RAL Tier-1 computers process their first data from CERN LHC detectors
Monday 23 November 2009
A visualisation of CERN LHC run 30764, event 198 reconstructed from data gathered by the LHCb experiment detectors.
Image courtesy of CERN.
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At ten o'clock in the evening of Friday 20th November a clockwise circulating beam was established at the CERN Large Hadron Collider (LHC) starting it again after the accident which closed it after only nine days running last September. The computer systems at the STFC Rutherford Appleton Laboratory (RAL) received their first data from the ATLAS experimental detector on Saturday and even fully reconstructed data gathered by the LHCb detector over the weekend.
The beams of protons are being circulated around the ring at the speed at which they are injected into it (450 GeV/c) because they are not yet being accelerated by the magnets which surround the beamline. Beams have been operated in both directions, with the first collisions being seen on Monday afternoon. Before the collisions, data was collected by the detectors when a beam particle hit a residual atom drifting around inside the pipe (events called beam gas) and when beam particles were deliberately steered into the beam collimators to generate showers of particles (called beam splash). Collecting this data allows detector scientists to more precisely tune the detectors since up to now, all the data they have recorded has come from cosmic rays rather than particle beams.
The data collected from the experimental detectors on the LHC is passed from CERN to 11 Tier-1 sites around the world for storage and processing. RAL hosts the Tier-1 site at which researchers in UK universities can access data. The data represents measurements at different locations in the detectors when events occur. It has to be re-processed in order to reconstruct the particle events that took place to give rise to these measurements. Both the RAL Tier-1 computer and Tier-2 computers at UK universities perform this reconstructive processing.
During the next few weeks the beams will be accelerated to produce higher energy collisions. These will enable the experimental collaborations to carry out important calibration work. This will lead to 10-11 months of intensive data taking before the shutdown in winter 2010. It is expected after a few months that the total collision energy will be increased towards 10 TeV. First papers with early results may come in summer 2010.
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