Eur. Phys. J. H 42, 475{505 (2017) DOI: 10.1140/epjh/e2017-80052-8 THE EUROPEAN PHYSICAL JOURNAL H Oral history interview The LHC timeline: a personal recollection (1980{2012)? Luciano Maiani1 and Luisa Bonolis2,a 1 Dipartimento di Fisica and INFN, Piazzale A. Moro 5, 00185 Rome, Italy 2 Max Planck Institute for the History of Science, Boltzmannstraße 22, 14195 Berlin, Germany Received 14 August 2017 / Received in final form 12 September 2017 Published online 4 December 2017 c The Author(s) 2017. This article is published with open access at Springerlink.com Abstract. The objective of this interview is to study the history of the Large Hadron Collider in the LEP tunnel at CERN, from first ideas to the discovery of the Brout{Englert{Higgs boson, seen from the point of view of a member of CERN scientific committees, of the CERN Council and a former Director General of CERN in the years of machine construction. 1 The SppS¯ collider and LEP L. B. During the 1980s, at the time when LEP, the Large Electron Positron collider, was being completed, you began to be deeply involved with CERN. 1 L. M. Nicola Cabibbo had been in the Scientific Policy Committee (SPC) in the 1970s, when they had advised CERN to approve the construction of the proton{ antiproton collider proposed by Carlo Rubbia and Simon van der Meer to search for the Intermediate Vector Bosons. It was a difficult machine and the positive recommendation of the SPC was a far-sighted decision. The pp¯-project of Rubbia, initiated in 1976, was based on the conclusion that with the unified theory of the electroweak interactions (Glashow, 1961; Weinberg, 1967; Salam, 1968) and the measurement of sin 2θ from Gargamelle, the predicted mass of the charged intermediate vector boson W was around 70 GeV, requiring a proton{antiproton collider to reach such energies. However, at FermiLab, Bob Wilson was not interested in the project. Rubbia, after strong opposition, convinced finally L´eonvan Hove and John Adams of a pp¯ collider, at the CERN SPS, based on the Stochastic Cooling project of Simon van der Meer. The Spp¯S started operation in 1981, after only 5 years of construction. An immediate outcome was the appearance of narrow jets even in a hadron machine ? The text presented here has been revised by the authors based on the original oral history interview conducted by Luisa Bonolis and recorded in Rome, Italy, 1{3 March 2016. a e-mail: [email protected] 1We are indebted to Prof. Dieter Haidt for very informative exchange on the arguments discussed in this section. 476 The European Physical Journal H (Banner et al., 1982), a possibility doubted earlier by prominent physicists and a strong confirmation of the reality of confined quarks and gluons in the hadrons. The observation of W and Z, with predicted masses and other properties followed in 1983, see e.g. Di Lella & Rubbia (2015). I was elected in the Scientific Policy Committee of CERN in 1984, after Nicola, when the Large Hadron Collider was first considered in the SPC as the next CERN large facility. In those years, during LEP construction, the discussion started about future accel- erators, beyond the SppS¯ , Tevatron and LEP. We realised that the way to go to higher energies was with p{p rather than p{¯p colliders or e+e− colliders. At energies above LEP, there are so many gluons in a proton or in an antiproton that new particle production will be dominated by gluon{gluon fusion. It was a great simplification: you would not need quark{antiquark annihilation, as was the case at the SppS¯ , and all the gymnastic around antiproton beam cooling could be avoided. Also, due to asymptotic freedom, we understood that a hadron machine could be almost as effec- tive as an electron{positron machine to disentangle the basic particle reactions. So it didn't pay to go beyond LEP with electron{positron, the next machine could be proton{proton. L. B. The years 1980s saw the realisation in Europe of two big high energy machines: HERA at DESY, and LEP at CERN. How was discussion and planning of two such large enterprises organised? L. M. The scene was set by the rising of the Standard Model in the 1970s after the discoveries of neutral weak current neutrino events and of charm, see e.g. the reconstruction presented in Maiani (2017). New particles were expected to be observed at high energy (W and Z, new quark and lepton flavours) and the theoretical progress after the discovery of asymptotic freedom called for better experiments at higher energy, to test the detailed predictions about the violations of Bjorken scaling described by the Altarelli{Parisi equations (Altarelli & Parisi, 1977; Dokshitzer, 1977; Gribov & Lipatov, 