Effect of HPD/PMT gain drift in HCAL towers
•
Powel/Dima/Vladimir has shown that the LED gain in HPD is varies over time and
shift in not uniform.
•
Signal in cosmic muon also support that shift.
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What is the impact of this non-linear shift of gains in HPD tower ?
•
Can we use this readout system till 2016-17 ?
•
Try to look for various scenario and prepare ourself for the worst
1
Effect of HPD/PMT gain drift in HCAL towers
Ratio of LED signal in Oct2011 and May 2011
https://twiki.cern.ch/twiki/pub/CMS/HPDgainStability2011/HCAL_LED_
ratio_May_Oct_2011_1colmn.xls
•
What is the impact of this non-linear shift of gains in HPD tower ?
•
Can we use this readout system till 2016-17 ?
•
Try to look for various scenario and prepare ourself for the worst
2
Existing correction factors of HCAL towers
https://twiki.cern.ch/twiki/pub/CMS/HcalRespCorrsTags2011/etaPhiCorr_030
111_period1.txt
Existing gain variation is ~10%, where shift in HPD gain ~2.5%
3
MC sample and modifications of codes
A. Heering talk in HCAL General Meeting on 23rd Feb
https://indico.cern.ch/getFile.py/access?subContId=1&contribId=1&resId
=0&materialId=slides&confId=179186
“We know that QE is a function of Electric field specially for high red
sensitive Photocathodes.”
After
~2 weeks
of 13 kV
•
Assumption : QE of photo cathode is changing, both increasing and decreasing.
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Change in signal (increasing or decreasing) is also with same proportion, except the
saturation effect.
•
Need to correct it in calibration.
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Modifications of DIGI and RECO code to implement change in HPD gain (before
the production of photo-electron) and calibration correction
4
Speculations
•
Was it due to the problem of calibration system ?
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Verify it with other source
– Muon signal in those tower
5
Muon signal in HB : Towards an independent intercalibration
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Intercalibration of HO tower is done with muon in physics event.
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Can we use that for HB tower too ? HE is not possible due to lack of triggered
muon at high eta.
•
SingleMu triggered events are used for Data
•
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May10ReReco, promptReco 2011A_V4,V5&6, 2011B_V1
Both Z/*μμ and Wμ to have a consistency check
•
Basic concepts :
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Extrapolate muon from outer
part of tracker to the front
and back face of HCAL
geometry (18-sided polygon
shape for HB and plane for
HE)
•
Muon should passed the
same geometrical tower in
entrance and exit point.
In r- plane
6
Track extrapolation and associated HB tower
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Muon must be global and tracker muon for better purity
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Outer vector of tracker muon is extrapolated to front and back face of HO
– Choice of this vector is to minimse extrapolation error on HCAL surfaces
– Extrapolation : on polygon of 18 sides, not on cylinder
•
Nearest HB cell at the front face of hcal geometry
(geometry->getClosestCell(GlobalPoint pos))
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HO tower in reco geometry is inside
a cylinder.
•
That is not effecting here much, but
has an effect on low momentum
particle, extrapolation may be in
another
7
Simulation of HPD gain drift in HCAL towers
Ratio of LED signal in Oct2011 and May 2011
•
Confirm with muon signal too
8
MC sample and modifications of codes
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MC sample without pileup: /QCD_Pt15to3000_TuneZ2_Flat_7TeV_pythia6/Summer11-START311_V2-v1/GEN-SIM
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CMSSW_4_2_8, GlobalTag : START42_V12::All
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Modifications of DIGI and RECO code to implement change in HPD gain (before
the production of photo-electron) and calibration correction
• DIGI
•
SimCalorimetry/CaloSimAlgos/interface/CaloHitResponse.h add extra
member function setHBHEScale() and declare arrays[eta/[phi][depth] for scale
factor hcal_en_scale[100][72][4];
•
Put this scale in database (change the existing database with this factor)
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SimCalorimetry/CaloSimAlgos/src/CaloHitResponse.cc set the HEBHE scale
factor through setHBHEScale() and in
double CaloHitResponse::analogSignalAmplitude() changed the simulated
energy deposit according to scale factor, before going to calculate number of
photoelectron
•
SimCalorimetry/HcalSimProducers/src/HcalDigitizer.cc
Call setHBHEScale() in the default constructor
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Modification of Reconstruction code
• RECO
•
RecoLocalCalo/CaloTowersCreator/interface/CaloTowersCreationAlgo.h
define inverse scale factor
double hcal_en_invscale[100][72][4];
•
RecoLocalCalo/CaloTowersCreator/src/CaloTowersCreationAlgo.cc
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Put inverse scale factor in default constructor
CaloTowersCreationAlgo::CaloTowersCreationAlgo(double EBthreshold,
double EEthreshold,..
