(r1) ClusterShaperIntroduction < CMS

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---+++Introduction

Track finding in a high density environment is rather difficult with silicon pixel and strip detectors, looking at both efficiency and fake rate. Track fitting uses hits associated by the previous track finding phase, thus the proper functioning of this latter is essential.

In the present track finding method seeding starts from pixel layers. Seeds are produced by combining pixel clusters from the two innermost pixel layers. If they are compatible a further check is made on the existence of another compatible hit in the third pixel layer. Due to the combinatorical nature of the process, the number of possible combinations grow with track/cluster multiplicity _N_ as _N&sup3;_.

Up to know only the position, a kind of center of gravity, of pixel clusters have been used for track finding and fitting. Here new methods for using all information available is presented. These are
   * length of the cluster
   * direction of the cluster
   * enegy deposited in the channels of the cluster

The application of these methods are
   * fast vertex finding with clusters only, before track finding
   * reduction of compatible cluster seeds, resulting in faster tracking, higher efficiency and lower fake rate; in fact, track finding in track parameter space becomes possible
   * direct usage for determining specific energy loss of a particle ("dE/dx")

Of course these advantages come at a price: a proper modelling of the detector is necessary with the use of some powerful tools from numerical analysis.



-- Main.FerencSikler - 11 Jan 2006

Topic revision: r1 - 2006-01-11 - FerencSikler

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