status and prospects of the h → γγ analysis jim branson - marco pieri - sean simon ucsd meeting...
DESCRIPTION
11-Mar-08Marco Pieri 3 forward jets Photons from Higgs decay qqH → qq γγ M H = 120 GeV H→ γγ Signal SIGNAL: two isolated photons with large E t Gluon-gluon fusion WW and ZZ fusion (Weak Boson Fusion) WH, ZH, ttH (additional leptons and MET) Total σ x BR ~95 fb for M H = GeV Very good mass resolution H → γγ M H = 115 GeV Jets from qq are at high rapidity and large Δ ηTRANSCRIPT
Status and Prospects of the H→γγ Analysis
Jim Branson - Marco Pieri - Sean Simon
UCSD Meeting March 11th 2008
11-Mar-08 Marco Pieri 2
Introduction
H→ γγ analysis will start to be more important for Int L >~ 1 fb-1
UCSD has played a major role in the PTDR studies and is expected to play a major role in the next years
Other people/groups contributing are: Caltech, Lyon, Notre Dame, Saclay, ….
For 2008 not much to be expected in H→ γγ channel In addition the ECAL calibration will not be optimal Related analyses: γ+jet, γγ from SM (except Higgs) – Should
collaborate more with people working on them Since about 1 month started revisiting the analysis framework to have it
more flexible and common with other analyses For now we ran over small MC samples: ~100k GamJet + ~100k Higgs +
~ 100k QCD + photonsJets + ~50k Dy All what shown here very preliminary News: In CMSSW 2_0_0 photons a 5 GeV Et cut an H/E cut at 0.2 will
be applied for reconstructing photons
11-Mar-08 Marco Pieri 3
forward jets
Photons from Higgs decay
qqH → qqγγ MH = 120 GeV
H→ γγ Signal
SIGNAL: two isolated photons with large Et Gluon-gluon fusion WW and ZZ fusion (Weak Boson Fusion) WH, ZH, ttH (additional leptons and MET) Total σ x BR ~95 fb for MH = 110-130 GeV Very good mass resolution
H → γγ MH = 115 GeV Jets from qq are at
high rapidity and large Δη
11-Mar-08 Marco Pieri 4
BACKGROUND ‘irreducible’ backgrounds, two real photons
gg→ γγ (box diagram) qq→ γγ (born diagram) pp→ γ+jets (2 prompt γ)
‘reducible’ backgrounds, at least one fake photons or electrons pp→ γ+jets (1 prompt γ + 1 fake γ) pp→ jets (2 fake γ) pp→ ee (Drell Yan) when electrons are mis-identified as photons
Handles for Irredicible BG – Kinematics Handles for Reducible BG – Until now only Isolation
Background to H→ γγ
Process Pthat (GeV) Cross section (pb) Events/1 fb-1
pp→γγ (born) >25 82 82Kpp→γγ (box) >25 82 82Kpp→ γ+jets >30 90x104 90Mpp→jets >25 1x108 1x1011
Drell Yan ee - 4x103 4M
11-Mar-08 Marco Pieri 5
Cross section and K-factors
Signal cross sections and BR used for the PTDR (NLO M. Spira)
K-factors for the background used for the PTDR (to be re-evaluated if needed)
pp→γγ (born) 1.5pp→γγ (box) 1.2pp→ γ+jets (2 prompt) 1.72pp→γ+ jets (1 prompt+ 1 fake) 1pp→jets 1
M=115 GeV M=120 GeV M=130 GeV M=140 GeV M=150 GeVσ (gg fusion)(pb) 39.2 36.4 31.6 27.7 24.5σ (IVB fusion) (pb) 4.7 4.5 4.1 3.8 3.6σ (HW, HZ, Hqq) (pb) 3.8 3.3 2.6 2.1 1.7Total (pb) 47.6 44.2 38.3 33.6 29.7BR (H→ γγ) 2.08x10-3 2.21x10-3 2.24x10-3 1.95x10-3 1.40x10-3
Inclusive σ x BR (fb) 99.3 97.5 86.0 65.5 41.5
11-Mar-08 Marco Pieri 6
PTDR Mass Spectrum of Selected Events
All plots are normalized to an integrated luminosity of 1 fb-1 and the signal is scaled by a factor 10
Fraction of signal is very small (signal/background ~0.1) Use of background MC can be avoided when we will have data Data + signal MC can be used for optimizing cuts, training NN and
precise BG estimation
11-Mar-08 Marco Pieri 7
MC Samples Requests at:
https://twiki.cern.ch/twiki//bin/view/CMS/HiggsWGMCRequestsForHiggsToGamGam Higgs Signal (Pythia) masses between 60 and 160 GeV (at Fnal, Cern, Lyon)
gluon-gluon fusion, IVB fusion , WH, ZH, ttH
Background came late at it is not yet complete
GamJet 1.9 M events Lyon, Cern, SanDiego - OK Twophoton_Born 450 K events Lyon - 1/2 of requested Twophoton_Box 950 K events Lyon - OK Jets_pt50up 14 M events Cern - 1/6 of requested DY – Enough I think Twophoton Skims at UCSD, we will soon run on them
