Bruno Pontecorv O AND NEUTRINO PHYSICS

1. Bruno PontecorvO AND NEUTRINO PHYSICS There is not any idea on neutrino phyics that has nos been put forward by Pontecorvo (VTelegdi)

2. Plan of the Seminar • Brief introduction on neutrino physics • The life of Bruno Pontecorvo • Scientific activity of Pontecorvo • Pontecorvo big intuition • OSCILLATIONS : discovery and • present status of the research • Conclusions

3. The history of neutrino did start 80 years ago. What we know now • Neutrinos are fermions that have only weak interactions. • They interact trough W (charged currents) or Z0 exchange (neutral • currents) • The V-A theory requires that only neutrinos (anti neutrinos) left-handed (right-handed) are active. • In the Minimum Standard Model (MSM) there are 3 types of neutrinos and the corresponding number of anti neutrinos. • Interactions have the same strength for the 3 species: Universality • Neutrinos are coupled to the corresponding charged leptons • so we have 3 leptonic doublets

4. Neutrino sources • Solar Neutrinos ***** • Atmospheric neutrinos ***** • Geo neutrinos • Galactic and extra galactic • Man made • reactors ***** • accelerators ***** Relic Cosmic background radiation E=1.7 10-4 Ev

5. Neutrino birth In 1930 Pauli introduced the Neutrino Pauli letter to a meeting in Tubingen. He introduces the neutrino to save energy conservation in beta decay. He called this particle neutron , Fermi renamed it neutrino In his beta decay theory It is well known that to explain his absence at the meeting he wrote that he had to participate in a un ball in Zurich From Pauli letter……… I ask you to listen graciously … I will explain the continuous beta Spectrum……. I have hit upon a desperate remedy to save the energy theorem. It could exist in the nucleus electrically neutral particles ,that I wish to call neutrons, …… in the beta decay a neutron is emitted . So that the sum of the energy of neutron and electron is constant. I dont’ feel sure enough to publish ,so I first turn confidentially to you dear radioactives …..

6. The process was nbar +p >> n+ e+ The neutrino remained an hypothesis until the years 50 when Cowan and Reines did show his interactions in the study of the process Antineutrino + proton neutron + positron al nuclear reactor of the Savanna river Plant (USA) Pag 159 The detection was obtained with a delayed coincidence in a scintillator of the annihilation signal of the positron and the one of the gamma emitted in the reaction n ( thermalized) + cadmium The same technique is still used in the detection of antineutrinos at the reactors i.

7. The Life Bruno Pontecorvo Pisa 1913 –Dubna 1993 He did start his studies in the Pisa University and then in 1929 he continued In the “corso di laurea in Fisica” in Roma where he then become the youngest Fermi collaborator . In 1936 he moved to Paris, in the Joliot-Curie laboratory. When Germans occupied France (he was of yewish family) he went in the United State where he found a job in 1940 in the “ Well Surveys” company a company for the search of oil wells. In 1943 he was invited to participate in the construction of a nuclear reactor .ln Canada In 1948 he become British citizen and went to England , called by J. Cockroft, In 1950 , he left Italy, where he was on holyday, went to Stockholm and from there to . Soviet Union in the Dubna laboratories. In 1978 he made his first trip to Italy ,this trip was followed by many others He stayed in Dubna until 1993 when he died

8. The scientific career of Pontecorvo • Italy, Rome participates to the famous experiment on slow neutrons • France, Paris • collaborates with Joliot Curie in the study of nuclear isomers • United States Tulsa, Oklahoma • He works in a company for the detection of oil wells • He developed a method for detection of under ground light elements . • A pit , a strong neutron source ,an ionization chamber. • Neutrons slowed down in light elements increase counts in the chamber. • This method, still used, shows the experimental ingenuity of BP. • Neutron well logging • A new Geological method based on nuclear Physics • Oil and gas Journal 40,32,1941 . • Canada, will be described later • England :Harwell • He participates in the building of the Harwell reactor , • He works in the study of cosmic rays

9. Soviet Union Dubna experimental activities Experiments at the Dubna Sincrociclotron Works on capture of muons in He3 For example Measurement of the total muon capture rate in He3 O.A.Zaimidoroga et al Physics letters 6,100,1963 Theoretical activities OSCILLATIONS, see later Two types of neutrinos, see later Intermediate boson in weak interactions High energy conference Kiev 1959 Neutrino and astrophysics Universal Fermi interactions and astrophysics Zh exp theor fiz 36,1615, 1959 Many papers were publidshed in russian, of many translation can be found in Bruno Pontecorvo selected scientific works SIF 1997

10. CANADA 1946 1950 Of activities in Canada We recall a) Study of muons decay B) considerations on the nature of neutrinos 1)Universality 2)detection of neutrinos C) proportional counters

