The Gap Trigger Problem

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