Cluster cleaning bug fix, renamed hiSecond to hiLowPt

[mandrenguyen]

One line bugfix to cluster cleaning between before low pT step of HI tracking sequence, introduced by recent addition of a detached triplet step.
The line:
oldClusterRemovalInfo = cms.InputTag("hiDetachedTripletStepClusters")
was missing from PR #7393
The effect is that only clusters from the step immediately preceding the low pT step were removed (but not those from the intial step), leading to duplication of work.

We take advantage of the opportunity to change 'hiSecondPixelTriplet' to 'hiLowPtPixelTriplet', as the low pT step is no longer second (as promised in the comments of #7393). This follows the style of the pp code.

[cmsbuild]

A new Pull Request was created by @mandrenguyen for CMSSW_7_4_X.

Cluster cleaning bug fix, renamed hiSecond to hiLowPt

It involves the following packages:

RecoHI/HiTracking

@cmsbuild, @cvuosalo, @nclopezo, @slava77 can you please review it and eventually sign? Thanks.
@echapon, @jazzitup, @dgulhan, @appeltel, @yenjie, @kurtejung, @richard-cms, @yetkinyilmaz this is something you requested to watch as well.
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[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: be926f4
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7686/2525/summary.html

[cvuosalo]

+1

For #7686 be926f4

This PR is described as a small bug fix to reduce duplication of work in the HI tracking sequence and a simple renaming for clarity. It turns out to cause numerous small changes in the distributions of quantities related to HI tracks, as will be illustrated below.

The code change is satisfactory, and most the Jenkins tests are OK. But it appears that Jenkins somehow included some other PRs in its tests, so several spurious differences appear in the results in the alternative-comparisons and validateJR.

Matrix tests were run against baseline CMSSW_7_4_X_2015-02-12-0200, and they show no significant differences except for workflow 140.53_RunHI2011+RunHI2011+RECOHID11+HARVESTDHI. An extended test for 100 events was run for 140.53 to obtain higher statistics.

In terms of technical performance of the new code, the extended test results show a small decrease of 1-2% in processing time per event, a small 0.4% decrease in total product size, and a small decrease of about 2% in memory usage.

Many differences in reconstruction-related distributions show up for 140.53. Some of the larger ones are below. The red is new, the black is the reference.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_4_X IBs unless changes (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @ktf, @smuzaffar

[davidlange6]

+1