The triangle singularity interpretation of the $a_1(1420)$ observed by the COMPASS Collaboration has been widely accepted. In this work, we investigate the triangle mechanism in the decay $B^0 \to D^- \pi^+ a_0(980)(\pi^0 \eta)$ , where the $a_0(980)$ is treated as a dynamically generated state. The $\bar{K}^{*0}$ - $K^+$ - $K^-$ triangle loop originates from the decay $B^0 \to D^- K^+ \bar{K}^{*0}$ , which has been observed by the Belle Collaboration, followed by the subsequent decay $\bar{K}^{*0} \to K^- \pi^+$ . The triangle amplitude develops a pronounced peak around 1420 MeV, which is reflected in the invariant mass spectrum of the $\pi a_0(980)$ system. The differential decay width is calculated and exhibits a narrow peak around $980~\mathrm{MeV}$ in the $\pi^0 \eta$ invariant mass distribution. Furthermore, the invariant mass distribution of the $\pi^+ \pi^0 \eta$ system shows a clear peak around $1420~\mathrm{MeV}$ , which further confirms the triangle singularity explanation of the $a_1(1420)$ . We expect that the proposed $B^0$ decay mode could provide a potential platform for further exploring the triangle-singularity nature of the $a_1(1420)$ and could be tested in future experiments such as LHCb, BESIII, and Belle II.

China

Wei Wang

Dazhuang He

Xuan Luo

The role of triangle singularity in the $ {B^0 \to D^- \pi^+ a_0(980)(\pi^0 \eta)}$ decay * Dazhuang He is supported by the Heze University doctoral fund project (010008002039037). Xuan Luo is supported by the National Natural Science Foundation of China (12205002)

The color-octet (CO) mechanism is a cornerstone of nonrelativistic QCD, yet knowledge of its long-distance matrix elements remains limited, preventing stringent tests of the theory. We demonstrate that the Artru-Collins asymmetry in hadronic decays of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>P</mi></math>-wave bottomonium state <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>b</mi><mn>2</mn></mrow></msub></math> provides a direct probe of CO dynamics. At leading order, the asymmetry arises exclusively from the CO decay channel, whereas the color-singlet (CS) contribution affects only the unpolarized rate, so that a nonzero signal constitutes unambiguous evidence of the CO mechanism. This observable provides a novel way to extract the ratio <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mn>8</mn></msub></math> between CO and CS matrix elements. Focusing on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><mi mathvariant="normal">ϒ</mi><mo stretchy="false">(</mo><mn>2</mn><mi>S</mi><mo stretchy="false">)</mo><mo stretchy="false">→</mo><mi>γ</mi><msub><mrow><mi>χ</mi></mrow><mrow><mi>b</mi><mn>2</mn></mrow></msub></mrow></math> at Belle, we show that the asymmetric beam configuration preserves the asymmetry in the laboratory frame and avoids the strong suppression present in the center-of-mass frame. With the Belle II dataset, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mn>8</mn></msub></math> could be determined with sufficient precision to address the long-standing discrepancy between the lattice calculations and phenomenological determinations.

Zhi-Guo He

Guanghui Li

Yu-Jie Tian

Xin-Kai Wen

Bin Yan

Probing the Color-Octet Mechanism via Dihadron Fragmentation in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>χ</mi></mrow><mrow><mi>b</mi></mrow></msub></mrow></math> Decays

The total decay widths of heavy mesons can be systematically calculated in terms of an expansion in the two parameters 1/$\textit{m}$ and $\textit{α}$ ($\textit{m}$ ), where $\textit{Q}$ = $\textit{c}$, $\textit{b}$ denotes the heavy quark. The dominant contributions to meson lifetime splittings stem from terms which are suppressed by $$ 1/{m}_Q^3 $$ with respect to the leading universal contribution to the total decay width. We calculate three-loop contributions of order $$ {\alpha}_s^2/{m}_q^3 $$ to the lifetime ratios $$ \tau \left({B}^{+}\right)/\tau \left({B}_d^0\right) $$ , $\textit{τ}$($\textit{D}$ )/$\textit{τ}$($\textit{D}$ ), and $$ \tau \left({D}_s^{+}\right)/\tau \left({D}^0\right) $$ in the limit of exact isospin and V-spin symmetry, respectively. Furthermore, we present new $$ {\alpha}_s/{m}_q^3 $$ corrections to the Cabibbo-suppressed terms in $$ \tau \left({B}^{+}\right)/\tau \left({B}_d^0\right) $$ . Combining our perturbative coefficients with hadronic matrix elements calculated from Heavy Quark Effective Theory sum rules, we find $$ \tau \left({B}^{+}\right)/\tau \left({B}_d^0\right) $$ = 1.072 ± 0.024. Using hadronic matrix elements from a recent lattice QCD calculation we find $\textit{τ}$($\textit{D}$ )/$\textit{τ}$($\textit{D}$ ) = 2.344 ± 0.170 and $$ \tau \left({D}_s^{+}\right)/\tau \left({D}^0\right) $$ = 1.289 ± 0.042. We find good agreement of our predictions with experimental data, which constitutes a successful probe of the calculations of hadronic matrix elements and permits estimates of the unknown $$ 1/{m}_Q^4 $$ contributions as well as the V-spin breaking terms in $$ \tau \left({D}_s^{+}\right)/\tau \left({D}^0\right) $$ .

