Neutrino Physics Alain Blondel University of Geneva 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 1

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. Evaluation Examen 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?

! Majorana neutrinos or Dirac neutrinos? e+  e– since Charge(e+) = – Charge(e–). But neutrinos may not carry any conserved charge-like quantum 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 ! then, nothing distinguishes from violation of fermion number….

implies adding a right-handed neutrino. 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) nL  n- + n+ m/E

L NR R NL L R R L L R In the most general way: MR  0 mD  0 Dirac + Majorana MR  0 mD  0 Dirac + Majorana L NR R NL ½ 0 ½ 0 4 states , 2 mass levels MR = 0 mD  0 Dirac only, (like e- vs e+): L R R L ½ 0 ½ 0 4 states of equal masses MR  0 mD = 0 Majorana only L R ½ ½ 2 states of equal masses m m m Iweak= Iweak= Iweak= Some have I=1/2 (active) Some have I=0 (sterile) All have I=1/2 (active) m1 have I=1/2 (active) m2 have I=0 (sterile)

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

wrong L R L R R L L ‘R ‘ NR NL 0 0 L R 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 R I= ½ ½ L R R L ½ 0 ½ 0 L ‘R ‘ ½ ½ NR NL 0 0 L R ½ ½ X 3 Families 6 massless states 3 masses 12 states 3 active neutrinos 3 active antinu’s 6 sterile neutrinos… 3 mixing angles 1 CP violating phase 0v = 0 6 active states No steriles 3 CP violating phases 0v  0 6 masses More mixing angles and CPV phases  Leptogenesis and Dark matter wrong Mass hierarchies are all unknown except m1 < m2 Preferred scenario has both Dirac and Majorana terms … … many physics possibilities and experimental challenges

Most attractive wisdom: via the see-saw mwchanism, 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 states in a split doublet with heavy neutrinos of mass scale interestingly similar to the grand unification scale. m M = <v>2 with <v> ~= mtop =174 GeV  for mn.= O(10-2) eV  M ~1015 GeV

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

Pion decay with massive neutrinos + nL nL nLc = nR (mn /E)2 1 (.05/30 106)2 = 10-18 no problem

n1 n2 n3 ne m would measure a distribution with three values of mass with the following probabilities ¦U1e¦2 ¦U2e¦2 ¦U3e¦2 The smallest possible flavor neutrino mass? <m ne>=¦U1e¦2 m1 + ¦U2e¦2 m2 + ¦U3e¦2 m3 Valeurs présentes

have Majorana mass term

ce que mesure le 0nbb est <m> : m1 m2 m3 are physical masses of active neutrino (I=1/2) which in this case are just the same as in oscillation experiments

(GF)4

NEMO typical 2nbb evenement Criteria to select bb events: Vertex emission Deposited energy: E1+E2= 2088 keV Internal hypothesis: (Dt)mes –(Dt)theo = 0.22 ns Common vertex: (Dvertex) = 2.1 mm NEMO Criteria to select bb 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 (g rejection) No delayed track (214Bi rejection) typical 2nbb evenement

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

KAMLAND

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’ Alain Blondel NUFACT12 23-07- 2012

1989 The Number of light neutrinos ALEPH+DELPHI+L3+OPAL in 2001 N = 2.984 0.008 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

Alain Blondel NUFACT12 23-07- 2012

Thierry Lasserre Alain Blondel NUFACT12 23-07- 2012

Shaewitz Neutrino 2012 Alain Blondel NUFACT12 23-07- 2012

source detector active,  sterile active,  Sterile neutrino search a global view: Detected by mixing between sterile and active neutrino ideal experiments: source detector active,  known process known process 1. disappearance, not necessarily oscillatory best is NC disappearance sterile 0. if sterile cannot be produced (too heavy) apparent deficit in decay rate active,  2.   appearance (at higher order) Alain Blondel NUFACT12 23-07- 2012

Alain Blondel NUFACT12 23-07- 2012

CONCLUSIONS 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