19 July 2012Page 1 Neutrino Mass Julia Sedgbeer High Energy Physics, Blackett Laboratory

19 July 2012Page 2 ‘Standard Model’ of particle physics SM developed since 1960’s 3 ‘generations’ of particles including 3 neutrinos (massless) plus the ‘force carriers’ neutrinos massless in ‘minimal’ SM all ordinary matter made from 1 st generation

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19 July 2012Page 4 The Neutrino - a little history …. 1910’s -1920’s – studies of nuclear β decays N 1 → N 2 + e - did not appear to conserve energy! Wolfgang Pauli postulated Neutrinos in order to save energy conservation N 1 → N 2 + e - + “I have done a terrible thing. I have postulated a particle that cannot be detected” - no charge, no mass, very feeble interaction, just a bit of energy finally discovered by Cowan and Reines using a nuclear reactor. Nuclear reactors produce lots of neutrinos. Nobel prize 1995 nucleielectron

19 July 2012Page 5 Why interest in neutrinos? 2nd most abundant particle in the Universe after the photon ~6,000,000,000,000 through you per second! As many produced in Big Bang as photons Only 1% of energy from supernova appears as photons. Other 99% is neutrinos Neutrinos are crucial for our understanding how the Sun shines Very important for heavy element formation in stars Neutrino astronomy: used to study distant objects Recent surprise: neutrinos have non-zero mass. We don ’ t know what the mass is but it is less than: g

19 July 2012Page 6 Neutrino-proton cross-section ~ cm 2 (actually energy dependent ~ linear with E) WEAK interaction mediated by W and Z bosons Cf. gamma-proton cross section ~ cm 2 factor of ~ between cross-sections Electromagnetic interaction (charged particles) mediated by photons The Neutrino - interactions …. u d d(-1/3) u(2/3) W - e- e neutron proton

19 July 2012Page 7 The Neutrino interactions …. mean free path i.e. average distance travelled before interacting is: ~1 light year of lead 1 light year ~ km = 10,000,000,000,000 km

19 July 2012Page 8 Sources of Neutrinos Atmospheric neutrinos Solar – from nuclear reactions in sun Atmospheric – from cosmic rays Artificially created (reactors, accelerators) Natural background radiation (from rocks etc) Supernovae Cosmic background – relic neutrinos from Big Bang

19 July 2012Page 9 Neutrino oscillations and neutrino mass Neutrino oscillation experiments have established that neutrinos have mass but they only measure mass squared differences e.g. Δm 2 = m 1 2 -m 2 2 The absolute mass scale and the mass hierarchy are still not known m2m2 m12m22m32m12m22m32 Degenerate m 1 ≈m 2 ≈m 3 » |m i -m j | Normal hierarchy m 3 > m 2 ~m 1 Inverted hierarchy m 2 ~m 1 >m 3 ?

19 July 2012Page 10 How to measure neutrino mass ? β decay experiments Cosmological observations Neutrinoless Double Beta Decay (0νDBD) experiments

19 July 2012Page 11 Tritium β-decay – direct neutrino mass measurement 3 H  3 He + + e - + e with E 0 =18.6 keV Measurement of T 2 β-decay spectrum in the region around the endpoint E 0

19 July 2012Page 12 KATRIN Present upper limit on electron neutrino mass: 2eV KATRIN Experiment - 5 years of running for 0.2 eV sensitivity

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19 July 2012Page 14 Weighing neutrinos. Cosmology. Map the Cosmic Microwave Background (CMB) radiation - relic of the Big Bang - look at anisotropy Fluctuations ~ K (in ~3 K) Clustering of matter in the universe depends on the total mass of neutrinos

19 July 2012Page 15 Boltzmann Const = eV/K = J/K CMB at ~3K → Energy ~ eV = MeV → wavelength =hc/E h= MeV s c = m/s → wavelength = ( x ) / ( ) m ~ m = m ~7cm Aside: CMB – energy …

19 July 2012Page 16 CMB  m i < 0.4 – 2.0 eV

19 July 2012Page 17 Oscillation experiments  Neutrino is massive but cannot solve problem of the origin of neutrino mass Double Beta Decay Dirac or Majorana?  = Majorana neutrinos favoured in most GUT and supersymmetric models This information can be obtained in Double  - Decay experiments, which are also sensitive to absolute masses, mixing and phases

19 July 2012Page 18 (A,Z)  (A,Z+1) + e - + e  -decay (A,Z)  (A,Z+2) + 2 e - 0  - Beta and double beta decay (A,Z)  (A,Z+2) +2 e e 2  n  p + e - + e - - Double beta decay Beta decay changing Z by two units while leaving A constant

19 July 2012Page 19 Double Beta Decay (2  ) np e-e- e np e-e- e (A,Z) (A,Z+1) (A,Z+2) Only ~35 isotopes known in nature (A,Z)  (A,Z+2) + 2 e e The lepton-number conserving process, 2νββ decay has been observed in several nuclei e.g. 76Ge > 76Se + 2e- + 2ν e with a measured half life of ~10 21 years

19 July 2012Page  decay e - e - d d u u W W e e  = G(Q,Z) |M nucl | 2 2 rate of DDB -0 Phase spaceNuclear matrix elements EffectiveMajorana neutrino mass  L=0  L=2 !

