C11. Commission on Particles and Fields

Report to the Council and Commission Chair Meeting, Mexico, September 28-29, 2001

Peter I. P. Kalmus

This Commission meets only once per year, always during the major international conference. The rest of our business is conducted electronically. This year we met at the Lepton-Photon Symposium in Rome at the end of July 2001.

We heard reports on the previous conference (held last year in Osaka), on this year's conference, progress report on the next two conferences, and suggestions for conferences further in the future.

We discussed proposals for possible sites for future meetings, and recommend to IUPAP that the 2004 International Conference on High Energy Physics should be held in Beijing. At previous meetings we had already determined that the next two meetings should be in Amsterdam in 2002, and at Fermilab in the USA in 2003.

Following guidance from IUPAP we considered (via email) suitable candidates for the next Chair and Secretary of C11, to serve from 2002 to 2005, and came up with recommendations. Recommendations for other new members will be considered during the next months, following the timetable suggested by IUPAP. The actual decisions will be made at the IUPAP General Assembly in Berlin in October 2002.

We had a verbal report from C19 (Astrophysics) and a short written report from C12 (Nuclear Physics).

We discussed whether future Conference Proceedings should continue to be in the form of traditional bound books or change to electronic format. For the Amsterdam Conference we accepted the proposal from the organisers that they produce 300 bound copies as archive material for libraries, but that participants should receive the proceedings on a CD-ROM. The latter costs about 1 US dollar per copy, as against about 50 dollars for a printed volume.

The past year has been an exciting one for particle physics, and several interesting new results were presented at the Rome meeting. Lepton-Photon Symposia do not have parallel sessions, there are only plenary sessions with invited speakers. Written contributions, of which there were about 350, were available beforehand to the invited speakers, some of whom acted as rapporteurs. The meeting which was held in the Auditorium della Tecnica in the EUR district in the South of Rome was well organised. One innovation was that all speakers were required to present their slides in electronic PDF format, either by producing them electronically, or by having their transparencies scanned in. Scientific secretaries were very helpful in facilitating this, and as a result talks were available on the Web in almost real time (Click on "Slides" in http:// www.lp01.infn.it). Following the tradition of the past few years there was also a public lecture "The Quantum and the Cosmos". I was unable to see this as it coincided with an ICFA meeting, but I was told that it was an excellent presentation, using two screens (English and Italian). This can also be seen on the above website.

There were many interesting new results ranging from proton structure to the possibility of large extra dimensions in the universe. I will just mention two.

CP violation (which distinguishes matter from antimatter) was first seen in 1964. Up till this year it was only seen in the decay of neutral kaons, and the violation was small: a fraction of a percent difference between particles and antiparticles. Reports at this conference by international groups from the Belle experiment in Japan and BaBar in the USA, using the new "B meson factories" have now definite evidence of CP violation in the neutral B meson system, where the asymmetry is much greater. In addition "direct" CP violation as well as "indirect" has been seen in these experiments, and also in the neutral kaon system at CERN and Fermilab*. These results narrow down the theoretical suggestions and are likely to be a significant step towards telling us why matter and antimatter, which presumably must have existed in equal quantities at the time of the Big Bang, did not fully annihilate, leading to the present universe and our existence.

Interesting results in neutrino physics were presented. The main results come from solar neutrinos and atmospheric neutrinos (those produced as decay products in cosmic ray interactions in the atmosphere). Excellent results came from two large international collaborations using deep underground detectors: SuperKamiokande in Japan and SNO - the Sudbury Neutrino Observatory in Canada (which also includes a significant number of UK physicists). Taking the results from these experiments and others, it is now clear that muon-type neutrinos can change into another type. Results also show that the "Solar Neutrino Problem", the fact that too few solar neutrinos are observed on Earth, is caused by electron-type neutrinos changing into another active species. The experiments are completely consistent with theories of neutrino oscillations, whereby the neutrino mass eigenstates are different from the observed weak interaction eigenstates (although actual oscillations have not yet been observed). The results favour the so-called large angle mixing solution and give likely values for the (squared) mass differences between neutrino species. They are also consistent with the "Standard Solar Model" which calculates in detail the complicated contributions to the electon-neutrino spectrum from the various nuclear processes in the Sun.

* Direct CP violation implies that the meson decays into the "wrong" CP eigenstate, whereas indirect implies that the meson first turns into its antiparticle which then decays into this eigenstate.

P. I. P. Kalmus
8 August 2001