Recently the Belle II Collaboration has reported a measurement of the $\textit{B}$ → $$ {K}^{+}\nu \overline{\nu} $$ rate that is higher than the standard-model expectation. Since the emitted neutrinos are unobserved, the excess could be due to the $\textit{B}$ decaying into a $\textit{K}$ and a dark-matter pair. We entertain this possibility in a two-Higgs-doublet model supplemented with a real singlet scalar boson acting as the dark matter. This model also accommodates strangeness-changing interactions providing new sources of $\textit{CP}$ violation which can affect hyperon and kaon nonleptonic transitions. We find that the resulting $\textit{CP}$ violation in the hyperon sector can be significant, reaching the current empirical bounds, after taking into account constraints from kaon mixing and decay and from dark-matter relic-density data and direct searches including the Migdal effect. We demonstrate that the hyperon and kaon processes are complementary probes of this new-physics scenario. Its prediction for sizable hyperon $\textit{CP}$ violation is potentially testable in ongoing experiments, such as BESIII, Belle II, and LHCb, and in next-generation ones like PANDA and at the Super Tau Charm Facility.

China

Xiao-Gang He

Xiao-Dong Ma

Jusak Tandean

Australia

German Valencia

$\textit{B → K}$+ invisible, dark matter, and $\textit{CP}$ violation in hyperon decays

We search for the leptonic decay $ D^+\to e^+\nu_{e} $ using an $ e^+e^- $ collision data sample with an integrated luminosity of 20.3 fb $ ^{-1} $ collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. Significant signal is not observed, and an upper limit on the branching fraction of $ D^+\to e^+\nu_{e} $ is set as $ 9.7 \times 10^{-7} $ , at a confidence level of 90%. Our upper limit is an order of magnitude smaller than the previous limit for this decay mode.

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

Germany

O. Afedulidis

X.C. Ai

R. Aliberti

Italy

A. Amoroso

Q. An

Y. Bai

O. Bakina

I. Balossino

Y. Ban

H.R. Bao

Poland

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

United States

R.A. Briere

A. Brueggemann

H. Cai

X. Cai

A. Calcaterra

G.F. Cao

N. Cao

Türkiye

S.A. Cetin

X.Y. Chai

J.F. Chang

G.R. Che

Y.Z. Che

G. Chelkov

C. Chen

C.H. Chen

Chao Chen

G. Chen

H.S. Chen

H.Y. Chen

M.L. Chen

S.J. Chen

S.L. Chen

S.M. Chen

T. Chen

X.R. Chen

X.T. Chen

Y.B. Chen

Y.Q. Chen

Z.J. Chen

Z.Y. Chen

S.K. Choi

G. Cibinetto

F. Cossio

J.J. Cui

H.L. Dai

J.P. Dai

A. Dbeyssi

R.E. de Boer

D. Dedovich

C.Q. Deng

Z.Y. Deng

A. Denig

I. Denysenko

M. Destefanis

F. De Mori

B. Ding

X.X. Ding

Y. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

M.C. Du

S.X. Du

Y.Y. Duan

Z.H. Duan

P. Egorov

Y.H. Fan

J. Fang

S.S. Fang

W.X. Fang

Y. Fang

Y.Q. Fang

R. Farinelli

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

Y.T. Feng

M. Fritsch

C.D. Fu

J.L. Fu

Y.W. Fu

H. Gao

Search for the leptonic decay ${\boldsymbol D^{\bf +}{\bf\to}{\boldsymbol e}^{\bf +}\boldsymbol\nu_{\boldsymbol e}}$ * Supported in part by the National Key R&D Program of China (2023YFA1606000, 2020YFA0406400, 2020YFA0406300), the National Natural Science Foundation of China(NSFC) (11635010, 11735014, 11935015, 11935016, 11875054, 11935018, 12025502, 12035009, 12035013, 12061131003, 12192260, 12192261, 12192262, 12192263, 12192264, 12192265, 12221005, 12225509, 12235017, 12361141819), the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program, the CAS Center for Excellence in Particle Physics (CCEPP), the Joint Large-Scale Scientific Facility Funds of the NSFC and CAS (U2032104, U1832207), the 100 Talents Program of CAS, the Excellent Youth Foundation of Henan Scientific Commitee (242300421044), the Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology, the German Research Foundation DFG (FOR5327), the Istituto Nazionale di Fisica Nucleare, Italy, the Knut and Alice Wallenberg Foundation (2021.0174, 2021.0299), the Ministry of Development of Turkey (DPT2006K-120470), the National Research Foundation of Korea (NRF-2022R1A2C1092335), the National Science and Technology Fund of Mongolia, the National Science Research and Innovation Fund (NSRF) via the Program Management Unit for Human Resources & Institutional Development, Research, and Innovation of Thailand (B16F640076, B50G670107), the Polish National Science Center (2019/35/O/ST2/02907), the Swedish Research Council (2019.04595), the Swedish Foundation for International Cooperation in Research and Higher Education (CH2018-7756), and the US Department of Energy (DE-FG02-05ER41374).

