WG2 WG3 joint meeting on CP violation in extended Higgs sector

304/1-001 (CERN)



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LHCHWG2 meeting
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Giacomo Ortona
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Sarah Heim, Ken Mimasu
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Talk by Arturo de Giorgi
Q - Henning Bahl: What you compare r_t^2 to? Exp. results assume no CP-odd component
A: Yes, we neglect ktilde, since from the eDM limits is constrained to be small, and check at posteriori that the validity of the assumption
Talk by Marc Hannig
Q - Andrei Gritstan: Cannot compare CMS/ATLAS bounds since they are related to different final state. 
Also, within CMS we don't see big differences to simular distributions as the one you see in slide 7. Hard to draw strong conclusion from differences in the tails. Some dependence of the results on the mathing between ME and PS might also be importnt
Talk by Akanksha Bhardwaj 
Q - Henning Bahl: Do you know any concrete model for CPV HEFT?
A - Ken Mimasu: CHMs
Talk by Romal Kumar
Q - Elina Fuchs: how you calculate Z factors in slide 15? Are they calculated or are they fixed to some representative values
A: They are chosen as example, this is still work in progress
Q - Elina Fuchs: ok, these could be useful information, if made public once available
Talk by Rahool Kumar Barman
Q - Henning Bahl: Do you expect a strong impact from background effects?
A: bkg can be in principle elminated with a sgn vs bkg classifier, the unfolding model might have not to deal with the bkg
Q - Henning Bahl: but not completely...
A: yes, it will give some degradation, but the results shouldn't vary too much
There are minutes attached to this event. Show them.
    • 1
      Speaker: Dr Daniele Barducci (Sapienza Universita e INFN, Roma I (IT))
    • 2
      Flavour and Higgs physics in Z2-symmetric 2HD models near the decoupling limit

      With no evidence of any exotic particle detected so far beyond the Standard Model, the new physics may lie above the presently accessible energies at colliders and, at low-energies, can be accounted for via an effective description. The interplay of flavour and Higgs physics data allows setting stringent bounds on the parameters of the effective Lagrangian. In this paper, we focus on Z2-symmetric two Higgs doublet models near the decoupling limit: the corresponding effective description relies on only a few parameters, thus predicting many interesting correlations between observables that work as tests of the theory. We present the results of a global fit to the existing data, updating and extending over the past literature. We comment on the triple Higgs coupling as a probe of an extended scalar sector and on the recent CDF II measurement of the W-mass.

      Speaker: Arturo de Giorgi
    • 3
      Classifying the CP properties of the ggH coupling in H+2j production

      The Higgs–gluon interaction is crucial for LHC phenomenology. To improve the
      constraints on the CP structure of this coupling, we investigate Higgs production with two jets using machine learning. In particular, we exploit the CP sensitivity of the so far neglected phase space region that differs from the typical vector boson fusion-like kinematics. Our results suggest that significant improvements in current experimental limits are possible. We also discuss the most relevant observables and how CP violation in the Higgs–gluon interaction can be disentangled from CP violation in the interaction between the Higgs boson and massive vector bosons. Assuming the absence of CP-violating Higgs interactions with coloured beyond-the-Standard-Model states, our projected limits on a CP-violating top-Yukawa coupling are stronger than more direct probes like top-associated Higgs production and limits from a global fit.

      Speaker: Marco Menen
    • 4
      Non-linear top-Higgs CP violation

      A possibility which is so far unexplored at the LHC is a significant non-linear realization of CP-violation, which is naturally described in non-linear Higgs Effective Field Theory (HEFT). We perform an analysis of the HL-LHC potential to constrain such interactions considering a large range of single and double Higgs production processes, including differential information where this is statistically and theoretically possible. In this talk, I will discuss distinguishing expected correlations in the Standard Model Effective Field Theory from those attainable in HEFT.

      Speaker: Dr Akanksha Bhardwaj (University of Glasgow)
    • 5
      Analysis of interference effects in the di-top final state for CP-mixed scalars in extended Higgs sectors

      Various extensions of the Standard Model predict the existence of additional Higgs bosons. If these additional Higgs bosons are sufficiently heavy, an important search channel is the di-top final state. In this channel interference contributions between the signal and the corresponding QCD background process are expected to be important. If more than one heavy Higgs boson is present, besides the signal-background interference effects associated with each Higgs boson also important signal-signal interference effects are possible. We perform a comprehensive model-independent analysis of the various interference contributions within a simplified model framework. We consider two heavy CP-mixed Higgs bosons and take into account large resonance-type effects arising from loop-level mixing between the scalars. The interference effects are studied both in an analytic way at parton level and with Monte Carlo simulations for the di-top production process at the LHC. We demonstrate that signatures can emerge from these searches that may be unexpected or difficult to interpret.

      Speaker: Romal Kumar
    • 4:25 PM
      Go get a coffee/tea
    • 6
      Returning CP-observables to the frames they belong

      Optimal kinematic observables are often defined in specific frames and then approximated at the reconstruction level. We show how multi-dimensional unfolding methods allow us to reconstruct these observables in their proper rest frame and in a probabilistically faithful way. We illustrate our approach with a measurement of a CP phase in the top Yukawa coupling. Our method makes use of key advantages of generative unfolding, but as a constructed observable it fits into standard LHC analysis frameworks.

      Speaker: Rahool Kumar Barman (Oklahoma State University)
    • 7
      Probing CP violation in H -> tau+ tau- gamma

      Existing studies of Higgs-tau Yukawa coupling allows for the presence of a non-zero CP-odd contribution. This is usually probed and constrained at the LHC by studying the distribution of events with respect to the angle between the two tau decay planes in H -> tau+ tau- decay. We study another interesting signature of CP violation, namely forward-backward asymmetry in the decay H -> tau+ tau- gamma. This CP-asymmetry interestingly requires interference of tree and one-loop level contributions. We focus on how this asymmetry can be quantified without the need to reconstruct the tau decay planes, or the need to boost to any specific frame of reference. Currently we are studying its feasibility in the high luminosity phase of LHC. A publication looking at the detector response and reconstruction simulation is in progress.

      Speaker: Dibyakrupa Sahoo
    • 8
      Search for an invisible scalar in tt final states at the LHC

      We use the current tt¯experimental analysis to look for Dark Matter (DM) particles hidden in the final state. We present a phenomenological study where we successfully perform the reconstruction of a tt¯ system in the presence of a scalar mediator Y0, that couples to both Standard Model (SM) and to DM particles. We use a MadGraph5 aMC@NLO simplified DM model, where signal samples of pp → ttY¯ 0 are generated at the Large Hadron Collider (LHC) with both Charge-Parity (CP) -even and CP-odd couplings of Y0 to the top quarks. Different mass scales for the Y0 mediator are considered, from the low mass region (∼ 0 GeV) to masses close to the Higgs boson mass (125 GeV). The dileptonic final states of the tt¯ system were used in our analysis. The reconstruction of the tt¯system is done with a kinematic fit, without reconstructing the mediator. All relevant SM backgrounds for the dileptonic tt¯ search at the LHC are considered. Furthermore, CP angular observables were used to probe the CP-nature of the coupling between the mediator and top-quarks, which allowed to set confidence level (CL) limits for those Yukawa couplings as a function of the mediator mass.

      Speaker: Rodrigo Capucha (Centro de Física Teórica e Computacional, FCUL)