**1 — The discovery that Nuclear Antimatter is part of the Logic of Nature**.
Subnuclear Physics started in 1947. Ten years were needed in order to discover the violation of many fundamental Symmetry Operators. The crisis of the Relativistic Quantum Field Theory description of the fundamental interactions and the successes of the S-Matrix Theory, gave in the middle sixties a central position to the search for the first example of Nuclear Antimatter. Sixty-four years later, the CPT invariance of the nuclear binding forces is understood only in terms of an “effective” theory whose roots are in Quantum Chromodynamics (QCD), which is in turn another “effective” theory whose origin, at the String Unification scale, makes the CPT Theorem lose its foundations. In other words, the existence of Nuclear Antimatter rests on purely experimental grounds.
The observation of the Antideuteron in 1965 is the first experimental proof that Nuclear Antimatter exists, independently of the thinking of theorists at that time. These were times of great troubles because Symmetry Operators were experimentally found not to be valid in real life and no one was able to build a theory of Strong Interactions along the basic lines of a Relativistic Quantum Field Theory (RQFT). Lev Landau in his paper “*Fundamental Problems*”, published in “Pauli Memorial Volume” [Interscience, New York, p. 245 (1960)], wrote: “*It is well known that theoretical physics is at present almost helpless in dealing with the problem of strong interactions*. ...”, and quoting F. Dyson he concluded: “... *the correct theory will not be found in the next hundred years*”. The validity of the celebrated CPT Theorem [1] was based on RQFT but the Strong Forces seemed to open an entirely new horizon in physics. A horizon where there was no RQFT. “*Field Theory was in disgrace, S-Matrix Theory was in full bloom*” recalls D. Gross in his lecture at the Third International Symposium on History of Particle Physics [Cambridge University Press (1994)]. The S-Matrix Theory was the antidote of RQFT. The collapse of the Symmetry Operators, and the fact that Strong Interactions seemed not to need a RQFT, focused our attention on the importance of establishing whether nuclear binding forces were CPT invariant. The success of describing Strong Interactions via S-Matrix Theory was a point of great relevance in my discussions with the CERN-DG (Professor Victor F. Weisskopf) when I had to convince him to support the construction of the “partially separated”, negatively charged beam and the R&D work needed for the most advanced time-of-flight (TOF) electronic device to be built. To establish the existence of the Antideuteron became badly needed. This is why, once its existence was proved at CERN, the most alert physicists in Brookhaven jumped on it (as reported by Professor Bernard Gregory at CERN Seminar).
Thirty years later I am pleased to recall the exciting times when we were working hard to build the most intense negative beam of the world and the most sophisticated time-of-flight system able to achieve 100 ps resolution (ps 10^{}^{12} s).
Here I will first start by discussing the collapse of the Symmetry Operators (§ 2). I will then describe the collapse of Relativistic Quantum Field Theory (RQFT) (§ 3). In § 4 I will discuss the crisis of Field Theory and the relevance of the Antideuteron discovery when S–Matrix was ……….. apex. This will bring me to the point why the existence of the Antideuteron needed to be established (§ 5). In § 6 I will illustrate the new era started in 1957. The experiment on the first example of Nuclear Antimatter will be the content of § 7. A comment on Matter and Antimatter in § 8. Conclusions in § 9.
**2 — The collapse of the Symmetry Operators in the fifties and middle sixties**.
The fact that the antiparticle of the electron had to be with the same mass as the electron was the starting point to believe that all antiparticles had to have the same mass as their particle states. When H. Weyl discovered that is a solution of the Dirac Equation with positive energy and the same mass, m, which appears in the Dirac Equation for , Dirac became enthusiastic about the C operator. The intrinsic mass of a particle state was considered to be the same as its other intrinsic properties, like the absolute value of the electric charge and the spin: they had to be the same for particle and antiparticle states. This belief went on until Lee and Yang discovered that there was no experimental proof for the validity of Charge Conjugation Invariance (C) and of Parity Symmetry (P) in all processes involving the Weak Forces. Up to that moment the general belief was that the equality
_{}_{}_{}_{} (2.1)
was a proof of C invariance. Lee and Yang pointed out that if the muon decay processes were governed by Weak Interactions and these interactions were C non-invariant, the equality (2.1) above was a consequence of CPT invariance, not of C invariance. In other words, if Weak Interactions were C invariant, this implied _{}_{}_{}_{}, but if C invariance was violated, _{}_{}_{}_{}had to hold because of CPT. What about the intrinsic masses?
As the origin of these masses was unknown, many great fellows were convinced that the intrinsic mass of a particle had to obey Charge Conjugation Invariance. Even today we do not know the origin of the intrinsic masses of the elementary constituents of the world: quarks and leptons. If we believe that the intrinsic masses obey C invariance then the problem of the equality between particle and antiparticle masses is settled. But, if the intrinsic masses originate from so far unknown forces, whose C properties are unknown, it would be sufficient to postulate these forces to be describable by a Relativistic Quantum Field Theory (RQFT) for the masses of particles and antiparticles to be identical. In fact this result follows from the CPT Theorem, which is proven to hold in the context of a RQFT.
