introduction to low energy neutrino physics · introduction to low energy neutrino physics thierry...

Introduction to Low Energy Neutrino Physics

Thierry Lasserre (CEA, [email protected])

June 15 2015, Neutrino Geoscience 2015, IPGP, Paris

Neutrino: definition

The neutrino is an elementary particle. It has a spin 1/2, thus it�s a fermion. Neutrinos belong to the family of the

leptons. It has a non vanishing mass

Neutrinos interact only with matter through the weak interaction and are thus insensitive to strong and

electromagnetic interaction. Thus the probability of interaction of neutrinos with matter is tiny.

There exist three familly (or flavour) of neutrinos :

electron-neutrinos �e, muon-neutrinos �� and tau-neutrinos tauique �τ.

T. Lasserre – Neutrino Geoscience 2015

Neutrinos (ν) are everywhere

The material around us is made by electrons, protons and of neutrons but the latter are indeed

In minority in the Universe …

For each proton and neutron in the Universe there are 1 000 000 000 neutrinos !

Human body contains 30 millions ‘Big-Bang’ neutrinos Human body is crossed by 100 000 billion Solar neutinos/s


Radioactivity

ν

Champ Magnétique

α$

β$

γ$T. Lasserre – Neutrino Geoscience 2015

The β-decay problem (1914)

1914: Measurement of the beta-decay spectrum by Chadwick A nucleus (A,Z) changes into another nucleus (A,Z+1) and emits an electron

The electron energy should be fixed by the mass difference of both nuclei...

Bi 210

83 Po + e 210

84

0

-1

T1/2≈5 j


Zürich, 4 décembre 1930 Liebe radioaktive Damen und Herren, Wie der Überbringer dieser Zeilen, den ich huldvollst anzuhören bitte, Ihnen des näheren auseinandersetzen wird, bin ich ... auf einen verzweifelten Ausweg verfallen, um den Wechselsatz der Statistik und den Energiesatz zu retten. Nämlich die Möglichkeit, es könnten elektrisch neutrale Teilchen, die ich Neutronen nennen will, in dem Kern existieren, welche den Spin ½ haben und das Ausschließungsprinzip befolgen ... Das kontinuierliche β-Spektrum wäre dann verständlich unter der Annahme, daß beim β-Zerfall mit dem Elektron jeweils noch ein Neutron emittiert wird, derart, daß die Summe der Energien von Neutron und Elektron konstant ist. ... Ich gebe zu, daß mein Ausweg vielleicht von vornherein wenig wahrscheinlich erscheinen mag ... Aber nur wer wagt, gewinnt ... Also, liebe Radioaktive, prüfet und richtet. - Leider kann ich nicht persönlich in Tübingen erscheinen, da ich infolge eines in der Nacht vom 6. zum 7. Dezember in Zürich stattfindenden Balles hier unabkömmlich bin. Mit vielen Grüßen ... Euer untertänigster Diener W. Pauli.

The Pauli hypothesis (1930)


β Decay Theory (1934) 1932: Chadwick discovers the neutrinos

Atoms are made of a nucleus (p,n) surrounded by an electron cloud

1934: Fermi build the first β-decay theory Neutrino first appearance as a energy quantum of the theory!

β-

β+

Neutrino interact weakly!

Interaction probability between a (solar) neutrino and a human body is about 1/ 10 000 000 000 000 000

Neutrino detection is challenging…

Our vision Neutrino perspective


Very weakly… Only 1 neutrino per 10 000 billions

Low energy neutrino (MeV) is intercepted!

ν

ν

ν

ν

ν

ν

ν 66 billions Solar neutrinos

per cm2 / s

But situation changes at very energy… Earth is not transparent anymore to PeV neutrinos


Can we detect neutrinos ?

Nuclear bomb Nuclear Reactor

1934: First estimation of the neutrino cross section by Fermi ~1 light year of lead on average to stop a neutrino

Theoreticians are pessimistic. A huge quantity of neutrinos is necessary.

Experimentalists take on the exciting challenges

Searching Neutrinos with Nuclear Explosion

!  Pyramidal ton scale liquid scintillator coupled to 4 PMTs !  2 second free-fall in a vacuum shaft detector in coincidence with the nuclear blast " several interactions at 50 meters for a 20-kiloton bomb

!  But J. M. B. Keylogg pushed for an experiment close to a fission reactor & Reines & Cowan considered (e+,n) coincidence detection ! project canceled

Approved experiment (early 1950’s) Reines & Cowan’s Group


The neutrino discovery (1956) 1956: Reines et Cowan detected (anti-) neutrino emitted

by the Savannah river (USA) nuclear reactor

Réacteur OFF: 1 événements/heure Réacteur ON: 4 événements/heure

ν + p " e+ + n


The Savannah River Experiment

liquid scintillator tank (I, II, III)

cadmium doped water tank (A, B)

electronics truck water soaked

sawdust (d=0.5)

fluid handling system (4,500 l steel tanks)


