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Monophoton Update Bhawna Gomber, Sandhya Jain Satyaki Bhattacharya SINP Kolkata, INDIA

CMS INDIA MEETING 18th - 20thDecember, 2012

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Outline

➔ Introduction

➔ Datasets Used

➔ Event Selection

➔ Backgrounds

➔ Electron faking photon background

➔ Pile-up Reweighting

➔ Results

➔ Summary and Conclusion

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Brief Introduction

➔ Excess of event with high PT photons with large MET could be a signal of Large Extra

Dimensions(ADD) and Dark Matter

Dark matter

ADD

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Datasets Used and Selection

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Backgrounds

Many Backgrounds mimics γ+MET final state

Collision Backgrounds :✔ pp → Zγ →ννγ irreducible background ✔ pp → W→eν electron mis-identified as photon ✔ pp →jets →γ +MET one jet mimics photon, MET

from jet mis-measurement ✔ pp → γ +jet MET from jet mis-measurement ✔ pp → Wγ → lνγ charged lepton escapes detection ✔ pp → γ γ one photon mismeasured to give MET

Non Collision Backgrounds✔ Beam Halo✔ Ecal Spikes✔ Cosmics

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Event Selection - I

Event Cleaning ➔ Standard vertex and beam scraping veto

Triggers Used ➔ HLT_Photon135_v*, HLT_Photon150_v*, HLT_Photon160_v* ➔ HLT_Photon70_CaloIdXL_PFMET100_v* ➔ Explicitly require prescale = 1

Photon Selection ( Egamma recommended medium Id )➔ P

T

γ > 145 GeV➔ |ηγ| < 1.4442➔ Rho corrected PF charged hadron isolation < 1.5 ➔ Rho corrected PF neutral hadron isolation < 1.0 + 0.04*P

T

γ

➔ Rho corrected PF photon isolation < 0.7 + 0.005*PT

γ

➔ H/E < 0.05➔ σ

iηiη< 0.011 and conversion safe electron veto

MET selection ( MET filters & corrections recommended by JET-MET group)➔ PFMET > 140 GeV

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Event Selection - II

Additional Spike Cleaning➔ | Largest Intra-Cluster Time Difference | < 5 ns➔ | t

seed| < 3 ns and r9 < 1.0

➔ σiηiη

> 0.001 and σiϕiϕ

> 0.001

Veto Selection ➔ Jet Veto : no pf-jet with P

T> 40 GeV and |η| < 3.0

➔ Track Veto : no track with PT > 20 GeV with ∆R> 0.04 from

candidate➔ Cosmic Muon : No standalone muon tracks in the event

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Trigger Efficiency

Denominator Lower threshold prescaled triggers, Photon75, Photon90, both with and without

isolation. Require a good photon of 125 using photon medium id. Numerator

Or of Photon135, Photon150, Photon160, Photon70_PFMET100

Bin by bin efficiency Integral Efficiency

Above Photon Et>145 GeV, MET>140 GeV, efficiency of triggers = 0.985 ± 0.009

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Electron faking photon rate- I

➔ Inclusive estimate of electron faking a photon from data➔ Electron misidentified as a photon if its ECAL supercluster doesn't have a reconstructed pixel match

For conversion safe electron veto/pixel seed efficiency➔ Consider Z->ee sample :

➔ Require trailing electron to have a pixel match(fail the conversion safe electron veto)

➔ Require leading electron for my efficiency calculation➔ Let ε

T (ε

L) be the efficiency of trailing(leading) electron to have pixel match

or failing the conversion safe electron veto➔ N

ee = ε

L ε

T N

Z

➔ Neγ

= εT(1-ε

L) N

Z

Solving these equations : ➔ 1-ε

L = N

eγ/N

ee+N

eγ➔ This will be applied for the case where all Z->ee events will have one and only one

electron with pt>100 GeV( which is our interest)

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Electron faking photon rate- II

➔ We fit the mass of Z->ee peak in ee and eγ spectrum for pt>100 GeV case

➔ Selection➔ Use medium photon id as mentioned in slide 6 with conversion safe

electron veto/pixel seed to distinguish between photon and electron➔ Diphoton triggers used :

➔ HLT_Photon36_R9Id85_Photon22_R9Id85➔ HLT_Photon36_R9Id85_Photon22_CaloId10_Iso50➔ HLT_Photon36_CaloId10_Iso50_Photon22_CaloId10_R9Id85

➔ PDF used for fitting ➔ Signal PDF used : Convolution of CB*BW➔ Background PDF used : Error function* exponential

