REVIEW
Signatures of the anomalous $Z\gamma$ and ZZ production at the lepton and hadron Colliders
High Energy Physics - Phenomenology · Submitted 19 Oct 1999 · 21 references
Pith's verdict: The factor-i fix to the ZγV vertices is a real service to the field; the sensitivity tables are illustrations, and the h3 = −f5 relation is not checkable here because the loop derivation sits in an unpublished companion.
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Referee report
The paper
The paper claims
The standard parametrization of the neutral triple-gauge vertices (ZZZ, ZZ$gamma$, Z$gamma$$gamma$) is missing a factor of $i$, and putting it back makes the effective Lagrangian hermitian and reverses which new-physics terms interfere with
The reading
What carries the argument
The load-bearing object is the corrected vertex function: $Gamma^{alpha beta mu}_{ZZV}$ carrying the two CP-odd couplings $f^V_4, f^V_5$ and $Gamma^{alpha beta mu}_{Zgamma V}$ carrying $h^V_1$ through $h^V_4$, with the inserted factor of $i$ in the second. Translated through the equations of motion into contact $fbar f ZZ$ and $fbar f Zgamma$ interactions, these vertices generate the new-physics helicity amplitudes that are added to the Standard Model fermion-exchange amplitudes. The amplitude-level statement that CP-conserving couplings give real terms and CP-violating ones purely imaginary terms is what converts a sign convention into an experimentally visible interference pattern in angular distributions and in the left-right polarization asymmetry.
Extended reading notes
Core claim
The paper argues that the general $V_1V_2V_3$ vertex for two on-shell neutral bosons and one off-shell $Z$ or photon requires an extra factor of $i$ in the $Zgamma V$ sector relative to the standard reference form, so that the effective Lagrangian generating the $ZZZ$, $ZZgamma$ and $Zgammagamma$ vertices is hermitian. The authors state that with the old convention the interference pattern of CP-conserving and CP-violating new-physics amplitudes with the Standard Model was reversed, and that while existing experimental limits are barely affected because they are dominated by the quadratic term, increasing accuracy would eventually produce non-intuitive results. On that corrected basis they give the new-physics helicity amplitudes for $fbar f o ZZ$ and $fbar f o Zgamma$, note that CP-conserving couplings give real amplitudes that interfere linearly with the Standard Model while CP-violating ones give imaginary amplitudes that enter only quadratically, and collect one-standard-deviation sensitivity estimates for each coupling at LEP2, a 500 GeV linear collider, the Tevatron and the LHC. The heavy-fermion toy model supplies the testable prediction $h^Z_3 = -f^gamma_5$ together with the vanishing of $h^Z_4$ and $h^gamma_4$.
Load-bearing premise
The sensitivity numbers quoted for each coupling rest on assumed rather than derived experimental inputs: a LEP2 luminosity of 150 inverse picobarns with a factor-two selection loss, a linear-collider sample of 100 inverse femtobarns with one percent accuracy, and a claim of negligible background for $Zgamma$ at large angles.
Editorial extensions
If this is right
- Any fit to $Zgamma$ production data that assumed the old convention and sat in the interference-dominated regime should be re-examined for a sign flip in the extracted CP-conserving couplings.
- At a 500 GeV linear collider with polarized beams, the left-right asymmetry $A_{LR}$ departs from its Standard Model values of about 0.28 for $ZZ$ and 0.14 for $Zgamma$ in a way that differs sharply between photon-type and Z-type couplings, giving a handle for separating them.
- If the heavy-fermion loop picture is right, measuring $h^Z_3$ and $f^gamma_5$ should return equal magnitudes and opposite signs, while $h^Z_4$ and $h^gamma_4$ should come out consistent with zero.
- Because no neutral triple-gauge vertex arises from dimension-six operators in the linear representation, observing any of these couplings would point either to enhanced higher-dimensional operators or to a nearby new-physics scale.
- Sensitivity to the dimension-eight couplings $h^V_2$ and $h^V_4$ grows faster with energy than to the dimension-six ones, so they should be bounded more tightly at the same collider.
Reading between the lines
- The sign correction is the kind of error that is invisible until interference terms matter, which suggests the same convention should be checked in the charged triple-gauge literature where interference is already large.
- The proposal to quote limits in narrow bins of subprocess invariant mass, rather than with multiplicative form factors, would make collider comparisons meaningful but also would require each experiment to publish a correlated set of limits rather than a single number.
- If $h^Z_3 = -f^gamma_5$ holds, a global fit imposing it halves the number of free parameters in the CP-conserving sector, which would tighten the remaining bounds more than the naive gain from one fewer parameter.
- The one-loop estimate of order $10^{-3}$ for these couplings at a few-hundred-GeV fermion mass implies that observability at LEP2 or the Tevatron needs an enhancement factor of order $10^2$, so a null result there constrains strongly interacting new-physics sectors more than weakly coupled ones.
Original abstract
The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.
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.
