CERN Accelerating science

ATLAS Note
Report number	ATL-SOFT-2004-005 ; ATL-COM-SOFT-2004-007 ; CERN-ATL-COM-SOFT-2004-007
Title	Proposal for Compactification of CaloCell Objects
Author(s)	Menke, S ; Usai, G L
Publication	2004
Imprint	2004
Number of pages	13
Subject category	Detectors and Experimental Techniques
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	ESD ; Compactification ; Calorimeter
Abstract	All ATLAS calorimeters together have 187652 cells. In the reconstruction software of ATLAS for each cell an object of type CaloCell with 195 bits of information for energy, time, gain and quality is created. Saving all the calorimeter cells with the LCG POOL persistency service consumes in excess of 1 MB (the 1 MB is of course dependent on the persistency service used because POOL does a gzip equivalent). In this proposal we are investigating algorithms to compactify the calorimeter data as much as possible without harming the resolution. Using a cubic root compactification method for the energy and a logarithmic compactification method for the time for the  10% of the cells with calculated time the average size per cell could be reduced to 17.6 bits. This note describes the "lossy" algorithms to achieve this goal and their implementation in the ATLAS reconstruction software.
Copyright/License	Preprint: (License: CC-BY-4.0)

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