g.cerati (ucsd) beam spot for hl-lhc trk pog meeting - sep. 09, 2013

G.Cerati (UCSD)

Beam Spot for HL-LHCTRK POG meeting - Sep. 09, 2013

2G. Cerati (UCSD) TRK POG meeting - 2013/09/09

Introduction


Vertex Acceptance

Sample of 20 muons per event, with pT=10 GeV and random |eta|<2.5. Muons originate from the same vertex, produced with flat probability in the range [-35,+35] cm.The assumed detector geometry is Phase1.The

tracking configuration has been adapted to run with a very wide beam spot along z (without any optimization).We are fully efficient up to |z|~15 cm and beyond ~20 cm the efficiency loss is

>5%.Note that this is very optimistic scenario with only 20 tracks per event; with large PU performance should dramatically degrade outside the pixel acceptance.

First question: what is the maximum beam spot width we can tolerate?


Vertex Density

RelVal samples (<PU>=20)

2012 geometryPhase1 geom

1.28 vtx/mm 0.65 vtx/mm

MC association: sim vtx matches reco vtx if within 3σz

plot by M.Geisler

to 0th order this does not depend on PU, need to

check higher order effects (worse tracking

performance in high density region)

Second question: what is the maximum vertex density we can tolerate?

Efficiency plateau down to ~1 vtx/mm. Done on low PU samples, does the picture change ay high PU? (see later in this talk)


Private samples

Release used: CMSSW_6_1_2_SLHC8_patch1

MinBias sample for PU: 10k eventsTTbar sample: 500 events

Geometry: Phase1PU conditions: AVE_140_BX_25nsReconstruction: PU140 tracking

The produced samples do not contain TrackingParticles and TrackingVertices;comparison with MC truth using

GenParticles and PileupSummaryInfo


Sample with gaussian BS

GAUSSIAN BS**** MINBIAS no PU ****cmsDriver.py MinBias_TuneZ2star_14TeV_pythia6_cff --python_filename step1_gaus_minbias_GEN_SIM.py -s GEN,SIM --conditions STAR17_61_V1A::All \--geometry Extended2017 --beamspot HLLHC \--datatier GEN-SIM -n 10000 \--eventcontent FEVTDEBUG \--customise SLHCUpgradeSimulations/Configuration/combinedCustoms.cust_2017 --fileout file:minbias_gaus_step1P1_0.root --no_exec****TTBAR w/ PU 140 ****cmsDriver.py TTbar_Tauola_14TeV_cfi --python_filename step1_gaus_ttbar_GEN_SIM.py -s GEN,SIM --conditions STAR17_61_V1A::All \--geometry Extended2017 --beamspot HLLHC \--datatier GEN-SIM -n 500 \--eventcontent FEVTDEBUG \--customise SLHCUpgradeSimulations/Configuration/combinedCustoms.cust_2017 --fileout file:ttbar_gaus_step1P1_0.root --no_execcmsDriver.py step2_gaus_ttbar -s DIGI,L1,DIGI2RAW --conditions STAR17_61_V1A::All \--geometry Extended2017 \--datatier GEN-SIM-DIGI-RAW -n -1 \--eventcontent FEVTDEBUGHLT \--customise SLHCUpgradeSimulations/Configuration/combinedCustoms.cust_2017,SLHCUpgradeSimulations/Configuration/combinedCustoms.noCrossing,SLHCUpgradeSimulations/Configuration/combinedCustoms.fixEcalConditions_150 \--pileup AVE_140_BX_25ns --pileup_input file:minbias_gaus_step1P1_0.root \--filein file:ttbar_gaus_step1P1_0.root --fileout file:ttbar_gaus_PU_step2P1_0.root --no_execcmsDriver.py step3_gaus_ttbar -s RAW2DIGI,L1Reco,RECO,DQM --conditions STAR17_61_V1A::All \--geometry Extended2017 \--datatier GEN-SIM-RECO,DQM -n -1 \--eventcontent FEVTDEBUGHLT,DQM \--customise SLHCUpgradeSimulations/Configuration/combinedCustoms.cust_2017,SLHCUpgradeSimulations/Configuration/combinedCustoms.fixEcalConditions_150 \--pileup AVE_140_BX_25ns --pileup_input file:minbias_gaus_step1P1_0.root \--filein file:ttbar_gaus_PU_step2P1_0.root --fileout file:ttbar_gaus_PU_step3P1_0.root --no_exec


