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First interpretation of the 750 GeV di-photon resonance at the LHC

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Stefano Di Chiara, Luca Marzola, Martti Raidal

High Energy Physics - Phenomenology · Submitted 15 Dec 2015 · 38 references

Pith's verdict: A competent early 750 GeV interpretation: the negative 2HDM/MSSM result is more robust than the reader thinks, and the positive singlet claim is weaker than the abstract sounds.

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arXiv ID1512.04939 (version 3)
Pith ID4XFA5WXK, Pith's permanent record of this paper and its review
CitationLuca Marzola, Martti Raidal, Stefano Di Chiara. "First interpretation of the 750 GeV di-photon resonance at the LHC." arXiv:1512.04939 (2015). https://pith.science/paper/4XFA5WXK
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The paper

The paper claims

A single new pseudoscalar can account for the 750 GeV di-photon bump while staying invisible in every other channel the LHC has checked.

The reading

Both ATLAS and CMS reported a modest excess of two-photon events clustering near 750 GeV in their 13 TeV data, and CMS saw a compatible bump when its 8 TeV data were folded in. The authors first ask whether these two bumps can be the same object, converting each experiment's event counts into a production rate times branching ratio and finding the two rates agree at the $1.8$ sigma level, with a combined value of $6.26$ fb. The real question is why nothing similar shows up in di-jets, top pairs, weak bosons, or leptons, since any new particle heavy enough to be produced at the LHC should usually decay in several of those ways. The paper's answer is that a single new spin-zero particle, communicating with Standard Model gauge bosons only through heavy charged intermediaries, can be tuned to produce the observed photon pairs while its decays to $W$, $Z$ and $t$ pairs stay below the non-observation limits. The same tuning does not work for the standard two-doublet scalar extensions or for the minimal supersymmetric model, which the authors argue are pushed out by the top-pair search unless new coloured particles are added.

What carries the argument

Two pieces of machinery carry the argument. The first is the effective Lagrangian of Eq. (7), in which a pseudoscalar $phi$ couples to the dual field-strength tensors of QCD and of the electroweak gauge group with coefficients $kappa_s alpha_s / (4 pi v)$ and $kappa_w alpha / (4 pi v)$, plus a relative weight $b$ between the hypercharge and $SU(2)$ terms. Because the photon rate depends on a combination of $kappa_s$ and $kappa_w$ while the di-gluon rate depends only on $kappa_s$, the model has enough freedom to hit the observed di-photon rate for any acceptable $kappa_s$; the parameter $b$ then sets the ratios among $WW$, $ZZ$ and $gamma Z$ final states, and $|b| < 1$ is what keeps them under the limits. The second is Eq. (15), which turns the 8 TeV top-pair limit into a bound on a single number: assuming the 750 GeV state decays only to tops and gluons, the predicted $pp to phi to tbar t$ rate is written as the Standard Model rate rescaled by $a_t^2$, with the pseudoscalar's gluon width entering through a factor $kappa_A = 1.41$. That conversion is what produces the bound $|a_t| < 1.34$ and therefore the exclusion of the two-doublet models and the MSSM.

Extended reading notes

Core claim

The paper argues that the 750 GeV di-photon excess, taken at face value, selects a narrow class of explanations. Its central positive result is that an effective singlet — a single new spin-zero field coupling to gluons and electroweak gauge bosons through dimension-five operators suppressed by the electroweak scale, with free coefficients $kappa_s$, $kappa_w$ and $b$ — reproduces the combined signal rate of $6.26$ fb while keeping the di-boson and $gamma Z$ rates suppressed whenever $|b| < 1$; the di-gluon rate fixes $kappa_s$ alone, so $kappa_w$ can always be adjusted to match the photon rate. Its central negative result is that the four flavour-conserving two-Higgs-doublet models, despite fitting the measured signal strengths well (best $chi^2$/d.o.f. $= 0.78$ for Type II, with a common solution $alpha = -1.51$, $beta = 0.063$), require a top coupling rescaling $|a_t| > 1.34$ that the 8 TeV ATLAS limit of $680$ fb on $pp to H to tbar t$ forbids. The minimal supersymmetric model inherits this problem, because its low-energy limit is the Type II two-doublet model and the stop contribution can only rescale the top coupling by a factor near unity. Adding two vector-like quarks to a Type I two-doublet model restores viability — a viable point is found with $m_U = 755$ GeV, $m_Q = 850$ GeV, $y_{LQ} = 10.3$, $y_{RQ} = 9.22$ — at the price of Yukawa couplings that become non-perturbative near the resonance mass itself.

Load-bearing premise

The exclusion of the two-doublet models and the MSSM depends on the assumption that the 750 GeV resonance decays essentially only to top quarks and gluons, so that the 8 TeV top-pair limit can be converted into a bound on one rescaling factor of the top coupling.

