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Correction for error in TLA Photon chain step

Marco Montella requested to merge mmontell/athena:TLAPhoton into master

This MR addresses the error in the Photon TLA sequence reported in [ATR-23448].

The error was caused by an erroneous handling of the Photon EventView within TrigEgammaTLAPhotonHypoAlg.cxx, by which events where two and more Photons had been reconstructed within the same EventView would sometimes fail to find a successful match between the original and the deep-copied TLA Photon.

The HypoAlg workflow has been substantially altered to conform to the prescription for EventView and container handling discussed here.

After the modifications implemented in this MR, the error is no longer observed in the Reco_tf test discussed in the JIRA ticket.

Additionally, this MR implements a dynamic threshold for the transverse energy of Photons to be saved to the TLA container. This is done by extracting the HLT photon threshold from the chain dictionary in PhotonChainConfiguration, passing the value to the TLA sequence and finally setting the TLA threshold to be (HLT_threshold - 20 GeV) if such number is greater than zero (TrigEgammaTLAPhotonConfig.py in TrigEgammaRec). No energy threshold is required if the HLT threshold is less than 20 GeV. Tagging @rbielski to double check that this strategy is sound.

Many thanks,

Marco and @doglioni

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