EDM4hep Event Data Explorer: eedE
===========================================

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:::{admonition} Page contributors
:class: callout dropdown

Xunwu Zuo
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The [EDM4hep event data explorer (eedE)](https://key4hep.github.io/eede/release/index.html) is a tool for visualizing the association between various objects in EDM4hep events. It is lightweight and self-explanatory. This section explains the usage of eedE. 

## edm4hep2json

Please note that the `edm4hep2json` command provided in stack `2022-12-23` does not work. You can open a new SSH connection and source a more recent stack, for example
```
source /cvmfs/sw.hsf.org/key4hep/setup.sh -r 2024-03-10
``` 

eede takes json files as inputs. The `edm4hep2json` command converts the edm4hep data into a json format.
```
edm4hep2json my-file.edm4hep.root
```
You can use the command with the following options
```
Usage: edm4hep2json [olenfvh] FILEPATH
  -o/--out-file           output file path
                            default: "?edm4hep.root" --> ".edm4hep.json"
  -l/--coll-list          comma separated list of collections to be converted
  -e/--events             comma separated list of events to be processed
  -n/--nevents            maximal number of events to be processed
  -f/--frame-name         input frame name
                            default: "events"
  -v/--verbose            be more verbose
  -h/--help               show this help message
```

For example, one can call it with 
```
edm4hep2json -l ReconstructedParticles,Particle,MCRecoAssociations -e 2,3,5,7,11 my-file.edm4hep.root
```
to save only "ReconstructedParticles,Particle,MCRecoAssociations" object collections, and only the 2nd, 3rd, 5th, 7th, and 11th events in the file.
An example output can be found at [example.edm4hep.json](https://fccsw.web.cern.ch/fccsw/tutorials/eede-tutorial/example_eedE_tutorial.edm4hep.json)

## Using eedE

Once the data has been converted into a json format via edm4hep2json, one can then head to the website of [eedE](https://key4hep.github.io/eede/release/index.html). After pressing the Start button, one is required to upload the EDM4hep json file via the Browse button. You can then select the type of association (`view`) to visualize.
```{image} eede_upload.png
:align: center
:width: 600px
```

### Visualizing the MC particle Tree

Here we take the MC particle tree as an example.
In the tree shown in the picture illustrates a collision at 91 GeV, where both the electron and positron emit a ISR photon before they merge into an on-shell Z boson, which decays into a pair of b quarks.
```{image} eede_Zbb_example.png
:align: center
:width: 400px
```
For each MC particle, values for `p`, `t`, `m`, `q` represents the momentum in lab frame, time of production, invariant mass, and charge, while `d` gives the displacement from the origin of lab frame (0,0,0) to the position where the particle is produced.