Conference in Honour of
Murray Gell-Mann's 80th Birthday Celebrations
MURRAY GELL-MANN
AND THE LAST FRONTIER
OF LHC PHYSICS:
THE QGCW PROJECT
A. Zichichi
INFN and University of Bologna, Italy
CERN, Geneva, Switzerland
Enrico Fermi Centre, Rome, Italy
Ettore Majorana Foundation and Centre for Scientific Culture, Erice, Italy
Table of Contents
Introduction 2
1 The () mixing in 1955 and its consequences 2
2 From the proliferation of mesons and baryons to the Effective-Energy, EHAD, in all interactions, no matter the difference between the interacting particles 8
3 The QCD colour, the QGCW Project and Complexity 12
References 13
24–26 February 2010
Nanyang Executive Centre, Nanyang Technological University, Singapore
MURRAY GELL-MANN
AND THE LAST FRONTIER OF
LHC PHYSICS: THE QGCW PROJECT
INTRODUCTION
This paper is my personal testimony of the role played, in those experimental and technological activities where I have been directly involved, by some of Murray Gell-Mann original ideas which go from the isospin ½ for the q–meson to SU(3) flavour, to SU(3) colour, to Complexity. The starting point is the q–meson having isospin ½ [1a, b, c] and the () mixing in 1955 [1d, e]; it continued in 1960 [2] with the parameter e, proposed in order not to spoil the universality of the Fermi–coupling. In the same paper [2] Gell-Mann and Lévy proposed the s–model whose consequences end up with the prediction of the top–quark. One year later, 1961, the eightfold way was elaborated [3] and in 1964 “A schematic model of baryons and mesons” was proposed having SU(3)–flavour [4] with “quarks” as building blocks. In 1968, the (h–h') mesonic mixing [5] was investigated where from, the vector meson (w, f) mixing problem came out. The existence of the QCD “colour” [6, 7, 8] is the basis of the present QGCW (Quark–Gluon–Coloured–World) Project, which is the first step. The next one being linked to the ELN collider with 300 km ring and total energy in the Pev range. Finally, Complexity in 1995 [9, 10]. If Complexity exists at the fundamental level, then for the years to come, what should be discovered at the frontier of our knowledge is in the field of totally unexpected events.
1 THE () MIXING IN 1955 AND ITS CONSEQUENCES
The first reason to be grateful to Murray is the establishment of the Ettore Majorana Foundation and Centre for Scientific Culture in Erice (EMFCSC). I was the youngest member of the Italian delegation at the 1955 International Conference in Particle Physics where the most powerful group of experimental physics, led by Patrick M.S. Blackett, was expected to present their most recent cosmic rays results obtained at Jungfraujoch, in Switzerland.
The report was presented by a fellow of the Blackett group and the chairman of the session was the famous Buthler, co-discoverer with Rochester of the first experimental evidence for the existence of two totally unexpected particles called by Blackett V0, since they appeared in the cloud chamber as inverted V’s. These two V0 were in fact a baryon L0 and a meson q0. No one knew the reason for their existence. In order to describe their production and decay properties Murray proposed the existence of a new quantum number called Strangeness, conserved at production and violated at decay. The great news presented by the Blackett group [11] was a series of observations where the following reaction was needed to explain the results:
q0 + N ® L + N'
A young fellow, at the end of the presentation, stood up and said: I am sorry but I would like to point out that this reaction violates “strangeness–conservation”. Silence in the over-crowed lecture hall. The chairman saw another young fellow who wanted to say something; his English was broken, but apparently he was defending the Blackett group results. So he was invited by the chairman to go to the blackboard and using the chalk he explained that in the “strangeness theory” proposed by Gell-Mann [1a, b, c] the q-meson isospin was ½, therefore the q neutral component had to be with positive and negative strangeness. Furthermore according to a very recent paper by Gell-Mann and Pais [1d] the q0-meson, produced with strangeness +1, becomes a mixture of strangeness +1 and -1; thus the production of L0 could indeed be via the reaction
0 + N ® L0 + N'.
