Searching for signs of the second Higgs · A simplified parameter space After EWSB there are 9 free...

Searching for signs of the second Higgs

Nathaniel CraigIAS + Rutgers

Based on work with J. Galloway, S. Thomas; J. Evans, R. Gray, S. Somalwar, S. Thomas.

!"

Emmanuel Contreras-Compana, John Paul Chou, Nathaniel Craig, Jared Evans, Yuri Gershtein, Richard Gray, Yevgeny Kats, Can Kilic, Michael Park, Sunil Somalwar, Matt Walker

Monday, July 1, 2013

The state of EWSB

• We’ve discovered a (more or less) SM-like Higgs at ~126 GeV. Its couplings are SM-like to within ~25%.

• We’ve discovered no evidence thus far for degrees of freedom that could ensure the naturalness of the Higgs mass.

• What do we do now?


Abandon all hope


Look for the second Higgs.


1. Fine-tuning is not a meaningful guide, no problem with light scalars.

2. Fine-tuning is a meaningful guide, the weak scale is natural, but we haven’t seen the relevant d.o.f. yet.

3. Fine-tuning is a meaningful guide, the weak scale is tuned, but it’s anthropic.

At the very least, finding a second scalar associated with EWSB could partly differentiate between:

Unlikely that (3.) can explain two light scalars.


• Higgs sector of the MSSM/NMSSM...

• Twin Higgs models and their variants

• Superconformal technicolor

• Composite Higgs models [e.g., SO(6)/SO(4)xSO(2) or Sp(6)/Sp(4)xSU(2)]

Plus additional Higgs scalars often arise in natural theories of EWSB.


Perhaps as important as looking for top partners!(even if we find one, it will be hard to verify its role)

We should look as hard as we can for evidence of additional Higgs scalars.


Today’s talkA compact

parameterization of additional Higgses

Implications of coupling measurements of the SM-like Higgs

Searching in standard channels

Searching in non-standard channels







There is enormous room for improvement here.


Looking for another Higgs

1. Study the couplings of the recently-discovered SM-like Higgs.

2. Search for additional scalars in standard Higgs channels.

3. Search for additional scalars in non-standard Higgs channels.

Useful to develop a concrete framework in which all three avenues are related.


2HDM• For the purposes of this talk, I’ll focus on

extended EWSB sectors whose IR physics is described by two Higgs doublets.

• This covers a broad class of known models and allows for convenient parameterization.

• ...but many of the qualitative features are shared by other extended EWSB sectors.

• I’ll keep the focus on bottom-up phenomena, generalizing beyond SUSY 2HDM.


A simplified parameter space• Need to develop an efficient parameterization. General parameter space of 2HDM is vast, but there are well-motivated simplifying assumptions:

• Flavor limits suggest 2HDM should avoid new tree-level FCNC; satisfied by four discrete choices of couplings to fermions.

• Lack of large CP violation suggests new sources of CP violation coupled to SM are small; motivates focusing on CP-conserving 2HDM potentials.

• Imposing these constraints leads to tractable parameter space for signals & relations between search avenues.


A simplified parameter space

After EWSB there are 9 free parameters in CP-conserving scalar potential.

mh, mH , mA, mH±

λ5, λ6, λ7

λ6,7 = 0 λ5,6,7 = 0

Useful basis of 4 physical masses, 2 angles, 3 couplings:

tanβ ≡ �Φ2�/�Φ1�

Discrete symm. for flavor: MSSM:

�√2 Re(Φ0

2)− v2√2 Re(Φ0

1)− v1

�=

�cos α sin α−sin α cos α

� �h

H

�

(only appear in trilinear couplings)

Couplings of scalars to fermions, vectors only depend on angles.

Physical d.o.f. are (8-3=5): h, H, A, H±

α :


Alignment limit• Couplings of the observed Higgs

are approximately SM-like

• Strongly suggests proximity to the alignment limit

• In this limit h is the fluctuation around the vev, while remaining scalars are spectators to EWSB

• (Limit obtainable via decoupling or accidentally)

• Useful to expand in

α ≈ β − π/2

δ = β − α− π/2

ggH,ttHµ

-1 0 1 2 3

VBF,

VHµ

0

2

4

6!! "H

WW"H ZZ"H bb"H ## "H

CMS Preliminary -1 19.6 fb$ = 8 TeV, L s -1 5.1 fb$ = 7 TeV, L s


• Scalar self-couplings have additional parametric freedom.

