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Trigger studies for GMSB with photons
(Internal note for approval)
Shilei ZangBernadette Heyburn, Uriel Nauenberg
University of Colorado, Boulder
TSG Meeting, 19th Mar. 2008
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Outline
• GMSB with photons• Signal and background samples• Efficiency and rate for default triggers• A new method to optimize triggers• Optimization of 3 triggers• Results• Compare rate with other studies• Summary
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G~
01
~
01
~
p p
q
q
q
q ~…
…
jet
jet
jet
jet
G~
~
GMSB with photons
• Gauge Mediated Supersymmetry Breaking models
• NLSP (neutralino) LSP (gravitino) + photon
• Prompt decay (ctau=0)
• high pT photons• large MET due to
gravitinos• multi-jets
Experimental signature
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GMSB parameters
• Λ: scale of the SUSY beraking
• M: messenger mass scale
• tanβ: the ratio of the Higgs vev
• N5: number of messengers
• sign(μ): the sign of Higgsino mass term
• Cgrav : sets NLSP lifetime
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• CSA07 samples of GMSB photons to estimate the signal efficiency.
GEN-SIM: 1_4_X; DIGI-RAW: 1_6_7.
• 100k for each point: GM1b, GM1c, GM1e, GM1f, GM1g
• 1_6_0-PreCSA07 (or 1_6_7-CSA07) samples are used to estimate the background rates, which include:
• Photon jets (all pt bin) (CMSSW_160-PreCSA07)
• QCD jets (all pt bin) (CMSSW_160-PreCSA07)
• Wenu, Zee (CMSSW_167-CSA07)
• Totally processed about15 million events to minimize the error of rate.
GMSB signal samples:
Background samples:
The study have been done under 1_6_0, and optimized for start-up luminosity of 1032 cm-2s-1.
HLTriggerOffiline/Egamma package is used for the study.
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6 paths with thresholds
Single Photon
Relaxed Single Photon
Double Photon
Relaxed Double Photon
EMHighEt(modified-HighEt)
EMVeryHighEt
Et (GeV)
>30 >40 >20 >20 >80 >200
Iso-Ecal (GeV)
<1.5 <1.5 <2.5 <2.5 <5.
Iso-Hcal (Barrel)
<6. <6. <8. <8. H(ΔR<0.15)/Et<5% &&H(0.15<ΔR<0.3)<8.(modified: IHcal<12.)Iso-Hcal
(Endcaps)<4. <4. <6. <6.
Iso-track <1 <1 <3 <3 <4
HLT paths for photons
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QCD Jets
N QCD Jets
N Photon Jets
N Bkg N
0_15 295,613 _470 88,086 0_15 500,000 Wenu 205,707
15_20 1,255,976 _600 55,000 15_20 509,825 Zee 162,219
20_30 2,513,934 _800 21,974 20_30 606,680
30_50 2,416,441 _1000 33,330 30_50 510,094
50_80 2,451,439 _1400 5,299 50_80 169,741
_120 1,161,823 _1800 _120 164,000
_170 499,389 _2200 _170 69,993
_230 428,888 _2600 _300 24,993
_300 172,619 _500 15,554
_380 82,998 _7000 6,666
Number of bkg events processed for rate estimation
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Efficiency and rate for default triggers
RD
RS
D
S
H
VH
SS, RSS, RS, DS, RS, D, RDS, RS, D, RD, Hall
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• Three triggers for GMSB photons:• Optimize the two triggers: EMHighEt (H), and
EMVeryHighEt (VH).• Choose another one from: D, RD, RS, MET, or Jets
Strategy:
How to optimize the triggers?
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Problem: How to optimize the trigger thresholds with figures of Efficiency vs. Rate in an objective way ?
Optimize trigger thresholds
• Usually the cuts are determined by eye to give reasonable values of efficiency and rate. Threshold,
how to set?
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Physics Analysis
• Selection criteria are optimized to maximize statistics (Optimize relative error of BR; Significance; 90% CL limit, etc)
• Selection criteria are optimized to minimize the mass uncertainty in mass measurement (e.g. top mass measurement)
• Artificially reduced the error of physical result!
• Not Really Blind !!
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• N events, the amount of information : log2 N.
• N is number of messengers;
physical results are the meaning of information taken by such N messengers.
• For BR, number of messengers is the meaning of info.;
• For width, mass, … , meaning of info. is taken by the messengers; depends on the kinematics (not just on the number of events).
• Good property: log (xy)= log(x) + log(y).
Information theory
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• Amount of information: log(NS ), log(NB )
• Signal efficiency ε and background efficiency b
• After the cut: log(NS ε), log(NB b)
• Reductions of information: -log(ε), -log(b)
• Ratio of the reductions: log(ε)/ log(b)
• the smaller log(ε)/ log(b), the better
• log(ε)/ log(b) <a ε > ba (0< ε, b, a ≤1).
