Based on Belle data, the structure around 1435 MeV and the role of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Σ</mi><mo>(</mo><mn>1380</mn><mo>)</mo></mrow></math> resonance in the decay process <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mo>→</mo><mi mathvariant="normal">Λ</mi><msup><mi>π</mi><mo>−</mo></msup><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>+</mo></msup></mrow></math> are investigated. The <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Λ</mi><msup><mi>π</mi><mo>±</mo></msup></mrow></math> invariant mass spectra are approximately reproduced by the contribution from the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Σ</mi><mo>(</mo><mn>1385</mn><mo>)</mo></mrow></math>, modeled as a Breit-Wigner resonance combined with background. However, an additional contribution is required to account for the pronounced enhancement near 1435 MeV. To describe this structure, two scenarios are considered for the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Σ</mi><mo>(</mo><mn>1435</mn><mo>)</mo></mrow></math>: one as a Breit-Wigner resonance with spin-parity <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> described via effective Lagrangians, and the other as a rescattering effect arising from coupled-channel interactions. Specifically, the channels <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mover accent="true"><mi>K</mi><mo>¯</mo></mover><mn>0</mn></msup><mi>p</mi></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mn>0</mn></msup><msup><mi mathvariant="normal">Σ</mi><mo>+</mo></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mo>+</mo></msup><msup><mi mathvariant="normal">Σ</mi><mn>0</mn></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mo>+</mo></msup><mi mathvariant="normal">Λ</mi></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>η</mi><msup><mi mathvariant="normal">Σ</mi><mo>+</mo></msup></mrow></math> are included for the positively charged mode, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>K</mi><mo>−</mo></msup><mi>n</mi></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mn>0</mn></msup><msup><mi mathvariant="normal">Σ</mi><mo>−</mo></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mo>−</mo></msup><msup><mi mathvariant="normal">Σ</mi><mn>0</mn></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mo>−</mo></msup><mi mathvariant="normal">Λ</mi></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>η</mi><msup><mi mathvariant="normal">Σ</mi><mo>−</mo></msup></mrow></math> for the negatively charged mode. The rescattering contributions are evaluated using the quasipotential Bethe-Salpeter equation approach. Simulated invariant mass spectra are generated and fitted to the experimental data. Both the Breit-Wigner and rescattering mechanisms provide reasonable descriptions of the enhancement near 1435 MeV. The rescattering approach naturally generates a cusp-like structure near threshold, which closely resembles the feature observed in the data. Furthermore, the inclusion of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Σ</mi><mo>(</mo><mn>1380</mn><mo>)</mo></mrow></math> resonance with spin-parity <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> significantly improves the fit in the low-energy region and further enhances the description near 1435 MeV through interference effects. These results underscore the essential roles of the two <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Σ</mi><mo>*</mo></msup><mrow><mo>(</mo><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup><mo>)</mo></mrow></mrow></math> states in accurately describing the invariant mass distributions in the decay <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mo>→</mo><mi mathvariant="normal">Λ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></mrow></math>.

China

Jun He

Role of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Σ</mi><mo>*</mo></msup><mrow><mo>(</mo><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup><mo>)</mo></mrow></mrow></math> baryons in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mo>→</mo><mi mathvariant="normal">Λ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></mrow></math> decay

