1. Song LIANG CMS-IHEP/Beijing group meeting
ECAL Reconstruction
Song LIANG
CMS-IHEP/Beijing group meeting
2019/5/21

2. Introduction of Clusters
The showers of e andγ deposit their energy in several crystals.
Summing the energy measured in such fixed arrays gives the best performance for unconverted photons, or for electrons.
Because of the strong magnetic field the energy reaching the calorimeter is spread in φ.
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3. Cluster basic cluster Island algorithm
From the seed crystal scanning first in φ and then in η.
For a crystal to be added to a cluster the following must be true:
The crystal contains a rechit with positive energy.
The crystal has not been assigned to another cluster already.
The previous crystal added (in the same direction) has higher energy.
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4. Island algorithm The only parameter:ET(seed threshold)
Find all seeds: by the condition E>ET, loops over seeds and removes those seeds that are adjacent to higher energy ones.
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5. Scan sequence:
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6. The features of Island algorithm:
1)it will not split two showers due to an electron and a radiated soft photon if the two showers are close enough;
2) it will split two showers coming from the two legs of a pi0 decay if the opening angle is sufficiently large;
3) energy deposited in crystals below the seed threshold may remain unclustered
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7. Standalone reconstruction of pi0 using island clusters for different pT
Larger the PT,
smaller the
openning angle.
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8. Supercluster
The closest cluster to a single electron most energetic island cluster lies in a very narrow η slice, as opposed to the single pi0 case.
The plot on the left shows the η2- η1 distribution for single electrons and pi0s.
A super-cluster algorithm (right) collects all calorimetric clusters satisfying a given geometric condition (e.g. lying in a certain region around the “main” cluster) into a collection of clusters
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9. Reconstructed transverse energy for 30 GeV pT electrons using a single island cluster (hatched) and a supercluster collected in a 1-crystal-wide window in h around it (solid filled).
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10. Hybrid algorithm
1)starting from a seed crystal(ET>EThybseed),1x3 crystal dominoes are made in η.
2)Ecenter domino crystal >Ewing,1x5 domino is used.
3)Scan Nstep crystals in φ,when E<Ethresh ,the dominoes are eliminated.
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11. Default values of control parameters for Hybrid algorithm
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12. Procedure
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