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 meetingJanuary 20th 2006

CERN

• Used simulated data and analysis techniques • Invariant mass and mass resolution for different cut series• Overview data sets and tracker misalignment• Conclusions and outlook

• ~ 61000 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. “su05_pyt_LM5” instead of “su03_msugra_lm5” (4 trials on GRID result in ~ 61000 events of the ~98500 events available)

• 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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BUG FOUND!

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. Try all possible combinations of reconstructed b tagged jets within each hemisphere.

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Summary of former applied selection cuts

• Number of jets 4

• Number of b-jets 2

• Missing Transverse Energy (MET) 200 GeV

• Highest “jet transverse momentum” 150 GeV

• 2nd Highest “jet transverse momentum” 100 GeV

• B-tagging quality estimator S > 1.5

Old invariant mass distribution

SUSY background

SUSY signal

Signal with two b jets coming from the Higgs

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

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BG

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Bug: cut on Pt of jet > 30 GeV not applied

“Old data files”

New invariant mass distribution

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)

The corresponding mass resolutionThe width of the signal peak is mainly determined by the jet resolution of the detector as the intrinsic decay width varies from 3.3 MeV to 4.3 MeV.

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Reconstructed Higgs mass – Generated Higgs mass (GeV)

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bbh 0

Optimising analysis cuts using “GARCON”(M. Spiropulu, A. Drozdetskiy, G. Karapostoli, et al.)

• B-tagging quality estimator S > 1.5

• Number of b-jets 2

• Missing Transverse Energy (MET) 200 GeV

• Highest “jet transverse momentum” 150 GeV

• 2nd Highest “jet transverse momentum” 100 GeV

• Number of jets 4

The cuts remain fix for now!

• Missing Transverse Energy (MET) > 101 GeV

• 2nd Highest “jet transverse momentum” > 162 GeV

• 4th Highest “jet transverse momentum” > 55 GeV

• Highest “jet transverse momentum” > 283 GeV

• 3rd Highest “jet transverse momentum” > 66 GeV

• Highest “b-jet transverse momentum” > ~ 30 GeV

• 2nd Highest “b-jet transverse momentum” > ~ 30 GeV

GARCON

“The softer cut on METis compensated by hardcuts on the Pt jets”

Analysis results “GARCON”

bbh 0# = 456# = 81tt

Invariant Mass (GeV)

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Reconstructed Higgs mass – Generated Higgs mass (GeV)

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“Samecolour code”

Cross-check analysis results “GARCON”

Increase cut value of MET cut from 200 GeV to 250 GeV!

• B-tagging quality estimator S > 1.5• Number of jets 4• Number of b-jets 2• Missing Transverse Energy (MET) 250 GeV• Highest “jet transverse momentum” 150 GeV• 2nd Highest “jet transverse momentum” 100 GeV

Results cross-check

Invariant Mass (GeV)

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Reconstructed Higgs mass – Generated Higgs mass (GeV)

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# = 484# = 84

bbh 0

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“Samecolour code”

Check influence of b-tagging quality estimator S

Increase cut value of b-tagging quality estimator S from S > 1,5 to S > 2 !

• B-tagging quality estimator S > 2• Number of jets 4• Number of b-jets 2• Missing Transverse Energy (MET) 250 GeV• Highest “jet transverse momentum” 150 GeV• 2nd Highest “jet transverse momentum” 100 GeV

Results check b-tagging quality estimator S

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Invariant Mass (GeV)

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Reconstructed Higgs mass – Generated Higgs mass (GeV)

“Samecolour code” bbh 0

tt# = 381# = 55

Check the space angle between the two b-tagged jets

• 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

2

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21 R is typically smaller for signal events

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Results: cut on space angle#

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GeV

Invariant Mass (GeV)

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Reconstructed Higgs mass – Generated Higgs mass (GeV)

“Samecolour code” bbh 0

tt# = 289# = 25

Overview data samples

• SUSY events:

~ 61000 SUSY events generated “su05_pyt_LM5” ( = 7,5 pb) • SM background events:

~ 1300000 events generated “jm03b_Ttbar_inclusive” ( = 830 pb) Z+jet ~ 50000 events “jm03b_Zjets_250_400”W+jet ~ 50000 events “jm03b_Wjets_250_400” qcd ~ 200000 events “jm03b_qcd_50_80”qcd ~197000 events “jm03b_qcd_170_230”qcd ~ 100000 events “jm03b_qcd_300_380”

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No event passes previously described series of cuts

Tracker misalignment• the “short term” misalignment scenario (strips: 100 m / pixels: 10 m): 17 % reduction in signal selection efficiency

• the “long term” misalignment scenario (strips: 20 m / pixels: 10 m): 10 % reduction in signal selection efficiency

Conclusions and outlook

• The analysis has been re-made using the latest SUSY signal events at LM5.

• The bug “jet Pt > 30 GeV” is fixed!

• Increasing the cut on the b-tagging quality estimator S reduces with ~ 35 % while SUSY signal is reduced with ~ 21 %.

• More Standard Model backgrounds ( , W + jet, Z + jet, QCD) are included in the analysis results.

• The problem of the combinatorial background might get solved by selecting only that combination of b-tagged jets with the smallest for that event. • 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.

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Backup: Jet resolution of the detector