Neutrino physics -- Alain Blondel Alain Blondel University of Geneva Neutrino Physics 1. What are...

Neutrino physics -- Alain Blondel

Alain Blondel University of Geneva

Neutrino Physics

1. What are neutrinos and how do we know ?

2. The neutrino questions

3. Neutrino mass and neutrino oscillations

4. neutrino oscillations and CP violation

5. on-going and future neutrino experiments on oscillations

6. on-going and future neutrino-less double-beta experiments 7. Conclusions


Les neutrinos interagissent très peu et ont une masse extrêmement faible. Pourtant il se pourrait bien qu'ils détiennent la clé de plusieurs questions fondamentales en physique des particules. On passera en revue les expériences les plus marquantes par lesquelles les propriétés des neutrinos ont été établies, puis on fera un bilan des questions actuelles et du programme d'expériences prévu pour y répondre.

1. Propriétés des neutrinos: découverte, hélicité, neutrinos et antineutrinos, les familles de neutrinos. 2. Interactions des neutrinos, courant charges et courants neutres, les neutrinos dans le Modèle Standard. 3. La découverte des neutrinos du soleil, et le mystère des neutrinos solaires. Les neutrinos atmosphériques et la découverte des transmutations de neutrinos. 4. Propriétés des neutrinos massifs, les oscillations. Oscillations de neutrino oscillations avec trois familles. Les expériences neutrino auprès des réacteurs nucléaires. 5. La recherche de l'angle manquant theta_13. Les effets de matière et la violation de CP, le programme expérimental futur sur les oscillations. 6. Les mesures directes de la masse des neutrinos. Les neutrinos et la cosmologie.

7. Questions théoriques sur les masses des neutrinos, masses de Dirac ou de Majorana ? La recherche de la désintégration double beta sans neutrinos. Envoi sur le rôle des neutrinos pour façonner l'univers.

EvaluationExamen oral.Sessions : Juin - Août/Septembre ECTS : 3.5


Neutrinos have mass and mix

This is NOT the Standard Model

why cant we just add masses to neutrinos?


e+ e– since Charge(e+) = – Charge(e–).But neutrinos may not carry any conserved charge-likequantum number.There is NO experimetal evidence or theoretical need for a conserved Lepton Number L as L(ν) = L(l–) = –L(ν) = –L(l+) = 1

ii

ii Majorana neutrinosMajorana neutrinos

or

Dirac neutrinos?Dirac neutrinos? ii

ithen, nothing distinguishes i from

!violation of fermion number….


Adding masses to the Stadard model neutrino 'simply' by adding a Dirac mass term

implies adding a right-handed neutrino. No SM symmetry prevents adding then a term like

and this simply means that a neutrino turns into a antineutrino (the charge conjugate of a right handed antineutrino is a left handed neutrino!)

this does not violate spin conservation since a left handed field has a component of the opposite helicity (and vice versa)

L - + + m/E


In the most general way:

MR 0mD 0Dirac + Majorana

MR = 0mD 0Dirac only, (like e- vs e+):

L R R L

½ 0 ½ 04 states of equal masses

m

Iweak=

Some have I=1/2 (active)Some have I=0 (sterile)

MR 0mD = 0Majorana only

L R

½ ½ 2 states of equal masses

m

Iweak=

All have I=1/2 (active)

MR 0mD 0Dirac + Majorana

L NR R NL

½ 0 ½ 04 states , 2 mass levels

m

Iweak=

m1 have I=1/2 (active)m2 have I=0 (sterile)


Note that this is not necessary As one can have M anywhere…

Neutrinos : the New Physics there is… and a lot of it!