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in CaloTowersCreationAlgo::assignHit(const CaloRecHit * recHit)
use inverse scale factor to compensate loss of gain.
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Obtain modified weight (gain) factor through
CaloTowersCreationAlgo::getThresholdAndWeight(Const DetId&,
double & threhold, double& weight)
10
Jet/MET with different scenario
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Event selection : All, no noise filter
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Jet selection
– No JetID
– Pt>50 GeV and ||<2.5
No JEC, similarly for MET (no correction)
•
•
Here just compared these four scenarios for calojet (tcMet) and PFJets (PFMET)
•
Default setup
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Ratio : Varies gain/correction factor of hcal towers with the ratio plot
•
5 Ratio: Varies gain/correction factor of hcal towers fifth time more than the
ratio plot
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10% : Randomly reduce gain of 10% tower by 10% and increase gain of
another 10% tower by 10%
•
20% : Randomly reduce gain of 20% tower by 50% and increase gain of
another 20% tower by 50%
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-mod : Varies gain/correction factor of hcal towers as 1+ 0.0025  (i - 36)
11
Distributions
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Top : Superimpose of all different scenario
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Remaining : Ratio of all other plots with respect to first one (Default)
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Fit the ratio with 1st order polynomial and put those fitted values along with
2/ndf to quantify the similarity/difference
12
CaloJet
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Number of jets
PFJet
Less than 1-2% effect, except larger gain variation (50%)
13
CaloJet
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Pt of jets
PFJet
Pt spectrum are nearly same except large variation of gain (50%) , same is true for
leading, next-to leading jet …..
14
CaloJet
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Pseudorapidity of jets
PFJet
Same as Pt spectrum , which are nearly same except large variation of gain (50%)
15
CaloJet
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Azimuthal angle of jets
PFJet
All looks fine
16
Invariant mass of two leading jets
CaloJet
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No variation is observed, except large change in gain
PFJet
17
Missing transverse momentum
tcMet
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Variation for larger gain variation
PFMet
18
tcMet
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Azimuthal angle of MET
PFMet
Variation due to large gain variation, -modulation in gain
19
Azimuthal angle of MET (MET>30 GeV)
tcMet
•
PFMet
Larger amplitudes : large gain variation, -modulation in gain
20
Resolution : First look
CaloJet
PFJet
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Jet Energy resolution : (PtRecPtGen)/PtGen
CaloJet
(|R|<0.2)
PFJet
Do not see much deviation in Energy resolution, bias can be corrected in offline.
Difficult to make any conclusion before using correction factor
22
CaloJet
Phi resolution of jets
|(PtRecPtGen)/PtGen +0.2/0.0|<0.4/0.2
PFJet
Deterioration with larger deviation in gain, effect in PFJet is more than CaloJet !
23
Eta resolution of jets
CaloJet
|(PtRecPtGen)/PtGen +0.2/0.0|<0.4/0.2
PFJet
Deterioration with larger deviation in gain, effect in PFJet is more than CaloJet !
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Conclusion
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No significant deviation is observed with 5 times more variation (observed in six
months)
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50% change is gain does effect the measurement on Pt spectrum of jet, dijet
invariant mass as well as phi-modulation in MET.
•
No significant deterioration of Jet resolutions
•
~10-20% Modulation of azimuthal angle of Jet/MET
– For random change in gain by 50% of 20% channels
– For known periodic gain variation of amplitude 10% gain variation in HPD
We are going to generate events for various scenarios 2014, 2016 and 2018
and check the performances using new calibrations
1. Generation of Minbias events for calibration using phi symmetry
2. Look for the effects in physics events
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Leading jet within ||<2.0
CaloJet
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Same variation as all jets
PFJet
26
Ratio of LED gain in Oct11/May11
https://twiki.cern.ch/twiki/pub/CMS/HPDgainStability2011/HCAL_LED_
ratio_May_Oct_2011_1colmn.xls
27