Development of a Particle Flow Algorithms (PFA) at Argonne Presented by Lei Xia ANL - HEP.
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Transcript of Development of a Particle Flow Algorithms (PFA) at Argonne Presented by Lei Xia ANL - HEP.
Development of a Particle Development of a Particle Flow Algorithms (PFA) at Flow Algorithms (PFA) at
ArgonneArgonne
Presented by
Lei Xia ANL - HEP
June 5-9, 2006 CALOR 2006
IntroductionIntroduction Measure jets in the PFA way…Measure jets in the PFA way…
Clear separation of the 3 parts is the key issue of PFAClear separation of the 3 parts is the key issue of PFA Charged particle, photon and neutral hadron: all deposit their energy in the calorimCharged particle, photon and neutral hadron: all deposit their energy in the calorim
eterseters Maximum segmentationMaximum segmentation of the calorimeters is needed to make the separation poss of the calorimeters is needed to make the separation poss
ibleible One Major R&D issue: development of PFAOne Major R&D issue: development of PFA
Show that the ILC goal for jet energy resolution (30%/sqrtE) can be achieved by PFAShow that the ILC goal for jet energy resolution (30%/sqrtE) can be achieved by PFA Develop a PFA that can be used for detector optimizationDevelop a PFA that can be used for detector optimization
Argonne has two parallel efforts on PFA development, this talk shows result frArgonne has two parallel efforts on PFA development, this talk shows result from one of themom one of them
Particles in JetsParticles in Jets Fraction of jet energyFraction of jet energy Measured withMeasured with
ChargedCharged 65% Tracker, negligible uncertainty
PhotonPhoton 25% ECal, 15%/ √ E
Neutral hadronNeutral hadron 10% ECal + HCal, ~50-60%/ √ E
June 5-9, 2006 CALOR 2006
Perfect PFA: NO algorithm effectPerfect PFA: NO algorithm effect
Take MC track momentum as the energy of charged particlesTake MC track momentum as the energy of charged particles Remove calorimeter hits associated with charged particles by looking at MC infomationRemove calorimeter hits associated with charged particles by looking at MC infomation Sum up everything else in the calorimeter as neutral energySum up everything else in the calorimeter as neutral energy
Apply appropriate sampling fractions for photon hits and neutral hadron hits Apply appropriate sampling fractions for photon hits and neutral hadron hits Use MC information to separate photon hits and neutral hadron hitsUse MC information to separate photon hits and neutral hadron hits
Z-pole events, just event energy sum, no jet algorithm appliedZ-pole events, just event energy sum, no jet algorithm applied
Example: SiD aug05_np
central peak ~2.3 GeV (~80%) (no event selection)
We have room for PFA development
June 5-9, 2006 CALOR 2006
PFA effort: overviewPFA effort: overviewCalorimeter Hits
Reconstructed TracksCalorimeter Clusters
ClusteringAlgorithm
PhotonIdentification
EM Clusters Hadron Clusters
‘Neutral’ Clusters Matched Clusters
Track-clustermatching
Charge fragmentidentification
Neutral Clusters Fragments
Ephoton Eneu-had 0 0 Ptrack
Hadron sampling fraction
EM sampling fraction
Total event
energy
Tracker Hits
Track findingAlgorithm
This is strangeWill explain
June 5-9, 2006 CALOR 2006
Clustering algorithm: hit densityClustering algorithm: hit density
I
J RijVf
Vb
V1V2
}{
)||/|(|)||/|(|)||/|(| )(2
332
222
11
ij
VRVVRVVRVi
ijijij eeeD
With V3 = Vf (if (Vf•Rij) > 0) or Vb (if (Vb•Rij) > 0)
• Hit density reflects the closeness from one hit i to a group of hits {j}• {j} = {all calorimeter hits} to decide if hit i should be a cluster seed• {j} = {all hits in a cluster} to decide if hit i should be attached to this cluster
• Consider cell density variation by normalizing distance to local cell separation • Density calculation takes care of the detector geometry• Clustering algorithm then treat all calorimeter hits in the same way
June 5-9, 2006 CALOR 2006
Clustering algorithm: grow a Clustering algorithm: grow a clustercluster
Find a cluster seed: hit with highest density among remaining hitsFind a cluster seed: hit with highest density among remaining hits Attach nearby hits to a seed to form a small clusterAttach nearby hits to a seed to form a small cluster Attach additional hits based on density calculationAttach additional hits based on density calculation
