Antonino Zichichi
SID COLEMAN
AND
ERICE
SID COLEMAN AND ERICE(*)
Antonino Zichichi
CERN, Geneva, Switzerland
Enrico Fermi Centre, Rome, Italy
INFN and University of Bologna, Italy
Ettore Majorana Foundation and Centre for Scientific Culture
INTRODUCTION
This lecture is an attempt to recall the extraordinary, original and fascinating contributions by Sidney Coleman to the Erice Subnuclear Physics School. The lecture consists of three parts.
The first part containsthe “starting point”: when I “discovered” Sid Coleman. The year was 1965. This was a period when problems that are taken for granted today, were far from being understood. For example the apparent triumph of the S-matrix (the negation of quantum field theory, QFT) accompanied by the breaking of all symmetry operators (P, C, CP, T) cast serious doubts on QFT as the basic theoretical structure for all fundamental forces of Nature, whose fundamental example was QED. In this great theoretical confusion experimental physics was dominated by the Bubble-Chamber Technology which gave an enormous number of discoveries all in the
(*)Opening Lecture at the 46th Course of the International School of Subnuclear Physics, 30 August 2008.
field of new mesons and baryons. The last one, with strangeness 3, was named because it was believed to be the last particle ever to be discovered, and therefore given the name of the last letter in the Greek alphabet. Why so many hadrons and only one heavy lepton, the muon? Would another heavy lepton have been seen if its mass was in the GeV range? The incredible quasi degeneracy in the () masses was the reason why the muon was all over the place.
The year 1965 brought an enormous number of mesons and baryons but not a single piece of nuclear antimatter, not even the simplest one, the antideuteron, . Are the nuclear forces described by a QFT? Or is the absence of a sign to understand the reason why S-matrix is dominating and the symmetry operators are all broken?
It was during this exciting period that Sid Coleman became a star of the Subnuclear Physics School. The first part ends with a synthesis of the Standard Model whose roots are in the second part.
In the second part I have selected some crucial problems discussed in his superb series of lectures; a few pages per problem will – I hope – stimulate the young generation to reflect on many achievements taken for granted today despite their complex origin. The pencil marks on some pages have their origin in my reading these fascinating lectures. The selection of pages is intended to be a stimulus in order to read all lectures, which are the proof that each crucial step in building the Standard Model was identified and first discussed at the Erice Subnuclear Physics School by Sid Coleman. And this is a world record.
The third part is devoted to some pictures of Sid in Erice, including those taken when he was awarded the Gold Medal as “Best Lecturer” on the occasion of the 15th anniversary of the International School of Subnuclear Physics in 1979.
FIRST PART
The first part
The formidable developments in our field played a crucial role in the establishment of the “Ettore Majorana Centre for Scientific Culture”. The lectures by Sid span fourteen years, from 1966 to 1979. Let me quote Sid’s words[1]: «This was a great time to be a high-energy theorist, the period of thefamous triumph of quantum field theory. And what a triumph it was, in the old sense of the world: a glorious victory parade, full of wonderful things brought back from far places to make the spectator gasp with awe and laugh with joy».
This victory gave us the Standard Model. Since this is a School I will close this first part with a few words on the Standard Model.
Let me go back to how I “discovered” Sidney Colemanin 1965. As mentioned in the Introduction, it happened in the midst of the great confusion generated by the apparent dominance of the S-matrix and the breaking of all Symmetry operators (P, C, PC, T). The School started in 1963 and during the years 1963–1966 the crises of QED and of QFT were, from the experimental point of view, corroborated for instance by the absence of the first example of antinuclear matter, , the antideuteron. The existence of the antideuteron was expected to be the proof that the nuclear forces acting between two antinucleons were producing the same binding energy as two nucleons. This could be granted if the nuclear forces were described by a QFT. But this was not the case and the S-matrix was the negation of QFT. The existence of the antiparticles could not guarantee the existence of the antinuclei, having the same masses as the nuclei. This confusion is still going on at present, as testified by the famous Dirac statement [2] recently reported in my lecture celebrating the 50th anniversary of Karlsruhe (the first page of this lecture is reproduced on page 6). Sid was very interested to know if the was there. It was searched for at the 107 level for the ratio and not found to be there. The reason being that an order of magnitude of accuracy in fighting against background was needed. In order to discover the antideuteron it was necessary to have a new high precision Time-of-Flight electronic circuit capable of reaching the ratio of 108. Let me quote Luciano Maiani: «The Discovery of the antideuteron gave more confidence to the search for a field theoretical basis for the strong interactions, that today seems so obvious to us» [3].
I was very interested in the theoretical problems concerning the existence of a relativistic quantum field theory (RQFT) whose guide was QED since one of my first experiments was to check QED in the field outside the electron and the photon, i.e. in muon physics, via the high precision determination of the muon anomalous magnetic moment: (g–2). All these problems are now taken for granted but were open to front line research 50 years ago.
Some of you know that the problem of why we should believe in RQFT has been discussed at this School on many occasions by the world leader Arthur S. Wightman.
As all of you know I am not a theorist. How is it that our School is heavily oriented towards theoretical fellows, one of which is Sidney Coleman? The answer is in my origin. I had the privilege of being a pupil of Lord Patrick Maynard Stuart Blackett to whom the building where we are is dedicated.
