Transcript h1 → a1a1 → + + µ µτ τ ATLAS Experiment: Search of Higgs Boson decaying into a1 in Next to Minimal SuperSymmetric Model By: Hou Keong(Tim)

h1 → a1a1 →
+
+
µ µτ τ
ATLAS Experiment:
Search of Higgs Boson decaying into a1 in
Next to Minimal SuperSymmetric Model
By: Hou Keong(Tim) Lou
Rutgers University
With: Catherine Laflamme
Advisor: Chris Potter
McGill University
SuperSymmetry




A symmetry relating
Bosons to Fermions
How do I lose some weight naturally?
~Λ2
Higgs mass too low,
requires unnatural
cancellations
SuperSymmetry
solves the Hierarchy
problem (explains
The Planck scale
why actual Higgs
mass ⋘ bare mass)
Allows unification of
Higgs
Obesity is a major problem,
specially for the Higgs Boson
(N)MSSM
•
By adding a minimal number of fields, one
gets Minimal SuperSymmetric Model
(physics on a diet)
•
µ-problem: scale of a superpotential is
unnatural
•
Promote µ term to a superfield, one gets
Next to MSSM
Higgs Sector in NMSSM
•
Different Higgs Particles:
•
– 3 CP-even, 2 CP-odd, 2 charged
Higgs
Lightest CP-even Higgs – h1 behaves
like the Standard Model Higgs except its
decay channels.
•
If a1 is light ~a few GeV (lightest CP-odd
Higgs)
•
h1 → ZZ*, WW*, bbar, τ τ may be
strongly suppressed.
* The ideal NMSSM scenario, see arXiv:0811.3537v1, by R.+Dermisek
and J. Gunion for details
Phenomenology of a1
•
a1 decays primarily into the heaviest particles it
can decay to (and gluons)
Branching Ratio of a1 decaying
into two gluons
Branching Ratio of a1 decaying
into two tau leptons
* figures obtained from arXiv:0811.3537v1, by R. Dermisek and J. Gunion
Event Simulation
•
Official Athena 14.2.25.10 Atlas production
version + scripts
•
PYTHIA → Detector Sim → Digitization →
Reconstruction → D3PD ntuple → Analysis
•
a1 mass = 5 GeV, h1 mass = 100 GeV
•
Demand a1a1 → µµ + hadronic τ
•
Produced 7588 events
Phenomenology of a1


a1 can decay into 2 gluons, 2 leptons, 2
quarks
For 200 pb-1 data* (a1mass = 5 GeV and h1
mass = 100 GeV)

4µ
0.26 events
 2µ 2g (2c) 5.12 events
 2µ 2τ
82 events (our
focus)
 4τ
6560 events
decay branching ratio obtained from arXiv:0811.3537v1, by R. Dermisek and J. Gunion
* a1
** h1 production x-section from Standard Model gluon fusion
Tau decay modes


τ neutrino production due to τ lepton number
conservation
τ decay modes:

35% leptonically, 2 neutrinos
•

Catherine Laflamme is currently studying leptonic
tau decay channels
65% hadronically with 1 neutrino
•
My primary focus: Both τ decaying hadronically
Signal vs. Background
•
µ+ µ- low mass
resonance
•
2 oppositely
charged τ jets
•
No quarks/gluon
jets
Making sure the background
doesn't eat away the signal
Background
•
W+jets and Z events (both negligible)
•
QCD + ttbar (main background)
•
QCD:
•
–
Huge cross sections
–
Expect ~103 M events in 200 pb-1 data
–
Impossible to produce enough simulation data
Event selection:
–
Exactly two oppositely charged muons
–
At least two oppositely charged tau jets
Huge QCD background
after scaling, must
eliminate at all costs
By demanding at least two oppositely charged tau jets, exactly two oppositely charged muons
and no electron, the mass of the muon pair is plotted. The result is scaled to 200 pb-1
Natural Selection
By demanding the number of jets to be less than 2 in all events, QCD + ttbar backgrounds are
removed.
Efficiency
Signal
QCD
Hadronic top
Leptonic top
No cut
34.6
8380 M
33.6 k
41.1 k
Muon cut
14.2 (0.411)
163 k (1.94e-5)
1330 (0.040)
1620 (0.04)
Tau Jet cut
3.7 (0.107)
2260 (2.7e-7)
156 (0.0046)
172 (0.0042)
µµ mass cut
3.68 (0.106)
615 (7.3e-8)
2.97 (8.84e-5)
3.02 (7.34e-5)
# of jets cut
1.3 (0.038)
0
0
0
•
Muon cuts: exactly two oppositely charged muons, PT > 10 GeV, |η|<2.5
•
Tau Jet cut: at least two oppositely charged tau jets, PT > 10 GeV, |η|<2.5
•
µµ mass cut: muon pair mass between 3-10 GeV
•
# of jets cut: at most two jets are present (PT > 15 GeV, |η|<2.5)
Survival of the Fittest
The uneaten
After signal remains
After demanding at most two jets exist in an event (PT > 15 GeV), all QCD and ttbar backgrounds
are gone.
Higgs Transverse Mass
•
mT2 = m2 + pz2
By adding the four vectors of the two tau jets, two muons, and missing transverse
momentum in the xy plane, the transverse mass mT is plotted. mT is always greater than
the actual mass (100 GeV in this case), resulting in an edge.
Conclusion
•
Realistic NMSSM model
•
Background is negligible
•
Expect 1 signal event in 200 pb-1
•
For τ decaying leptonically, also expect 1
signal event
•
This decay channel has not been studied
previously by ATLAS/CMS
Questions?
Comments?
Concerns?
Remarks?
Ideas?