Within the standard model of particle physics, the evidence for electrons and quarks being massless particles before their interaction with the Higgs field is primarily based on theoretical considerations and experimental observations. Here are the key points:
Theoretical Framework: The standard model incorporates a mechanism known as "electroweak symmetry breaking" to explain the origin of particle masses. According to this framework, prior to symmetry breaking, both electrons and quarks are described as massless particles.
Higgs Mechanism: The Higgs mechanism, proposed in the 1960s by Peter Higgs and others, explains how certain particles acquire mass within the standard model. It introduces a scalar field called the Higgs field, which permeates all of space. When particles interact with the Higgs field, they acquire mass. Electrons and quarks are postulated to gain mass through their interactions with the Higgs field.
Discovery of the Higgs Boson: In 2012, the Large Hadron Collider (LHC) at CERN announced the discovery of a particle consistent with the Higgs boson, which is associated with the Higgs field. This discovery provided experimental confirmation of the Higgs mechanism and its role in the generation of particle masses.
Precision Electroweak Measurements: Measurements of the properties of particles, such as their masses, electric charges, and interaction strengths, have been performed with high precision. These measurements are in agreement with the predictions of the standard model, including the postulate that electrons and quarks are initially massless.
It's important to note that while the standard model provides a successful description of many observed phenomena, including the masses of particles, it is not a complete theory of particle physics. There are still unanswered questions, such as the origin of particle masses, the nature of dark matter, and the unification of fundamental forces, which are subjects of ongoing research.
In summary, the evidence supporting the conclusion that electrons and quarks are initially massless particles within the standard model is based on the theoretical framework of electroweak symmetry breaking, the Higgs mechanism, the discovery of the Higgs boson, and the agreement between experimental measurements and model predictions.