The young fellow was me and this is how I became the pupil of the great Blackett, whose cloud chamber was a powerful instrument producing very interesting pictures. In two of them I found two examples of pair production of heavy mesons () and () [12], thus proving the correctness of the Gell-Mann strangeness model [1a, b, c, d, e]. Blackett was very happy that old pictures had finally found the right interpretation and contributed to the understanding of the “strange” world started with the V0–particles.
Let me add a few details on these very exciting years.
The V0–particles gave also rise to the (q-t) problem [13], which culminated in the discovery of the breaking of the symmetry operators C and P. The discovery of the non-invariance of these symmetry operators was suggested (1956) in a detailed analysis of all weak processes by T.D. Lee and C.N. Yang [14]; the first experimental evidence was provided by C.S.Wu and collaborators one year later [15]. This is how the q–mesons became K–mesons.
Seven years after my arrival in the Blackett group, in 1962, the document establishing the existence of the Majorana Centre in Erice (EMFCSC) was signed by Blackett, Bell, Rabi, Weisskopf and myself at CERN in Geneva. Murray, thanks to his isospin ½ for the q–meson and to the () mixing, contributed to the foundation of the Erice Centre, despite his signature not being in the 1962 document.
In Figure 1 there is a picture showing the celebration by the Minister of Home Affairs of the Italian Government of the bronze dedicated to the founding paper of the Ettore Majorana Centre (EMFCSC).
Figure 1: The Minister of Home Affairs, Dr. Enzo Bianco, unveils the bronze reproduction of the document which established the constitution of the Ettore Majorana Foundation and Centre for Scientific Culture (EMFCSC) signed by J.S. Bell, P.M.S. Blackett, I.I.Rabi, V.F. Weisskopf and A. Zichichi at CERN on May 8th of 1962. In his inaugural address (Erice, May 8th, 2000) H.E. the Minister Enzo Bianco recalled how in 1964 he was named one of the 100 “best students” in Italy in an EMFCSC competition. At the extreme right Enzo Iarocci, President of the INFN (1998–2004).
Let me go back to the “strangeness mixing”. This mixing predicts the existence of two mesons, and , on the basis of the validity of C invariance in weak interactions. The discovery by Lederman of ® 3p [16] was interpreted as a proof that C invariance holds in weak interactions. With the discovery of C and P breaking, the (q-t) mesons became, as mention before, a unique particle, the K-meson, which splits into two components, and , each one thought to be an eigenstate of the symmetry operator CP proposed by Landau [17] to replace the two broken P and C invariances.
In 1956, Lee, Oehme and Yang (LOY), before parity violation was experimentally proved by C.S. Wu, pointed out that the existence of could not be taken as a proof of C invariance, nor as a proof of CP invariance [18]; LOY showed that “strangeness mixing” does not imply C invariance. In fact, even if CP is not valid, there would still be a long-lived neutral K–meson and, in order to prove that “strangeness mixing” is or is not CP invariant, other experiments had to be done in K decay physics. In 1964, it was discovered that CP invariance is indeed broken [19] and this is why the two neutral K–mesons (, ), became (, ), as foreseen in 1957 by LOY [18].
Let me quote an amusing detail of this great discovery, started with the () mixing. The experiment [19] was not planned to search for the 2p decay mode of the meson. The aim of the experiment was to check the anomalous regeneration in hydrogen, previously reported by Robert Adair et al. [20] (and found [19] to be more than an order of magnitude lower). The search for the 2p decay mode of the long-lived was proposed by us at CERN, but rejected because the neutral beam in the PS experimental hall had already been allocated to another group’s programme. On the other hand, we were already engaged with the PAPLEP (Proton AntiProton Annihilation into LEpton Pairs) experiment to search for the production of the 3rd lepton through the (em) final state produced in () annihilation [21], using the CERN-PS beam which was next to the neutral beam we wanted for the ® 2p search. I was told by the CERN Research Director of the time “give other people the chance”, when trying to convince him that the existence of the long lived was not proof of CP invariance as shown by LOY in 1957 [18], therefore the search for the ® 2p decay mode, violating CP invariance, was not in contradiction with the existence of the long lived meson. It would have been too much to give two PS beams to the same group, he told me later. Moreover we were not proposing to check the anomalous regeneration in hydrogen (a proposal considered very interesting by many CERN theorists). Our aim was to follow the LOY theoretical deep remark and check if CP was really valid in decay.
