H 4 m in the low mass region e meoni l larotonda m antonelli f cerutti
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H -> 4 m in the low mass region E.Meoni, L.Larotonda, M.Antonelli, F.Cerutti. Introduction ATLFAST++ and MOORE/MuID performance Irreducible background rejection Reducible bkg. Rejection Status and prospects. Introduction. Study started more then 1 year ago with twofold goals:

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H 4 m in the low mass region e meoni l larotonda m antonelli f cerutti
H -> 4 m in the low mass regionE.Meoni, L.Larotonda, M.Antonelli, F.Cerutti

  • Introduction

  • ATLFAST++ and MOORE/MuID performance

  • Irreducible background rejection

  • Reducible bkg. Rejection

  • Status and prospects


Introduction
Introduction

  • Study started more then 1 year ago with twofold goals:

    • Validate ATLFAST++ and ATHENA Moore/MuID

    • Improve analysis w.r.t. TDR by using multivariate techniques against irreducible (ZZ->4m) and reducible (tt and Zbb) backgrounds

  • Started with ATHENA release 6.0.3

  • Mass region studied: MH[130-180] GeV (low mass is the most challenging because of the off-shell Z and higher bkg)

  • Here results showed for MH=130 GeV


Introduction1
Introduction

  • Samples produced with PYTHIA 6.2 with the exception of Zbb (ACERMC ME)

  • Filter: 4 m with Pt>4 GeV and |h|<2.7


Introduction pt and h spectra
Introduction: Pt and h spectra

Pt(GeV)

h

ATLFAST++, MH=130 GeV


Introduction analyses chain
Introduction: analyses chain

COMMON PRESELECTION

4 muons, null total charge :

2 with pT > 20 GeV and | | < 2.5

2 with pT > 7 GeV and | | < 2.5

Analysis with

Multivariate methods

TDR analysis

Couples µ+ µ- with invariant mass :

M12= Mz ± 15 GeV M34> 20 GeV

( mH= 130GeV )

M12= Mz ± 10 GeV M34>30 GeV

( mH= 150GeV )

M12=Mz ± 6 GeV M34>60 GeV

( mH= 180GeV )

Angular cut

likelihood/NN (with angular variables and M12 & M34) cuts

Lepton isolation cut

likelihood/NN (with isolation variables) cut

Mass window cut (mH  2 )

to compute significance

Lepton isolation cuts

(single variable cuts)

Mass window cut (mH  2 )

to compute significance


Introduction software codes
Introduction: software codes

  • ATLFAST++ (object oriented version of ALTAS fast simulation implemented in ATHENA framework)

  • ATHENA: MOORE/MuID with muon spectrometer in standalone and combined

    • started with version 6.0.3 many bugs found

    • latest results with 7.0.2

  • First step check of general performance

    • Efficiency

    • Pt resolution

    • MH resolution


Selection efficiency
Selection efficiency

  • Acceptance after kinematic cuts (4m and M12 and M34 cuts):

    • ATLFAST++: 33.0%

    • TDR: 33.5%

    • MOORE/MuID combined 6.0.3: 9%

    • Inefficiency concentrated in low Pt region

Muid Combined

Athena6.0.3


Selection efficiency1
Selection efficiency

  • Improved with version 7.0.2

    • MOORE/MuID combined 7.0.2: 23%

    • Inefficiency concentrated eta~2 region

Muid Combined

Athena7.0.2


Mass resolution
Mass resolution

  • Performance muon spectrometer:

    • TDR: 2.7 GeV

    • MOORE 7.0.2: 3.0 GeV

  • Combined (including Z mass constraint):

    • TDR: 1.4 GeV

    • ATLFAST++: 1.5 GeV

    • MOORE/MUID comb 7.0.2: 1.7 GeV


Irreducible bkg zz 4 m
Irreducible bkg.: ZZ->4m

  • Multivariate analyses: in addition to MH, M12 and M34 there are other 9 independent kinematic variables (12 in total)

  • Try to select variable sensitive to the spin and parity of the signal

  • Combine all variables with multivariate techniques: likelihood and NN

  • Likelihood function (and neural network)

  • with 11 variables:

  • Angle of the decay planes of the two Z in Higgs rest frame

  • (see ATL-COM-PHYS-2003-001,Buszello et al.)

