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Discovering the Higgs with Low Mass Muon Pairs

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Talk given at BSM-LHC in June 2009 on discovering the Higgs bosons with low invariant mass muon pairs.

Talk given at BSM-LHC in June 2009 on discovering the Higgs bosons with low invariant mass muon pairs.


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  • 1. Discovering the Higgs with Low Mass Muon Pairs Jay Wacker SLAC June 3, 2009 with Mariangela Lisanti arXiv:0903.1377
  • 2. Plan of the Talk Motivation for New Higgs Decay Modes Analysis of Higgs Decaying into PNGBs Searching for the Higgs at Hadron Colliders
  • 3. Where is the Higgs Boson? The shrinking parameter space LEP Excluded by Excluded by Indirect Exclusion Tevatron Searches 95% 95% 90% 95% 100 120 140 160 180 200 Higgs Mass (GeV) h0 e+ Z 0∗ W+ g 0 h W− W− Z0 b, τ − 0 h e− g ¯ τ+ b, W − ω−
  • 4. Most BSM predicts light Higgs LEP Limit usually leads to Little Hierarchy Problem (1 - 10% fine tuning) Tension is between solving the Big Hierarchy Problem & Higgs Mass Λ ∼ MGUT A.) Higgs is an elementary scalar (i.e. susy) quartic coupling is IR free and runs weak B.) Higgs is a composite PNGB (i.e. LH or A5) quartic generated radiatively off SM couplings C.) Higgs is a strongly interacting composite (RS) quartic is large, but usually Flavor/Precision EW problems Mcomposite ∼ 10 − 30 TeV
  • 5. If there is BSM Physics, Higgs discovery can be easily altered b Γh0 SM 3m2 h 0 = b ∼ 10−4 ¯ mh0 4πv 2 b New physics could open up unsuppressed decay channels X Γh0 BSM 2 ghX X ¯ h 0 = ∼ 10−2 ¯ mh0 4π X Br(h → SM) ∼ 10 0 −2 Existing search strategies could be ineffective
  • 6. EWSB/Higgs sector is extended Additional approximate symmetries Light PNGBs New Higgs decay modes Not a complicated story!
  • 7. Minimal Module: 2 HDM + Singlet 3 U(1) Symmetries Hypercharge + 2 Global Hu Hd S Use Exp. basis for pseudoscalars Hu ∼ v sin β eiau /vsβ Hd ∼ v cos β e iad /vcβ S ∼ s eias /s 3 Pseudoscalars Eaten Z0 Goldstone Active A0 Inert a0
  • 8. Higgs Potential Globally invariant terms 2 4 V0 ∼ |φ| , |φ| Gives mass to non-PNGBs and EWSB
  • 9. Higgs Potential Globally invariant terms 2 4 V0 ∼ |φ| , |φ| Gives mass to non-PNGBs and EWSB Explicit breaking of 1st U(1) † † V1 = λ 1 S 2 Hu Hd + h.c. Gives mass to A0 v Defines mixing angle between active tan θa = sin 2β and inert pseudoscalars S Determines all coupling not suppressed by ma0
