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Calibration of CMS detector usingParticle Flow Objects
Sunanda Banerjee Gobinda Majumder
Swagata Mukherjee
India CMS MeetingSaha Institute of Nuclear Physics, Kolkata
18 – 21 December , 2012
19 Dec. 2012 S. Mukherjee 2
OutlineOutline
● Reason to introduce PF calibration● Scenario without HO● Scenario with HO● Future Plans
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What is Particle Flow and Why is it important ?
Aims to reconstruct all stable particles in an event and returns a single list of reconstructed particles → Photon, Charged Hadron, Neutral Hadron, Muon, Electron.
Particle Flow reconstruction provides a global pp-collision event description by using information from different sub-detectors and combining it in the best possible way
Higher level physics objects can be built from the particle list
Jets , Missing transverse Energy etc.
19 Dec. 2012 S. Mukherjee 4
Why is Particle Flow Calibration needed?Why is Particle Flow Calibration needed?✔ HCAL and ECAL are already calibrated. PF calibration is done
on top of it.
✔ Energy reconstructed in PF algorithm, by combining ECAL and HCAL RecHit energies, is far from the true energies of the hadrons.
✔ This is especially true for low energy hadrons → energy is underestimated due to noise and threshold conditions.
✔ Estimating scale factors separately for ECAL and HCAL energies →
• Better estimate of the reconstructed energy
• Improvement in the energy resolution
• A smooth transition from low energy regime to high energy regime
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Samples UsedSamples Used
✔ Hadron samples are used for this calibration work
➢ Events are generated using CMSSW version 6_0_0_pre3 with particle gun event generator
➢ Separate samples are created with K+, K-, KL
0 , neutrons,
protons, anti-neutrons, anti-protons, π+ and π- ➢ Flat energy spectra of particles between 10 GeV and 1 TeV
are generated in the range |η| < 1.5 using a flat η distribution ➢ More or less 600k events are generated for each particle type
Thanks to Salavat
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Scenario 1 : Without HOScenario 1 : Without HOFor a hadron we expect energy deposit in the HCAL along with MIP like or higher energy (early showers) in the ECAL.
● ETrue
is fitted by (a+b.EECal
+c.EHCal
) =(ECorr
, say)
● 'a' is independent of energy, supposed to correct for ECAL and HCAL thresholds. 'b' and 'c' depends on E
True .
● Coefficients 'b' and 'c' are calculated by minimizing
● σi for barrel :
● → Two equations involving 'b' and 'c'
‘abc ’ Fit
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Inverting the resulting linear equations ,
Coeff 'a' cannot be obtained this way : To be put by hand
● Take 'a=0' for simplicity (Not a good choice)● Non zero 'a' → ◮ a = 3.5GeV (for E
ECal ≠ 0, E
HCal ≠ 0 )
◮ a = 3.0GeV (for EECal
= 0 )
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Why include HO ?Why include HO ?
➢ Around April 2012 , a study of MET measurements prompted that energy measured in HO rings 0 and 1 will be used for physics analysis.
➢ We extended the original code used to get the scales for ECAL and HCAL to include those for HO.
➢ Ntuples are created containing the information of energy in EB, HB, HO (separately for rings 0,1,2), η and the true energy of the particle.
➢ Modified macro is used on this ntuple to produce the plots within the ROOT version in CMSSW 5_2_0_pre6.
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Onto the plots ...Onto the plots ...
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Energy Calibration Coefficients : Without HOEnergy Calibration Coefficients : Without HO
Case 1 : EECal
> 0 , EHCal
> 0
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Case 2 : EECal
> 0 , EHCal
= 0
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Case 3 : EECal
= 0 , EHCal
> 0
Now, Response can be calculated as :
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Response : Scatter Plots (without HO)Response : Scatter Plots (without HO)*
*
* An eta correction has been used. Details are in Back Up
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Response : Profile Histogram (without HO)Response : Profile Histogram (without HO)
* An eta correction has been used. Details are in Back Up
*
*
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What is the effect of the What is the effect of the ηη correction on the response ? correction on the response ?
Magenta : No η correctionBlue : η Corrected
η Correction doesn't really help much
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Energy Resolution Plots (without HO)Energy Resolution Plots (without HO)
* An eta correction has been used. Details are in Back Up
*
*
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Scenario 2 : With HOScenario 2 : With HO
● ETrue
is fitted with (a + b.EECal
+ c.EHCal
+ d.EHO
)
● Coefficients 'b' , 'c' and 'd' are calculated by minimizing
● Where σi =
● → Three equations involving
'b' , 'c' and 'd'
‘abcd’ Fit
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Inverting the resulting linear equations ,
Value of 'a' is taken same as before
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Plots after including Ring 0 only
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Energy Calibration Coefficients : Energy Calibration Coefficients : With HO Ring 0With HO Ring 0
Case 1 : EECal
> 0 , EHCal
> 0 , EHO
> 0
Large fluctuation in HO coefficient while true energy is less than 100 GeV
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Case 2 : EECal
> 0 , EHCal
> 0 , EHO
= 0
With HO Ring 0With HO Ring 0
Coefficients are almost constant beyond 100 GeV
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Case 4 : EECal
= 0 , EHCal
> 0 , EHO
> 0
With HO Ring 0With HO Ring 0
Coefficient is almost constant throughout the whole energy range
Some fluctuations in low energy (< 100 GeV)
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Response : Profile Histogram (with HO Ring 0)Response : Profile Histogram (with HO Ring 0)
* An eta correction has been used. Details are in Back Up
*
*
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Energy Resolution Plots (with HO Ring 0)Energy Resolution Plots (with HO Ring 0)
* An eta correction has been used. Details are in Back Up
*
*
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But ...But ...
