Update on Search for light Higgs in SUSY cascades

Update on Search for light Higgs in SUSY cascades

Filip Moortgat (CERN)Philip Olbrechts (CERN)

Alain Romeyer (Mons – Belgium)

SUSY-BSM meetingFebruary 17th 2006

CERN

• Simulated data and analysis techniques used• Invariant mass and mass resolution• Fitting procedure: extraction of Higgs mass and significance• Systematics: jet calibration • Conclusions and outlook

• ~ 98500 events - containing all SUSY channels - were produced at LM05. ~ 20 % is the desired signal. The main background contribution is expected to come from the 80 % remaining SUSY events. 9 trials on GRID result in ~ 97000 events “su05_pyt_LM5”.

• SM background events have been included. ~ 1300000 events (PubDB: jm03b_Ttbar_inclusive) Z+jet ~ 50000 events (PubDB: jm03b_Zjets_250_400) W+jet ~ 50000 events (PubDB: jm03b_Wjets_250_400) qcd ~ 200000 events (PubDB: jm03b_qcd_50_80) qcd ~197000 events (PubDB: jm03b_qcd_170_230) qcd ~ 100000 events (PubDB: jm03b_qcd_300_380)• The jet reconstruction is based on the “iterative cone algorithm” (cone size: 0.5) using the “SplittedEcalPlusHcalTowerUEInput” input.

• The combined b-tagging algorithm was applied using jets with Pt > 30 GeV. • The Jet calibration is based on the official Jet calibration (GammaJet).

• DST information was read, using ORCA_8_7_4.

Data samples / Reconstruction

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Analysis techniques• First selection is based on Level 1 trigger and JetMET HLT trigger with a total signal selection efficiency of 79.5 %

• Reconstruction of the b invariant mass spectrum: Jet pairing is crucial as there are many possibilities. Application of the ‘model independent’ hemisphere separation algorithm. Take only that combination of reconstructed b tagged jets for which the space angle is smallest and

b

2

21

2

21 R 5.1R

Overview of selection cuts applied

• B-tagging quality estimator S > 1.5

• Number of jets 4

• Number of b-jets 2

• Missing Transverse Energy (MET) 200 GeV

• Highest “jet transverse momentum” 200 GeV

• 2nd Highest “jet transverse momentum” 150 GeV

• 3rd Highest “jet transverse momentum” 50 GeV

• < 1.52

21

2

21 R

(See backup slides for individual distributions)

Overview of selection/rejection efficiencies

DATA TRIGGER NJET NBJET MET MAXPTJET MAXPT2JET MAXPT3JET DR SIGNAL 17480 17332 7234 5095 4950 4077 4033 1385 SUSY BG 62490 57489 7598 5755 5584 4547 4431 1175 TTBAR 234580 215720 44623 8384 7146 2860 2609 212 Z+JET 9.9e+06 1.7e+06 20176 6725 6725 0 0 0 W+JET 1.1e+08 2.2e+07 196395 78558 58919 39279 19640 0

DATA TRIGGER NJET NBJET MET MAXPTJET MAXPT2JET MAXPT3JET DR SIGNAL 100 99.2 41.3 29.1 28.3 23.3 23.1 7.9 SUSYBG 100 92.0 12.2 9.2 8.9 7.3 7.1 1.9 TTBAR 100 92.0 19.0 3.6 3.0 1.2 1.1 0.09 Z+JET 100 16.9 2.0 0.07 0.07 0 0 0 W+JET 100 19.8 0.18 0.07 0.05 0.04 0.02 0

Number of events (weighted to the SUSY events) that pass the sequential cuts, starting with the trigger requirement.

The same number of events in %, normalised to the number of events thatpass the trigger.

Note: - due to limited statistics the , Z+jets and W+jets have the weights 7.8 , 6725.3 and 19639.5 respectively! - the hemisphere and b-tagging discr. cuts are not accounted for.

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Invariant mass distribution without SM bg

Invariant Mass (GeV)

# E

ven

ts /

10 G

eV

SUSY signal

Signal with two b jets coming from the Higgs

SUSY background

SUSY signal + SUSY background

SUSY signal + SUSY background+ W+jet + Z+jet + + QCD

SUSY signal

Signal with two b jets coming from the Higgs

SUSY background

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Invariant Mass (GeV)

# E

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ts /

10 G

eV

Invariant mass distribution with SM bg

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# = 482# = 21 x 7.8 = 164

bbh 0

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The corresponding mass resolution

Reconstructed Higgs mass – Generated Higgs mass (GeV)

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Fitting procedureIn order to extract the higgs mass and evaluate the signal significance, a simple fit method has been developed.

BBackground

),m(GSignal h polynom of order 5with the followingparameters:

par 0 = -124.252par 1 = 5.31716par 2 = -0.0440705par 3 = 0.000152914par 4 = -2.44607e-07par 5 = 1.49237e-10

# E

ven

ts /

10 G

eV

Invariant Mass (GeV)

Fitting procedureThe global fit function F is where N is a normalisation factor and alpha is the fraction of signal in the global distribution.

),()1(),,( hh mGBNmF

),m(GB)1(N),m,(F hh

9.14.17)GeV(

8.19.105)GeV(m

02.061.0

5.1ndf

fb13osityminLu

h

2

1

The significance S is extracted within a 2 sigma region around the fitted higgs mass and

is defined as: 20944

609

N

NS

Background

Signal

# E

ven

ts /

10 G

eV

Invariant Mass (GeV)

Systematics: jet calibrationChanging the correction factor of the “HepLorentzVector” of the jets by – 7.5 %

and +7.5 % results in a shift of -6.8 GeV and + 8.2 GeV respectively.

Nu

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f ev

ents

Conclusions and outlook

• The SUSY event sample su05_pyt_LM5 is now complete (bug in PubDB).

• The problem of the combinatorial background is solved by selecting the combination of b-tagged jets with the smallest space angle.

• The fitting procedure results in a higgs mass = 105.9 +/- 1.8 GeV while a higgs mass = 116 GeV is expected (status b-jet calibration correction ?)

• The higgs mass resolution is 17.4 +/- 1.9 GeV while a significance S ~ 20 is obtained.

• The analysis note is being finalized and is planned to be released on the 28th of February 06. • The work on the endpoint distributions - to extract the sparticle masses – is progressing, but also other methods are being considered.

• We will use FAMOS to study the CMS reach, i.e. scan the MSUGRA parameter phase space so that a sensitivity region in the (m0,m1/2) plane can be provided for several luminosities.

Number of jets 4

SUSY background

SUSY signal

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Z + jet W + jet

Number of b-jets 2

SUSY background

SUSY signal

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Z + jet W + jet

Missing Transverse Energy (MET) 200 GeV

SUSY background

SUSY signal

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Z + jet W + jet

Highest “jet transverse momentum” 200 GeV

SUSY background

SUSY signal

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Z + jet W + jet

2nd Highest “jet transverse momentum” 150 GeV

SUSY background

SUSY signal

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Z + jet W + jet

3rd Highest “jet transverse momentum” 50 GeV

SUSY background

SUSY signal

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Z + jet W + jet

Space angle between two b-tagged jets < 1.5

SUSY background

SUSY signal

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Z + jet W + jet

Backup: Jet resolution of the detector