The X17 boson and the $^3$H$(p,e^+ e^-)^4$He and $^3$He$(n,e^+ e^-)^4$He processes: a theoretical analysis

A. Kievsky; C. Gustavino; E. Filandri; L.E. Marcucci; L. Girlanda; M. Viviani; R. Schiavilla

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The X17 boson and the $^3$H$(p,e^+ e^-)^4$He and $^3$He$(n,e^+ e^-)^4$He processes: a theoretical analysis

M. Viviani, E. Filandri, L. Girlanda, C. Gustavino, A. Kievsky, L.E. Marcucci, R. Schiavilla

Nuclear Theory · Submitted 15 Apr 2021

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The authors' main claim Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross section for such a process.

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arXiv ID2104.07808 (version 2)

Pith ID7JM2AZY3, Pith's permanent record of this paper and its review

CitationA. Kievsky, C. Gustavino, E. Filandri, L.E. Marcucci, L. Girlanda, M. Viviani, R. Schiavilla. "The X17 boson and the $^3$H$(p,e^+ e^-)^4$He and $^3$He$(n,e^+ e^-)^4$He processes: a theoretical analysis." arXiv:2104.07808 (2021). https://pith.science/paper/7JM2AZY3

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What the abstract itself states, as probabilities: claims first 0.05 · states limitation 0.76 · human participants 0.01 · controlled comparison 0.47 · randomized assignment 0.01 · states quantitative result 0.05 · compares with prior results 0.41 · mentions code or data availability 0.02.

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The present work deals with $e^+$-$e^-$ pair production in the four-nucleon system. We first analyze the process as a purely electromagnetic one in the context of a state-of-the-art approach to nuclear strong-interaction dynamics and nuclear electromagnetic currents, derived from chiral effective field theory ($\chi$EFT). Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross section for such a process. We consider several possibilities, that this boson is either a scalar, pseudoscalar, vector, or axial particle. The ab initio calculations use exact hyperspherical-harmonics methods to describe the bound state and low-energy spectrum of the $A\,$=$\,4$ continuum, and fully account for initial state interaction effects in the $3+1$ clusters. While electromagnetic interactions are treated to high orders in the chiral expansion, the interactions of the hypothetical boson with nucleons are modeled in leading-order $\chi$EFT (albeit, in some instances, selected subleading contributions are also accounted for). We also provide an overview of possible future experiments probing pair production in the $A\,$=$\,4$ system at a number of candidate facilities.facilities.

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What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	The present work deals with $e^+$-$e^-$ pair production in the four-nucleon system.	contribution 0.79	0.41	0.03	asserted 0.78
s1	We first analyze the process as a purely electromagnetic one in the context of a state-of-the-art approach to nuclear strong-interaction dynamics and nuclear electromagnetic currents, derived from chiral effective field theory ($\chi$EFT).	contribution 0.61	0.79	0.03	asserted 0.92
s2	Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross section for such a process.	contribution 0.98	0.72	0.04	unclear 0.31
s3	We consider several possibilities, that this boson is either a scalar, pseudoscalar, vector, or axial particle.	contribution 0.77	0.56	0.03	hedged possibility 0.74
s4	The ab initio calculations use exact hyperspherical-harmonics methods to describe the bound state and low-energy spectrum of the $A\,$=$\,4$ continuum, and fully account for initial state interaction effects in the $3+1$ clusters.	method 1.00	0.86	0.03	asserted 1.00
s5	While electromagnetic interactions are treated to high orders in the chiral expansion, the interactions of the hypothetical boson with nucleons are modeled in leading-order $\chi$EFT (albeit, in some instances, selected subleading contributions are also accounted for).	method 0.80	0.80	0.04	asserted 0.99
s6	We also provide an overview of possible future experiments probing pair production in the $A\,$=$\,4$ system at a number of candidate facilities.facilities.	future work 0.95	0.61	0.03	asserted 0.61

What kind of paper the classifier reports this is: theoretical result 0.73 · evidence from simulation or computation 1.00.

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The paper

Original abstract

The present work deals with $e^+$-$e^-$ pair production in the four-nucleon system. We first analyze the process as a purely electromagnetic one in the context of a state-of-the-art approach to nuclear strong-interaction dynamics and nuclear electromagnetic currents, derived from chiral effective field theory ($\chi$EFT). Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross section for such a process. We consider several possibilities, that this boson is either a scalar, pseudoscalar, vector, or axial particle. The ab initio calculations use exact hyperspherical-harmonics methods to describe the bound state and low-energy spectrum of the $A\,$=$\,4$ continuum, and fully account for initial state interaction effects in the $3+1$ clusters. While electromagnetic interactions are treated to high orders in the chiral expansion, the interactions of the hypothetical boson with nucleons are modeled in leading-order $\chi$EFT (albeit, in some instances, selected subleading contributions are also accounted for). We also provide an overview of possible future experiments probing pair production in the $A\,$=$\,4$ system at a number of candidate facilities.facilities.

