1. h 1 → a 1 a 1 → µ + µ - τ + τ - ATLAS Experiment: Search of Higgs Boson decaying into a 1 in Next to Minimal SuperSymmetric Model By: Hou Keong(Tim) Lou Rutgers University With: Catherine Laflamme Advisor: Chris Potter McGill University

2. SuperSymmetry A symmetry relating Bosons to Fermions Higgs mass too low, requires unnatural cancellations SuperSymmetry solves the Hierarchy problem (explains why actual Higgs mass ⋘ bare mass) Allows unification of coupling parameters ~Λ 2 How do I lose some weight naturally? Higgs Obesity is a major problem, specially for the Higgs Boson The Planck scale

3. (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

4. Higgs Sector in NMSSM Different Higgs Particles: – 3 CP-even, 2 CP-odd, 2 charged Higgs Lightest CP-even Higgs – h 1 behaves like the Standard Model Higgs except its decay channels. If a 1 is light ~a few GeV (lightest CP-odd Higgs) h 1 → ZZ*, WW*, bbar, τ + τ - may be strongly suppressed. h 1 → a 1 a 1 may become dominant If the ideal Higgs version of NMSSM* is correct, we will not find the Higgs through all the standard discovery channels! * The ideal NMSSM scenario, see arXiv:0811.3537v1, by R. Dermisek and J. Gunion for details

5. Phenomenology of a 1 a 1 decays primarily into the heaviest particles it can decay to (and gluons) * figures obtained from arXiv:0811.3537v1, by R. Dermisek and J. Gunion Branching Ratio of a 1 decaying into two gluons Branching Ratio of a 1 decaying into two tau leptons

6. Event Simulation Official Athena 14.2.25.10 Atlas production version + scripts PYTHIA → Detector Sim → Digitization → Reconstruction → D3PD ntuple → Analysis a 1 mass = 5 GeV, h 1 mass = 100 GeV Demand a 1 a 1 → µµ + hadronic τ Produced 7588 events

7. * a 1 decay branching ratio obtained from arXiv:0811.3537v1, by R. Dermisek and J. Gunion ** h 1 production x-section from Standard Model gluon fusion a 1 can decay into 2 gluons, 2 leptons, 2 quarks For 200 pb -1 data* (a 1 mass = 5 GeV and h 1 mass = 100 GeV)  4µ 0.26 events  2µ 2g (2c)5.12 events  2µ 2τ 82 events (our focus)  4τ 6560 events 2 µ low mass resonance (between 2τ and 2b, 4~8 GeV) Phenomenology of a 1

8. 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 50% - 1 prongs (1 charged pion) → τ jet 15% - 3 prongs (3 charged pions) → τ jet

9. 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

10. Background W+jets and Z events (both negligible) QCD + ttbar (main background) QCD: – Huge cross sections – Expect ~10 3 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

11. 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 Huge QCD background after scaling, must eliminate at all costs

12. After By demanding the number of jets to be less than 2 in all events, QCD + ttbar backgrounds are removed. Natural Selection

13. Efficiency SignalQCDHadronic topLeptonic top No cut34.68380 M33.6 k41.1 k Muon cut14.2 (0.411)163 k (1.94e-5)1330 (0.040)1620 (0.04) Tau Jet cut3.7 (0.107)2260 (2.7e-7)156 (0.0046)172 (0.0042) µµ mass cut3.68 (0.106)615 (7.3e-8)2.97 (8.84e-5)3.02 (7.34e-5) # of jets cut1.3 (0.038)000 Muon cuts: exactly two oppositely charged muons, P T > 10 GeV, |η|<2.5 Tau Jet cut: at least two oppositely charged tau jets, P T > 10 GeV, |η|<2.5 µµ mass cut: muon pair mass between 3-10 GeV # of jets cut: at most two jets are present (P T > 15 GeV, |η|<2.5)

14. After After demanding at most two jets exist in an event (P T > 15 GeV), all QCD and ttbar backgrounds are gone. The uneaten signal remains Survival of the Fittest

15. Higgs Transverse Mass m T 2 = m 2 + p z 2 By adding the four vectors of the two tau jets, two muons, and missing transverse momentum in the xy plane, the transverse mass m T is plotted. m T is always greater than the actual mass (100 GeV in this case), resulting in an edge.

16. 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

17. Questions? Comments? Concerns? Remarks? Ideas?