11. A) Study of mu meson decay • It was known that • Mu mesons decay with a life time of 2.2 ms • b) Only one charged particle is emitted in the decay • C) it was not clear the nature of neutral(s) particles emitted. Results of the experiment di Pontecorvo e Hinks Pag 102

12. Conclusions The average energy and the form of the energy spectrum of decay electrons are ,within the accuracy of theory and experiments, in agreement with the theoretical expectations for the “ Electron + 2 neutrinos process “ Graphite source Meson stop Graphite absorber Decay products detected

13. Considerations on the nature of weak interactions Universality The coupling constant with the intermediate bosons is the same for all leptons The interest of Pontecorvo was aroused by the results of an experiment made in Rome on the behavior of the hard component of cosmic rays (1943-1947). The experiment was made during and soon after the German occupation. The experiment was equipped with a magnet that allowed the determination of the sign of the observed particles

14. The modern particle physics started during the last days of world war II when a group of italian physicists Conversi, Pancini and Piccioni, started a very important experiment L. Alvarez (lNobel lecture 1968). The Conversi,Pancini and Piccioni experiment The result of the experiment was that the negative hard component of cosmic rays (mu mesons) was not absorbed in light elements.. The conclusion was that these particles could not be the Yukawa ones , but had to be subjected to a new type of interactions Marcello Conversi Phys Rev 71 ,1947,209

15. He started to study the problem and he did express his ideas in a letter to Gian Carlo Vick in 1947 Deep River 8 Maggio 1947 Caro Giancarlo …. Se ne deduce una similarità tra processi beta e processi di assorbimento e di emissione di mesoni, che,assumendo che non si tratti di una coincidenza, sembra di carattere fondamentale Translation we can deduce a similarity between beta processes and muon capture ,assuming it is not a coincidence ,it seem of fundamental character

16. His considerations were pulished in B Pontecorvo Nuclear capture of mesons and Meson Decay Phys Rev 72 246 1947

17. After two years the concept of universality was proposed and accepted. G Puppi Nuovo Cimento 5 587 1948 Tiomno j,Wheeler J.A Rev Mod Phys 21 144 ,1948 Lee T.D ,Rosenbluth M,Yang C.N. Phys Rev 75 905 1949 The first proposal of Universality of B.P. was not recognized In the quoted papers. This has been noticed by J. Steimberger J Steinberger .Personal debt to Bruno Pontecorvo Selected works of Bruno Pontecorvo pg 455 Conclusions of the JS paper There are few of us in particle physics who can boast of a single original and important idea . Bruno’swealth of seminal suggestion establish him as a unique contributor to the advance of particle physics

18. Neutrini detection Neutrinos cross section was computed ,on the basis of Fermi theory by Bethe e Peierls nel 1934 (10-44 cm2). The value of this cross section had convinced many physicists That these particles could not be detected directly. B.P. did show in a note Bruno Pontecorvo “ Inverse b processes” chalk river report PD-205 1946 The flux of neutrinos from a nuclear reactor 1020 neutrini /sec could allow their detection. Pontecorvo did consider the possibility of their detection using the reaction n + Cl37 Ar37+e . This process was used in the Davis experiment on solar neutrinos.. The deficit of their flux did origin to the Neutrino puzzle That was resolved considering OSCILLATIONS . First results were published in 70’ In the final paper B. T. Cleveland et al astrophysical journal 496,505,1998 was recognized the Pontecorvo suggestion..

19. Proportional counters Pontecorvo did contribute to the development of proportional counters technique. High multiplication proportional counters for energy measurements G.C.Hanna , D.H.W. Kirkwood and Bruno Pontecorvo Phys Rev 75 985 1949 These counters were used in the measurement of the electron spectrum of the tritium decay The beta spectrum of 3H Phys rev 75 983 1949 First measurement of the mass of the electron neutrino (M<500 eV) Proportional counters Were used by Davis in the solar neutrino experiment. 3He proportional counters were used in the SNO experiment.

