Transcript ZHH channel: software and detector performances for ILC Michele Faucci Giannelli

ZHH channel:
software and detector
performances for ILC
Michele Faucci Giannelli
Fabrizio Salvatore
Mike Green, Tao Wu
OUTLINE
This is an update to the LC note LC-PHSM-2007-003
• ZHH Channel: summary of reconstruction
and software used
• Generator differences
• Tracking performances
• Particle Flow Algorithm performances
• Detector comparison
• First look at background
• Conclusions
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ZHH Channel
• The e+e-→ZHH channel is an excellent
benchmark for many steps of the simulation:
– Different generators give different cross sections
– Test physics lists available in detector simulation
– Requires high performances from all detectors
• Vertexing
• Tracking
• Clustering
– Thus can be used to test particle flow algorithms
– Finally can be used to compare different detector
models
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Generation and Simulation
• Events have been generated using
Pandora-Pythia and Whizard
• The reconstruction was performed by
Mokka (V06-03p02):
– Some information @ generation level:
• ECM = 500 GeV
• M(Higgs) = 120 GeV/c2
• Polarized 80% electron beam
• Two detector model (LDC00Sc and
LDC01Sc)
• Z→l+l- (muons and electrons)
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Marlin Processors
Marlin 0.9.7 + MarlinReco 0.3
– Processors used:
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VTXDigi
FTDDigi
TPCDigi
Tracking Processors
PFA Processors
PairSelector
SatoruJetFinder
BosonSelector
MyROOTProcessor
Tracking Processors:
– FullLDC:
• LEPTrackingProcessor
• SiliconTracking
• FullLDCTrackin
– TrackCheater
PFA Processors:
– Wolf:
• TrackWiseClustering
• Wolf
• ClusterMerge
– PandoraPFA:
– TrackBasedPFA:
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ZHH selection
• Select and extract the two leptons which better
reconstruct the Z.
• Combine all the other particles in 4 jets.
– Reconstruct the two Higgs minimizing the quantity:
D2hh  m12  m h   m 34  m h 
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2
• Look at different variables to compare the two
available PFA algorithms:
– D2 and other combinations of jet-jet inv. Mass
• The mass of the Higgs used in the analysis is 114
GeV instead of 120 GeV to take into account the
effect of invisible particles
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Invisible particles
PANDORA
Black: normal reconstruction
Red: with neutrinos
WOLF
On average, contribution from
‘invisible particles’ ~ 6 GeV
Adding this contribution,
reconstructed H mass with Wolf
higher than mH value used in the
generation.
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LDC01Sc
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Generators
Tree generators:
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Pandora Pythia
Pandora Phytia with K, S,
X, p NOT decayed
Whizard
No visible
difference noticed
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Tracking
Two Tracking algorithms:
– FullLDC Tracking
– TrackCheater
No visible
difference noticed
Tracking is good enough
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PFA Comparison
Three PFA available:
Z→ee
– PandoraPFA
– Wolf
– TrackbasedPFA
Z→mm
Problem in TrackbasedPFA with
particle identification
Cut on Z mass in the Higgs Plot
to select good events
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Higgs Mass
Z→mm
Pandora has a very good RMS for
muons, probably too low mean
Wolf reconstructs too high mass Higgs
The problem with muon id affects the
Higgs reconstruction in TrackbasedPFA
Z→ee
Pandora has some problem with electron
id, high energy tail (bremsstrahlung?)
Wolf reconstructs too high mass Higgs
TrackbasedPFA has a very good
performance with electrons!
 Algorithm works!!
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Higgs discrimination: D plot
• D is defined as
Dhh  m12  m34  2 * m h
Z→mm
For muons PandoraPFA
is the best algorithm
Z→ee
For electrons Pandora and
TrackbasedPFA are comparable
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Higgs discrimination: D2 plot
• D2 is defined as
D  m12  m h   m 34  m h 
2
hh
2
2
Z→mm
Z→ee
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Detector comparison
Z→mm
PandoraPFA
LDC00SC
LDC01Sc
Z→ee
No differences in the muon case
LDC01Sc is better than LDC00Sc
for electron, less material then less
bremsstrahlung?
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First look at Background(I)
LDC00Sc
TrackbasedPFA
Z→ee
ZHH
ZZH
ZZZ
PandoraPFA
Pandora is better not only
for a more efficient signal
reconstruction but for a
smaller contamination too
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First look at Background (II)
LDC00Sc
PandoraPFA
Z→mm
ZHH
ZZH
ZZZ
Z→ee
Good discrimination for
muons, a factor 2 better than
electrons.
ParticleID has a crucial role,
more effort are needed!
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First look at Background (III)
LDC00Sc
PandoraPFA
ZHH
ZZH
ZZZ
Same as previous
slide, linear scale
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Conclusion
• Comparison between generators:
– No visible differences between generators
• Comparison between tracking:
– FullLDC is as good as cheater for our analysis
• Comparison between PFA:
– Trackbased almost as good as Pandora, both need
a better Particle ID.
• Comparison of LDC00/01Sc using PandoraPFA
– Small differences once electron ID is solved, both
detector models can be used to reconstruct this
channel
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Conclusion
• Studies on SM backgrounds
– ZZH and ZZZ have been simulated and
reconstructed:
it is possible to discriminate the signal!!
• Future Plans
– Study high cross section channels
• Understand how to apply cut at generation level to
reduce the amount of events to simulate in Mokka
– Move to 6 jets analysis
• B tagging is necessary
• Looking at a new strategy for Z selection
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Backup slides
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Preparation: calibration
• Check calibration for pions and electrons
Black Pandora
Red Wolf
Pions
Electrons
GeV
LDC01Sc
GeV
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