Calorimeter Calibration for p17

Andy Haas / Columbia University

for the Cal. Calib. Task Force:
Marco Verzocchi, Jan Stark,
Krisztian Peters, Jiri Kvita, Andy Haas, Mikolaj Cwiok, and Amnon Harel

Vancouver Meeting

June 16, 2005

Introduction / EM Calibration

Determine a multiplicative calibration constant for each cell of the calorimeter
- maximize energy resolution

Constants are measured using data, since calibration pulses do not account for all effects

Divide task into EM and Hadronic calibration

Initial EM calibration was completed a few months ago:
Jan Stark and Matt Wetstein

Response normalized in phi at fixed eta using special calibration data

Response for each eta ring calibrated using Z->ee events, and known Z mass

Significant progress was made in understanding the Z->ee resolution in data (2.9 GeV) vs. MC (2.0 -> 2.4 GeV)

Incomplete material description in MC (solenoid, etc.) is the main cause

Remaining difference due to charge collection effects?

13%!

Hadronic Calibration: 3 months ago...

Hadronic Calibration Overview

Goal was to have constants available for p17 re-processing by July

Task force was formed, divided in two groups, led by :
Jan Stark and Marco Verzocchi

Inter-phi calibration :
Krisztian Peters and Jiri Kvita

Normalize response in phi at each fixed eta for all layers, using special calibration data

Eta-ring / overall calibration :
Andy Haas and Mikolaj Cwiok

Use phi/layer constants from inter-phi calibration

Provide a constant for each eta value and an overall hadronic energy scale

Use p17 di-jet data

Additional method being pursued by Amnon Harel based on jet profiles -- results will be cross-checked, where they can

Hadronic Inter-phi Calibration

Use same concepts and code that worked for the EM inter-phi calibration

Assume phi symmetry of energy deposition in detector

Count the number of times each cell has
ET > 9 GeV

Use average layer fractions to calibrate each layer of each tower

Special calibration data was collected during physics running, starting March 12, 2005

Nearly unbiased w.r.t. 9 GeV offline cut

L1 tower > 5 GeV

L2 tower > 5 GeV in fine hadronic (FH)

L3 precision tower > 7 GeV in FH

>15M events collected so far

Beware of “bad” cells

Dead trigger towers, dead towers, dead cells, low / high energy noisy cells...

These must not harm the calibration of other cells

before...

after...

|eta|

Hadronic Inter-phi Calibration Results

So far, 6.5 M events are analyzed

Errors are <1% in CC

Towers used at high |eta| due to low statistics

Constants vary by ~5% for good cells

A few miscalibrated modules found, by ~10%

Some long-range effects found, by ~5%

No constants for CH or ICD cells, yet

Amnon's method does have access to these

Constants have
RMS=~5%

phi

+10%

Hadronic Eta Calibration

Determine an overall calibration constant for each eta-ring

64 constants from -3.2<eta<3.2

Determine an overall constant for each layer within each eta-ring

Up to 6 constants for each eta-ring:
ICR,FH1,FH2,FH3,FH4,CH

Method: use QCD di-jet events, and minimize the total missing pT fraction of the events, using the cells within the jets

Assume EM layers are calibrated

An overall Hadronic scale can be determined since the EM fractions of jets are uncorrelated in each event

Also, Amnon has provided numbers based on jet profiles that we will cross-check with

<-jet 1

jet 2->

EM

EM

Had

Had

Calibrated

Had. mis-calibrated by 50%

6%
imbalance

20%
imbalance

Hadronic Eta Calibration: Event Samples, etc.

p17 QCD data skim – 21M events, so far
p14 QCD MC – about 1M events

Special Rootuple maker that reconstructs cone 0.5, 0.7, 1.0 jets and keeps their associated cell info

Perform a 64 parameter Minuit fit, to determine eta constants

Need to loop over all the events ~5,000 times, adjusting the eta calibration constants each time

Solution was to “pre-chew” the events

store only the events passing cuts

sum the cells in phi

discard info about EM sublayer

store all needed data in an STL structure in memory (~2 GB)

