The standard model of particle physics gets a jolt
- May 10, 2022
- Posted by: OptimizeIAS Team
- Category: DPN Topics
The standard model of particle physics gets a jolt
Subject: Science and Technology
Section: Basic Science
Context: The Collider Detector at Fermilab (CDF) Collaboration now reports a precise measurement of the W boson mass
In physics, the W and Z bosons are the elementary particles that mediate the weak force. Their discovery has been heralded as a major success for the Standard Model of particle physics.
The W particle is named after the weak nuclear force. The Z particle was semi-humorously given its name because it was said to be the last particle to need discovery. Another explanation is that the Z particle derives its name from the fact that it has zero electric charge.
Two kinds of W bosons exist with +1 and −1 elementary units of electric charge; the W+ is the antiparticle of the W−. The Z boson (or Z0) is electrically neutral and is its own antiparticle. All three particles are very short-lived with a mean life of about 3 × 10−25 seconds.
The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics.
The Higgs boson was the last missing component of the model. After observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model.
The observation of the Higgs boson at the Large Hadron Collider has validated the last missing piece of the standard model (SM) of elementary particle physics
Z bosons are the particles that mediate the weak nuclear force, and they can decay into any of the known quarks and leptons except for the top quark.
What is Z boson and W boson?
W and Z bosons are a group of elementary particles. The Z boson is a neutral elementary particle which – along with its electrically charged cousin, the W – carries the weak force. They are bosons, which mean that they have a spin of 0 or 1.
Both had been found in experiments by the year 1983. Together, they are responsible for a force known as “weak force.” Weak force is called weak because it is not as strong as the strong force. Discovered in 1983 by physicists at the Super Proton Synchrotron at CERN, the Z boson is a neutral elementary particle. Like its electrically charged cousin, the W, the Z boson carries the weak force.
Z boson: the weak force
Like its electrically charged cousin, the W, the Z boson carries the weak force. The weak force is essentially as strong as the electromagnetic force, but it appears weak because its influence is limited by the large mass of the Z and W bosons.
Inspired by the success of quantum electrodynamics, in the sixties, Sheldon Glashow, Abdus Salam and Steven Weinberg developed the similar but more general, ‘electroweak’, theory in which they predicted these three particles and how they mediated the weak interactions.
They were given the Nobel prize for their efforts in 1979. The W boson was first seen in 1983 at CERN, located in the Franco-Swiss border. Unlike the photon, which is massless, the W bosons are quite massive, which results in the force they mediate — the weak force — being very short ranged.
Z particle (subatomic particle), massive electrically neutral carrier particle of the weak force that acts upon all known subatomic particles. It is the neutral partner of the electrically charged W particle.
Experimental measurements and theoretical predictions for the W boson mass.
Why is the standard model believed to be incomplete?
The standard model is thought 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. The other gap in the standard model is that it does not include a description of dark matter particles. So far these have been detected only through their gravitational pull on surrounding matter.
The recent experiment which measured the mass of the W boson as 80,433.5 +/- 9.4 Mev/c2 is more than what is expected from the standard model. The expected value using the standard model is 80,357 +/- 8 MeV/c2. This implies the incompleteness of the standard model description
Dark matter is composed of particles that do not absorb, reflect, or emit light, so they cannot be detected by observing electromagnetic radiation. Dark matter is material that cannot be seen directly.
A gauge boson is a bosonic elementary particle that acts as the force carrier for elementary fermions. Elementary particles, whose interactions are described by a gauge theory, interact with each other by the exchange of gauge bosons, usually as virtual particles.
This mass discrepancy of the W boson needs to be checked and confirmed to the same accuracy by other research facilities.