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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
19 Dec. 2012 S. Mukherjee 3
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
19 Dec. 2012 S. Mukherjee 5
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
19 Dec. 2012 S. Mukherjee 6
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
19 Dec. 2012 S. Mukherjee 7
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 )
19 Dec. 2012 S. Mukherjee 8
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.
19 Dec. 2012 S. Mukherjee 9
Onto the plots ...Onto the plots ...
19 Dec. 2012 S. Mukherjee 10
Energy Calibration Coefficients : Without HOEnergy Calibration Coefficients : Without HO
Case 1 : EECal
> 0 , EHCal
> 0
19 Dec. 2012 S. Mukherjee 11
Case 2 : EECal
> 0 , EHCal
= 0
19 Dec. 2012 S. Mukherjee 12
Case 3 : EECal
= 0 , EHCal
> 0
Now, Response can be calculated as :
19 Dec. 2012 S. Mukherjee 13
Response : Scatter Plots (without HO)Response : Scatter Plots (without HO)*
*
* An eta correction has been used. Details are in Back Up
19 Dec. 2012 S. Mukherjee 14
Response : Profile Histogram (without HO)Response : Profile Histogram (without HO)
* An eta correction has been used. Details are in Back Up
*
*
19 Dec. 2012 S. Mukherjee 15
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
19 Dec. 2012 S. Mukherjee 16
Energy Resolution Plots (without HO)Energy Resolution Plots (without HO)
* An eta correction has been used. Details are in Back Up
*
*
19 Dec. 2012 S. Mukherjee 17
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
19 Dec. 2012 S. Mukherjee 18
Inverting the resulting linear equations ,
Value of 'a' is taken same as before
19 Dec. 2012 S. Mukherjee 19
Plots after including Ring 0 only
19 Dec. 2012 S. Mukherjee 20
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
19 Dec. 2012 S. Mukherjee 21
Case 2 : EECal
> 0 , EHCal
> 0 , EHO
= 0
With HO Ring 0With HO Ring 0
Coefficients are almost constant beyond 100 GeV
19 Dec. 2012 S. Mukherjee 22
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)
19 Dec. 2012 S. Mukherjee 23
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
*
*
19 Dec. 2012 S. Mukherjee 24
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
*
*
19 Dec. 2012 S. Mukherjee 25
But ...But ...
Is there any improvement in Energy Resolution after including Ring 0 ?
19 Dec. 2012 S. Mukherjee 26
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 ?
19 Dec. 2012 S. Mukherjee 27
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
19 Dec. 2012 S. Mukherjee 28
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
19 Dec. 2012 S. Mukherjee 29
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
19 Dec. 2012 S. Mukherjee 30
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
19 Dec. 2012 S. Mukherjee 31
Back Up SlidesBack Up Slides
19 Dec. 2012 S. Mukherjee 32
Plots after including Ring 0+1
19 Dec. 2012 S. Mukherjee 33
Energy Calibration CoefficientsEnergy Calibration Coefficients
Case 1 : EECal
> 0 , EHCal
> 0 , EHO
> 0
With HO Ring 0+1With HO Ring 0+1
19 Dec. 2012 S. Mukherjee 34
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
19 Dec. 2012 S. Mukherjee 36
Response : Scatter Plots (with HO Ring 0+1)Response : Scatter Plots (with HO Ring 0+1)
19 Dec. 2012 S. Mukherjee 37
Response : Profile Histogram (with HO Ring 0+1)Response : Profile Histogram (with HO Ring 0+1)
19 Dec. 2012 S. Mukherjee 38
Energy Resolution Plots (with HO Ring 0+1)Energy Resolution Plots (with HO Ring 0+1)
19 Dec. 2012 S. Mukherjee 39
Plots after including Ring 0+1+2
19 Dec. 2012 S. Mukherjee 40
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)
19 Dec. 2012 S. Mukherjee 44
Response : Profile Histogram (with HO Ring 0+1+2)Response : Profile Histogram (with HO Ring 0+1+2)
19 Dec. 2012 S. Mukherjee 45
Energy Resolution Plots (with HO Ring 0+1+2)Energy Resolution Plots (with HO Ring 0+1+2)
19 Dec. 2012 S. Mukherjee 46
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)
19 Dec. 2012 S. Mukherjee 47
Plots for Plots for ηη coefficients coefficients
→ Without HO
With HO Ring 0 ←
19 Dec. 2012 S. Mukherjee 48
Weight Factors of Different Hadrons
19 Dec. 2012 S. Mukherjee 49
Snippets from our Snippets from our ππ+ + ntuplentuple
19 Dec. 2012 S. Mukherjee 50
2D plots of “Energy in ECAL” vs “Energy in HO” when true energy is less than 100 GeV(With π+ ntuple )
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