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11 arXiv papers cite this in 26 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 · 22 sentences without a confident label

Uses its method or tool 1 paper

The matrix elements $j^μ_EM$ and $j^c_X$ can be decomposed i) by expressing the initial scattering wave function $Ψ_m_2,m_1$ in components of definite total angular momentum and parity and ii) performing a multipolar expansion of the operators (for more details, see Ref. [ref] ).

The X17 boson and the d(p,e+ e-)3He and d(n,e+ e-)3H processes: a theoretical analysis · Decomposition of the matrix elements · 0.95

Uses its data or values 1 paper

These values were obtained in Ref. [ref] by reproducing the 2019 ATOMKI data for the process $(p,e^+ e^-)$, using the same NVIa3N interaction employed here.

The X17 boson and the d(p,e+ e-)3He and d(n,e+ e-)3H processes: a theoretical analysis · Results including the X17 boson · 0.99

Cites it as background 1 paper

The signals have generated a great deal of theoretical interest in both the particle and nuclear physics communities [ref] .

Quantum Chromodynamics Resolution of the ATOMKI Anomaly in ${\rm {^4He}}$ Nuclear Transitions · Introduction · 0.95

What it cites · 104 sentences without a confident label

Uses the method or tool of 7 papers

HH methods, as described in considerable detail in Refs. [ref] , are used to calculate the $A$=$3$–4 bound- and scattering-state wave functions.

Study of $n+{}^3$H, $p+{}^3$He, $p+{}^3$H, and $n+{}^3$He scattering with the HH method · Hamiltonians and wave functions · 0.99
HH methods, as described in considerable detail in Refs. [ref] , are used to calculate the $A$=$3$–4 bound- and scattering-state wave functions.

A high-precision variational approach to three- and four-nucleon bound and zero-energy scattering states · Hamiltonians and wave functions · 0.99
HH methods, as described in considerable detail in Refs. [ref] , are used to calculate the $A$=$3$–4 bound- and scattering-state wave functions.

The Hyperspherical Harmonics method: a tool for testing and improving nuclear interaction models · Hamiltonians and wave functions · 0.99

Uses data or values from 10 papers

In the more recent Ref. [ref] , “background-free” $(p,e^-e^+)$ reaction data are also reported, obtained by subtracting the counting rate due to “external” pair conversion (EPC) processes.

A new anomaly observed in $^4$He supports the existence of the hypothetical X17 particle · Numerical results: angular correlations · 0.81
For $M_X≈17$ MeV, the most stringent lower bound, $|ε_e| > 2 ×10^-4$, comes from the SLAC E141 experiment [ref] , while the upper bound $|ε_e|< 2 ×10^-3$ has been set by the KLOE-2 experiment [ref] .

Limit on the production of a low-mass vector boson in $\mathrm{e}^{+}\mathrm{e}^{-} \to \mathrm{U}\gamma$, $\mathrm{U} \to \mathrm{e}^{+}\mathrm{e}^{-}$ with the KLOE experiment · Motivation and current status · 1.00
One of the most stringent limits was provided by the NA48/2 experiment, which set $ε< 8 ×10^-4$ at $90$% confidence level [ref] .

Search for the dark photon in $\pi^0$ decays · Motivation and current status · 0.98

Compares with 4 papers

From our fit to the 2019 ATOMKI data, the nucleon coupling constant, Eq. ([ref]), is estimated to be $g^P_0≡e η_0^P≈0.3$, two orders of magnitude larger than obtained in Refs. [ref] .

New Physics Suggested by Atomki Anomaly · Comparing to previous determinations of the X17 coupling constants · 0.98
From our fit to the 2019 ATOMKI data, the nucleon coupling constant, Eq. ([ref]), is estimated to be $g^P_0≡e η_0^P≈0.3$, two orders of magnitude larger than obtained in Refs. [ref] .

Signals of the QCD axion with mass of 17 MeV/c^2: nuclear transitions and light meson decays · Comparing to previous determinations of the X17 coupling constants · 0.98
In Ref. [ref] the coupling constants $ϵ_u$ and $ϵ_d$, entering $V$ exchange, were obtained by fitting the branching ratio for the $$ anomaly, with typical values of the order $∼ 10^-3$.

Protophobic Fifth Force Interpretation of the Observed Anomaly in $^8$Be Nuclear Transitions · Comparing to previous determinations of the X17 coupling constants · 0.91

Cites as background 21 papers

In Ref. [ref] , a number of alternatives—that the X17 could be a scalar, a pseudoscalar, or a vector boson—were analyzed.

Protophobic Fifth Force Interpretation of the Observed Anomaly in $^8$Be Nuclear Transitions · Motivation and current status · 0.83
Soon after, the possibility that the X17 could be a spin-1 particle interacting via axial couplings to the $u$ and $d$ quarks was explored in Ref. [ref] .

Light Axial Vectors, Nuclear Transitions, and the $^8$Be Anomaly · Motivation and current status · 0.93
In a more recent paper [ref] —see also Ref. [ref] for a similar study—the possibility that the peak seen in the $$ experiment could be caused by higher-order QED effects, beyond the one-photon-exchange approximation, has been investigated.

X17: A new force, or evidence for a hard $\gamma +\gamma$ process? · Motivation and current status · 0.84

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