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Abstract |
LHCb has introduced a novel real-time detector alignment and calibration strategy for
LHC Run 2. Data collected at the start of the fill will be processed in a few minutes
and used to update the alignment, while the calibration constants will be evaluated for
each run. This procedure will improve the quality of the online alignment. For example,
the vertex locator is retracted and reinserted for stable beam collisions in each fill
to be centred on the primary vertex position in the transverse plane. Consequently its
position changes on a fill-by-fill basis. Critically, this new real-time alignment and
calibration procedure allows identical constants to be used in the online and offline
reconstruction, thus improving the correlation between triggered and offline selected
events. This offers the opportunity to optimise the event selection in the trigger by
applying stronger constraints. The required computing time constraints are met thanks
to a new dedicated framework using the multi-core farm infrastructure for the trigger.
The motivation for a real-time alignment and calibration of the LHCb detector is
discussed from both the operational and physics performance points of view. Specific
challenges of this novel configuration are discussed, as well as the working procedures
of the framework and its performance.
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