True Signals (from Reines, Cowan, Harisson, et al. 1960) !  a) neutrino-like signal -  e+ scope (I,II): EI=0.3 MeV, EII=0.35 MeV, Δt<0.2 µs -  n scope (I,II): EI=5.8 MeV, EII=3.3 MeV, Δt<0.2 µs -  2.5 µs coincidence time

!  b) neutrino-like signal -  e+ scope (II,III): EII=0.3 MeV, EIII=0.35 MeV, Δt<0.2 µs -  n scope (II,III): EI=2.0 MeV, EII=1.7 MeV, Δt<0.2 µs -  13.5 µs coincidence time !  c) electrical noise signal -  e+ scope (I,II): strange non physical pulse shape -  n scope (I,II,II): cosmic ray induced event

!  d) background signal -  e+ scope (I,II,III): cosmic ray event -  n scope (I,II): ? but rejected since extra-pulse in II


Another type of neutrino (1963)

L.M. Lederman M. Schwartz J. Steinberger

Muons are majoritarily detected in the spark chamber. There exist two kind (flavour) of neutrinos: νe & νµ

production détection

20 m


Neutrinos in the Standard Model of Particle Physics


Standard Model of Particle Physics

Boson de Higgs + Découvert en 2012

au LHC (CERN)

Matière Stable


Interactions

Neutrinos feel weak and gravitational interaction

Between masses Between strong charges

Between weak Charges Between electric charges

Higgs

‘Give’ Mass to all particles

Maybe not for

neutrinos


β-decays & weak interaction

β-

β+


Neutrino sources: Distance

Nuclear Reactor 10-106 m

Accelerator 10-105 m

Earth (Crust) <105 m

Atmosphere 104-107 m

Sun 1,5 1011 m

Supernova 1,5 1021 m (1987A)

Astrophysical accelerator Up to z=5 !

Universe … everywhere …


Neutrino sources: Energy

Nuclear Reactors E < 10 MeV

Neutrino beams E ~ GeV

Terrestrial Crust E < 3 MeV

Atmoshpere E ~GeV

Sun E < 20 MeV

Supernova E < 50 MeV

Astrophysical accelerator TeV, and beyond ?

Universe … E = 0,0004 eV


A neutrino bath in Paris

10 000 milliards /cm2/sec

66 milliards /cm2/sec

5 millions /cm2/sec

3 millions /cm2/sec


Reactor Neutrino Emission


Nuclear Chain Reaction & Neutrinos

!  Nuclear reactors are copious, isotropic sources of electron antineutrinos

!  Neutrinos come from β-fission fragments, not directly from the fission !  Fission of 235U, 238U, 239Pu, 241Pu

!  β-decay of neutron rich fission fragments !  X(A,Z)"Y(A,Z+1)+e-+anti-ve +Q !  Q ≈ 200 MeV / fission released !  Fission rate ≈ 4 GW/200 MeV ~ 2.1020 /s !  6 anti-veemitted per fission !  7.5 1020 anti-ve/s for a 4 GW nuclear core


Reactor ν Yield

Φν (E, t) =Pth (t)αk (t)Ek

k∑

× αk (t)Skk∑ (E)

€

k=235U,238U,239Pu,241Pu

Thermal power, δPth ≤1%

Fraction of fissions from isotope k, δαk=few % but large anti-correl @ fixed Pth

E released per fissions of isotope k, δEk≈0.3%

ν spectrum per fission

Reactor data

Nuclear databases

Reactor evolution codes


Reactor Neutrino Detection


Detection Principle


Inverse Beta Decay Process

νe + 11H→ e+ +n


IBD Cross Section

Detected Spectrum

!  Threshold : 1.8 MeV (neutrino energy)

!  Mean neutrino energy : 3.6 MeV

Ex: 235U" 6.6(1)10-43 cm2


How do we ‘see’ Reactor Neutrinos


Double Chooz

http://doublechooz.org/

France

Germany

Japan

Brazil

Spain

U.S.A

Russia

U.K.

Liquid Scintillator

Carbon Atom Hydrogen Atom

C18H30


Fluorescence


$

$

Energy Transfer

$

e-


Photomultuplier Tubes Stage 1: photons ! electrons conversion

(photoelectric effect)

Transformation of a flux of photons (light) into a flux of electrons (electric current)


Signal pre-amplification Stage 2: multiplication of the electrons x 106


Contained Single Event


39

e+ n

Δt

Neutrino Selection Criteria

Positron Cut Neutron Cut Time Coincidence Cut


Hunting Neutrinos at Chooz

Backgrounds


n Gd

Σγ ~ 8 MeV

Neutron slowing/thermalisation

Correlated Background Accidental Background

n

Gd

Σγ ~ 8 MeV

+ γ

Eγ >~ 1 MeV

Backgrounds Types


Detector Design

Outer Veto: plastic scintillator strips (400 mm)

ν-Target: 10,3 m3 scintillator doped with 1g/l of Gd compound in an acryclic vessel (8 mm)

γ-Catcher: 22,3 m3 scintillator in an acrylic

vessel (12 mm)

Buffer: 110 m3 of mineral oil in a stainless steel vessel (3 mm) viewed by 390 PMTs