Dirac was convinced that C invariance had to be valid insofar as the intrinsic properties of an elementary particle were concerned. Dirac was not convinced that the proof of the CPT Theorem was on firm grounds (see later).
In particular, there was no reason to believe that the nuclear binding forces **had to be** CPT invariant.
The collapse of C and P invariance in the middle fifties was crucial for questioning the validity of the Symmetry Operators. The discovery that CP was conserved confirmed the faith in the Time Reversal Invariance (T). Nevertheless a lot of confusion was around in those years. For example the “strangeness mixing”, invented by Gell-Mann and Pais, to describe the () physics, brought them to predict the existence of K_{1} and K_{2} , on the basis of the validity of C invariance. The discovery by Lederman of K_{2} 3 was interpreted as a proof that C invariance holds in Weak Interactions. Very few people know that Lee, Oehme and Yang [2], before Parity Violation was experimentally proved by C.S. Wu, pointed out that the existence of K_{2} could not be taken as a proof of C invariance, nor as a proof of CP invariance. Lee, Oehme and Yang showed that “strangeness mixing” does not imply C invariance as claimed by Gell-Mann and Pais. In fact, even if CP is not valid, K_{2} would still be there and, in order to prove that “strangeness mixing” **is** or **is not** CP** invariant**, other experiments needed to be done in K decay physics, as suggested by LOY. This flavour mixing problem and its CP **invariance** or** non**-**invariance**, is extremely topical today with many experiments being planned in order to understand the basic distinction between “flavour mixing” and CP invariance, for all flavours. The fact that the authors of the basic distinction between “flavour mixing” and CP invariance are Lee, Oehme and Yang has been forgotten.
Nevertheless those who were following this physics knew that CP could be violated despite the observation of K_{2} 3. This is why some careful fellows were seriously thinking that the proof for the existence of Antimatter was badly needed, in order to be sure about the invariance of all Symmetry Operators.
From CPT one could argue that the Antideuteron had to be there but, as we will see in the next chapter, the dominant Strong Interaction Theory of the sixties was not a RQFT but the S-Matrix Theory. The S-Matrix Theory negates completely the Relativistic Quantum Field Theory, upon which the CPT Theorem is based. So, not only some Symmetry Operators (C and P) had been found to be broken, but, at the same time, the only theory able to describe Strong Interactions was not a RQFT but the negation of it.
And this is not all. In 1964 another pillar collapsed: the CP invariance. Thus endangering the Symmetry Operator T, considered as “sacred” by Dirac, Wigner and Heisenberg. In order to save T, the product of all Symmetry Operators, CPT, had to be broken. Clearly, there was no consensus among theorists. The decisive step had to be taken by experimentalists.
The discovery in 1964 of CP violation in K decays, while confirming the suggestion of Lee, Oehme and Yang, and recalling their correctness of the distinction between “strangeness mixing” and CP invariance, prompted doubts on all symmetries, thus far considered as granted, like CP, T and CPT.
The collapse of Symmetry Operators has its origin in experimental physics, with the () puzzle. The crisis of the fundamental mathematical structure, RQFT, has its origin in theoretical physics. Both structures are needed for Matter-Antimatter symmetry to hold. Having discussed the collapse of the Symmetry Operators, we now turn to the collapse of RQFT.
**3 — The collapse of RQFT in the middle fifties and sixties**.
For some time the only example of a Relativistic Quantum Field Theory was Quantum Electrodynamics (QED). Guided by QED, Fermi succeeded to successfully describe beta decays and Yukawa to propose a field for Nuclear Forces, thus predicting the existence of the meson, soon discovered. The RQFT, originally developed for the description of Electromagnetic Interactions, appeared to be the natural tool for describing the dynamics of elementary particles, no matter their interaction: **Electromagnetic**, **Weak** or **Strong**.
After some decades of successes, RQFT started to show its severe limitations and deep troubles.
**In QED**, with the “zero-charge” problem discovered by Landau, who, by studying the high energy behaviour of QED, concluded that the physical charge vanishes, no matter the value of the bare charge, as we let the ultraviolet cut-off become infinite. This ultraviolet limit is needed in order to achieve a Lorentz-invariant theory [L.D. Landau and I. Pomeranchuk, Dokl. Akad. Nauk SSSR **102**, 489 (1955)]. Thus Landau concluded: “*We reach the conclusion that within the limits of formal electrodynamics a point interaction is equivalent, for any intensity whatever, to no interaction at all*”.
On the other hand the renormalizability was the pillar of QED and the main reason for its great achievements, such as the ability to compute the Lamb shift (the first radiative effect ever measured) and the muon (g2), the most precise determination of an intrinsic property of a particle which was not the electron itself. But Dirac and Wigner, founding fathers of QED, were convinced that renormalization was a trick and that the physical meaning of renormalization was not truly understood, despite the basic new frontier opened by A. Peterman and E. Stueckelberg [3] implying the running with q^{2} of all physical quantities. At the 1961 Solvay Conference Feynman said: “*I still hold to this belief and do not subscribe to the philosophy of renormalization*” [R. Feynman in “The Quantum Theory of Fields”, Proceedings of the 12th Solvay Conference, Interscience, New York (1961)].
