Neutrino Physics: Now and the Future. Alain Blondel University of Geneva

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1 Neutrino Physics: Now and the Future Alain Blondel University of Geneva

ν e 1930 Neutrinos: Neutrinos: the birth of the idea Dear Radioactive Ladies and Gentlemen, Pauli's letter of the 4th of December 1930 dn de e - spectrum in beta decay few MeV E As the bearer of

upon a desperate remedy to save the "exchange theorem" of statistics and the law of conservation of energy.

2 ν e 1930 Neutrinos: Neutrinos: the birth of the idea Dear Radioactive Ladies and Gentlemen, Pauli's letter of the 4th of December 1930 dn de e - spectrum in beta decay few MeV E As the bearer of these lines, to whom I graciously ask you to listen, will explain to you in more detail, how because of the "wrong" statistics of the N and Li6 nuclei and the continuous beta spectrum, I have hit upon a desperate remedy to save the "exchange theorem" of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spin 1/2 and obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass and in any event not larger than 0.01 proton masses. The continuous beta spectrum would then become understandable by the assumption that in beta decay a neutron is emitted in addition to the electron such that the sum of the energies of the neutron and the electron is constant... I agree that my remedy could seem incredible because one should have seen those neutrons very earlier if they really exist. But only the one who dare can win and the difficult situation, due to the continuous structure of the beta spectrum, is lighted by a remark of my honoured predecessor, Mr Debye, who told me recently in Bruxelles: "Oh, It's well better not to think to this at all, like new taxes". From now on, every solution to the issue must be discussed. Thus, dear radioactive people, look and judge. Unfortunately, I cannot appear in Tubingen personally since I am indispensable here in Zurich because of a ball on the night of 6/7 December. With my best regards to you, and also to Mr Back. Your humble servant. W. Pauli Wolfgang Pauli

3 Reines and Cowan discover interactions of neutrinos from reactors they do this: + νe + p e + n 1959 Ray Davis established that (anti) neutrinos from reactors do not interact with chlorine to produce argon reactor : n p e - ν e or ν e? they don t do this: ν e + 37 Cl 37 Ar + e - The neutrinos from reactors are called «antineutrinos»

4 1956 Parity violation in Co beta decay: electron is left-handed (C.S. Wu et al) 1957 Neutrino helicity measurement M. Goldhaber et al Phys.Rev.109(1958)1015 neutrinos have negative helicity (... If massless this is the same as «left-handed») anti-neutrinos have positive helicity (... If massless this is the same as «right-handed») neutrinos are differenciated from antineutrinos by two things -- helicity -- sign of lepton they produce when they interact (leptonic or fermionic charge) if neutrinos are massless the two statements are equivalent, since the weak interaction couples to left-handed particles; with mass they are not. In the SM neutrinos are massless and fermionic charge is then conserved for all. There is no unique way to introduce mass for neutrinos in the SM.

5 1989 The Number of Neutrinos e+e- collider experiment: LEP N ν determined from the visible Z cross-section at the peak (most of which are hadrons): the more decays are invisible the fewer are visible: hadron cross section decreases by 13% for one more family of neutrinos final (2001): N ν = ±0.008

6 charged leptons The Standard Model: 3 families of spin 1/2 quark and leptons interacting with spin 1 vector bosons ( γ, W&Z, gluons) e µ τ neutral leptons = neutrinos mc 2 = GeV ν e mc 2?=? <1 ev GeV ν µ <1 ev ν τ 1,77 GeV <1 ev quarks d strange beauty mc 2 =0.005 GeV GeV 5 GeV u charm top mc 2 =0.003 GeV First family 1.5 GeV Seconde family mc 2 =175 GeV Third family

7 neutrino definitions the electron neutrino is present in association with an electron (e.g. beta decay) the muon neutrino is present in association with a muon (pion decay) the tau neutrino is present in association with a tau (W τν decay)

Ar + e - they are neutrinos Davis detected neutrinos from the sun!

