LHC Report: Take Five

The LHC is continuing to perform well and an integrated luminosity of over 5fb^-1 has now been delivered to ATLAS and CMS. While keeping a close eye on beam induced heating and vacuum quality, the bunch current has been gently raised to over 1.4x10¹¹ protons per bunch. This has given a peak luminosity of 3.6x10³³ cm^-2s^-1. Some long fills have helped production and recent high points include 120pb^-1 delivered in one fill and 580pb^-1 delivered in one week.

Time has also been devoted to some special physics runs for TOTEM and ALFA. In these runs, the beam is de-squeezed to a ß* of 90 m in ATLAS and CMS. This is instead of the usual 1m ß*, and gives a larger beam size at interaction points. The increased beam size results in a reduced beam divergence at the interaction points. This permits TOTEM and ALFA to probe low-angle scattering and allows them to measure the total cross section of proton-proton interactions and the absolute luminosity calibration.

The LHC finishes its 2011 proton physics programme on Saturday 29 October. Then it will go into a 6-day machine development period where, among other things, there will be a first look at proton-lead operation. After this, the operations team will start setting up for the lead ion run before a 5-day technical stop.

The experiments discuss their plans for the upcoming heavy-ion run in this week's Bulletin. 

by Mike Lamont for the LHC Team