The processes of $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ and $ K^- p \to \pi^0 \Lambda(1405) $ are studied within the effective Lagrangian approach. In addition to the “background” contribution from the $\textit{u}$-channel nucleon pole term, the contribution from the $ \Sigma(1660) $ resonance with spin-parity $ J^P=1/2^+ $ is also considered. For the $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ reaction, we perform a calculation for the total and differential cross sections by considering the contribution from the $ \Sigma(1660) $ intermediate resonance decaying into $ \pi^0 \Lambda(1405) $ with $ \Lambda(1405) $ decaying into $ \pi^0 \Sigma^0 $ . With our model parameters, the available experimental data on both the $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ and $ K^- p \to \pi^0 \Lambda(1405) $ reactions can be fairly well reproduced. It is shown that the contribution from the $ \Sigma(1660) $ resonance is necessary, and that these experimental measurements could be used to determine some properties of the $ \Sigma(1660) $ resonance.

China

Xing-Yi Ji

Si-Wei Liu

Wen-Tao Lyu

De-Min Li

En Wang

Ju-Jun Xie

Role of Σ(1660) in the $\textit{K}$ $^{−}$ $\textit{p}$ → $\textit{π}$ $^{0}$ $\textit{π}$ $^{0}$Σ$^{0}$ reaction * Supported by the National Key R&D Program of China (2023YFA1606703, 2024YFE0105200), the National Natural Science Foundation of China (12435007, 12475086, 12192263, 12361141819, 1252200936), the Natural Science Foundation of Henan (232300421140, 252300423951) and the Zhengzhou University Young Student Basic Research Projects (PhD students) (ZDBJ202522)

Motivated by the observations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>c</mi><mover accent="true"><mi>s</mi><mo stretchy="false">¯</mo></mover><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mn>2900</mn><msup><mo stretchy="false">)</mo><mn>0</mn></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>c</mi><mover accent="true"><mi>s</mi><mo stretchy="false">¯</mo></mover><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mn>2900</mn><msup><mo stretchy="false">)</mo><mrow><mo>+</mo><mo>+</mo></mrow></msup></math>, we propose to search for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mrow><msub><mi>T</mi><mrow><mi>c</mi><mover accent="true"><mi>s</mi><mo stretchy="false">¯</mo></mover><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mn>2900</mn><mo stretchy="false">)</mo></mrow><mn>0</mn></msup></math> in the cleaner process <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>−</mo></msup><msup><mi>D</mi><mn>0</mn></msup><msup><mi>K</mi><mn>0</mn></msup></math>. In the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mo>*</mo></msup><msup><mi>K</mi><mo>*</mo></msup></math> molecular picture, our estimates suggest that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>c</mi><mover accent="true"><mi>s</mi><mo stretchy="false">¯</mo></mover><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mn>2900</mn><msup><mo stretchy="false">)</mo><mn>0</mn></msup></math> should contribute significantly to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mn>0</mn></msup><msup><mi>K</mi><mn>0</mn></msup></math> invariant mass distribution in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>−</mo></msup><msup><mi>D</mi><mn>0</mn></msup><msup><mi>K</mi><mn>0</mn></msup></math>, as reported by the Belle II Collaboration. The corresponding fit fraction is estimated to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><mn>9.72</mn><mo>±</mo><mn>3.92</mn><mo stretchy="false">)</mo><mo>%</mo></math> or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><mn>7.09</mn><mo>±</mo><mn>5.88</mn><mo stretchy="false">)</mo><mo>%</mo></math> in different fitting schemes. Further precise measurements of this process at Belle II and LHCb could be helpful for clarifying the nature of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>c</mi><mover accent="true"><mi>s</mi><mo stretchy="false">¯</mo></mover><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mn>2900</mn><mo stretchy="false">)</mo></math>.

Man-Yu Duan

Guan-Ying Wang

Yun Liang

Xiang Liu

Dian-Yong Chen

Finding the clean process <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mi>K</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> to probe absolutely exotic four-quark states