process pythia lev cuts gen level cuts gen sigma
sim sigma
gen level cuts reduction factor
# of gen evts
# of sim evts
Int L (fb-1)
gg->gamgam (box)
pthat>25 GeV none 36 pb 36 pb 1 1M 1M ~28
qq->gamgam (born)
pthat>25 GeV none 45 pb 45 pb 1 1M 1M ~22
pp->gam +jet pthat>25 GeV Special cuts (~sel B' in CMS IN 2005/018)
90 nb 0.6 nb ~150 300M 2M ~3.3
pp->jets pthat>50 GeV Special cuts (~sel C' CMS IN 2005/018)
24 ub 4.8 nb ~5000 50G 10M ~2.1
11-Mar-08 Marco Pieri 8
Important Points – Reconstruction Level Trigger and Skims
L1 Trigger HLT Skims
Photon isolation
Primary Vertex estimation
Energy Measurement Ecal crystal calibration SuperCluster calibration Photon energy scale Energy Resolution and Error (maybe optional, was done
before)
Photon conversion identification and π0 rejection
11-Mar-08 Marco Pieri 9
Electromagnetic trigger towers are classified in two categories depending on the energy deposition in the calorimeter trigger towers: non-isolated, isolated.
Single isolated Et>23 GeV
Double isolated Et>12 GeV
Double non-isolated Et>19 GeV
At startup thresholds lower
Total electron+photon Level-1 trigger rate ~ 4 kHz Level-1 trigger efficiency for H→ γγ larger than 99% Perhaps could still optimize the threshold at which all Isolation L1 cuts
are removed, never done until now
Level-1 Trigger
11-Mar-08 Marco Pieri 10
H → γγ signal has two isolated photons Dominant background from di-jets and γ+jet has at least one candidate
from jet fragmentation that is not well isolated
We keep early conversions in the double stream HLT trigger efficiency 88% - almost 100% for events selected in the analysis Trigger is relatively easy for H→ γγ because of high Et photons Total rate for photons after HLT ~5 Hz Need to make some improvements, particularly for pre-scaled triggers, I
also would like to add the double from single L1 HTL paths (also for electrons?)
HLT for Photons
PTDR HLT photon selection (still the same I think)
11-Mar-08 Marco Pieri 11
Skim for H→ γγ
I made a very simple skim selection last summer For now very simple:
Double Photon HLT .OR. Single Photon HLT with an additional SC – to easily study trigger efficiency
Will hopefully keep it simple forever Skimmed datasets not too large ~1-3 Hz for photons
RECO format planned to be used for now PDPhoton Skim higgsTo2Gamma files are at UCSD now We should run on them
No veto for electrons – Stream can also be useful to study electrons
11-Mar-08 Marco Pieri 12
Reducible backrounds (π0’s and mis-identified jets) have other particles near at least one photon candidate
We are in process of repeating and improving the study we carried out for the PTDR
Most of discriminating variables are built by summing up the Et or Pt of calorimeter deposits or tracks within a cone
ΔR = (Δη2+ Δφ2)
To study the performance of isolation variables we use individual photon candidates match or not within ΔR < 0.2 to a prompt generator level photon
Signal is: 120 GeV H→γγ gg-fusion reconstructed photon with Et>30 GeV matched with a generated photon within ΔR<0.2, background is: a super-cluster with Et>40 GeV NOT matched with a generated photon
Low statistics for now, cannot really look at correlations Trigger (L1 and HLT) not included
Photon Isolation
ΔR
11-Mar-08 Marco Pieri 13
Photon Isolation – Barrel – QCD pthat 80 – 120 GeV
Two possible views, first better for high purity, second better for high efficiency
Trigger not included
11-Mar-08 Marco Pieri 14
Photon Isolation – Barrel – QCD pthat 50 – 80 GeV
Trigger not included
11-Mar-08 Marco Pieri 15
Photon Isolation – Endcaps – QCD pthat 80 – 120 GeV
Trigger not included
11-Mar-08 Marco Pieri 16
Photon Isolation – Endcaps – QCD pthat 50 – 80 GeV
Trigger not included
11-Mar-08 Marco Pieri 17
Photon Isolation II For low pthat, isolation much less effective Should study it better – need more statistics at low pthat Note that pre-selected QCD events below 50 GeV pthat not simulated
Run on Gumbo skims – already at UCSD
