Transcript Slide 1
Data based method for
background subtraction:
Z →μ+μHalina Bilokon, Vitaliano Chiarella,
Simonetta Gentile, Giovanni Nicoletti
Laboratori Nazionali di Frascati, Università di Roma
La Sapienza, INFN
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Outline
Motivation.
Example of application: bb Z m+ m-
Method proposed
Software & Generators
• Simulation, Reconstruction, Analysis.
Sample
Conclusion and future development
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
MonteCarlo
Isajet
Ariadne
Sherpa
Cojest
Les Houches Guidebook hep-ph/040345
Jetset
Herwig
Pythia
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Shower MonteCarlo
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Motivation
It is then extremely important to rely
on alternative method to MonteCarlo, as much we
can
We propose a method based on a different
data sample of experimental data
Only hypothesis: lepton universality.
Example of application: bb Z m+ m(most copious background of bb h0/A m+ m- studies (14/12/2005)
S.G. presentation, ATLAS-PHYS-2003-015, June 2003.)
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Signal & background
~ 0.2 - 0.01 pb
~ 22.8 pb
(even lower)
h0 bb→ m- m+bb
Zbb → m-m+ bb
(Pythia 6.226)AcerMC (v.2.3) interfaced
with Pythia 6.2 (hep/ph0405247).
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Background Subtraction Method
Precise Knowledge of
background is crucial
Experimental method
proposed based on
Z→ m+ m- and Z→ e+ e Relying on experimental data
Br( h0→ e+ e-) neglegible
2
mm
m
e
Different Inner
Bremsstrahlung
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Z production
gg hbb m + m -bb
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Software Release & Sample
Generation Athena 9.0.4 - Pythia (v.6.226) - Acer (v.
2.3)
Simulation, Digitalization, Reconstruction Athena
10.0.1
Analysis based on CBNT (root –ntuples).
Final study in scenario Ldt 30 fb
~ 600000 events
In this presentation Lint ~ 20 fb-1
~ 400000 events
-1
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Study performed
Different Inner Bremsstrahlung
Zbb → m-m+ bb (g) Ng ~ 0.086 Nev=464522
Zbb → e-e+ bb (g) Ng ~ 0.157 Nev=442828
Different Detector Response
The most significative variable of
bb h0/A m+ m- analysis has be chosen Minv as test .
NB. The combination of a same flavor lepton
originating from b and one of Z are included inevitably
in the plots
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Bremsstrahlung Photons
Zbb → m-m+ bb
Zbb → e-e+ bb
Ng MC ~ 0.086
Ng MC ~ 0.157
e
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Bremsstrahlung Photons
Zbb → m-m+
bb
Zbb → e-e+ bb
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generator level: Zbb → m-m+ bb
Minv(m+m-)
Minv(m+m-)g
M
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generator level: Zbb → m-m+ bb
Minv(m+m-)
Minv(m+m-)g
Only events with a g of Bremsstrahlung
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generator level: Zbb →
Minv(e+e-)
+
ee
bb
Minv(e+e-)g
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generator level: Zbb →
Minv(e+e-)
+
ee
Minv(e+e-)g
Only events with a g of Bremsstrahlung
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
bb
Generator level: Zbb →
+
ee
bb
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generator level
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generator level
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
muons
Leptons
electrons
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Photons: Zbb → m-m+ bb
R
η2 + φ 2
All photons
Bremsstrahlung photons
watch the different scale!
PT vs.Halina
Distance
between
g
and
m
Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN. Subsample(~25000 ev)
Photons: Zbb → m-m+ bb
All photons
R
Bremsstrahlung photons
η2 + φ 2
R ~ 0.15
Distance
between
g andSimonetta
m
Halina Bilokon,
Vitaliano Chiarella,
Gentile, Giovanni
Nicoletti
watch
the different scale!
Higgs Meeting 18 April 2006,CERN.
R
η + φ
2
All photons
2
Photons: Zbb →
+
ee
bb
Bremsstrahlung photons
5x5 cluster in ATLAS
watch the different scale!
PT vs. Distance
between
g
and
e
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Subsample(~25000 ev)
Higgs Meeting 18 April 2006,CERN.
Photons: Zbb →
All photons
R
+
ee
bb
Bremsstrahlung photons
η2 + φ 2
R ~ 0.25
Distance between g and e
watch the different scale!
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Photons
If the photon is emitted close to electron,
only one cluster is reconstructed and the combined
4-momentum is measured. For η + φ R
the g is effectively absorbed in the same cluster of the
electron.
R η + φ 0.125 corresponds to a 5x5 cluster in
ATLAS. The energy of electron is measured in e.m.
calorimeter, q and f are measured in tracker.
Photons, inside cone R, are taken in account summing
their 4-momentum to the 4-momentum of the nearest
lepton.
Photons reconstructed are e.m. clusters without track
associated (h 0.025,f =0.05 ) and PT >5GeV, |h| >2.5.
2
2
2
2
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
All Photons: Zbb → m-m+ bb
Zbb → m-m+ bb
Zbb → e-e+ bb
PT g> 5 GeV |h| >2.7 recontructed g
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Reconstruction
Muons: combined reconstruction (inner detector +
spectrometer), PT >10 GeV, |h| >2.5.
Electrons: energy measured in calorimeter,(q,f) measured from
tracker, PT >10 GeV , |h| >2.5.
Photons: e.m. cluster without track associated :
h 0.025, f =0.05, PT > 5 GeV, |h| >2.5.
Brem photons: >2 leptons reconstructed +
g reconstructed in a cone around lepton direction < R.
Electrons sample only one cluster is reconstructed.
Muon sample: m track near photon cluster, misidentification.
The number events reconstructed with g brem identified is at
percent level.
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Reconstruction: Zbb → m-m+ bb
Minv(m+m-)
Minv(m+m-)g
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Reconstruction: Zbb → m-m+ bb
Minv(m+m-)
Minv(m+m-)g
Only
events with a g of Bremsstrahlung
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Reconstruction: Zbb →
Minv(e+e-)
+
ee
Minv(e+e-)g
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
bb
Reconstruction: Zbb →
Minv(e+e-)
+
ee
bb
Minv(e+e-)g
Only
events with a g of Bremsstrahlung
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Reconstruction
Only events with a g of Bremsstrahlung
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Reconstruction
The number g bremsstrahlung reconstructed separatly
in muons events is higher than electron events, where are mostly absorbed
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
in the electron
cluster
Higgs Meeting 18 April 2006,CERN.
Generation-reconstruction
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Generation-reconstruction
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Conclusions
A study for an experimental method of background
subtraction is developed based on fully simulated
samples, Lint ~ 20 fb-1 of:
bb Z m+ m- and
bb Z e+ ecomparing:
the Bremsstrahlung of the two samples.
the ATLAS detector response.
The study is preliminary and needs careful tuning on
data collected.
R is an extremely important parameter, that
should be carefully tuned.
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Conclusions
In the region Minv 98 -135 GeV the ratio is reasonably
stable and the effect of Bremsstrahlung is negligible
with respect to detector response
The same method can be applied to H→ tt and in
general to all decays where the electron decay is
negligible in the signal.
The method relies on lepton universality and needs a
good knowledge of detector response for different
leptons
The method doesn’t need an implementation on MC of
higher order corrections
Acknowledgements: Borut Kersevan, Dirk Zerwas,Donatella Cavalli
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Riserve
Riserve
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Matching track narrow
h 0.025 f =0.05
Isolation broad
h 0.05 f =0.10
R =0.07 size of cluster 5x 5 h= 0.025 f =0.05
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.
Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti
Higgs Meeting 18 April 2006,CERN.