Neutrino properties, oscillations, present status Gaston Wilquet IIHE - Université Libre de Bruxelles 1 Urs Fest, Bern, 21/1/2011

2 A very brief history of the neutrinos Neutrino Mixing Neutrino nature: Dirac or Majorana particle? Neutrino-less  -decay Direct mass measurements Neutrino oscillations – phenomenology First evidences of neutrino oscillations: a selection Observation of neutrino oscillations at reactors and accelerators: a selection Near future (current decade) as conclusions I shall not talk about the OPERA experiment: see next talk by Henri Pessard Contents

A very brief history of the neutrinos 3

Pierre Becquerel (1886) discovers radioactivity Ernest Rutherford (1897) identifies  and  radioactivity J.J.Thomson and others (1897) discover electron Pierre and Marie Curie (1902) show that  -rays are electrons 40 K  40 Ca + e - Lise Maitner and Otto Hahn and James Chadwick (1914) measure the  -rays energy spectrum: incompatible with 2-body decay. Angular momentum is not conserved. C.D. Ellis et W.A. Wooster (1927) and Lise Meitner and W. Orthman (1930) do a calorimetric measurement of the total energy released in the  radium E  ( 210 Bi) decay: incompatible with 2-body decay and with 3-body decay involving a  -ray Niels Bohr and others contemplates the possibility that energy-momentum is not conserved in  decays From the discovery of radioactivity to the “energy crisis” 4

Letter from Pauli retained by a ball in Zurich to the “Gruppe der Radioaktiven” in meeting in Tübingen “Invention” of the neutrino and the weak interaction formalism Wolfgang Pauli “invents” the neutrino (1930): the Columbus egg  -decay is a 3-body decay involving a “neutron”: light spin ½ neutral particle Enrico Fermi (1933) names the “neutrino” and develops the  -decay theory – the base of the electroweak theory in the Standard Model James Chadwick had discovered the neutron in 1932 Local 4-fermions current-current interaction based on the 4-spinor Dirac description of Fermions 5

Enrico Fermi (1933) offers a case of champagne to whom will detect the first neutrino. Hans Bethe and Rudolf Peierls (1934) Mean free path of moderate energy in lead: tens to thousands ly Fred Reines et Clyde Cowan ( ) detect the first neutrino interactions at Savannah River nuclear power plant The experimental discovery of the neutrino 6

Ray Davis et al. ( ) confirm the difference neutrino/antineutrino Neutrino, antineutrino and neutrino families Bruno Pontecorvo (1959):electron and muon have different partners e and  Leon Lederman, Melvin Schwartz, Jack Steinberger at al (1962) discover the  DONuT Collaboration (2001) observes the  at Fermilab 7

Neutrino Mixing 8

Mixing matrix 9

PMNS parameterization of mixing matrix Bruno Pontecorvo (1957) - Ziro Maki, Masami Nakagawa, Shoichi Sakata (1962) 10

Neutrino nature: Dirac or Majorana particle? Neutrino-less  -decay 11

The Standard Model Weyl neutrino Tsung Dao Lee and Chen Nin Yang (1956) predict P violation in weak interactions Chien Shiung Wu et al. (1957) observe maximum P violation in  -decay Maurice Goldhaber et al. (1958) measure the neutrino helicity ( ) are fully polarized: h = -1/2 (+1/2) 12

Massive neutrinos: Dirac or Majorana ? 13

14 Dirac vs. Majorana? Neutrino-less  -decay © LHEP website 4 crystals

Direct mass measurements 15

Very high energy resolution & counting rate Very low background e effective mass - electron energy spectrum in Tritium  -decay 16

e effective mass - status of Tritium experiments Both experiments have reached their intrinsic limit of sensitivity Troitsk gaseous T 2 -source Mainz frozen T 2 -source Magnetic adiabatic electron collimation followed by an electrostatic filter 17

