LHC Higgs Working Group WG3 (BSM) -- Extended Higgs Sector subgroup meeting

Tuesday 31 Oct 2023, 15:20 → 18:00 Europe/Zurich

40/S2-D01 - Salle Dirac (CERN)

Lidija Zivkovic (Institute of physics Belgrade (RS)), Mariarosaria D'Alfonso (Massachusetts Inst. of Technology (US)), Nikolaos Rompotis (University of Liverpool (UK)), Rui Santos (ISEL and CFTC-UL), Santeri Laurila (CERN), Tania Robens (IRB Zagreb)

ExtSec_Oct31_part1.mp4

ExtSec_Oct31_part2.mp4

15:20 → 15:25 Introduction

15:25 → 15:45 A 95 GeV Higgs Boson within a 2-Higgs Doublet Model (15+5)

This talk will focus on the explanation and implications of the excesses around 95 GeV in the di-photon and di-tau invariant mass distributions recently reported by the CMS collaboration at the LHC, together with the long-standing discrepancy observed at the Large Electron-Positron (LEP) collider in the b-bbar invariant mass. The latest ATLAS results in the di-photon final state similarly reveal an excess of events within the same mass range, albeit with a bit lower significance, thereby corroborating the observations made by CMS. We have found that all three excesses can be explained simultaneously within the general 2HDM Type-III where the lightest CP-even Higgs boson serves as the source of the excesses, while satisfying up-to-date theoretical and experimental constraints. Characteristic features of the model parameter space explaining the data will also be pointed out making way for further exploration of the model in the near future. In particular, the 2HDM Type-III predicts a significant enhancement in the ttbar associated production of the SM-like 125 GeV Higgs boson. Such an effect can be tested soon at the High Luminosity LHC (HL-LHC).

Speaker: Manimala Chakraborti

95GeV.pdf

15:45 → 16:05 Resonant top pair searches at the LHC: a window to electroweak phase transition (15+5)

The dynamics of electroweak phase transition could have profound consequences for particle physics and cosmology. We study the prospects for the HL-LHC to probe the strong first-order electroweak phase transition (SFOEWPT) regime in the 2HDM. We focus on the Higgstrahlung channel pp→ZH/A with a resonant top-quark pair final state H/A→tt. We find that the top-quark pair final state renders the largest sensitivity to the SFOEWPT regime, in comparison to the other Higgstrahlung searches already performed by ATLAS and CMS, that focus on the H/A→bb and H→WW final states. Furthermore, we derive the complementarity of the Higgstrahlung searches with other relevant classes of searches at the HL-LHC and compare them with the gravitational wave sensitivity at LISA.

Speaker: dorival Gonçalves (Oklahoma State University)

Dorival_WG3.pdf

16:05 → 16:25 Semi-invisible h -> Z X Higgs decays: an extended scalar window into dark matter (15+5)

We explore semi-invisible 125 GeV Higgs boson decays arising in extended scalar sectors which connect to dark matter. We focus on h -> Z X, with X invisible BSM particle(s), for which an experimental search by ATLAS or CMS does not yet exist. Such decay could be present in extended Higgs sectors featuring a light pseudoscalar, as well as in theories of axion-like-particles. We analyze the h -> Z X sensitivity at the LHC, showing that it can probe regions of parameter space not directly accessible with current searches.

Speaker: Jose Miguel No (IFT-UAM/CSIC)

LHCHiggsWG_JMNo_Final.pdf

16:25 → 16:40 Coffee/Tea

17:00 → 17:20 The importance of Interference in resonant di-Higgs production (15+5)

Within the RxSM (the SM extended by a real singlet) we focus on a parameter region giving rise to a SFOEWPT. It is shown that taking into account the pure resonant diagram, in di-Higgs production, gg -> H -> hh, is not sufficient to obtain reliable results for the resonant di-Higgs production.

Speakers: Alain Verduras, Alain Verduras

LHCHiggsWG3_AV.pdf

17:20 → 17:40 Higgs interference effects in top-quark pair production in the 1HSM (15+5)

We present an NLO study of the process pp -> {h1,h2} -> ttbar+X in the 1-Higgs-singlet extension of the Standard Model with an additional heavy Higgs boson h2 that mixes with the light Higgs boson h1. This process is subject to large interference effects between loop-induced Higgs-mediated amplitudes and the QCD continuum background which tend to overcompensate any resonance contributions. A reliable modelling of the resulting top-pair invariant mass shapes requires the inclusion of higher-order QCD corrections, which will be presented. The computation of these NLO corrections is exact in all contributions but in the class of non-factorisable two-loop diagrams which are included in an approximate way such that all infrared singular limits are preserved. We present numerical results for several benchmark points with heavy Higgs masses in the range 700--3000 GeV considering the production of stable top quarks. We find that the interference effects dominate the BSM signal yielding sharp dip structures instead of resonance peaks. The significance and excludability of the BSM effect is explored for the LHC Run 2, Run 3 and HL-LHC.

Speaker: Alexander Lind (Subatech, IMT Atlantique)

LHCHiggsWG3_Lind.pdf