1. An excess on Zh production at LHC explained with the 2HDM
A Higgs Days Baby or
An excess on Zh production at LHC explained with the 2HDM
Pedro Ferreira
ISEL and CFTC, UL
Lisbon, Portugal
Higgs days 2018, 11/09/2018
P.M. Ferreira, S. Liebler, J. Wittbrodt, Phys. Rev. D 97, (2018)

2. ONCE UPON A TIME, DURING HIGGS DAYS 2017...
WHAT’S THAT, STRANGE PORTUGUESE PERSON? YOU CAN FIT IT WITH THE 2HDM?
THERE’S AN EXCESS IN Zh PRODUCTION IN ATLAS.
NO, REALLY, THERE IS.
AND DON’T YOU DARE TO WRITE A 2HDM INTERPRETATION WITHOUT ME!

3. THE *£#Ϫ%&@ᴥ!! TITLE PRD SADDLED US WITH:
THE REALLY COOL TITLE:
THE TITLE PRD SADDLED US WITH:
BUT WE MANAGED TO SNEAK IN SOME COOL ACKNOWLEDGEMENTS...

4. THE INCREDIBLY SIGNIFICANT (NOT REALLY...) ATLAS EXCESS IN Zh
arXiv:
Roughly 01 – 0.3 pb above SM background for an invariant mass of ~ 440 GeV...
Very low statistical significance! Interesting that it is above the 𝑡 𝑡 threshold.

5. Two-Higgs Doublet Models in a nutshell
They are perhaps the simplest Standard Model extension – instead of a single scalar doublet, we have two, Φ1 and Φ2, structure determined by gauge group.
They do not affect the most successful predictions of the Standard Model.
They have a richer scalar particle spectrum.
They are included in more general models, such as the Supersymmetric one.
They allow for the possibility of minima with spontaneous breaking of CP... (T.D. Lee, Phys. Rev. D8 (1973) 1226)
G.C. Branco, P.M. Ferreira, L. Lavoura, M. Rebelo, M. Sher, J.P Silva,
Physics Reports 716, 1 (2012)

6. Softly broken Z2 potential
Impose Z2 symmetry – Φ1 → - Φ1 and Φ2 → Φ2 – and softly break it with m12 (allows for decoupling limit).
EIGHT real independent parameters.
The symmetry must be extended to the whole lagrangian, otherwise the model would not be renormalizable.
Reason behind this symmetry – to prevent tree-level Higgs-mediated flavour changing neutral currents (FCNC) which are very strongly experimentaly constrained in B and K meson physics.
Coupling to fermions
MODEL I: Only Φ2 couples to fermions.
MODEL II: Φ2 couples to up-quarks, Φ1 to down quarks and leptons.
. . .

7. Scalar sector of the 2HDM is richer => more stuff to discover
Two doublets => 4 neutral scalars (h, H, A) + 1 charged scalar (H±).
h, H → γ γ
h, H → ZZ, WW (real or off-shell)
h, H → ff
H → hh (if mH>2mh) … h H
A CP-odd scalar
(pseudoscalar)
CP-even scalars
A→ γ γ
A→ ZZ, WW
A→ ff
A→ Zh …
Certain versions of the model provide a simple and natural candidate for Dark Matter – INERT MODEL, based on an unbroken discrete symmetry.
Deshpande, Ma (1978); Ma (2006); Barbieri, Hall, Rychkov (2006); Honorez, Nezri, Oliver, Tytgat (2007)

8. (h, H: CP-even scalars):
Doublet field components:
Both doublets may acquire vevs, v1 and v2, such that
Definition of β angle:
Definition of α angle
(h, H: CP-even scalars):
(without loss of generality: -π/2 ≤ α ≤ + π/2)

9. The α angle is the diagonalization angle of the 2×2 mass matrix of the CP-even scalars, h and H

10. Coupling to Fermions
Each type of fermion only couples to ONE of the doublets. Four possibilities,
with the convention that the up-quarks always couple to Φ2 :
Up quarks
Down quarks
Leptons

11. THEORETICAL BOUNDS ON 2HDM SCALAR PARAMETERS
Potential has to be bounded from below:
Theory must respect unitarity:

12. Constraints from b-physics and others
Most important and reliable constraints from b → sγ and Γ(Z → bb) observables.
Significant theory uncertainties!
Also include Electroweak precision constraints from S and T.
To good approximation, then:
Model I, Lepton Specific: 𝒕𝒂𝒏𝜷≥𝟏
Model II, Flipped: 𝒕𝒂𝒏𝜷≥𝟏 and 𝒎 𝑯 + ≥ 500 GeV

13. Parameter space scan chosen
The observed 125 GeV scalar is the lightest CP-even state (h).
It behaves very much like the SM Higgs is supposed to behave.
This is obtained by requiring that the ratios
are all close to the SM-expected value (1) for X = ZZ, WW, 𝒃 𝒃 , 𝝉 𝝉 and γγ deviating by no more than 20%. Use ScannerS and SusHi.
This implies that the 2HDM is close to alignment, in which the vevs are almost aligned with the doublets, and as a consequence
Extra scalar masses:
𝒔𝒊 𝒏 𝜷 − 𝜶 ≅ 𝟏

