s u p e r n e m o c o l l a b o r a t i o n Double beta decays study with NEMO 3 and SuperNEMO CHAUVEAU Emmanuel on behalf of the NEMO collaboration University of Manchester Rencontres de Moriond, Electroweak session CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 1 / 20
Two-neutrinos and neutrinoless double beta decays -60 Mass exces (MeV) Arbitrary unit -65 82 Zr 82 82 ββ2ν Ge Y 82 As -70 -75 82 Rb 82 Br ββ0ν 82 Sr 82 Se -80 β β 82 Kr -85 0.0 0.2 0.4 0.6 0.8 1.0 32 34 36 38 40 Atomic Number Z (E1 + E2) / Q ββ Two-neutrino double beta decay ( ββ 2 ν ) Neutrinoless double beta decay ( ββ 0 ν ) → ( A , Z + 2 ) + 2 e − + 2 ¯ → ( A , Z + 2 ) + 2 e − ( A , Z ) − ν e ( A , Z ) − � second-order weak process � violates lepton number conservation ∼ 10 20 years T ββ 2 ν � requires a Majorana neutrino ( ν = ¯ ν ) 1 / 2 � allowed by Standard Model and observed � new physics : m ββ , V+A, Majoron, SUSY... � input to nuclear physics model CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 2 / 20
Detection of neutrinoless double beta decay Available observables � Electron energy sum E 1 + E 2 Discrimination ββ 2 ν vs. ββ 0 ν � � Individual energy E 1 , E 2 Study on possible ββ 0 ν mechanisms � Angular distribution cos θ Mass Mechanism (MM) Electron energy difference Angular distribution u u d d Γ⁻ ¹ d � / d( Δ E) Γ⁻ ¹ d � / d(cos Θ ) d u ⁸ ²Se ⁸ ²Se ( V - A ) W⁻ e⁻ L ⁻ 1,5 V+A 1,5 � e R � e L ( V - A ) MM e⁻ W⁻ L d u d d u u 1,0 1,0 MM Right Handed V+A Current (V+A) 0,5 0,5 u u d d u d ( V - A ) W⁻ e⁻ L Eur. Phys. J. C. 70 p. 927(2010) � e R ⁻ 0 0 � e R 0 0,2 0,4 0,6 0,8 1,0 -1 -0,6 -0,2 0,2 0,6 1 ( V + A ) e⁻ W⁻ R | Δ E| / Q ββ cos Θ d u d d u u CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 3 / 20
Double beta decay experiments categories pure calorimeter approach V excellent detection efficiency e ⁻ 1 e ⁻ V good energy resolution 2 X no identification of electrons X high background source = calorimeter tracker + calorimeter approach X low detection efficiency e ⁻ 1 X poor energy resolution V electron recognition, ββ kinematic calorimeter e ⁻ V background measurement + rejection tracker or TPC 2 source CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 4 / 20
The NEMO 3 detector (1) Ultra low background detector � γ shielding : pure Iron (18 cm) � n shielding : borated water (30 cm) + wood (40 cm) � radon trapping facility from october 2004 → radon-free air buffer around detector � location in Modane underground laboratory (LSM) in Frejus tunnel : 4800 m.w.e. zoom in a NEMO 3 sector A(NEMO 3) ∼ 1000 Bq / 200 tons CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 5 / 20
The NEMO 3 detector (2) NEMO-3 "camembert" (source top view) Double beta decay 48 Ca 5 4 150 Nd 6 3 ¹ ⁰⁰ Mo 6,9 kg 96 Zr 100 Mo 82 S e 100 Mo 2 7 E1 E2 ⁸ ²Se 0,93 kg 82 S e 100 Mo β ⁻ t1 t2 1 8 β ⁻ θ nat Te 100 Mo ¹³ ⁰ Te 0,45 kg 0 9 130 Te Cu ¹¹ ⁶ Cd 0,40 kg 100 Mo nat Te Measured + rejected background 10 19 ¹ ⁵⁰ Nd 36,5 g 116 Cd 100 Mo 11 18 130 Te 100 Mo ⁹⁶ Zr 9,43 g � 100 Mo � 12 100 Mo 17 100 Mo 100 Mo ⁴⁸ Ca 6,99 g 13 16 14 15 � � "crossing" e ⁻ Unique features � Multi-source detector : 7 ββ isotopes e ⁻ � Particles identification : α , β − , β + , γ e ⁺ or e ⁻ � Kinematics of ββ decay : E 1 , E 2 , cos θ , ∆ t ⇒ Topological signature of events ⇒ Background rejection + measurement internal Δt ~ 0 ns external Δt > 3 ns ⇒ Study of ββ 0 ν , ββ 2 ν , ββ *, ... CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 6 / 20
Selection of candidate ββ events Event candidate for ββ2ν decay from ¹⁰⁰Mo foil E1 + E2 = 1.097 MeV Run : 3478 internal hyp. : |Δt meas - Δt calc | = 0.33 ns calorimeter hit Event : 6930 external hyp. : |Δt meas - Δt calc | = 5.21 ns Date : 09/11/2004 (Δvertex) t = 4.4 mm (Δvertex) z = 3 cm track vertex Top view Side view � Two tracks Q < 0 � Internal hypothesis (external event rejection) � Two calorimeter E > 200 keV � No other calorimeter hit ( γ rejection) � Association track – calorimeter hit � No delayed track ( 214 Bi rejection) � Common vertex CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 7 / 20
