SciPost Submission Page
Pseudoscalar pair production via off-shell Higgs in composite Higgs models
by Diogo Buarque Franzosi, Gabriele Ferretti, Li Huang, Jing Shu
This is not the current version.
|As Contributors:||Diogo Buarque Franzosi · Gabriele Ferretti|
|Arxiv Link:||https://arxiv.org/abs/2005.13578v1 (pdf)|
|Date submitted:||2020-06-03 02:00|
|Submitted by:||Buarque Franzosi, Diogo|
|Submitted to:||SciPost Physics|
|Subject area:||High-Energy Physics - Phenomenology|
|Approaches:||Theoretical, Experimental, Phenomenological|
We propose a new type of search for a pseudoscalar particle $\eta$ pair produced via an off-shell Higgs, $pp\to h^*\to \eta\eta$. The search is motivated by a composite Higgs model in which the $\eta$ is extremely narrow and decays almost exclusively into $Z\gamma$ in the mass range $65$ GeV$\lesssim m_\eta \lesssim 160$ GeV. We devise an analysis strategy to observe the novel $Z\gamma Z\gamma$ channel and estimate potential bounds on the Higgs-$\eta$ coupling. The experimental sensitivity to the signatures depends on the power to identify fake photons and on the ability to predict large photon multiplicities. This search allows us to exclude large values of the compositeness scale $f$, being thus complementary to other typical processes.
Submission & Refereeing History
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Anonymous Report 2 on 2020-9-5 Invited Report
The paper discusses the collider signatures of a light pseudo-scalar decaying to $Z\gamma$. The scenario is motivated by a class of composite Higgs models. A detailed analysis of the LHC reach is performed and the relevance of photon identification is stressed.
I think the paper presents new interesting results and is well-written. Before being able to recommend it for publication, however, I would ask the authors to make a few adjustments:
— In the Introduction: why is the coupling of $\eta$ to $\gamma\gamma$ small/absent? Please refer to an explicit model or postpone an explanation of how/why this happens to Section 4.
— Also, why isn’t there a CP-odd coupling to gluons? How much do your results depend on the absence of it?
— The sentence “.. via doubly suppressed anomalous interactions in a loop…” is rather unclear, especially if what the authors mean is essentially what is explained about the $\eta\to bb$ rate when discussion Fig 3.
— Still in the Introduction, in the paragraph below (1.1) it is said that “in models of PC this assertion needs to be better qualified”. Please anticipate that this is done in a later section, if this is the case.
— Regarding the collider analysis, a very basic question: how hard are the photons required to be? I do not see this information in (3.1) nor find it in the text. It would be useful to discuss how such a cut helps to reduce the background.
— Using the ingredients in Eq.(2.2) and (4.5) I estimate that the ratio between the cross section for $\eta$ pair production mediated by the contact top vertex and the one mediated by an off-shell Higgs scales as the fourth power of $(v m_\eta/fm_h)$. Do the authors agree? If so, it would be very useful to have this rough estimate in the text. The regime of interest (light $\eta$ and large $f$) is immediately identified.
— Unfortunately, the above ratio becomes of order unity for the models of Sec. 4, see (4.10), unless one fine-tunes the parameters of the theory such that the mass of $\eta$ is much smaller (as might happen in a couple of models discussed in sec 4). Fine-tuning is necessary if we want to have an unsuppressed $\eta^2 h$ coupling and simultaneously a small $\eta$ mass. Please comment on this important aspect in the text.
Anonymous Report 1 on 2020-7-2 Invited Report
1) Complete phenomenological study, from detailed model-building to collider
2) Impeccable LHC simulation and search proposal
3) Well motivated and novel
1) Proposed signature, while possible, is non generic
This wel-written article provides a thorough of composite-Higgs models in which the Higg sector contains an additional scalar singlet field (as Pseudo Goldstone boson). The authors show that in certain regions of parameter space (possible and protected by a symmetry) the extra singlet decays predominantly to Zgamma, and a favorable search channel is h_>eta eta->ZgammaZgamma. The article provides a detailed study of the discovery perspective at LHC (for 300 and 3000 1/fb).
I've a few minor comments:
1) In the intro (p2) it is said that the singlet "couplings to fermions are also typically small". It seems to me that they rather "can be small" in certain regions of parameter space protected by a symmetry (i.e. a generic embedding in the 6 representation would have sizeable fermion couplings)
2) In the statistical analysis (p11) the authors provide formula 3.3. This appears to me slightly out of context: I'd rather provide more details about how this formiula is used, or omit it.
3) In the conclusions (p19) it is said that "...allows us to exclude large values of f". This is not completely obvious from fig 12 (for which the bulk of the exclusion is at small f); so perhaps the authors could specify that they refer to the small m_eta region, if this is what is meant.