19 july 2012page 1 neutrino mass julia sedgbeer high energy physics, blackett laboratory
TRANSCRIPT
19 July 2012 Page 1
Neutrino Mass
Julia Sedgbeer
High Energy Physics, Blackett Laboratory
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‘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 1st generation
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The Neutrino - a little history ….
• 1910’s -1920’s – studies of nuclear β decays N1 → N2 + e-
did not appear to conserve energy!
• 1930 - Wolfgang Pauli postulated Neutrinos in order to save energy conservation
N1 → N2 + 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
• 1956 - finally discovered by Cowan and Reines using a nuclear reactor.
Nuclear reactors produce lots of neutrinos. Nobel prize 1995
nuclei electron
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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:
0.00000000000000000000000000000001 g
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• Neutrino-proton cross-section ~ 10- 43 cm2 (actually energy dependent ~ linear with E)
WEAK interactionmediated by W and Z bosons
• Cf. gamma-proton cross section ~ 10- 27 cm2 factor of ~ 1016 between cross-sections
Electromagnetic interaction (charged particles) mediated by photons
The Neutrino - interactions ….
u u
d d
d(-1/3) u(2/3)
W-
e-
e
neutronproton
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The Neutrino interactions ….
mean free path i.e. average distance travelled before
interacting is:
• ~1 light year of lead
• 1 light year ~ 1013 km
• = 10,000,000,000,000 km
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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
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Neutrino oscillations and neutrino mass• Neutrino oscillation experiments have established that neutrinos have mass
• but they only measure mass squared differences e.g. Δm2 = m12-m2
2
The absolute mass scale and the mass hierarchy are still not known
m2
m1
2
m2
2
m3
2
Degeneratem
1≈m2≈m3» |mi-mj|
Normal hierarchym
3> m
2~m
1
Inverted hierarchym
2~m
1>m
3
?
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How to measure neutrino mass ?
• β decay experiments
• Cosmological observations
• Neutrinoless Double Beta Decay (0νDBD) experiments
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Tritium β-decay – direct neutrino mass measurement
3H 3He+ + e- + e with E0=18.6 keV
m > 0
m = 0
10 -13
-3 -2 -1 0E - E0 [eV]
cou
nt
rat
e [
a.u
.]
0 5 10 15 20energy E [keV]
0
0.2
0.4
0.6
0.8
1.0
1.2
Measurement of T2 β-decay spectrum in the region around the
endpoint E0
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KATRIN Present upper limit on electron neutrino mass: 2eV KATRIN Experiment - 5 years of running for 0.2 eV sensitivity
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Weighing neutrinos. Cosmology.
• Map the Cosmic Microwave Background (CMB) radiation - relic of the Big Bang - look at anisotropy
• Fluctuations ~ 0.0002 K (in ~3 K)
• Clustering of matter in the universe depends on the total mass of neutrinos
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• Boltzmann Const = 8.6 10-5 eV/K• = 1.38 10-23 J/K• CMB at ~3K • → Energy ~3 10-6 eV = 3 10-12 MeV• → wavelength =hc/E h=6.6 10-22 MeV s• c = 3 108 m/s• → wavelength = (6.6 10-22 x 3 108) / (3 10-12) m• ~6.6 10-2 m = 0.066 m ~7cm
Aside: CMB – energy …
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CMB
mi < 0.4 – 2.0 eV
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• Oscillation experiments Neutrino is massive
• but cannot solve problem of the origin of neutrino mass
•
Double Beta DecayDouble 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
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• (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- + 2e 2
• n p + e- + e-
-Double beta decay
Beta decay
changing Z by two units while leaving A constant
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Double Beta Decay (2)
n p
e-
e
n p
e-
e
0+1+
0+(A,Z)(A,Z+1)
(A,Z+2)
Only ~35 isotopesknown in nature
(A,Z) (A,Z+2) + 2 e- + 2e
The lepton-number conserving process, 2νββ decay has been observed in several nuclei e.g. 76Ge > 76Se + 2e- + 2νe with a measured half life of ~1021 years
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u e -
d
d
e -W
u
e
e
2 - decay
W
0 - decay
e -
e -
d
du
u
W
We
e
= G(Q,Z) |Mnucl|2 <m>2
rate of DDB-0 Phase space Nuclear matrix elements
EffectiveMajorana neutrino mass
L=0 L=2 !
