10? 6.66? Eleventeen?

Today (Wednesday) the CERN management is going to reach a decision that will affect the life of everybody on this planet. Namely, the operating energy of the LHC machine in the first year will be decided today. Senior readers may remember that the LHC used to be a 14 TeV collider. However that energy cannot be achieved in near future due to poor quality of the magnets provided by industry. Reaching the nominal energy will require a long process of magnet training, and the prospect for upgrade seem unlikely within the next 3 years. For this reason, 10 TeV was the energy planned for the last year false start, as well as for the restart scheduled for mid-November.

However, the rumor is that even this smaller energy will not be achieved next year due to the well known problems with bad splices. The hundreds of individual magnets around the LHC ring are connected using a process called soldering - an advanced cutting-edge technique whose many aspects are clouded in mystery. There are in fact two separate problems with soldering that have been detected at the LHC. One is a poor quality of interconnections between the superconducting magnets. That leads to excessive resistance (like nanoohms) and, in consequence, the current flowing through the interconnection generates heat that triggers a quench of the superconductor. The other problem are faulty interconnections between copper bus bars who are supposed to carry the current when the superconductor quenches. It is suspected that the solder in the bus bars was sometimes accidentally melted during subsequent soldering of the superconducting cable connections. In fact, it was a combination of the two above mentioned problems that triggered the fireworks of September 19.

Bad splices are known to be present in the LHC ring, and those residing in cold sectors cannot be repaired without a considerable slip to the schedule. So the alternative is to either postpone the LHC restart or run at slightly lower energies (the latter implies slightly smaller currents running through magnets and thus a slightly smaller risk of another catastrophe). During the last few months numerous simulations and experiments have been performed to determine the maximum safe current.

After a careful study of the plot above, listening to the experts, and weighing all pros and cons, the director general is going to roll a pair of dice, and the sum of dots will determine the LHC energy for the coming restart. As for the rumors, I have heard any rational number between 4 and 10 TeV. So, now is the last moment place your bets. Theoretical analysis of the 2-dice experiment suggests that 7 is the most likely outcome :-).

Once we know the operating energy, we will have a better idea what kind of results to expect in the first year. It is already certain that for a while the LHC cannot compete with the Tevatron in the area of Higgs searches. In fact, almost all reasonable new physics signatures require at least one inverse femtobarn of integrated luminosity, much more than the 100 inverse picobarns expected in the first year. This leaves boring standard model signatures, including slightly less boring top quark physics (but even in the case of the top quark competing with the Tevatron results may be tough if the center-of-mass energy is lower than 10 TeV). However, some spectacular (and unlikely) signatures like a new 1 TeV Z' gauge boson or light superparticles may be within reach if the center of mass energy is not much less than 10 TeV. But realistically, we have to keep patient until at least 2012.

And the winner is...

Seven!