LHC Updates: Watch this Space

Hi everyone,

I’d like to try something unusually blog-like on The Everything Seminar. As some of you know, the Large Hadron Collider (LHC) will come online sometime this fall to answer basic questions in particle physics, and some of these questions have been waiting for 20, 30, or even 40 years (the Higgs mechanism was proposed in 1964).  My day-job is to commission the Compact Muon Solenoid (CMS) experiment, one of the two general-purpose particle detectors on the ring (the other is ATLAS), “general-purpose” meaning that it is designed for surprises, a discovery machine.  Since it seems that I won’t be interrupting any math conversations, I’d like to give short updates on what’s going on and when things will be working, and maybe correct some newspapers.  I’ll be spending some of the first data runs in the CMS Centre at CERN, and can relay a little bit of what it’s like in the first days of a new particle physics experiment.

This morning, I discovered LHCCountdown.com, which says that the LHC will “start” in two days and several hours.  It’s unclear which milestone to take as the actual “start” of the LHC— the first beam in the machine, the first beam to go all the way around the machine, the first counter-rotating beams, the first collisions, the first collisions at full energy (whether you take that to be 10 TeV or 14 TeV)— but for any reasonable definition, the LHC will not “start” on Thursday.  It isn’t even possible to run a beam around the full circle until the experiments are completely closed, which will happen in the last week of August for CMS.  The Official LHC start-date is September 2, 2008, though it’s not clear that this will correspond to any specific milestone.  Certainly not colliding beams.

The problem, other than a litany of specific technical issues that all had to be corrected and the unyielding fact that schedules slip, is that the people who are building and commissioning the LHC are the same people who make the schedules.  I’ve even seen schedules presented with the caveat, “This is wrong, but we don’t want to divert people to update it.”  So even the experimenters are guessing at the start dates.  The concensus of rumors has first collisions happening sometime in October, a total integrated luminosity (amount of data) for 2008 of about 10 pb^-1, a collision energy of 10 TeV (rather than the design 14 TeV), and then a shut-down at the end of the year to allow the beam and the detectors to fix everything we found out was wrong in the first few months.

This is modest.  It won’t be the final word on anything: most predictions for the LHC require more data than 10 pb^-1 to be distinguished from familiar Standard Model signals.  But if there are any “obvious” new physics signals, like excessive decays to easily-identified electrons or muons, or better yet, resonances that form spikes or cascade decays that form triangular edges on top of the smooth Standard Model distributions, we’ll see them right away.  The 2008 run represents a factor of 5 increase in energy above the Tevatron, so anything that was just out of reach before will now be in plain view, as long as the signal we’re considering obviously can’t be produced by the Standard Model or a detector malfunction.

For my part, I’m studying high-energy muons.  Every few weeks now, we read in about a week’s worth of cosmic ray muon data and I use them to study the alignment of the detectors.  (Super-precise position measurements don’t do you any good if you don’t know where the measuring devices are!)  Meanwhile, our muon detectors are moved every time someone needs to install or wire something up in the core of CMS, so the algorithms that were designed to identify misalignments on the micron-to-millimeter scale first need to search for the detectors, sometimes meters from their design positions.  And oh yeah, these detectors are five stories tall.

There are some nice pictures in the Boston Globe.  More later.

Tags: CMS, LHC, physics