LHC delivers collisions at record energy
After a three-month winter maintenance stop, the Large Hadron Collider [LHC] at CERN has resumed operation, with beams, on 14 March. Two days later, low intensity beams were accelerated to 4 TeV for the first time, achieving a new world record.
During the preceding month, all machine components – including almost 2,000 superconducting magnet circuits – were tested for operation at currents which allow these accelerating beams of up to 4 TeV. The LHC previously ran at 3.5 TeV in 2010-11.
Following the machine’s re-commissioning particular attention has been given to the so-called squeeze process, during which the beam size is reduced at the centre of the LHC’s four detectors – ALICE, ATLAS, CMS and LHCb – where the beams are brought into collision. The beam size at the interaction points has been further reduced this year, by grater focusing of the beams with the machine’s powerful superconducting quadrupoles. Beam sizes of less than 20 µm have been attained within the ATLAS and CMS experiment.
The first collisions, between two low-intensity beams, were obtained on 30 March – at the same time the European Physical Society Council meeting was being held at CERN – and the first data-taking runs started on 5 April, following careful verification of the machine’s performance and the status of its protection systems.
Thanks to the smaller beam sizes, a mere six days of LHC operation has delivered an integrated luminosity of 0.2 fb-1 to ATLAS and CMS, the two high luminosity experiments; this is the equivalent number of collisions to that delivered in the first six weeks of data taking last year.
The number of protons in the two counter-rotating beams is being augmented: with the aim, in the next few weeks, of significantly increasing the maximum instantaneous rate of events delivered to the experiments. The LHC aims to deliver enough luminosity – in of the order of 15 fb-1 – to ATLAS and CMS, in order to allow them to either discover or exclude existence of the Higgs by the end of the year.