We can use statistics log(ε)/ log(b) to optimize trigger thresholds!
Good property: Blind Analysis!
log(ε)/ log(b) depends on the amount of information; does not depend on the meaning of information.
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log(ε)/ log(b) <a ε > ba .
a=1.0
a=0.7
a=0.5
a=0.3a=0.2a=0.1
a=0.05a=0.02
a=0.01
ε = ba
(1.,1.)
(0.,0.)
Trigger Study
MVA
b
ε ε
ε
b
1-b
K ID
ε
b
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How to deal such a problem in Physics Analysis?
Solution: log(ε)/ log(b) to optimize selections with final ε and b after the kinematics cut.
Our method will give worse physical results, but they are blind analysis and can be trusted.
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log(ε)/ log(b) vs. Cuts (default EMHighEt)
0.0350.129
Min=0.129
Min=0.101 Min=0.00470.0170.102
• Et>80; Iecal<5; Ihcal<12; Itrack<4
• Itrack is better than Iecal and Ihcal.
• Each figure is plotted with other cuts applied.
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log(ε)/ log(b) vs. Cuts (proposed EMHighEt)
• Et>60; Itrack<2
• Itrack is better only when the Itrack cut point <5
0.022Min=0.174
Min=0.190 0.068
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Et>40GeV
Et>40GeV Et>40GeV
Relaxed Single Photon candidates
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• Propose two new triggers:
p-EMHighEt (pH): Et>60GeV, Itrack<2
p-EMVeryHighEt (pVH): Et>120GeV
• Propose to use: pH, pVH, D for our physics.
I. Isolation is useful at low Et region to suppress bkg , but bad in high Et region for our signal.
II. Track isolation (cut position <6) is better than other isolaitons
III.GMSB points with small Lambda parameter (GM1b) have more events with two signal photons at generator level, so the Double trigger is helpful for them.
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Trigger H pH VH pVH H, VH pH, pVH
Rate (Hz) 0.63 2.01 0.13 0.97 0.753 2.888
Efficiency GM1b GM1c GM1e GM1f GM1g Rate (Hz)
RS, H, VH 81.31 85.68 89.58 90.52 91.10 3.510
pH, pVH, D 87.70 91.02 93.27 93.78 93.96 3.139
pH, pVH, RS 88.72 92.28 94.44 94.71 94.72 5.226
2.14 Hz
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efficiency GM1b GM1c GM1e GM1f GM1g Rate (Hz)
pH, pVH, D 87.70 91.02 93.27 93.78 93.96 3.139
pH, pVH, mD 89.77 92.24 93.81 94.14 94.22 3.762
• D: Et>20; Iecal<2.5; Ihcal<8 or 6; Itrack<3 (0.26 Hz)
• mD: Et>20; Itrack<3 (0.90 Hz)0.64 Hz
Further possible improvement
• It’s easy to reach 92% or 93% efficiency with 3.5 Hz, but difficult to reach 95% efficiency within 5.5 Hz!
• 98.6% events have signal photons at generator level; after SusyAnalyzer, only 93.5% events have reconstructed photons.
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Efficiency and Rates for each group of triggers
0: H, VH1: H, VH, RS2: H, VH, RD3: H, VH, D
10: pH, pVH11: pH, pVH, RS12: pH, pVH, RD13: pH, pVH, D
15: pH, pVH, mD
pH, pVH, D
pH, pVH, mD
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Compare the rates with other studies in 13X and 16X
Default Trigger Path
S RS D RD HighEt VeryHighEt
Our Rate (160) (Hz)All bkg
8.96±0.24
2.93±0.09
0.26±0.05
1.90±0.14
0.63±0.01(m-H)
0.13±0.00
13X exercise (Hz) All bkg
8.4±0.7
2.8±0.2
0.6±0.4
1.8±0.5
0.5±0.0
0.1±0.0
16X (Hz)(Matthias Mozer)w/o PhotonJets.
0.8 0.14
16X (Hz)(Aram Avetisyan)w/o PhotonJets;Fewer events.
10.06±4.79
5.82±3.39
0.04±0
6.69±4.61
0.43±0.13
0.07±0.01
Agree well
Agree with error
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• We give the rates of all HLT paths on photons, which are comparable with 13X exercise and other studies in 16X.
• Our rates have small errors.
• We propose to modify EM1HighEt and EM1VeryHighEt tirggers (basically loosen the isolation variables and Et).
• We propose to use 3 triggers for GMSB photons, which can reach ~93% efficiency with 3.2 Hz.
• We find a new method for trigger study, and physics analysis.
Summary
Thank you!
The draft of the note:
http://www-hep.colorado.edu/~slzang/cmsnote_gmsb_trigger_v3.ps