Data Processing

The LHC accelerator creates extremely high energy particle collisions, which in turn create new particles that decay in very complex ways as they move through the detectors. The detectors register the passage of these particles with a vast number of sensors and, finally, a digitised summary of this is recorded as what we call an "event".

The raw data per event is around a million bytes (1 Mb), produced at a rate of about 40 million events per second. To reduce the amount of data, and to keep only events which are potentially worth studying, an intelligent selection filter is applied to reduce the number of events recorded to around 100,000 per second.

In a second selection stage, this is reduced again to around 100 or 200 events per second by processing the data using more specialised algorithms. This raw data is then recorded at a rate around 1.5 CDs per second (~1050 Mb/sec).

This two-stage data re-processing is performed several times a year on all data acquired since the LHC start-up. Methods to detect interesting events through the processing algorithms, as well as improvements in detector calibration, are in continuous evolution and development.

By re-processing data, it is more likely that new physics discoveries will be made.