20. TWO neutrinos In the fifties in Dubna BP started to consider the possibility of neutrino experiments at accelerators Proton accelerators are a source of neutrinos produced in the decay of p mesons. The problem was: are they the same of the beta decay? The problem was discussed in Electron and muon neutrinos Zh Exsp Teor fiz 37,1751,1959 In the same period this problem was studied by Mel Schwartz: Possibility of using H.E. neutrinos to study weak interactions Phys Rev Letters 4 307 1960

21. An experiment was done at the National Laboratory of Brookhaven. The result was neutrinos produced by the decay of p mesons,produced from protons of the AGS, interacting produce m mesons but not electrons Observation of high energy neutrino interactions and the existence of two kind of neutrinos. G. Damby et al ( Lederman,Schwartz,Steimberger) Phys Rev Lett 9 36 1962 For what concern accelerator neutrinos in 1975 Bruno proposed the beam dump. A proton beam is stopped in a heavy element produces pai e k interact before decaying , only charmed particles can decay giving rise to an equal mixture of nm e ne B Pontecorvo Zh Exsp teor phys 69 452 1975

22. Wide band beam Beam dump

23. le oscillazioni The experimental establishment of neutrino oscillations can be considered a real triumph of Bruno Pontecorvo who first introduced this concept and pursued this idea for many years when the general consensus did support Mass less neutrinos, with no possibility of Oscillations Samuel Bilenki

24. Bilenky Pontecorvo :Mister Neutrino Neutrino Workshop Venezia 2006

25. A little bit of theory The weak interactions eigenstates na ne nm nt are not the mass eigenstates n1 n2 n3 ni We have na=Uai. Ni A littele The matrix U (unitary) is the Pontecorvo-Maki-Nakagawa-Sakata matrix

26. The matrix elements can be expressed in terms of 3 angles q12 , q23 ,q13and possibly a phase The expression of the probability of oscillation in the simple case of two family mixing is written as P(12)= sin2(q(12))Sin2(1.27DM212L/E) L distance from source( Km, m), E Energy (Gev Mev) DM212=M12 –M22 Dove M1 e M2 are the mass of 1,2 eigenstates Many of these parameters are known For q13 we have only limits The best limit is given by the CHOOZ experiments Apollonio et al EPJ C 27,331,2003 For the value of these parametersI quote myself U.Dore,D.Orestano: Experimental results on neutrino oscillations Rept.progr.phys 71 106201 2008 arXiv:0811.1194

27. Oscillation probability • P(12)= sin2(q(12))Sin2(1.27DM212L/E) • Oscillations can be observed when • the oscillating term is different from zero • It must be • L/E DM212 large enough to give appreciable effects • Oscillation can be observed • in experiments • Disappearence a neutrino deficit is observed • Appearance neutrinos not present • at production are observed

28. In 1958 a rumor reached Pontecorvo (The new was false) Davis had observed the reaction Example of violation of lepton number He did then assume the existence of a new form of interaction that violates leptoni number and so allows the transition in vacuum B. Pontecorvo Mesonium and antimesonium Sov Phys Jept 6,429,1957 B.Pontecorvo Inverse beta processes and no conservation of lepton charge Sov Phys Jept 7,172,1958

29. When BP introduced oscillations the existence of two neutrino types was not known. He then introduced the possibility of different flavor oscillations Bilenky,Pontecorvo Physics reports 41,225,1978

30. SENSITIVITY to oscillations with different neutrinos sources

31. Experimental history of oscillations started with the so called “neutrino puzzle”. The Davis experiment on solar neutrinos gave for the ratio between the flux of neutrinos measured in the experiment and the ones predicted by the standard solar model (SSM) (Main author J Bahcall) Was smaller than one f(Davis)/f(SSM)=0.34 ±0.04 First results J.Bahcall,R,Davis Science 191,264,1976 final results B.T Cleveland et al. Measurement of solar neutrino flux with the Homestake detector Astrophysica journal 496 505 1998

32. Solar neutrino energy spectrum Neutrinos are produced in the fusion process in the sun core Fundamtal  P +P >H2+n+e process Neutrinos energy (Ev)

33. Davis experiment The Experiment detected solar neutrinos trough the (Pontecorvo ) reaction n + Cl37 >> Ar37+e 30000 gallons di tetrachloroethylene in a large tank In the Homestake mine in South Dakota At a depth of 4800meters Argon is radioactive ,it was extracted and the decay products were detected in proportional counters.

34. Many interpretations were for this result • Wrong Experiment • Problems with the SSM • Neutrino decay • Etc • Only BP defended the interpretation of the result • as an effect of oscillations of th ne emitted by the sun • Lepton mixing and the solar neutrino puzzle • Bilenky,Pontecorvo • Dubna Report E 10545 1977 “It appearsthat the explanation in terms of neutrino mixing … Is much more actractive and much more natural than other Explanations”

35. The deficit of solar neutrinos was confirmed in various experiments. Mainly Large water Cerenkov in Japan in the Kamioka Kamiokande,SuperKamiokande Fukuda et al phys rev lett. 81 98 1998 And from Gallium Radiochemical experiments Gallex,GNO Gran SAsso,SAGE,Baksan Cleveland,Gavrin Radiochemical Nucl-ex/0703012