8 Neutrinos astrophysical neutrinos Ray Davis since ~1968 Homestake Detector Solar Neutrino Detection 600 tons of chlorine. Detected neutrinos E> 1MeV fusion process in the sun solar : pp pn e + ν e (then D gives He etc ) these ν e do ν e + 37 Cl 37 Ar + e - they are neutrinos Davis detected neutrinos from the sun! BUT the rate of (electron) neutrinos detected is three times less than predicted! solar neutrino puzzle since ! solution: 1) solar nuclear model is wrong or 2) neutrino oscillate

9 The final solution to the solar neutrino puzzle: SNO experiment Aim: measuring non ν e neutrinos in a pure solar ν e beam How? Three possible neutrino reaction in heavy water: only ν e equally ν e + ν µ + ν τ in-equally ν e ( ν µ + ν τ ) 1000 ton of D m diam PMTs

10 Kamland 2002

11 neutrinos transform in their travel neutrinos have mass! km/gev 2005 from solar neutrinos we know that θ e1 is less than 45 degrees. (the lightest neutrino of the solar pair is the most rich in electron neutrino) this is possible thanks to matter effects in the sun

12 Atmospheric Neutrinos (since mid 80 s up-down muon asymmetry) Path length from ~20km to km

13 Super-K detector Water Cerenkov detector tons of pure light water PMTs 41.3 m 39.3 m C Scientific American

14 µ/e Background Rejection e/mu separation directly related to granularity of coverage. Limit is around 10-3 (mu decay in flight) SKII coverage OKOK, less maybe possible

15 Atmospheric ν : up-down asymmetry Super-K results 1998 ν e ν µ up down

16 Atmospheric Neutrinos SuperKamiokande Atmospheric Result 500 km/gev

Oscillation maximum 1.27 m 2 L / E =π/2 Atmospheric m 2 = 2.

17 Oscillation maximum 1.27 m 2 L / E =π/2 Atmospheric m 2 = ev 2 L = GeV Solar m 2 = ev 2 L = 1 GeV Consequences of 3-family oscillations: I There will be ν µ ν e and ν τ ν e Oscillations of 250 MeV neutrinos; P (ν µ ν e ) appearance at L atm P (ν µ ν e ) max =~ ½ sin 2 2 θ 13 + and disappearance P(ν e ν e ) max =1- sin 2 2 θ 13 II There will be CP or T violation for appearance CP: P (ν µ ν e ) P (ν µ ν e ) P (ν e ν e ) from reactor T : P (ν µ ν e ) P (ν e ν µ ) III we do not know if the neutrino ν 1 which contains more ν e is the lightest one (natural?)

P(ν e ν µ ) = A 2 + S 2 + 2 A S sin δ P(ν e ν µ ) = A 2 + S 2-2 A S sin δ P(ν e ν µ ) - P(ν e ν µ ) sinδ sin ( m 2 12 L/4E) sin θ 12

13 need APPEARANCE P(ν e ν e ) is time reversal symmetric (reactors or sun are out) can be large (30%) for suppressed channel (one

18 P(ν e ν µ ) = A 2 + S A S sin δ P(ν e ν µ ) = A 2 + S 2-2 A S sin δ P(ν e ν µ ) - P(ν e ν µ ) sinδ sin ( m 2 12 L/4E) sin θ 12 sinθ 13 P(ν e ν µ ) + P(ν e ν µ ) = A CP α sin2 2θ 13 + solar term need large values of sin θ 12, m 2 12 (LMA) but *not* large sin2 θ 13 need APPEARANCE P(ν e ν e ) is time reversal symmetric (reactors or sun are out) can be large (30%) for suppressed channel (one small angle vs two large) at wavelength at which solar = atmospheric and for ν e ν µ, ν τ asymmetry is opposite for ν e ν µ and ν e ν τ

20 arxiv: near detectors: Observation of disappearance (5sigma on 8 March 2012) The best-fit values are sin 2 2θ 13 = and m 2 ee = (2: ) 10-3 ev 2 Far detectors

SuperKamiokande detector (50kton W.Č., 22.

