We measure the <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><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mn>0</mn></msup></math> decays reconstructed in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collisions at the Belle II experiment using a dataset corresponding 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>. A control sample of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msubsup><mi>K</mi><mi>S</mi><mn>0</mn></msubsup></math> decays is used to correct for detection and production 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><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mn>0</mn></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mo>−</mo><mn>1.8</mn><mo>±</mo><mn>0.9</mn><mo>±</mo><mn>0.1</mn><mo stretchy="false">)</mo><mo>%</mo></math>, where the first uncertainty is statistical and the second systematic, is the most precise determination to date. It agrees with the prediction of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> symmetry from the standard model and with results of previous measurements.

I. Adachi

L. Aggarwal

H. Ahmed

H. Aihara

N. Akopov

S. Alghamdi

M. Alhakami

A. Aloisio

K. Amos

M. Angelsmark

N. Anh Ky

C. Antonioli

D.M. Asner

H. Atmacan

V. Aushev

M. Aversano

R. Ayad

V. Babu

H. Bae

N.K. Baghel

P. Bambade

Sw. Banerjee

S. Bansal

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

V. Bhardwaj

B. Bhuyan

F. Bianchi

D. Biswas

A. Bobrov

D. Bodrov

A. Bondar

G. Bonvicini

J. Borah

A. Boschetti

A. Bozek

M. Bračko

P. Branchini

R.A. Briere

T.E. Browder

A. Budano

S. Bussino

Q. Campagna

M. Campajola

L. Cao

G. Casarosa

C. Cecchi

M.C. Chang

P. Cheema

L. Chen

B.G. Cheon

K. Chilikin

J. Chin

K. Chirapatpimol

H.E. Cho

K. Cho

S.J. Cho

S.K. Choi

S. Choudhury

I. Consigny

L. Corona

J.X. Cui

S. Das

E. De La Cruz-Burelo

S.A. De La Motte

G. De Pietro

R. de Sangro

M. Destefanis

A. Di Canto

Z. Doležal

I. Domínguez Jiménez

T.V. Dong

X. Dong

M. Dorigo

K. Dugic

G. Dujany

P. Ecker

D. Epifanov

J. Eppelt

R. Farkas

P. Feichtinger

T. Ferber

T. Fillinger

C. Finck

G. Finocchiaro

F. Forti

A. Frey

B.G. Fulsom

Measurement of the <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><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mn>0</mn></msup></math> decays at Belle II

The nature of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3872</mn><mo stretchy="false">)</mo></math> and other exotic hadrons has been a subject of extensive investigation since the first observation of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3872</mn><mo stretchy="false">)</mo></math> in 2003. While various theoretical models have been proposed, including hadronic molecular and compact tetraquark interpretations, some experimental evidence suggests that the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3872</mn><mo stretchy="false">)</mo></math> may be a mixture state of a hadronic molecule and a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> core. In this work, we perform a systematic study of the hidden-charm tetraquark candidates <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3860</mn><mo stretchy="false">)</mo></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3872</mn><mo stretchy="false">)</mo></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo stretchy="false">(</mo><mn>3930</mn><mo stretchy="false">)</mo></math> using a coupled-channel model that incorporates both <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> states and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup><msup><mrow><mover accent="true"><mrow><mi>D</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup></mrow></math> hadronic molecular components. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> sector is described based on the constituent quark model predictions for the <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>2</mn><mi>P</mi><mo stretchy="false">)</mo></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>=</mo><mn>0</mn></math>, 1, 2) states, while the meson-meson interactions are modeled using pseudoscalar and vector-meson exchange potentials. The model parameters are fixed to reproduce the masses of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3872</mn><mo stretchy="false">)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo stretchy="false">(</mo><mn>3930</mn><mo stretchy="false">)</mo></math>, and the resulting framework is used to predict the mass and structure of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>J</mi><mrow><mi>P</mi><mi>C</mi></mrow></msup><mo>=</mo><msup><mn>0</mn><mrow><mo>+</mo><mo>+</mo></mrow></msup></math> state associated with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3860</mn><mo stretchy="false">)</mo></math>. Our results support the mixture interpretation of these exotic hadrons, exhibiting strong attractions from the transition potential between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup><msup><mover accent="true"><mi>D</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup></math> components. The molecular component is found to dominate in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3872</mn><mo stretchy="false">)</mo></math>, while the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> component plays a more prominent role in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>3860</mn><mo stretchy="false">)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo stretchy="false">(</mo><mn>3930</mn><mo stretchy="false">)</mo></math>.

Japan

Kotaro Miyake

Yasuhiro Yamaguchi

Hidden-charm tetraquarks in a mixture model: Coupled-channel analysis with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> and hadronic molecular components

We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasielasticlike interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasielasticlike event candidates were selected from T2K data corresponding to an exposure of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1.76</mn><mo>×</mo><msup><mn>10</mn><mn>20</mn></msup></math> protons on target. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math> ray signals resulting from neutron captures were identified using a neural network. The flux-averaged mean neutron capture multiplicity was measured to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mn>1.37</mn><mo>±</mo><mn>0.33</mn><mtext> </mtext><mo stretchy="false">(</mo><mi>stat</mi><mo>.</mo><mo stretchy="false">)</mo></mrow><mrow><mo>−</mo><mn>0.27</mn></mrow><mrow><mo>+</mo><mn>0.17</mn></mrow></msubsup><mtext> </mtext><mo stretchy="false">(</mo><mi>syst</mi><mo>.</mo><mo stretchy="false">)</mo></mrow></math>, which is compatible within 2.3 sigma than predictions obtained using our nominal simulation. We discuss potential sources of systematic uncertainty in the prediction and demonstrate that a significant portion of this discrepancy arises from the modeling of hadron-nucleus interactions in the detector medium.

K. Abe

S. Abe

R. Akutsu

United Kingdom

H. Alarakia-Charles

Y.I. Alj Hakim

Switzerland

S. Alonso Monsalve

L. Anthony

S. Aoki

K.A. Apte

T. Arai

T. Arihara

S. Arimoto

Y. Ashida

E.T. Atkin

United States

N. Babu

JINR

V. Baranov

G.J. Barker

G. Barr

D. Barrow

P. Bates

L. Bathe-Peters

Poland

M. Batkiewicz-Kwasniak

N. Baudis

Italy

V. Berardi

L. Berns

S. Bhattacharjee

CERN

A. Blanchet

France

A. Blondel

P.M.M. Boistier

S. Bolognesi

S. Bordoni

S.B. Boyd

C. Bronner

A. Bubak

M. Buizza Avanzini

Spain

J.A. Caballero

F. Cadoux

N.F. Calabria

Vietnam

S. Cao

S. Cap

D. Carabadjac

S.L. Cartwright

M.P. Casado

M.G. Catanesi

J. Chakrani

A. Chalumeau

D. Cherdack

Russia

A. Chvirova

J. Coleman

G. Collazuol

Canada

F. Cormier

A.A.L. Craplet

A. Cudd

D. D’ago

C. Dalmazzone

T. Daret

Hungary

P. Dasgupta

C. Davis

Yu. I. Davydov

P. de Perio

G. De Rosa

T. Dealtry

C. Densham

A. Dergacheva

R. Dharmapal Banerjee

F. Di Lodovico

G. Diaz Lopez

S. Dolan

D. Douqa

T.A. Doyle

O. Drapier

K.E. Duffy

J. Dumarchez

P. Dunne

K. Dygnarowicz

A. Eguchi

J. Elias

S. Emery-Schrenk

G. Erofeev

A. Ershova

First measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasielasticlike interactions using an accelerator neutrino beam