➔ To cross chek with MC, we perform two test➔ Case I : we repeat the same fitting procedure on DYtoEE Monte Carlo

sample.➔ Case II : We use gen match information of Monte Carlo

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Electron faking photon rate- III

➔ Fit plots for pt>100 GeV case using conversion safe electron veto from data

➔ Fake rate = (8.38 +/- 0.28) %

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Electron faking photon rate- IV

➔ Fit plots for pt>100 GeV case using conversion safe electron veto from MC

➔ Fake rate = (3.53 +/- 0.34) %

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Electron faking photon rate- V

➔ Fit plots for pt>100 GeV case using pixel seed from data

➔ Fake rate = (1.24 +/- 0.11) %

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Electron faking photon rate- VI

➔ Fit plots for pt>100 GeV case using pixel seed from Monte Carlo

➔ Fake rate = (0.62 +/- 0.14) %

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Electron faking photon rate- VII

➔ In eg fitting plot from MC , statistic is so low at high pt that we cann't trust the fit result as if we would have got more statistic, the fit would have given different result

➔ To assign the systematic uncertainity from fit, we use a conservative approach. ➔ We calculate the fake rate with no bkg under the peak➔ Assign the systematic as difference betweent the fitting and no bkg case

➔ Case II of Monte Carlo ➔ Denominator : No of id'ed superclusters matched with gen-electron

coming from Z have pt>100 GeV➔ Numerator : Out of denominator superclusters we count how may fail the

pixel seed (pass the conversion safe electron veto)

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Fake rate results

Case I (fitting method)

Case II (counting method)

Conversion safe electron veto from data 8.38 +- 0.28 +/-0.07

Conversion safe electron veto from MC 3.53 +/- 0.34 +- 1.60 5.00 +/- 0.19

Pixel seed using data 1.24 +/- 0.11 +- 2.01

Pixel seed using MC 0.62 +- 0.14 +/- 0.32 0.90 +/- 0.08

For Pt >100 GeV case

To check the consistency between the results, we repeated the fititing and counting method For low pt pt regime, i.e when both the superclusters has pt>40 GeV case

Case I (fitting method)

Case II (counting method)

Conversion safe electron veto from data 8.24 +- 0.04 +/-0.56

Conversion safe electron veto from MC 5.01 +/- 0.04 +- 0.38 5.28 +/- 0.02

Pixel seed using data 2.95 +/- 0.02 +- 0.22

Pixel seed using MC 1.60 +- 0.02 +/- 0.03 1.48 +/- 0.01

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Pile-Up Reweighting

Used true interaction to reweight the Monte Carlo samples

Applied event by event reweighting to the good vertices

Good Vertices plot for Znunugamma MC and

data

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Results : SM vs Data using Conversion safe electron veto

Backgrounds Estimate

γ+jet 0.50 ± 0.42

γγ 0.08 ± 0.08

Wµν 0.09 ± 0.03

Wτν 1.38 ± 0.20

Weν 53.68 ± 2.95

QCD 4.11 ± 1.23

Beamhalo 3.70 ± 2.60

Zννγ 68.82 ± 6.13

W(lν)γ 7.72 ± 0.95

Z(ll)γ 0.41 ± 0.05

Candidate Events 125

Expected : 140.49 ± 7.46 eventsObserved : 125 events

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Results : SM vs Data using pixel seed

Backgrounds Estimate

γ+jet 0.05 ± 0.15

γγ 0.04 ± 0.003

Wµν 0.08 ± 0.03

Wτν 0.15 ± 0.04

Weν 4.46 ± 0.46

QCD 14.81 ± 4.44

Beamhalo 4.10 ± 4.10

Zννγ 52.71 ± 5.39

W(lν)γ 7.36 ± 0.91

Z(ll)γ 0.39 ± 0.05

Candidate Events 74

Expected : 92.50 ± 6.65 events Observed : 81 events

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Summary & Plans

➔ We have added new Photon+MET trigger in our analysis ➔ Data driven estimation of electron faking photon rate with new pf based isolation has been done.➔ All Monte Carlo estimates are done. ➔ Observed data events are in agreement with standard model predictions.➔ Working on systematics and limits➔ Also working on k factor measurement of Z(nunu)gamma ➔ We will be doing a limit with both the pixel seed and conversion safe electron veto case

to make sure if pixel seed gives better limits. Then we will avoid using conversion safe electron veto.