i = hit been considered, {j} = {existing hits in this cluster}i = hit been considered, {j} = {existing hits in this cluster} EM hits, DEM hits, Dii > 0.01 > 0.01 HAD hits, DHAD hits, Dii > 0.001 > 0.001 Grow the cluster until no hits can be attached to itGrow the cluster until no hits can be attached to it
Find next cluster seed, until run out of hitsFind next cluster seed, until run out of hits
Hit been considered
seed
Hits of a cluster
June 5-9, 2006 CALOR 2006
Density driven clusteringDensity driven clustering
ParticleParticle ECal hit efficienECal hit efficiencycy
HCal hit efficienHCal hit efficiencycy
Overall hit Overall hit efficiencyefficiency
Overall energy Overall energy efficiencyefficiency
Photon (1GeV)Photon (1GeV) 89%89% 43%43% 89%89% 91%91%
Photon (5GeV)Photon (5GeV) 92%92% 54%54% 92%92% 96%96%
Photon (10GeV)Photon (10GeV) 92%92% 61%61% 92%92% 97%97%
Photon (100GeV)Photon (100GeV) 95%95% 82%82% 95%95% >99%>99%
Pion (2 GeV)Pion (2 GeV) 78%78% 59%59% 75%75% 71%71%
Pion (5 GeV)Pion (5 GeV) 81%81% 70%70% 79%79% 80%80%
Pion (10GeV)Pion (10GeV) 84%84% 80%80% 83%83% 85%85%
Pion (20GeV)Pion (20GeV) 85%85% 87%87% 88%88% 91%91%
• Typical electron cluster energy resolution ~ 21%/sqrt(E)• Typical pion cluster energy resolution ~70%/sqrt(E)• All numbers are for one main cluster (no other fragments are included)
June 5-9, 2006 CALOR 2006
Cluster purity : Z pole (uds) eventsCluster purity : Z pole (uds) events
Most of the clusters (89.7%) are pure (only one particle contributes)Most of the clusters (89.7%) are pure (only one particle contributes) For the remaining 10.3% clustersFor the remaining 10.3% clusters
55% are almost pure (more than 90% hits are from one particle)55% are almost pure (more than 90% hits are from one particle) The remaining clusters contain merged showers, some of them are ‘trouble makers’The remaining clusters contain merged showers, some of them are ‘trouble makers’
On average, 1.2 merged shower clusters/Z pole eventOn average, 1.2 merged shower clusters/Z pole event This will result in double counting or underestimating of jet energy which leads to poor resolutionThis will result in double counting or underestimating of jet energy which leads to poor resolution Will re-visit clustering algorithm after other PFA components are more of less settledWill re-visit clustering algorithm after other PFA components are more of less settled
Number of contributingparticles in a cluster
Fraction from largest contributorfor clusters with multi-particles
June 5-9, 2006 CALOR 2006
Photon id – longitudinal H-matrixPhoton id – longitudinal H-matrix
EEphotonphoton 0.100.10 0.250.25 0.500.50 0.750.75 1.01.0 2.02.0 5.05.0 10.10. 20.20. 50.50. 100.100.
Eff(%)Eff(%) 1.131.13 43.943.9 89.789.7 95.795.7 96.896.8 98.498.4 98.398.3 96.696.6 93.993.9 83.683.6 52.552.5
If I use a single cut: log(Prob(chisqD)) > -10If I use a single cut: log(Prob(chisqD)) > -10log(Prob(chisqD)) is calculated from default H-matrixaccumulated from a wide energy range of photons
Trouble comes in at the two endsBut that’s not all yet…
Photon: 1GeV Photon: 5GeV
June 5-9, 2006 CALOR 2006
Photon id – longitudinal H-matrixPhoton id – longitudinal H-matrix
Efficiency of photons still need to improveEfficiency of photons still need to improve Try to accumulate longitudinal H-matrix(es) at smaller photon energy regionsTry to accumulate longitudinal H-matrix(es) at smaller photon energy regions
Efficiency of hadrons is way to highEfficiency of hadrons is way to high Take neutral hadrons as photons results in using wrong calibration constantTake neutral hadrons as photons results in using wrong calibration constant Take charged hadrons as photons results in double counting of energy directlyTake charged hadrons as photons results in double counting of energy directly
Current (temporary) solution: still subject ‘photons’ to track-cluster matching which will Current (temporary) solution: still subject ‘photons’ to track-cluster matching which will recover charged hadrons but as the same time will lose some real photonsrecover charged hadrons but as the same time will lose some real photons
Will use more variables to eliminate hadrons: first IL layer, shower depth/shape, etc.Will use more variables to eliminate hadrons: first IL layer, shower depth/shape, etc. A single cut on longitudinal H-matrix is NOT enough to identify photonsA single cut on longitudinal H-matrix is NOT enough to identify photons
EE 1.01.0 2.02.0 5.05.0 10.10. 20.20.
