The world of particle physics is bustling with new discoveries, most recently the precise measurement of the mass of the W boson by researchers from Collider Detector at Fermilab (CDF) Collaboration based in the US. This revolutionary discovery however, deviates from the customary estimates presented by the standard model of particle physics.
About the W Boson
The W boson, first witnessed in 1983 at CERN, a nuclear and particle physics laboratory located on the Franco-Swiss border, stands out from other particles due to its massive size. Unlike the photon which is massless, the W boson exhibits substantial mass, making the weak force it mediates extremely short-ranged.
The W-plus and W-minus, variants of the W boson, are not only massive but also carry electric charge. This characteristic allows them to facilitate interactions such as the transformation of a neutron into a proton, a key process in beta decay, a radioactive interaction happening in the sun.
Understanding the Standard Model of Elementary Particle Physics
The standard model of elementary particles is a theoretical construct that articulates the connectivity of particles of matter and their interaction. It dictates that these particles are interconnected through mathematical symmetry.
Based on this model, there is a finite number of fundamental particles represented by characteristic eigen states. The model has accurately predicted the existence of several particles like the Z boson, and the Higgs boson which was discovered last in 2012 and contributes to the mass of heavy particles.
The Incomplete Standard Model
Despite the merits of the standard model, it is widely considered incomplete. This is due to its incapability to present a harmonized picture of all four fundamental forces of nature: electromagnetic, weak nuclear, strong nuclear, and gravitational interactions. Moreover, it fails to encompass a description of dark matter particles, which have so far only been detected through their gravitational pull.
The Connection between Symmetries and Particles
The symmetries of the standard model, known as gauge symmetries, are generated by gauge transformations – continuous transformations similar to rotation. Each symmetry is linked to a gauge boson. The photon is associated with electromagnetic interactions while W and Z bosons are connected with weak interactions.
UPSC Civil Services Examination, Previous Year Questions
In 2013, UPSC potential candidates were asked about the significance of discovering the Higgs boson particle. The correct answer was that its discovery will enable us to understand why elementary particles possess mass.
Understanding the Electro-Weak Force and the Higgs Boson
The Unified Theory’s basic equations outline the electro-weak force and its associated force-carrying particles, namely the photon, and the W and Z bosons. This theory, proposed by theorists Robert Brout, Francois Englert and Peter Higgs, leads to the idea of an “Higgs field” that pervades the universe and gives mass to the W and Z bosons when they interact with it.
Post Big Bang, the Higgs field was zero but increased spontaneously as the universe cooled down below a crucial temperature point. This led to particles interacting with it and acquiring mass. The more a particle interacts with this field, the heavier it becomes. The Higgs boson is the evident manifestation of the Higgs field. Fundamentally, particles not interacting with this field, like the photon, are left with negligible mass.