Thank You

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Backup

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Collision Backgrounds - 2a

Jet Faking Photon : Inclusive estimate of jet faking photons from data Used QCD like sample with MET < 30 GeV and no jet and track veto Fake ratio is measured in data similar to our trigger and E

T

Fake Ratio = N selected / N EM-like jet Fake Photon + MET = “ EM-like jet + MET “ x Fake RatioNumerator

Same medium photon IDs as our candidate selectionDenominator

At least one of these (loose photon id)➔ Rho corrected PF charged hadron isolation > 2.6➔ Rho corrected PF charged hadron isolation > 3.5 + 0.04*P

T

γ

➔ Rho corrected PF charged hadron isolation > 1.3 + 0.005*PT

γ

Also➔ Rho corrected PF charged hadron isolation < Min(5.0*(2.6), 0.20*P

T

γ)

➔ Rho corrected PF charged hadron isolation < Min(5.0*(3.5 + 0.04*PT

γ), 0.20*PT

γ)

➔ Rho corrected PF charged hadron isolation < Min(5.0*(1.3 + 0.005*PT

γ), 0.20*PT

γ) H/E < 0.05 σ

iηiη < 0.013(to reject beam halo) and conversion safe electron veto

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Collision Backgrounds - 2b

Numerator of the fake ratio contains real photon which are estimated by using σ

iηiη templates

Real photon templates are used from Photon+Jet MC sample QCD templates are taken from data using : PF charged hadron isolation > 1.5 && PF charged hadron isolation < 6.0

Estimate : 4.11 ± 1.23 events Fit function = P0 + (B/ P

T^P1)

P0 = 0.08122, P1 = 3.12, B = 50000

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MIP Tag – New Item

➔ MIP Track Fitting A search cone is defined based on the seed cell. The cells associated with the shower are removed (bordered in red) and a linear fit is imposed on the the remaining cells within the cone. Total number of points(Hits) and sum of cell energies are used as MIP track variables for halo.

https://indico.cern.ch/getFile.py/access?contribId=0&resId=0&materialId=slides&confId=144302

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MIP Tag – Performance Plots

➔ We have 2 variables: ➔ No of hits in the cone➔ MIP track energy

➔ Here are the uncleaned photons for those events which the tracker identifies as prompt and those which are tagged by hcal as halo➔ We will scan across each variable and

form efficiency plots

No of crystals in the cone vs MIP track energy

Choosing 99% Efficiency for prompt for each

variable, we arrive at cuts:MipTotal Energy < 4.5 GeV MipNhitCone < 17

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Non Collision Backgrounds

Beam Halo : Use seed time template method to estimate the remaining contamination in theprompt window

Prompt : Full candidate selection with reverse trackIsolation to make sure ECAL activity originates from interaction point

Halo : HE Tag

➔ CaloTower in HE, energy > 1.0 GeV➔ ∆ϕ(γ-caloTower) < 0.2➔ CaloTower isolations from tracks < 2.0 GeV➔ 110 cm < caloTower Radial Position < 140 cm

Mip Tag➔ MipTotalEnergy > 4.5 GeV➔ MipNhitsCone > 17

Spike : Full candidate selection and reverse the topological shower shape spike cleaning

Estimate : 3.7 ± 2.6Templates are in backup

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Recap: Moriond 12 Approval

➔ Analysis was approved for Moriond-11 with 5.0fb-1 of integrated luminosity.

10.1103/PhysRevLett.108.261803

EXO-11-096

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Recap: Moriond 12 Approval

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QCD Fitter plots for new Id

Pt bin 160-180Pt bin 200-250

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QCD fractions

Corrected fake ratio and fractions in different pt bins

Pt Bins True Photon fraction

140-150 0.0951 +/- 0.0117

150-160 0.0751 +/- 0.0060

160-180 0.0684 +/- 0.0035

180-200 0.0681 +/- 0.0050

200-250 0.0549 +/- 0.0043

NumDen

Pt Bins Corrected Fake ratio

140-150 0.1054 +/- 0.0131

150-160 0.0899 +/- 0.0073

160-180 0.0807 +/- 0.0041

180-200 0.0901 +/- 0.0066

200-250 0.0861 +/- 0.0069

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Efficiency of MIP tagger within timing window

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Out of time background templates

We see 2855.37 +/- 106.55 within the timing window. MIP tag only 2/1525 events pass the shower shape cut, so 3,7 events in the end.

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Width vs Timing for MIP

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Timing vs Eta

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Candidate Timing vs Eta

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MIP tagger Definition