10/05/1995 07:00:00

Caltech Physicist Shares Prize from European Physical Society for Role in Finding Gluons

PASADENA—Caltech Professor of Physics Harvey Newman and his collaborators on the MARKJ physics project shared a special prize in July from the European Physical Society with three other research groups "for establishing the existence of the gluon."

Gluons are the fundamental packets of energy that bind together quarks—the fundamental building blocks of matter—to form more complex particles such as pions and kaons, and the protons and neutrons that make up the core of every atom. Gluons carry the "strong force" that, along with gravity, electromagnetism, and the weak force, make up the four fundamental forces of nature.

The scientists proved that gluons exist by means of the MARKJ project, which operated at the DESY laboratory in Hamburg, Germany, from 1978 to 1986. The experiment succeeded in accurately measuring the energy and direction of jets of particles produced in high-energy collisions between electrons and positrons. Normally such high-energy collisions produce quarks and antiquarks, which appear as two jets of particles. But sometimes the collisions also produce a third jet, clearly separated from the other two, that originates from a high-energy gluon.

Newman led the team of physicists that was able to isolate events in which a third jet was present, and to show that both the rate of production and the shape of the jets agreed with predictions based on the theory of quantum chromodynamics. This was the first direct observation of gluons.

The MARKJ experiment used a "calorimetric" detector that surrounds the point where the electrons and positrons collide and annihilate each other. It measured the energy of jets by sampling the energy deposited in layers of a plastic scintillator interleaved with layers of lead and iron.

The work was done by a collaboration of 57 physicists from the University of Aachen in Aachen, Germany; the DESY Laboratory in Hamburg, Germany; MIT in Cambridge, Massachusetts; the NIKHEF Laboratory in Amsterdam, Holland; the University of Madrid in Spain; and the University of Beijing in China. Newman was cospokesman for the experiment, and headed the data analysis effort that led to the gluon discovery.

Contact: Jay Aller (818) 395-3631 aller@caltech.edu

Written by John Avery