We present a systematic QCD sum-rule analysis of the in-medium properties of the charged kaon doublet <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mo>±</mo></msup></math> over the full <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><mi>T</mi><mo>,</mo><mi>ρ</mi><mo stretchy="false">)</mo></math> plane relevant to current and forthcoming heavy-ion experiments. Working within the QCD sum-rule framework and incorporating temperature- and density-dependent quark, gluon, and mixed condensates, we derive Borel-transformed sum rules for the effective masses <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><msup><mi>K</mi><mo>±</mo></msup></msub></math>, the pseudoscalar decay constants <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><msup><mi>K</mi><mo>±</mo></msup></msub></math>, and the vector self-energy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Σ</mi><mi>v</mi></msub></math> of both charged states simultaneously. Our vacuum results, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><msup><mi>K</mi><mo>−</mo></msup></msub><mo>=</mo><msubsup><mn>494.6</mn><mrow><mo>−</mo><mn>6.9</mn></mrow><mrow><mo>+</mo><mn>4.9</mn></mrow></msubsup><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><msup><mi>K</mi><mo>−</mo></msup></msub><mo>=</mo><msubsup><mn>157.3</mn><mrow><mo>−</mo><mn>2.9</mn></mrow><mrow><mo>+</mo><mn>4.1</mn></mrow></msubsup><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> (with near-degenerate <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mo>+</mo></msup></math> values), are in excellent agreement with Particle Data Group values at the subpercent level. In the medium, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><msup><mi>K</mi><mo>±</mo></msup></msub></math> decreases monotonically with increasing baryon density and temperature, signaling progressive partial restoration of chiral symmetry. A pronounced mass splitting <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><mi>m</mi><mo>=</mo><msub><mi>m</mi><msup><mi>K</mi><mo>−</mo></msup></msub><mo>−</mo><msub><mi>m</mi><msup><mi>K</mi><mo>+</mo></msup></msub></math> develops in baryonic matter, driven by the opposite sign of the Weinberg–Tomozawa vector interaction for the two charge states; it reaches <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><mi mathvariant="normal">Δ</mi><mi>m</mi><mo stretchy="false">|</mo><mo>∼</mo><mn>0.35</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> near <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi><mo>≃</mo><mn>3.2</mn><mtext> </mtext><msub><mi>ρ</mi><mrow><mi>sat</mi></mrow></msub></math> at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi><mo>=</mo><mn>0</mn></math> and is partially quenched by thermal fluctuations. A central outcome of this study is the extraction of the critical onset density <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mi>c</mi></msub></math>, defined as the threshold beyond which the in-medium modifications of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mo>−</mo></msup></math> properties signal the onset of the transition toward the chirally restored phase. We stress that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mi>T</mi><mo stretchy="false">)</mo></math> should not be interpreted as a precise determination of the QCD critical point—a task beyond the reach of any current effective framework—but rather as an indicator of the density regime where hadronic descriptions begin to break down and quark degrees of freedom become increasingly relevant. With this interpretation, our results reveal a pronounced temperature dependence: <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mi>c</mi></msub><mo>≃</mo><mo stretchy="false">(</mo><mn>1.2</mn><mi>–</mi><mn>1.4</mn><mo stretchy="false">)</mo><msub><mi>ρ</mi><mrow><mi>sat</mi></mrow></msub></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi><mo>≲</mo><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, reflecting the robustness of the hadronic phase under cold compression, and a sharp reduction to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mi>c</mi></msub><mo>≃</mo><mn>0.45</mn><mtext> </mtext><msub><mi>ρ</mi><mrow><mi>sat</mi></mrow></msub></math> near the pseudocritical temperature <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mi>c</mi></msub><mo>≃</mo><mn>155</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>. This dramatic downward shift reflects the synergistic destabilization of the chiral condensate by combined thermal and density fluctuations, and establishes temperature as a more efficient driver of chiral restoration than baryon density alone in the regime accessible to current experiments. Our findings provide quantitative, QCD-based theoretical input for interpreting kaon observables at HADES/GSI, CBM/FAIR, STAR/RHIC, and NA61/SHINE/CERN-SPS, and carry direct implications for kaon condensation in neutron star matter and the hadronic equation of state at supranuclear densities.

Iran

Türkiye

K. Azizi

G. Bozk𝚤r

N. Er

A. Türkan

Kaons in hot and dense QCD

An amplitude analysis of the $${{{B} ^0} \!\rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-}} $$ decays with $${\eta _{c}} (1S) \rightarrow {p} {\overline{{p}}} $$ is performed using a sample corresponding to an integrated luminosity of 9 $$\,\text {fb} ^{-1}$$ of $$p $$ $$p $$ collision data collected by the LHCb detector at centre-of-mass energies of $$\sqrt{s}$$ = 7, 8 and 13 $$\,\text {Te\hspace{-1.00006pt}V}$$ . The data are described with a model including only intermediate contributions from known $${K} ^{*0}$$ resonances. Evidence for an exotic resonance in the $${\eta _{c}} (1S) {{\pi } ^-} $$ system, reported in a previous analysis of this decay channel, is not confirmed. The inclusive branching fraction of the $${{B} ^0} \rightarrow {\eta _{c}} (1S) {{K} ^+} {{\pi } ^-} $$ decays is measured to be where the first uncertainty is statistical, the second systematic, and the third arises from the limited knowledge of external branching fractions.