Sample with flat BS

step3 (tracking customization):

process.initialStepSeeds.RegionFactoryPSet.RegionPSet = cms.PSet( precise = cms.bool(True), originRadius = cms.double(0.02), originHalfLength = cms.double(11.0),#nSigmaZ = cms.double(4.0), beamSpot = cms.InputTag("offlineBeamSpot"), ptMin = cms.double(0.7) )process.highPtTripletStepSeeds.RegionFactoryPSet.RegionPSet = cms.PSet( precise = cms.bool(True), originRadius = cms.double(0.02), originHalfLength = cms.double(11.0),#nSigmaZ = cms.double(4.0), beamSpot = cms.InputTag("offlineBeamSpot"), ptMin = cms.double(0.7))process.lowPtQuadStepSeeds.RegionFactoryPSet.RegionPSet = cms.PSet( precise = cms.bool(True), originRadius = cms.double(0.02), originHalfLength = cms.double(11.0),#nSigmaZ = cms.double(4.0), beamSpot = cms.InputTag("offlineBeamSpot"), ptMin = cms.double(0.2) )process.lowPtTripletStepSeeds.RegionFactoryPSet.RegionPSet = cms.PSet( precise = cms.bool(True), originRadius = cms.double(0.015), originHalfLength = cms.double(11.0),#nSigmaZ = cms.double(4.0), beamSpot = cms.InputTag("offlineBeamSpot"), ptMin = cms.double(0.35) )process.detachedQuadStepSeeds.RegionFactoryPSet.RegionPSet = cms.PSet( precise = cms.bool(True), originRadius = cms.double(0.5), originHalfLength = cms.double(11.0),#nSigmaZ = cms.double(4.0), beamSpot = cms.InputTag("offlineBeamSpot"), ptMin = cms.double(0.3) )

step1 (beam spot customization):

--beamspot Flatprocess.VtxSmeared.MaxZ = 11.0process.VtxSmeared.MinZ = -11.0

same as before but:

Two customizations needed for flat BS:- beam spot simulation- tracking assuming gaussian beam spot

(track quality might also depend on beam spot but not changed)


Simulated Beam Spot

Verified that the two samples have ~same number of simulated vertices, distributed along z with a gaussian (σ=5.3 cm)

and a flat distribution (z=[-11,11] cm) respectively.

z [cm] z [cm]


Reco Results

BS shapes roughly as expected.Flat BS sample has more

vertices and more HP tracks per event.

caveat: HP selection depends on BS and could be not properly defined for flat

BS

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G. Cerati (UCSD) TRK POG meeting - 2013/09/09

Vertex ΣpT2

Additional vertices in flat BS sample mostly at low ΣpT2.

Distribution of Max(ΣpT2) compatible with current statistics.

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Vertex merging


P(Merged): number of reco vertex associated to >1 sim vtx / number of sim vertices.

Flat BS has flat merged rate vs z, gaussian BS has more merged vertices for |z|<5 cm.

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Vertex efficiency

1.28 vtx/mm 0.65 vtx/mm


Efficiency: number of associated reco vertices / number of simulated vertices.No selection on simulated vertices (plateau at 80% efficiency).

Efficiency losses can be due to: vertex not reconstructed at all, vertex reconstructed out of 3σz, vertex merging.

Efficiency vs density does not depend on PU (as expected).Flat BS has flat efficiency vs z,

gaussian BS loses up to 10% efficiency at |z|<5 cm.

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Tracking Efficiency

MC: GenParticles (from ttbar event only), association by pull (chi2<50)Efficiency: number of associated tracks / number of simulated tracks.

Selection: loose track quality, pT(sim)>0.9 GeV

Similar tracking efficiency for signal event for the two beam spot configurations.

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Conclusions

• Acceptance is maximum for |z|<15 cm• With Phase1 detector (4-pixel layers), vertex reconstruction

efficiency drops below density of 1 vtx/mm- algorithms not optimized for high PU, can possibly be improved

• With 140PU, a flat beam spot with z=[-11,11] cm has a lower density than a gaussian with σ=5.3 cm- lower merged vertices rate for |z|<5 cm- higher vertex efficiency, mostly for |z|<5 cm and low ΣpT

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• Signal vertex well reconstructed in both cases- similar Max(ΣpT

2) distribution- similar tracking efficiency- a bigger sample could help finding small effects; - other variables may show bigger differences

‣ other POG/PAG are welcome to peform other tests too

g.cerati (ucsd) beam spot for hl-lhc trk pog meeting - sep. 09, 2013

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