Germany

Francesco Moretti

Ulrich Nierste

Pascal Reeck

Matthias Steinhauser

Next-to-next-to-leading QCD corrections to the $$ {\mathrm{B}}^{+}-{\mathrm{B}}_{\mathrm{d}}^0 $$ , D+ − D0, and $$ {\mathrm{D}}_{\mathrm{s}}^{+}-{\mathrm{D}}^0 $$ lifetime ratios

We study the nonleptonic weak decays of doubly charmed baryons (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>c</mi><mi>c</mi></mrow></msub></math>) into singly charmed baryons (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mi>c</mi></msub></math>) and vector mesons (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi></math>), denoted as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>c</mi><mi>c</mi></mrow></msub><mo stretchy="false">→</mo><msub><mi mathvariant="script">B</mi><mi>c</mi></msub><mi>V</mi></math>. The short-distance contributions are calculated within the naive factorization hypothesis, while the long-distance final-state interaction effects are modeled via hadronic triangle diagrams. Unlike previous approaches, which compute only the imaginary part using the Cutkosky cutting rule, we evaluate the complete loop integrals to obtain both the real and imaginary parts of the amplitudes. These provide the nontrivial strong phases essential for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> violation. The model parameters are determined using experimental data. With this improved calculation method, we predict the branching ratios and decay asymmetry parameters for various decay channels, as well as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> violations for short-distance dominated and singly Cabibbo-suppressed channels. This strengthens our theoretical framework for future study of doubly charmed baryons. Certain decays, primarily driven by long-distance effects, have been calculated, and their observation in future experiments could help clarify the role of final-state interactions in charm baryon decays. Therefore, our calculation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>c</mi><mi>c</mi></mrow></msub><mo stretchy="false">→</mo><msub><mi mathvariant="script">B</mi><mi>c</mi></msub><mi>V</mi></math> provides crucial predictions for branching ratios, decay asymmetry parameters, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> violation, which are essential for guiding experimental study at LHCb.

Xiao-Hui Hu

Fu-Sheng Yu

Ye Xing

Final-state rescattering mechanism of doubly-charmed baryon decays: <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>c</mi><mi>c</mi></mrow></msub><mo stretchy="false">→</mo><msub><mi mathvariant="script">B</mi><mi>c</mi></msub><mi>V</mi></math>

We analyze the semileptonic $$B \rightarrow T\ell ^+\ell ^-$$ , $$B \rightarrow T(\rightarrow PP)\ell ^+\ell ^-$$ , and $$B \rightarrow T(\rightarrow PV)\ell ^+\ell ^-$$ decays with $$\ell =e,\mu ,\tau $$ based on flavor SU(3) analysis in the standard model ($\textit{T}$ denotes the light tensor meson, $\textit{P}$ denotes the light pseudoscalar meson, and $\textit{V}$ denotes the light vector meson). The hadronic amplitudes of the $$B \rightarrow T\ell ^+\ell ^-$$ decays are related by the nonperturbative parameters, and all branching ratios of the $$B \rightarrow T\ell ^+\ell ^-$$ decays are obtained by the experimental data of the branching ratio of $$B^0_s\rightarrow f^{\prime }_{2}(1525)\mu ^+\mu ^-$$ in three cases, and then the branching ratios of the $$B \rightarrow T(\rightarrow PP)\ell ^+\ell ^-$$ and $$B \rightarrow T(\rightarrow PV)\ell ^+\ell ^-$$ decays are predicted by the narrow width approximation and further considering finite width effects of the intermediate resonances. Compared with the narrow width results, the finite width effects slightly reduce the branching fractions for most decays. However, sizeable finite width effects are found in some near threshold modes. For the subthreshold $$K_2^*(1430)\rightarrow K\eta '$$ relevant channels, the finite width of the tensor resonance can open a nonzero contribution. Compared with the measured $$B \rightarrow PP\ell ^+\ell ^-$$ and $$B \rightarrow PV\ell ^+\ell ^-$$ decays, we find that the branching ratios with the tensor resonance states are small. Therefore, other resonances, for example, the vector mesons, the scalar mesons, the axial-vector mesons or their excited states, might give the dominant contributions to the relevant decays. Our results might be tested in current and future experiments.