**In Weak Interactions** the powerful and accurate description of beta decay processes was undermined by the fact that the theory was not renormalizable, thus losing any predictive power beyond the Born approximation.
**In Strong Nuclear Forces** the early successes of Yukawa Field Theory were confronted with severe difficulties, such as the infinities beyond the lowest order perturbation theory and the lack of any understanding of the dynamics of the Nuclear Strong Forces at the non perturbative level. A totally unexpected fact was the rapid proliferation of strongly interacting mesons and baryons, thus depriving the nucleon and the pion fields of their privilege of being “fundamental”. All the hadrons appeared to have the right of being considered as fundamental as the pion and the nucleon. Which field had to be used?
Thus RQFT, originally modelled to describe **Electrodynamics** and soon applied to the **Weak **and to the **Nuclear Forces**, thus appearing to be the natural tool for describing the dynamics of elementary particles, after some decades of successes, started to lose its power and its credibility as the basic mathematical formalism to describe the fundamental processes. In fact RQFT was not able to account for the explosion of experimental discoveries.
Furthermore, while RQFT was showing all its weakness, a completely different approach to describe Nuclear Interactions appeared to be very successful. This was the celebrated S-Matrix Theory, based on Unitarity and Analyticity, not on the Field concept. The basis of S-Matrix Theory is that the description of the interaction between particles should be based on analyticity as a **primary** rather than a **derived** concept.
The analytic S-Matrix is supposed to give the appropriate framework in which to find a theory where no singularities are arbitrary but all are determined by general principles.
The Field concept involves a larger set of functions than those derived by the analytic continuation of the S-Matrix. Unfortunately no one knows how to construct Fields purely in terms of analytic Scattering Amplitudes. Scattering Amplitudes are “on the mass shell” while Fields imply extension to “off the mass shell”.
Let me quote a detailed example, familiar to my work (in the early sixties I determined the existence of a strong form factor of the proton in the time-like q^{2} range). **Form Factors** are not Scattering Amplitudes, nevertheless they do exist and they are due to Strong Interactions.
The conjectured analyticity properties of the nuclear scattering matrix is a very restricted concept, if compared with the concept of a Field.
S-Matrix Theory is not designed to describe experiments in which interactions between particle states do take place while momentum measurements are being performed. In other words all the physics due to virtual processes fell outside the physics described by the S-Matrix Theory.
**4 — The crisis of Field Theory and the relevance of the Antideuteron discovery when the S–Matrix Theory was at its apex.**
J.A. Wheeler (1937) and W. Heisenberg (1943) are the founders of the S-Matrix Theory. They pointed out a number of important advantages of S-Matrix Theory over conventional Relativistic Quantum Field Theory (RQST). However, Heisenberg and the other physicists working with S-Matrix Theory lost interest when they realized they had **no way to compute** **interparticle** **forces**.
It is later, with the so called “maximal analyticity”, that the S-Matrix Theory gained a dynamical content and became a competitor of RQST. The development of the dynamical content in analyticity occurred during the late fifties and involved many names, including Gell-Mann, Goldberger, Landau, Mandelstam, Pomeranchuck, and the author of “Nuclear Democracy” G.F. Chew.
In 1961, at the 12th Solvay Conference devoted to “The Quantum Theory of Fields” **Marvin Goldberger said**: “*From a philosophical point of view and certainly from a practical one the S-Matrix approach at the moment seems to me by far the most attractive*” [Proceedings of the 12th Solvay Conference, Interscience, New York (1961)].
**Geoffrey Chew**, in 1963, wrote: “*Let me say at once that I believe the conventional association of fields with strong interacting particles to be empty. It seems to me that no aspect of strong interactions has been clarified by the field concept. Whatever success theory has achieved in this area is based** **on** **the unitarity** **of the analytically continued** **S-matrix plus symmetry principles. I do not wish to assert (as does Landau) that conventional field theory is necessarily wrong, but only that it is sterile with respect to the strong interactions and that, like an old soldier, it is destined not to die but just to fade away.*” [G. Chew, “S-Matrix Theory”, W.A. Benjamin Inc. (1963)].
**The general feeling** was that there had to be compelling reasons for RQFT to be wrong. The only members of the very small RQFT club were the practitioners. They had in M. Gell-Mann the most active fellow. In order to be convinced of the true spirit in which they were working, it is probably best to recall what Gell-Mann — the father of Current Algebra (the most successful field-theoretical attempt towards the theory of hadrons) — wrote in 1964 [M. Gell-Mann, “The Symmetry Group of Vector and Axial Vector Currents”, Physics, **1**, 63 (1964)]: “*In order to obtain such relations that we conjecture to be true, we use the method of abstraction from a Lagrangian field theory model. In other words, we construct a mathematical theory of the strongly interacting particles, which may or may not have anything to do with reality, find suitable algebraic relations that hold in the model, postulate their validity, and then throw away the model.*”
And this means: use RQFT to get results and then throw away Field Theory.
**Murray Gell-Mann** in 1964 wrote, i.e.: “*We may compare this process to a method sometimes employed in French cuisine: a piece of pheasant meat is cooked between two slices of veal, which are then discarded*.” [the same reference quoted above].