  • Angle between m- in Z rest frame and Z boost in Higgs rest

  • frame (both for on-shell Z and off-shell Z)

  • (see ATL-COM-PHYS-2003-001,Buszello et al.)

  • Angle between Z (both on-shell and off-shell) direction in

  • Higgs rest frame and the Higgs boost

  • Angle between the two m+ in Higgs rest frame

  • Angle between the two m- in Higgs rest frame

  • Angle between the two m of Z (both on-shell and off-shell)

  • Invariant masses of the two m+ m- couples (M12 and M34)


Angle between m- in the Z

rest frame and Z boost in Higgs rest frame

Angle between the decay

planes of the two Z

in Higgs rest frame

Angle between on-shell Z direction in Higgs rest frame and Higgs boost

H4

H4

H4

ATLFAST

ATLFAST

ATLFAST

ZZ4

ZZ4

ZZ4

ATLFAST

ATLFAST

ATLFAST

H4

H4

H4

FULL REC.

FULL REC.

FULL REC.

ZZ4

ZZ4

ZZ4

FULL REC.

FULL REC.

FULL REC.


Results with fast simulation
Results with Fast simulation

Improvement: mainly coming from M12 and M34 optimization

angles relevant only at higher MH


Reducible background
Reducible background

  • 2 out of 4 muons not isolated in tt and Zbb background

  • Likelihood (and neural network) with 6 variables:

  • the 2 largest normalized impact parameters(IP) in trasverse plane of the 4 IP

  • the 2 largest pT reconstructed inside a cone of R=0.2 around the 4 µ tracks

  • the 2 largest total transverse energy depositions in calorimeters (EM+HC) in a cone of R=0.2 around the 4µ tracks

We have added in CBNT ntuple block of Moore/Muid the energy deposition in cones of different radii around the “muon track”

“muon track” defined in 4 ways: moore trk, muid statandalone trk, muid combined trk, iPat trk

Best results with: energy of radius R=0.2 around “iPat” trk


Largest energy loss

Around iPat track

Signal

ttbar

Zbb

Signal

ttbar

Zbb

Largest IP

Signal

ttbar

Zbb

Largest pT

After pT &  cuts

and m12 & m34 cuts


Neural

Network

Likelihood

After pT &  cuts

and m12 & m34 cuts



Mass plots
Mass plots

  • Preselection (as in TDR) : 4 m , total charge =0, pT &  cuts

  • Angular cut: likelihood- 11 variables

  • Isolation cut : likelihood– 6 variables

After preselection (4m,Qtot=0,pT& h cuts)

Signal

ZZ 4m

ZZ 2m2t

ttbar

Zbb

All channels

Signal

ZZ 4m

ZZ 2m2t

ttbar

Zbb

All channels

After overall analysis (preselection+ ang. lik cut+isol lik cut)


Conclusions and prospects
Conclusions and Prospects

  • ATLFAST++ and MOORE/MuID (7.0.2) comb. performance studied on H->4m (low mass): worse performance then TDR, still low efficiency at |h|~2 to be understood

    Prospects

  • Add Noise and pileup, relevant for lepton isolation

  • Control samples to study lepton isolation variables on data: tt-> WWbb: W->l W->jj select b jet with Mbjj=Mtop (b forced to leptonic decay)

  • Wait for bug fixes ?

  • Produce documentation: ATLAS note and SN

  • Participation to DC2 validation very important:

    • New digitization

    • New simulation GEANT4

    • New output data format

    • New reconstruction release


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