We consider the constraints on new physics affecting rare kaon and hyperon decay as parametrized by a low energy effective theory that can be obtained from high-p observables at LHC. To this end, we match the relevant low energy Wilson coefficients onto those in SMEFT at dimension six and compute their contributions to charged dilepton, monolepton, monojets, and VH searches by ATLAS and CMS. Constraints from rare kaon decays are generally more restrictive, with the ones arising from high-p measurements complementing them along directions in parameter space to which the former are not sensitive. We also illustrate the effect of a high luminosity LHC run in reducing the viable parameter regions.

Arnab Roy

High-p

Using an electron-positron collision data sample corresponding to $ (1.0087\pm0.0044)\times10^{10} $ $ J/\psi $ events collected using the BESIII detector at the BEPCII collider, we firstly search for the lepton number violation decay $ \phi \to \pi^+ \pi^+ e^- e^- $ via $ J/\psi\to \phi\eta $ . No obviously signals are found. The upper limit on the branching fraction of $ \phi \to \pi^+ \pi^+ e^- e^- $ is set to be $ 1.3\times10^{-5} $ at the 90% confidence level.

M.R. An

S.C. Coen

United Kingdom

K. Fischer

Y.N. Gao

Yang Gao

S. Garbolino

I. Garzia

Search for the lepton number violation decay $\textit{ϕ}$ → $\textit{π}$ $^{+}$ $\textit{π}$ $^{+}$ $\textit{e}$ $^{−}$ $\textit{e}$ $^{−}$ via $\textit{J}$/$\textit{ψ}$ → $\textit{ϕη}$ * The BESIII Collaboration appreciates the staff of BEPCII and the IHEP Computing Center for their strong support. This work is supported in part by the National Key R&D Program of China (2020YFA0406300, 2020YFA0406400); National Natural Science Foundation of China (NSFC) (12035009, 11635010, 11735014, 11835012, 11935015, 11935016, 11935018, 11961141012, 12025502, 12035013, 12061131003, 12192260, 12192261, 12192262, 12192263, 12192264, 12192265, 12221005, 12225509, 12235017); the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics (CCEPP); Joint Large-Scale Scientific Facility Funds of the NSFC and CAS (U1832207); CAS Key Research Program of Frontier Sciences (QYZDJ-SSW-SLH003, QYZDJ-SSW-SLH040); 100 Talents Program of CAS; the Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement (894790); the German Research Foundation DFG (455635585), the Collaborative Research Center CRC 1044, FOR5327, GRK 2149; Istituto Nazionale di Fisica Nucleare, Italy; Knut and Alice Wallenberg Foundation (2021.0174, 2021.0299); Ministry of Development of Turkey (DPT2006K-120470); National Research Foundation of Korea (NRF-2022R1A2C1092335); National Science and Technology Fund of Mongolia; National Science Research and Innovation Fund (NSRF) via the Program Management Unit for Human Resources & Institutional Development, Research and Innovation of Thailand (B16F640076); Polish National Science Centre (2019/35/O/ST2/02907); Swedish Research Council (2019.04595); the Swedish Foundation for International Cooperation in Research and Higher Education (CH2018-7756); and the U. S. Department of Energy (DE-FG02-05ER41374).

We analyse the <italic>Z</italic> and Higgs boson decays <math altimg='si1.svg'><mi>Z</mi><mo stretchy='false'>&#8594;</mo><msup><mrow><mi>&#8467;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup><msup><mrow><mi>&#8467;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo></mrow></msup></math> ( <math altimg='si2.svg'><mi>&#8467;</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi>e</mi><mo>,</mo><mi>&#956;</mi><mo>,</mo><mi>&#964;</mi></math>), <math altimg='si3.svg'><mi>H</mi><mo stretchy='false'>&#8594;</mo><mi>&#947;</mi><mi>&#947;</mi></math> and <math altimg='si4.svg'><mi>H</mi><mo stretchy='false'>&#8594;</mo><mi>Z</mi><mi>&#947;</mi></math> that are induced at one-loop level in models with a doubly-charged isosinglet scalar. After discussing current constraints, we derive the parameter space that will be probed by the HL-LHC and the possible future colliders the ILC, CEPC and FCC. We then apply those constraints to lepton triality models which are based on a discrete <math altimg='si5.svg'><msub><mrow><mi>Z</mi></mrow><mrow><mn>3</mn></mrow></msub></math> family symmetry and were recently studied in the context of charged-lepton flavour-violating processes at Belle II and the proposed <math altimg='si6.svg'><msup><mrow><mi>&#956;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup><msup><mrow><mi>&#956;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup></math> and <math altimg='si7.svg'><msup><mrow><mi>&#956;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo></mrow></msup></math> collider known as <italic>&#956;</italic>TRISTAN. We find that the future constraints that can be imposed by <math altimg='si1.svg'><mi>Z</mi><mo stretchy='false'>&#8594;</mo><msup><mrow><mi>&#8467;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup><msup><mrow><mi>&#8467;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo></mrow></msup></math> on the lepton flavour conserving couplings of the triality models reduce the viable parameter space to probe lepton flavour violating processes. The constraints from Higgs boson decays are the first on the Higgs portal sector of the triality models.

