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Bruno PontecorvO AND NEUTRINO PHYSICS

There is not any idea on neutrino phyics that has nos been put forward by Pontecorvo(V Telegdi)

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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

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The history of neutrino didstart 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

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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

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Neutrino birthIn 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 neutrinoIn 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 …..

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The neutrino remained an hypothesis until the years 50 when Cowan and Reines did show his interactions in the study of the processAntineutrino + proton neutron + positron al nuclear reactor of the Savanna river Plant (USA)

The detection was obtained with a delayed coincidence in a scintillator of the annihilation signal of the positron and the oneof the gamma emitted in the reaction n ( thermalized) + cadmiumThe same technique is still used in the detection of antineutrinos at the reactors i.

Pag 159

The process was

barp >> n+ e+ enp

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The LifeBruno 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 theUnited State where he found a job in 1940 inthe “ 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 .lnCanada 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

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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 wellsHe 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 PhysicsOil 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

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Soviet Union Dubna experimental activities Experiments at the Dubna SincrociclotronWorks 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 interactionsHigh energy conference Kiev 1959

Neutrino and astrophysicsUniversal Fermi interactions and astrophysics Zh exp theor fiz 36,1615, 1959

Many papers were publidshed in russian, of many translation can be found inBruno Pontecorvo selected scientific works SIF 1997

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CANADA 1946 1950

Of activities in CanadaWe recall

a) Study of muons decayB) considerations on the nature of neutrinos 1)Universality 2)detection of neutrinosC) proportional counters

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A) Study of mu meson decay It was known thata)Mu mesons decay with a life time of 2.2 sb) Only one charged particle is emitted in the decayC) it was not clear the nature of neutral(s) particles emitted.

Results of the experiment di Pontecorvo e Hinks

Pag 102

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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 sourceMeson stop

Graphite absorberDecay products detected

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Considerations on the nature of weak interactions

The interest of Pontecorvo was aroused by theresults of an experiment made in Rome on the behaviorof 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

UniversalityThe coupling constant with the intermediate bosons is the same for all leptons

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The Conversi,Pancini and Piccioni experiment

Marcello Conversi

The result of the experiment was that the negativehard component of cosmic rays (mu mesons)was not absorbed in light elements.. The conclusion was that these particles could not bethe Yukawa ones , but had to be subjected to a new type of interactions

The modern particle physics started during the last days of world war II when a group of italian physicistsConversi, Pancini and Piccioni, started a very important experiment L. Alvarez (lNobel lecture 1968).

Phys Rev 71 ,1947,209

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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 1947Caro Giancarlo ….Se ne deduce una similarità tra processi beta e processidi 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

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B Pontecorvo Nuclear capture of mesons and Meson Decay Phys Rev 72 246 1947

His considerations were pulished in

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After two years the concept of universality was proposed and accepted.

G Puppi Nuovo Cimento 5 587 1948Tiomno j,Wheeler J.A Rev Mod Phys 21 144 ,1948Lee 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 PontecorvoSelected works of Bruno Pontecorvo pg 455 Conclusions of the JS paperThere are few of us in particle physics who can boast of a single original and important idea . Bruno’s wealth of seminalsuggestion establish him as a unique contributor to the advance of particle physics

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Neutrini detection

Neutrinos cross section was computed ,on the basis of Fermi theory byBethe e Peierls nel 1934 (10-44 cm2).

The value of this cross section had convinced many physicistsThat 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 Cl37 Ar37+e .This process was used in the Davis experiment on solar neutrinos.. The deficit of their flux did origin to the Neutrino puzzleThat was resolved considering OSCILLATIONS . First results were published in 70’In the final paperB. T. Cleveland et al astrophysical journal 496,505,1998was recognized the Pontecorvo suggestion..

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Proportional countersPontecorvo did contribute to the developmentof proportional counters technique.High multiplication proportional counters for energy measurementsG.C.Hanna , D.H.W. Kirkwood and Bruno Pontecorvo Phys Rev 75 985 1949

These counters were used in the measurement of the electronspectrum of the tritium decayThe beta spectrum of 3HPhys rev 75 983 1949First 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.