Proton Accelerator Research Complex (JPARC)

75MW/50GeV Proton Synchrotron -- baseline

~600 MeV achievable by pion-decay beam at 2.

21 Idea of T2K was born hep-ex/ combining: -- existing SuperKamiokande detector (50kton W.Č., 22.5 kton fiducial) -- JAERI-KEK Japanese Proton Accelerator Research Complex (JPARC) at TOKAI including a high power, 0.75MW/50GeV Proton Synchrotron -- baseline 295 km neutrino energy for first maximum is ~600 MeV achievable by pion-decay beam at 2.5 degrees off-axis Alain Blondel UNIGE seminar -- The T2K experiment theta_13 21

D 87, 092003 (2013) Phys. Rev. Lett. 111, 211803 (2013) sterilev searchcomingup!

22 discovery of ν µ ν e appearance 28 evts ν µ disappearance ν µ cross-section PRL 112, (2014) 40 Alain Blondel CHIPP 2014Mar07 (M. Ravonel s thesis) Phys. Rev. D 87, (2013) Phys. Rev. Lett. 111, (2013) sterilev searchcomingup! (Davide Sgalaberna) NB very nice collaboration among swiss groups at post-docs and PhD level

23 Alain Blondel CHIPP 2014Mar07 begins to exclude part of phase space in {mass hierarchy, δ CP }

24 General framework : 1. We know that there are three families of active, light neutrinos (LEP) 2. Solar neutrino oscillations are established (Homestake+Gallium+Kam+SK+SNO) 3. Atmospheric neutrino (ν µ > ) oscillations are established (IMB+Kam+SK+Macro+Sudan) 4. At that frequency, (ν µ > ν e ) oscillations are small (5%) but have been observed (T2K) and ν e disappearance has been measured (Daya Bay, Reno, Double Chooz) θ ~30 0 m 122 ~ ev 2, θ 23 ~45 0 m 2 23 ~ ± ev 2, θ with several unknown parameters => an exciting experimental program for at least 25 years *) including leptonic CP & T violations 13 *)to set the scale: CP violation in quarks was discovered in 1964 and there is still an important program (K0pi0, B-factories, Neutron EDM, BTeV, LHCb..) to go on for 10 years i.e. a total of ~50 yrs. and we have not discovered leptonic CP yet!

25 neutrino definitions the electron neutrino is present in association with an electron (e.g. beta decay) the muon neutrino is present in association with a muon the tau neutrino is present in association with a tau (pion decay) (W τν decay) these flavor-neutrinos are not (as we know now) quantum states of well defined mass (neutrino mixing) the mass-neutrino with the highest electron neutrino content is called ν 1 the mass-neutrino with the next-to-highest electron neutrino content is ν 2 the mass-neutrino with the smallest electron neutrino content is called ν 3

26 food for thought: what result would one get if one measured the mass of a ν e (in K-capture for instance)? what result would one get if one measured the mass of a ν µ (in pion decay)? Is energy conserved when neutrinos oscillate? Why do neutrinos oscillate and quarks do not?

27 The neutrino mixing matrix: 3 angles and a phase δ ν 3 Normal hierarchy ν e is lightest m 2 23= ev 2 ν 2 1 m 2 12= ev 2 OR? θ 23 (atmospheric) = 45 0, θ 12 (solar) = 32 0, θ 13 ~ 10 0 ν 2 1 ν 3 m 2 12= ev 2 m 2 23= ev 2 Inverted hierarchy ν e is heaviest (?) Unknown or poorly known 2 phase δ, hierarchy (sign of m 13 )

30 neutrino mixing (LMA, natural hierarchy) m 2 ν ν 3 2 sin θ13 sin 2 θ 12 cos 2 θ 13 ν 2 ν 1 cos 2 θ 12 cos 2 θ 13 ν e is a (quantum) mix of ν 1 (majority, 60%) and ν 2 (minority 30%) with a small admixture of ν 3 ( 10%)

31 so we know they are all <2.2 ev!

