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andrey-popov / PEC-tuples

CMSSW package to save basic physics objects in a simple ROOT format
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Double counting of heavy-flavour hadrons in GenJetsInfo #49

Closed andrey-popov closed 9 years ago

andrey-popov commented 9 years ago

It might happen that decay products of a heavy-flavour hadron end up in two separate jets. In this case the GenJetsInfo plugin would assign non-zero b-quark multiplicities to both jets, which is not necessarily the desired behaviour.

An easy alternative would be to account for the b hadrons in the harder jet only.

andrey-popov commented 9 years ago

Average number of b jets per event:

Double counting Number of b jets
allowed 1.34
not allowed 1.24

Calculated with 1k of ttbar events at 13 TeV. Jets with pT > 8 GeV considered.

Only a bit less than 50% of events have at least two b-quark jets, which is suspicious. It's not because of two b quarks merging in same jets because if I sum up b-hadron multiplicities of all jets in an event, in almost 60% of events (w/o the double counting) there are less than two b hadrons.

andrey-popov commented 9 years ago

There was a bug in calculation of b/c-hadron multiplicities (issue #50). After the fix the number of b-quark jets in ttbar events have changed:

Double counting Average Nb Nb = 0 Nb = 1 Nb = 2
allowed 1.98 0% 8.2% 86.8%
not allowed 2.28 0% 4.4% 70.9%

This is calculated with 5k of 13 TeV ttbar events. The effect of double counting of hadrons is significant; thus, it is strongly recommended to account for it.