Standard model; how the Higgs works (Introduction)

by David Turell , Monday, April 14, 2025, 22:18 (4 days ago) @ David Turell

A sneaky look so far:

https://phys.org/news/2025-04-atlas-hood-higgs-mechanism.html

"The detection of longitudinally polarized W boson production at the Large Hadron Collider is an important step towards understanding how the primordial electroweak symmetry broke, giving rise to the masses of elementary particles.

"In 2012, the discovery of the Higgs boson by the ATLAS and CMS collaborations at CERN opened a new window on the innermost workings of the universe. It revealed the existence of a mysterious, ancient field with which elementary particles interact to acquire their all-important masses.

"This process is governed by a delicate mechanism called electroweak symmetry breaking, which was first proposed in 1964 but remains among the least understood phenomena of the Standard Model of particle physics. To probe this critical mechanism in the evolution of the universe, physicists require a very large dataset of high-energy particle collisions.

***

"Using the full proton–proton collision dataset from LHC Run 2, which was collected at an energy of 13 TeV from 2015 to 2018, the team presented the first evidence of a key process involving the W boson—one of the mediators of the weak force.

***

"In the Standard Model of particle physics, the electromagnetic and the weak interactions are two sides of the same coin, unified as the electroweak interaction. It is thought that the electroweak interaction prevailed in the immediate aftermath of the Big Bang, when the universe was extremely hot. But the symmetry between the two interactions somehow got broken, since the carriers of the weak interaction, the W and Z bosons, are observed to be massive; whereas the photon, which mediates the electromagnetic interaction, is massless.

"The breaking of this symmetry is realized in the Standard Model through the Brout-Englert-Higgs (BEH) mechanism. The discovery of the Higgs boson provided the first experimental confirmation of this mechanism. The next step is to measure the properties of the new particle, in particular how strongly it interacts with other elementary particles. These measurements are currently under way, with the aim of confirming that the masses of elementary matter particles are also the result of their interaction with the BEH field.

"But the BEH mechanism also makes other predictions. Two processes in particular must be measured to confirm that the mechanism is indeed as the Standard Model predicts: the interaction between longitudinally polarized W or Z bosons and the interaction of the Higgs boson with itself.

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"For particles, polarization refers to the way in which their spin is oriented in space. Longitudinally polarized particles have their spin perpendicular to the direction of their momentum, something that is only possible for particles that have mass. The existence of longitudinally polarized W and Z bosons (WL and ZL) is a direct consequence of the BEH mechanism, and the way in which these states interact with each other is therefore a very sensitive test of how the electroweak symmetry is broken."

Comment: the Standard Model is an outline of a measurement in progress. The particle zoo is difficult to keep track of.