• Gives a map between current fits to the Higgs couplings and the possible size of NP signals.

• H, A are similar d.o.f. in alignment limit

2HDM I 2HDM II 2HDM III 2HDM IV

u Φ2 Φ2 Φ2 Φ2

d Φ2 Φ1 Φ2 Φ1

e Φ2 Φ1 Φ1 Φ2

y2HDM/ySM 2HDM 1 2HDM 2

hV V 1− δ2/2 1− δ2

/2

hQu 1− δ/tβ 1− δ/tβ

hQd 1− δ/tβ 1 + δtβhLe 1− δ/tβ 1 + δtβ

HV V −δ −δHQu −δ − 1/tβ −δ − 1/tβ

HQd −δ − 1/tβ −δ + tβ

HLe −δ − 1/tβ −δ + tβ

AV V 0 0

AQu 1/tβ 1/tβ

AQd −1/tβ tβ

ALe −1/tβ tβ

δ = β − α− π/2

Four discrete 2HDM types. All couplings to SM states fixed in terms of two angles.


(1) Study the couplings


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Type 1: Combined Fit �68, 95� CL�




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Room for excitementTotal width & hgg drop

but hVV large.

Zero in fermion couplings


• We live near the alignment limit, but precisely how near depends sensitively on the 2HDM type.

• This proximity has little to do with directly measuring the coupling to vectors, and a lot to do with the total width and gluon coupling.

• There is room for surprises, especially in future measurement of VBF diphoton.


Look directly for the second Higgs


Second Higgs Doublet Alignment

Decay Topology Limit

H → WW,ZZ −H,A → γγ �H,A → ττ, µµ �

H,A → tt �

A → Zh −H → hh −

t → H±

b �


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• Even in the exact alignment limit, the scalars H and A have large gluon fusion production cross sections, since their top couplings are nonzero.

• Even close to the exact alignment limit, processes such as H>VV can be appreciable because the competition is only with H > bb below the top pair threshold.


(2) Look in standard Higgs channels


17

(GeV)Hm200 400 600 800 1000

SM!/

!95

% C

L lim

it on

-110

1

10

210ObservedExpected

! 1±Expected ! 2±Expected

-1=8 TeV, L=5.3 fbs -1=7 TeV, L=5.1 fbsCMS

" 2l2# ZZ #H

Figure 9: Observed (solid line) and expected (dashed line) 95% CL upper limit on the ratio ofthe product of the production cross section and branching fraction to the SM expectation forthe Higgs boson in the H → ZZ → 2�2ν channel.

(GeV)Hm200 400 600 800 1000

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% C

L lim

it on

-110

1

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210 Expected 2l 2q" ZZ "H

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Combined

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it on

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# 2l 2" ZZ "H $ 4l + 2l 2" ZZ "H

Combined

-1 5.3 fb%=8 TeV, Ls -1 5.1 fb%=7 TeV, LsCMS

Figure 10: (left) Expected and (right) observed 95% CL limits for all individual channels andtheir combination. The horizontal dashed line at unity indicates the SM expectation.

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H > WW, ZZ


17

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it on

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1

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! 1±Expected ! 2±Expected

-1=8 TeV, L=5.3 fbs -1=7 TeV, L=5.1 fbsCMS

" 2l2# ZZ #H

Figure 9: Observed (solid line) and expected (dashed line) 95% CL upper limit on the ratio ofthe product of the production cross section and branching fraction to the SM expectation forthe Higgs boson in the H → ZZ → 2�2ν channel.

(GeV)Hm200 400 600 800 1000

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it on

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210 Expected 2l 2q" ZZ "H

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# 2l 2" ZZ "H $ 4l + 2l 2" ZZ "H

Combined

-1 5.3 fb%=8 TeV, Ls -1 5.1 fb%=7 TeV, LsCMS

Figure 10: (left) Expected and (right) observed 95% CL limits for all individual channels andtheir combination. The horizontal dashed line at unity indicates the SM expectation.

