The W boson part III
Experiment and Discovery

How do we recognize a W or Z boson?

How fast will the W and Z bosons decay?

Short-lived particles can only be detected indirectly by decay products.

The large masses of the bosons will cause them to decay much more quickly than lighter particles.

Decay was expected to proceed in less than 10-24 seconds.

Recognizing a W or Z boson...

Decay products of a Z0 boson

There are many different modes of decay.

The majority of which are quark-antiquark decays.

Unfortunately, these decays are much harder to separate from other collision processes, and are not useful in identification.

There are two characteristic decays (~6% decays):

Electron and positron.

Muon and antimuon.

Recognizing the W or Z boson...

Decay products of a W- and W+ bosons.

Again, the majority of decays are quark-antiquark, and not helpful in identification.

There are three characteristic decays for the W- (~1/12 decays):

Electron and antineutrino.

Muon and antineutrino.

Tau and antineutrino.

(respective decays for the W+ can be found by interchanging particle with antiparticle)

The UA1 Experiment

The search for the W and Z bosons took place at CERN , in 1981 using the newly finished proton-antiproton collider.

The collaboration was led by Carlo Rubbia, and incorporated groups from most European countries as well as some from the US, and brought together a large number of physcists, including our very own Dr. Wahl.

Rubbia and Simon van der Meer, who made the proton-antiproton collider possible, shared a nobel prize for their work.

UA1

In the collider, W and Z bosons are produced by quark-antiquark annihilations.

To produce W and Z bosons with a mass of 80-90 GeV, the accelerated protons must have an energy of 270 GeV.

.

UA1

The detector:

Central detector:

Electromagnetic calorimeter:

Hadron calorimeter:

Forward detectors:

Muon detector:

The Detector:

The Discovery of the W

A W event observed by the UA1 detector in 1982.

A high transverse momentum electron is indicated by the

arrow.

The Discovery of the Z0

The production of a Z0 event in the UA1 detector. In May 1983, the central detector of UA1 revealed the signature of the Z particle as it decayed into an electron-positron pair.

UA2

A seperate experiment called UA2 was also searching for W and Z bosons.

It was led by Pierre Darriulat, and was being conducted at the same time at CERN, and provided confirmation for the results.

Conclusion:

In January 1983 the discovery of the W was publicly announced, and in June of 1983 the discovery of the Z was also made public.

The observed behavior had all been predicted by the electroweak theory, and the two independent experiments provided confirmation for the theory.

Rachel Goodlett

2003-11-18T18:22:23