Trigger Criteria for Level 1

Joel Butler

Objective• The use of the requirement of “N” detached tracks

EACH with impact parameter greater then “M” standard deviations as the Level 1 requirement has been with us from the earliest days of the Level 1 Trigger development

• It is natural to ask whether – Some other criteria would have somewhat improved

efficiency. Possible gains are small for B’s but potentially large for charm where efficiency is low

– What effect this trigger criteria has on the proper time distribution (an effect of the current trigger first observed by Harry Cheung) and whether some other criteria would have a smaller effect.

Game Plan

• Study the effect on the efficiency and proper time distribution for our usual trigger for “typical states” of B and charm decay

• Study alternatives

Trigger Efficiency B-->D* for Final Signal Events

Trigger Efficiency for B-->D* for all signal events

Level 1 Trigger Efficiency

For generated minbias:

Upper left: 300 MeV/c

Upper right: 500 MeV/c

Lower left: 700 MeVc

NormalTrigger

Proper time for B-->D*

Affect of proper timeResolution seen clearlyIn untriggered curve to1 ps and to triggeredthrough whole distribution

Reduced proper time for B-->D*’ = - Nwhere N is the L/ cut

It means you start thedecay clock after N. This works only if doesnot depend on . This is useful for lifetimemeasurements but not formixing where the interactionstarts the clock.The lifetime fit with no trigger

Is very close to the MC value.

Notrigger

L1Trigger

Fit Results

The result of the fit to the “untriggered” ’ distribution: 1.67ps

The result of the fit to the “triggered” ’ distribution: 1.98ps

The uncertainty is about 0.02. One can probably do a bit betterBy tailoring the ranges, but the f(’) will still not be flat.

Nothing here is fatal but it would be very good to improve the situation

Conclusion from B study

• The trigger affects the time distribution requiring “f()” corrections. These are always subject to complaint and should be kept as small as possible

Charm Study

• Study undertaken with directly produced Do--> K.

• Used a “candidate driven” algorithm to build the primary vertex for each candidate D. This is the first time I have a completely “unprompted” analysis. Valid only for all charged final states

• Consider also Pt cut on “detached” candidates

Level 1 Trigger Efficiency

For generated CCBAR:

Upper left: 300 MeV/c

Upper right: 500 MeV/c

Lower left: 700 MeVc

Level 1 Trigger Efficiency

For generated D0-->K:

Upper left: 300 MeV/c

Upper right: 500 MeV/c

Lower left: 700 MeVc

Charm

• Pt cuts cause less trouble than I would have imagined

• The “standard” trigger has an efficiency of around 10%, which is not bad. Roughly, speaking, the “effective” charm luminosity is 15-20% of the B luminosity

• Improvements would be welcome

In progress

• Change trigger criteria– Require two tracks each with M>3– Require sum of normalized detachment squared

greater than some number, like 72 (2X62) and then explore from there

Sum of normalized impact parameters

squared for all detached tracks associated with

each primary

Each track must have at least 3 , which for two tracksgives 9, so a sum of 18 min isalready required