1. Stathes Paganis ATLAS UK meeting Durham, 18-Sep-2006
Higgs  4 leptons
Stathes Paganis
ATLAS UK meeting
Durham, 18-Sep-2006

2. UK contribution e/g calibration (long weights) in ATLAS
e/g data analysis (CTB04 papers)
Vertexing in ATLAS offline (Kirill Prokovief)
H  4l CSC note coordination (SP)
Artemis EU Network:
Durham, Sheffield, UCL, Saclay, Pisa, MPI, Aristotle University
16-May-06

3. Signal and Backgrounds
Higgs Mass
(GeV)
130
150
180
200
300
Xsection (pb)
20.75
16.35
12.04
10.07
5.40
Xsection (TDR)
(18.8)
(15.4)
(12.9)
N/A
BR(H->ZZ)
0.2613
0.3075
BR(ZZ->4l)
Xsection*BR (fb)
3.61
6.138
3.1375
11.92
7.525
Background
Initial NLO  (pb)
pp  ZZ
29.0
pp  Zbb
276.3
pp  ttbar
840
Irred
R~250
R~1000
16-May-06

4. Definitions (this analysis)
Electron
An egamma cluster (98%)
SW 3x7, 3GeV Energy Threshold, Cluster Corrections
(TDR: optimum is 5x5 in the EndCap)
A cluster/track match (92%)
An isolated cluster (Recon. flag eg_ISEM=0)
Track Quality: at least 9 Silicon hits, E/p<2.3
Muon
A combined (muon-Spec)+(ID) “cb” muon
Refitting Quality: fitcodecb=0.
16-May-06

5. H->4l analysis cuts Apply EM corrections to ‘electrons’
Use Et from LAr, h, f from tracks
Combine Et from ID and Et from LAr (TDR)
Apply TDR-like cuts
4 leptons with pt(1,2)>20, pt(3,4)>7GeV with |h|<2.5
EM isolation cuts (eg_ISEM=0)
Only for electrons
ID isolation cuts
Electrons Spt(0.01 < dR < 0.2) < 10 GeV
Muons Spt(0.01 < dR < 0.2) < 5 GeV
Impact Parameter cut
Electrons a0vert/s < 10 (for 4e), 5 (for 2e2m)
Muons a0vert/s < 3.5
Z, Z* mass cuts M12, M34 and Higgs mass window as in TDR
For high masses: isolation and impact parameter cuts are relaxed for
the 4e and 2e2m case.
16-May-06

6. Comparison with TDR (30fb-1 low lumi)
Higgs Mass
(GeV)
130
150
180
TDR signal (events)
11.4
26.8
19.7
This Analysis
11.294
25.737
16.893
TDR background
2.61
2.98
3.1
This analysis
3.43
2.64
9.359
Bill Quayle
The increase of the background at 180GeV has been previously noted: it is driven by the ZZ background which rises fast at the M(ZZ)=180GeV region (not included in TDR analysis)
16-May-06

7. EventView and HiggsToFourLeptons (12.0.x)
AOD
ElectronInserter
MuonInserter
TruthParticleAssociator
EventViewInserters
TruthParticleInserter
EVUDAssociators
TrackParticleAssociator
GenParticleInserter
EV_H4lPreselector
ClusterAssociator
PassedIsEM
PassedEgamma
PassedTrkIso
Electron
AANtuple
Muon
Local Analysis
GenParticle
TrueE, TrueMu
16-May-06

8. Critical Issues
16-May-06

9. Background Extraction in (cand) Signal Region
From “theory”:
PDF error 4-5%
Renorm/Factor. Scales error 3-5%
Efficiency error ?%
Luminosity error (5-10% ?)
How about the Zbb (low mass 20-50% error but only a fraction of ZZ)?
From Normalization
Lumi/Efficiency errors reduced
Ratio less sensitive to scale/PDF uncertainties
How about the Zbb (low mass)?
From Sidebands
Limited statistics at low masses
Difficult below 130GeV due to kinematic turnover
But, error well defined using a profile likelihood (i.e. use MINOS errors of multiple fits with different background parameterization assumptions).
Abdulin et al, hep-ph/ (pg 113)
Jan Conrad et al
16-May-06

10. ZZ background Pt lepton > 5 GeV. No Z mass cuts.
Notice the turn-over at 120GeV.
Notice the turn-on of ZZ at 180GeV.
16-May-06

11. Sideband fitting: 30fb-1 background only
Assume a test for Higgs(130GeV). We ran 1M experiments.
3sigma test finds: 1712 events passing out of 1350 expected from fluctuations
16-May-06

12. Sidebands: 30fb-1 130GeV Signal+Bgnd
<B>=5, <S>=12 events
Fit may exclude/include
“signal region” (here the fit excludes the sr)
For every experiment we know the true Signal and Background, so we can check how well a fitting method does in extracting the signal significance (coverage study).
16-May-06

13. Sidebands: S+B relaxing Z mass cuts
<B>=15, <S>=12 events
16-May-06

14. Accuracy of Background prediction
Background extraction using an unbinned extended likelihood fit
<B> unbiased
5 Background events in signal region:
RMS of prediction: 2 events
15 Background events in signal region:
RMS of prediction: 3.5 events
3sigma test finds: 1712/1M events passing out of 1350 expected from fluctuations:
This undercoverage can be corrected analytically (in the large statistics limit):
K.Cranmer, S.Paganis ATL-COM-PHYS-2005
16-May-06

