The Higgs boson and the rise of the standard model of particle physics in the 1970s

The Higgs boson and the rise of the standard model of particle physics in the 1970s

Paul Musset (center), then a representative of the Gargamelle collaboration, stood in the control room of the balloon chamber of the same name in 1974. Gargamel provided the first direct evidence of the existence of neutral currents in 1973. Credit: CERN

At the dawn of the 1970s, the idea of ​​a massive scalar boson as the cornerstone of a unified theoretical model of weak and electromagnetic interactions was still not anchored in a field that is still learning to live with what we now know as the standard model of particle physics. As the various breakthroughs of the decade gradually consolidate this theoretical framework, the Braut-Englert-Higgs (BEH) field and its boson emerge as the most promising theoretical model for explaining the origin of mass.

In the 1960s, there were remarkably few citations to articles by Sheldon Glashaw, Abdus Salam, and Steven Weinberg on the theory of combined weak and electromagnetic interactions. However, all this changed in 1971 and 1972, when in Utrecht Gerard ‘t Hoft and Martinus Weltman (former CERN employee) proved that calibration theories using the Broute-Englert-Higgs mechanism to generate calibration boson masses are re-normalized, and are therefore mathematically consistent and can be used to perform reliable and accurate calculations for weak interactions. This breakthrough was widely publicized in an influential speech by Fermilab’s Benjamin Lee at the ICHEP conference in 1972, in which he spoke at length about the Higgs Fields.

Encouraged in particular by CERN theorists Jacques Prentchi and Bruno Zumino, Gargamelle’s collaboration gave priority to the search for low neutrino current interactions in CERN’s neutrino beam, and their representative Paul Musset presented the first direct evidence of them at a CERN seminar on 19 July 1973. This first experimental support for the integration of electromagnetic and weak interactions attracted great interest and careful consideration, but was generally accepted within a few months. The discovery of neutral current convinced physicists that the nascent standard model was on the right track. Former CERN CEO Luciano Mayani, quoted in a 2013 CERN Courier article, put it this way: “At the beginning of the decade, people usually didn’t believe in standard theory, even though theory had done everything. Neutral current signals changed that. Since then, particle physics has had to test standard theory. “

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 pronounced lepton-antilepton pair decays. Many theoretical interpretations were offered, which we at CERN discussed over the phone in excited midnight seminars with Fred Gilman at SLAC (almost 40 years before Zoom!). The winning interpretation was that J / psi is a related state of the charming quark and its antiquark. The existence of this fourth quark was proposed by James Bjorken and Sheldon Glashaw in 1964, and its use to suppress taste-changing neutral weak interactions was suggested by Glashow, John Iliopoulos and Maiani in 1970. Mary K. Gayard (long-time visiting scientist) at CERN), John Rosner and Lee wrote an influential article on the phenomenology of charm in 1974, and the experiments gradually followed their predictions, with final confirmation coming in 1976.

Then the attention of most theoretical and experimental communities was focused on the search for the massive W and Z vector bosons responsible for weak interactions. This motivated 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 Rubia.

However, it seemed to Mary K. Gayard, Dimitri Nanopoulos and me at CERN that the key issue was not the existence of massive weak vector bosons, but rather that of scalar Higgs. boson which allowed the standard model to be physically consistent and mathematically computable. At that time, the number of articles on the phenomenology of the Higgs boson could be counted on the fingers of one hand, so we set out to describe its phenomenological profile in some detail, covering a wide range of possible masses. Among the production mechanisms we looked at was the possible production of the Higgs boson in conjunction with the Z boson, which sparked considerable interest in the days of LEP 2. Among the Higgs decay regimes we calculated was the photon pair. This distinctive channel is particularly interesting because it is generated by quantum effects (cycle diagrams) in the standard model.

Despite our belief that something like the Higgs boson should have existed, our article ended with a warning note that was a bit ridiculous: “We apologize to the experimenters for not having an idea of ​​the mass of the Higgs boson… in its relations with other particles, except that they are probably all very small. For these reasons, we do not want to encourage large-scale experimental research on the Higgs boson, but we believe that people conducting experiments that are vulnerable to the Higgs boson should know how it can turn out. ”

This caution was partly because the senior physicists of the time (Dimitri and I were under 30 at the time) were looking at ideas about breaking electroweak symmetry and the Higgs boson with rather yellowish eyes. However, over time, the massive W and Z were discovered, the existence or absence of the Higgs boson rose to the experimental agenda, and no plausible alternative theoretical assumptions about the existence of something like the Higgs boson emerged. Experimentalists, first in LEP and later in Tevatron and LHC, focused more and more on the search for the Higgs boson as the last building block of the standard model, culminating in the discovery on July 4, 2012.

Focusing on the interaction of the Higgs boson with the quark of charm

Quote: The Higgs boson and the rise of the standard model of particle physics in the 1970s (2022, May 12), retrieved on May 13, 2022 from higgs-boson-standard-particle- physics.html

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