Berlin 2005 – scientific programme

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T: Teilchenphysik

T 610: Trigger und DAQ III

T 610.1: Talk

Tuesday, March 8, 2005, 16:30–16:45, TU H4105-4106

Impact of a b-jet trigger on searches for tt-resonances and heavy Higgs bosons at ATLAS — •Anca Siebel and Peter Mättig — Bergische Universität Wuppertal, Fachbereich C, Gaußstr. 20, 42097 Wuppertal

At LHC, every year ≈8 million top quark pairs will be produced per experiment at low luminosity. Searches for new particles will be most sensitive if in addition to the channels containing leptons also the fully hadronic tt decay mode can be exploited.

The final state of a fully hadronic tt-event consists, in the absence of initial or final state radiation, of six jets (including two b-jets), no high E_T isolated lepton, and small missing E_T. Therefore the trigger decision is based only on E_T and the number of jets.

The trigger "menus" examined by ATLAS consider multi-jet triggers up to four jets, for which a jet E_T threshold of 65(110) GeV is applied at first(LVL1) and second (LVL2) level trigger at low luminosity. Due to high E_T thresholds required at LVL2 the trigger efficiency for fully hadronic tt-events is on the order of 2%.

With a b-jet identification available at LVL2, QCD background can be suppresed effectively. This would allow for lowering the E_T thresholds and thereby increasing the trigger efficiency for tt-events.

In this talk the impact of introducing b-tagging into the trigger system on the discovery of tt-resonances and heavy Higgs bosons via the decay H→ t t is discussed. Special attention is paid to the improvement of the discovery prospects due to lowering the E_T thresholds of the actual jet trigger menu.