36. Pontecorvo death was in 1992 so he could not se that the oscillation phenomenon was experimentally proved This did happen in 2003 for solar neutrinos 2003 “annus mirabilis” • The SNO Experiment • The Kamland experiment Another phenomenon in which oscillations have been observed Is the muonic atmospheric neutrinos disappearance

37. The SNO experiment SNO is a Cerenkov heavy water detector in the Sudbury mine in Canada Three reactions can be observed:

38. Results Aharmin et al Phys Rev C 75,045502,2007 Reaction 1) is depressed Reazione 2) is in agreement with the SSM predictions Reazione 3) neutrino electron scattering is depressed as already observed by the water Cerenkov detectors (Kamiokande) Electron neutrini become t o m in their travel from Sun to earth Clear evidence of oscillations

39. ne scattering on electrons electron neutrini :Charged and Neutral current mu e tau neutrinos only neutral current s(ne)= 6xs(nm,nt)

40. Araki et al Phys rev lett. 94 08891 1994 2005 The Kamland experiment (Kamioka mine in Japan) did look lto antineutrinos coming from reactors. The experiment was made in Japan, there are many reactors in Japan. the weighted flux average distance from the detector was 150 km The experiment has shown a reduction of the flux of antineutrinos. This reduction interpreted in terms of oscillations has given results compatible with the ones obtained from solar neutrinos . Probabilità di sovravvivenza P=1-P1-P2

41. The KAMLAND experiment At small distances sensitivity to q13 (Chooz) Dm2=2.510-3 L=1 km E =MEv Dm2L/E~1 At large distances and q13 small, sensitivity toq12 (solar) sen2(2q)=0.83 Dm2=5.510-5 ev2 L=100 km ,E =Mev Dm2L/E~1

42. After the two quoted experiments The Existence of oscillations became a well founded experimental fact. The oscillations did happen both for neutrinos and antineutrinos. The figure shows the results of a fit using solar and Kamland results

43. Atmospheric neutrino oscillations Atmospheric neutrinos are created in the decay of p (k) produced by the interaction of primary cosmic rays. m neutrinos produced in the p decay, Electron and mu neutrinos produced in the mu decay Detection of atmospheric neutrinos requires under ground laboratories to reduce the muon contamination

44. The figure shows the neutrino flux vs the q angle, angle with the vertical electron behave as expected there is reduction of mu neutrinos coming from the bottom SuperKamiokande collaboration Y. Fukuda et al phys rev lett 82 ,2644,1999 Similar results: Macro Gran Sasso,Ambrosio et al. EPJ C36 33 2004 Sudan II coll Phys Rev D 68 13004

45. these disappearance experiments can be interpretednmnx, the simplest one nmnt .nmve are forbidden by Chooz and SK Parameters of this oscillation are shown in figure. Two accelerator confirm these results K2K measurement of neutrino disappearence Han et al PrD 74 072003 First obervation of atm neutrinos in Minos Adamson et al PrD 73 092003

46. The interpretation of the oscillations as nmnt oscillations has not been confirmed directly The OPERA experiment at the Gran Sasso laboratories, will try to verify this interpretation detecting t neutrinos produced by oscillations in the path CERN -Gran Sasso in a beam of m neutrinos from the CERN SPS . Opera is a detector with very high spatial granularity based on nuclear emulsions that make possible the detection of the produced short lifetime t .

47. Present situation on the knowledge of oscillation parameter • From solar neutrinos ,Neutrino e oscillations • From atmospheric neutrino mu oscillations These parameters are reasonably well determined for q13 we have only an upperlimit Sin2q13<0.1 Futuri esperimenti

48. q13 is the aim of present experiments Accelerator experiments T2K Start data collection in 2010 NOVA proposal in Fermilab these want to detect oscillation probability P(nmne) At the first order P(nmne)=0.5 sin2(2q13)sin2(1.27Dm223L/E) If q13 will be not too small then the determination of of the phase d of the mixing matrix will make possible The study of CP violation in neutrino interactions Reactor Experiments (P(nenx)= sin2(2q13)sin2(1.27Dm223L/E) Daya Bay in China will allow an improvement of a factor 10 in the CHOOZ limits

49. OpenProblems in neutrino Physics • 1) Majorana o Dirac • A fundamental problem that concerns the nature of neutrinos • Are they Dirac or Majorana particles ? • Dirac one neutrino and one antineutrino • Majorana only one neutrino with two elicity states • 2) Absolute values of neutrinos masses • 3) Mass hyerarchy

50. 1) Majorana o Dirac? One process that allows the solution of the problem is the neutrino-less beta decay this process consists in the direct emission of only two electrons of two electrons from a nucleus (A,Z) that decays in (A,Z+2) The neutrino-less process is possible only for Majorana neutrinos The observation of this process will be the demonstration thati neutrinos are Majorana neutrinos