Gabriela Lichtenstein

Michael A. Schmidt

Raymond R. Volkas

Z and Higgs boson decays with doubly-charged scalars at one-loop: Current constraints, future sensitivities, and application to lepton-triality models

Motivated by the LHCb measurement of the hyperon decay mode <math><mrow><msup><mrow><mi>Σ</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mi>p</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> and prospects for improvement, we revisit the estimates for the rate and muon forward-backward asymmetry within the standard model and beyond. The standard model prediction has a fourfold ambiguity, and we suggest ways to resolve it with other measurements, including possible studies of <math><msup><mi>Σ</mi><mo>+</mo></msup><mo>→</mo><mi>p</mi><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> in the BESIII and LHCb experiments. We use the recent BESIII measurements of <math><msup><mi>Σ</mi><mo>+</mo></msup><mo>→</mo><mi>p</mi><mi>γ</mi></math> and <math><msup><mi>Σ</mi><mo>+</mo></msup><mo>→</mo><mi>N</mi><mi>π</mi></math> to reduce the uncertainty in the long-distance contribution to <math><msup><mi>Σ</mi><mo>+</mo></msup><mo>→</mo><mi>p</mi><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math>. Beyond the standard model, we consider a general effective Hamiltonian at low energy with ten operators whose Wilson coefficients parametrize the new physics. We derive expressions for the <math><msup><mi>Σ</mi><mo>+</mo></msup><mo>→</mo><mi>p</mi><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math> rate and the associated muon forward-backward asymmetry in terms of these coefficients. Finally, we present the constraints on these Wilson coefficients that result from both kaon and hyperon decays and emphasize their complementarity.

<math><msup><mi>Σ</mi><mo>+</mo></msup><mo>→</mo><mi>p</mi><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> decays within the standard model and beyond

Recently Belle II reported the first measurement of B + → K + + invisible(inv), which is 2.7σ above the standard model (SM) prediction. If confirmed, this calls for new physics beyond SM. In the SM, the invisible particles are neutrino-anti-neutrino pairs. There are more possibilities when going beyond the SM. In this work, we focus on decays to dark matter (DM) and show that the B → K + inv excess from Belle II and DM relic density can be simultaneously explained in a simple extension of the SM. The model introduces a real scalar singlet ϕ acting as a DM candidate, and two heavy vector-like quarks Q, D with the same quantum numbers as the SM left-handed quark doublet and right-handed down-type quark singlet, respectively. All these new particles are odd under a ℤ2 symmetry while the SM particles are even. The model can successfully explain the Belle II anomaly and DM relic density for TeV-scale heavy quarks with hierarchical Yukawa couplings involving b and s quarks. At the same time, it can easily satisfy other flavour physics constraints. Direct detection searches utilizing the Migdal effect constrain some of the parameter space.

Michael Schmidt

Raymond Volkas

Scalar dark matter explanation of the excess in the Belle II B + → K ++ invisible measurement

