr 48 Ca 82 Se 136 Xe 2 3 4 5 Q [MeV]

Generally Two Techniques Source ≠ Detector Source = Detector Detector β 1 β 1 Source Detector β 2 Detector β 2 Pros: Pros: +Easy to change source +Energy resolution isotope +Mass +Background mitigation +Detection Efficiency +Topology Cons: Cons: -Mass -Background mitigation -Detection Efficiency -Topology

Incomplete (and outdated) overview of experiments Q ββ Isotope Experiment Technique Mass Enriched Start/Stage [MeV] 130 Te Cuoricino TeO 2 bolometers 40.7kg No 2.6 Done 82 Se, 100 Mo NEMO-3 tracko-calo 0.9kg/6.9kg Yes 3.37 Done 136 Xe EXO LXe [tracking] 170kg 80% 2.458 Done 76 Ge Ge diodes in LAr 18kg/35kg 86% 2.04 2011/2015 GERDA Phase I/II 76 Ge Majorana Ge diodes 30kg 86% 2.04 2015 136 Xe Isotope in LS 380/750kg 90% 2.458 2011/2019 KamLAND-Zen 130 Te TeO 2 bolometers CUORE 204kg No 2.53 2016 130 Te SNO+ Isotope in LS 750kg No 2.53 2020 136 Xe nEXO LXe [tracking] 5000kg 80% 2.458 2027? 76 Ge LEGEND Ge diodes in LAr 200/1000kg 86% 2.04 ? 82 Se, 150 Nd SuperNEMO tracko-calo 7kg/100kg Yes 3.37 ? 136 Xe NEXT GXe 100kg yes 2.458 ? 116 Cd COBRA CdZnTe semicond No 2.8 Prototype 48 Ca CaF 2 cryst in LS CANDLES 0.35kg No 4.27 Prototype 82 Se Lucifer bolom+scintill 100 Mo MOON tracking 1t No 3.03 Prototype DARWIN

KamLAND(-Zen) detector • 1 kton Scintillation Detector • 6.5m radius balloon filled with: } • 20% Pseudocumene (scintillator) • 80% Dodecane (oil) • PPO • 34% PMT coverage • ~1300 17” fast PMTs 20 m • ~550 20” large PMTs • Water Cherenkov veto • Operational since 2002 1800 m 3 Buffer Oil Water Cherenkov 3200 m 3 Outer Detector

Mini-Balloon • Requirements Corrugated nylon tube (7 m) • Chemical compatibility with LS Vectran strings (12) • Mechanically strong, low radioactivity PEEK connector • Barrier against Xe: Tube • loss < 220g/yr Cone • Transmission of scintillation light Straps (12) 1.54m • 99.4% at 400nm Balloon (24 gores) Belt and polar cap • Material: 25 μ m thick ultra- pure nylon • U/Th/K ≲ 10 -12 g/g • 1/4 & full scale tests in air and water

Mini-Balloon Construction: May-Aug 2011 Near Sendai

Difference in refractive index LS and Xe-LS 29