Blackett used to tell us young fellows, «We experimentalists are not like theorists: the originality of an idea is not for being printed in a paper, but for being shown in the implementation of an original experiment». This explains the difference between theory and experiment.
And now the reason why we have to invite our theoretical friends to speak. Here comes the second part of Blackett’s teaching: «We must know what boils in the brain of our theoretical friends. Not because they are able to predict our physics discoveries, but just for intellectual pleasure». Sid Coleman was an incredible source of “intellectual pleasure”.
Let me recall when at CERN he visited my experiment called PAPLEP (Proton antiproton annihilation into Lepton pairs) whose purpose was to see if a lepton heavier than the muon was produced. This new lepton was called HL [4] and was being searched for by looking for acoplanar (e) pairs in the final state of () annihilation. The point being that if its mass was for example at 1 GeV it would not had been seen, the incredible miracle of the muon-pion small mass difference being the only reason why there are so many muons around. Having found no HL at CERN, I moved to Frascati where the new (ee) machine (ADONE) was being implemented. Sid came there once and was encouraging me to go on proposing to increase the ADONE energy to higher levels. The HL was found at SLAC following exactly the same strategy [(e) acoplanar pairs] but giving to HL the name . Sid phoned to congratulate me on the final discovery many years after PAPLEP at CERN and reminded me of what Rabi said in Erice, on the occasion of the tenth anniversary of the Subnuclear Physics School, concerning those who open a new field in physics. Sid asked me to have Rabi’sstatement reproduced in bronze in the Rabi Institute Hall (see photo on page 12).
From 1965 on, during long conversations in Erice or via transatlantic phone calls, I discussed with Sid what was Past, Passing and to Come in Subnuclear Physics. Needless to say I am very grateful to Sid for his words in the Preface of his book where his Erice lectures have been collected[1].
And now let me close this first part with a few words on the Standard Model.
A few words on the Standard Model
At present, the Standard Model is the most formidable synthesis of all phenomena known to exist, from the inner structure of a proton to the extreme border of the universe. The Standard Model is based on:
i)matter particles (quarks or leptons), fermions, and therefore described by the Dirac spinor function ; these particles have spin ½ ;
ii)gauge particles [the photon (g), the weak bosons (W±, Z0) and the gluons (g)], all being of vector nature; these particles have spin 1;
iii)scalar particles, with imaginary masses; these particles have zero spin. They cause Spontaneous Symmetry Breaking (SSB), thus providing real masses to matter particles (spin ½) and gauge particles (spin 1) in addition to themselves (spin zero particles), called Higgs particles. We denote these particles by the letter H.
All fundamental interactions in the Standard Model are based on simple Feynman diagrams of which the one below is, at the tree level, the prototype:
(1)
The basic ingredient of the Standard Model is the covariant derivative, which must have a term for each local gauge invariance; in fact, the way a gauge force is generated is through the substitution of the standard derivativewith the covariant derivative D.
Since the local gauge invariances are U(1), SU(2) and SU(3), there will be three gauge couplings g1 , g2 , g3 , respectively, with
i = (i = 1, 2, 3).
Each symmetry group has its generators
U(1)Y
SU(2)i 1 , 2 , 3
SU(3)a 1 , 2 .... 8 .
Each gauge invariance generates a gauge boson
U(1)B
SU(2)
SU(3)
The covariant derivative of the Standard Model is therefore:
The photon, described by the field A, is the result of a mixing between the field B and the neutral component of the weak boson field, ; the values of the gauge couplings are not given by theory but by experiment, as well as all masses. More precisely, the Standard Model needs the following inputs:
3Gauge couplings: g1, g2 , g3 .
1Non-perturbative vacuum-angle parameters:3 for the non-Abelian gauge forces SU(3).
6Quark masses (which range from few MeV up to 180 GeV for the top quark).
3Charged lepton masses (which range from 0.5 MeV up to 1.77 GeV for the third lepton).
3Neutral lepton masses (which are very small, not zero, and with very small mass differencesm2 – 103eV2).
4Mixing angle parameters in the quark sector (which come from the experimentally measured transitions across quark flavour states, including a phase angle to describe CP violation in the flavour-changing charged currents).
4(Presumably) mixing angle parameters in the lepton sector.
2Weak boson mass parameters (which can be taken as MW± and MHiggs).
These 26 parameters are the reason why we need to search for new physics beyond the Standard Model. But how could we start this search if we were unable to find a firm basis for the structure of the Standard Model? This firm basis could indeed be achieved and the key-source was the effective theoretical understanding of renormalization. Note that, if gravitational forces are included, there are two more parameters in a theory beyond the Standard Model: i.e. the Newton constant and the cosmological constant.
More details in Reference [5].
I.I. Rabi - 1972
Bronze plate in the I.I. Rabi Institute Hall.
SECOND PART
I have selected some crucial problems discussed in the superb series of Coleman lectures [1]; a few pages per problem will – I hope – stimulate the young generations to reflect on many achievements taken for granted today despite their complex origin. The pencil marks on some pages have their origin in my reading these fascinating lectures. The selection of pages is intended to be a stimulus in order to read all lectures, which are the proof that each crucial step in building the Standard Model was identified and first discussed at the Erice Subnuclear Physics School by Sid Coleman. And this is a world record.
1