19 July 2012Page 21 The dominant problem - Background Cosmogenics thermal neutrons How to measure half-lives beyond years??? The usual suspects (U, Th nat. decay chains) 2  Alphas, Betas, Gammas High energy neutrons from muon interactions The first thing you need is a mountain, mine,...

19 July 2012Page 22 Background: Typical half-life years

19 July 2012Page 23 NEMO3 LSM Modane, France (Tunnel Frejus, depth of ~4,800 mwe )

19 July 2012Page 24 NEMO-3 AUGUST 2001

19 July 2012Page 25 3 m 4 m B (25 G) 20 sectors Source : 10 kg of  isotopes cylindrical, S = 20 m 2, e ~ 60 mg/cm 2 Tracking detector : drift wire chamber operating in Geiger mode (6180 cells) Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H 2 O Calorimeter : 1940 plastic scintillators coupled to low radioactivity PMTs Magnetic field: 25 Gauss Gamma shield: Pure Iron (e = 18 cm) Neutron shield: 30 cm water (ext. wall) 40 cm wood (top and bottom) (since march 2004: water  boron) Able to identify e , e ,  and  The NEMO3 detector Fréjus Underground Laboratory : 4800 m.w.e.

19 July 2012Page 26  isotope foils scintillators PMTs Calibration tube Cathode rings Wire chamber

19 July 2012Page 27 coil Iron shield Water tank wood NEMO-3 Opening Day, July 2002 Start taking data 14 February 2003

19 July 2012Page 28 Drift distance 100 Mo foil Transverse view Longitudinal view Run Number: 2040 Event Number: 9732 Date: Geiger plasma longitudinal propagation Scintillator + PMT Deposited energy: E 1 +E 2 = 2088 keV Internal hypothesis: (  t) mes –(  t) theo = 0.22 ns Common vertex: (  vertex)  = 2.1 mm Vertex emission (  vertex) // = 5.7 mm Vertex emission Transverse view Longitudinal view Run Number: 2040 Event Number: 9732 Date: Criteria to select  events: 2 tracks with charge < 0 2 PMT, each > 200 keV PMT-Track association Common vertex Internal hypothesis (external event rejection) No other isolated PMT (  rejection) No delayed track ( 214 Bi rejection)  events selection in NEMO-3 Typical  2 event observed from 100 Mo Trigger: 1 PMT > 150 keV 3 Geiger hits (2 neighbour layers + 1) Trigger rate = 7 Hz

19 July 2012Page 29 Search for 0νββ Total mean 0ν efficiency ε = Mo T 1/2 (0ν) > C.L. < 0.31 – 0.96 eV NME [1-5] Total mean 0ν efficiency ε = Se T 1/2 (0ν) > C.L. < 0.94 – 1.71 eV NME [1-4] < 2.6 eV NME [6]

19 July 2012Page 30 Scale up the NEMO concept by ~10 Aim to reach half life ~10 26 years and mass < ev Currently building the first module of 20 Data taking will start in 2014/15 SuperNEMO

19 July 2012Page modules for 100 kg Top view Source (40 mg/cm 2 ) 12m 2 Tracking (~ Geiger cells). Calorimeter (600 channels) 5 m 1 m Total:~ – geiger cells channels ~ PMT SuperNEMO conceptual design

19 July 2012Page 32 Schedule Demonstrator Module construction and commissioning Demonstrator Module running. “Klapdor” sensitivity end of Installation in LSM Construction and deployment of successive SuperNEMO modules Continuous operation of ≥1 SuperNEMO module

19 July 2012Page 33 …. measuring neutrino masses is challenging …… Questions?

19 July 2012Page 34 2νββ Results First direct observation: 7.7σ significance Indirect observations: - ~2.7 x yrs in 10 9 yr old rocks - ~8 x10 20 yrs in yr old rocks Indication from MIBETA Coll in isotopically enriched crystals: 6.1 ± 1.4(st) (sy) x10 20 yrs IsotopeMass (g)Q ββ (keV)T 1/2 (2ν) (10 19 yrs)S/BCommentReference 82 Se ± 1.04World’s best!Phys.Rev.Lett. 95(2005) Cd ± 0.310World’s best! 150 Nd ± World’s best!Phys. Rev. C 80, (2009) 96 Zr ± 0.211World’s best!Nucl.Phys.A 847(2010) Ca ± (h.e.)World’s best! 100 Mo ± World’s best!Phys.Rev.Lett. 95(2005) Te ± 140.5First direct detection!!!Phys. Rev. Lett. 107, (2011)