Editorial extensions

If this is right

  • If the excess is real and the singlet interpretation holds, the 750 GeV state should show up in $WW$, $ZZ$ and $gamma Z$ channels at rates fixed by the single parameter $b$, giving a sharp prediction to test against the same datasets that currently show nothing.
  • Because the di-gluon and di-photon rates are controlled by independent combinations of couplings, a future measurement of the di-jet channel at 750 GeV would pin $kappa_s$ and leave the photon rate as a consistency check rather than a fit.
  • Any supersymmetric explanation of the excess must go beyond the minimal model, since the Type II structure inherited by the MSSM forces the top coupling into a region the top-pair search already excludes.
  • In the two-doublet model with two vector-like quarks, the same large Yukawa couplings needed for the photon rate drive the theory non-perturbative at energies of order a TeV, so the explanation carries an intrinsic upper limit on its own validity.
  • If the resonance is a composite pseudoscalar of a strongly coupled sector, the same dimensional estimates put spin-one companions at masses of several TeV, within reach of the next LHC run.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The entire negative half of the result rests on a single number, the $|a_t| < 1.34$ bound, which assumes the 750 GeV width is saturated by tops and gluons; a sizeable invisible or exotic partial width would relax it and reopen the two-doublet and supersymmetric options without touching any other part of the analysis.
  • The paper treats the ATLAS and CMS bumps as one object largely on the strength of the quoted $O(1)%$ photon energy calibration; an independent cross-calibration of the two detectors' energy scales at 750 GeV is the cheapest way to confirm or dissolve the whole interpretation.
  • The spin-zero assignment is a choice, not a measurement: a spin-two resonance would produce a different angular distribution in the photon pair, and the paper's fits say nothing about that distribution, so the singlet Lagrangian should be read as the simplest option consistent with the counts rather than as evidence for scalar nature.
  • The framework predicts correlated rates across $WW$, $ZZ$ and $gamma Z$ at 750 GeV that are more informative than the photon rate itself, because they depend on $b$ alone and cannot be absorbed by retuning the overall normalisation.
Original abstract

We scrutinise the evidences recently reported by the ATLAS and CMS collaborations for compatible 750 GeV resonances which appear in the di-photon channels of the two experiments in both the 8 TeV and 13 TeV datasets. Similar resonances in di-boson, di-lepton, di-jet and $t\bar t$ final states are instead not detected. After discussing the properties and the compatibility of the reported signals, we study the implications on the physics beyond the Standard Model with particular emphasis on possible scalar extensions of the theory such as singlet extensions and the two Higgs doublet models. We also analyse the significance of the new experimental indications within the frameworks of the minimal supersymmetric standard model and of technicolour models. Our results show that a simple effective singlet extension of the SM achieves phenomenological viability with a minimal number of free parameters. The minimal supersymmetric model and the two Higgs doublet model, on the other hand, cannot explain the 750 GeV di-photon excess. Compatibility with the observed signal requires the extension of the particle content of these models, for instance by heavy vector quarks in the case of the two Higgs doublet model.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,739 input tokens.

What the abstract itself states, as probabilities: claims first 0.48 · states limitation 0.27 · human participants 0.01 · controlled comparison 0.12 · randomized assignment 0.01 · states quantitative result 0.16 · compares with prior results 0.63 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v3. Results and the main claim are underlined; .

We scrutinise the evidences recently reported by the ATLAS and CMS collaborations for compatible 750 GeV resonances which appear in the di-photon channels of the two experiments in both the 8 TeV and 13 TeV datasets. Similar resonances in di-boson, di-lepton, di-jet and $t\bar t$ final states are instead not detected. After discussing the properties and the compatibility of the reported signals, we study the implications on the physics beyond the Standard Model with particular emphasis on possible scalar extensions of the theory such as singlet extensions and the two Higgs doublet models. We also analyse the significance of the new experimental indications within the frameworks of the minimal supersymmetric standard model and of technicolour models. Our results show that a simple effective singlet extension of the SM achieves phenomenological viability with a minimal number of free parameters. The minimal supersymmetric model and the two Higgs doublet model, on the other hand, cannot explain the 750 GeV di-photon excess. Compatibility with the observed signal requires the extension of the particle content of these models, for instance by heavy vector quarks in the case of the two Higgs doublet model.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We scrutinise the evidences recently reported by the ATLAS and CMS collaborations for compatible 750 GeV resonances which appear in the di-photon channels of the two experiments in both the 8 TeV and 13 TeV datasets. contribution 0.83 0.57 0.03 asserted 0.74
s1 Similar resonances in di-boson, di-lepton, di-jet and $t\bar t$ final states are instead not detected. result 0.68 0.24 0.04 asserted 1.00
s2 After discussing the properties and the compatibility of the reported signals, we study the implications on the physics beyond the Standard Model with particular emphasis on possible scalar extensions of the theory such as singlet extensions and the two Higgs doublet models. contribution 0.98 0.72 0.06 unclear 0.48
s3 We also analyse the significance of the new experimental indications within the frameworks of the minimal supersymmetric standard model and of technicolour models. contribution 0.94 0.83 0.03 asserted 0.58
s4 Our results show that a simple effective singlet extension of the SM achieves phenomenological viability with a minimal number of free parameters. result 0.96 0.92 0.67 asserted 1.00
s5 The minimal supersymmetric model and the two Higgs doublet model, on the other hand, cannot explain the 750 GeV di-photon excess. result 0.99 0.88 0.26 asserted 1.00
s6 Compatibility with the observed signal requires the extension of the particle content of these models, for instance by heavy vector quarks in the case of the two Higgs doublet model. result 0.57 0.74 0.09 asserted 0.84

