monophoton update - tifr
TRANSCRIPT
18-12-2012 1
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