  • 10. Higgs Potential Globally invariant terms 2 4 V0 ∼ |φ| , |φ| Gives mass to non-PNGBs and EWSB Explicit breaking of 1st U(1) † † V1 = λ 1 S 2 Hu Hd + h.c. Gives mass to A0 v Defines mixing angle between active tan θa = sin 2β and inert pseudoscalars S Determines all coupling not suppressed by ma0 Explicit breaking of 2nd U(1) V2 = λ2 S Hu Hd + h.c. 2 V2 = λ2 S + h.c.4 Gives mass to a0 Determines symmetry breaking couplings
  • 11. Higgs Decaying Into PNGBs Exists for exact Goldstones v 0 m2 0 0 0 0 ˜h a h a a Lint = ch ˜ 0 µ 0 h ∂µ a ∂ a − d S 2 v Symmetry preserving a0 → a0 + S acts as decay constant S 2 sin2 2β 4 ch = sin2 θa 2 = ˜ v 2 sin2 2β Max size at sin θa = 1 v 1+ tan2 β S 2 h0 (∂a0 )2 v
  • 12. Higgs Decaying Into PNGBs Exists for exact Goldstones v 0 m2 0 0 0 0 ˜h a h a a Lint = ch ˜ 0 µ 0 h ∂µ a ∂ a − d S 2 v Symmetry preserving a0 → a0 + S acts as decay constant S 2 sin2 2β 4 ch = sin2 θa 2 = ˜ v 2 sin2 2β Max size at sin θa = 1 v 1+ tan2 β S 2 h0 (∂a0 )2 v Symmetry violating ˜ dh = 1 λ2 λ2 ˜ 1 >1 λ2 tan2 θa dh = ∼ if λ2 − 1+ 2λ2 sin 2β 2 sin 2β λ2 tan2 θa
  • 13. Branching Fraction to a0 Γh0 →a0 a0 ˜h h c2 m4 0 ˜ d2 m4 0 ∼ + h 2 a mh0 S 4 v 2 mh0 Symmetry preserving decays dominate moderate S unless a0 fine tuned light Up to 98% into PNGBs! 100% 1.00 Min Br(h0 → SM) 50% 0.50 1.00 100% aa 20% 0.20 1 Max Br h 0.50 50% 10% 0.10 Br(h0 → a0 a0 ) 5% 0.05 0.20 20% 100 120 140 160 180 200 aa 100 120 m_h GeV 160 140 180 200 0.10 10% mh0 (GeV) Br h 0.05 5% symmetry-preserving interaction dominates ˜ dh = 1 0.02 2% below 1 TeV 0.01 1% mh0 = 100 GeV ˜ dh = 0 500 1000 1500 2000 s sin2b GeV S / sin 2β (GeV)
  • 14. Coupling to SM Fermions mf ¯ Lint = igf f γ5 f a 0 v cot β (up-type quarks) suppressed by 2 powers of tan β gf = sin θa tan β (down-type quarks/leptons) v sin θa ∼ S tan β Small S → strong coupling of a0 to fermions
  • 15. Coupling to SM Fermions mf ¯ Lint = igf f γ5 f a 0 v cot β (up-type quarks) suppressed by 2 powers of tan β gf = sin θa tan β (down-type quarks/leptons) v sin θa ∼ S tan β Small S → strong coupling of a0 to fermions Below bottom threshold, a0 decays to taus over charm quarks Possible dominant Higgs decay mode: h → a a → (τ τ )(τ τ ) 0 0 0 + − + −
  • 16. Living Beneath 114 GeV... LEP famously only searched for h → a a → (τ τ )(τ τ ) if mh0 ≤ 86 GeV 0 0 0 + − + − If there is a large BR into a0s and 3.5 GeV ≤ ma0 ≤ 9.5 GeV mh0 ≤ 114 GeV and may be less fine tuning 800 h0 → SM S / sin 2β (GeV) h0 → 4τ (LEP) 600 (LEP) GeV 400 S 200 0 85 90 95 100 105 110 115 Higgs Mass (GeV) Higgs Mass GeV
  • 17. Direct a0 searches CLEO places bounds on a0 coupling γ Br(Υ → a γ) 0 2 GF mΥ Υ 0 Br(Υ → µ+ µ− ) = √ 4 2πα 2 gd a 2.0 1.5 S / sin 2β ∼ 250 GeV mh0 ≤ 114 GeV Becoming constrained −gd 1.0 ∆ S / sin 2β ∼ 500 GeV unless explicit symmetry 0.5 S / sin 2β ∼ 1000 GeV breaking decays 1% tuning of a0 mass 0.0 4 5 6 7 8 9 mm_a(GeV) a0 GeV
