Singapore meeting recalls 75 years since Solvay 1933
On 27–29 November 2008, more than 120 physicists from around the world gathered at the Nanyang Executive Centre in Singapore to reflect on progress in particle physics and look to exciting new frontiers at the Particle, Astrophysics and Quantum Field Theory conference.
The meeting took place 75 years after the Solvay Congress of October 1933, which featured, among others, the accelerator pioneers John Cockcroft and Ernest Lawrence. With the public airing of the neutrino hypothesis by Wolfgang Pauli at the congress, followed by the publication of the paper on four-fermion interactions by Enrico Fermi, dated 31 December, 1933 was indeed a seminal year. Seventy-five years later, the field of particle physics has now crossed a new threshold with the recent inauguration of the LHC.
Eminent speakers at the meeting in Singapore included Gerard ’t Hooft, Martin Perl, Harald Fritzsch and Kazuo Fujikawa. Reports on current experiments included Daniel Green on CMS, Jim Thomas on discoveries at RHIC, Tatsuya Nakada on flavour physics at the LHC, Takaaki Kajita on neutrino oscillations and Yifang Wang on the Daya Bay experiment.
• The conference was organized by the Institute of Advanced Studies, Nanyang Technological University (NTU), and co-sponsored by the National University of Singapore. For further information, see www.ntu.edu.sg/ias/upcomingevents/PAQFT08/Pages/default.aspx.
Diffraction attracts physicists to the Riviera
Last September, the Mediterranean resort of La Londe-les-Maures, France, welcomed participants to the International Workshop on Diffraction in High-Energy Physics, "Diffraction 2008". With a rich and multifaceted scientific programme, the fifth meeting in this series of biennial workshops proved a particular hit, attracting 110 participants from 20 countries.
In a nutshell, diffraction in particle physics refers to hadronic collisions at high energies and moderate momentum-transfers. Such processes are dominated by the vacuum quantum-number exchange known as the Pomeron, whose nature and properties are still unclear. Diffraction provides the opportunity to scan the "hardness" of the interaction in a broad region, making it a unique tool for studying the interplay between "soft" and "hard" phenomena of strong interactions. This is reflected in the variety of theoretical approaches, which can be based on perturbative quarks and gluons, take inspiration from Regge-theory for Pomeron exchange or introduce new degrees of freedom characteristic of strongly coupled theories.
DESY’s electron–proton collider, HERA, has dominated the experimental study of diffraction over the past decade. Although data-taking at HERA has now stopped, new analyses continue to appear, as DESY’s Voica Radescu revealed. The ZEUS, H1 and HERMES collaborations also presented their recent results on inclusive and various exclusive reactions, in particular on deeply-virtual Compton scattering, which theorists are actively studying. With new data from the Tevatron proton–antiproton collider at Fermilab, and in anticipation of the LHC era, the focus is now shifting towards diffractive phenomena at hadronic colliders.
There were reports on new diffraction results from the Tevatron,as well as prospects for the LHC, from Dino Goulianos of the Rockefeller University and Risto Orava from Helsinki. One burning topic concerned the production of central systems separated from the protons by large rapidity gaps, a major goal being the double-diffractive production of Higgs bosons at the LHC. Subtle details of this calculation sparked many lively discussions during the workshop.
The spin-physics programme was exceptionally rich this time. Barbara Badelek of Warsaw reviewed new results from the COMPASS experiment at CERN and there were also reports on new data from the CEBAF Large Acceptance Spectrometer at Jefferson Lab, HERMES at DESY, as well as the PHENIX and STAR experiments at RHIC at Brookhaven. There are currently various proposals for phenomenological approaches to spin asymmetries in hadronic reactions to improve understanding of the proton’s spin structure.
The theory part of the workshop benefited from talks on the rise of the total cross-section, presented by CERN’s André Martin, Claude Bourrely of the Université de la Méditerranée, and Peter Landshoff of Cambridge. Perturbative QCD approaches based on the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) and the Balitsky–Fadin–Kuraev–Lipatov (BFKL) equations also dominated the theory presentations. These govern the evolution of the nucleon structure as the process becomes "harder" or more energetic. Joachim Bartels of Hamburg, Lev Lipatov of the Petersburg Nuclear Physics Institute and Victor Fadin of the Budker Institute of Nuclear Physics presented new results on the properties of the BFKL equation, while several younger theorists discussed its application to various processes.
There is an ever increasing consensus that new nonlinear collective-QCD phenomena become increasingly important at high energies. These do not simply call for modifications of the BFKL and DGLAP approaches but may require a new language and formalism. Examples of this metamorphosis were presented at the workshop. One topic that has particularly flourished in recent years is AdS/QCD – QCD in terms of the anti-de-Sitter space/conformal field theory correspondence. This is a vast programme exploiting duality between higher-dimensional gravity and certain four-dimensional gauge theories to gain insight into strong interactions at large coupling, when the perturbative methods fail. Stanley Brodsky from SLAC, Guy de Téramond of the University of Costa Rica and Yuri Kovchegov of Ohio State University explained the emergent picture of hadrons in this approach.
• Diffraction 2008 was co-organized by Université de la Méditerraneée and IN2P3; DESY-Hamburg, Università della Calabria and INFN, and Temple University, Philadelphia. For further details of the programme, visit www.cs.infn.it/diff2008.