Light higgs decay in SUSY
cascade - Status report
Filip Moortgat (CERN)
Alain Romeyer (Mons - Belgium)
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Introduction
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Trigger efficiency

B tagging

Jet calibration
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Invariant mass reconstruction

Likelihood fit
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Conclusion
Alain Romeyer - January 2005
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Introduction
MSUGRA 5 parameters : m0, m1/2, A, tan b, sign(µ)
S. Abdullin – L. Pape
Update II of the new MSUGRA
test points proposal
Benchmark point LM5
Tan b = 10
AO = 0
µ>0
m g ~ 860 GeV
M1/2 = 360 GeV
M0 = 230 GeV
m ~ 800 GeV
q
m χ 0 ~ 273 GeV
m χ 0 ~ 142 GeV
m H0 ~ 570 GeV
m h 0 ~ 116 GeV
2
χ 10
Signature :
q/g
χ 02
1
LSP
MET
b
h0
Alain Romeyer - January 2005
B tagging
b
2
Simulated events
FULL SIMULATION CHAIN

generator
Isajet 7.69
+
Pythia 6220
+
CMKIN

OSCAR
2_4_6


digitisation
ORCA
7_6_1
Signal events : all SUSY channel (easier
for later event reweighting)


simulation
Production of signal events and pile-up

~20% contains our decay chain
Digitisation : merge pile-up and signal
official 100 000 evts production at CERN
available
our reconstruction strategy launched on
digis
First results
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« Reconstruction » strategy

Simulated
events
ORCA_8_6_1
Reconstruction
I – L1 +HLT
Efficiency ?
Analysis
• event selection
• IV - b ̅b inv mass reco.
II - Jet Reconstruction :
• Iterative Cone Algo.
• cone size : 0.5
• tower Et thr. : 0.5 GeV
• seed Et thr. : 1 GeV
Jet sel.
Pt > 10 GeV
III - B tagging :
• By Track Counting
• Number of tracks above
minimum significance : 2
MET :
• MET from EcalHcalTower
Alain Romeyer - January 2005
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Trigger efficiency
Generated
HLT
100 000
96 462 (19 338)

L1 : 99.9 % - HLT : 96 %
Trigger
Condition (GeV)
% of evts
1 jet
Et > 571
23.5
3 jets
Et > 209
21.7
4 jets
Et > 122
32.7
B jet
1 Jet Et > 237
77.4
MET calo
1 jet > 180 GeV + MET
> 123
79.5
MET jets
1 jet > 180 GeV + MET
> 123
79.8
~ all events !!!
Caveat : ~ same efficiency for SUSY bkg.
Alain Romeyer - January 2005
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Btagging
Track Counting Algo. (default setting)
Number of jets
Number of tagged
jets
Efficiency /
Inefficicenc
y (%)
b
95593
47310
49.5
u
123 807
9408
7.6
d
97409
7957
8.2
c
50728
9103
17.9
Global efficiency : 49.5 %
Global inefficiency : 9.4 %
Need to be optimised
Filip
Nhiggs = Nhiggs after HLT * ( Btag Eff. )² ~ 4700 evts
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Efficiency / inefficiency
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Efficiency / inefficiency…
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Select b jets from
0
h
Select only b jets coming from h0 decay
No jet energy calibration
(from parton content
in a 0.3 cone)
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Jet reconstruction accuracy
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Jet calibration

Jet calibration method following CMS-note 1999/066



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
Association between rec. Jets and generated partons before
hadro. (cone < 0.3)
2 types of jets : b jets and other
Etruejet = sum(Equarks,gluons)
Correction Factor C = Etruejets / Erecjets
Fit of the correction factor surface in the E vs || plane :
f(|η|)
C  η, E  = a1+ a 2
E
f(|η|) = b1 + b 2 |η|+ b3 |η| + b 4 |η|
2
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E correction for b jets
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E correction for non b jets
Same operation isAlain
done
with
the
Romeyer
- January
2005 jet momentum
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Impact on Minv
Select only b jets coming from h0 decay
Calibrated jets
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Impact on jet reco. accuracy
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Invariant mass (no cuts)
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Likelihood fit


Follow the Z’  µµ strategy (CMS AN 2004/018)
Unbinned method
NS
NS
P(mh )=
Ps (m h ,σ) + [1 ] Pbg (m h )
N tot.
N tot.
Fraction of signal


Normalised
Gaussian
Extract from background fit
No constraints on the absolute background level
only on the background shape
NS
3 parameters : mh, s and
N tot.
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Fit result (full stat)
S=
L
  14.1
2 ln  S+B
L B 

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Various running time
50 000 evts – S = 10.9
100 000 evts – S = 14.1
25 000 evts – S = 7.95
15 000 evts – S = 5.8
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Conclusion

For the first time the full analysis chain is working

higgs peak visible with significance above 5
~15000 evts (~ 40 days of understood data)

Future :
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Include SM background
Improve S/B ratio (cuts, b tagging optimisation…)
Reduce the width of the invariant mass
Run the code on the Zbb sample for cross check and optimisation
of the reconstruction strategy
Fast simulation (FAMOS) in order to explore the SUSY parameter
phase space
Contour plot for the CMS reach
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