The **crisis of RQFT was not a momentary crisis**, **in fact in 1972**, the inventor of new field-theoretical entities, quarks and gluons, in his closing speech at the XVI International Conference on High Energy Physics [M. Gell-Mann, Proceedings **Vol. 4**, 135 (1972)] held at Chicago Fermi-Lab said: “*Let us end by emphasizing our main point, that it may well be possible to construct an explicit theory of hadrons, based on quarks and some kind of glue, treated as fictitious, but with enough physical properties abstracted and applied to real hadrons to constitute a complete theory*”. The father of quarks and gluons concludes by saying: “*Since the entities we start with are fictitious, there is no need for any conflict with the bootstrap or conventional dual parton point of view*”. In other words, it appeared to be not proper for a member of the very small RQFT club to use RQFT without apologies, to say the least. For the great RQFT religion there was not a single real believer left, apart from Victor F. Weisskopf.
Thus, the only Lorentz-invariant quantum theory where the concept of Field was the primary ingredient, appeared to be in trouble during many years as recalled by David Gross: “*A powerful dogma emerged, that field theory was fundamentally wrong, especially in its application to the strong interactions*”* *[D. Gross, Proceedings of the Third International Symposium on History of Particle Physics, Cambridge University Press (1994)].
The dominant theory of particle physics in the sixties was not a RQFT but the S-Matrix Theory, the antidote of RQFT which is the basis of the CPT Theorem.
The existence of the Antideuteron was predicted by the CPT Theorem. But the reason for the validity of CPT had vanished.
Why should the nuclear binding forces be CPT invariant if all known examples of fundamental interactions (**Electromagnetism**, **Nuclear Forces**, **Weak Interactions**) had serious troubles when described in terms of a Relativistic Quantum Field Theory (RQFT)? How could anyone take for granted that the Antideuteron had to exist on the basis of the existence of the Deuteron? Indeed, the Antideuteron could really not be there, thus confirming the enormous series of difficulties encountered in the description of all natural phenomena using the mathematical formalism of RQFT. It is the discovery of the antideuteron at CERN – in March 1964 [4] – which gave «*confidence to the search of a field theoretical basis for the strong interactions, that today seems so obvious to us*», as stated by Luciano Maiani [5]. Today we know that the uniqueness of the S-Matrix Theory was a dream. There are as many S-Matrices as we want, all satisfying the basic principles. In fact, any non Abelian Gauge theory, with any Gauge group and an arbitrary number of fermions (provided that they are not too many in order to avoid the loss of asymptotic freedom) will have its S-Matrix.
5 — **Why the existence of the Antideuteron needed to be established**.
The great Paul Dirac was not impressed when he was told that the had been discovered by Emilio Segrè et al. [6] and even more so when he learned, a year later, that the had been discovered by Oreste Piccioni et al. [7].
Dirac's enthusiasm was not so great because he was firmly convinced that C invariance had to be a Fundamental Invariance of Nature. But, Paul Dirac reacted with enthusiasm to the discovery of the Antideuteron and he wanted to meet me. And this was the beginning of a long, “unforgettable”, friendship (Fig. 1).
Why ? In the early thirties, in his Nobel Lecture, Dirac proposed the existence of all antiparticles: not only the positron but also the and the had to exist. This is because of_{ }C invariance, a Symmetry Property Dirac never doubted about. For a person such as Paul Dirac — extremely careful and cautious — to postulate the existence of all antiparticles had to be a great effort; motivated by the incredible success of his theory and by H. Weyl [8]. His enthusiasm brought him to formulate the hypothesis that Antimatter, Antistars and Antigalaxies had to exist. How things went has been illustrated by T.D. Lee [9] in the opening Lecture.
Let me briefly summarize the basic points.
**The validity of C invariance from 1927 to 1956.**
After the discovery by Thomson in 1897 of the first example of an elementary particle, the Electron, it took the genius of Dirac to theoretically discover the Antielectron thirty years after Thomson.
Only a few years were needed, after Dirac's theoretical discovery, to experimentally confirm (Anderson, Blackett and Occhialini [10]) the existence of the Dirac Antielectron.
Twenty-three years after the Antielectron, the two Nuclear Antiparticles were finally discovered by Segrè () and Piccioni () ; in 1955, the validity of C invariance in Strong Interactions appeared to be on firm experimental grounds.
Moreover the discovery of the second K meson,
in 1956 [11] was interpreted as proof of C invariance in Weak Interactions.
The conclusion of this first phase is that C invariance appeared to be perfect up to 1956, no evidence for the breaking of Fundamental Symmetry Laws had ever been found.
Fig. 1 – Letter by Mrs Manci Dirac.
**6 — ****The breaking of the Fundamental Symmetry Operators. In 1957 a new era started. **
Two fundamental Symmetry Operators were first proposed [12] and then found [13] to be fully broken in Weak Interactions. This started to cool down Dirac's original enthusiasm.
However, the product of the two broken Symmetry Laws (CP) appeared to be conserved. And this was, by some fellows, considered as the correct interpretation of Lederman's experiment [11] (remember LOY [2] previously quoted). But in 1964 a new effect was discovered, 2 [14] , showing that also CP invariance was violated, as anticipated by Lee, Oehme and Yang [2].
