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Charge Subtraction, Weizmann Clusterizer , and Pattern RecognitionPowerPoint Presentation

Charge Subtraction, Weizmann Clusterizer , and Pattern Recognition

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### Charge Subtraction, Weizmann Clusterizer, and Pattern Recognition

Mihael Makek

Weizmann Institute of Science

HBD Fest, Stony Brook, 2010

Charge Subtraction

- HBD occupancy in the most central events > 95 %
- Subtracted is the average charge per cell:
- on event-by-event basis
- for each particular HBD module
- taking into account pad area

- Occupancy reduced to ~30 % in the most central events

before subtraction:

after subtraction:

M. Makek - WIS

HBD – charge subtraction

- The subtraction is justified by the fact that the number of the scintillation photons grows linearly with number of tracks in CA
- The example shows this for a single HBD module:

- The bars represent the sigma of the gaussian fit to the average charge distribution (for given centrality)

M. Makek - WIS

Weizmann Clusterizer

- Seed preblobs on pads with q > 3 pe
- Add the six neighbors if they are above threshold (centrality dependant ~ 0-2 pe)
- Merge preblobs if they have overlapping pads with the „main“ preblob
- Match the cluster to the closest hit

M. Makek - WIS

Weizmann Clusterizer

- The charge measured in HBD is obtained after matching cuts on hbddphi and hbddz
- The background is estimated by swapping (CA tracks projected to a different module, x is swapped)
- The background is normalized to the matching distributions tail-to-tail and subtracted

signal+background

background

M. Makek - WIS

Pattern Recognition

- The random matching in HBD is due to the fact that CA electron tracks originating from conversions in and after the HBD backplane have no real matching hit in the HBD
- The rejection of the random is achieved in three steps:
- Requirying positional matching of the CA track projection and HBD cluster (3 sigma)
- Rejection of 1 pad clusters
- Rejection of clusters with the maximum pad charge below a certain threshold. This threshold is centrality dependent

- The preblobs with qmax > 80 pe are rejected
- Pattern recognition is done on preblob level

peripheral

central

signal

background

M. Makek - WIS

Pattern Recognition

Before p.r.

After p.r.

- The pattern recognition significantly improves HBD signal to randoms, but costs the efficiency
- The efficiency is estimated from MC simulation of single electrons embedded with HBD MB data

S/R ~ 2.2

S/R ~ 1.1

M. Makek - WIS

Pattern Recognition

- variables monitored, but not as useful:
qmax-qmin

qmin/qmax

qmin/qtot

qmax/qtot

- variables defined but not yet used:
(yloc,zloc) of all pads in the cluster

M. Makek - WIS

Summary

I. WIS Clusterizer with clustersize>1 && qmax<80

II. Pattern recognition + I.

M. Makek - WIS

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