The W boson’s heavy cousin

The W’ boson is a hypothetical, much more massive, cousin of the W boson. This article describes a new search for it.

In the late 1960s, theorists were able to mathematically show that the electromagnetic and weak nuclear forces were actually two facets of a single common force, now called the electroweak force. This new theory postulated two new particles called the W and Z bosons. The theory was vindicated in 1983 with the discovery of both of them by the UA1 experiment at CERN.

In the intervening years, scientists discovered quarks. Quarks are located at the center of atoms. Nestled inside protons and neutrons, two specific kinds of quarks (called up and down) are primary building blocks of the universe.

However, scientists also discovered that, in addition to the ubiquitous up and down quarks; other types of quarks exist that are carbon copies of the common ones. The charm quark is very similar to the up quark, except heavier. The top quark, discovered at Fermilab in 1995, is also similar to the up quark but even heavier still. (The down quark also has two cousins, the strange quark and the bottom quark.)

Given that duplicates (scientists call them “generations”) of the quarks exist; it is natural to wonder if there are heavier cousins of the W & Z bosons. While wholly hypothetical, these particles have names: the Z’ and W’ (pronounced W-prime and Z-prime) bosons. In a popular scenario, these particles are essentially identical to their lighter relatives (although there have been alternate proposals).

DZero scientists recently searched for the W’ boson. In order to maximize the chances of finding this theoretical particle, they looked for the specific decay mode in which the W’ boson decayed into a top/bottom and quark/antiquark pair.

Unfortunately, the data didn’t support the hypothesis of the existence of the W’, but the measurement did increase the range of excluded possible W’ boson mass by about 15 percent. This increase is a significant advance in our understanding of the universe.

–Don Lincoln

These physicists from Brown University were responsible for this analysis.

A successful particle experiment only analyzes a tiny fraction of the total number of collisions in the detector. Picking which collisions to record is one of the most important responsibilities on the experiment and these physicists are responsible for getting it right.