effeffK0K0
(%)(%) 26.126.1 30.830.8 33.233.2 36.136.1 35.235.2
effeffnn
(%)(%) 6.616.61 18.618.6 33.033.0 38.38. 37.737.7
effeffnbarnbar
(%)(%) 49.149.1 48.848.8 46.946.9 40.940.9 38.538.5
neutron: 5GeV
E(Pi-)E(Pi-) 2.02.0 5.05.0 10.10. 20.20.
Eff (%)Eff (%) 13.313.3 8.18.1 7.07.0 3.83.8
June 5-9, 2006 CALOR 2006
Photon id – try H-matrix(E)Photon id – try H-matrix(E)
Efficiency of photon looks much better, however, at the cost of Efficiency of photon looks much better, however, at the cost of accepting even more hadrons (not shown here)accepting even more hadrons (not shown here)
The energy range that one H-matrix can cover is still to be studied The energy range that one H-matrix can cover is still to be studied I am studying other variables to remove hadronsI am studying other variables to remove hadrons
First interaction layer, shower size/shape, etcFirst interaction layer, shower size/shape, etc
Eventually, after photon identification is done rather well, I will no Eventually, after photon identification is done rather well, I will no longer subject identified photons to track-cluster matchinglonger subject identified photons to track-cluster matching
EEphotonphoton 0.100.10 0.250.25 0.500.50 0.750.75 1.01.0 2.02.0 5.05.0 10.10. 20.20. 50.50. 100.100.
Eff(%)Eff(%) 95.695.6 95.995.9 96.996.9 97.497.4 97.697.6 97.497.4 98.598.5 98.398.3 97.997.9 97.197.1 97.097.0
Still use a single cut: log(Prob(chisqD)) > -10Still use a single cut: log(Prob(chisqD)) > -10But log(Prob(chisqD)) is calculated from individual H-matrixaccumulated at the same energies of the photons
June 5-9, 2006 CALOR 2006
Charge fragment Charge fragment identification/reductionidentification/reduction
Use geometrical parameters to diUse geometrical parameters to distinguish real neutral hadron cluststinguish real neutral hadron clusters and charge hadron fragmentsers and charge hadron fragments
Energy of matched clusters
From neutralparticles
From chargedparticles
Energy of clusters not matched toany track: neutral candidate
From neutralparticles
From chargedparticles(fragments)
From neutralparticles
From chargedparticles(fragments)
After charge fragmentidentification/reduction
1 : 1.24 0.88 : 0.35
June 5-9, 2006 CALOR 2006
PFA: Z-pole (uds) performancePFA: Z-pole (uds) performance
Barrel events: 60%
3.22 GeV @88.2GeV 59% 9.95 GeV 41%
All events:
3.41 GeV @87.9GeV 58.5% 10.4 GeV 41.5%
SiD aug05_np
Barrel: -45 deg < Theta (uds quark) < 45 deg
SiD aug05_np
The broad tails of the distribution need to be reduced significantly, otherwise, physics performance is not going to be good…
June 5-9, 2006 CALOR 2006
TimelineTimelineC
on
firm
/tun
e M
C sim
ula
tion
Test BeamPFA development
Working PFA
Z-pole, 2 jets
>= 500 GeV, multiple jets
Establish jetPFA E~
Optimize detector design
Done
In progressShould be done by a few months’effort
Hard to tell at this moment(doesn’t seem to be a trivial job!)
June 5-9, 2006 CALOR 2006
Summery Summery
Particle Flow Algorithms are being developed at Argonne Two ‘complete’ PFA’s are available to play with Performance of both PFA’s looks promising, and will be improved
Current performance of this PFA at Z-pole looks promising but not good enough yet Already identified several components that need to be worked on Will continue to work on it in the next few month Need to achieve ~30%/sqrtE with small tail component at this energy
Need to study PFA performance over the entire ILC interested jet energy range and with more complicate final states Need to show that ILC jet energy resolution goal can be achieved Get PFA ready for optimizing detector design
Test beam data need to come in time!