The SIF awards 2011 Enrico Fermi prize
The 2011 Enrico Fermi prize of the Italian Physical Society (Società Italiana di Fisica, SIF) has been awarded, for work in the field of experimental particle physics, to Dieter Haidt of the DESY Laboratory at Hamburg and to Antonino Pullia of the University of Milano Bicocca and Istituto Nazionale di Fisica Nucleare, “for their fundamental contribution to the discovery of weak neutral currents with the Gargamelle bubble chamber at CERN”.
The prize is awarded yearly to members of the society who especially honour physics by their discoveries. The prize was first awarded in 2001, to commemorate the centenary of the great scientist’s birth. The award was presented at the opening session of the 97th SIF National Congress, at the University of L’Aquila, Coppito, on 26 September.
The fundamental forces between the elementary constituents of matter, which we call elementary interactions, are very few in number and, we think today, are probably expressions of a unique interaction.
Atoms are made of a nucleus with positive electric charge and negative electrons that attract each other. Quantum mechanics describes the electromagnetic interaction as mediated by the exchange of photons, emitted by one of the charges and absorbed by another. As photons carry no electric charge, the electromagnetic current is neutral.
The nuclear weak interaction is responsible for the activity of the Sun and the stars. A simple weak process is the decay of a neutron into a proton, an electron and an antineutrino. It was Fermi, in 1934, who developed the first theory of weak interactions; in which the neutron emits the charged electron-antineutrino pair, in an analogy to the photon emission in electromagnetism. Thus, the concept of weak charged currents was developed.
Glashow (in 1961), Salam (in 1968) and Weinberg (in 1967) developed a unified model of electromagnetic and weak interactions. It postulated the existence of particles mediating these interactions, the vector bosons W+, W– and Z0. Three of them were necessary: two charged, one neutral. The existence of the latter would imply a new class of phenomena, the weak neutral currents, that no one had observed.
In the 1960s CERN was one of the world leading laboratories for high intensity neutrino beams. The ideal detector for physics on such beams was the ‘gigantic’ bubble chamber, conceived by André Lagarrigue, which was approved by the French CEA in 1965. Named after the mother of Gargantua (a giant in a story by François Rabelais), Gargamelle measured 4m by 2 m diameter, weighed 1000 tonnes, and contained 18 tonnes of liquid Freon.
The Gargamelle Collaboration on neutrino physics (Aachen, Brussels, CERN, Ecole Polytechnique, Milan, Orsay and UCL) was formed in 1968, under Lagarrigue’s leadership.
In July 1973, a groundbreaking discovery was announced in CERN’s main auditorium: the Gargamelle collaboration had found the first direct and certain evidence of the weak neutral current.
This was the first great discovery to be made at CERN, beating the competing HPWE experiment at Fermilab, in the USA. The three vector bosons were to be discovered ten years later, again at CERN, in the Carlo Rubbia lead UA1 experiment.
To be sure that a discovery is really such it is necessary to establish, beyond any reasonable doubt, that the observed effects are really not due to a more mundane effect – in this case, neutron interactions, which are very similar. Haidt and Pullia contributed in an essential way to the difficult data analysis which was necessary to reach a conclusion in this case.
Two years ago, the Gargamelle Collaboration was also awarded the prestigious European Physical Society High Energy and Particle Physics Prize ‘”for the observation of the weak neutral current interaction”.
For more information on the Enrico Fermi Prize, please visit the Italian Physical Society website.
