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Update: High energy photon pairsSearch for RS-1 Gravitons

Vladimir Litvin, Toyoko OrimotoCaltech

QCD Meeting11 December 2007

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Introduction

• Feasiblity study for RS-1 G*• Relevance to QCD group:• QCD backgrounds are amongst our largest

• MC Samples: • Produced privately at Caltech & Fermilab (no pileup)

• CMSSW_1_6_7

• Signal RS-1 G:

• MG=750, 1250, 1000, & 1500 GeV (with c = 0.1 & 0.01)

• Main Backgrounds:

• Irreducible qqbar & gg (Born & Box)

• Gamma+jets (Brem), in which one photon comes from the hard interaction, and the second comes from FSR from an outgoing quark OR the decay of a neutral hadron

• QCD jets: where we get photons from the decay of neutral hadrons

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MC Samples

Signal Samples

Background Samples

• Box and Born produced with CKIN(3)=200 (low limit of the invariant mass of the two outgoing photons, with high end is set to infinity).

• Filters were used when producing Brem and QCD samples, with selection rates 1:80 and 1:1200, respectively.

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HLT EG Efficiency

• e- related HLT paths

• HLT1EMHighEt: 1 SC with pt>80 GeV and loose isolation:

ECAL isol: < 5 GeV in R<0.3 + H/E: <5% , HCAL isol + <8 GeV in 0.15<R<0.3 + tracker iso: <4 tracks in R<0.3

• HLT1EMVeryHighEt: 1 Super-Cluster (SC) with pt>200 GeV

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Selection: Invariant Mass

Only requirement here: photon SC pt > 100 GeV… “final” cut is a 3window around MG

750=15

1000=19

1250=22

1500=28

Born Box Brem QCD

Signal Samples

Background Samples

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Selection: photon pt

Red = All candidates

Blue = MC Truth required

750 1000 1250 1500

750 1000 1250 1500

Born Box Brem QCD

Higher pt photon

Lower pt photon

Born Box Brem QCD

Each photon candidate is identified as a SC in ECAL. We require:

SC pt > 100 GeV

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Selection: ECAL Isolation

Red = All candidates

Blue = MC Truth required

750 1000 1250 1500

750 1000 1250 1500

Born Box Brem QCD

Born Box Brem QCD

Higher pt photon

Lower pt photon

ECAL Iso = ET within cone of R < 0.5

ECAL Iso < 2%

Plotted here are the Log of Ecal Iso

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Selection: H/E

Red = All candidates

Blue = MC Truth required

750 1000 1250 1500

Born Box Brem QCD

Higher pt photon

Lower pt photon

750 1000 1250 1500

Born Box Brem QCD

H/E = E of HCAL RecHits within cone of R < 0.3 / ET of SC

H/E < 5%

Plotted here are the Log of H/E

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Selection: Tracker Isolation, nTracks

Red = All candidates

Blue = MC Truth required

750 1000 1250 1500

Born Box Brem QCD

Higher pt photon

Lower pt photon

750 1000 1250 1500

Born Box Brem QCD

Tracker Isolation = number of tracks within cone of R < 0.3

nTracks <= 3

Plotted here are the Log of nTracks

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Selection: Tracker Isolation, pt Tracks

Red = All candidates

Blue = MC Truth required

750 1000 1250 1500

Born Box Brem QCD

Higher pt photon

Lower pt photon

750 1000 1250 1500

Born Box Brem QCD

Tracker Isolation = pT of tracks within cone of R < 0.3 / pT of SC

pT of tracks / SC pT< 1%

Plotted here is the Log of this variable.

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“Final” Selection Rates

• Selection rates after applying cascade of afore-mentioned cuts (%)

• With HLT1EMHighEt requirement

• Signal efficiencies ~40-50%, low (all <0.2%) background effiiency

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“Final” Selection Rates

• Selection rates after applying cascade of afore-mentioned cuts (%)

• With HLT1EMVeryHighEt requirement

• Signal efficiencies ~40-50%, low (all <0.2%) background effiiency

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Mass Distributions After Selection

750 1000 1250 1500

Born Box Brem QCD

• Numbers of events scaled to 1 fb-1

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Next Steps

• Analysis:• Finalizing analysis and working on note based on MC studies

• Systematic Errors

• Comparison with ORCA results

• Currently, this is a simple MC analysis but we will eventually develop a more robust strategy for dealing with real data

• Production:• 167: have produced signal with c=0.01, will include next

• 171: produced a couple samples before realizing huge memory usage in this release.. Noticed some large differences in efficiencies and selection variable distributions..

• 172: just produced a few samples, currently checking

• Working on gamma+jets and 2gamma+jets Alpgen or CompHEP samples to better emulate backgrounds

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Backup Slides

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Comparison of HLT EG in 167 vs 171

• E-gamma HLT path efficiencies

167 171

Appears that EG efficiencies in HLT have changed significantly from 167 to 171

167 171Born Box

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167 vs 171 Selection: photon pt

Red = 167

Blue = 171

Born bkg Box bkg

Higher Et photon

Lower Et photon

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167 vs 171 Selection: ECAL Iso

Red = 167

Blue = 171

Born bkg Box bkg

Higher Et photon

Lower Et photon

Strange peaks

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167 vs 171 Selection: H/E

Red = 167

Blue = 171

Born bkg Box bkg

Higher Et photon

Lower Et photon

More narrow H/E distributions

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167 vs 171 Selection: Tracker Isolation (pt_tracks)

Red = 167

Blue = 171

Born bkg Box bkg

Higher Et photon

Lower Et photon

Significant change in tracker isolation distributions

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167 vs 171 Selection: Tracker Isolation (N_tracks)

Red = 167

Blue = 171

Born bkg Box bkg

Higher Et photon

Lower Et photon

Decrease in tracking

efficiency?