Belle II recently reported the new measurement <math><mi>B</mi><mo>(</mo><msup><mi>B</mi><mo>+</mo></msup><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>ν</mi><mover><mi>ν</mi><mo>¯</mo></mover><mo>)</mo><mo>=</mo><mo>(</mo><mn>2.3</mn><mo>±</mo><mn>0.7</mn><mo>)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math> [I. Adachi et al. (Belle-II Collaboration), arXiv:2311.14647] which is two times larger than their previous result (although consistent within errors) and about <math><mn>2.7</mn><mi>σ</mi></math> higher than the SM prediction. We reexamine new physics scenarios we discussed previously, which can enhance this rate to determine if they can accommodate the higher value reported in the new measurement. We use consistency with existing bounds on <math><mi>B</mi><mo>→</mo><msup><mi>K</mi><mo>*</mo></msup><mi>ν</mi><mover><mi>ν</mi><mo>¯</mo></mover></math>, <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math>, <math><mi>B</mi><mo>→</mo><msup><mi>D</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mo>ℓ</mo><mover><mi>ν</mi><mo>¯</mo></mover></math>, and <math><msub><mi>B</mi><mi>s</mi></msub></math> mixing to limit possible explanations for the excess. For the case of lepton flavor violating neutrino couplings, we find that only two leptoquarks remain viable requiring a large <math><msubsup><mi>C</mi><msup><mn>9</mn><mo>′</mo></msup><mrow><mi>τ</mi><mi>τ</mi></mrow></msubsup><mo>=</mo><mo>−</mo><msubsup><mi>C</mi><mrow><msup><mn>10</mn><mo>′</mo></msup></mrow><mrow><mi>τ</mi><mi>τ</mi></mrow></msubsup></math>. For models with different types of light dark matter particle pairs (scalar, fermion, or vector), the preliminary <math><msup><mi>q</mi><mn>2</mn></msup></math> distribution from Belle II, which shows that the excess appears mostly for bins with <math><mn>3</mn><mo>≤</mo><msup><mi>q</mi><mn>2</mn></msup><mo>≤</mo><mn>7</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>GeV</mi></mrow><mrow><mn>2</mn></mrow></msup></math> [I. Adachi et al. (Belle-II Collaboration), arXiv:2311.14647], implies only the vector current operators with scalar or vector dark matter particles with masses in the hundreds of MeV can match the anomaly.

Taiwan

Revisiting models that enhance <math><msup><mi>B</mi><mo>+</mo></msup><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>ν</mi><mover><mi>ν</mi><mo>¯</mo></mover></math> in light of the new Belle II measurement

We analyse the potential of the proposed <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup></math> and <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> collider μTRISTAN to complement the searches for charged-lepton flavour-violation (CLFV) that can be carried out by Belle II. μTRISTAN offers the possibility of directly producing and studying new resonances that could mediate CLFV for a certain range of masses. In addition, we find that it can produce competitive bounds to those from Belle II for cases where the new resonance lies beyond direct reach. We illustrate these points with three <math><msub><mrow><mi>Z</mi></mrow><mrow><mn>3</mn></mrow></msub></math> “lepton triality” models, where we also find an example that can only be probed by μTRISTAN. These three models feature doubly-charged scalars, denoted <math><msub><mrow><mi>k</mi></mrow><mrow><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn></mrow></msub></math> respectively, that induce both CLFV and flavour-conserving processes. Tree-level <math><msub><mrow><mi>k</mi></mrow><mrow><mn>1</mn></mrow></msub></math> exchange induces the CLFV scattering process <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup></math>, while <math><msub><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msub></math> interactions induce <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><msup><mrow><mi>τ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup></math>, <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>τ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></math> and make a non-SM contribution to the flavour-conserving scattering <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup></math>. The <math><msub><mrow><mi>k</mi></mrow><mrow><mn>3</mn></mrow></msub></math> model has a non-SM contribution to the flavour-conserving process <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math>. Other scattering processes involving <math><msub><mrow><mi>k</mi></mrow><mrow><mn>1</mn></mrow></msub></math>, <math><msub><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msub></math> or <math><msub><mrow><mi>k</mi></mrow><mrow><mn>3</mn></mrow></msub></math> are not relevant for μTRISTAN and outside the scope of our analysis. We quantify the sensitivity of μTRISTAN for each of these processes. For the <math><msub><mrow><mi>k</mi></mrow><mrow><mn>1</mn></mrow></msub></math> and <math><msub><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msub></math> cases we compare the μTRISTAN reach to the expected sensitivity of Belle II to the crossing symmetry related CLFV τ decays.

Complementarity of TRISTAN and Belle II in searches for charged-lepton flavour violation

Hyperon nonleptonic decays that change strangeness by two units, such as <math><mrow><mi>Ξ</mi><mo>→</mo><mi>N</mi><mi>π</mi></mrow></math> and <math><mrow><msup><mrow><mi>Ω</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><mi>n</mi><msup><mrow><mi>K</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>,</mo><mi>Λ</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>,</mo><msup><mrow><mi>Σ</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mi>π</mi></mrow></math>, are highly suppressed in the standard model. Only a few of them have been searched for to date, leading to experimental upper bounds that are many orders of magnitude above the expectations of the standard model. This leaves ample opportunity to look for indications of new physics in these processes. At the same time, most, but not all, <math><mi>Δ</mi><mi>S</mi><mo>=</mo><mn>2</mn></math> interactions beyond the standard model are severely constrained by kaon-mixing data. We present two scenarios where new physics satisfying the kaon-mixing constraints can enhance the hyperon decay rates to levels that can be probed in future searches by BESIII and LHCb and at the proposed Super Tau-Charm Factory. Both scenarios require significant fine-tuning.

<math><mrow><mi>Δ</mi><mi>S</mi><mo>=</mo><mn>2</mn></mrow></math> nonleptonic hyperon decays as probes of new physics