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Optimizing Gap Trigger Definitions in High Energy Physics: Insights from Tamsin Edwards

This document outlines the challenges and considerations in defining gap triggers for hard diffractive events, characterized by high pT jets where protons and antiprotons do not break up. Tamsin Edwards discusses current methods, including vetoing hits in luminosity monitors and future plans to incorporate energy cuts in forward calorimeters. The presentation reviews existing trigger strategies, contamination issues in gap samples, and the implications of timing problems on trigger decisions. The document also proposes potential solutions based on detailed analysis of data and cut parameters.

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Optimizing Gap Trigger Definitions in High Energy Physics: Insights from Tamsin Edwards

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  1. The Gap Trigger Problem Tamsin Edwards QCD Meeting 10 March 2003

  2. Hard Diffractive Events Characterized by: • high pT jets • gap(s) - proton and/or antiproton do not break up How to define in a trigger? - at the moment: veto on hits in the Luminosity Monitors - in the future: also cut on energy in forward calorimeter Tamsin Edwards

  3. Luminosity Monitors Two arrays of 24 scintillators mounted on calorimeter end caps 2.7 < |η| < 4.4 LM South LM North At the moment • no read-out of individual scintillators • only HIT or NO HIT info for each side • determined by voltage thresholds Tamsin Edwards

  4. Fastz & halo events min bias (fast z) coincidence antiproton halo S then N N then S proton halo Tamsin Edwards

  5. Diffractive events gap north S only gap south N only gap south & north neither Tamsin Edwards

  6. Triggers & motivation Triggers: • JT_25TT_NG 25GeV jet • JT_25TT_GAPS 25GeV jet + no hit LM South • JT_25TT_GAPN 25GeV jet + no hit LM North • JT_25TT_GAPSN 25GeV jet + no hit LM South + no hit LM North • min_bias • zero_bias Contamination in gap samples, particularly GAPS • Mike Strang, Pavel Demine have looked at this • Appears to be part diffractive, part non-diffractive • GAPS currently has higher prescale than GAPN to compensate for the difference in rates: we are losing genuine diffractive events Is there a timing problem in the L1 and/or terms...? Tamsin Edwards

  7. L1 and/or terms Trigger decisions are made with 256 L1 a/o terms. Five of these are: • fastz • timing: coincidence • ahalo • timing: S then N • phalo • timing: N then S - only one of these three can be issued at a time • lm south • hit: S • lm north • hit: N • both should be fired if fastz • or ahalo or phalo fired • - gap triggers veto these Tamsin Edwards

  8. L1 and/or terms In an event: • a/o terms are fired or not fired • sent in groups of 16 by sub-detectors to the Trigger Framework • TFWK waits for 25 ticks (some groups are very slow) then makes the L1 decision So the and/or terms could miss the boat somewhere and not be included in the L1 decision. ...a ‘not-fired’ lm a/o term looks to the trigger like a gap... Tamsin Edwards

  9. Data & Cuts Data • trigger list CMT-9.20 • reconstructed with p13.05.00 Cuts zero bias sample: • no primary vertex (to get rid of beam) all others: • at least 1 pvtx • at least 5 tracks matched to pvtx • | zpvtx| < 50cm • metc < 0.7* pT of leading jet • 2 jets with pt > 25 GeV (except min bias sample) Tamsin Edwards

  10. GAPS & GAPN events • None should have fastz/ahalo/phalo fired • GAPS very contaminated (~89%) • GAPN also contaminated (~24%) Tamsin Edwards

  11. NG & GAPSN events • NG: if fastz fired • 5.9% lm south did not fire • 0.1% lm north did not fire Tamsin Edwards

  12. Min bias & zero bias events • min bias: • 3% lm south does not fire • 0.2% lm north does not fire Tamsin Edwards

  13. Conclusion • LM N & S terms are sent to the Trigger Framework with fastz, which we know gets there on time*, so that isn’t the problem • The likely culprit: the N & S read-out • depends on the cables from the LM, pre-amps etc • we need to have this checked • Rich Partridge is going to re-examine it... *in fact, the TFWK timing is set to fastz! Tamsin Edwards

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