Fix PUPPI lowPUCorr config 90X

[ahinzmann]

Re-enable PUPPI lowPUCorr, which was unintentionally disabled in #15562.
With lowPUCorr disabled, we get a 1-5% worsening in jet response, though the impact on jet resolution is minor, as shown on slide 6:
https://indico.cern.ch/event/587258/contributions/2366495/attachments/1368938/2117761/satoshi_updatedAfterTheMeeting.pdf
What is labeled v10 is in the CMSSW_8_0_>=20 and CMSSW_8_1_X and CMSSW_9_0_X releases at the moment.
What is labeled v10 LowPUCorr is in CMSSW_8_0_<20 and in this PR.
For CMSSW_8_0_>=20, we have corrected for this response drop with the jet energy corrections, however, we would like to fix this for CMSSW>=8_1_X releases, even though the effect on resolution is minor.

The impact of this PR on jet and MET response and resolution has been validated.

This PR changes the MINIAOD PUPPI jet+MET collection, no changes to RECO/AOD event content.

[cmsbuild]

A new Pull Request was created by @ahinzmann for CMSSW_9_0_X.

It involves the following packages:

CommonTools/PileupAlgos

@cmsbuild, @cvuosalo, @slava77, @monttj, @davidlange6 can you please review it and eventually sign? Thanks.
@jdolen, @rappoccio, @gkasieczka this is something you requested to watch as well.
@slava77, @smuzaffar you are the release manager for this.

cms-bot commands are listed here #13028

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/17109/console Started: 2016/12/19 15:06

[cmsbuild]

+1
Tested at: cd3ff49
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17067/17109/summary.html

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17067/17109/summary.html

[slava77]

Some notable plots:

ttbar PU35

The excess at NH fraction ~1 looks like fakes and corresponds to a half of the increase in the number of puppi jets. (The DQM plots which are apparently made with a higher jet pt threshold do not have much change in the nh fraction distribution)

ZEE PU35 is somewhat similar in the jets distribution.
MET is roughly unchanged in absolute value, which is good.

Contribution of neutrals is considerably larger in MET (plots are from ttbar PU35, but they look similar in ZEE as well)

Trying to pick a channel with higher neutral component: H->gammagamma
there is a large increase in the photon component

which also comes with a reduced MET

The effect on jets is still significantly visible at PU35, but it is not really significant for MET where PU components is large.

[slava77]

@ahinzmann
is this rather large change in the photon component at low PU expected?

HGG no PU

It seems to be moving in the right direction for the signal, but it's unclear if it's accidental and can get even [worse] more significant for backgrounds with similar topologies.

[slava77]

+1

for #17067 cd3ff49

• the change in the configuration is as documented
• jenkins tests pass and comparisons show differences only in puppi-related variables
• local tests confirm moderate changes in jet response and also some significant improvements in MET in events with photons and low PU.

[ahinzmann]

@slava77 : At PU<5 and eta<1.3, a jet response increase of 5-10% is expected (slide 6 https://indico.cern.ch/event/587258/contributions/2366495/attachments/1368938/2117761/satoshi_updatedAfterTheMeeting.pdf). This is expected since, without the low PU correction, PUPPI will assign too large PU-probability to neutral particles even if no PU is present (charged particles are untouched by this change). So a rather large increase in the photon component is indeed expected.