1972). Large projects unavoidably entail long and international consultations and preparatory steps. The natural forum for these discussions was ECFA.2 The politics was not restricted to a single laboratory. DESY, under the leadership of Herwig Schop- per, had become a fully European Laboratory, competing with CERN for dimensions and scientific results. At the beginning of the 1980s, Schopper left DESY to become Director General at CERN and Volker Soergel became director of DESY. Both laboratories had running machines: 1. DESY: PETRA was running since 1978 (until 1986) and the next step had to be discussed; 2. CERN: SPS running since 1976 and Spp¯S started 1981 and the next step had to be discussed. It was an option for DESY to build an e+e− machine near to Hamburg, since there was a long tradition of electron colliders at DESY, just as was for hadron accelerators at CERN. The decision eventually went at CERN in favour of (the future) LEP. Instead, an electron{proton machine was proposed (1983/4) for DESY, which became HERA under the leadership of Soergel and of Bjorn Wiik, who later, in 1993, succeeded Soergel as director of DESY.3 2European Committee for Future Accelerators. 3HERA (Hadron-Electron Ring Accelerator) was built in a tunnel located under the DESY site around 15{30 m underground with a circumference of 6.3 km. Inside this tunnel, leptons and protons L. Maiani and L. Bonolis : The LHC Timeline: a personal recollection 477 The construction of the Large Electron{Positron collider at CERN started in September 1983, under the direction of Emilio Picasso, with Schopper Director Gen- eral. The first collisions were observed on July 4th, 1989, and the first Z0 on August 23 of the same year. At the time, the direction of CERN had passed to Carlo Rubbia.4 L. B. Which were the main goals of LEP? L. M. Initially, LEP was to be focused at the Z0 mass (that is at a total center-of-mass energy of about 90 GeV), to study the neutral mediator of the weak interactions discovered at the SppS¯ , which was expected to be abundantly produced in electron{positron annihilation. This phase was called LEP I, to be followed by a second phase, LEP II, where the energy would be increased to around 200 GeV. Aim of LEP II was to study the triple interactions W +W −γ and W +W −Z0, the latter being the salient aspect of the Yang{Mills interaction on which the unified electroweak theory was based (Glashow, 1961; Weinberg, 1967; Salam, 1968). These interactions are crucial for the consistency of the unified theory and had never been seen before. The production of W +W − pairs, at LEP, goes via two independent channels (a): e+e− ! γ ! W +W − and (b): e+e− ! Z0 ! W +W − The first is a purely electromagnetic process, already predicted in QED, while the second is the genuine signal of the Yang{Mills nature of the electroweak interaction. At LEP, the two amplitudes could be distinguished and studied separately from the kinematic characteristics of the overall reaction. L. B. At that time, which were the reasons to go for higher energies after LEP? L. M. The studies I just mentioned did not exhaust the possible verifications of the Standard Theory. For one, besides the intermediate bosons, there was one crucial particle missing, the Brout{Englert{Higgs boson (Englert & Brout, 1964; Higgs, 1964) responsible for the breaking of the electroweak symmetry, which is the source of the masses of quarks, leptons and of the intermediate bosons. The search and the consequent study of the Higgs boson5 in the full range of masses indicated by theory was one of the objectives | actually the most pressing one | of a high energy machine after LEP. In addition, there was the possibility of entirely new particles at higher mass, for which theoretical ideas were developed in the 1980s (see Box 1). In the mid-1980s, the need of a higher energy collider seemed so pressing as to lead Carlo Rubbia to suggest that perhaps one could dismiss LEP construction altogether and jump directly to make a Large Hadron Collider in the LEP tunnel. The idea met with a strong opposition in CERN and was fortunately dismissed by the CERN Management. were stored in two independent storage rings on top of each other. HERA began operating in 1992, with four large experiments: H1, ZEUS, HERMES and HERA-B. Electrons or positrons were collided with protons at a centre of mass energy of 318 GeV. It was the only lepton{proton collider in the world while operating. HERA was closed down on 30 June 2007. 4LEP was located in a tunnel at about 100 m underground, with a circumference of around 27 km, located near CERN, in the region between the Geneva Airport and the Jura mountain.