This opened the way to doubt about the validity of all Invariance Laws, including CPT.
Dirac started to worry about the possible non existence of Antimatter. In fact, ten years after Segrè's and Piccioni's discoveries of the Nuclear Antiparticles, there was no evidence for the existence of the first representative of Nuclear Antimatter: the Antideuteron.
On the other hand, in the middle sixties physics was between two earthquakes: **the collapse** of some invariance principles based on the fundamental Symmetry Operators (P, C, T), and **the collapse** of the fundamental mathematical structure called RQFT. These two big crisis were corroborated by experimental discoveries. The former in the field of Weak Interactions, the latter in the field of Strong Interactions. There were also pure theoretical reasons like the “zero-charge” in QED, proposed by Landau. How could anyone predict that the Nuclear Forces binding a Proton with a Neutron had to be the same as those acting between an Antiproton and an Antineutron? The description of the Strong Interactions was not based on a RQFT.
The Strong Forces acting between Nuclear Particles and Nuclear Antiparticles had no reason to obey an invariance principle, such as CPT. First, because invariance principles were experimentally found to be broken; furthermore because the description of the Strong Forces was not in terms of the mathematical structure, RQFT, where the invariance principle, CPT Symmetry, had been theoretically proved.
In no way could anyone take for granted that the nuclear binding forces had to be CPT invariant. The problem of Symmetry between Matter and Antimatter was entirely unresolved from the theoretical point of view. In other words, the existence of the Deuteron could by no means imply the existence of the Antideuteron. The search for was important, for two reasons closely linked together:
i) to see if in strong interactions CPT was a Symmetry Law not broken as
the other Symmetry Laws, C, P, CP, and T were in weak processes;
ii) to check if it were possible to think of Nuclear Forces as examples of a RQFT, despite the successes of the S-Matrix Theory.
It was necessary to experimentally establish if the first example of Nuclear Antimatter was there or not. “*It could well not be there*”, once W. Heisenberg said to me in John Bell’s office. Both Heisenberg and Bell were strong supporters of my experiment. In fact, in those years the invariance of the Symmetry Operators and the description of strong interactions in terms of a RQFT, were sourced of serious doubt. Consequently the so-called “theoretical prediction” for the existence of the Antideuteron was riddled with “theoretical confusion”.
**7 — The first example of Nuclear Antimatter: the Antideuteron**.
Why had no one been able to see the Antideuterons? Was the search for an easy experiment?
The data speak for themselves:
i) the production cross-section for has a factor 10^{}^{4} when compared to the production of (see Fig. 2 [15]);
ii) the ratio of Antideuteron to ^{} at the production was (and is) (see Fig. 3)
^{ in the energy range of the CERN discovery experiment.}
**Needed: a high rejection against pions**.
These are the reasons why it took a decade to discover the first example of Nuclear Antimatter, after the discovery of the Nuclear Antiparticles ( [6] and [7]).
Notice that the factor 10^{}^{4} is present also when we go, from to ^{3} and ^{3}. There are four orders of magnitude each time we add an Antinucleon, and therefore four orders of magnitude to go from the first example of Nuclear Antimatter — the Antideuteron — to the second one: Antitritium and Antihelium-3. The time interval: thirteen years.
Let me now go into the effective discovery experiment.
With Mario Morpurgo and Guido Petrucci we had built the most powerful beam of the world [16 a, b]. Years of work were needed to have the most accurate electronic device for time-of-flight (TOF) measurements at the 100 ps level of precision.
Fig. 2 – The differential inclusive production cross-section: a factor 10^{}^{4} is present when adding one Antinucleon (from Ref. [15]).
Fig. 3 – The ratio versus incident beam energy. Note the value 10^{}^{8} at production, in the energy range of the CERN discovery experiment (from Ref. [15]).
Our research on the Antideuteron experiment had as top priority the study of time-like photons produced in () annihilation. This source of time-like photons had to be as intense as possible (and therefore the beam had to be “partially separated”) in order to allow the search for a new type of heavy lepton, the HL^{}, carrying its own leptonic number and being coupled to its own neutrino, with typical signature acoplanar (e) pairs and missing energy, first searched at CERN in (p) , later at Frascati with the (e^{}e^{}) collider [17] and finally discovered at SLAC.
In Fig. 4 the first page of our work at CERN to build the most powerful antiproton beam is shown. This work (published in 1965) [16 b] was presented by me a year before at Dubna during the first International High Energy Physics Conference in the Soviet Union [16 a]. At that same conference the results on 2 were presented by Jim Cronin. This discovery gave Paul Dirac the doubt that Antimatter could indeed not exist and the search for Antideuterons started to gain a wide consensus.
We could do the experiment in a “record-time” because we had the most precise TOF device ever built and the most powerful beam of antiprotons in the world. In fact the Antideuteron () signal was detected [4] in a single night. “The one night story”, so much liked by Weisskopf and recalled by T.D. Lee [9] , could make those who are not familiar with Viki’s *geist* think that the CERN-DG considered the Antideuteron experiment a simple matter. This is not the case.
