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Luminosity

At the end of each year VSAT has provided a luminosity file to the STIC group to be used as a stability check on the STIC luminosity. The VSAT files were also used to cross-check the STIC data for any bad luminosity entries. Comparing the STIC and VSAT data has shown that a joint systematical error of the STIC and VSAT luminosity could be achieved below 1% (Fig. 8.1). The off-energy background heavily disturbs the VSAT Bhabha sample, but with optimized cuts and a good estimation of the remaining background this is fully under control. A good luminosity measurement could therefore still be obtained (Fig. 8.2), even during the worst background conditions in the beginning of 1999 (around fill 5800 in Fig. 3.5).

Figure 8.1: The relative difference between STIC and VSAT luminosity. The statistical error is here about 1.80-1.95%, so the joint systematical error is about 0.7-1.0%
Figure 8.2: The STIC and VSAT luminosity for 1999, the severe background storms in the beginning of 1999 does not seem to disturb the luminosity measurement.