Some more checks must still be carried out Study the correlation between isolation variables and specify
benchmark selections for photons
For the PTDR analysis we used a Neural Network with 2, 3 or 5 of following inputs: ΔR of the 1st track with Pt>1.5 GeV/c Sum ECAL Et within ΔR<0.3 The shower shape variable R9
Sum HCAL Et within ΔR<0.35 Sum tracks Et within ΔR<0.2
We did not use kinematical information, easy to combine these variables with reconstructed mass and photons Et in an optimized H→γγ analysis
Repeat the study in the near future
11-Mar-08 Marco Pieri 18
Primary Vertex Determination
New longitudinal interaction spread σ~7.5 cm (was 5 cm) Vertex estimated from the underlying event and recoiling jet In PTDR analysis the efficiency of determining the right vertex
was ~83% for H→ γγ events after selection Efficiency for the different types of background is similar and
basically irrelevant
First check of usage of identified converted photons – very preliminary
Currently we have datasets with no pileup Efficiency of reconstructing the right primary vertex ~98% on
all generated H→ γγ events
Must be compared with minimum bias events
11-Mar-08 Marco Pieri 19
Primary Vertex Determination II
Process Eff (%)H→γγ (gg fusion) 82H→γγ (IVB fusion) 89pp→γγ (born) 71pp→γγ (box) 72pp→γ+jet (2 prompt) 78pp→γ+jet (1 prompt + 1fake) 86pp→jets 90
PTDR low luminosity Efficiency of determining the primary vertex within 5 mm from the true one PTDR analysis
11-Mar-08 Marco Pieri 20
Primary Vertex Determination III
Generator level plots for different track pt cuts are provided in the Extra slides
11-Mar-08 Marco Pieri 21
Primary Vertex From Photon Conversions
At least 1
convpho identifiedAt least 1 selected convpho identified
All 35.0% 15.7%Vtx within 1 cm 19.7% 12.9%Vtx within 1 mm 10.2% 9.3%
Choose ConvPho with best e/p Selected convpho have e/p>0.3, 3DR_vtx < 30 cm Use all generated H→ γγ events (should apply selection)
11-Mar-08 Marco Pieri 22
Primary Vertex Studies
Wider longitudinal beam spot will: Worsen the Mass resolution for events with the wrong primary
vertex or no vertex Make easier the discrimination between different vertices with
converted photons When we want to optimize Primary Vertex finding we can also
use the direction of the total tracks transverse momentum that should be opposite to the Higgs pt
11-Mar-08 Marco Pieri 23
PTDR Selection for Cut-Based Inclusive Analysis
Photon selection: photon candidates are reconstructed using the hybrid clustering algorithm in the barrel and the island clustering algorithm in the endcaps ET1, ET2 > 40, 35 GeV |η|<2.5 Both photon candidates should match L1 isolated triggers with
ET > 12 GeV within ΔR < 0.5 Track isolation
No tracks with pt>1.5 GeV present within ΔR<0.3 around the direction of the photon candidate
Calorimeter isolation Sum of Et of the ECAL basic clusters within 0.06<ΔR<0.35 around
the direction of the photon candidate <6 GeV in barrel, <3 GeV in endcaps
Sum of Et of the HCAL towers within ΔR<0.3 around the direction of the photon candidate<6 GeV(5 GeV) in barrel (endcaps)
If one of the candidate has |eta|>1.4442 the other has to satisfy also: Sum of Et of the ECAL<3, Sum of Et of the HCAL<6 GeV
L1 + HLT inefficiency negligible after selection
11-Mar-08 Marco Pieri 24
Higgs MH=120 GeV
PTDR Selection for cut based analysis applied now We will soon improve the photon selection Results are in basic agreement with PTDR Still no pileup, efficiency will be somewhat lower
May provide a first estimate adding minimum bias events BG still to be evaluated
Efficiency Nevt/100 pb-1
Gluon-fusion 33.7% 2.7
IVB fusion 31.9% 0.3
WH, ZH, ttH 24.3% 0.2
Total 30.0% 3.2
11-Mar-08 Marco Pieri 25
Higgs Photons Efficiency Plots
Top plots photon finding efficiency Bottom plots photon isolation efficiency (PTDR cuts)
11-Mar-08 Marco Pieri 26
Higgs Mass Resolution
Barrel
Endcaps
R9>0.93
R9<0.93
Ecal calibration for 100 pb-1
Resolution ~1.5 GeV all (1.25 GeV Barrel, 2.1 GeV Endcaps)
