Higgs Physics

1
Higgs Physics Activities in Bonn/Siegen

• Jörn Große-Knetter
• ATLAS-Higgs-D Treffen
• München, 28.11.2006

2
Outline

• VBF Fusion
• forward jet tagging
• central jet veto NLO with SHERPA, different
  underlying event / PS models
• tau tagging
• Zjj background estimate for H??? from data
• Wjets background studies (M. Rast, not shown
  here)
• LVL1 trigger studies for H?invisible
• Other non-VBF studies not shown here
• Plans/potential for collaboration

3
Forward Jet Studies (Iris Rottländer)

• comparison of different jet algorithms (cone, KT
  with diff. pars), different generators
  (PYTHIA/HERWIG) and processes (dijet/VBF)
• ? efficiencies, fake rates, out of jet
  corrections

matching between truth jets (hadron level) and
reco jets within a ?R
different jet algos eff. vs. eta and Pt
Cone 07 Cone 04 ? Tower o Topo
4
Different MC Generators and Topologies
Pythia QCD Forwardjets Herwig QCD Dijets Pythia
6.3 VBF H-gttautau-gtll Herwig VBF H-gttautau-gtll

• Jets from hard process found easier than jets
  from shower
• Forward region jets from VBF found easier than
  jets from QCD
• Maybe slight dependence on generator (shower
  fragmentation model)

5
Central Jet Veto, NLO (Talea Köchling)

• Goal study effects of NLO on sensitivity esp.
  jet veto with SHERPA
• Def. 1st and 2nd jet ? tagging jets, 3rd
  jet ? apply veto
  

Signal 3rd jet properties (including underlying
event)
momentum SHERPA3jgtPYTHIAgtSHERPA2JEtgtHERWIG rapidi
ty SHERPA agree well, HERWIG slightly wider,
PYTHIA??
6
Survial Probability w.r.t central jet veto
Signal w/o underlying event
Signal with underlying event
Veto jets with Pt gt x GeV)
Veto jets with Pt gt x GeV)

• SHERPA H2j and H3j agree well ? NLO effect
  seems small?
• signficant difference among different MC
  generators
• reason not yet understood

7
Survial Probability w.r.t central jet veto
Zjj(EW) w/o underlying event
Zjj(QCD) with underlying event
Veto jets with Pt gt x GeV)
Veto jets with Pt gt x GeV)

• SHERPA H2j and H3j agree well only for EW
  process
• signficant difference in QCD process
• reason not yet understood

8
?-ID for VBF H????lh (A. Veenendaal)

• ? from VBF Higgs decay have relatively low pT
• Check performance of ID of hadronic decays for
  this channel tauRec and 1P3P
• Look for best discrimination method against
  W?lepton jets background
• Own production (CSC not ready) ? low MC statistics

9
Comparison tauRec/tau1P3P
10 GeV lt pT lt 20 GeV
avg. over all pT

• Find best working point tauRec better for
  pTgt20GeV, 1P3P for pTlt20GeV
• Combine both algorithms?

10
Background Estimate for VBF H????ll4n from data
(M. Schmitz)

• signature tagging jets 2 leptons large
  missing transverse energy

H?tt?em
collinear approximation
ATLAS
30 fb-1

• sM /M 10
• dominated by Emiss

• expected DBG 5 to 10 (Scientific note)
• for MH gt 125 GeV side band
• for MH lt 125 normalisation from Z-peak, shape
  from Z?mm

11
VBF, H??? determination of bkgr. from data (M.
Schmitz)

• Idea jjZ?µµ and jjZ????µµ with identical
  topology
• muons are MIPS ? same energy deposition in
  calorimeters (checked!)
• only difference momentum spectra of muons
• Method select Z ? µµ events
• randomise µ-momenta according
  to Z ? ?? ? µµ4? MC (works!)
• apply usual selection and mass
  reconstruction

shape of background can be extracted precisely
from data itself
towards mass determination - subtract BG
prediction - Gaussian fit ? mass
12
Prospects for mass determination with limited
luminosity
30fb-1, only ? mm decay 6 out of 8 fits fine
120fb-1, ? mm decay 30fb-1, ?ll decays? all
fits fine
13
Invisible Higgs boson decays
invisble Higgs decays SUSY H?LSP LSP, ADD,
Majoron,
95 CL exclusion with 30 fb-1
VBF result assumes trigger on jets up to h 4.9
VBF most sensitive, but how to trigger on 2 jets
missing energy? ? LVL1 trigger study for jets
including FCAL
14
Ongoing LVL1 Trigger Study (Guilherme Hanninger)
Goal determine efficiencies and rates for
various options of trigger menues for
combinations of ET miss central jet forward
jet
plain cuts
15
Estimation of LVL1 trigger efficiencies, rates
topological cuts

• Maybe forward central good for background
  rejection?
• Gain from using topological cuts re-define
  boundaries?
• QCD LVL1 output rates extremely sensitive to
  ETmiss

16
Plans, collaboration options

• Tools
• Forward jet tagging
• Continue jet efficiency, jet energy scale studies
• Effects of pile-up, underlying event
• Tau ID
• Check other background to VBF Higgs sample
• Look for improvement in the few-10GeV pT region,
  revise LLH/NN with Higgs and its backgrd. samples
• Analysis
• Study central jet veto
• tune cuts to be less sensitive to MC models
• Continue SHERPA studies
• Continue invisible Higgs trigger studies LV2, EF
  ?
• Continue Zjj background studies e-channel
• Background studies (e.g. Wjets bg.)
• Start H?WW analysis?