In this manuscript we study the exclusive photoproduction of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub><mi>γ</mi></math> pairs in the collinear factorization framework. We found the coefficient functions for all possible spins and helicity projections of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub></math> mesons and final-state photons in the leading order in the strong coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>α</mi><mi>s</mi></msub></math>. In our analysis we focused on the contribution of the leading twist chiral-even generalized parton distributions (GPDs) and found that for all spin states of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub></math> the suggested process is largely determined by the behavior of the gluon GPDs <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mi>g</mi></msub></math>. Using the phenomenological parametrizations of the GPDs from the literature, we estimated numerically the photoproduction cross sections and the expected counting rates in the kinematics of medium-energy photoproduction experiments that could be realized at the Electron-Ion Collider. We observed that the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mn>1</mn></mrow></msub></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub></math> mesons are produced predominantly with the same polarization as the incoming photon, and the expected counting rates of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mn>1</mn></mrow></msub><mi>γ</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mi>γ</mi></math> pairs are sufficiently large for their experimental study. We also analyzed the angular distribution of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub></math> mesons in electroproduction experiments and noticed that for some helicity components there are sizable angular asymmetries, which can be used as complementary observables for experimental study. Finally, we estimated the role of this process as a potential background to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub></math> photoproduction, which has been recently suggested as a tool for studies of odderons. We found that the contribution of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub><mi>γ</mi></math> (with undetected photon) is on par with expected contributions of odderons and Primakoff mechanisms in the kinematics of small momentum transfer <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><mi>t</mi><mo stretchy="false">|</mo><mo>≲</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>GeV</mi></mrow><mrow><mn>2</mn></mrow></msup></math>, but becomes negligible at larger <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><mi>t</mi><mo stretchy="false">|</mo></math>.

Chile

Marat Siddikov

Ivan Zemlyakov

Exclusive photoproduction of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mi>c</mi></msub><mi>γ</mi></math> pairs

By analyzing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>2712.4</mn><mo>±</mo><mn>14.3</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>6</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo></mrow></math> events collected with the BESIII detector operating at the BEPCII collider, the decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>χ</mi></mrow><mrow><mi>c</mi><mn>0</mn><mo>,</mo><mn>1</mn><mo>,</mo><mn>2</mn></mrow></msub><mo stretchy="false">→</mo><mn>3</mn><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>∓</mo></mrow></msup></mrow></math> are observed for the first time with statistical significances greater than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>10</mn><mi>σ</mi></math>. The branching fractions of these decays are determined to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msub><mrow><mi>χ</mi></mrow><mrow><mi>c</mi><mn>0</mn></mrow></msub><mo stretchy="false">→</mo><mn>3</mn><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>∓</mo></mrow></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>7.95</mn><mo>±</mo><mn>0.50</mn><mo>±</mo><mn>0.65</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msub><mrow><mi>χ</mi></mrow><mrow><mi>c</mi><mn>1</mn></mrow></msub><mo stretchy="false">→</mo><mn>3</mn><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>∓</mo></mrow></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>2.62</mn><mo>±</mo><mn>0.08</mn><mo>±</mo><mn>0.19</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><msub><mrow><mi>χ</mi></mrow><mrow><mi>c</mi><mn>2</mn></mrow></msub><mo stretchy="false">→</mo><mn>3</mn><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>∓</mo></mrow></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>1.72</mn><mo>±</mo><mn>0.07</mn><mo>±</mo><mn>0.15</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></mrow></math>, where the first uncertainties are statistical and the second systematic.

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

X.C. Ai

Germany

R. Aliberti

Italy

A. Amoroso

Q. An

Y. Bai

JINR

O. Bakina

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

M.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.K. Chen

South Korea

S.K. Choi

X. Chu

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

Y.X. 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

G.F. Fan

J.J. Fan

Y.H. Fan

J. Fang

S.S. Fang

W.X. 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

Observation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>c</mi><mi>J</mi></mrow></msub><mo stretchy="false">→</mo><mn>3</mn><msubsup><mi>K</mi><mi>S</mi><mn>0</mn></msubsup><msup><mi>K</mi><mo>±</mo></msup><msup><mi>π</mi><mo>∓</mo></msup></math>