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TWO neutrinos

In the fifties in Dubna BP started to consider thepossibility of neutrino experiments at accelerators Proton accelerators are a source of neutrinos produced in the decay of mesons.The problem was: are they the same of the beta decay? The problem was discussed in Electron and muon neutrinosZh Exsp Teor fiz 37,1751,1959In 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

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An experiment was done at the National Laboratory of Brookhaven. The result was neutrinos produced by the decayof mesons,produced from protons of the AGS,interacting produce mesons but not electronsObservation 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 neutrinosin 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 eeB Pontecorvo Zh Exsp teor phys 69 452 1975

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Wide band beam

Beam dump

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le oscillazioni

The experimental establishment of neutrino oscillations can be considered a real triumph of Bruno Pontecorvowho 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

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Bilenky Pontecorvo :Mister Neutrino Neutrino Workshop Venezia 2006

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A little bit of theory

The weak interactions eigenstates

e

are not the mass eigenstates

i We have

Ui. i A

littele

The matrix U (unitary) is the Pontecorvo-Maki-Nakagawa-Sakata matrix

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The matrix elements can be expressed in terms of 3 anglesand possibly a phaseThe expression of the probability of oscillationin the simple case of two family mixing is written as P(12)= sin2(Sin2(1.27M2

L/E)L distance from source( Km, m), E Energy (Gev Mev)M2

12=M12 –M22

Dove M1 e M2 are the mass of 1,2 eigenstates Many of these parameters are known For we have only limits The best limit is given by the CHOOZ experimentsApollonio et al EPJ C 27,331,2003For the value of these parametersI quote myselfU.Dore,D.Orestano: Experimental results on neutrino oscillationsRept.progr.phys 71 106201 2008arXiv:0811.1194

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Oscillation probability

P(12)= sin2(Sin2(1.27M2L/E)

Oscillations can be observed when the oscillating term is different from zeroIt must be L/E M2

large enough to give appreciable effectsOscillation can be observed in experiments•Disappearence a neutrino deficit is observed •Appearance neutrinos not present at production are observed

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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 antimesoniumSov Phys Jept 6,429,1957B.Pontecorvo Inverse beta processes and no conservation of lepton charge Sov Phys Jept 7,172,1958

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Bilenky,PontecorvoPhysics reports 41,225,1978

When BP introduced oscillationsthe existence of two neutrino types was not known.He then introduced the possibility of different flavoroscillations

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SENSITIVITY to oscillations with different neutrinos sources

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Experimental history of oscillationsstarted with the so called “neutrino puzzle”.The Davis experiment on solar neutrinosgave for the ratio between the flux of neutrinosmeasured in the experiment and the ones predicted by the standard solar model (SSM) (Main author J Bahcall)Was smaller than one Davis)/SSM)=0.34 ±0.04

final resultsB.T Cleveland et al. Measurement of solar neutrino flux with the Homestake detectorAstrophysica journal 496 505 1998

First results J.Bahcall,R,Davis Science 191,264,1976

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Solar neutrino energy spectrum Neutrinos are produced in the fusion process in the sun core

Fundamtal P +P >H2+eprocess

Neutrinos energy (Ev)

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Davis experiment

Cl37 >> Ar37+e

The Experiment detected solar neutrinos trough the (Pontecorvo ) reaction

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 decayproducts were detected in proportional counters.

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Many interpretations were for this result•Wrong Experiment•Problems with the SSM•Neutrino decay •EtcOnly BP defended the interpretation of the resultas an effect of oscillations of th e emitted by the sun Lepton mixing and the solar neutrino puzzleBilenky,PontecorvoDubna Report E 10545 1977

“It appears that the explanation in terms of neutrino mixing …Is much more actractive and much more natural than otherExplanations”

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The deficit of solar neutrinos was confirmed in various experiments.Mainly Large water Cerenkov in Japan in the Kamioka Kamiokande,SuperKamiokandeFukuda et al phys rev lett. 81 98 1998And from

Gallium Radiochemical experimentsGallex,GNO Gran SAsso,SAGE,BaksanCleveland,Gavrin Radiochemical Nucl-ex/0703012

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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

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The SNO experimentSNO is a Cerenkov heavy water detector in the Sudbury mine in CanadaThree reactions can be observed:

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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 in their travel fromSun to earth Clear evidence of oscillations

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e scattering on electrons electron neutrini :Charged and Neutral current mu e tau neutrinos only neutral currente)= 6x(

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Araki et al Phys rev lett. 94 08891 1994 2005

The Kamland experiment (Kamioka mine in Japan) did looklto 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 kmThe 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 sovravvivenzaP=1-P1-P2

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At small distances sensitivity to 13 (Chooz)m2=2.510-3 L=1 km E =MEv m2L/E~1At large distances and 13 small, sensitivity

to (solar) sen2(2)=0.83 m2=5.510-5 ev2

L=100 km ,E =Mev m2L/E~1

The KAMLAND experiment

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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 fitusing solar and Kamland results