Inner Veto: 90m3 of scintillator in a steel vessel

equipped with 78 PMTs

Veto Vessel (10mm) & Steel Shielding (150 mm)

!  Large target size – contained events – 4π light collection system – low systematics – low background


Borexino 300 t

KamLAND 1000 t

Double Chooz & CHOOZ

~10 t

Nucifer 1 t

Neutrino Detector Scales

Neutrinos for fundamental Physics (and potentially far field monitoring) Neutrinos for

reactor monitoring


Backgrounds (arXiv:0145439)


Overburden

Chooz

KamLAND

Borexino


Neutrino Oscillation



Phenomenon of quantum interference during which a neutrino of a given flavor metamorphoses

spontaneously into a neutrino of another flavor

The observation of the oscillations implies that neutrinos have a mass me / 10 millions < m < me / 1 million


Neutrino Oscillation formalism

€

U =

1 0 00 c23 s230 −s23 c23

#

$

% % %

&

'

( ( ( ×

c13 0 s13e−iδ

0 1 0−s13e

iδ 0 c13

#

$

% % %

&

'

( ( ( ×

c12 s12 0−s12 c12 00 0 1

#

$

% % %

&

'

( ( ( ×

eiα1 / 2 0 00 eiα 2 / 2 00 0 1

#

$

% % %

&

'

( ( (

!  θ12 ≈ θsol ≈ 32°, θ23 ≈ θatm ≈ 35-55°, θ13 < 15°

cij ≡ cos θij, sij ≡ sin θij

Atmospheric Cross-Mixing Solar

~

Majorana CP phases!

!  δ would lead to P(να→ νβ) ≠ P(να→ νβ) CP

Flavour states"

Mixing Matrix U (Unitary)

δ Dirac CP violating phase

θ12 : “solar’’ mixing angle θ23 : “atm.’’ mixing angle θ13 2 Majorana phases

(L violating processes)

!  δ would lead to P(να→ νβ) ≠ P(να→ νβ) CP

!  3 masses m1, m2, m3 :

!  3-flavour effects are suppressed because : 1θ & )301( ΔmΔm 132atm

2sol <<<<

21

23

2atm

21

22

2sol mmΔm&mmΔm −=−=

€

P(ν x →ν x ) =1− sin2 2θ i( )sin 1.27Δmi

2 (eV2

)L (m)

E (MeV)

'

( )

*

+ ,


P(νe→ νe) = 1 - sin2(2θ) sin2(Δm2L/4E)

<500 m

θ12$$

Δm221$

Δm231$

θ13 = ?$

Neutrino Oscillation at Reactors


Δm221 & θ12

ν3

(Mas

s)2

νe νµ ντ |Uei|2 |Uµi|2 |Uτi|2

Δmsol2 = 8.10-5 eV2

ν1

ν2 Δm2 (eV2) ~ L (km) / E(GeV) L~100 km & E~MeV

Or MSW ‘flavor transition’

Borexino Gallex/GNO

Reactor Experiments

SNO

SuperK KamLAND

Experiment Baseline Size SuperK Sun 22.500 tons

SNO Sun 1000 tons

KamLAND 150 km 1200 tons

Borexino ~800 km 300 tons


ν3

(Mas

s)2


Δmatm2 = 2.5.10-3 eV2

Δmsol2 = 8.10-5 eV2

ν1

ν2

θ13

Double Chooz

Daya bay

Reno

Reactor Neutrino Experiments

Experiment Baseline Size Power Channel Double Chooz 400 m / 1.1 km 10 m3 8.6 GW (2) Reno 350 / 1.4 km 20 m3 16.4 GW (6) Daya Bay 400 / 1.7 km 100 m3 17.4 GW (6)

ee ν→ν


ν3

Neutrino Oscillation Status (M

ass)

2


Δmatm2 = 3.10-3 eV2

Δmsol2 = 8.10-5 eV2

ν1 + ν2 ~ νµ - ντ atmospheric maximal mixing

ν1

ν2

in solar MSW-LMA solution νe survival probability = νe fraction of ν2

atmospheric νµ/νe up/down ratio confirmed by long baseline νµ beam

ν3 ~ νµ + ντ atmospheric maximal mixing

νe reactor spectral distorsion at L~180 km νe solar spectral distorsion

νe reactor at L~1-2 km + Accelerators


Open questions !  What are the masses of the mass eigenstates νi?

ν3!

(Mass)2!Δm2

atm!

Δm2sol!

?!ν1!ν2!

ν flavor change

β decay, ββ0ν decay, Cosmology

!  Is the spectral pattern or ? ν behavior in earth matter, ββ0ν ( — )

0!

!  Is there any conserved Lepton Number (Dirac or Majorana neutrino) ? ββ0ν

!  What are the angles of the leptonic mixing matrix? !  Do the behavior of ν violate CP? !  Is leptonic CP responsible for the matter-antimatter asymmetry?

!  Are there sterile neutrinos?

ν flavor change


introduction to low energy neutrino physics · introduction to low energy neutrino physics thierry...

Documents