Alain Romeyer - Sept. 2004 1
Light Higgs search in SUSY cascades
Introduction (Previous studies)
Plans for this analysis
Simulation chain
Reconstruction and analysis framework
Conclusion
Alain Romeyer (Mons - Belgium)Filip Moortgat (CERN)
Alain Romeyer - Sept. 2004 2
Introduction
It has been shown in CMS-note 1997/070 :
• signal can be seen with only few months of data
• main bkg : SUSY
• SM bkg very low
• discrimination betweenSUSY signal and SUSY bkg is difficult
Signature :h0
01χ LSP
MET
b
bB tagging
02χ
q / g
Alain Romeyer - Sept. 2004 3
Plans for this analysis Using the Full simulation and reconstruction
On one particular MSUGRA point (LM5) Background study : SUSY and SM (t, W, Z + jets…) Optimise the reconstruction :
Trigger efficiency study Jet reconstruction and calibration B tagging efficiency
Reconstruct the bَb invariant mass and then… If visible : using end-points try to estimate the squark
masses
Using the Fast simulation study the CMS reach Scan the MSUGRA parameter phase space Provide a sensitivity region in the (m0,m1/2) plane for
several luminosities
Alain Romeyer - Sept. 2004 4
MSUGRA Point
Benchmark point LM5Tan = 10AO = 0µ > 0M1/2 = 360 GeVM0 = 230 GeV
MSUGRA 5 parameters : m0, m1/2, A, tan , sign(µ)
S. Abdullin – L. Pape Update II of the new MSUGRA test points proposal
0 02 1
0 0
g q
χ χ
H h
m ~ 860GeV m ~ 800 GeV
m ~ 273 GeV m ~ 142 GeV
m ~ 570 GeV m ~ 116 GeV
All SUSY channel : 4.9 pb 150 000 evts/year Low Lumi.
Alain Romeyer - Sept. 2004 5
0 0 02 1
0 0 02 1
0R L
0,±0 + -L 1,2
00 + -L 2
00R 1
0
>
χ χ + h 85%
χ χ + Z 12%g q +q (q q )
h b+b 72%q χ + q ~85%
h W +W 9%q χ + q 20-25% h τ +τ 9%q χ +q 99% h g +g 5%
h c+c 4%
Masses and Branching ratios
0T 2
0T 1
0T
T
p (χ ) =362.4GeV
p (χ ) = 206.9GeV
p (h ) =175.3GeV
p (b-b) = 72.5GeV
Branching ratio
~ 20% of SUSY events contain our decay chain (~ 30 000 evts/year)
From
Isaj
et
Alain Romeyer - Sept. 2004 6
Simulated events Production of signal events and pile-up
Signal events : all SUSY channel (easier for later event reweighting)
Private production of 10 000 evts @ Mons(~25 days)
~20% contains our decay chain
Digitisation : merge pile-up and signal
100 000 evts production readyusing Digiswaiting for DST
Isajet 7.69 +
Pythia 6220
+ CMKIN
OSCAR2_4_6
ORCA7_6_1
generator
simulation
digitisation
Low statistic -> only a first try
FU
LL S
IMU
LA
TIO
N C
HA
IN
Alain Romeyer - Sept. 2004 7
SignalBackground :
• SUSY• SM : top, QCD…
« Reconstruction » strategy
Simulatedevents
I – L1 +HLT
Reconstruction
II - Jet Reconstruction : • optimisation (large jet multiplicity)• calibration• Energy resolution •…
III - B tagging : • B tagging efficiency• mistagging rate• test of different algorithms• optimise for SUSY cascade (plenty of bs comming from tops and sbottom)
IV - MET• important for event selection
Efficiency tables
Alain Romeyer - Sept. 2004 8
Jet reconstruction
Test jet reconstruction and calibration with a Zbb sample (production of 50 000 events already asked)
Position of the peak Energy resolution
Iterative Cone Algorithm perhaps not adapted to our problems
Splitting and merging of jets is not implemented Midpoint Cone Algorithm could be an interesting solution
Alain Romeyer - Sept. 2004 9
Physics analysis
VII - Analysis
•b ̅b inv mass reco. select the 2 b jets
coming from the higgs decay
reliable fit strategy higgs mass
• CMS reach CMS sensitivity
VI - Event selection
• Reject SM and SUSY bkg MET Number of jets…
• Optimisation !!!
Alain Romeyer - Sept. 2004 10
Conclusion Full simulation of signal (and SUSY bkg) done
for SUSY LM5 using : ISAJET 7.69 Pythia 6.220 OSCAR_2_4_6 ORCA_7_6_1
Plans : First step : full higgs analysis chain on LM5
Study trigger efficicency (~95%) Study jet reconstruction in SUSY cascade environment
(calibration !!!) B tagging efficiency (~50 – 60%) Study background : SUSY and SM (top, Z+jets…) Optimize selection criteria (MET, number of jets…) Fit higgs mass
Alain Romeyer - Sept. 2004 11
Conclusion…
Second step : Try to reconstruct masses of sparticles in the cascade
decay chain using endpoints
Third step : CMS reach Scan the MSUGRA parameter phase space with fast
simulation (FAMOS)
For the moment we have used 10k events, now starting to run on 100k events
We have already some first results !!! will be shown in november SUSY BSM meeting.