Ru-Min Wang

Xiu-Ping Fan

Si-Yu Xu

Yi Qiao

Xiao-Dong Cheng

Yuan-Guo Xu

Studying the tensor resonance contributions in $$B \rightarrow PP\ell ^+\ell ^-$$ and $$B \rightarrow PV\ell ^+\ell ^-$$ decays

In the conventional gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> extension of the standard model, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> charge of the singlet scalar <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>χ</mi></math>, responsible for the breaking of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> symmetry, is taken to be 2, such that it can anchor type-I seesaw by giving Majorana masses to the right-handed neutrinos, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math>. In this paper, we consider instead the cases <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>χ</mi><mo>∼</mo><mn>3</mn></math> or 4 under <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math>, so that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math> may not acquire any Majorana mass and neutrinos are Dirac fermions. We then consider a vectorlike fermion <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math> with two units of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> charge, which becomes a good candidate for dark matter, either Dirac for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>χ</mi><mo>∼</mo><mn>3</mn></math> or Majorana for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>χ</mi><mo>∼</mo><mn>4</mn></math>. In both cases, spontaneous <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> breaking can induce a strong first-order phase transition, producing stochastic gravitational waves (GW), which can be tested at GW experiments. Moreover, the presence of light <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>R</mi></msub></math>s gives rise to an additional contribution to the effective number of relativistic degrees of freedom, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><msub><mi>N</mi><mi>eff</mi></msub></math>, providing complementary constraints from current and upcoming CMB observations.

United States

Ernest Ma

India

Partha Kumar Paul

Narendra Sahu

Naturally small Dirac neutrino mass and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> dark matter

Mesogenesis provides a path for generating the baryon asymmetry of the Universe, using only the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> violation furnished by the Standard Model in the decay of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> mesons. While this is an intriguing possibility, it is largely constrained by the data on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> meson branching fractions into baryons and missing energy carried into the dark sector. We point out that it is possible to make this branching fraction dominant only in the early Universe, through an ultralight scalar coupled to the dark sector and the Standard Model leptons. A scenario is examined where the thermal density of muons in the early Universe temporarily lowers the mass of a dark fermion, allowing for efficient <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> meson decays. This “dark” decay channel is shut off later when the muon number density falls, making the scenario compatible with flavor data. Our model can be consistent with the LHC constraints on color-charged heavy bosons required to implement mesogenesis; such states may be discovered in the future runs as their masses cannot be far above the current bounds. We also outline other possible signals, which can arise in future displaced vertex searches, long range force searches, and observations of neutron star binary mergers.

Hooman Davoudiasl

Rachel Houtz

Canada

Seyda Ipek

Mesogenesis through the ephemeral dark decay of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>B</mi></mrow></math> mesons

We perform a measurement of time-dependent $\textit{CP}$ violation parameters in $${B}^{0}\to {K}_{\text{S}}^{0}{\pi }^{0}\gamma $$ decays using a dataset of approximately 772 × 10 and 521 × 10 Υ(4$\textit{S}$) decays collected by the Belle and Belle II experiments, respectively. The measured parameters for the combined dataset in the $\textit{K}$ (892) dominated region ( $${M}_{{K}_{\text{S}}^{0}{\pi }^{0}}\in \left[{0.8,1.0}\right]$$ GeV/$\textit{c}$ ) are $\textit{S}$ = 0.09 $\textit{±}$ 0.16 $\textit{±}$ 0.02 and $\textit{C}$ = $\textit{−}$0.09 $\textit{±}$ 0.08 $\textit{±}$ 0.04. For the non-$\textit{K}$ (892) region ( $${M}_{{K}_{\text{S}}^{0}{\pi }^{0}}\in \left({1.0,1.8}\right]$$ GeV/$\textit{c}$ ), the corresponding values are $\textit{S}$ = −0.32 ± 0.33 ± 0.09 and $\textit{C}$ = −0.07 ± 0.17 ± 0.08. The first quoted uncertainties are statistical, while the second ones are systematic. These results are consistent with Standard Model predictions and more precise than previous measurements.

