The arduous quest to find the shape of the electron’s charge

Subject : Science and technology

Section: Msc

Concept :

Physicists use extreme precision tests to search for flaws in the Standard Model. A new study used a strong electric field in a molecule to measure the electric dipole moment of its valence electrons, and concluded by finding no evidence of ‘new physics’.
The result precludes the existence of certain hypothetical particles

Standard Model of Elementary Particle Physics

The standard model of elementary particles is a theoretical construct in physics that describes particles of matter and their interaction.
It describes the elementary particles of the world as being connected by mathematical symmetry, just as two objects are connected by bilateral (left-right) symmetry.
These are mathematical groups generated by continuous transformations from, say, one particle to another.
According to this model there are a finite number of fundamental particles which are represented by the characteristic “eigen” states of these groups.
The particles predicted by the model, such as the Z boson, have been seen in experiments.
The last to be discovered, in 2012, was the Higgs boson which gives mass to the heavy particles.

Why is the Standard Model believed to be Incomplete?

Because it gives a unified picture of only three of the four fundamental forces of nature — electromagnetic, weak nuclear, strong nuclear and gravitational interactions — it totally omits gravity.
So, in the grand plan of unifying all forces so that a single equation would describe all the interactions of matter, the standard model was found to be lacking.
Also, it does not include a description of dark matter particles.
So far these have been detected only through their gravitational pull on surrounding matter.

How are the Symmetries related to Particles?

The symmetries of the standard model are known as gauge symmetries, as they are generated by “gauge transformations”.
Gauge transformations are a set of continuous transformations (like rotation is a continuous transformation). Each symmetry is associated with a gauge boson.
For example, the gauge boson associated with electromagnetic interactions is the photon. The gauge bosons associated with weak interactions are the W and Z bosons. There are two W bosons — W+ and W-.