19 July 2012Page 35 km water equivalent 2.2 km water is approx. 1km rock → factor ~10,000 in muon rate Muon Flux as a function of Depth But note that there will also be some level of natural radioactivity from the rock Super-Kamiokande (Japan) Sudbury Neutrino Observatory - SNO (Canada) Boulby (Yorkshire)

19 July 2012Page 36 Oscillation ? - Quantum mechanics Schrodinger’s equation (1-dimension): (-h 2 /2m)(d 2 /dx 2 )Ψ(x,t) + V Ψ(x,t) = iħ(d/dt) Ψ(x,t) (cf F=ma = md 2 x/dt 2 in Newtonian mechanics) Solution of time dependent part …. T(t) =exp[-(i/ħ)Et] = exp[ -iωt ] = cos(ωt)-isin(ωt) i.e cos/sin wave

19 July 2012Page 37 Oscillation ? - Quantum mechanics Suppose state is superposition of 1 and 2 : x = a 1 + b 2 Put in time dependence: x = a 1 exp[-(i/ħ)E 1 t] + b 2 exp[-(i/ħ)E 2 t] If E 1 = E 2 no oscillation If E 1 = E 2 ‘beating’, i.e. oscillation masses must be different Type of neutrino x you actually measure depends on time (or distance travelled)

19 July 2012Page 38 Conclusions Very exciting time for neutrino physics in general and 0  in particular A positive signal is now a serious possibility in light of oscillation results SuperNEMO is so far the only project which will look at  signature

19 July 2012Page 39 Evidence for Neutrino Mass μ oscillates from one type to another and back again Oscillation can only happen if the types of involved have different masses Therefore at least one has non-zero mass - but don’t know the mass, only the mass difference! Mass difference ~ g Note: Sudbury Neutrino Oberservatory (2002) Studies of Solar – observe change of type

19 July 2012Page 40 Evidence for neutrino mass from SuperK (1998) and SNO (2002) 2002 Nobel prize to pioneers: Davis and Koshiba First evidence that the minimal Standard Model of particle physics is incomplete! Neutrino Oscillation Raised more questions: Why do neutrinos have mass at all? Why so small? What are the masses? Are neutrinos and anti-neutrinos the same? How do we extend the Standard Model to incorporate massive neutrinos? → Study Double Beta Decay

19 July 2012Page 41 USA MHC INL U. Texas Japan U. Saga KEK U Osaka France CEN Bordeaux IReS Strasbourg LAL ORSAY LPC Caen LSCE Gif/Yvette UK UC London U Manchester IC London Finland U. Jyvaskula Russia JINR Dubna ITEP Mosow Kurchatov Institute Ukraine INR Kiev ISMA Kharkov Czech Charles U. Praha IEAP Praha Marocco Fes U. Slovakia U. Bratislava NEMO collaboration + new laboratories ~ 60 physicists, 11 countries, 27 laboratories Spain U. Valencia U. Zarogoza U. Barcelona SuperNEMO

19 July 2012Page 42 From NEMO-3 to SuperNEMO 7 kg kg isotope mass M 8 % ~ 30 % isotope 100 Mo 150 Nd or 82 Se T 1/2 (  ) > ln 2  M    T obs N 90 N A A  NEMO-3 SuperNEMO internal contaminations 208 Tl and 214 Bi in the  foil 208 Tl: < 20  Bq/kg 214 Bi: < 300  Bq/kg 208 Tl <  Bq/kg if 82 Se: 214 Bi < 10  Bq/kg T 1/2 (  ) > 2 x y < 0.3 – 1.3 eV T 1/2 (  ) > 2 x y < meV energy resolution (FWHM) 3 MeV efficiency 

19 July 2012Page 43 Open setup 02 J.FORGET SuperNEMO LAL v09/2006 F. Piquemal (CENBG) Nuppec Bordeaux, November

19 July 2012Page 44 Water shielding  and neutron Foil source 5,7 m 14 m 3,75 m New cavern ~ 70m x 15m x15m Modane will have a new cavern or Canfranc – if a new cavern ? or Gran Sasso …? or Boulby ? ~ tonnes of water for 20 modules Detector scheme in water shielding