15. Softest lepton Pt and electron efficiency 12.0.x
Generated softest lepton pt
H120
H150
H180
IsEM only
Most of the soft electrons (and so the light Higgs events) are lost due to non optimized isolation cuts below 15GeV. Reminder (at NLO):
H(120GeV): xsection*BR*Acceptance ~ 2events/fb-1.
Similar problem in SUSY analyses. We will address the problem in coordination with the egamma group. Also 9GeV electron CTB data are available to study shower shapes. Extraction of efficiency at low pt using data is also an issue.
16-May-06

16. Fraction of energy outside a 3 strip core data vs MC 11.4.0 for
Very Preliminary
CTB04 Electrons
Fraction of energy outside a 3 strip core data vs MC for
6 energies.
Cut important for e-ID and g/p0 separation.
Maybe due to the physics list used in , or/and due to cross-talk. Notice larger departure at higher energies.
16-May-06

17. Very Preliminary
Lateral Width
16-May-06

18. (2nd maximum minus the minimum between the 2 maxima)
Very Preliminary
e1diff
(2nd maximum minus the minimum between the 2 maxima)
16-May-06

19. Electron Uniformity/Scale with pt>7GeV
Higgs electrons with pt>7GeV, 5x5 clusters
The gap region must be checked:
New calibration in 12.0.x is fine
16-May-06

20. Sample resolution/Escale eta bins (pt>7GeV)
New calibration in 12.0.x is fine
16-May-06

21. Weights from minimization: performance
Now into Athena
Linearity evaluated on H->4e events (no cracks) averaged on full eta range (0-2.5) with Athena out of the box
Low energy bias could be reduced by improving the low energy statistics for weights extraction
16-May-06

22. CTB04: Range of energies (periods 5,6)
Runs: , , , ,
Data/MC
9GeV 20GeV GeV GeV GeV
E 0.993(0.002) (0.001) (0.001) (0.001) (0.001)
PS (0.03 ) (0.02 ) (0.02 ) (0.02 ) (0.02 )
S (0.01 ) (0.007) (0.007) (0.009) (0.01 )
S (0.01 ) (0.005) (0.003) (0.003) (0.003)
S ( ) (0.03 ) (0.01 ) (0.01 ) (0.02 )
S1/S (0.02 ) (0.01 ) (0.01 ) (0.01 ) (0.02 )
S1/S2
Data PS MC
PS+S1+S2+S3
A 0.15X0 of far upstream material was added to simulate the beamline.
LAr/ID discrepancy: the ID data indicate no need for this. Trigger efficiency?
16-May-06

23. Data vs MC ONLY far material PS S1 Period 8 20GeV run 2397 RATIOS
Data/MC S2
E=20GeV Run= 2397
E 1.003
PS (0.006)
S (0.002)
S (0.002)
S (0.007)
S1/S (0.003)
PS+S1+S2+S3
S1/S2
Per Johansson+SP
16-May-06

24. CTB04: very low energy electrons
Good agreement between data and various MC versions/setups
16-May-06

25. CTB04: Linearity (TDR weights + offset)
Default configuration (0mm Al)
75mm Aluminium in front of cryostat
Data MC
Linearity at the 0.2% level:
very close to CTB beam-line systematic limit.
Absolute Scale? For 180GeV the syst. error is about 0.25% (beam line).
The TDR method is biasing at low Energies: the bias increases with the material (also seen in ATLAS, see L.Carminati’s talk).
16-May-06

26. Comparison between CTB04 and TB02
SP: August 2006
physics/
Analyses agree in sampling and c-term.
CTB04 Analysis with TDR weights + offset (Energy independent).
TB02 Analysis with new E-dependent calibration hit – like parametrization.
16-May-06

27. Summary
Significant efforts in muon/electron performance issues in progress (focus on electrons here).
CTB04 and commissioning data
Lepton efficiencies – Calibration – Linearity – Uniformity - Material effects – Misaligned detectors – HV problems – Xtalk – etc etc
Measurement of the Mzz background
Even with a few tens of events of statistics, an unbinned extended likelihood fit could do reasonably well. However the systematic due to the background shape must be investigated.
CSC note in progress
Its success will require a well coordinated effort by the (many!) authors.
16-May-06

28. Backup
16-May-06

29. Weights from minimization
Energies in the samplings are reconstructed with approximate sampling fraction at the cell level
Weights are extracted by a chi2 fit on a sample of single electrons in the [-2;+3] around the MPV (most prob. value) of the reconstructed energy distribution:
It’s a more refined version of the TDR/DC1 calibration: the introduction of the offset cures most of the low energy linearity problems (TB2002)
Only 4 energy independent parameters per cell!

30. Weights from minimization: eta dependence
Now into Athena
Weights extracted with E>20 GeV ‘official’ electrons samples (DC3-02 detector geometry)
offset w0  w3

31. Higgs events: electron efficiencies vs eta
Egamma cluster
egamma+track_iso
egamma+TrkIsEM
egamma+IsEM
16-May-06

32. Higgs events: electron efficiencies vs pt
Egamma cluster
egamma+track_iso
The problem is in caloIsEM
egamma+TrkIsEM
egamma+IsEM
16-May-06