After the first experience of running LEP above the Z
energy, it is clear that an interactive event display will be a powerful
and necessary tool for the DELPHI data analysis.
On the one hand the number of physics events is quite low outside the Z
peak, on the other all the searches for new particles or new physics
rely on a detailed understanding of the apparatus and of its hermeticity,
which must be continuously checked and monitored by visual event scans.
Furthermore the errors and the weaknesses of the analysis and filtering
programs must be spotted and corrected as far as possible.
In 1995 during P3 scanning shifts were organized at CERN running a new interactive version of DELGRA on two dedicated Alpha Vax machines under OSF[2]. The scan provided a very fast feedback on the filtering algorithms for different physics channels and on detector and software problems. However, not many physicists were involved in this work and those who could not be physically present at CERN were excluded, thus reducing the potential benefits of the scan. DELGRA could, of course, be installed locally in the collaborating institutions, but this would demand dedicated machines and perhaps a continous upgrade of the installed products.
We think that there is room for a simpler and faster tool which could facilitate the involvement of the entire collaboration in the physics analysis without penalizing groups with their base remote from CERN or with unsuitable hardware platforms.