1. Search for BSM Higgs at the LHC
Yaquan Fang
Institute of High Energy physics
The 1st China LHC Physics Workshop
Dec 19-21, 2015

2. Run 1 : legacy on Higgs discovery
ATLAS-CONF
CMS-PAS-HIG
One Higgs
“Multi-Higgs”
The measurements of the signal strength are consistent with SM prediction within 2s with the combined results between ATLAS and CMS.
It is possible that there is still some Beyond Standard Model (BSM) Higgs or Higgs like particle ?

3. theory: NMSSM
Supersymmetry (SUSY): a new symmetry between fermions and bosons and solve the so-called gauge hierarchy problem
Minimal Supersymmetric Standard Model (MSSM): simplest SUSY Model, but “-problem” – the Higgs mass parameter  in the superponential HuHd be of the order of magnitude of electroweak scale << Planck scale (the natura cutoff scale)
Next-to-Minimal Supersymmetric Standard Model (NMSSM): introduce a new gauge singlet only couples to the Higgs sector in a similar way as the Yukawa coupling and can give rise to an effective -term, solving the “-problem” naturally.
NMSSM: 7 Higgs boson in total, 3 CP-even, 2 CP-odd and 2-charged Higgses
In general, the Higgs sector of the NMSSM is described by the six parameters:

4. Theory: 2HDM model SM : 2HDM :
For complex SU(2) doublet, there are 8 fields, three eaten by W+/- Z
There are five left : H, h (CP-even), A (CP-odd), H+/-
tanβ is the ratio of the vacuum expectation values of the two
doublets.
a is the mixed angle between H and h .
Detail can be found at : arXiv: v3

5. BSM Higgs searches
Beyond the standard Model Higgs searches: MSSM (and other BSM models) neutral and charged Higgs bosons.
Recent activities also include analyses on nMSSM, pMSSM, 2HDM as well as Higgs to invisible and other exotic decays.
Physics domains:
Neutral Higgs (to bosons):
H->γγ/ww/ZZ (high mass search)
(H->)hh-> bbγγ,bbWW,Wwγγ,bbττ,γγττ
HZ - high mass search
HWW - high mass search
Hbb - A->Zh->llbb,vvbb
HBSM hh->Exotics
(H->)hh->bbbb (and ttbar high mass search)
Neutral Higgs (to fermions): A/H/h (Z') → ττ, A/H/h (Z') → tt
Charged BSM Higgs: H+ → τν, H+ → tb (resolved, boosted, t/s-channels), H+ → μν
Exotic Higgs decays with no MET ( NMSSM / Dark sector inspired): h → aa → bbμμ, h → aa → 4b
Exotic Higgs decays with MET (Dark/Hidden sector inspired Invisible h, mono-H): Zh → ll+INV, mono- H(→bb+χχ, DM particle), mono-H(→γγ+χχ), VBF H → inv, gg→H→INV (mono-jet)
Low mass Higgs …
NWA is often used in those analyses.

6. the searches for h/H/A->tt (ATLAS/CMS)
Categorize the events
with the decay of tau and
tagging of b.
Higher sensitivity at high tan(b)
arXiv: (ATLAS)
JHEP11(2014)056
arXiv: (CMS)
JHEP 10 (2014) 160

7. the searches for A -> Zh (ATLAS/CMS)
Physics Letters B 744 (2015)
arXiv:
Phys. Lett. B 748 (2015) 221
arXiv:
Z->ll,vv
Z->ll 7
IHEP led the combination of different channels from ATLAS side. 7

8. (H→)hh analyses The decay of h Resonance The bb, WW, tautau channels
have the highest BRs
gg has the di-photon mass resonance
(bump search)
channels studied in ATLAS : ggbb, ggWW,
bbtautau, bbbb (high mass region)
Non-resonance

9. Overview of different channels
ggbb : di-photon provides a decent mass peak and bb can further help to suppress QCD bkg in addition to di-photon requirements.
ggWW(lvqq): In principle, lvqq is not very sensitive at low mass due to huge QCD; however, di-photon can improve the situation here. Statistics will be low although it is clean.
bbtt: this channel has no mass peak and cannot be a discovery channel.
bbbb: only sensitive at high mass region using some method of the boosted jet

10. H→hh→ggbb analysis Assume xsection*BR = 1fb, we can
Achieve 5s only at high luminosity for LHC
arxiv: v3
P.R.D (2014)

11. The analyses of (H->)hh->ggbb in ATLAS/CMS
Phys. Rev. Lett. 114, ; arXiv:
3.0s for resonance search
2.4s for non-resonance search
Excess seen in ATLAS, not in CMS; limited by low statistics
CMS PAS HIG

12. WWgg analysis Signal Submitted to P.L.B bkg
For these analyses, both lvlv and lvqq
decays of ww are investigated.
They have comparable sensitivity with
300 fb-1 assuming xsection*Br = 5 fb.