32 KATRIN is a VERY large spectrometer aiming at m~0.2 ev

33 Halzen adding hot neutrino dark matter erases small structure m ν = 0 ev m ν = 1 ev m ν = 7 ev m ν = 4 ev

34 CPC peaks at twice the distance (half the energy) wrt the CPV term desambiguation best done with a wide band beam Alain Blondel CHIPP 2014Mar07

35 NOvA Alain Blondel NUFACT

36 in some regions will be able to determine mass hierarchy at 3σ in 6 years Alain Blondel NUFACT

37 mass hierarchy with reactor? Juno experiment China need resolution < separation between peaks <~ 2% at 3 MeV intrinsic from nuclear reaction smearing is 1%. Alain Blondel NUFACT

38 Alain Blondel NUFACT mass hierarchy with atmospherics?

39 Kamioka L=295km OA=2.5deg J-PARC 1.7MW P32 proposal (Lar TPC R&D) Recommended by J-PARC PAC (Jan 2010), arxiv: High priority project in Japan, LOI submitted to JPARC Hope to start construction ~2018

41 Majorana neutrinos ν = ν i i or Dirac neutrinos? ν i ν i 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 ν from i ν i! violation of fermion number. Neutrino physics -- Alain Blondel

42 Addingmasses to the Standard model neutrino 'simply' by addinga Dirac mass term implies adding a right-handed neutrino. No SM symmetrypreventsaddingthena termlike (Majorana mass term) and this simply means: 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) ν L ν - + ν + m/e No unique solution: Mass can be given by Dirac mass term (like all other SM fermions) or Majorana mass term (not forbidden, thus will happen) or BOTH (preferred theoretical scenario) Neutrino physics -- Alain Blondel

In the most general way: M R 0 m D 0 Dirac + Majorana + m I weak = M R = 0 m D

masses Some have I=1/2 (active) Some have I=0 (sterile) m I weak = M R 0 m D =

I weak = M R 0 m D 0 Dirac + Majorana ν L N R ν R N L ½ 0 ½ 0 4 states, 2 mass

43 In the most general way: M R 0 m D 0 Dirac + Majorana + m I weak = M R = 0 m D 0 Dirac only, (like e- vs e+): ν L ν R ν R ν L ½ 0 ½ 0 4 states of equal masses Some have I=1/2 (active) Some have I=0 (sterile) m I weak = M R 0 m D = 0 Majorana only ν L ν R ½ ½ 2 states of equal masses All have I=1/2 (active) m I weak = M R 0 m D 0 Dirac + Majorana ν L N R ν R N L ½ 0 ½ 0 4 states, 2 mass levels m1 have I=1/2 (active) Neutrino physics m2 have -- Alain I=0 Blondel (sterile)

44 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 ν L ν R I= ½ ½ ν L ν R ν R ν L ½ 0 ½ 0 ν L ν R ½ ½ N R N L 0 0 ν L ν R ½ ½ X 3 Families X 3 Families X 3 Families X 3 Families 6 masslessstates 3 masses 12 states 3 active neutrinos 3 active antinu s wrong 6 sterileneutrinos 3 mixing angles 1 CP violatingphase 0vββ ββ= 0 3 masses 6 active states No steriles 3 mixingangles 3 CP violating phases 0vββ 0 6 masses 12 states 6 active states 6 sterile neutrinos More mixingangles and CPV phases 0vββ 0 Leptogenesisand Dark matter Mass hierarchies are all unknown except m 1 < m 2 Preferred scenario has both Dirac and Majorana terms many physics possibilities and experimental challenges

45 Neutrino physics -- Alain Blondel

46 KAMLAND-ZEN NEMO3 CUORE

48 Higgsboson mass cornered (LEP H, M Z etc+tevatronm t, M W Higgs Boson discovered(lhc) Englert and Higgs get Nobel Prize (c) Sfyrla

