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VELO Misalignment Studies

Impact of misalignments on the analysis of B decays

This study investigates the effects of a misaligned tracking system on the analysis of B decays. Misalignment effects of both the vertex locator and the inner and outer T-stations have been studied. z -scaling effects of the vertex locator are also considered. It is shown that misalignments of the order of one third of the detector single-hit resolutions have little or negligible effects on the quality of the reconstruction and of the analysis of B decays. The studies were performed with a sample of B0(s) ->h+h'- decays, but the impact of misalignments on the performance of the pattern recognition algorithms and on the primary vertex resolutions, assessed for the first time, are rather general and not restricted to B0(s)h+h'- decays.

An LHCb note containing details of this study is available on Cern Document Server. You could access it here:

LHCb-note 2008-012

Study of the impact of VELO misalignments on the LHCb tracking and L1 trigger performance.

A study has been conducted to investigate the effect of VELO misalignments on the LHCb tracking and Level 1 trigger reconstruction. The aim of this study is to determine the level of precision required during assembly of the VELO and the determination of the position of the VELO after insertion.

This study considers translations and rotations of the half-boxes of the VELO as well as translations and rotations of the individual VELO-half-stations. In order to gauge the performance of the LHCb tracking a number of parameters are considered:

• Tracking efficiency.
• Tracking ghost rate.
• Track hit purity.
• Track hit efficiency.
• Impact parameter resolution.
• Single hit resolution.

This study has also been extended to consider the performace of the Level 1 trigger. In this section the VELO is misaligned and the performace of the Level 1 trigger in selecting B meson decaying to two Kaons is evaluated. The retention of minimum bias events are also considered.

An LHCb note containing details of the method used to misalign the VELO in the simulation and the results is available on Cern Document Server. You could access it here:

LHCb-note 2005-056