M. Abumusabh

I. Adachi

A. Aggarwal

Y. Ahn

H. Aihara

M. Akdag

N. Akopov

S. Alghamdi

M. Alhakami

N. Althubiti

K. Amos

M. Angelsmark

C. Antonioli

K. Arai

H. Atmacan

T. Aushev

V. Aushev

R. Ayad

V. Babu

H. Bae

N. Baghel

S. Bahinipati

P. Bambade

Sw. Banerjee

S. Bansal

M. Barrett

M. Bartl

J. Baudot

A. Beaubien

F. Becherer

J. Becker

G. Benfratello

J. Bennett

F. Bernlochner

V. Bertacchi

M. Bertemes

E. Bertholet

M. Bessner

S. Bettarini

V. Bhardwaj

B. Bhuyan

F. Bianchi

T. Bilka

D. Biswas

A. Bobrov

D. Bodrov

A. Bondar

G. Bonvicini

J. Borah

A. Boschetti

A. Bozek

M. Bračko

P. Branchini

N. Brenny

R. Briere

T. Browder

A. Budano

S. Bussino

F. Callet

Q. Campagna

M. Campajola

L. Cao

M. Carminati

G. Casarosa

C. Cecchi

P. Cheema

L. Chen

B. Cheon

C. Cheshta

H. Chetri

K. Chilikin

K. Chirapatpimol

H. Cho

K. Cho

S.J. Cho

S.K. Choi

S. Choudhury

S. Chutia

J. Cochran

J. Colorado-Caicedo

I. Consigny

L. Corona

H. Crotte Ledesma

S. Cuccuini

J. Cui

S. Das

E. De La Cruz-Burelo

S. De La Motte

G. Marino

G. De Nardo

G. De Pietro

R. Sangro

M. Destefanis

S. Dey

R. Dhayal

A. Di Canto

J. Dingfelder

Z. Doležal

X. Dong

D. Thanh

Measurement of time-dependent $\textit{CP}$ violation parameters in $${B}^{0}\to {K}_{\text{S}}^{0}{\pi }^{0}\gamma $$ decays at Belle and Belle II

We perform a model-independent study of new physics effects in the Higgs decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi mathvariant="normal">ϒ</mi><mi>γ</mi></math>, focusing on scenarios that spoil the accidental cancellation between the direct and indirect amplitudes. After imposing all existing constraints from Higgs production and decay measurements, we find that a wrong-sign <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>b</mi><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover></math> coupling is the only viable scenario capable of enhancing the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi mathvariant="normal">ϒ</mi><mi>γ</mi></math> decay width by nearly 2 orders of magnitude. Therefore, an observation of a significantly enhanced <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi mathvariant="normal">ϒ</mi><mi>γ</mi></math> rate at the LHC or future colliders would provide unambiguous evidence for a wrong-sign <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>b</mi><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover></math> coupling, directly pointing to the presence of an extended Higgs sector.

Portugal

Aditya Batra

South Korea

Sanjoy Mandal

Rahul Srivastava

<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi mathvariant="normal">ϒ</mi><mi>γ</mi></math> decay: Smoking gun signature of a wrong-sign <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>b</mi><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover></math> coupling

We introduce a new method for the determination of the ratio of production fractions $$ {R}^{\pm 0}=\mathcal{B}\left(\mathrm{Y}(4S)\to {B}^{+}{B}^{-}\right)/\mathcal{B}\left(\mathrm{Y}(4S)\to {B}^0{\overline{B}}^0\right) $$ based on $$ \overline{B}\to {D}^{\left(\ast \right)}\ell \overline{\nu} $$ decays. Given the importance of these modes, we perform a comprehensive analysis of the available data, extracting the information on their branching fractions and $\textit{R}$ in parallel and providing their correlations in order to avoid double-use of this information in phenomenological analyses. We obtain the most precise value for $\textit{R}$ from a single channel so far, about 2$\textit{σ}$ from unity. The combination with previously available determinations from other channels yields $\textit{R}$ = 1.062(19), constituting evidence for isospin violation in Υ(4$\textit{S}$) decays. This demonstrates the necessity to take this effect into account in experimental and phenomenological analyses. The results for the $$ \overline{B}\to {D}^{\left(\ast \right)}\ell \overline{\nu} $$ branching fractions are up to 1$\textit{.}$6$\textit{σ}$ larger compared to averages available in the literature, owing to the removal of overlooked inconsistencies in the treatment of older analyses and correcting for d’Agostini bias where possible, thereby reducing the $\textit{V}$ puzzle.

Italy

Martin Jung

United Kingdom

Stefan Schacht

$$ \overline{B}\to {D}^{\left(\ast \right)}\ell \overline{\nu} $$ branching ratios and evidence for isospin breaking in Υ(4$\textit{S}$) decays