The 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. How and why the quark flavours (u, c, t) and (d, s, b) mix and why this mixing is linked with the breaking of CP has no theoretical understanding, so far. All we can do is to measure the various flavour mixings and CP breakings.
Flavour mixing, started by Murray in 1955 [1], appears to be active also in the lepton sector as discovered by Koshiba et al. [22] and now being experimentally investigated the world over (see for example the proceedings of the Erice School of the last three years 2006, 2008, 2009).
Another chain of consequences originated by the existence of the V0–particles was the proliferation of mesons and baryons with two branches: “statics” and “dynamics”. The “static” proliferation gave rise, first to the eightfold way of Gell-Mann and Ne'eman [3], and then to the “flavour” global symmetry SU(3)ƒ based on the existence of three quark flavours: u, d, s [4]. SU(3)ƒ contributed to open the way towards SU(3)c . It is in fact the notion that two baryons
W- and
had to be fermions, but appeared to be perfectly symmetric in their quark composition [23], that prompted the idea for the existence of a new intrinsic quantum number [24, 25].
This chain of consequences, started with Murray’s strangeness, led to the discovery of Quantum Chromodynamics (QCD) [6, 7, 8]: the fundamental forces acting among quarks and gluons. This force was affected by a theoretical trouble: confinement, since from QCD it is not possible to predict it. And here comes another experimental game: to see if in a violent collisions the proton breaks into its pieces.
In fact DIS (Deep-Inelastic-Scattering) between electrons and protons revealed in 1968 at SLAC [26] a totally unexpected phenomenon: only some piece of the proton a “part” was involved in the interaction. The rest of the proton was totally inactive. If at high energy the proton behaves as if its pieces were “free” and therefore non-interacting among themselves, then in a high energy collision two protons should break up into their constituents, for example into the “quarks” of Gell-Mann.
The discovery of scaling at SLAC [26] prompted the implementation at CERN [27] of a sophisticated experimental set-up intended to establish if fractionally charged particles were “freely” produced at the highest energy (pp) collisions (using the ISR collider). No quarks were observed by us at ISR thus establishing a firm contradiction: at high energy the pieces of the protons were losing their coupling (this is the meaning of scaling) but no quarks were observed at ISR [27].
Scaling was finally understood as a consequence of the non-Abelian nature of the force acting between the constituents of a proton (or a neutron). Consequently, the non-existence of quarks, searched for at ISR in violent collisions [27], was understood in terms of the low energy behaviorof this new force. Thus, “asymptotic freedom” and “confinement” came in the construction of the Standard Model, with QCD as the third fundamental force of Nature, to be added to the other two forces: electroweak and gravitational.
Is is really incredible that the same mathematics, SU(3), first used to describe the proliferation of mesons and baryons, with SU(3)ƒ, became the basic structure of the third fundamental force of Nature with SU(3)c.
gluon a3 gluon
gluon
It is the non-Abelian property of QCD which allowed all of us, after many decades, to finally understand the origin of nuclear isospin and of SU(3)ƒ. It is the gluon-gluon interaction which guarantees the “flavour” independence of a3 as shown in the three–gluon diagram above.
2 FROM THE PROLIFERATION OF MESONS AND BARYONS TO THE EFFECTIVE-ENERGY, EHAD, IN ALL INTERACTIONS, NO MATTER THE DIFFERENCE BETWEEN THE INTERACTING PARTICLES