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T: Fachverband Teilchenphysik

T 74: DAQ und Trigger I

T 74.5: Vortrag

Montag, 28. März 2011, 17:45–18:00, 30.23: 2-11

MET trigger behavior and rate control in case of large number of interactions per bunch crossing at the ATLAS experiment. — •julien MOREL — II. Physikalisches Institut, Universität Göttingen

The Missing transerve energy (MET) triggers of the ATLAS experiment have been used successfully during the first year of LHC running. During 2011 the LHC will restart with a higher luminosity and ATLAS will have to deal with a larger number of pile-up. It appears that in case of pile-up, the MET trigger rates increase due to "fake" MET coming from the detector measurement and resolution. An analytical model of this "fake" MET can be used to predict the MET trigger rates for various pile-up scenarios. This shows that the rate increase can be very large and needs to be under control to be able to use the MET trigger menu with the 2011 expected luminosity.

The simplest way to lower the rate is to increase the trigger threshold, but in the case of large pile-up, the minimal thresholds can reach ~40 GeV and become a drawback of standard model studies. Pile-up studies are then required to find the best threshold/prescale configuration according to the pile-up scenario. One can also think of several other possible cuts at the different trigger levels. Among them, the "MET significance" looks interesting to fight against pile-up.