A symphony of data at LHCb

Like musical instruments in an orchestra, the main difficulty with the many detectors of LHCb is coaxing them into playing in harmony. On 8 February 2008, for the first time, the LHCb control room team managed to extract a symphony of data from an almost complete ensemble of LHCb detectors.

The LHCb control room team examining the data read out from the LHCb detectors.

Now that all the detectors of LHCb are installed in the cavern they can begin to play a tune. The week of 4 February was commissioning week for the LHCb control room, when, for the first time, data from the majority of the sub-detectors (VELO, RICH 1, RICH 2, ECAL, HCAL, MUON, L0Calo and L0DU) was read out, controlled from a single window on the main computer.

General view of the LHCb detector components.

Sixty electronic boards, which read out the fragments of triggered events, were used during the readout at a frequency of 100 Hz. As not all of the boards have been installed and/or commissioned yet, this represents only around 20% of the data that the detectors are capable of generating.

The exercise was an important test run to flag up any problems in the experiment before the next commissioning week in March. As the LHCb commissioning coordinator Olivier Callot points out, "Many problems were noted and the job list gets will only get longer after this week." Straightening out the kinks in the design of the system is an essential step towards the integration of the sub-detectors and the control system for the control room team.

There was also an indication that cosmic tracks had been recorded on the calorimeter system and the outer tracker. Because of the way that the LHCb is set up, with the detectors operating on a horizontal plane, it is hard for the normally vertically falling cosmic tracks to be recorded. However, there are some cosmic tracks that travel almost horizontally, but they are rare, as Olivier Callot explains: "The rate of such cosmic tracks is a fraction of Hz, and the main goal of the next commissioning week will be to collect cosmic events in all detectors together, allowing an initial time alignment of all components and providing some tracks to be used by reconstruction and alignment teams."

Next time, the team expects a full-blown opera in perfect pitch from the detectors!