49 Is itthe end?

50 Is itthe end? Certainlynot! --Darkmatter --Baryon Asymmetryin Universe --Neutrino masses are experimentalproofsthatthereismore to understand. Wemust continue ourquest

«sterile», very small coupling to known particles completelyunknownmasses

51 at least 3 piecesare stillmissing Since 1998 it is established that neutrinos have mass and this very probably implies new degrees of freedom «sterile», very small coupling to known particles completelyunknownmasses (ev to ZeV), nearlyimpossileto find.... but could perhaps explain all: DM, BAU,ν-masses

56 Manifestations of sterile neutrinos cosθ - θ cosθ c sinθ -- mixing with active neutrinos leads to various observable consequences -- if very light (ev), possible effect on neutrino oscillations --if mixingin % or permillevel, possiblymeasurableeffectson = light mass-eigenstate = heavy mass-eigenstate couples to weakint. doesnot PMNS matrix unitarity violation and deficit in Z invisible width occurrence of Higgsinvisible decaysh ν i Ν i violation of unitarityand lepton universalityin W or τ decays --etcetc.. today next times! --Couplingsare small (m D /M) and generallyout of reachof hadron colliders -- Require high statistics e+e- or other intensity frontir experiments Alain Blondel Future Circular Collider

57 Atthe end of LEP: Phys.Rept.427: ,2006 N ν = ± σ :^)!! This isdeterminedfromthe Z line shapescan and dominatedby the measurementof the hadronic cross-section at the Z peak maximum The dominant systematic error is the theoretical uncertainty on the Bhabha cross-section (0.06%) whichrepresentsan errorof ± on N ν Improving on N ν by more than a factor 2 would require a large effort to improve on the Bhabha cross-section calculation! Alain Blondel Future Circular Collider

Neutrino counting at TLEP given the very high luminosity, the following measurement can be performed, Γ ν Γ,µ The common γ tag allows cancellation of systematics due to photon selection, luminosity

58 Neutrino counting at TLEP given the very high luminosity, the following measurement can be performed, Γ ν Γ,µ The common γ tag allows cancellation of systematics due to photon selection, luminosity etc. The othersare extremelywellknowndue to the availabilityof O(10 12 ) Z decays. The full sensitivity to the number of neutrinos is restored, and the theory uncertainty on Γ ν Γ is veryverysmall. A good measurementcanbemade fromthe data accumulatedatthe WW threshold where σ(γz(inv) ) ~4 pbfor cosθ γ < GeV (10 7 s) running at1.6x10 35 /cm 2 /s x 4 exp 3x10 7 γz(inv) evts, Ν ν = adding5 yrsdata at240 and 350 GeV... Ν ν = A betterpoint maybe105 GeV(20pb and higherluminosity) mayallow Ν ν =0.0004? Alain Blondel FCC-ee for LHCB 1 st April 2014

59 Search for heavy neutral leptons searche + e - v N Nv(γ/Z) * monojet Find: one event in 4x10 6 Z: e + γ * e + e - e - Z * Alain Blondel FCC Future Circular Colliders

60 arxiv: H-> vn or Z-> vn LEP2 limits (DELPHI) (projected)? TLEP-Z? Alain Blondel Future Circular Collider

61 CONCLUSIONS 1. Neutrinos werea cornerstoneof 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 thereisno unique answerto thisin the Standard Model Dirac or Majoranamass term, or both? 3. There are threefamiliesof neutrinos and theymix This isthe source of neutrino oscillations and couldlead 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 Predictsthe existence of massive sterileneutrinos The huntisopen! 5. AND. Provide a beautiful dark matter candidate Provide an explanation for the matter-antimatter asymmetry of the Univers 6. BUT... THIS MAY TAKE A VERY LONG TIME! Neutrino physics -- Alain Blondel

Indication of ν µ ν e appearance in the T2K EXPERIMENT

Indication of ν µ ν e appearance in the T2K EXPERIMENT θ 13 Alain Blondel University of Geneva On behalf of the T2K collaboration Alain Blondel UNIGE seminar -- The T2K experiment theta_13 1 There are