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The dominant problem - Background
• Cosmogenics
• thermal neutrons
How to measure half-lives beyond 1020 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,...
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Background:
Typical half-life 1010 years
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NEMO3
LSM Modane, France(Tunnel Frejus, depth of ~4,800 mwe )
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NEMO-3
AUGUST 2001
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3 m
4 m
B (25 G)
20 sectorsSource: 10 kg of isotopes cylindrical, S = 20 m2, e ~ 60 mg/cm2
Tracking detector: drift wire chamber operating in Geiger mode (6180 cells)Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H2O
Calorimeter: 1940 plastic scintillators coupled to low radioactivity PMTs
Magnetic field: 25 GaussGamma 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.
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isotope foils
scintillators
PMTs
Calibration tube
Cathode rings Wire chamber
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coil
Iron shield
Water tank
wood
NEMO-3 Opening Day, July 2002
Start taking data 14 February 2003
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Drift distance
100Mo foil100Mo foil
Transverse view Longitudinal view
Run Number: 2040Event Number: 9732Date: 2003-03-20
Geiger plasmalongitudinalpropagation
Scintillator + PMT
Deposited energy: E1+E2= 2088 keVInternal hypothesis: (t)mes –(t)theo = 0.22 nsCommon vertex: (vertex) = 2.1 mm
Vertexemission
(vertex)// = 5.7 mm
Vertexemission
Transverse view Longitudinal view
Run Number: 2040Event Number: 9732Date: 2003-03-20
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 (214Bi rejection)
events selection in NEMO-3
Typical 2 event observed from 100Mo
Trigger: 1 PMT > 150 keV
3 Geiger hits (2 neighbour layers + 1)
Trigger rate = 7 Hz
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Search for 0νββ
Total mean 0ν efficiency ε = 0.13 100Mo T1/2(0ν) > 1.0 . 1024 y @90% C.L. <mv> < 0.31 – 0.96 eV NME [1-5]
Total mean 0ν efficiency ε = 0.1482Se T1/2(0ν) > 3.2 . 1023 y @90% C.L. <mv> < 0.94 – 1.71 eV NME [1-4] <mv> < 2.6 eV NME [6]
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Scale up the NEMO concept by ~10
Aim to reach half life ~1026 years
and mass < 0.04 - 0.10 ev
Currently building the first module of 20
Data taking will start in 2014/15
SuperNEMO
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20 modules for 100 kg
Top view
Source (40 mg/cm2) 12m2
Tracking (~2-3000 Geiger cells). Calorimeter (600 channels)
5 m
1 m
Total:~ 40 000 – 60 000 geiger cells channels ~ 12 000 PMT
SuperNEMO conceptual design
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Schedule
Demonstrator Module construction and commissioning
Demonstrator Module running. “Klapdor” sensitivity end of 2015
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Installation in LSM
Construction and deployment of successive SuperNEMO modules
Continuous operation of ≥1 SuperNEMO module
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…. measuring neutrino masses is challenging ……
Questions?
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2νββ Results
First direct observation: 7.7σ significance
Indirect observations:- ~2.7 x 1021 yrs in 109 yr old rocks- ~8 x1020 yrs in 107-108 yr old rocks
Indication from MIBETA Coll in isotopically enriched crystals: 6.1 ± 1.4(st) +2.9
-3.5(sy) x1020 yrs
Isotope Mass (g) Qββ(keV) T1/2(2ν) (1019yrs) S/B Comment Reference
82Se 932 2996 9.6 ± 1.0 4 World’s best! Phys.Rev.Lett. 95(2005) 483
116Cd 405 2809 2.8 ± 0.3 10 World’s best!