Studying exotic hadrons is a challenge against the conventional quark model, providing us with a good platform to deepen our understanding of the strong interaction. An inclusive study of the exotic hadrons in vacuum and at finite temperature is an intriguing approach to shed light on their nature. As a first step, we study the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><mo stretchy="false">)</mo></math> in both the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><msup><mover accent="true"><mi>D</mi><mo stretchy="false">¯</mo></mover><mo>*</mo></msup></math> hadronic molecular and the triangle singularity pictures, and discuss the behaviors of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><mo stretchy="false">)</mo></math> at finite temperature in these two different pictures. As a result, we show the properties that its mass becomes smaller and its width becomes larger when the temperature increases, which are seen commonly in the hadronic molecular picture and in the triangle singularity picture. The enhanced widths in hot medium indicate that the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><mo stretchy="false">)</mo></math> will be dissociated at a sufficiently high temperature. This feature is also reflected by a decrease of the effective couplings in the hadronic molecular picture. It is concluded that, not only in vacuum but also in hot medium, the behaviors of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><mo stretchy="false">)</mo></math> are similar in the two different interpretations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><mo stretchy="false">)</mo></math>.

Japan

Ying Zhang

Atsushi Hosaka

Qian Wang

Shigehiro Yasui

<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><mo stretchy="false">)</mo></math> in a hadronic molecule and a triangle singularity approach at finite temperature

We measure the time-integrated <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> asymmetry, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>A</mi></mrow><mrow><mi>C</mi><mi>P</mi></mrow></msub></mrow></math>, in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> decays reconstructed in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></mrow><mo stretchy="false">→</mo><mrow><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></mrow></math> events collected by Belle II during 2019–2022. The data corresponds to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>428</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow></math> decays are required to originate from the flavor-conserving <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mi>D</mi><mn>0</mn></msup><msup><mi>π</mi><mo>+</mo></msup></math> decay to determine the charm flavor at production time. Control samples of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mn>0</mn></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>−</mo></msup><msup><mi>π</mi><mo>+</mo></msup></math> decays, with or without an associated pion from a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mrow><mo>*</mo><mo>+</mo></mrow></msup></math> decay, are used to correct for detection asymmetries. The result, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mrow><mi>C</mi><mi>P</mi></mrow></msub><mo stretchy="false">(</mo><msup><mi>D</mi><mn>0</mn></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mn>0</mn></msup><msup><mi>π</mi><mn>0</mn></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>0.30</mn><mo>±</mo><mn>0.72</mn><mo>±</mo><mn>0.20</mn><mo stretchy="false">)</mo><mo>%</mo></math>, where the first uncertainty is statistical and the second systematic, is consistent with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> symmetry.

I. Adachi

Y. Ahn

N. Akopov

S. Alghamdi

M. Alhakami

A. Aloisio

N. Althubiti

K. Amos

M. Angelsmark

N. Anh Ky

C. Antonioli

D.M. Asner

H. Atmacan

T. Aushev

M. Aversano

R. Ayad

V. Babu

H. Bae

N.K. Baghel

S. Bahinipati

P. Bambade

Sw. Banerjee

M. Barrett

M. Bartl

J. Baudot

A. Baur

A. Beaubien

F. Becherer

J. Becker

J.V. Bennett

F.U. Bernlochner

V. Bertacchi

M. Bertemes

E. Bertholet

M. Bessner

S. Bettarini

B. Bhuyan

T. Bilka

D. Biswas

A. Bobrov

D. Bodrov

A. Bondar

J. Borah

A. Boschetti

A. Bozek

M. Bračko

P. Branchini

T.E. Browder

A. Budano

S. Bussino

M. Campajola

L. Cao

G. Casarosa

C. Cecchi

P. Cheema

B.G. Cheon

K. Chilikin

J. Chin

K. Chirapatpimol

H.E. Cho

K. Cho

S.J. Cho

S. Choudhury

I. Consigny

L. Corona

J.X. Cui

E. De La Cruz-Burelo

S.A. De La Motte

G. De Pietro

R. de Sangro

A. Di Canto

J. Dingfelder

Z. Doležal

I. Domínguez Jiménez

Measurement of the time-integrated <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> asymmetry in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mn>0</mn></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mn>0</mn></msup><msup><mi>π</mi><mn>0</mn></msup></math> decays at Belle II