Martin Perl and the Tau Lepton

‘Martin L. Perl, a professor at the Stanford Linear Accelerator Center (SLAC), [was] awarded the 1995 Nobel Prize in physics ... for his 1975 discovery of a new elementary particle known as the tau lepton. ... The tau lepton is a superheavy cousin of the electron, the carrier of electrical current in household appliances. The two particles are identical in all respects except that the tau is more than 3,500 times heavier than the electron and survives less than a trillionth of a second, whereas the electron is stable.

In the mid-1970s, working at the Stanford Positron-Electron Asymmetric Ring (SPEAR) in collaboration with 30 other physicists from SLAC and Lawrence Berkeley National Laboratory, Perl began to find events recorded by the detector that could not be explained by any of the known subatomic particles. After more than a year of analysis, Perl was able to convince the rest of his research team that they were in fact observing a new and different type of elementary particle, which he named the 'tau'.

In the standard model of particle physics, the elementary building blocks of matter appear in families, with two leptons and two quarks in each. Until Perl's discovery there were only two such families known to exist.

The tau turned out to be the first-discovered member of a third quark-lepton family. In 1976, the second particle in the family, the bottom quark, was discovered by scientists at Fermi National Accelerator Laboratory. It was not until 1995 that Fermi scientists discovered the third member, the top quark.

Addressing the question of the usefulness of the discoveries like that of the tau lepton, Perl said, "The use of the discovery of basic particles is indirect. We have found that everything of a complicated nature is made from three basic families of particles. Eventually, this will lead to an improved understanding of energy and time. From that we hope will come new ideas that lead to applications like a source of cheap energy which is truly safe."

Perl received his Ph.D. in 1955 from Columbia University ... [and] has been on the faculty at SLAC since 1963.'

Resources with Additional Information

Additional information about Martin Perl and his research is available in full-text and on the Web.

Documents:

The Discovery of the Tau Lepton and the Changes in Elementary Particle Physics in 40 Years, DOE Technical Report, 2003

The Discovery of the Tau, 1975 - 1977: A Tale of Three Papers, 1993

1. Evidence for Anomalous Lepton Production in e⁺ - e^- Annihilation; Physical Review Letters, Vol. 35, Issue 22, 1489-1492; 1975

2. "Properties of Anomalous e-mu Events Produced in e+e-Annihilation"; Physics Letters, Vol. 63B, Issue 4, 466; August 16, 1976

3. "Properties of the Proposed tau Charged Lepton"; Physics Letters, Vol.70B, Issue 4, 487; October 24, 1977

The Discovery of the Tau Lepton: Part 1, the Early History Through 1975; Part 2, Confirmation of the Discovery and Measurement of Major Properties, 1976--1982, DOE Technical Report, 1994

Status of Heavy-lepton Searches, DOE Technical Report, 1981

Review of Heavy Lepton Production in e⁺e^- Annihilation, DOE Technical Report, 1977

Threshold and Other Properties of U Particle Production in e⁺e^- Annihilation, DOE Technical Report, 1976

Additional Web Pages:

First Evidence of a Third Family of Fundamental Particles, DOE Office of Science

1995 Nobel Prize in Physics – Tau: The 3rd Electron-like Particle

Beam Line, "Discovery of the Tau: The Role of Motivation & Technology in Experimental Particle Physics", Winter 1995, Vol. 25, No. 4, pages 4 - 27

Perl compares the discovery of the tau with the discovery of the other leptons: electron, muon, electron neutrino, and muon neutrino.

Martin L. Perl, Professor, SLAC

Martin Perl, Stanford Report, October 3, 2001