11-Mar-08 Marco Pieri 27
Fake Photons from Jets
We ran on very low BG statistics, did not yet estimate the two photon BG
Start studying the single photon efficiency and fake rate Will compare between QCD and γ + jets
11-Mar-08 Marco Pieri 28
QCD Fake Photon Rate – 1 pb-1
Trigger not included
Fake Photon Rate Fake Photon Rate after isolation
11-Mar-08 Marco Pieri 29
Photon+jet Fake Photon Rate – 1 pb-1
Trigger not included??? Should check
Fake Photon Rate Fake Photon Rate after isolation
11-Mar-08 Marco Pieri 30
Fake Photon Isolation EfficiencyTrigger not included
11-Mar-08 Marco Pieri 31
One Photon Rate – 1 pb-1 Trigger not included
11-Mar-08 Marco Pieri 32
ECAL Calibration and Photon Energy Scale
Crystal Intercalibration Electrons from W→eν decays will be used Also π0 and/or η will be used
In CMSSW 2_0_0 there will only be SC corrections, no photon nor electron corrections anymore
Photon energy scale being studied from μμγ by Lyon, Florida State University and Kansas State University
μμγ events can also be used for efficiency studies
11-Mar-08 Marco Pieri 33
Photon Conversions
Most of the work carried out by Nancy Marinelli and Notre Dame University
They are currently trying to choose the best candidate Some changes Photon Objects in CMSSW 2_0_0 In my opinion much more word needed in order to use them for
photon identification
11-Mar-08 Marco Pieri 34
π0 Rejection
Start looking at the π0 rejection NN variables provided in CMSSW
Et photon 1 > 40 GeV Et photon 2 > 35 GeV Use unmatched photons for γ + jet Plots are normalized to unity No isolation cuts applied Some discrimination power seen at this stage R1 and R9 also show discrimination power at this stage
11-Mar-08 Marco Pieri 35
Π0 NN Variable
Barrel Endcaps
Barrel Endcaps
11-Mar-08 Marco Pieri 36
Other Shower Shape Variables – R1 and R9
Barrel Endcaps
Barrel Endcaps
11-Mar-08 Marco Pieri 37
Important points – Analysis Level We are restarting on this, just a few hints, we will
address these issues in a future presentation Background simulation
We previously studied generator level preselection for fake photons The Lyon group is working with DiPhox authors to have a full NLO irreducible
BG simulation (ATLAS is using ResBos) Anyway we should be able to carry out the analysis basically using the BG
from data, enough events from sidebands Signal Simulation (common with other Higgs Channels)
We should get NNLO calculations ad rescale Pythia and MC@NLO to those in order to exploit at best the signal topology
Real analysis – as much as possible from data Efficiency from data (Z->ee , Z->eeγ, Z->μμγ) Fake rate from data (not very useful for H→ γγ) Use data (sidebands) to optimize the selection and to estimate the BG
properties Study of systematic errors
Optimized Analysis Exploit the Different Production Modes (signatures 1l, 2l, MET, VBF) See how to avoid using MC background also for these Carry out optimized multivariate/multicategorized analysis
Related Analyses (to be studied since the beginning) Photon fake rate Gamma + jet cross section (Fake rate) Gamma-gamma cross section (Fake rate)
11-Mar-08 Marco Pieri 38
Effect of Systematic Errors
Input for CL calculation is: Background expectation from fit to the data (sidebands) Signal expectation from MCOrigin of systematic errors Error on the BG estimation (statistical from fit of sidebands +
uncertainty of the form of the fitted function) Error on the signal (theoretical σxBR, integrated luminosity,
detector + selection efficiency)Effect of systematic errors Systematic errors on the signal do not change the expected
discovery CL Systematic error on the signal makes exclusion more difficult Systematic error on the BG makes exclusion and discovery
more difficult
11-Mar-08 Marco Pieri 39
Main Systematic Errors
SIGNAL Theoretical error on cross
section times BR (~15%) Integrated luminosity (~5%) Higgs Qt distribution – effect
to be evaluated Selection efficiency (~10%)
Can assume a total of 20% (anyway not important in case of discovery)