As CERN-DG Weisskopf had decided to support the R&D work needed for the “partially separated” beam and for the TOF set-up to be built: the Antideuteron search being part of the main programme of my group, as mentioned above.
The first page of the paper on the experimental observation of Antideuteron production at CERN is shown in Fig. 5. The paper was submitted on March 13, 1965 to “Il Nuovo Cimento” and, following the standard routine, it was published 5 months later. Meanwhile, eight weeks after the CERN discovery, the American group led by Leon Lederman, with Sam Ting among its members, “published” in an American newspaper the Brookhaven results on the existence of Nuclear Antimatter. Weisskopf was upset by the Brookhaven experiment, because they ignored the CERN work. “The one night story” anecdote was in order to emphasize the eight weeks needed by the Brookhaven fellows to repeat our experiment. One night versus eight weeks.
Fig. 4 – The most powerful beam of the world. (Why? Because only partially separated).
Fig. 5 – The first experimental observation of Antideuteron production. The paper was submitted to “Il Nuovo Cimento” on March 13, 1965 and it was published on September 1st, 1965.
Years of work and a lot of ingenuity were needed to build the experimental detector for our research programme at CERN, and in particular the TOF and the “partially separated” beam. At Brookhaven no such BEAM existed and no such a TOF. Had these two devices been available at Brookhaven, the signal would have been confirmed “one night” after our result. Let me recall an example of how easy it is to find a signal once you know that it has to be there. It took one day to see the (J/) peak at Frascati using the (e^{}e^{}) ADONE collider, once they knew that it had been seen at SLAC. Years of work at Brookhaven to see the J peak, and years of work at SLAC to see the peak; one day at Frascati to see the (J/) peak. Please allow me a personal note. Five years before the 1974 November “revolution”, Frascati had refused to consider my proposal to raise the (e^{}e^{}) collider energy above the 3 GeV limit. The theoretical expectations were for the “tails” of the known vector mesons (, , ). Why take the risk of “burning” the collider? So hard was the wall against the search for something that no one had predicted and no one had ever seen, that after having completed my research programme at Frascati, I dismantled the experimental set-up and returned to CERN. In November 1974, with a much poorer set of detectors, the (J/) peak was observed at Frascati in a single day.
What about theoretical predictions? As mentioned above, for the (J/) there were none and, having for years a collider and an experimental set-up able to see it in one day, this search was forbidden. A search, I repeat, that needed one day to be accomplished.
For the case the theory predicting its existence was in serious troubles, as we have seen in the previous sections. The only laboratory where the check could be done in “one night” was CERN. And, thanks to V.F. Weisskopf, we did it. Brookhaven was not in the same position as Frascati was with respect to SLAC in the (J/) case. In other words, the experiment for the Brookhaven physicists was not as simple as looking at (J/) was for the Frascati fellows. When they knew the CERN result, it took them eight weeks to repeat it.
As reported by S.C.C. Ting in his Lecture [18], the existence of the first example of Nuclear Antimatter was confirmed at Brookhaven eight weeks after the CERN result.
Figure 6 shows what V.F. Weisskopf [19] recalls about the “very high intensity antiproton beam” conceived at CERN during his DG time. This was the first “partially separated” beam ever built. The bubble-chamber-dominated era did not allow to think that a very high intensity beam of interesting particles (, ) could be built for non-bubble-chamber physics. Figure 7 shows another page of the same paper by V.F. Weisskopf [19] where he recalls the date of the discovery of the first example of Nuclear Antimatter, with the correct time sequence between the CERN date [the birthday of Peter Standley, then Director of the CERN Proton Syncroton (PS)] and the date of Lederman's results announced in an American newspaper. A retrospective look at the 1965 experimental competition allows one to conclude that priority problems are over.
The invariance of the Symmetry Operators and the description of nuclear forces in terms of a Relativistic Quantum Field Theory seemed to have lost their foundations. Therefore the existence of a Symmetry Property between Matter and Antimatter had no basis: the existence of Nuclear Antiparticles could in no case be considered as a basis for the existence of Nuclear Antimatter. Thus, the experimental evidence for the existence of the Antideuteron became the only proof that the nuclear binding forces had to be CPT invariant, and therefore describable in terms of a RQFT. In those years of great theoretical confusion the proof that the first example of Nuclear Antimatter was there certainly contributed to reestablish confidence on the validity of CPT invariance and on the fact that Nuclear Forces had to be described by a RQFT, despite the successes of the S-Matrix Theory.
Forty-six years after the discovery of the first example of Nuclear Antimatter we still do not have the basis for the validity of an “effective” RQFT description of the Nuclear Forces. Thus Matter-Antimatter Symmetry is the consequence of an “effective” RQFT which describes the nuclear binding forces. These forces are now understood in terms of Van der Waals-type, QCD remnant forces, acting between QCD colour-neutral states (the nucleons) and mediated by other QCD colour-neutral states (the mesons). The source of this “effective” RQFT description of the nuclear forces is QCD: another “effective” RQFT, responsible for the interactions between the constituents of the nucleons, quarks and gluons. This non Abelian SU(3)_{C} Subnuclear colour gauge force should be unified with all other gauge forces at some scale. If this is the String scale (i.e. 10^{19} GeV), here RQFT loses its foundations because the basis of the mathematical structure is not the “point” but either a “string” or possibly a “membrane”. Thus QCD, its remnant forces and their invariance (CPT) properties are of “effective” nature.