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Atmospheric neutrino oscillationsAtmospheric neutrinos are created in the decay of produced by the interaction of primary cosmic rays.neutrinos produced in the decayElectron and mu neutrinos produced in the mu decay

Detection of atmospheric neutrinosrequires under ground laboratories toreduce the muon contamination

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The figure shows the neutrino flux vs the angle angle with the vertical electron behave as expected there is reduction of mu neutrinos coming from the bottomSuperKamiokande collaboration Y. Fukuda et al phys rev lett 82 ,2644,1999

Similar results: Macro Gran Sasso, Ambrosio et al. EPJ C36 33 2004Sudan II coll Phys Rev D 68 13004

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these disappearance experiments can be interpretedx, the

simplest one ve are forbidden by Chooz and SK

Parameters of this oscillation are shown in figure. Two accelerator confirm these resultsK2K measurement of neutrino disappearence Han et al PrD 74 072003 First obervation of atm neutrinos in Minos Adamson et al PrD 73 092003

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The interpretation of the oscillations as oscillationshas not been confirmed directly The OPERA experiment at the Gran Sasso laboratories, will try to verify this interpretation detecting neutrinos produced by oscillations in the path CERN -Gran Sasso in a beam of 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 .

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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 we have only an upperlimit Sin2

Futuri esperimenti

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is the aim of present experimentsAccelerator experiments T2K Start data collection in 2010 NOVA proposal in Fermilab these want to detect oscillation probability Pe) At the first order Pe)=0.5 sin2(2sin2(1.27m2

23L/E) If will be not too small then the determination of of the phase of the mixing matrix will make possibleThe study of CP violation in neutrino interactions Reactor Experiments (Pex)= sin2(2sin2(1.27m2

23L/E) Daya Bay in China will allow an improvement of a factor 10 in the CHOOZ limits

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Open Problems 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

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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 neutrinosThe observation of this process will be the demonstration thati neutrinos are Majorananeutrinos

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2) neutrinos mass In the Minimum Standard Model neutrinos are mass less.Oscillations are possible for massive neutrinos Oscillations give only the differences square masses . the absolute value of these masses is not knownWe have only upper limits

Per what concern the mass of the electron neutrino we have many experiments in progress or in construction or atthe level of proposal The Katrin experiments will reach limits of the order offraction of eV.We are now at the level of eV.

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Mass hyerarchy

We have two masses that are close: solar neutrinos and one that is far:Atmospheric neutrinos

Due possibilità

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Pontecorvo:Ideas for experiments giving rise to Nobel prizes

radiochemical methods for neutrinos detection Chlorine experiment , R. Davis premio Nobel 2002

Accelerators experiments : two types of neutrinos

L.Lederman,J.Steimberger e M.Schwarz Nobel 1988.

Oscillations Koshiba premio Nobel 2002

Inverse beta decay at reactors F. Reines Nobel 1995

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CONCLUSIONS

His critical spirit, his intuitions and hislove per the search of the truth must remain as an example for future generations

From my presentation I hope it comes out clearly the contribution of Bruno Pontecorvo to the development of neutrino physics.

In the future problems of neutrino physics still unresolved will be clarified

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Bruno Pontecorvo Selected scientific worksSocietà italiana di fisica 1997

S.Bilenky Bruno Pontecorvo: Mister Neutrino3° International workshop on NO-Ve neutrino oscillations 599,2006 ,

L. Bonolis Bruno Pontecorvo: from slow neutrons to oscillating neutrinos AmericanJournal of Physics 73,487,2004

F. Buccella Bruno Pontecorvo: un grande scienziato del novecento Albinoni.brera.unimi.it/SISFA/atti 2000-2006

U.Dore,D.Orestano: Experimental results on neutrino oscillationsRept.progr.phys 71 106201 2008arXiv:0811.1194

Miriam Mafai Il lungo freddo Mondadori 1992

References

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Translation from Miriam Mafai il lungo freddo 1992 Mondadori editore

The case of Bruno,who was a real scientific genius is quite dramatic,as it is one of the cases combining scientific comprehension, the forceof ideology and even charity toward mankind

Giorgio Salvini , the legacy of Bruno Pontecorvo, Venezia 1994

Bruno was an italian communist, at the time (arrival in the Soviet Union) he was a communist-idealist sincerely believing in the strenght and rightness of the type of development chosen by Russia

V.P.Dzhelepov The Genius of Bruno pontecorvo ,Dubna Selected scientific works pg 487 (translated from russian)

A unanswered question concern the life of Bruno Pontecorvo and of all the people that with fearless optimism blind innocence and faith that discouraged every rationality , in the past century has followed the dream of communism