The radiative corrections to the <math><mrow><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><mo>(</mo><msub><mrow><mi>P</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>P</mi></mrow><mrow><mn>2</mn></mrow></msub><msup><mrow><mo>)</mo></mrow><mrow><mo>−</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mi>τ</mi></mrow></msub></mrow></math> (<math><msub><mi>P</mi><mrow><mn>1</mn><mo>,</mo><mn>2</mn></mrow></msub><mo>=</mo><mi>π</mi></math>, <math><mrow><mi>K</mi></mrow></math>) decays are calculated for the first time including the structure-dependent real photon corrections, which are obtained using resonance chiral theory. Our results, whose uncertainty is dominated by the model dependence of the resummation of the radiative corrections and the missing virtual structure-dependent contributions, allow for precise tests of Cabibbo-Kobayashi-Maskawa unitarity, lepton flavor universality, and nonstandard interactions.

Spain

Rafel Escribano

Jesús Alejandro Miranda

Mexico

Pablo Roig

Radiative corrections to the <math><mrow><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><mo>(</mo><msub><mrow><mi>P</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>P</mi></mrow><mrow><mn>2</mn></mrow></msub><msup><mrow><mo>)</mo></mrow><mrow><mo>−</mo></mrow></msup><msub><mrow><mi>v</mi></mrow><mrow><mi>τ</mi></mrow></msub></mrow></math> (<math><mrow><msub><mrow><mi>P</mi></mrow><mrow><mn>1</mn><mo>,</mo><mn>2</mn></mrow></msub><mo>=</mo><mi>π</mi><mo>,</mo><mi>K</mi></mrow></math>) decays

The sensitivity of the rare decays <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>(</mo><mo>′</mo><mo>)</mo></mrow></msup><mo>→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>γ</mi><mi>γ</mi></mrow></math> and <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>→</mo><mi>η</mi><mi>γ</mi><mi>γ</mi></mrow></math> to signatures of a leptophobic <math><mi>B</mi></math> boson in the MeV–GeV mass range is analyzed in this work. By adding an explicit <math><mi>B</mi></math>-boson resonance exchange, <math><mrow><mi>η</mi><mo>→</mo><mi>B</mi><mi>γ</mi><mo>→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>γ</mi><mi>γ</mi></mrow></math>, to the Standard Model contributions from vector and scalar meson exchanges, and employing experimental data for the associated branching ratios, it allows us to improve the current constraints on the <math><mi>B</mi></math>-boson mass <math><msub><mi>m</mi><mi>B</mi></msub></math> and coupling to Standard Model particles <math><msub><mi>α</mi><mi>B</mi></msub></math>. From these constraints and the analysis of the available experimental <math><mi>γ</mi><mi>γ</mi></math> invariant mass distribution, we show that a <math><mi>B</mi></math>-boson signature in the resonant mass range <math><mrow><msub><mrow><mi>m</mi></mrow><mrow><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></msub><mo>≲</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>≲</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>η</mi></mrow></msub></mrow></math> is strongly suppressed and would be very difficult to experimentally identify, assuming that the leptophobic <math><mi>B</mi></math> boson only decays to Standard Model particles. In contrast, the limits outside this mass window are less stringent and the corresponding <math><mi>t</mi></math>- and <math><mi>u</mi></math>-channel signatures may still be observable in the data, as it occurs with the nonresonant Standard Model <math><mi>ρ</mi></math>, <math><mi>ω</mi></math> and <math><mi>ϕ</mi></math> meson exchanges. In addition, we make use of experimental data from the <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi><mi>γ</mi></math> and <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><mi>η</mi><mi>γ</mi><mi>γ</mi></math> decays to explore larger <math><mi>B</mi></math>-boson masses. Our results are relevant for the <math><mi>B</mi></math>-boson search programs at existing and forthcoming light-meson facilities, such as KLOE(-II) and Jefferson Lab Eta Factory experiments.

United States

Sergi Gonzàlez-Solís

Emilio Royo

Sensitivity of the <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>(</mo><mo>′</mo><mo>)</mo></mrow></msup><mo>→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>γ</mi><mi>γ</mi></mrow></math> and <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>→</mo><mi>η</mi><mi>γ</mi><mi>γ</mi></mrow></math> decays to a sub-GeV leptophobic <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>B</mi></msub></math> boson

This erratum corrects Eqs. (6) and (15), Table 1, and Fig. 2 of the original article. An additional footnote is added at the end of the first paragraph in Section III. Finally, the paragraph discussing the use of the energy-dependent width for the  $$\rho ^0$$  <math> <msup> <mi>ρ</mi> <mn>0</mn> </msup> </math>   propagator is modified.

