Pileup aware SimClustering

[lgray]

As mentioned via email, this is the topic branch for simclustering.
It needs some polish before going into CMSSW proper but the major functionality is there.

After you merge it you will have to rerun any sample you have already generated from the digitization step in order to access the sim clusters.

The sim clustering is implemented by following the GEANT sim information of each event fed to the mixing module, and keeping track of the per rechit energy normalization over all events. This yields a list of DetIds and fractions that are essentially "perfect".

This list of detids and fractions is then used to make PFClusters that take the fractions and apply it to the reconstructed per-cell energy.

The SimClusters are also organized into "CaloParticles" which you can think of as the logical equivalent of SuperClusters in the modern CMSSW reconstruction, they are groups of SimClusters which represent a single stable generator particle (i.e. before GEANT propagation).

@clelange Could you give this a try?

[lgray]

More instructions:

You can get the sim clusters with reconstructed energy assigned through the collection:
particleFlowClusterHGCal

The original sim clusters, which have the GEANT energy assigned, are in:
mix:MergedCaloTruth and are in a collection thats of type std::vector<SimCluster>

The "reco-level" sim clusters and the "sim-level" sim clusters are indexed the same and you can perform exact matching simply using the index.

The CaloParticles are available via:
mix:MergedCaloTruth and are in a collection that's of type std::vector<CaloParticle>

[lgray]

@clelange Can you regenerate the samples you made previously with this last commit included?

I had a fix a bug where the SimClusters where randomly including the first RecHit in the Hit list if a given hit gathered in the SimClustering step did not make it past the reconstruction because of noise or the signal energy being too small.

[clelange]

@lgray Yes, will do.

[clelange]

Samples are done in RECO step (only pi0 still running). Ntuples should be available soon. Date tag is 20160721.

[clelange]

Closing, not needed anymore.