Fig. 6 – Weisskopf’s paper recalling how the very high intensity Antiproton beam started to be conceived and built (from Ref. [19]).
Fig. 7a – Weisskopf’s paper recalling the discovery date and the time sequence between the CERN work and Lederman’s work announced in an American newspaper (from Ref. [19]).
Fig. 7b
It is reassuring to know that all these theoretical “effective” approaches are corroborated by the experimental result that the Antideuteron is indeed there.
**8 — Matter and Antimatter: a comment**.
Let me allow a digression on the concept of Nuclear Matter and Antimatter and on the masses associated with them. In the sixties the elementary particles were objects such as the proton (p) and the neutron (n) , with antiprotons () and antineutrons () as antiparticles. The existence of Nuclear Matter^{(*)} needs a nuclear binding between protons and neutrons.
(*) The Hydrogen atom needs the masses of two elementary particles the proton (p) and the electron (e), plus the electromagnetic binding between them (p, e). The existence of the Hydrogen atom has nothing to do with the existence of Nuclear Matter.
The mass of the most elementary nucleus of Matter, the Deuteron (D), needs, in addition to the masses of the two elementary particles (p, n), also the negative nuclear mass produced by their binding. In the sixties there was no understanding of the mathematical structure needed to describe these nuclear binding forces.
Since the middle sixties, our understanding of the nuclear binding forces has evolved a lot, as we have just seen, thanks to QCD. And now a problem arises. The basic ingredients of QCD are the gluons (massless) and the quarks (massive). No one knows the scale where the intrinsic quark masses originate. If it is at the String Unification scale (i.e. 10^{19} GeV), here (for the reasons mentioned above) the CPT Theorem loses its foundations [9] and therefore the mass of a quark has no reason to be the same as the mass of its antistate; thus we might expect
.
Let us disentangle :
i) the intrinsic mass associated with a quark (a structureless particle);
from
ii) the mass associated with a nucleon (a particle composed of three quarks plus many gluons);
and these two masses from
iii) the mass associated with Nuclear Matter, the simplest example being the Deuteron.
It is sometimes stated that the existence of a mass difference between the long-lived and the short-lived components of the (^{ }K^{0} ^{0}^{ }) system is the proof that Matter-Antimatter symmetry is broken at the level of K^{0} and ^{0}^{ }. The experimental result is
m_{K}_{L}_{K}_{S} m_{K}_{L} m_{K}_{S} ( 3.491 ± 0.009 ) 10^{}^{6} eV/c^{2} . (6.1 a)
However this is the mass difference between two particle states, K_{L} and K_{S}, each one consisting of a mixture of a particle ( K^{0}^{ }) and its antiparticle (^{ } ^{0} ). When (6.1 a) is translated into the mass difference between the K^{0} and the ^{0 }the result is
| m_{K}_{0} | 4 10^{}^{10} eV/c^{2} . (6.1 b)
In other words there is no final statement (in the case of a meson) for the existence of any asymmetry between the mass of a particle ( K^{0} , i.e. a q_{i}^{ } _{j} system) and its antiparticle ( ^{0} , i.e. a _{i}^{ }q_{j}^{ }system again). Let us point out again that, what in the
middle sixties was considered an elementary particle is now understood to be a system of either a quark-antiquark (q ) pair (mesonic state) bound by QCD colour confining forces, or a (q q q) triplet (baryonic state) bound by QCD colour confining forces. The masses of these particles (mesons and baryons) are the result of the intrinsic quark masses, m_{q} , plus the QCD confining (“Bag”) effects, m^{Bag}^{ }, plus some radiative effects, m^{Rad} .
As a meson is already a mixture of a quark plus an antiquark, the search for an asymmetry between particle and antiparticle masses should have its best source in those particle states which consist only of quarks (such as the baryons), and not of quark-antiquark mixtures (such as the mesons).
Keeping in mind the problem of the Deuteron and Antideuteron masses, let us consider the mass difference between a particle and its antiparticle each one composed of quarks and gluons. The simplest example is the proton, whose mass is the result of the following components:
m_{p} ^{} 2 m_{u} ^{} m_{d} ^{} + (6.2 a)
where: i) m_{u} , m_{d} are the intrinsic masses of the elementary constituents, the quarks;
ii) is the mass produced by the QCD colour forces acting between quarks and gluons and confining them within the proton radius.
The same parts appear in the mass of an antiproton:
^{} 2 ^{} ^{} + . (6.2 b)
If the interaction responsible for the intrinsic mass of a quark is CPT invariant, if the QCD confining effects and the radiative effects are all CPT invariant, the result is expected to be
^{} m_{p} ^{} ^{} zero ;
the experimental limit is
^{} (2 3 ± 42) eV/c^{2} zero ± 40 eV/c^{2} . (6.2 c)
And now, the Deuteron-Antideuteron masses:
m(D) ^{} m_{p} ^{} m_{n} ^{} + (6.3 a)
m() ^{} ^{} ^{} + (6.3 b)
In addition to the particle masses (m_{p}_{ }, m_{n}) and the antiparticle masses (, ), we now have the nuclear binding effects, and , which, contrary to the QCD “Bag” effects (that produce positive masses), subtract mass to the (p n) and () systems, respectively.
