Sampling Calorimeter Reconstruction Issues and Approaches: An Overview. Gary Bower & Ron Cassell, SLAC May 22, 2003 SLAC LCD Workshop

Transcription

1 Sampling Calorimeter Reconstruction Issues and Approaches: An Overview Gary Bower & Ron Cassell, SLAC May 22, 2003 SLAC LCD Workshop

2 (Evolutionary) Approaches in Order of Sophistication Naïve energy flow approach Crude cluster finding approach (old) Cluster identification (current) Refined cluster identification (future) Bower/Cassell SLAC LCD Workshop- 5/22/03 2

3 Why Energy Flow? Bower/Cassell SLAC LCD Workshop- 5/22/03 3

4 Naïve Energy Flow Three clear jets of particles in event. Individual tracks identify charged particles. No individual clusters to identify neutral particles. Thus, try to use the entire swarm of hits. Extend tracks through cal, eliminate charged hits. Left with energy flow of neutral hits. Necessary for coarse grained cals but not for fine grained. Bower/Cassell SLAC LCD Workshop- 5/22/03 4

5 Pictures can be misleading Most hits are very low energy photons. 3D structure projected on to 2D. It is possible to identify clusters of hits from individual particles in the cal. Bower/Cassell SLAC LCD Workshop- 5/22/03 5

6 Primer on cal clusters Principles Interaction length (hadronic) is long. Radiation length (EM) is short. Golf ball meets bowling ball. Three signature types: minimum ionization (mu, charged hadron) electromagnetic showers (electron, gamma) hadronic showers (charged & neutral hadron) Bower/Cassell SLAC LCD Workshop- 5/22/03 6

7 Gamma shower cartoon Bower/Cassell SLAC LCD Workshop- 5/22/03 7

8 Charged hadron shower cartoon Bower/Cassell SLAC LCD Workshop- 5/22/03 8

9 Neutral hadron shower cartoon Bower/Cassell SLAC LCD Workshop- 5/22/03 9

10 Crude cluster finding approach Make contiguous hits clusters (not regional) Make cluster energy cut. Assume EM clusters are gammas. Assume Had clusters have pion mass. Assume all point directly back at IP. Treat each cluster as a particle and analyze the event using jet finders, etc. Bower/Cassell SLAC LCD Workshop- 5/22/03 10

11 Crude clusters results Using neural net can identify event type as qqbar, ZZ, WW, ttbar, ZH(120). Bower/Cassell SLAC LCD Workshop- 5/22/03 11

12 % Efficiency with NN qq WW ZZ ZH tt Gen Level Sim Level Bower/Cassell SLAC LCD Workshop- 5/22/03 12

13 % Correct ID with NN qq WW ZZ ZH tt Gen Level Sim Level Note: assumes equal cross section for all 5 processes. Bower/Cassell SLAC LCD Workshop- 5/22/03 13

14 ZH event id rate sim level % identified as ZH 6% 8% 15% 67%* 5% were actually event type: qq WW ZZ ZH tt Note: assumes equal cross section for all 5 processes. Bower/Cassell SLAC LCD Workshop- 5/22/03 14

15 Cluster identification Use cluster properties + a neural net to identify the particle that created the cluster. The ClusterID algorithm ( by Bower, Cassell, Pathek) currently identifies gammas, charged hadrons, neutral hadrons and fragments. Available in CVS. Web page is underdevelopment. Bower/Cassell SLAC LCD Workshop- 5/22/03 15

16 ClusterID recon efficiency SD detector with no gap between EM and Had cals. Bower/Cassell SLAC LCD Workshop- 5/22/03 16

17 Zmass at Zpole Bower/Cassell SLAC LCD Workshop- 5/22/03 17

18 Refined Cluster Identification What limits efficiencies and purities of ClusterID? Using tools like Cluster Analysis (Ron s talk) can identify which cases are IDed wrong. Then think up new methods for those cases. Eg, fragments Point fragments back to their origin. Eg, overlapping clusters Raise hit E level to separate clusters. Shape algorithm to see two gamma bulges. Bower/Cassell SLAC LCD Workshop- 5/22/03 18

19 The essential elements Calorimeter hits (digital or analog). A cluster builder technique A cluster identification technique (can use tracking information). To reconstruct events: Make a reconstructed particle for each cluster and track. To study efficiency (& purity): Make a clusterlist (& reconstructed particles). Bower/Cassell SLAC LCD Workshop- 5/22/03 19

20 LCD Recon is Flexible Can use more than one algorithm to do the same task in an event loop (eg, tracking or cal recon). Thus, event by event in one job, can simultaneously compare several algorithms to accomplish a task. See how each performs on the same data. Combine results of several algorithms. Bower/Cassell SLAC LCD Workshop- 5/22/03 20

21 Neural Nets and collaboration Can view different on-going studies as trying different techniques to make and identify clusters. (eg, ClusterID uses contiguous hits cluster builder with ~10 measures on each cluster, others use cone algorithm to make clusters with their measures, etc) Can combine methods using a neural net. Bower/Cassell SLAC LCD Workshop- 5/22/03 21

22 An opinion on terminology When you are making clusters and identifying their origin, you are no longer doing energy flow. You are doing traditional particle reconstruction in a calorimeter. We should stop calling these techniques energy flow and start calling them calorimeter particle reconstruction. Jean-Claude and Henri have expressed the same opinion. Bower/Cassell SLAC LCD Workshop- 5/22/03 22