150Nd 37 3367 0.9 ± 0.07 2.7 World’s best! Phys. Rev. C 80, 032501 (2009)
96Zr 9.4 3350 2.35 ± 0.21 1 World’s best! Nucl.Phys.A 847(2010) 168
48Ca 7 4271 4.4 ± 0.6 6.8 (h.e.) World’s best!
100Mo 6914 3034 0.71 ± 0.05 80 World’s best! Phys.Rev.Lett. 95(2005) 483
130Te 454 2533 70 ± 14 0.5 First direct detection!!! Phys. Rev. Lett. 107, 062504 (2011)
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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)
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Oscillation ? - Quantum mechanicsSchrodinger’s equation (1-dimension):(-h2/2m)(d2/dx2)Ψ(x,t) + V Ψ(x,t) = iħ(d/dt) Ψ(x,t)
(cf F=ma = md2x/dt2 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
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Oscillation ? - Quantum mechanicsSuppose state is superposition of 1 and 2 :
x = a 1 + b 2
Put in time dependence:
x = a 1 exp[-(i/ħ)E1t] + b 2 exp[-(i/ħ)E2t]
If E1 = E2 no oscillation
If E1 = E2 ‘beating’ , i.e. oscillation
masses must be different
Type of neutrino x you actually measure depends on time (or distance travelled)
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Conclusions
Very exciting time for neutrino physics in general and 0 in particularA positive signal is now a serious possibility in light of oscillation resultsSuperNEMO is so far the only project which will look at signature
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Evidence for Neutrino Massμ oscillates from one type to another and back
againOscillation 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 ~ 10-34 g
Note: Sudbury Neutrino Oberservatory (2002) Studies of Solar – observe change of type
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• 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
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USAMHCINL
U. Texas
JapanU. Saga
KEKU Osaka
FranceCEN Bordeaux
IReS StrasbourgLAL ORSAY
LPC CaenLSCE Gif/Yvette
UKUC London
U ManchesterIC London
FinlandU. Jyvaskula
RussiaJINR DubnaITEP Mosow
Kurchatov Institute
UkraineINR Kiev
ISMA Kharkov
CzechCharles U. Praha
IEAP Praha
MaroccoFes U.
SlovakiaU. Bratislava
NEMO collaboration + new laboratories ~ 60 physicists, 11 countries , 27 laboratories
SpainU. ValenciaU. ZarogozaU. Barcelona
SuperNEMOSuperNEMO
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From NEMO-3 to SuperNEMO
7 kg 100-200 kg isotope mass M
8 % ~ 30 %
isotope 100Mo
150Nd or 82Se
T1/2 () > ln 2 M Tobs
N90
NA
A
NEMO-3 SuperNEMO
internal contaminations 208Tl and 214Bi in the foil
208Tl: < 20 Bq/kg214Bi: < 300 Bq/kg
208Tl < Bq/kg
if 82Se: 214Bi < 10 Bq/kg
T1/2() > 2 x 1024 y<m> < 0.3 – 1.3 eV
T1/2() > 2 x 1026 y<m> < 40 - 110 meV
energy resolution (FWHM) 8% @ 3MeV 4% @ 3 MeV
efficiency
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Open setup 02
J.FORGET SuperNEMO LALv09/2006
F. Piquemal (CENBG) Nuppec Bordeaux, November 7-8 2006
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Water shielding and neutron
Foil source
5,7 m
14 m
3,75 mNew cavern
~ 70m x 15m x15m
Modane will have a new cavernor
Canfranc – if a new cavern ?or
Gran Sasso …?or
Boulby ?
~ 2 000 tonnes of water for 20 modules
Detector scheme in water shieldingDetector scheme in water shielding