Detecting Neutrinos Hamish Robertson, INT Summer School, Seattle 2009

Transcription

1 Detecting Neutrinos Hamish Robertson, INT Summer School, Seattle 2009

2 A Brief History of Neutrinos 1930 Pauli s desperate remedy Bethe & Critchfield explain the sun s power Parity violation discovered in β decay 1956 The neutrino observed Neutrino helicity measured The µ neutrino discovered the τ neutrino makes 3. 2

3 I have created a particle that can never be detected W. Pauli ν e + p e + + n 3

4 Reines and Cowan s Telegram to Pauli Professor W. Pauli 14 June 1956 Zurich University Ooops! He was at ETH. Switzerland We are happy to inform you that we have definitely detected neutrinos from fission fragments by observing inverse beta decay of protons. Observed cross section agrees well with expected six times ten to minus forty-four square centimeters. Nite letter Frederick Reines & Clyde Cowan Box 1663 Los Alamos, New Mex

5 Pauli s answer 5

6 6x cm

7 t Hooft, PLB37, 195 (1971) σ ν,e T

8 NOT Detecting Neutrinos Helicity -- the Goldhaber-Grodzins-Sunyar experiment. Mass from the electron spectrum in beta decay. Neutrinoless Double Beta decay and the question of whether the neutrino and antineutrino are the same or different.

9 Helicity of the neutrino ν 152m Eu source 0 - Fe Coil Electron capture fs 152m Eu Pb γ The neutrino is left-handed: σ p ˆ = Sm γ detector Sm 2 O 3 Goldhaber, Grodzins, & Sunyar, PR 109, 1015 (1958)

10 Mass confusion Fermi 1932: Neutrinos could have mass, just like electrons, but seems much less. Hanna & Pontecorvo 1949: Neutrino mass < 1/1000 electron mass s: Parity violation discovered. Neutrino directly observed. Neutrino helicity measured. PV attributed to neutrinos. Glashow, Weinberg, Salam late 1960 s: Can t understand these things unless mass = 0. So, no RH neutrinos in the SM. 10

11 Determination of Neutrino Mass Neutrino Oscillations Beta Decay Tritium 187 Re Double beta decay Cosmology The mass is needed for Particle physics Cosmology

12 Direct Mass Limits: the History Mass Limit (ev, kev, or MeV) 12

13 Why is neutrino mass so small? Neutrino mass is not a feature of the SM A signal of unification? Seesaw model: m ν = m 2 D M ν 3 : ν 2 : ν 1 : ev

14 The Universe -- A very odd place And why is there matter but no antimatter? Sakharov s criteria: Baryon number not conserved CP violated Universe not in equilibrium at some point

15 Minimum mass: Σm ν > 55 mev (oscillations) Neutrinos and cosmology (total about 20% of the mass of stars) Maximum mass: Σm ν < 6900 mev (tritium), about 8% of closure.

16 Even small m ν influences structure SDSS + 2dFGRS Barger et al. hep-ph/ Σm ν 280 mev 1500 mev 3000 mev

17 KATRIN Minimum mass: Σm ν > 60 mev (oscillations) Σm ν, ev 2 Fogli et al. Phys.Rev.D75:053001,2007

18 Planck Launched May 15, 2009 Planck will provide 3 separate ΛCDM constraints on Σm ν : 1. Planck + SDSS 0.2 ev 2. Planck only 0.26 ev 3. CMBR + grav. lensing 0.15 ev From Planck Bluebook

19 β-decay electron spectrum shape determines the absolute neutrino mass squared: i K ~ [ g v2 M F 2 + g A2 M GT 2 ] F(E,Z) = Fermi function m ν = mass of electron (anti-)neutrino = Σ i U ei 2 m i = m ν in quasi-degenerate region. Present Limit: 2.3 ev (95% CL) Kraus et al. hep-ex/

20 The Mainz Neutrino Mass Experiment Phase 2: After all critical systematics measured by own ex (inelastic scattering, self-charging, neighbor excit (. C.L m 2 (ν) = -0.6 ± 2.2 ± 2.1 ev 2 m(ν)< 2.3 ev (95% C. Kraus et al., Eur. Phys. J. C 40 (2005) 447

21 Kinematics of β-decay Model-independent determination of mass. Independent of: whether neutrinos Dirac or Majorana, nuclear matrix elements, phases, cosmological models.