  • 18. Finding the Higgs if 2mτ ≤ ma0 ≤ 2mb Only have hadron machines... make a lot, but difficult to see Dominant decay mode is h → (τ τ )(τ τ ) 0 + − + − g τ τ h 0 a0 a0 τ g τ ντ ντ τ τ 35% π− + 65% ν¯ −π π A heterogenous decay mode! Br(τ τ ) τh τ h τh τ h τh 17.6% 38.0% 10.4% 1 E ≤ mh0 τh 20.4% 11.2% 12 3 GeV < pT < 10 GeV ∼ ∼ 1.5%
  • 19. Using a Subdominant Decay Mode Always have coupling to muons Γ(a → µ µ ) 0 + − m2 µ For 7 GeV a0: = Br(a0 → µ+ µ− ) = 0.4% Γ(a 0 → τ +τ −) m2 1 − (2mτ /ma0 )2 τ Br(a0 → τ + τ − ) = 98% g τ τ a0 h0 a0 µ g µ Br(h → (µµ)(τ τ )) ∼ 0.8% 0 Large gluon fusion production cross section overcomes small branching fraction to muons
  • 20. Geometry of Decays τ a 0 a 0 µ ET τ 0 µ h MET pointing away from muons Mass of a0 reconstructed Higgs mass reconstructable High pT muons pT > 15 GeV ∼ Enough striking characteristics to be very clean channel 25 700 600 500 Events 20 Events 400 300 200 100 15 Events Events 0 4 5 6 7 8 9 Muon Muon Invariant Mass GeV(GeV) Invariant Mass 10 5 0 4 5 6 7 8 9 Muon Invariant Mass (GeV) Muon Invariant Mass GeV
  • 21. Clean up Cuts Signal Efficiency Selection Criteria Relative Cumulative Pre-Selection Criteria 26% 26% Jet veto 99% 26% Muon iso & tracking ∼ 50% 13% Mµµ < 10 GeV 98% 13% µµ pT > 40 GeV 76% 9.8% ET > 30 GeV 29% 2.8% ∆φ(µ, ET ) > 140◦ 73% 2.1% * ∆R(µ, µ) >0.26 63% 1.8% * Removes muons from semileptonic hadron decays
  • 22. Continuum Backgrounds after cuts Have many ~20 mass bins fb/GeV TeV LHC DY+j 0.15 0.24 + W W − 0.03 0.08 ¯ tt 0.02 0.14 b¯ b < 0.001 ∼ ∼ 0.03 Υ+j 0.001 0.002 µµ+τ τ 0.001 < 0.001 ∼ J/ψ + j 0.001 0.001 Total 0.20 0.49
  • 23. Tevatron Sensitivity Getting close to the necessary sensitivity 10.0 TeV (pb) 5.0 5 fb−1 10 fb−1 σprod × Br(h0h →aaa a0 ) 20 fb−1 0 2.0 Σ Br 1.0 0.5 LEP Exclusion 50 S / sin 2β 25 0 0 0.2 100 120 140 160 180 200 Higgs Mass GeV Higgs Mass (GeV)
  • 24. LHC Projected Sensitivity An early LHC Higgs search and will probe 1% BRs 100 LHC (pb) 50 .5 fb−1 5 fb−1 σprod × Br(h0 →aa0 a0 ) 20 a 10 S / sin 2β Σ Br h 5 250 2 LEP 10 500 Exclusion 75 00 0 1 100 120 140 160 180 200 Higgs Mass GeV Higgs Mass (GeV)
  • 25. D0 Results 4 events in relevant mass window 0.2 fb −1 × 6.5 GeV × 3.7 fb = 4.4 Events GeV Drell-Yan + Jet peaked at lower invariant mass
  • 26. Summary Having additional Higgs decay modes is “generic” Some model-independent tension with “hiding the Higgs” with 4 tau decay mode Could alter Higgs discovery even if mh0 > 114 GeV ∼ 2 mu 2 tau decay mode is better than 4 tau Could lead to early discovery at LHC, even if mode is not the dominant decay mode