Report to the 1999 General Assembly for 1996-99
Research in particles and fields is carried out with broad international participation. Experimental facilities are located at large accelerator centers that provide a focus for research in the field. The membership of C11 is geographically distributed to broadly represent the regions, countries and centers involved in the field.
The composition of C11 approved by the 1984 IUPAP General Assembly is as follows: China 1; Western Europe 4; Japan 1; USA 2; the former Soviet Union and Eastern Europe 2; and the rest of the world ("fourth region") 2. In addition, in 1986 the Executive Council of IUPAP appointed as Vice Chairman an additional member from an industrial background.
The European members of C11 are rotated as follows: three of the four members are rotated among the large countries - France, Germany, Great Britain and Italy, and the fourth member is chosen from the other European countries. There are two members from the USA and the former Soviet Union because of the traditionally large concentration of physicists and facilities in those countries.
There is important intellectual overlap between C11 and several other commissions: Cosmic Ray Physics (C4), Nuclear Physics (C12) and Astrophysics (C19). C11 has an Associate member from each of these commissions who are invited to C11 meetings and give a report on the activities of their commission. The creation of PANAGIC will provide an important new link between these commissions. PANAGIC is a new subcommittee covering the emerging areas of non-accelerator or particle astrophysics that overlap the physics of these commissions.
Commission C11 has an annual meeting which is held at the large IUPAP sponsored conferences: ICHEP in the even years and LP in the odd years. The rest of the business is conducted by correspondence and email. The major conferences during the past three years were LP97 in Beijing, ICHEP98 in Vancouver and LP99 that will be held at Stanford, CA USA. Attendance was very high, international representation good and balanced in both speakers and delegates. These meetings provide the intellectual focus for the field and are largely regarded as the premier meetings in the field.
The general aims of the Commission are:
ICFA meets twice per year (once per year, the meeting is attended by the directors of the main HEP accelerator laboratories) and has four active subpanels. The chairman of C11 serves as an ex-officio member of ICFA. ICFA has an impressive record of leadership in the development of future accelerators.
IUPAP Sponsored Conferences (1997-99)
1997 International Symposium on Lepton Photon Interactions (LP97) was held at DESY in Hamburg, Germany from July 28 - August 1, 1997
1998 International Conference on High Energy Physics (ICHEP98) was held in Vancouver, Canada from July 23 - 29, 1998
1998 Particle Accelerator Conference was held in Dubna, Russia in September 1998
1999 International Symposium on Lepton Photon Interactions (LP99) will be held at Stanford, CA USA from August 9-14, 1998
C onferences sponsored by C11 have met the IUPAP guidelines concerning international participation, free circulation of scientists, visas, registration fees, etc. We have received no complaints during this term.
New Developments in the Field
Elementary particle physics is the study of the basic constituents of nature and to the forces between them. The center point of the field for the past two decades has been the standard model. In electroweak theory, three massive particles mediate the weak force: the charged W+ and W- particles and the neutral Zo particle, having masses about 100 times that of the proton, join the photon as the carriers of the electroweak force. The intrinsic strengths of these carriers are identical, but the massive nature of the W and Z particles limits their range to very short distances, a consequence of the uncertainty principle. In collisions at relatively low energies, the particles do not approach each other sufficiently closely for W or Z exchange to occur. However at energies of around 100 GeV close encounters are common, showing electroweak unification. The most spectacular experimental verification of this theory was the discovery of the W and Z particles at CERN in 1983. Electroweak theory has now been tested to high precision and these many tests, especially at the CERN LEP facility have been a very important advance during the past few years, though they have not yet led to the physics beyond the standard model.
Electroweak theory and Quantum Chromodynamics (QCD) make up what is called the standard model of particle physics. Although this model works very well it suffers from a number of defects. There are rather a lot of arbitrary numbers, which are not intrinsic to the theory but have to be obtained from experiment. The theory predicts nonsensical results at energies slightly higher than now available - equivalent to processes having a probability greater than unity! In addition the theory requires that the W and Z particles, like the photon, should be massless. A mechanism which gives mass to particles by allowing them to interact with a field was first suggested by Peter Higgs. This would have a carrier object - the Higgs boson, which has so far not been detected. The search for the Higgs or other explanations of mass represent the central motivation for the Large Hadron Collider (LHC) being built at CERN.
Symmetries play a significant role in particle physics. Lack of symmetry has proven to give us strong guidance into new physics. For example, parity violation led to the theory of weak interactions. Similarly, it was later found that the product CP was violated in some weak interactions involving neutral kaons. This CP violation was small. Its origin is not fully understood, but it is believed to be one of the ingredients required in the very early universe to produce the present tremendous preponderance of matter over antimatter. Two "B factories'", one in Japan and one in California will start operating in 1999, and will investigate the origin of CP violation, as well as observing oscillations in the Bo meson system, analogous to Ko oscillations which have been observed since the 1960s. The first direct evidence for T violation was observed in the neutral kaon system at CERN and at Fermilab. The product CPT is believed to remain conserved.
The major thrusts of theoretical physics the past few years include theories that unite the electroweak and strong forces. These are known as grand unified theories, GUTs. Some possible consequences of these theories include baryon instability (inspiring searches for proton decay), magnetic monopoles and neutrino mass. Another theory which is receiving a great deal of attention is supersymmetry, which unites the building blocks the quarks and leptons with the force carriers. This requires new partner particles for all these objects, none of which has so far been discovered.
Finally, a whole branch of theory has developed around superstrings, which require supersymmetry, and treat particles as excitations of strings. This avoids objectionable infinities, which arise when particles are treated as point objects. Superstring theories do however require more than the usual three space and one time dimension. The unobserved dimensions are assumed to be compactified - curled up so that they are too small to be observable. Superstring theories have the potential to provide a quantum theory of gravity and unite it with the other forces, and there is much activity in this field.
The most exciting development in the past year is very strong evidence for neutrino oscillations in atmospheric neutrinos. . These neutrino oscillations can only occur if neutrinos have mass, and such mass could be significant for cosmology, as part of the dark matter problem. Not all experiments are fully compatible with each other, but it seems likely that this will be settled within the next couple of years. The origin of CP violation will be discovered within the next few years from the new B factories. The Fermilab Tevatron has been upgraded and the large hadron collider, LHC, being constructed at CERN, will start operations in around 2005. Prospects in the field of research of particles and fields seems especially promising for the future with the combination of theoretical advances, and the new experimental facilities being developed.
B. Barish, C11 Chairman