SM Dirac mass term only

Majorana mass term only

Dirac AND Majorana Mass terms

L RI= ½ ½

L R R L ½ 0 ½ 0

L ‘R ‘ ½ ½

NR NL

0 0L R ½ ½

X 3 Families X 3 Families X 3 Families X 3 Families

6 massless states 3 masses 12 states3 active neutrinos3 active antinu’s6 sterile neutrinos… 3 mixing angles 1 CP violating phase 0v = 0

3 masses 6 active states No steriles3 mixing angles 3 CP violating phases0v 0

6 masses12 states6 active states 6 sterile neutrinos…More mixing angles and CPV phases0v 0 Leptogenesis and Dark matter

Mass hierarchies are all unknown except m1 < m2

Preferred scenario has both Dirac and Majorana terms …… many physics possibilities and experimental challenges

wrong


The mass spectrum of the elementary particles. Neutrinos are 1012 times lighter than other elementary fermions. The hierarchy of this spectrum remains a puzzle of particle physics.

Most attractive wisdom: via the see-saw mwchanism, the neutrinos are very light because they are low-lying statesin a split doublet with heavy neutrinos of mass scale interestinglysimilar to the grand unification scale.

mM <v>2 with <v> ~= mtop =174 GeV

for meV M ~1015GeV


One often considers that MR ~ MGUT ~ 1010 to 1015 GeV


Pion decay with massive neutrinos

L+

L

1 (m /E)2

(.05/30 106)2 = 10-18

no problem

Lc = R


The smallest possible flavor neutrino mass?

Valeurs présentes

<m e>=¦U1e¦2 m ¦U2e¦2 m ¦U3e¦2 m


have Majorana mass term

ce que mesure le est <m> :

m1 m2 m3 are physical massesof active neutrino (I=1/2) which in this case are just the same as in oscillation experiments

GIF2004 Alain Blondel

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)

Deposited energy: E1+E2= 2088 keVInternal hypothesis: (t)mes –(t)theo = 0.22 nsCommon vertex: (vertex) = 2.1 mm

Vertexemission

typical 2evenement

NEMO


GERDA has accumulated enough statistics now to confirm of not HdM result by summer 2013


KAMLAND

Alain Blondel NUFACT12 23-07- 2012

Sterile neutrinos ( right handed neutrinos)

Sterile neutrinos can have masses extending from(essentially 0) all the way to GUT-inspired 1010 GeV!

We have many hints for ‘something that could be indications for sterile neutrinos ‘ in the ~ few eV2 range

In general these hints are not performed with the desired methodological quality -- no near detector -- no direct flux measurement -- no long target hadroproduction with full acceptance -- etc.. etc… -- none is 5 sigma

-- need decisive experiments (> 5 significance) -- look wide! other ranges than LSND ‘effect’

1989 The Number of light neutrinos

ALEPH+DELPHI+L3+OPAL in 2001 N = 2.984 0.008

ZeevsqqZee ,

Error dominated by systematics on luminosity.


At the basis of the experiment: background to golden channel is low, because there is no known neutrino interaction that produces a fast electromagnetic signal followed by a ‘slow neutron’ capture signal

However we do not know all neutrino reactions at these low energies.


Can be fit by oscillation signal


Thierry Lasserre

Alain Blondel NUFACT12 23-07- 2012Shaewitz Neutrino 2012


Sterile neutrino search a global view:Detected by mixing between sterile and active neutrino

ideal experiments:

known process

active, known process

source detector

sterile

active,

1. disappearance, not necessarily oscillatory best is NC disappearance

0. if sterile cannot be produced (too heavy) apparent deficit in decay rate

2. appearance (at higher order)


CONCLUSIONS

1. Neutrinos were a cornerstone of the construction of the Standard Model helicity of neutrinos is LEFT (???) discovery of neutral currents and determination of nucleon structure of quarks

2. Neutrinos have mass there is no unique answer to this in the Standard Model Dirac or Majorana mass term, or both?

3. There are three families of neutrinos and they mix This is the source of neutrino oscillations and could lead to observable CP violation 4. If neutrinos have both Majorana and Dirac mass terms A possible explanation of small masses of active neutrinos Predicts the existence of neutrinoless double beta decay Predicts the existence of massive sterile neutrinos

5. AND…. Provide a beautiful dark matter candidate Provide an explanation for the matter-antimatter asymmetry of the Univers

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