The abstract, sentence by sentence
The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. | contribution 0.84 | 0.61 | 0.07 | hedged possibility 0.58 |
| s1 | Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. | contribution 0.96 | 0.70 | 0.06 | asserted 0.75 |
| s2 | Experimental limits obtained or expected on each coupling are collected. | contribution 0.58 | 0.23 | 0.09 | asserted 0.94 |
| s3 | A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. | method 0.99 | 0.77 | 0.04 | asserted 0.95 |
| s4 | In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure. | interpretation 0.47 | 0.55 | 0.29 | asserted 0.66 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:hep-ph/9910395 by the authors.
References
How the literature uses it
32 arXiv papers cite this in 76 sentences
Papers citing it · 40 sentences without a confident label
Contests it 2 papers
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On the other hand, our $_4^$ bound in Eq.[ref] is much weaker than the ATLAS bounds on $(h_4^, h_4^Z)$, by a large factor of $∼32$, because the conventional nTGC form factor formulae are incompatible with the gauge-invariant SMEFT formulation of dimension-8 (including spontaneous electroweak gauge symmetry breaking), as we explain in Appendix [ref] and Table [ref].We emphasize that the existing ATLAS result [ref] used the conventional on-shell nTGC formula of the vertex $ZV^*$ [ref] for analyzing the $νν̅$ channel, which caused a significant underestimate of the sensitivity to $_3^$ by about $60%$.
Probing Neutral Triple Gauge Couplings with $Z^* \gamma\, (\nu \bar \nu \gamma)$ Production at Hadron Colliders · . Probing nTGCs with $Z^*(νν̅)$ Production at Hadron Colliders · contest 0.87
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[For the toy model [ref] states that the NTGC scales as $m_Z^2/M_F^2$, which is obviously not the correct scaling for a coupling generated from $d=8$ operators.
Fermionic UV models for neutral triple gauge boson vertices · Introduction · contest 0.90
Uses its method or tool 1 paper
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The results are then reinterpreted to constrain aNTGC using an effective vertex function approach [ref] .
Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in $ZZ \to 4\ell$ events with the ATLAS detector at $\sqrt{s} = 13$ TeV · Introduction · 0.95
Compares with it 3 papers
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We present this comparison in Table [ref], where the third row (red color) depicts the sensitivity reaches on $_4,2^$ obtained by using our nTGV formula [ref], and the last two rows (blue color) show the sensitivity reaches on $h_4,2^V$ that would be obtained by using the (incorrect) conventional nTGV formulas [ref] [ref] .Table [ref] demonstrates that the sensitivity reaches on the conventional nTGC form factors $h_4,2^V$ are erroneously stronger than those for our new formulation [ref] by about a factor of $O(20)$ at the LHC and by about a factor of $O(170)$ at a 100TeV $pp$ collider.
Probing Neutral Triple Gauge Couplings with $Z^* \gamma\, (\nu \bar \nu \gamma)$ Production at Hadron Colliders · . Matching $Z^*V^*$ Form Factors to the SMEFT Operators · 0.83
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In doing so, we compare the results for the form factor $h_3^γ(s)$ [ref] with a full (UV) theory example mentioned above, merely as a demonstration of the validity of our procedure.
Chiral Anomaly Cancellation and Neutral Triple Gauge Boson Vertices in the SM EFT · Introduction · 1.00
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This is suggested by a comparison with results in Hagiwara:1986vm and [ref] , respectively.] We use the definitions:
Anomalous triple-gauge-boson interactions in vector-boson pair production with RECOLA2 · EFT framework for triple-gauge-boson interaction · 0.81
Cites it as support 2 papers
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From a phenomenological point of view, there are many cases where dimension-6 operators are absent, but the dimension-8 operators show up [ref] .
Using k-means assistant event selection strategy to study anomalous quartic gauge couplings at muon colliders · Introduction · 0.98
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Thus better limits can be obtained for $h_2/4^V$ [ref] .
Anomalous couplings in $Z\gamma$ events at NNLO+PS and improving $\nu\bar\nu\gamma$ backgrounds in dark-matter searches · Introduction · 0.96
Cites it as background 13 papers
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The MSSM contribution to the trilinear neutral gauge couplings has been calculated in the references [ref] .
New Physics Contribution to Neutral Trilinear Gauge Boson Couplings · MSSM · 0.80
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Keeping these considerations in mind, the issue of sensitivity to linear order of CP-violating anomalous gauge boson couplings, denoted by $λ_1$ ($γZ Z$) and $λ_2$ ($γγZ$) to be defined later, that contribute to the process $e^+e^-→γZ$ with longitudinal beam polarization was considered in Ref. [ref] , and with transverse beam polarization in Ref. [ref] (for earlier discussions in the context of unpolarized beams see Ref. [ref] , and Ref. [ref] for beam polarization effects).
Isolating CP-violating \gamma ZZ coupling in e+e- \to \gamma Z with transverse beam polarizations · Introduction · 0.83
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The most general parametrization of nTGCs in $ZZ$ and $Zγ$ production is given by [ref] , cf. also [ref] ,
Constraining CP violating operators in charged and neutral triple gauge couplings · Neutral aTGCs · 0.81
Discussion
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