Going beyond the Standard Model

1 March 2006

A five-part workshop has been launched at CERN to study the interplay between the physics of particle flavour and the physics achievable at particle colliders. In particular, it aims to consider the future directions for flavour physics when the Large Hadron Collider (LHC) starts up at CERN in 2007.


Flavour physics and charge-parity (CP) violation have played an outstanding role in the exploration of particle-physics phenomenology for more than four decades. After a long and exciting history of K-decay studies, the experimental stage is currently dominated by the decays of B+ and B0d mesons. Thanks to the efforts at the e+e B-factories at SLAC and KEK, with their detectors BaBar and Belle respectively, CP violation is now well-established in the B-meson system, and for the first time several strategies to test the flavour structure of the Standard Model can be confronted with experimental data.

Further valuable insights can be obtained from studies of the B0s system, with first results from experiments at CERN’s Large Electron-
Positron collider and the SLAC Linear Collider, as well as from Fermilab’s Tevatron. In future, the physics potential of B0s decays can be fully exploited at the LHC, in particular by the LHCb experiment. Moreover, there are also plans for a “super B-factory”, with a significant increase in luminosity relative to the e+e colliders currently operating.

As far as the kaon system is concerned, the future lies in particular in investigations of the very rare decays K+ → π+vbar v and KL → π+vbar v, which are very clean from the theoretical point of view, but unfortunately hard to measure. There is a new proposal to measure the former channel at CERN’s Super Proton Synchrotron, and efforts to explore the latter at KEK/J-PARC in Japan. There are also many other fascinating aspects of flavour physics, such as charm and top physics, flavour violation in the charged lepton and neutrino sectors, electric dipole moments and studies of the anomalous magnetic moment of the muon.

The hope and final goal of these flavour studies is to find indications of physics beyond the Standard Model and to study its properties. So far, the Standard Model remains in good shape, with the exception of a couple of flavour puzzles that do not give definite conclusions on the presence of new physics. On the other hand, neutrino oscillations, as well as the evidence for dark matter and the baryon asymmetry of the universe, show that the Standard Model is incomplete. Moreover, specific extensions of the model usually contain new sources of flavour and CP violation, which may manifest themselves at flavour factories.

The LHC, it is hoped, will provide direct evidence for physics beyond the Standard Model through the production and decays of new-physics particles that arise, for example, in supersymmetric extensions of the Standard Model. There should be a very fruitful interplay between these “direct” studies of new physics and the “indirect” information provided by flavour physics.

The goal of the new CERN workshop, Flavour in the era of the LHC, is to outline and document a programme for flavour physics for the next decade, addressing in particular the complementarity and synergy between the LHC and the flavour factories with respect to the discovery and exploration potential for new physics. The workshop follows the standard CERN format, consisting of three working groups, which are devoted to the collider aspects of flavour physics at high-Q, the physics of the B-, K- and D-meson systems, and flavour physics in the lepton sector.

The opening meeting with plenary sessions to review the state-of-the-art of these topics, which also started the working group activities, took place at CERN on 7-10 November 2005. This attracted more than 200 participants from all over the world, and was followed by a second meeting at CERN on 6-8 February. There will be two further meetings before the final plenary meeting at the end of 2006 or the beginning of 2007. A CERN report will then publish the results and conclusions of the workshop.

• Anyone interested in joining the workshop is still very welcome. For information, see The next meeting will be at CERN on 15-17 May.

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