If all these processes are CPT invariant, we expect the mass difference between the Deuteron and the Antideuteron to be zero
^{} m_{D} ^{} ^{} zero .
The experimental limit is
^{} zero ^{} 80 MeV/c^{2} . (6.3 c)
It would be interesting in future to see how these results [(6.1 b); (6.2 c); (6.3 c)] compare among themselves, once they would reach the needed sensitivity. Notice that the accuracy in (6.1 a) is nearly ten orders of magnitude higher than the accuracy which characterises the best mass difference so far measured in a particle-antiparticle system made up of three quarks (6.2 c). Apart from being — as already emphasised — a mass difference between two particle states (not between a particle and its antiparticle), the reason for the extraordinary accuracy in m_{K}_{L}_{K}_{S} is in the fact that what is measured is a time-dependent “oscillation”, whose value depends on m. Nevertheless, neither (6.1 a, b) nor (6.2 c) are measurements of mass differences between Nuclear Matter and Nuclear Antimatter states, the QCD-induced nuclear binding, which produces effects opposite in sign to the QCD confining forces, being absent in (6.1a, b) and (6.2 a, b, c).
To recapitulate, in these last thirty years, our understanding of the mass differences between Particle-Antiparticle and Matter-Antimatter states has developed and, apart from radiative effects, can be described in terms of three sources:
i) the intrinsic mass of some fundamental fermions (the quarks);
ii) the “Bag” effects due to QCD colour forces; these effects produce positive masses;
iii) the binding effects due to QCD colour-neutral states (the mesons) acting between other QCD colour-neutral states (the nucleons); these effects produce negative masses.
All these sources of masses, the intrinsic fermionic ones, the QCD colour confining ones and the QCD colour-neutral binding, appear in Nuclear Matter and Antimatter.
**9 — Conclusions**.
Forty-six years ago the key point was to establish if the Antideuteron was there or not. In fact the collapse of many Symmetry Operators and the successes of the S-Matrix in the description of Strong Interactions, did not allow anyone to take for granted that the nuclear binding forces had to be CPT invariant. Now in the framework of new physics at the Planck length, such as String Theory, the CPT Theorem has lost its foundations, and the CPT invariance of the nuclear forces is based on the validity of an “effective” theory. Forty-six years after the experimental proof that the nuclear binding forces obey CPT invariance, this invariance is understood in terms of an “effective” theory, the fundamental one (what we now think to be the fundamental one) being again in trouble. Therefore the fact that the nuclear binding forces are CPT invariant rests on purely experimental grounds: i.e. the existence of Nuclear Antimatter.
There are three sources of masses: the one which produces the intrinsic quark masses is certainly not due to QCD. It could be due to the BEH effect (Brout, Englert, Higgs). Professor Englert will report on this effect which is called “God particle”. The other two are both due to QCD. The QCD confining effects produce positive masses; the QCD-induced nuclear binding effects produce negative masses. All these three sources are present in the mass of Antimatter. It would be interesting to study and compare quark-antiquark masses, particle-antiparticle masses, and Matter-Antimatter masses.
Let me turn to the search for Antimatter in Space. Had the CERN group [4] proved in 1965 that Antimatter did not exist, it would not have been possible to think of the AMS Project. Thirty years after the discovery of Nuclear Antimatter on Earth, a project is being implemented in order to search for Nuclear Antimatter in Space. Thirty years ago, to establish the existence of Antimatter had to do with the CPT Theorem. Now, the existence of Antimatter in Space has to do with the beginning of the Universe. The theoretical predictions are for the non existence of Antimatter in Space. However these predictions are not based on a theorem and should be experimentally tested as precisely as possible.
**References.**
[1] __CPT__. Let me allow a digression on CPT. The theorem came after three Symmetry Operators had been discovered: 1) Charge Conjugation, C, by H. Weyl and P.A.M. Dirac; 2) Parity, P, by E.P. Wigner; 3) Time Reversal, T, by E.P. Wigner.
To the best of my knowledge, the CPT Theorem was first proved by W. Pauli in his article “*Exclusion Principle, Lorentz Group and Reflection of Space-Time and Charge*”, in “Niels Bohr and the Development of Physics” [Pergamon Press, London, p. 30 (1955)], which in turn is an extension of the work of J. Schwinger [Phys. Rev. **82**, 914 (1951); **91**, 713 (1953); **91**, 728 (1953); **94**, 1362 (1954)] and G. Lüders, “*On the Equivalence of Invariance under Time Reversal and under Particle-Anti-particle Conjugation for Relativistic Field Theories*” [Dansk. Mat. Fys. Medd. **28**, 5 (1954)], which referred to an unpublished remark by B. Zumino. The final contribution to the CPT Theorem was given by R. Jost, in “*Eine Bemerkung zum CPT Theorem*” [Helv. Phys. Acta **30**, 409 (1957)], who showed that a weaker condition, called “weak local commutativity” was sufficient for the validity of the CPT Theorem.
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