The Fourth Generation Quark and the 750 GeV Diphoton Excess

Zhang, Yujie; Zhou, Benchun; Sun, J.

doi:10.48550/arxiv.1602.05539

Cited by 6 publications

(6 citation statements)

References 27 publications

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“…The colored particles in the bound state can annihilate into gauge bosons, so that they can give a relatively clean diphoton signature. The possibility to observe such a resonance at hadron colliders has been studied extensively for the scalar top case in the past [12][13][14][15][16][17][18] and in the context of the 750 GeV excess [19][20][21]. However, such a colored particle of the mass ∼ 375 GeV (750/2 GeV) is severely constrained by the current LHC data.…”

Section: Introductionmentioning

confidence: 99%

Heavy fermion bound states for diphoton excess at 750 GeV — collider and cosmological constraints

Han

Ichikawa

Matsumoto

et al. 2016

J. High Energ. Phys.

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A colored heavy particle with sufficiently small width may form non-relativistic bound states when they are produced at the large hadron collider (LHC), and they can annihilate into a diphoton final state. The invariant mass of the diphoton would be around twice of the colored particle mass. In this paper, we study if such bound state can be responsible for the 750 GeV diphoton excess reported by ATLAS and CMS. We found that the best-fit signal cross section is obtained for the SU(2) L singlet colored fermion X with Y X = 4/3. Having such an exotic hypercharge, the particle is expected to decay through some higher dimensional operators, consistent with the small width assumption. The decay of X may involve a stable particle χ, if both X and χ are odd under some conserved Z 2 symmetry. In that case, the particle X suffers from the constraints of jets + missing E T searches by ATLAS and CMS at 8 TeV and 13 TeV. We found that such a scenario still survives if the mass difference between X and χ is above ∼ 30 GeV for m X ∼ 375 GeV. Even assuming pair annihilation of χ is small, the relic density of χ is small enough if the mass difference between X and χ is smaller than ∼ 40 GeV.

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Section: Introductionmentioning

confidence: 99%

Heavy fermion bound states for diphoton excess at 750 GeV — collider and cosmological constraints

Han

Ichikawa

Matsumoto

et al. 2016

J. High Energ. Phys.

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“…Assuming that the number of observed events in the signal region follows the Poisson distribution, and by adding the statistical uncertainty as well as the systematic uncertainty in quadrature, the number of excessive events due to new physics are: N BSM = 18.4 ± 6.3 in the Run 1 analysis, (5) N BSM = 10.7 ± 5.1 in the Run 2 analysis. (6) We have used the following pipeline to estimate the on-Z excess fit of our model: MadGraph 5 v2.2.3 [28,29] for event generation, Pythia 6.4 [30] for parton shower and Checkmate [31,32] for…”

Section: Vector-like Quarks and Atlas On-z Excessmentioning

confidence: 99%

“…The formation of 750 GeV bound state requires Γ X 1MeV, which translates to m ũ 1TeV for O(1) Yukawa couplings. 6 Let us briefly discuss other aspects of the χ model. Monojet constraints have been discussed in Ref.…”

Section: Model Xy Bφ With Quasi-degenerate or Heavy Bmentioning

confidence: 99%

“…The ATLAS shows a local (global) significance of 3.9σ (2.0σ), while the CMS reported a local (global) significance of 2.8-2.9 σ (< 1σ) depending on the spin hypothesis recently [3,4]. Among many possible interpretations, one of the most attractive scenarios is the 750 GeV quarkonium, i.e., a QCD bound state of heavy vector-like quark with a mass of about 375 GeV [5][6][7][8]. Unlike many other diphoton models, the necessary ingredients for the diphoton excess in this scenario is extremely simple; just the existence of the vector-like quark X with a small width, Γ X Γ(S → γγ) O(MeV), can lead to a diphoton resonance, and it does not require an additional 750 GeV singlet field nor new strong dynamics other than the Standard Model (SM) gauge group.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Models of a 750 GeV quarkonium and the LHC excesses

Hamaguchi

Liew

2016

Phys. Rev. D

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We investigate models involving a vector-like quark (X), which forms a 750 GeV bound state and reproduces the observed diphoton signals at the LHC, in connection with other excesses in the LHC data. An exotic hypercharge of −4/3 is required to fit the signal cross section, which indicates that there is additional particle(s) that mediates the decay of X in the full theory. We find that, introducing an SU(2) doublet vector-like quark of mass around 600 GeV in our UV-complete framework can accommodate not only the diphoton but also the on-Z excess (and potentially a slight excess in the monojet events). Our models also include a dark matter candidate. The most useful way to probe the models at the LHC is via monojet searches. The relic dark matter density is largely determined by coannihilation effects, and indirect detection of dark matter annihilation signals is the alternative and complementary probe of our models.

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“…It seems natural to classify the various models in accordance with the fermion properties. The simplest explanation for the structure underlying the bump in the diphoton spectrum could be that of a QCD bound state of a heavy vector-like quark Q, with a mass around 375 GeV [12][13][14][15][16][17][18]. For this model, the signal rate can be explained by a scalar Q Q bound state η Q , with Q transforming as (3, 1, −4/3) under the SU (3)⊗SU (2)⊗U (1) Y gauge groups of the SM [16,17].…”

Section: Introductionmentioning

confidence: 99%

Constraints on 750 GeV colorless Q-onia from running couplings

Anchordoqui,

Goldberg,

Huang

2016

Preprint

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We present yet another composite model explaining the relatively broad peak in the diphoton invariant mass distribution around 750 GeV recently observed at the LHC experiments. We consider the excess originates in bound states of vector-like fermions Q transforming under the electroweak group (but not QCD) of the standard model and which are also charged under a new SU (N TC ) QCD-like confining force. Since the new uncolored fields transform as SU (2) doublets they can acquire a mass through Yukawa interactions with the electroweak Higgs doublet, as quarks and leptons. We parametrize the Q-onium bound state using the Coulomb approximation and give a numerical fit to the diphoton excess consistent with no strong coupling effects up to about 30 TeV, which is the energy scale for next generation colliders. The range of allowed hypercharge Y Q is given by 2.26 ≤ Y Q ≤ 2.53 for N TC = 2 and 2.17 ≤ Y Q ≤ 2.31 for N TC = 3. The smoking gun for the model would be the discovery of Q-onia decaying into Higgs and Z-boson.

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The Fourth Generation Quark and the 750 GeV Diphoton Excess

Cited by 6 publications

References 27 publications

Heavy fermion bound states for diphoton excess at 750 GeV — collider and cosmological constraints

Heavy fermion bound states for diphoton excess at 750 GeV — collider and cosmological constraints

Models of a 750 GeV quarkonium and the LHC excesses

Constraints on 750 GeV colorless Q-onia from running couplings

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