Search for MSSM neutral Higgs bosons in the decay channel A/H→μ+μ- with the ATLAS detector

Giorgos Dedes , Nectarios Benekos , Sandra Horvat , Sergey Kotov, Hubert Kroha, and Susanne Mohrdieck – Möck

Max-Planck-Institut für Physik, München

Deutsche Physikalische Gesellschaft, Dortmund 2006

Outline

The bbA, A->+- decay channel Muon distributions (ATLFAST – Full Simulation) b-jet distributions (ATLFAST – Full Simulation) Analysis results Cut optimization Additional cuts – improvements Summary

Processes bbH/A, H/A-> +- for tan = 30 , L= 30fb-1

Higgs mass

150 GeV 200 GeV 300 GeV 350 GeV 450 GeV

xBR

bbA59.6 fb 20.9 fb 4.2 fb 2.2 fb 0.7 fb

xBR

bbH57.2 fb 20.8 fb 4.2 fb 2.2 fb 0.7 fb

Data Samples

ATLFAST

(CBNT – 8.7.0)Full

(AOD - 10.0.4)

bbH/A

mH/A = 150 GeV 20k events ---

mH/A = 200 GeV 20k events20k events

(only A)

mH/A = 300 GeV 20k events32k events

(only A)

mH/A = 350 GeV 20k events ---

mH/A = 450 GeV 20k events18k events

(only A)

tt 1M events 90k events

Z 1M events ---

Z+jets 1M events ---

ATLFAST Pythia No filters

Full Simulation Pythia

bbA: MultiLeptonFilter: Generated only events with

plT > 5 GeV , |l |<2.7

tt: HiggsMultiLeptonFilter: Generated only events with

mll > 180 GeV, plT > 5 GeV , |l |< 2.7

Approximately 10% of events passed in the specified mass range

Muon Reconstruction (bbA sample, 300 GeV)

Average muon

reconstruction efficiency ~ 90%

ATLFASTATLFAST

FullSimFullSim

ATLFAST (8.7.0): CBNT

Full sim (10.0.4): AOD high-pt muons pT > 5 GeV , || < 2.7 no muon isolation

pt/pt of matched muonspt/pt of matched muons eta/eta of matched muonseta/eta of matched muons

eta/eta of matched muonseta/eta of matched muons Efficiency in ptEfficiency in pt

Efficiency in etaEfficiency in eta Efficiency in phiEfficiency in phiMeVMeV

ATLFASTATLFAST = 3.2% = 3.2%

FullFull = 3.4% = 3.4%

b-jet Recostruction (bbA sample, 300 GeV)

ATLFASTATLFAST

FullSimFullSim

ATLFAST (8.7.0): CBNT

Full sim (10.0.4): AOD pT > 15 GeV , || < 2.5 Likelihood b-tagging

variable used (>0.9) Gen_AOD container for

truth

pt/pt of matched bjetspt/pt of matched bjets eta/eta of matched muonseta/eta of matched muons

phi/phi of matched bjetsphi/phi of matched bjets Efficiency in ptEfficiency in pt

Efficiency in etaEfficiency in eta Efficiency in phiEfficiency in phi

Full simulation: Average b-jet efficiency of ~ 45% ATLFAST: Average b-jet efficiency of ~ 35%

MeVMeV

ATLFASTATLFAST = 18% = 18%

FullFull = 24% = 24%

Muon/b-jet Distributions (bbA sample, 300 GeV) Very good agreement between fast and full simulation

Single muon ptSingle muon pt Single muon phiSingle muon phi

No

rma

lize

d n

um

be

r o

f e

ve

nts

No

rma

lize

d n

um

be

r o

f e

ve

nts

Number of reco muonsNumber of reco muonsH ptH pt

MeVMeV

bjet ptbjet pt

Single muon etaSingle muon eta

bjet etabjet etabjet phibjet phiNumber of reco bjetsNumber of reco bjets

ATLFASTATLFAST

FullSimFullSim

MeVMeV MeVMeV

ETmiss Distributions

In 10.0.4 data contribution from muons made ETmiss broader

MET_Calo + MET_Cryo + MET_MuonMET_Calo + MET_Cryo + MET_Muon

bbA samplebbA sample

MET_Topo + MET_Cryo + MET_MuonMET_Topo + MET_Cryo + MET_Muon

bbA samplebbA sample

MET_Topo + MET_Cryo + MET_TruthMuMET_Topo + MET_Cryo + MET_TruthMu

bbA samplebbA sample

ATLFASTATLFAST

FullSimFullSim

MET_Topo + MET_Cryo + reco dimuon PMET_Topo + MET_Cryo + reco dimuon PTT

bbA samplebbA sample

The contribution in missing energy from the muon spectrometer

is - p- p22x(y)x(y)