Netherlands

R. Aaij

United Kingdom

A.S.W. Abdelmotteleb

Switzerland

C. Beteta

F. Abudinén

T. Ackernley

United States

A. Adefisoye

Spain

B. Adeva

M. Adinolfi

Sweden

P. Adlarson

France

C. Agapopoulou

C. Aidala

Z. Ajaltouni

S. Akar

K. Akiba

Italy

P. Albicocco

Germany

J. Albrecht

Lithuania

R. Aleksiejunas

F. Alessio

P. Cartelle

R. Amalric

Brazil

S. Amato

J. Amey

Y. Amhis

L. An

L. Anderlini

M. Andersson

P. Andreola

M. Andreotti

S. Estrada

A. Anelli

D. Ao

C. Arata

F. Archilli

Z. Areg

M. Argenton

Costa Rica

S. Cuendis

L. Arnone

A. Artamonov

M. Artuso

E. Aslanides

R. Silva

M. Atzeni

B. Audurier

J. Authier

D. Bacher

I. Perea

S. Bachmann

M. Bachmayer

J. Back

P. Rodriguez

V. Balagura

A. Balboni

W. Baldini

Z. Baldwin

L. Balzani

H. Bao

J. Souza Leite

C. Pretel

M. Barbetti

I. Barbosa

R. Barlow

M. Barnyakov

S. Barsuk

W. Barter

J. Bartz

Poland

S. Bashir

B. Batsukh

P. Battista

A. Bay

A. Beck

M. Becker

F. Bedeschi

I. Bediaga

N. Behling

S. Belin

A. Bellavista

K. Belous

I. Belov

I. Belyaev

G. Benane

G. Bencivenni

E. Ben-Haim

A. Berezhnoy

R. Bernet

S. Andres

A. Bertolin

C. Betancourt

F. Betti

J. Bex

Ia. Bezshyiko

Ukraine

O. Bezshyyko

J. Bhom

M. Bieker

N. Biesuz

P. Billoir

A. Biolchini

M. Birch

F. Bishop

A. Bitadze

A. Bizzeti

Amplitude analysis of $$B^0 \rightarrow \eta _c(1S) K^+ \pi ^- $$ decays

We report a search for an invisible particle <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> in the decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>K</mi></mrow><mrow><mi>L</mi></mrow><mrow><mn>0</mn></mrow></msubsup><mo stretchy="false">→</mo><mi>γ</mi><mi>X</mi></mrow></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">→</mo><mtext>invisible</mtext></math>), where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> can be interpreted as a massless or massive dark photon. No evidence for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> was found, based on 13 candidate events consistent with a predicted background of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>12.66</mn><mo>±</mo><mn>4.4</mn><msub><mrow><mn>2</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>2.1</mn><msub><mrow><mn>3</mn></mrow><mrow><mi>syst</mi></mrow></msub></mrow></math> events. Upper limits on the branching ratio of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>K</mi><mi>L</mi><mn>0</mn></msubsup><mo stretchy="false">→</mo><mi>γ</mi><mi>X</mi></math> were set for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math> mass range <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>0</mn><mo>≤</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>X</mi></mrow></msub><mo>≤</mo><mn>425</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. For massless <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math>, the upper limit was <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3.4</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></math> at the 90% confidence level, improving the previous indirect bound by over three orders of magnitude. This result yielded a new lower bound of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4.1</mn><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> on the probed effective mass scale governing flavor-changing dark-photon couplings, representing approximately two orders of magnitude improvement on existing constraints. For massive <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi></math>, the upper limits in the searched mass region ranged from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup><mo stretchy="false">)</mo></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mo stretchy="false">)</mo></math>.

T. Wu

Taiwan

Y.C. Tung

Y.B. Hsiung

South Korea

J.K. Ahn

Japan

M. Gonzalez

E.J. Kim

T.K. Komatsubara

K. Kotera

S.K. Lee

G.Y. Lim

C. Lin

T. Matsumura

H. Nanjo

Y. Noichi

T. Nomura

T. Nunes

K. Ono

J. Redeker

N. Shimizu

S. Shinohara

K. Shiomi

R. Shiraishi

Y. Tajima

Y.W. Wah

H. Watanabe

T. Yamanaka

H.Y. Yoshida

Search for Dark Particles in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>K</mi></mrow><mrow><mi>L</mi></mrow><mrow><mn>0</mn></mrow></msubsup><mo stretchy="false">→</mo><mi>γ</mi><mi>X</mi></mrow></math> at the KOTO Experiment

Based on a sample of (10087 ± 44) × 10 $\textit{J}$/$\textit{ψ}$ events collected at the center-of-mass energy $$ \sqrt{s}=3.0969 $$ GeV with the BESIII detector, we search for the charmonium rare weak decay $$ J/\psi \to {\overline{D}}^0{\overline{K}}^{\ast 0}+\textrm{c}.\textrm{c}. $$ . No significant signal is observed, and the upper limit on its decay branching fraction at the 90% confidence level is set as 1.4 × 10 , improving the sensitivity of the previous best limit by an order of magnitude.

M. Ablikim

Russia

M. Achasov

X. Ai

R. Aliberti

A. Amoroso

Q. An

Y. Bai

O. Bakina

Y. Ban

H.R. Bao

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

R. Briere

A. Brueggemann

H. Cai

M. Cai

X. Cai

A. Calcaterra

Search for the charmonium weak decay $$ J/\psi \to {\overline{D}}^0{\overline{K}}^{\ast 0}+\textrm{c}.\textrm{c}. $$