Erratum to: A theoretical analysis of the semileptonic decays  $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mrow> <mo>(</mo> <mo>′</mo> <mo>)</mo> </mrow> </msup> <mo>→</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   and  $$\eta ^\prime \rightarrow \eta l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mo>′</mo> </msup> <mo>→</mo> <mi>η</mi> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>

In this work we investigate the prospect of observing new-physics signatures via CP violation in η (′) → π 0 μ + μ  −  and η′ → ημ + μ  −  decays at the REDTOP experiment. We make use of the SMEFT to parametrise the new-physics CP-violating effects and find that the projected REDTOP statistics are not competitive with respect to nEDM experiments. This reasserts the η → μ + μ  −  process as the most promising channel to find CP-violation at this experimental facility.

Pablo Sanchez-Puertas

New-physics signatures via CP violation in η (′) → π 0 μ + μ  −  and η′ → ημ + μ  −  decays

In theories with a warped extra dimension, composite fermions, as e.g. the right-handed top quark, can be very strongly coupled to Kaluza-Klein (KK) fields. In particular, the KK gluons in the presence of such composite fields become very broad resonances, thus remarkably modifying their experimental signatures. We have computed the pole mass and the pole width of the KK gluon, triggered by its interaction with quarks, as well as the prediction for proton-proton cross-sections using the full propagator and compared it with that obtained from the usual Breit-Wigner approximation. We compare both approaches, along with the existing experimental data from ATLAS and CMS, for the   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$ ,   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>W</mi> </math>  $$ t\overline{t}W $$ ,   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>Z</mi> </math>  $$ t\overline{t}Z $$ ,   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>H</mi> </math>  $$ t\overline{t}H $$ , and   <math> <mi>tt</mi> <mover> <mi>tt</mi> <mo>¯</mo> </mover> </math>  $$ tt\overline{tt} $$  channels. We have found differences between the two approaches of up to about 100%, highlighting that the effect of broad resonances can be dramatic on present, and mainly future, experimental searches. The channel   <math> <mi>tt</mi> <mover> <mi>tt</mi> <mo>¯</mo> </mover> </math>  $$ tt\overline{tt} $$  is particularly promising because the size of the cross-section signal is of the same order of magnitude as the Standard Model prediction, and future experimental analyses in this channel, especially for broad resonances, can shed light on the nature of possible physics beyond the Standard Model.

Germany

Mikel Mendizabal

Mariano Quirós

On broad Kaluza-Klein gluons

The original version of this article was revised as the authors were only affiliated to one affiliation in the published version.

Erratum to: A theoretical analysis of the semileptonic decays  $$\eta ^{(\prime )}\rightarrow {\pi ^0}{l}^+{l}^-$$  <math> <mrow> <msup> <mi>η</mi> <mrow> <mo>(</mo> <mo>′</mo> <mo>)</mo> </mrow> </msup> <mo>→</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> <msup> <mrow> <mi>l</mi> </mrow> <mo>+</mo> </msup> <msup> <mrow> <mi>l</mi> </mrow> <mo>-</mo> </msup> </mrow> </math>   and  $$\eta ^{\prime } \rightarrow \eta {l}^+{l}^-$$  <math> <mrow> <msup> <mi>η</mi> <mo>′</mo> </msup> <mo>→</mo> <mi>η</mi> <msup> <mrow> <mi>l</mi> </mrow> <mo>+</mo> </msup> <msup> <mrow> <mi>l</mi> </mrow> <mo>-</mo> </msup> </mrow> </math>

A complete theoretical analysis of the C- conserving semileptonic decays  $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mrow> <mo>(</mo> <mo>′</mo> <mo>)</mo> </mrow> </msup> <mo>→</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   and  $$\eta ^\prime \rightarrow \eta l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mo>′</mo> </msup> <mo>→</mo> <mi>η</mi> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   ( $$l=e$$  <math> <mrow> <mi>l</mi> <mo>=</mo> <mi>e</mi> </mrow> </math>   or  $$\mu $$  <math> <mi>μ</mi> </math>  ) is carried out within the framework of the Vector Meson Dominance (VMD) model. An existing phenomenological model is used to parametrise the VMD coupling constants and the associated numerical values are obtained from an optimisation fit to  $$V\rightarrow P\gamma $$  <math> <mrow> <mi>V</mi> <mo>→</mo> <mi>P</mi> <mi>γ</mi> </mrow> </math>   and  $$P\rightarrow V\gamma $$  <math> <mrow> <mi>P</mi> <mo>→</mo> <mi>V</mi> <mi>γ</mi> </mrow> </math>   radiative decays ( $$V=\rho ^0$$  <math> <mrow> <mi>V</mi> <mo>=</mo> <msup> <mi>ρ</mi> <mn>0</mn> </msup> </mrow> </math>  ,  $$\omega $$  <math> <mi>ω</mi> </math>  ,  $$\phi $$  <math> <mi>ϕ</mi> </math>   and  $$P=\pi ^0$$  <math> <mrow> <mi>P</mi> <mo>=</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> </mrow> </math>  ,  $$\eta $$  <math> <mi>η</mi> </math>  ,  $$\eta ^{\prime }$$  <math> <msup> <mi>η</mi> <mo>′</mo> </msup> </math>  ). The decay widths and dilepton energy spectra for the two  $$\eta \rightarrow \pi ^0l^+l^-$$  <math> <mrow> <mi>η</mi> <mo>→</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   processes obtained using this approach are compared and found to be in good agreement with other results available in the published literature. Theoretical predictions for the four  $$\eta ^{\prime }\rightarrow \pi ^0l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mo>′</mo> </msup> <mo>→</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   and  $$\eta ^\prime \rightarrow \eta l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mo>′</mo> </msup> <mo>→</mo> <mi>η</mi> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   decay widths and dilepton energy spectra are calculated and presented for the first time in this work.

