I am having this image from ATLAS Detector.

![](https://i.imgur.com/2dnmlHK.jpg)

In gray you can see the ATLAS's Si Tracker.In Green you see the Electromagnetic Callorimeter. In red there is the Hadron Callorimeter and in Blue there are the muon Telescope.

Those two traces are suppossed to be elecrtrons. My question is, why cannot they be photons?
Nuclear Physisists are using Si Detectors for gamma ray spectroscoopy, which means that they can actually detect photons, with them.

Just for the record, there is a cut in transversal momentum, of 10GeV...

Any ideas on why to reject those particles from being photons?

![](https://i.imgur.com/zM2DY8g.jpg)