Result: can process at > 100kHz, iteration takes ~1 minute, full fit takes only ~1 hour

Loose selection cuts:

Exactly 2 jets, both passing quality cuts

Leading jet pT above trigger bias

Additional tight selection cuts:

MET < 50 GeV

d-phi > 2.9 rad.

|eta| of both jets < (3.2 - conesize)

jet pT

Hadronic Eta Calibration: A Few Checks

Adding a miscalibration recovers the full miscalibration and does not effect other constants

No significant dependence on the jet cone size used

The statistical errors returned by the fit are close to the true statistical variation

Hadronic Eta Calibration: Dependence on pT

For most eta-rings, the constant which maximizes resolution increases vs. jet pT

A similar dependence is observed in data and MC

What does this mean?

Weighting the hadronic cells more heavily includes more noise into the jets?

Non-compensation effects?

Essentially, the EM and Hadronic calorimeters have different performances for jets as functions of energy
A tradeoff between stochastic and constant terms in the energy resolution

Data

MC

Hadronic Eta Calibration: Data / MC

At any given pT range, data seems to be overweighted, compared to MC, for most eta-rings

10% caused by known pulser problem?
(Larger capacitances of hadronic cells leads to reflections in the calibration pulses.)

The ratio of data / MC remains fairly constant vs. jet pT range

Even in MC, the eta-ring calibration factors would reach unity only for very high pT jets (>500 GeV)

Current layer weights were determined using single pions with pT = 20 GeV

Should we re-calibrate the MC ?!

Is the cone jet algorithm optimal? Couldn't the calibration constants be adjusted for cells in a jet once an initial measurement of the jet energy is made?

Data
MC

Hadronic Eta Calibration: Layer Constants

Layer constants can be determined:

overall, averaged over all eta-rings

for each section: CC, ICR, EC

or for each eta-ring individually

CH is disfavored in the central regions

Noisier?

ICD/MG layers seem to be underweighted in the data

ICD FH1 FH2 FH3 FH4 CH

EC1 ICR1 CC1 CC2 ICR2 EC2

EC1 ICR1 CC1 CC2 ICR2 EC2

Data

MC

Hadronic Calibration: Jet pT Resolution

The phi-intercalibration has little effect on the overall jet energy resolution

This was surprising at first, but can be understood, since jets average over N cells... non-coherent effects will be reduced by a factor of ~1/sqrt(N)

The layer weights seem to have little effect on the jet energy resolution... only the ICD/MG and CH have significant modifications

The stochastic term can be reduced in data and also MC by the eta-ring calibration-> better resolution at low pT

The calibrations do not seem to improve the constant term -> little improvement for high pT jets
Why so much worse than MC? Run I?

Material effects? More non-compensating in Run II (different sampling time)? Less complete response to slow neutrons?

Data

MC

after phi only
after eta-ring
after layer

after phi only
after eta-ring
after layer

Conclusions

p17 will have an improved calorimeter calibration, available in July

EM calibration

Z->ee resolution is ~13% better than p14

Better modeling of material in MC

To do: Check constants on more recent data, and verify stability

Hadronic calibration

The goal was ambitious: complete the calibration in ~3 months

But we will succeed, and on time!

The group works well together, and has good leadership

Better jet energy resolution. Better MET resolution?

To do:

Perform some final tests... constants stable over time?

Inter-phi: run over full 20M event special calibration sample

Inter-eta: run over a larger p17 QCD data sample

Understand / interpret results in data / MC

Longer term:

Continue to take calibration data to the monitor stream

Document! We'll want to re-run the calibration for future data sets...

Try to understand the difference in the constant term between Run II data and MC

Perhaps an understanding will lead to a partial solution?

Backup Slides...

Hadronic Inter-phi Calibration Constants

Good

Bad, negative...

Bad, too high...

Bad, too low...

Data/MC Ratios for Hadronic Eta Calibration

MC, with / without inter-phi

Adding wrong phi intercalibration constants

to the MC has almost no effect on the

jet pT resolution

Andy Haas

2004-07-07T15:59:13