We correct by adding this value to

MET_Topox(y) + MET_Cryox(y)

instead of MET_Muonx(y)

MeVMeV

MeVMeV

MeVMeV

MeVMeV

Selection Cuts (TDR)N

orm

ali

zed

nu

mb

er

of

No

rma

lize

d n

um

be

r o

f e

ve

nts

ev

en

ts

bbAbbA

tttt

Fully simulated dataFully simulated data

ppT T //MeVMeV

ppT T > 20 GeV , trigger selection> 20 GeV , trigger selection

1.1.

ppTT22

//MeVMeV

3.3.

ppTT22

< 100 GeV< 100 GeV

ppTTmissmiss

< 20 GeV< 20 GeV

2.2.

ppTTmiss miss //MeVMeV

N(b-jets) > 0N(b-jets) > 0

4.4.

Event LoopEvent Loop

ppTT> 20 GeV> 20 GeV

ppTTmissmiss < 20 GeV < 20 GeV

ppTT22< 100 GeV< 100 GeV

mm22 = m = mAA ±± mm mm22 = m = mAA ±± mm

N(b- jets) = 0N(b- jets) = 0 N(b- jets) > 0N(b- jets) > 0

Results – TDR cuts

150GeV150GeV 200GeV200GeV 300GeV300GeV 350GeV350GeV 450GeV450GeV

S/S/√√B ATLFASTB ATLFAST 14.3 (7.6*) 6.5 (2.9*) 1.9 1.0 0.3

S/S/√√B Full simulationB Full simulation --- 5.4 1.7 --- 0.5

bbA, A-> +- for tan = 30 , L= 30fb-1

*Z background

MeVMeV

A boson invariant mass (ATLFAST)A boson invariant mass (ATLFAST)

bbAtt

bbA + ttZ

A boson invariant mass (Full Sim)A boson invariant mass (Full Sim)

bbAtt

bbA + tt

MeVMeV

Results – TDR cuts

150GeV150GeV 200GeV200GeV 300GeV300GeV 350GeV350GeV 450GeV450GeV

S/S/√√B ATLFASTB ATLFAST 14.3 (7.6*) 6.5 (2.9*) 1.9 1.0 0.3

S/S/√√B Full simulationB Full simulation --- 5.4 1.7 --- 0.5

bbA, A-> +- for tan = 30 , L= 30fb-1

*With Z background included

bbAtt

bbA + ttZ

MeVMeV

H/A boson invariant mass (ATLFAST)H/A boson invariant mass (ATLFAST) H/A boson invariant mass (Full Sim)H/A boson invariant mass (Full Sim)

bbAtt

bbA + tt

MeVMeV

Cuts Optimization We tune the selection cuts in fast and full simulation by

maximizing signal/background ratio for each step

TDR cutsTDR cutsATLFASTATLFAST

optimizedoptimizedFull Simulation Full Simulation

optimizedoptimized

EETTmissmiss 20 GeV 17 GeV 26 GeV

ppTT22 100 GeV 48 GeV 50 GeV

ppTTbjetbjet --- 35 GeV 48 GeV

ppTTbjet bjet //MeVMeVN

orm

aliz

ed n

um

ber

of

even

tsN

orm

aliz

ed n

um

ber

of

even

ts

bbA (full)bbA (full)

tt (full)tt (full)

tt (fast)tt (fast)

bbA (fast)bbA (fast)

Additional Cut (in FullSim) Muons from A are mostly back to back in the phi plane (single body decay)

Δφ-> 3.14 In the case of tt background this is not so pronounced -> broader distribution

bbAbbA

tttt

Muons Muons Δφ

The value of this cut is obtained through the same method for optimizing signal/background ratio

No

rma

lize

d n

um

be

r o

f e

ve

nts

No

rma

lize

d n

um

be

r o

f e

ve

nts

Δφ > 2.7

150GeV150GeV 200GeV200GeV 300GeV300GeV 350GeV350GeV 450GeV450GeV

S/S/√√B ATLFAST B ATLFAST (opt)(opt) / / (TDR)(TDR) 26.8 / 14.3 10.1 / 6.5 3.0 / 1.9 1.5 / 1.0 0.7 / 0.3

S/S/√√B Full simulation B Full simulation (opt)(opt) / / (TDR)(TDR) --- 7.2 / 5.4 2.4 / 1.7 --- 0.4 / 0.5

S/S/√√B Full simulation B Full simulation (+ (+ ΔφΔφ)) --- 19.8 2.5 --- 0.4

Summary

Study of the A(H) discovery potential in the A -> μ+ μ- decay channel , using ATLFAST and fully simulated data

ATLFAST and Full simulation are in good agreement except for b-jet efficiency (better in fullsim) and Etmiss (correction applied)

Selection cuts were optimized leading to the improvement of the signal significance

Additional selection on pTbjet and Δφμμ used and improved signal

significance