13. ATLAS WWgg analysis
We IHEP proposed WWgg analysis with WW decaying into lvqq to ATLAS and complete the analysis.
Phys.Rev.D 92,092004(2015)
arxiv: v1
Continuous bkg is estimated from sideband.
The total SM Higgs bkg is /-0.07, the uncertainty driving by parton-shower modeling.
The significance is ~1.8 s.

14. ATLAS bbtt analysis Non-resonance MH=300 GeV
The difficulty of this analysis is that it can not reconstruct a reasonable narrow mass peak.
Different data driven methods have to be implemented to estimate bkgs.

15. Combination of ggbb, ggWW, tautaubb,4b
Due to the downward fluctuation of tatutaubb, the overall
significance is 2.5s.
IHEP take over the combination of the analysis as well.

16. Low mass BSM h → with Run1 8TeV data (CMS)
Run1: no significant excess is observed
max. ~1.9 at ~97.5 GeV
Theoretical paper published at Chin. Phy. C 38 (2014): (J. Fan, J. Tao* et al, CPC Highlights result in 2014)
No obvious excess has been seen as the right plot shows, but still 1.9s at 97.5 GeV.
IHEP is dominant in this analysis（CMS AN-2014/172, CMS PAS HIG ）：results presented at “Higgs Hunting 2015”

17. Cooperation between theorists and experimentalists in China
For the physics beyond Standard Model, it is important the theorists can give us some guide.
The discussion with experimentalists can help theorists understand results and propose more reliable models.
Make sure not to break the confidential agreement in the collaboration for the experimentalists.
Deviation from SM
Discussion with
theorists and
publish two
gg related
papers together
(ggbb,ggWW)
Propose that in
ATLAS and finish
the analysis

18. Search for heavy Higgs in HZZ
Motivation:
Search for a high-mass Higgs boson in HZZ in the mass range of 140 GeV < mH < 1 TeV and extend and improve the earlier 7 TeV search results
Analysis overview:
Four separate searches are performed: ZZ4l, ZZllnn, ZZllqq, ZZnnqq
No significant deviation from the Standard Model predictions is observed
Results from the 4 channels are combined to extract limits:
NWA assumption and 2HDM (type I and II) context.
arXiv:
Peking
arXiv:
accepted by EJPC
USTC plays a leading role in ATLAS H->ZZ analysis

19. ZHll+MET No excess from SM
USTC plays
a leading role
In this anaysis.
No excess from SM
PhysRevLett (selected as Synopsis)
4/16/2014
Lailin Xu

20. High mass Di-photon search
Irreducible background (gamma-gamma) :
Reducible background (gamma-jet and jet-jet faking as diphoton):
For di-photon mass at 750 GeV, the pt of the single photon is around 370GeV.
With such a boosted photon, photon conversion may not be an issue.
The calibration of the photon has to be considered carefully.
How to choose isolation criteria for photons to further suppress reducible bkgs
is somehow crucial.
ATLAS

21. Di-photon searches with Run1 data
HIG
With run1 data, no excess higher than 2s can be seen.

22. di-photon excess at the high mass
3.9s (local),2.3s (global)
LW hypothesis
3.6s(local),2.0s(global)
NWA
2.6s (local), 2.0s (global)
NWA

23. Run2 HBSM Statistics is still limited. No significant excess.
Limits have been extended to 1.2 TeV

24. Conclusion
BSM Higgs searches are important topics after the Higgs discovery.
Keep in mind that yesterday’s signals are today’s backgrounds.
A lot of HBSM event signatures have the investigated with Run1 data.
No significant excess has been observed.
The searches with Run2 data have started.
High mass di-photon shows interesting bump, more data will tell us whether it can survive.
It is expected that 2016 will be a very promising and fruitful year for BSM Higgs searches.
More cooperation between theorists and experimentalists will certainly helps.

25. Backup slides

26. IBL added in the pixel detector
One more layer IBL is added and functions well:

27. Performance of physics objects.
ATL-PHYS-PUB
ATL-PHYS-PUB
ATL-PHYS-PUB
Electron/photon
muon
jet
ATL-PHY-PUB
ATL-PHY-PUB
B-taggomg
The performance difference of electron is due to mismodeling of G4 shower shape.
B-tagging is obviously improved w.r.t Run1.
Ready for Higgs physics study.

28. W/Z,top measurements ATLAS-CONF-2015-039 ATLAS-CONF-2015-049
Consistent with theoretical prediction within 2s