Neutrino oscillations phenomenology 18

Neutrino propagation in vacuum: Neutrino oscillation 19

Flavour transition caused by matter effects 20

Neutrinos oscillation: what we know in 2010 ? ? Normal hierarchy ? Inverted hierarchy ? eV 2 Degeneracy

First evidences of neutrino oscillations: a selection 22

First evidences: atmospheric and solar neutrinos First experimental indications of neutrino oscillations were incidental. Experiments designed to study the interior of the Sun (Ray Davis at Homestake mine in 1968 …) and cosmic rays through interactions in the atmosphere (IMB at Morton mine in 1986 …) using neutrinos as messengers. (Almost) all evidences based on disappearance: deficit in flux of a neutrino flavour measured at distant point the from its source. Evidences first confirmed by several experiments using natural neutrinos sources. Astrophysical and instrumental explanations of the deficits progressively abandoned. Undisputed interpretation as neutrino oscillation dates from about a decade: Atmospheric neutrinos (…Kamiokande, Super-Kamiokande-1998…) Solar neutrinos (Homestake,… Kamiokande, Super-Kamiokande, SNO-2002…) 23 Pioneers: Ray Davis: Homestake radiochemical experiment, first solar neutrino detection Masatoshi Koshiba: first large water Cerenkov experiment Kamiokande – solar and atmospheric neutrinos

Atmospheric neutrinos : Super-Kamiokande p e 20 km km p   e

Super-Kamiokande results arXiv:hep-ex/

sin 2   sin 2    m 2 32 (eV 2 ) Super-Kamiokande results arXiv:hep-ex/ ?

5t 17t 90t90t E CHOOZ reactor experiment: confirms that no e in 3 27 Detector : liquid scintillator vessel doped with high neutron capture cross-section

Solar neutrinos: measured event rates vs. SSM predictions (Bahcall and Pinsonneault) 28

29 Solar neutrinos: SNO 2002 results SNO NC

Solar neutrinos results explained by matter effects 30 adiabatic

Observation of neutrino oscillations at reactors and accelerators: a selection 31

What about oscillation experiments at accelerators and nuclear reactors? Until late 1990’s No theoretical prediction Theoretical prejudice: small mixing c.f. quarks Hot dark matter models: large m > 10 eV → large  m 2 Accelerator experiments From ~2000: U and  m 2 known with reasonable precision: Design experiments for specific L/E & oscillation channel. 32

Probing atmospheric neutrinos solution:  disappearance or its appearance into  at accelerators K2K : KEK to Kamioka LBL experiment ( ) 33

MINOS : the LBL Fermilab NuMI beam (2005  ) Ratio of data to expected for no oscillations P. Vahle, Neutrino

35 Probing solar neutrinos solution: e disappearance at nuclear reactors KamLAND LBL experiment at Kamioka 13 m diameter balloon

KamLAND results 36 arXiv:hep-ex/ Common fit to KamLAND and solar neutrinos results

Near future (current decade) as conclusions 37

We know with good precision the few we knew ? Observations made with natural neutrinos sources confirmed with manmade neutrinos sources and measurements improved A lot that we do not know 10 years later

Oscillation: Why will it be difficult and maybe very difficult ? sin 2 2  13 =0.25 sin 2 2  13 =0.09 sin 2 2  13 =0.17 ○  CP =0 ▼  CP =  ●  CP =  ▲  CP =3  /2 39

T2K (Tokai to Kamioka) experiment Oscillation experiments at accelerators 2.4× – 0.02 NO A experiment at Fermi Lab –

Oscillation experiments at reactors East Reactor West Reactor 351 m 465 m 1115 m 998 m Double-CHOOZ Daya Bay, China 41

Direct mass and 0  -decay : why will it be very difficult ? Katrin Tritium experiment - Karlsruhe Degenerate masses 0  -decay experiments 42

Ten years of collaboration with Before doing physics with the OPERA detector from 2008, we built together the OPERA Target Tracker between 2000 and 2007 Scientific knowledge Wisdom Kindness Perpetual smile In particular with 43

Scientific knowledge Wisdom Kindness Perpetual smile Thank you, Urs 44