Origin and mechanisms of NEMO 3 background � External γ from detector radioactivity, neutrons and cosmics � Internal contamination in β emitter with Q β ≥ Q ββ ( ≈ 3 MeV) 214 Bi in 238 U chain ( Q β = 3.3 MeV) 208 Tl in 232 Th chain ( Q β = 4.9 MeV) � Radon inside tracking detector decay then deposit of daughter on wire and foil surfaces → feed contamination in 214 Bi � ββ 2 ν background for ββ 0 ν signal Foil Foil Foil e ⁻ e ⁻ e ⁻ � � � e ⁻ e ⁻ e ⁺ Pair Compton Double creation + Møller Compton CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 8 / 20
Origin and mechanisms of NEMO 3 background � External γ from detector radioactivity, neutrons and cosmics � Internal contamination in β emitter with Q β ≥ Q ββ ( ≈ 3 MeV) 214 Bi in 238 U chain ( Q β = 3.3 MeV) 208 Tl in 232 Th chain ( Q β = 4.9 MeV) � Radon inside tracking detector decay then deposit of daughter on wire and foil surfaces → feed contamination in 214 Bi � ββ 2 ν background for ββ 0 ν signal Foil Foil Foil β β β � � e ⁻ e ⁻ e ⁻ Beta Beta + Beta + + IC Møller Compton CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 8 / 20
Origin and mechanisms of NEMO 3 background � External γ from detector radioactivity, neutrons and cosmics � Internal contamination in β emitter with Q β ≥ Q ββ ( ≈ 3 MeV) 214 Bi in 238 U chain ( Q β = 3.3 MeV) 208 Tl in 232 Th chain ( Q β = 4.9 MeV) � Radon inside tracking detector decay then deposit of daughter on wire and foil surfaces → feed contamination in 214 Bi � ββ 2 ν background for ββ 0 ν signal Foil ²²²Rn 3.8 days β ²¹⁴Bi Q = 3.27 MeV β e ⁻ Beta + Möller CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 8 / 20
Origin and mechanisms of NEMO 3 background � External γ from detector radioactivity, neutrons and cosmics � Internal contamination in β emitter with Q β ≥ Q ββ ( ≈ 3 MeV) 214 Bi in 238 U chain ( Q β = 3.3 MeV) 208 Tl in 232 Th chain ( Q β = 4.9 MeV) � Radon inside tracking detector decay then deposit of daughter on wire and foil surfaces → feed contamination in 214 Bi � ββ 2 ν background for ββ 0 ν signal Arbitrary unit ββ2ν ββ0ν 0.0 0.2 0.4 0.6 0.8 1.0 (E1 + E2) / Q ββ CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 8 / 20
Measurement of NEMO 3 background CHANNEL BACKGROUND MEASUREMENT e γ external external background : 40 K, 60 Co, 226 Ra, ... e crossing pure β emitters in foil : 234 m Pa, 40 K, 90 Y, ... e 0 e γ e crossing event β + γ emitters in foil : 207 Bi, 208 Tl, 214 Bi, ... e γγ e γγγ 222 Rn in gas, 214 Bi on foil and wires e α � Internal, external and radon background measurement X + � Analysis through independent channels � Model validation with a dedicated control foil (pure Cu) 8 e γ external event [ NIM A606 (2009) 449-465 ] CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 9 / 20
Measurement of NEMO 3 background : example with radon 222 Rn activity in NEMO 3 (mBq/m 3 ) channel e α : pure sample of "BiPo" events ²³⁸U ²²²Rn ²¹⁴Po β 164 µs 8 ²¹⁴Bi α 19,7 m α X + ²¹⁰Pb O 0,02% β 21,4 a e α event ²¹⁰Tl 1,3 m 10 5 NIM A 606 (2009) 449-465 54.70 / 51 P1 0.1917E+05 16.05 P2 0.6688 0.1878E-01 P3 162.9 0.1633 P4 0.3174E+05 0.2284E+05 P5 16.31 2.481 10 4 Fraction of non α events: 0.59 ± 1.33 % T 1/2 = 162.9 μs 10 3 0 200 400 600 800 1000 α track delay (µs) CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 10 / 20
NEMO 3 results : ββ 2 ν with 100 Mo (phase 2 : 7 kg x 4 years) Energy sum of 2 electrons Single electron energy Angular distribution � > 700000 events from 100 Mo � signal / background ratio = 76 � T ββ 2 ν x 10 18 years = 7.16 ± 0.01 (stat) ± 0.54 (sys) [preliminary] 1 / 2 x 10 18 years phase 1 : 7.11 ± 0.02 (stat) ± 0.54 (sys) [Phys. Rev. Lett. 95 182302 (2005)] � ultimate background component for ββ 0 ν signal CHAUVEAU Emmanuel Double beta decays study with NEMO 3 and SuperNEMO 11 / 20
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