1. Search for non-standard-model Higgs at the LHC with ATLAS
Dimitris Fassouliotis
University of Athens
on behalf of the ATLAS Collaboration

2. Outline MSSM Higgs sector: h, H, A and H± Emphasis is put on:
Investigate decay channels in particles
h/H/A→τ+τ-, μ+μ light / heavy H± → τν, tb
Investigate decay channels in sparticles
4l + Missing ET final states (and one scenario for invisible Higgs decays)
Probe E-W symmetry breaking by the vector boson scattering at high mass
Especially useful in case that no Higgs boson discovered.
Emphasis is put on:
Use of most recent theoretical calculations
Detailed detector simulation
Detailed consideration of systematic uncertainties in each channel
Data driven methods for the background estimation
Analyses included concern data at 14 TeV
Results shown without pile-up and cavern bkg (effect small at L=1033 cm−1s−1)
Details can be found at:
CERN-OPEN (ATLAS, arXiv: )
ATL-PHYS-PUB
Several studies in progress not mentioned here

3. h/H/A→τ+τ- / μ+μ- Production Direct Production Associated Production
Several benchmark scenarios for the study of MSSM Higgs at LHC.
At tree level, the Higgs sector described by two parameters mA and tanβ
Results shown here for this study within the mh-max scenario
mh-max scenario
Η and A mass degenerate for most of the parameter space → Cross sections added
Direct Production
Associated Production
(dominant at large tanβ)
Production
Decay channels:
Advantage: High branching ratio
Advantage: Excellent mass resolution

4. h/H/A → τ+τ- →l+l-4v (event selection)
Backgrounds:
Event selection
Trigger: single + double lepton triggers
Two isolated, opposite sign leptons
≥1 b-jet and no central jet activity
missing ET required
mττ reconstruction collinear approximation
L=30fb-1
L=30fb-1

5. h/H/A → τ+τ- →l+l-4v (background control – results)
Systematic uncertainties
Theoretical: <20% on signal and ~10% on bkg
Experimental: <10% on signal and ~10% on bkg
(jet energy scale /resolution and b-tagging)
Evaluation of backgrounds from data
Estimation of the irreducible
from the control samples
Shape: replace real e/μ with simulated τ
Normalization (<3% systematic uncertainty):

6. h/H/A → μ+μ- (event selection)
Mass resolution 3% for mA=200 GeV
Backgrounds:
Event selection
Trigger: single high pT muon
Two isolated, high pT, opposite sign muons
Low missing ET
0 b-jet or ≥1 b-jet and no central jet activity
L=30fb-1, tanβ=20
0 b-jet
analysis
≥1 b-jets
analysis
Low efficiency in b-jet analysis due to soft b-jets in signal

7. h/H/A → μ+μ- (background control – results)
5σ discovery
95% CL limit
Systematic uncertainties
Theoretical: <20% on signal and ~10% on background
Experimental: % on signal and ~10% on background
(mainly b-tagging)
Evaluation of backgrounds from data
Side band fit together with
Control samples
(signal free samples with same dilepton mass spectrum)
Estimation accuracy
background estimation

8. H±→τν / bt H± decay modes Light H± (mH<mtop) Heavy H± (mH>mtop)
tanβ=35
tanβ=2
H±→τν / bt
mh-max scenario
H± decay modes
Light H± (mH<mtop)
Heavy H± (mH>mtop)
Production:
Decay:

9. Light Η± t → H+b, H+→ τ±ν (event selection)
Backgrounds:
Event selection
Trigger
tau and ETmiss
Single lepton and/or ETmiss
Single lepton or tau and ETmiss
Objects kinematics
1τ-jet, 2b-jets, ≥ 4jets, ETmiss
1l, 2b-jets, ≥4 jets, ETmiss
≥ 1l,τ ≥ 1b-jets, ≥3 jets, ETmiss
W, top reconstruction
|mWrec-mW|<30 GeV
|mtrec-mt|<40 GeV
Angular-charge correlation
100<mtrec<300 GeV
3 ν make complete event reconstruction difficult
tt suppression
Likelihood discriminant
l - t angle in W rest frame
tanβ=20
mH=130 GeV
L=10fb-1
If the charged Higgs boson is light, then BR(t →bW) is smaller:

10. H+t → tbt→ bWbbW →bqqbblν
Heavy Η± H+t → tbt→ bWbbW →bqqbblν (event selection)
(gg→ tbH+ →bqqbτ(had)ν / gb→ tH+ →bqqτ(had)ν similar selection as in light Η± case)
H+t → tbt→ bWbbW →bqqbblν
Trigger
Single lepton and ETmiss or tau and ETmiss
Object multiplicity Kinematics
1 isolated lepton , ≥ 3b-jets, ≥ 5jets, ETmiss
W, top reconstruction
Constraint on W mass / Likelihood function for combinatorial bkg
tt suppression
Likelihood discriminant
L=1fb-1
tanβ=35
H+t→ τ(had)ν bW→τ(had)νbqq
H+t → tbt→ bWbbW →bqqbblν
tanβ value for high significance
L=1fb-1
bqqbblν
bqq[b]τ(had)ν