22 What are we measuring? Writing the transition probability as the matrix element of some operator T, In the degenerate regime where all the masses are the same, the unitarity of U gives us back the original expression for a single massive neutrino, an electron neutrino with mass p e E(E E 0 ) 2 1 m ν 2 (E E 0 ) 2 In fact, because U e3 is so small, this expression is good all the way down to about 10 mev! 1/ 2

23 KATRIN at Forschungszentrum Karlsruhe unique facility for closed T2 cycle: Tritium Laboratory Karlsruhe TLK ~ 75 m long with 40 s.c. solenoids 5 countries 13 institutions 100 scientists

24 Mass Range Accessible KATRIN Average mass > 20 mev Present Lab Limit 2.3 ev Δm 122 Δm 232

25 Experimental Arrangement 70 m Rear Source Transp/Pump Pre-spectrometer Main spectrometer Detector 3 H ν e β-decay e e - /s e e - /s e e - /s e - 1 e - /s 3 He 3 He 3 He mbar - 1 ± 1 kv 0 kv mbar kv mbar kv Rear System: Monitor source parameters Source: Provide the required tritium column density Transp. & Pump system: Transport the electrons, adiabatically and reduce the tritium density significantly Pre-spectrometer: Rejection of low-energy electrons and adiabatic guiding of electrons Main-spectrometer: Rejection of electrons below endpoint and adiabatic guiding of electrons Detector: Count electrons and measure their energy 25

26 Arrival in Leopoldshafen: Nov 24,

27 Voyage of the main spectrometer

28 Adiabatic magnetic guiding of β s along field lines in stray B-field of s.c. solenoids: B max = 6 T B min = T Energy analysis by static retarding E-field with varying strength: High pass filter with integral β transmission for E>qU

29 Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter ( 345 (1992) 63 Meth. (A. Picard et al., Nucl. Instr ev KATRIN sharp integrating transmission function without tails: ΔE = E B min /B max = E A s,eff /A analyse = 0.93 ev, KATRIN ( Mainz (4.8 ev,

30 Check of transmission function (Mainz Expt.) Conversion electrons from 83m Kr (e.g. A. Picard et al., Z. Phys. A 342 (1992) 71) qu E e [kev] ( ev transmission function convoluted with Lorentzian (Γ = 2.83

31 Molecular Excitations A window to work in

32 Systematic Uncertainties

33 KATRIN: sensitivity and discovery potential Expectation for 3 full beam years: σ syst ~ σ stat 5σ discovery potential: ( 5σ ) m ν = 0.35eV ( 3σ ) m ν = 0.3eV sensitivity: ( 90%CL ) m ν < 0.2eV KATRIN will search 1 order of magnitude below present upper bound.

34 Sensitivity with run time

35 Mass Range Accessible KATRIN Average mass > 20 mev Present Lab Limit 2.3 ev Δm 122 Δm 232

36 The Last Order of Magnitude If the mass is NOT in the mev window, but the mev window instead, how can we measure it? KATRIN may be the largest such experiment possible. σ = 0.36 ev Size of experiment now: Diameter 10 m. Next diameter: 300 m! Source T 2 column density near max Rovibrational states of THe +, HHe + molecule

37 MIBETA: Kurie plot of Re ß-decay events (E > 700 ev) MANU2 (Genoa) metallic Rhenium m(ν) < 26 ev Nucl. Phys. B (Proc.Suppl.) 91 (2001) crystals: 8751 hours x mg (AgReO 4 ) MIBETA (Milano) AgReO 4 m(ν) < 15 ev Nucl. Instr. Meth. 125 (2004) 125 E 0 = ( ± 0.5 stat ± 1.6 syst ) ev m ν 2 = (-112 ± 207 ± 90) ev 2 MARE (Milano, Como, Genoa, Trento, US, D) Phase I : m(ν) < 2.5 ev hep-ex/

38 The Last Order of Magnitude KATRIN-type experiment limit: Source and detector are separate. Can evade by making them the same. MARE 187 Re uses microcalorimeters: source=detector. BUT pileup limits size of each to ~ 100 µg. Tritium 187 Re Endpoint kev 2.47 kev Branch to last ev 2 x x Half-life y 4.32 x y Mass (1 dis/d in last 200 mev) Mass (1 dis/d in last 20 mev) 20 µg 13 kg 20 mg kg

39 New schemes Decay of 187 Re (Q = 2.47 kev) observed in bolometers. For 20 mev, need 13 T of Re or 20 mg of 3 H. Atomic T in a trap, full kinematic reconstruction: arxiv 0901:3111 For 200 mev, need 1,000 s of separate sources. Decay of radioactive ions in a storage ring at a specific momentum: arxiv 0904:1089 For 200 mev, need decays in beam. Detection of RF cyclotron radiation from β orbiting in B- field: arxiv 0904:2860? Needs further thought, might be feasible.

40 Cyclotron motion of electrons in B field B. Monreal, J. Formaggio, MIT: arxiv: [nucl-ex]