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

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