11. Η± (background control – results)
Main background in H± searches is
Systematic uncertainties
Theoretical: <20% on signal and ~12% on bkg
Experimental: % signal and bkg
(mainly due to jet energy scale and b-tagging)
Evaluation of main background from data:
Control samples
Replace real μ with simulated τ
Estimation accuracy <10%
W mT for real/scaled btνbjj events
mh-max scenario
mh-max scenario

12. Higgs bosons decaying into SUSY cascades to 4 leptons + ETmissing
Final state with 4 leptons +ETmissing explored (as in the example)
MSSM or mSUGRA scenarios with decays to light
or heavier neutralinos / charginos investigated
Backgrounds:
Event selection
2 pairs of opposite sign
opposite flavor isolated leptons
from the interaction vertex
kinematics, lepton pT
dilepton masses to reduce Z, ZZ
ETmissing to reduce Z, ZZ, SUSY
Jet multiplicity to reduce tt,SUSY
Systematic uncertainties
Experimental uncertainties: small
Signal depends strongly on slepton masses
Main SM background after cuts
Can be evaluated from data via control samples
MSSM Set 2
H/A and tH± included

13. Vector boson scattering at high mass (event selection)
Standard Model can be a low energy effective theory
New physics can be seen in vector boson pair resonances
Higgs-like scalar resonances and/or
technicolour-like vector resonances
If resonances not produced the vector boson scattering cross
sections must be measured
Event signature
Forward jets
Central jets that might be merged
(decaying vector boson may be seen
as one single wide and heavy jet)
Dileptons in the central region
Missing ET from W, or Z → νν
Backgrounds: q
W,Z
Z,W
Res W Z
jj.ll,νν
jj.lν j
Event selection:
Trigger: single or double lepton, single or double jet
Isolated high pT leptons
2 forward tag jets
Central jet veto (except jets originating from W,Z)
Top rejection 130 < mt < 240 GeV
W,Z mass selection

14. Vector boson scattering at high mass (results)
Some of the results (normalized to 1fb-1)
WZ→lνll
WZ→llj(j)
L≈60 fb-1 for discovery
of resonances up to 800 GeV
Systematic uncertainties
Theoretical: Background cross section factor ~ 2
Data driven background estimation needed
Experimental: small
Underlying event: ~ 5%
ZZ→llνν

15. Summary Neutral MSSM Higgs Charged MSSM Higgs
h/H/A → ττ With 30fb-1 provides good coverage of the parametric space (mA-tanβ plane).
h/H/A → μμ Competitive channel, helps to increase sensitivity, provides sharp mass peak.
Charged MSSM Higgs
From the channels presented, H± → τν → τ(had)νν provides the highest sensitivity.
With 1fb-1 of well understood data, the Tevatron limits can be superseded.
With 30 fb-1 the combined results, cover almost completely the parameter space for low masses
(except tanβ ≈7). For high masses, large tanβ values are also covered.
MSSM Higgs decays in SUSY particles
4leptons +ETmissing With ~100 fb-1, high mass MSSM Higgs bosons can be discovered.
Vector boson scattering at high mass
Resonances that provide information for different mechanisms of EW symmetry breaking
can be discovered with ~60 fb-1.
Data driven methods to evaluate backgrounds have been formed and will be studied in detail as real data are accumulated.
One final comment:
The outcome of most analyses was presented in the context of specific models. This however, is not mandatory and results can also be presented in a model independent way.

16. Back up slides

17. Sensitivity to an Invisibly Decaying Higgs Boson
Model independent study of
As an example, in R-parity conserving SUSY
Higgs decay to lightest neutralinos
Systematic uncertainties
VBF qqH
Theoretical background shape: ~10%
Experimental background shape: ~ 5%
(jet energy scale /resolution) ZH
Theoretical background: ~6%
Experimental background: ~4%
(lepton energy scale /resolution)
Topologies studied: VBF qqH, ZH
VBF qqH
Backgrounds:
Event selection
Trigger: ETmiss, forward jets
ETmiss not close to jet, forward jets
lepton veto, central jet veto
counting experiment / shape distribution φjj ZH
Trigger: Single lepton, dilepton, ETmiss
Two leptons compatible with mZ
ETmiss, b-jet veto
BDT with kinematic variables
L=30fb-1

18. Theoretical uncertainties
Neutral MSSM Higgs
Direct production
NLO calculation
M. Spira, HIGLU: A Program for the Calculation of the Total Higgs Production Cross Section at Hadron Colliders via Gluon Fusion including QCD Corrections, 1995
Associated production
Inclusive approach NLO (Reliable when both b at high pT)
S. Dittmaier, M. Kramer, and M. Spira, Higgs radiation off bottom quarks at the Tevatron and the LHC, 2004.
S. Dawson, C.B. Jackson, L. Reina, and D. Wackeroth,, Phys. Rev. Lett. 94 (2005)
Exclusive Approach NNLO
The theoretical uncertainty on the production cross-section, is estimated taking into account contributions from the scale uncertainty and from the uncertainty on the parton distribution functions.
The scale uncertainty is obtained from
Harlander, R. V. and Kilgore, W. B., Phys. Rev. D 68 (2003)
The contribution from the PDFs is estimated by exchanging MRST2002 for MRST2004 (conservative approach).
Charged MSSM Higgs
E. Boos and T. Plehn, Phys. Rev. D 69 (2004)
T. Plehn, Phys. Rev. D 67 (2003)