14. Always have the same sign 𝒌 𝑫 can have the opposite sign of other two
THE WRONG-SIGN LIMIT
Restrictions/conventions: 𝒕𝒂𝒏𝜷≥𝟏 𝑨𝑵𝑫 -π/2 ≤ α ≤ + π/2
MODEL I
MODEL II
𝒌 𝑽 =𝒔𝒊𝒏⁡(𝜷 − 𝜶)
𝒌 𝑼 = 𝒄𝒐𝒔 𝜶 𝒔𝒊𝒏⁡𝜷
𝒌 𝑫 = 𝒄𝒐𝒔 𝜶 𝒔𝒊𝒏⁡𝜷
𝒌 𝑫 =− 𝒔𝒊𝒏 𝜶 𝒄𝒐𝒔⁡𝜷
Always have the same sign
𝒌 𝑫 can have the opposite sign of other two

15. THIS IS NOT JUST A THEORIST’S DELIRIUM...
CMS-PAS-HIG

16. FITTING AN EXCESS ON Zh WITH THE WRONG SIGN REGIME
An excess on Zh is a “golden channel” to detect the presence of a pseudoscalar, since it is one of the CP-allowed decays of that type of particles, A → Zh.
Gluon-gluon production cross section of a pseudoscalar is enhanced by a factor of ~2.3 compared with the production of a CP-even scalar of identical mass, at masses of ~440 GeV.
The decay amplitude of A → Zh is proportional to 𝒄𝒐𝒔 𝜷 − 𝜶 , which can assume values of up to ~0.6 in the wrong sign limit ( |𝒄𝒐𝒔 𝜷 − 𝜶 |≤𝟎.𝟏 in the correct sign regime).
Further, A → Zh can even be the dominant decay channel of the pseudoscalar, even above the 𝒕 𝒕 threshold.
The wrong sign regime also prefers higher values of tan β which enhances production cross sections for a pseudoscalar A (both gluon-gluon fusion and the 𝒃 𝒃 channels).

17. LARGE A → Zh LIKES WRONG SIGN AND INTERMEDIATE tan β
Red points: wrong sign regime.

18. WRONG SIGN NEEDS LARGE 𝒄𝒐𝒔 𝜷 − 𝜶 AND tan β
AND IMPLIES LARGE PRODUCTION CROSS SECTIONS
Red points: wrong sign regime AND

19. INTERMEDIATE tan β IMPLIES 𝒃 𝒃 AND GLUON-GLUON SIMILAR CROSS SECTIONS

20. pp → A → Zh IN THE WRONG-SIGN 2HDM
Blue – All 2HDM type-II points generated, including...
Green – Wrong-sign + tanβ > 7.5
Yellow – Wrong-sign + 5 < tanβ < 7.5
Red – Wrong-sign + 1 < tanβ < 5
Black line – observed signal in ATLAS

21. WHAT WOULD THIS IMPLY IN OTHER CHANNELS? AND THE CHARGED MASS?
Green – Wrong-sign + tanβ > 7.5
Yellow – Wrong-sign + 5 < tanβ < 7.5
Red – Wrong-sign + 1 < tanβ < 5
Black line – 2σ exclusion from ATLAS
Red – Wrong-sign +
“Seeable” at LHC in H → ZZ!

22. WHAT ABOUT H → hh ? Yellow line – limit from CMS.
Same thing for H → hh → 𝒃 𝒃 𝒃 𝒃 search limits – results are typically one order of magnitude below current search bounds.
CMS PAS HIG

23. PRECISION MEASURAMENTS IN ZZ AND γγ ARE IMPORTANT FOR THIS WRONG-SIGN GAME!
Red points: wrong sign regime AND
Yellow points are subset of red ones (fit A→Zh excess in wrong sign) and all μX within 10% of SM value.
BUT notice region is away from (1,1) – irreducible, non-decoupling contribution!

24. BLOODY CMS SPOILSPORTS!!! FIDUCIAL vs TOTAL CROSS SECTION...?
CMS PAS HIG
Is it truly dead, though? Howard Haber commented that CMS sensitivity in this channel, compared with ATLAS’s, isn’t enough to rule out the ATLAS excess...
FIDUCIAL vs TOTAL CROSS SECTION...?

25. CONCLUSIONS
Cool paper born out of HiggsDays!
Not trivial to explain an excess in Zh at 440 GeV in the 2HDM – need model II, in the wrong sign regime. Not possible in SUSY (ask Carlos Wagner).
Testable consequences: ought to see H → ZZ in LHC, charged mass below ~600 GeV, some deviations from SM behaviour (5-10%) in μγγ and μZZ.
Alas, CMS might have
killed it...