Is there any improvement in Energy Resolution after including Ring 0 ?
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Blue : Without HOMagenta : With Ring 0
Here all the particles in the η range-1.479 to +1.479 has been taken
What if I take only those particles which lies What if I take only those particles which lies in the in the ηη range -0.34 to +0.34 ? range -0.34 to +0.34 ?
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Plots after including Ring 0+1*
* Plots of Energy Calibration Coefficients, Response and Resolution are in Back Up.
Let's take a look only at the Resolution Comparison plotResolution Comparison plot
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Blue : Without HOMagenta : With Ring 0Green : With Ring 0+1
All the particles in the η range -1.479 to +1.479 has been taken
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Resolution Comparison Plot after including Resolution Comparison Plot after including Ring 0+1+2 Ring 0+1+2 *
Blue : Without HOMagenta : With Ring 0Green : With Ring 0+1Black : With Ring 0+1+2
Blue : Without HOMagenta : With Ring 0Green : With Ring 0+1Black : With Ring 0+1+2
* Other plots are in Back Up
All the particlesin the η range-1.479 to +1.479has been taken
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Summary & OutlookSummary & Outlook
● Energy scale factors are computed for the PF algorithm with energies from ECAL, HB and HO
● Inclusion of energy measurements from HO improves energy resolution of single particles
● Ring 2 has very little effect on the improvements
● Verify these factors in jets
● Calculate the scale factors using dijet events and gamma+jet events.
● We plan to use the scale factors in real data
Thank You
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Back Up SlidesBack Up Slides
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Plots after including Ring 0+1
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Energy Calibration CoefficientsEnergy Calibration Coefficients
Case 1 : EECal
> 0 , EHCal
> 0 , EHO
> 0
With HO Ring 0+1With HO Ring 0+1
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Case 2 : EECal
> 0 , EHCal
> 0 , EHO
= 0
Case 3 : EECal
> 0 , EHCal
= 0 , EHO
= 0
With HO Ring 0+1With HO Ring 0+1
19 Dec. 2012 S. Mukherjee 35
Case 4 : EECal
= 0 , EHCal
> 0 , EHO
> 0
Case 5 : EECal
= 0 , EHCal
> 0 , EHO
= 0
With HO Ring 0+1With HO Ring 0+1
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Response : Scatter Plots (with HO Ring 0+1)Response : Scatter Plots (with HO Ring 0+1)
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Response : Profile Histogram (with HO Ring 0+1)Response : Profile Histogram (with HO Ring 0+1)
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Energy Resolution Plots (with HO Ring 0+1)Energy Resolution Plots (with HO Ring 0+1)
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Plots after including Ring 0+1+2
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Energy Calibration CoefficientsEnergy Calibration Coefficients
Case 1 : EECal
> 0 , EHCal
> 0 , EHO
> 0
With HO Ring 0+1+2With HO Ring 0+1+2
19 Dec. 2012 S. Mukherjee 41
Case 2 : EECal
> 0 , EHCal
> 0 , EHO
= 0
Case 3 : EECal
> 0 , EHCal
= 0 , EHO
= 0
With HO Ring 0+1+2With HO Ring 0+1+2
19 Dec. 2012 S. Mukherjee 42
Case 4 : EECal
= 0 , EHCal
> 0 , EHO
> 0
Case 5 : EECal
= 0 , EHCal
> 0 , EHO
= 0
With HO Ring 0+1+2With HO Ring 0+1+2
19 Dec. 2012 S. Mukherjee 43
Response : Scatter Plots (with HO Ring 0+1+2)Response : Scatter Plots (with HO Ring 0+1+2)
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Response : Profile Histogram (with HO Ring 0+1+2)Response : Profile Histogram (with HO Ring 0+1+2)
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Energy Resolution Plots (with HO Ring 0+1+2)Energy Resolution Plots (with HO Ring 0+1+2)
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η correction of reconstructed energyη correction of reconstructed energy
The following angular correction has been used :
We have also tried the following types of angular corrections, which gave more or less similar results.
Coefficients are calculated by minimizing
→ Type_0 (say)
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Plots for Plots for ηη coefficients coefficients
→ Without HO
With HO Ring 0 ←
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Weight Factors of Different Hadrons
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Snippets from our Snippets from our ππ+ + ntuplentuple
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2D plots of “Energy in ECAL” vs “Energy in HO” when true energy is less than 100 GeV(With π+ ntuple )
