DST Output format summary

This document summarizes what would be preserved in the output DST for different dst MC format. The dst MC format of HLT2 reconstruction is controlled by the dstformat option in LbExec.py of the LHCb reposity.Following the experience from Run2, three types of dst format: uDST, DST and xDST are introduced. The following table summarized what's contained in different format.

Location	uDST	DST	xDST	Example of the location name
Rec. RawBanks	✅	✅	✅	/Event/DAQ/RawBanks
MC Header	✅	✅	✅	/Event/MC/Header
MC Truth	✅ (signal particles in trigger line)	✅ (All particles)	✅ (All particles)	/Event/MC/Particles
MC Relations	✅	✅	✅	/Event/HLT2/Relations/ChargedPP2MCP
MC Hits			✅	/Event/MC/Rich/Hits
Pileup events			✅	/Event/Prev/MC/Rich/Hits
Generator Header		✅	✅	/Event/Gen/BeamParameters
Boole to MCP links		✅	✅	/Event/Link/Raw/Ecal/Digits2MCParticles
Boole to MCHit links			✅	/Event/Link/Raw/UT/Clusters2MCHits
Boole Summaries		✅	✅	Event/Sim/Rich/DigitSummaries

For supplement to these basic dst format, more locations can be preserved by different flags (for DST and xDST). More details can be found in codimd.web.cern.ch/100wK4IxSYKgrUZo_RH3vA .

**Note: For uDST, it's possible to preserved all the protoparticles. One need to enable the persistreco option for the interested HLT2 line. We don't plan to implement it as a global option at the current stage **