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Gamma Finding procedure for Realistic PFA

Gamma Finding procedure for Realistic PFA. T.Fujikawa(Tohoku Univ.), M-C. Chang(Tohoku Univ.), K.Fujii(KEK), A.Miyamoto(KEK), S.Yamashita(ICEPP), T.Yoshioka(ICEPP) On behalf of ACFA-SIM-J Group. Motivation.

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Gamma Finding procedure for Realistic PFA

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  1. Gamma Finding procedurefor Realistic PFA T.Fujikawa(Tohoku Univ.), M-C. Chang(Tohoku Univ.), K.Fujii(KEK), A.Miyamoto(KEK), S.Yamashita(ICEPP), T.Yoshioka(ICEPP) On behalf of ACFA-SIM-J Group

  2. Motivation To get high energy resolution in multi jet event, we use the tracker information for charged particles and calorimeter hit information for neutral particles. (tracker resolution is much better than calorimeter’s.) Particle Flow Algorithm (PFA) is studied to achieve an event reconstruction. We studied part of PFA, “gamma finding method” for GLD detector, using full simulator (Jupiter).

  3. - Current Scheme of the PFA • 1.Small Clustering (collect fired cells with its neighbors) • → Define thrust and broadening for each small cluster. 2. Gamma Finding (Separate gamma/e from hadron) → Small Cluster based. 3. Cluster-Track Matching (Separate charged to neutral) → Calorimeter Cell based. Flow to make PFObject Note: → Cheating method is used for charged hadrons in the Endcap region. → Assuming the remaining clusters be neutral hadrons. Clustering flow for GLD detector

  4. 210 cm 40 cm Full One Tower EM + HD 270 cm 6.1λ 27 X0 Detector configuration Y.Yamaguchi (Tsukuba Univ.) In current Jupiter geometry, calorimeter has 4cmx4cm/12cmx12cm scintillator tile size in ECAL/HCAL as a default setting. We used this configuration in our study.

  5. Why good gamma finding is necessary? Expected jet-event in the future ILC, it has about 20% gamma contribution. Also, if we can separate gamma (and also electron) well, it make the charged hadron clustering easier. good gamma/charged hadron separation is necessary! (Z->qqbar @ Ecm = 91.2 GeV)

  6. The flow of Gamma Finding • Find “large” small cluster within ECAL region (we call it “mother small cluster”). • Apply “Gamma-Fitter” chi-square /ndf cut. (cut 1) • Apply “the distance from the nearest track” cut for mother small cluster. (cut 2) • Collect small clusters within a tube. Flow of the gamma finding As a first step of the clustering, we collect hit cells with its neighbors (with ~50MeV energy deposit upper limit). We call it “small cluster”. Our gamma finding method is performed based on the small clusters.

  7. Gamma finding method • Gamma Fitter (chi-square cut of fit) Find large small cluster within ECAL region and make a small tube along its thrust axis. Take an average of energy deposit for each 3-layers within a tube and fit the total energy deposit by Gamma distribution function. The result of chi-square/ndf is used to separate gamma/electron from hadrons.

  8. Gamma Fitter: algorithm Choose large small cluster (mother small cluster) within ECAL region and make a small tube (R = 5cm) along to its thrust axis. Fit the longitudinal shower profile of the energy deposition within a tube as an electromagnetic cascade (gamma distribution function). HCAL projection axis take an average energy deposit for each 3-layers ECAL Energy deposit in three layers are merged to reduce fluctuation. mother small cluster

  9. Gamma Fitter: single particle test The result of fitting for a single particle case (gamma at 3GeV)

  10. 1 GeV 3 GeV Yellow: gamma Red : pion 5 GeV 10 GeV Comparison of chi2/ndf (single particle) We can separate gamma/electron from pion using chi2/ndf cut.

  11. Blue : efficiency Red : purity Gamma Fitter: efficiency and purity The “Gamma fitter” works good for z->qqbar event, too. But it doesn’t have high efficiency for electron/gamma finding. (maximum ~ 90%) (Z->qqbar @ Ecm = 91.2 GeV)

  12. Yellow: e/gamma Red : all particles Chi2/ndf (Z->qqbar @ Ecm = 91.2 GeV) We set a cut position at 1.0 for below gamma finding. (~70% efficiency and ~70% purity) cut position

  13. Gamma finding method 2. The distance from the nearest track Calculate the distance between mother small cluster and its nearest track. The distance is used to separate gamma from charged particles. HCAL mother small cluster ECAL distance gamma track

  14. Yellow: Gamma Blue : electron Red : all particles Distance from the nearest track This plot shows the distribution of the distance from the nearest track for all small clusters within ECAL region. (energy-weighted) (Z->qqbar @ Ecm = 91.2 GeV)

  15. Yellow: Gamma Blue : electron Red : all particles After Chi2/ndf < 1.0 cut cut position Distance distribution (Z->qqbar @ Ecm = 91.2 GeV) We set a lower limit at 13cm. It kills the electron as well, but can reduce large amount of charged hadron contamination. We gain the benefit anyway.

  16. The result of Gamma finding 1. efficiency Finally, we got efficiency ~ 60% using “gamma fitter cut” and “the distance cut”.

  17. w/o n,KL contamination Purity ~ 93% Purity ~ 99% The result of Gamma finding 2. purity contamination is almost caused by n/KL

  18. Realistic gamma finder Cheated gamma finder The result of energy sum

  19. Other idea (not used now) 1. Energy deposit comparison between ECAL/HCAL region Assume a tube region and compare the total energy deposit between ECAL/HCAL region within a tube. HCAL E1 ECAL E2 separate events using E1/E2

  20. Other idea (not used now) 2. Energy waited Broadening/Thrust ratio of the cluster Calculate thrust and broadening for the cluster, then calculate these ratio. (EM shower has lower value compare to HD shower’s.) HCAL cluster ECAL cluster In general, (B/T)EM > (B/T)HD

  21. Other idea (not used now) 3. Calculate energy deposition ratio within a tube in ECAL Set the tube and “Maximum layer” according to cluster energy, then calculate the energy ratio between upper/lower region of Maximum layer within a tube (region 1 and 2). region 1 Maximum layer (energy dependent) region 1 region 2 region 2 ECAL Tube radius is also energy dependent gamma hadron All of them are not effective “after” gamma fitter cut…

  22. Summary • Good gamma finding (clustering) method is necessary for future LC experiment. • We got ~60% efficiency and ~99% purity using Gamma Fitter (chi2/ndf) + the nearest track distance requirement. • Current gamma finding method has high purity but which doesn’t have enough efficiency.

  23. Next step • Combine other gamma finding method (or study another method other than “gamma fitter”) to get high efficiency/purity. • Do the cut value optimization. • Study other method which use transverseshowerprofile. • Study the “relationship” with clustering method for charged hadron.

  24. Backup The result of other gamma finding method with gamma fitter chi-square cut

  25. Yellow: e/gamma Red : all particles HCAL/ECAL e-dep comparison The plot shows the energy deposit comparison between HCAL/ECAL regions after applying the chi-square cut for Z->qqbar event. After Chisquare/ndf < 1.0 cut

  26. Yellow: e/gamma Red : all particles Broadening/Thrust Broadening/Thrust ratio for the cluster after applying the chi-square cut for Z->qqbar event. After Chisquare/ndf < 1.0 cut

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