Nevertheless systematic errors on the signal may cause the analysis to be less optimized
BACKGROUND Statistical error on the fit of
the sidebands (~0.3% for ~20 fb-1)
Systematic error on the shape of the fitted function (~0.3%)
No other errors when data available
11-Mar-08 Marco Pieri 40
Outlook We started revising the H→ γγ analysis framework so that it can also be
used for all other analyses We only ran over small samples for now We can now run on larger samples
We are also trying to organize the CMS-wide effort in order not to be alone in the analysis as it was for the PTDR
Getting other groups to contribute to the H→ γγ analysis
NEXT STEPS Continue the studies presented here Include HLT (and re-optimize it) in our analysis Need to re-optimize the basic selection for the cut-based analysis Study more converted photons and π0 rejection to see if they can be
used in the analysis Get NNLO description of the signal and rescale Pythia – Also check
MC@NLO Look at all issues of the real analysis on data Look again at the optimization of the analysis
11-Mar-08 Marco Pieri 41
End of the talk
End of the talk
11-Mar-08 Marco Pieri 42
EXTRA
EXTRA
11-Mar-08 Marco Pieri 43
Barrel – pthat 80 – 120 GeVTrigger not included
11-Mar-08 Marco Pieri 44
Barrel – pthat 80 – 120 GeVTrigger not included
11-Mar-08 Marco Pieri 45
Track Isolation BarrelTrigger not included
11-Mar-08 Marco Pieri 46
Track Isolation EndcapsTrigger not included
11-Mar-08 Marco Pieri 47
Ecal Isolation BarrelTrigger not included
11-Mar-08 Marco Pieri 48
Ecal Isolation EndcapsTrigger not included
11-Mar-08 Marco Pieri 49
Hcal Isolation BarrelTrigger not included
11-Mar-08 Marco Pieri 50
Hcal Isolation EndcapsTrigger not included
11-Mar-08 Marco Pieri 51
Generator Level, charged pt>1.5 GeV |eta|<2.5
11-Mar-08 Marco Pieri 52
Generator Level, charged pt>0.3 GeV |eta|<2.5
11-Mar-08 Marco Pieri 53
Z + Z + , , ZZA clean source of photons, A clean source of photons,
can determine, with real data: can determine, with real data:
• Efficiency of photon triggers Efficiency of photon triggers
• Determination of photon energy scale Determination of photon energy scale
• Determination of photon id efficiencyDetermination of photon id efficiency
• Determination of photon energy corrections Determination of photon energy corrections PTDR I: Y. Gershtein, AN 2005/040: Results based on fully-PTDR I: Y. Gershtein, AN 2005/040: Results based on fully-reconstructed Z+jets background (ORCA) and smeared generator-level reconstructed Z+jets background (ORCA) and smeared generator-level signal signal
Current objective: Validate AN 2005/040 selection and event rate Current objective: Validate AN 2005/040 selection and event rate predictions in CMSSW with all fully-simulated and reconstructed signal predictions in CMSSW with all fully-simulated and reconstructed signal and background samples, including those backgrounds not previously and background samples, including those backgrounds not previously studiedstudied
Susan Gascon Shotkin
General Interest of Z + , Zll « Inner Brem »
11-Mar-08 Marco Pieri 54
ZZμμγμμγ
ALPGEN
Summary Z Signal Z + jets + jets (*) Bbar ttbar
Nevents (/pb-1) 26.2 2750.3 1.706E08 (**) 7.8E06 (**) 561
After (1) 19.1 336.3 0.127 (**) 990.8 (**) 14.6
(2) 16.7 41.0 0.127(**) 381.7 (**) 12.3
(4) 13.7 3.28 0.121(**) 136.6 (**) 5.5
(5) 6.2 0.234 0.116(**) 70.4 (**) .82
(6) 4.0+ 0.6 + 0.03=4.63 --- ---
(7) --- 0.029 <0.03(**) 8.74 + 3.02 + 0.24=12 (**) 0.08
11-Mar-08 Marco Pieri 55
Since 170 up until 180_pre9 sizeable reduction in the reconstruction efficiencyI could not find out why
167180_pre4/5
Conversion radius eta (1/ptrec-1/ptsim)/1/ptsim
167180_pre10/180
MUCH better in 180_pre10 and 180. No intervention from my side ….. Still would wishto know what happened because in 200_pre2 the situation is as before 180_pre10
eta (1/ptrec-1/ptsim)/1/ptsimConversion radius
Photon Conversions – Nancy MarinelliLast Egamma Meeting