Vladimir litvin toyoko orimoto caltech qcd meeting 11 december 2007
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Vladimir Litvin, Toyoko Orimoto Caltech QCD Meeting 11 December 2007. Update: High energy photon pairs Search for RS-1 Gravitons. Introduction. Feasiblity study for RS-1 G*  Relevance to QCD group: QCD backgrounds are amongst our largest. MC Samples:

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Vladimir Litvin, Toyoko Orimoto

Caltech

QCD Meeting

11 December 2007

Update: High energy photon pairsSearch for RS-1 Gravitons


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


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.


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


Selection:  Invariant Mass

Signal Samples

1000

=19

750

=15

1250

=22

1500

=28

Background Samples

Born

Box

Brem

QCD

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


750

1000

1500

1250

Born

Box

Brem

QCD

750

1000

1500

1250

Born

Box

Brem

QCD

Selection: photon pt

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

SC pt > 100 GeV

Higher pt photon

Lower pt photon

Red = All candidates

Blue = MC Truth required


750

1000

1500

1250

Born

Box

Brem

QCD

750

1000

1500

1250

Born

Box

Brem

QCD

Selection: ECAL Isolation

ECAL Iso =  ET within cone of R < 0.5

ECAL Iso < 2%

Plotted here are the Log of Ecal Iso

Higher pt photon

Lower pt photon

Red = All candidates

Blue = MC Truth required


750

1000

1500

1250

Born

Box

Brem

QCD

750

1000

1500

1250

Born

Box

Brem

QCD

Selection: H/E

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

Higher pt photon

Lower pt photon

Red = All candidates

Blue = MC Truth required


750

750

1000

1000

1500

1500

1250

1250

Born

Born

Box

Box

QCD

QCD

Brem

Brem

Selection: Tracker Isolation, nTracks

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

nTracks <= 3

Plotted here are the Log of nTracks

Higher pt photon

Lower pt photon

Red = All candidates

Blue = MC Truth required


750

1000

1250

1500

750

1000

1500

1250

Born

Born

Box

Box

QCD

QCD

Brem

Brem

Selection: Tracker Isolation, pt Tracks

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.

Higher pt photon

Lower pt photon

Red = All candidates

Blue = MC Truth required


“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


“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


Mass Distributions After Selection

750

1250

1500

1000

Box

QCD

Born

Brem

  • Numbers of events scaled to 1 fb-1


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


Backup Slides


Comparison of HLT EG in 167 vs 171

  • E-gamma HLT path efficiencies

Born

Box

171

171

167

167

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


167 vs 171 Selection: photon pt

Red = 167

Blue = 171

Born bkg

Box bkg

Higher Et photon

Lower Et photon


167 vs 171 Selection: ECAL Iso

Red = 167

Blue = 171

Born bkg

Box bkg

Strange peaks

Higher Et photon

Lower Et photon


167 vs 171 Selection: H/E

Red = 167

Blue = 171

Born bkg

Box bkg

Higher Et photon

More narrow H/E distributions

Lower Et photon


167 vs 171 Selection: Tracker Isolation (pt_tracks)

Red = 167

Blue = 171

Born bkg

Box bkg

Significant change in tracker isolation distributions

Higher Et photon

Lower Et photon


167 vs 171 Selection: Tracker Isolation (N_tracks)

Red = 167

Blue = 171

Born bkg

Box bkg

Decrease in tracking efficiency?

Higher Et photon

Lower Et photon


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