News from the LHC Performance Workshop, Chamonix

Johannes Wessels

‘I have to go to Chamonix.' What a statement to make. Most people would think of clear blue skies, some of the most prominent pinnacles of the Alps and lots of powdery snow just waiting for the ambitious skier. Now, you are talking to a sailor, who normally would appreciate strong wind, but not at -12 oC during daytime. Nevertheless, it was still really exciting.

Every year about 80 machine physicists and engineers, a few experimentalists, and a significant fraction of CERN management gather for a week in Chamonix to assess every aspect concerning the operation of the accelerator complex during the past year and to devise the optimum running scenario for all experiments for the year to come. To a non-accelerator physicist it is truly amazing to see how intricate the interplay of all components (the injector chain, pre-accelerators, magnet systems, high-frequency systems, collimator systems, vacuum systems, cryogenics, controls, and – not the least – safety and access systems) is in order to provide the experiments with so-called ‘stable beams'. The diligence devoted to each of the components clearly transpires through the many heated discussions, which, in the end, lead to the running scenario for the coming year.

And the boundary conditions are tough: with the long shutdown scheduled to start at the end of November, ATLAS and CMS have their priority set to each collect at least 15 fb-1, likely enough to close the case on the Higgs. They will profit from the fact that it has been decided to operate the machine at a slightly higher energy this year – 8 TeV. That favourably increases the production cross section for the Higgs. ALICE will – of course – also run at that energy and will leave a few more bunches to the big experiment, because of a very special mode of operation. Adjacent to the main particle bunches are so called ‘satellites' in the beam. A special setup of the machine allows ALICE to collide only those satellites which would produce just the right luminosity for our experiment.

Excitement in ALICE will again peak towards the end of the year, when, for the first time ever, collisions of protons and Lead nuclei will take place in the LHC. Owing to the big asymmetry in the system, ALICE has requested operation of both beams in either direction. These measurements will provide another anchor point for our heavy ion results, an in-depth measurement of the cold nuclear matter response to high-energy protons.

What an exciting week it was at Chamonix and what exciting prospects for our programme.

Alice Matters