What kind of paper the classifier reports this is: theoretical result 0.88 · evidence from analysis of existing data 0.96.

What was examined, and what was not

sources read
  • arXiv listing abstract v3
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1. The production cross section times branching ratios
Figure 2. FIG. 2. 68%, 95%, and 99% CL contour plots in 1
Figure 3. FIG. 3. 68%, 95%, and 99% CL contour plots in 1

Figures reproduced from arXiv:1512.04939 by the authors.

References
How the literature uses it

92 arXiv papers cite this in 111 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 35 sentences without a confident label

Builds on it 1 paper
  • Such a scenario has been considered independently in Refs. [ref] , but in this work we extend such models to a case where the new strongly coupled sector (dark QCD) has an exact dark $G$-parity and demonstrate that this model has a viable dark matter candidate as the lightest $G$-odd pion.

    A 750 GeV Dark Pion: Cousin of a Dark G-parity-odd WIMP · Introduction · 0.99

Uses its data or values 6 papers
Compares with it 1 paper
Cites it as support 1 paper
Cites it as background 64 papers

What it cites · 16 sentences without a confident label

Uses data or values from 6 papers
  • We determine the values of the mixing angles $α$ and $β$ by performing a fit to the signal strengths, defined in Eq. [ref], by minimizing χ^2=∑_i (μ_i^exp-μ_i^th/σ_i^exp )^2, where $μ_i^exp$ and $σ_i$ are the experimental values of $μ_γ,H$, Eq. [ref], and $μ_γ,h$, $μ_Z,h$, $μ_W,h$, $μ_b,h$ $μ_τ,h$, with their respective uncertainties, as measured at ATLAS and CMS [ref] , while $μ_i^th$ are the 2HDM predictions obtained by rescaling the production cross sections and branching ratios of a 750 GeV SM Higgs, reported in [ref] , each with its corresponding coupling coefficient.[All the formulas necessary to perform the fit can be found for example in [ref] .]

    Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables · Two Higgs Doublet models · 0.99

  • We determine the values of the mixing angles $α$ and $β$ by performing a fit to the signal strengths, defined in Eq. [ref], by minimizing χ^2=∑_i (μ_i^exp-μ_i^th/σ_i^exp )^2, where $μ_i^exp$ and $σ_i$ are the experimental values of $μ_γ,H$, Eq. [ref], and $μ_γ,h$, $μ_Z,h$, $μ_W,h$, $μ_b,h$ $μ_τ,h$, with their respective uncertainties, as measured at ATLAS and CMS [ref] , while $μ_i^th$ are the 2HDM predictions obtained by rescaling the production cross sections and branching ratios of a 750 GeV SM Higgs, reported in [ref] , each with its corresponding coupling coefficient.[All the formulas necessary to perform the fit can be found for example in [ref] .]

    Handbook of LHC Higgs Cross Sections: 2. Differential Distributions · Two Higgs Doublet models · 0.99

  • We determine the values of the mixing angles $α$ and $β$ by performing a fit to the signal strengths, defined in Eq. [ref], by minimizing χ^2=∑_i (μ_i^exp-μ_i^th/σ_i^exp )^2, where $μ_i^exp$ and $σ_i$ are the experimental values of $μ_γ,H$, Eq. [ref], and $μ_γ,h$, $μ_Z,h$, $μ_W,h$, $μ_b,h$ $μ_τ,h$, with their respective uncertainties, as measured at ATLAS and CMS [ref] , while $μ_i^th$ are the 2HDM predictions obtained by rescaling the production cross sections and branching ratios of a 750 GeV SM Higgs, reported in [ref] , each with its corresponding coupling coefficient.[All the formulas necessary to perform the fit can be found for example in [ref] .]

    LHC Data and Aspects of New Physics · Two Higgs Doublet models · 0.99

Cites as background 7 papers

Discussion

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