# Presentation: 265854

## Triggers for calorimeter calibration

- Don’t discuss here electronics calibration
- Taken between fills, outside physics run
- Physics samples for calorimeter calibration:
- Random triggers
- Electrons for pulse shape studies
- “single track” for hadronic calibration purpose
- “Standard” candles for EM objects and jets in situ calibration

## Random triggers

- Aim:
- Check pedestal in physics vs calibration runs
- Could derive pedestal shift corrections
- Measure total noise autocorrelation function (=> input for signal reconstruction in DSP)
- Provide samples for overlay to MC events
- Simulate noise and pileup effects
- Goals above require to readout ADC samples for all cells
- “Big” events (~2 times larger than “standard” one)
- (implementation in DSP code still to done)
- Should not be MB trigger, but real random trigger on non empty bunch crossings (don’t trigger on holes in LHC train)
- Random is different from MB at 1031
- Foreseen in the express stream
- Rate ?
- O(1Hz) is probably OK
- Much less will not give enough events to measure autocorrelation
- Much more is not realistic
- Should try to quantify a little more

## Electrons for pulse shape studies

- Aim:
- Check pulse shape (for EM cells) by looking at 5 time samples and compare to predictions
- Physics pulse shape prediction is one of the most difficult part of the calorimeter cell level calibration, if not done correctly O(few %) miscalibration effect could be introduced
- If check is OK, then have some confidence in procedure to predict physics pulse shape AND amplitude bias (from calibration and/or first principle computations)
- If check is not OK, would need to directly measure detailed physics pulse shape
- Special runs with more time samples (impact on L1) and/or different trigger timing
- Would like to avoid is possible...
- Current idea:
- Take single electron trigger from full chain
- DSP code allows to readout 5 samples in cells with energy > threshold (already implemented)
- This allow to take the necessary data with a very small increase in full event size
- Should also quantify the increase for the L2 region of interest size
- To reduce the amount of data to process and analyse for this (dedicated) study would like a special stream where only calo+ID data in the electron region of interest are written out (event size < 10% of normal events).  Some discussion with TDAQ people have been initiated, to be followed up
- Rate ?
- If possible take all EF electrons/photons
- In 1 day at 50 Hz, would get ~ 50-100 electrons per middle cell of EM calo
- Systematics related to purity had to estimate. In principle any “electron/photon” candidate should do the job, but need to be able to play with purity to check
- Noise effect on pulse shape measurement goes with 1/energy
- Not clear what is the tradeoff betwen energy cut and purity

## “single tracks”

- Aim:
- Check “single” hadron calibration (E/p)
- Try to extend Pt reach above what we can get from MB events
- Some discussion started between trigger and hadronic calibration group (E.Torrence)
- Probably would use some L1 tau trigger and tracking at HLT
- Should try to get bias from L1 calorimeter cuts as low as possible
- Need to study/quantify how to setup prescale vs Pt to have the most relevant pt spectra at the end
- => Hadronic calibration group to check if L1 tau trigger + L2 tracking is OK
- Rate:
- Fraction of 1Hz can probably be allocated at the EF filter
- Should this go in a special stream ?

## “Standard candles”

- EM calibration:
- Z,W are the best
- Absolute scale    (already doable with small statistics)
- Intercalibration (need O(100pb-1) to reach <% inter-region statistical accuracy  )
- More inclusive electron sample also useful for studies like calorimeter/tracker alignment, local corrections within one cell (using E/p over one calorimeter cell)
- Any menu which is efficient for Z,W and has a significant rate of single electrons/photons should be OK at first order. Obviously the accuracy of the calibration will depend on how many “golden” events we have.
- Hadronic calibration
- Di-jet , Z+jet and gamma-jet balancing
- How low to we want to go in Et(gamma)? (prescaled)
- Top events later
- Z and (depending on the lumi) some of the other events can go on the express stream for checks/monitoring
- Not clear how much we will be able to improve within 24h from these physics samples to the Tier0 processing, especially at the beginning...