The Higgs boson and the emergence of the Standard Model of particle physics in the 1970s

The Higgs boson and the emergence of the Standard Model of particle physics in the 1970s

Paul Musset (center), then a representative of the Gargamelle collaboration, stands in the control room of the eponymous bubble room in 1974. Gargamelle provided the first direct evidence of neutral currents in 1973. Credit: CERN

At the dawn of the 1970s, the idea of ​​a standard massive boson was not the bedrock of a unified theoretical model of electromagnetic and weak interactions well established in a field that was still learning to coexist with what we now know as the standard model of particle physics. As various nodal breakthroughs gradually reinforced this theoretical framework, the Brout-Englert-Higgs (BEH) field and its boson have emerged as a promising theoretical model to explain the origin of mass.

In the 1960s, there were remarkably few citations from papers by Sheldon Glashaw, Abdus Salam and Stephen Weinberg on the theory of electromagnetic and weak unified interactions. However, that all changed in 1971 and 1972 when Gerard Hooft and Martinus Veltmann (former employee of CERN) in Utrecht demonstrated that measurement theories using the Brout-Englert-Higgs mechanism to generate masses of measured bosons are reconfigurable, and thus are mathematically consistent and usable To make accurate and reliable calculations of weak interactions. This breakthrough was widely publicized in an influential talk by Benjamin Lee of Fermilab during the ICHEP conference held there in 1972, where he spoke at length about the “Higgs Fields”.

Encouraged, in particular, by CERN theorists Jacques Brentke and Bruno Zumino, Gargamelle’s collaboration prioritized the search for current weak neutral interactions in the CERN neutrino beam, and their representative Paul Musset presented their first direct evidence at a symposium at CERN on July 19, 1973. This attracted support The first experimental standardization of electromagnetic and weak interactions received great interest and close scrutiny, but was generally accepted within a few months. The discovery of neutral current convinced physicists that the emerging Standard Model was on the right track. In a 2013 CERN Courier article, former CERN General Director Luciano Majani said: “At the beginning of the decade, people generally did not believe in the normative theory, although the theory did everything. Neutral current signals have changed that, and since then, it has been On particle physics a standard theory test.

The next breakthrough came in 1974, when two experimental groups working in the United States, led by Sam Ting at Brookhaven and Burt Richter at SLAC, discovered a narrow vector resonance, J/psi, with prominent decay in lepton-antilepton pairs. Several theoretical explanations have been proposed, which we at CERN discussed over the phone in at midnight seminars with Fred Gilman at SLAC (almost 40 years before Zoom!). The winning explanation was that J/psi was a bound state of the charm quark and its antiquark. The existence of this fourth quark was proposed by James Bjorken and Sheldon Glashow in 1964, and Glashow, John Iliopoulos and Maiani in 1970 suggested its use to suppress flavor-changing weak neutral interactions. A visiting scientist at CERN), John Rosner and Lee wrote an influential paper on occult phenomena in 1974, and experiments gradually agreed with their predictions, with final confirmation in 1976.

The attention of most of the theoretical and experimental communities was then drawn towards the search for the massive W and Z vector bosons responsible for the weak interactions. This spurred the construction of high-energy Hadron colliders and led to the discovery of the W and Z bosons at CERN in 1983 by a team led by Carlo Rubbia.

However, it seemed to Mary K. Gillard, Dimitri Nanopoulos and myself at CERN that the main question was not the existence of massive weak vector bosons, but rather the scalar Higgs question. boson which enabled the Standard Model to be both physically consistent and mathematically computed. At that time, it was possible to count the number of papers on the Higgs boson phenomenon with the fingers of one hand, so we proceeded to describe its apparent profile in some detail, covering a wide range of possible masses. Among the production mechanisms we considered was the potential production of the Higgs boson in association with the Z boson, which generated great interest in the days of LEP 2. Among the Higgs decay patterns we calculated was that in a pair of photons. This characteristic channel is particularly interesting because it is generated by quantum effects (ring plots) in the Standard Model.

Although we were convinced that there must be something like the Higgs boson, our research ended with a cautionary note that was somewhat of a tongue: “We apologize to the experiment for having no idea what the Higgs boson mass was… making sure it was paired with other particles, except that they’re probably all very small.” For these reasons, we don’t want to encourage large experimental searches for the Higgs boson, but we feel that people who are conducting experiments prone to the Higgs boson should know how it might happen.”

This warning was in part because the leading physicists of the time (Dmitriy and I were under 30 at the time) looked at the ideas surrounding electroweak symmetry breaking and the Higgs boson with jaundiced eyes. However, over time, the discovery of the massive W and Z, the presence or absence of the Higgs boson raised the experimental agenda, and no plausible alternative theoretical suggestions for the existence of such a Higgs boson emerged. Experimenters, first at the LEP and later at Tevatron and LHC, increasingly focused on the search for the Higgs boson as the final building block of the Standard Model, culminating in discovery on July 4, 2012.

Homing a Higgs boson with a charm quark

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