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Contours are essentially just Htt, not HVV

H > WW, ZZ


H,A > tau tau

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tan

05

101520253035404550 CMS -1 = 7+8 TeV, L = 17 fbsPreliminary,

= 1 TeVSUSY

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ObservedExpected

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LEP

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M

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Expected LimitB-TagNo B-TagCombined

Sum of h, H, A signals(no mass resolution)

Sensitivity at large tan beta coming from enhanced

production modes, rather than decay couplings.


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CMS preliminary (MVA)"" #H

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H,A > diphoton

mA (GeV)

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10 fb

1 fb

One of the most promising channels at low tan beta in alignment limit!


H,A > t tbar?

[TeV]ttM0.5 1 1.5 2 2.5 3

x B

[pb]

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Upp

er L

imit

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Z' 10.0% width

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2 s.d.±Expected

= 8 TeVs, -1CMS, L = 19.6 fb Z' with 10% Decay Width

Another final state we don’t typically pursue because subdominant to VV in SM-like heavy Higgs.

But at low tan beta the cross section for H, A > ttbar can be large! Needs further study.

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• H>VV is useful even quite near the alignment limit, since the coupling must be radically suppressed before it’s beaten by light fermions.

• Ditau and diphoton are the best states for the exact alignment limit. But H,A > tau tau only works at large tan beta in Type 2 2HDM.

• So we desperately need to extend our reach in diphoton past 150 GeV.

• Top pairs???


(3) Look in non-standard Higgs

channels


Second Higgs Doublet Alignment

Decay Topology Limit

H → WW,ZZ −H,A → γγ �H,A → ττ, µµ �

H,A → tt �

A → Zh −H → hh −

t → H±

b �


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TYPE 2: Inclusive Σ�Br�H�hh� �pb�, mH�300 GeV, Λ5�0

H > hh

Appreciable rates (~1000 x SM) consistent with

fits and VV limits.


H > hh while we wait• Two promising ways to look for

resonant H>hh: in diphoton+bb, and in multileptons.

• Resonant production from a heavier state pushes events out to lower-background channels. 400 600 800 10005

6

7

8

9

10

mH �GeV�

Σ�Br�H�

hh��pb�

95� Observed Exclusion

• Using 5/fb, 7 TeV CMS multilepton results (no b-tags, no had. taus), observed limit is ~6pb. Using full 8 TeV set + b-tags, expect closer to ~3pb.

• With this motivation, CMS is doing a dedicated hh search in above channels with 8 TeV data. Sensitivity should be at ~few pb level.


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TYPE 2: Inclusive Σ�Br�A�Zh� �pb�, mA�300 GeV

A > Zh

Appreciable rates (~few x SM) consistent with

fits and Zh cross section limits (~3 x SM).


A > Zh while we wait

400 600 800 10002

3

4

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7

mA �GeV�

Σ�Br�A�

Zh��pb�

95� Observed Exclusion• Most promising way to look for A>Zh is in ll+WW, with approx. kinematic reconstruction. But pure multi-leptons also not bad.

• Resonant production from a heavier state pushes events out to lower-background channels.

• Using 5/fb, 7 TeV CMS multilepton results (no b-tags, no had. taus), observed limit is ~2.5pb. Slightly worse than 8 TeV Zh cross section limit.

• With this motivation, CMS is doing a dedicated Zh search with 8 TeV data. Sensitivity should be at ~pb level, better than Zh cross section limit.


• There can be appreciable rates for H>hh and A>Zh even quite close to the alignment limit, for the same reason as H>VV.

• We are not (yet, publicly) searching in these channels, but there can be observation-level rates consistent with the couplings of h.

• Sensitivity is currently in the range of ~pb using only crude search techniques, so there’s considerable room for refinement.







(Close to alignment limit but with room for surprises)

(We look in H>VV, H,A > tau tau, but given prox. to alignment,

crucial to look in H,A > diphoton )

(Look in H>hh, A>Zh!)


Searching for signs of the second Higgs · A simplified parameter space After EWSB there are 9 free...

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