A theoretical analysis of the semileptonic decays  $$\eta ^{(\prime )}\rightarrow \pi ^0l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mrow> <mo>(</mo> <mo>′</mo> <mo>)</mo> </mrow> </msup> <mo>→</mo> <msup> <mi>π</mi> <mn>0</mn> </msup> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>   and  $$\eta ^\prime \rightarrow \eta l^+l^-$$  <math> <mrow> <msup> <mi>η</mi> <mo>′</mo> </msup> <mo>→</mo> <mi>η</mi> <msup> <mi>l</mi> <mo>+</mo> </msup> <msup> <mi>l</mi> <mo>-</mo> </msup> </mrow> </math>

The scalar and vector meson exchange contributions to the doubly radiative decays <math><msup><mi>η</mi><mrow><mo>(</mo><mo>′</mo><mo>)</mo></mrow></msup><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi><mi>γ</mi></math> and <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><mi>η</mi><mi>γ</mi><mi>γ</mi></math> are analyzed within the linear sigma model and vector meson dominance frameworks, respectively. Predictions for the diphoton invariant mass spectra and the associated integrated branching ratios are given and compared with current available experimental data. While a satisfactory description of the shape of the <math><mi>η</mi><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi><mi>γ</mi></math> and <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi><mi>γ</mi></math> decay spectra is obtained, thus supporting the validity of the approach, the corresponding branching ratios cannot be reproduced simultaneously. A first theoretical prediction for the recently measured <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><mi>η</mi><mi>γ</mi><mi>γ</mi></math> by the BESIII Collaboration is also presented.

China

Romania

Renata Jora

Theoretical analysis of the doubly radiative decays <math><msup><mi>η</mi><mrow><mo>(</mo><mo>′</mo><mo>)</mo></mrow></msup><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>γ</mi><mi>γ</mi></math> and <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><mi>η</mi><mi>γ</mi><mi>γ</mi></math>

An enhanced phenomenological model that includes isospin-symmetry breaking is presented in this letter. The model is then used in a number of statistical fits to the most recent experimental data for the radiative transitions VPγ (<math><mi>V</mi><mo>=</mo><mi>ρ</mi></math>, <math><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math>, ω, ϕ and <math><mi>P</mi><mo>=</mo><mi>π</mi></math>, K, η, <math><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup></math>) and estimations for the mixing angles amongst the three pseudoscalar states with vanishing third-component of isospin are obtained. The quality of the performed fits is good, e.g. <math><msubsup><mrow><mi>χ</mi></mrow><mrow><mtext>min</mtext></mrow><mrow><mn>2</mn></mrow></msubsup><mo>/</mo><mtext>d.o.f</mtext><mo>=</mo><mn>1.9</mn></math>. The current experimental uncertainties allow for isospin-symmetry violations with a confidence level of approximately 2.5σ.

- - ′ Mixing From → And → Decays

The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays and (; or ) are predicted by means of a data-driven approach based on the use of rational approximants applied to and transition form factor experimental data in the space-like region.

A data-driven approach to and single and double Dalitz decaysSupported by the FPI scholarship BES-2012-055371 (S.G-S), the Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya under grant 2014 SGR 1450, the Ministerio de Ciencia e Innovación under grant FPA2011-25948, the Ministerio de Economía y Competitividad under grants CICYT-FEDER-FPA 2014-55613-P and SEV-2012-0234, the Spanish Consolider-Ingenio 2010 Program CPAN (CSD2007-00042), and the European Commission under program FP7-INFRASTRUCTURES-2011-1 (283286) S.G-S also Received Support from the CAS President’s International Fellowship Initiative for Young International Scientist (2017PM0031)