A dark photon is an Abelian gauge boson arising from a new $ U(1)_D $ gauge symmetry, coupled to the Standard Model through kinetic mixing. The mixing parameter $\textit{ϵ}$ induces an effective coupling to the electromagnetic current, while $ g_\chi $ couples the dark photon to a stable dark matter particle $\textit{χ}$. We study $ J/\psi $ two-body and four-body decays mediated by a light dark photon ( $ m_U \lt 3.0 $ GeV) within the non-relativistic QCD (NRQCD) framework, considering both visible decays of the dark photon into SM fermions and invisible decays into dark sector particles. We investigate the detection sensitivity of BESIII and STCF experiments to the dark photon mass $ m_U $ and kinetic mixing parameter $\textit{ϵ}$. Our results show that, for two-body final states with $ m_U \lt 2m_\chi $ , BESIII sets $\textit{ϵ}$ upper limits of $ 9.3\times10^{-4} $ and $ 7.6\times10^{-4} $ for lepton-pair and hadronic signals, respectively, while STCF yields $ 3.7\times10^{-4} $ and $ 3.1\times10^{-4} $ . For invisible decays ( $ m_U\ge 2m_\chi $ ), BESIII achieves an $\textit{ϵ}$ limit of $ 1.4\times10^{-3} $ in the mass range $ 0.3\sim0.8 $ GeV, and STCF reaches $ 2.3\times10^{-4} $ in $ 0.3\sim1.9 $ GeV; no signals are expected in other mass regions, and visible decays are severely suppressed throughout. For four-body decay channels, BESIII yields an $\textit{ϵ}$ upper limit of $ 7.6\times10^{-5} $ for $ m_U \lt 2.2 $ GeV, whereas STCF achieves $ 1.2\times10^{-5} $ over the full mass range. When $ m_U\ge 2m_\chi $ , visible modes are nearly excluded; BESIII and STCF set $\textit{ϵ}$ limits from invisible decays of $ 8.8\times10^{-5} $ for $ m_U \lt 2.4 $ GeV and $ 1.4\times10^{-5} $ for $ m_U \lt 2.8 $ GeV, respectively, with no detectable signals at higher masses. Except for the limit of $ 9.3\times10^{-4} $ , all the above $\textit{ϵ}$ bounds lie in regions that are not currently excluded by collider experiments. Compared with the constraints from two-body final state processes, the limits derived from four-body decay channels lie well below existing experimental bounds, providing supportive references for constraining this parameter in BESIII and STCF experiments. Numerical results for the decay ratios $ \Gamma/\Gamma_{J/\psi} $ , expected event numbers, significance $ S/\sqrt{B} $ , and $ p_T $ distributions are presented where applicable.

China

Xiao Liang

Chun-Yuan Li

Bin-Peng Shang

Zong-Guo Si

Hong-Xin Wang

Xing-Hua Yang

Dai-Xing Zhang

Searching for dark photons in $\textit{J/ψ}$ decays * Supported in part by the National Natural Science Foundation of China (12105162, 12305106, 12235008, 12321005), the Natural Science Foundation of Shandong Province (ZR2021QA058, ZR2021QA040), and the Youth Innovation Technology Project of Higher School in Shandong Province (2023KJ146)

We investigate the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math>-wave <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>η</mi><mi>c</mi></msub><msub><mi>η</mi><mi>c</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi></math> scattering in 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><mo stretchy="false">(</mo><mn>0</mn><mo>,</mo><mn>2</mn><msup><mo stretchy="false">)</mo><mrow><mo>+</mo><mo>+</mo></mrow></msup></math> channels up to a center-of-mass energy of 6.6 GeV. The calculations are carried out at two unphysical pion masses, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>π</mi></msub><mo>≈</mo><mn>420</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> and 250 MeV in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>f</mi></msub><mo>=</mo><mn>2</mn></math> lattice QCD. For each <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>π</mi></msub></math>, we extract the finite-volume energy levels on two lattices with an identical lattice spacing (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>a</mi><mo>≃</mo><mn>0.136</mn><mtext> </mtext><mtext> </mtext><mi>fm</mi></math>) but different spatial volumes. Since the coupled-channel effects between the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>η</mi><mi>c</mi></msub><msub><mi>η</mi><mi>c</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi></math> channels are found to be negligible, we analyze the corresponding scattering properties using the single-channel L"uscher method. We find that the interactions in these dicharmonium systems are dominated by the quark rearrangement effect. In the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>0</mn><mrow><mo>+</mo><mo>+</mo></mrow></msup></math> channel, the near-threshold attraction in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi></math> and repulsion in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>η</mi><mi>c</mi></msub><msub><mi>η</mi><mi>c</mi></msub></math> can be explained through the Fierz rearrangement. The attractive interaction in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mo>​</mo><mn>1</mn></msup><msub><mi>S</mi><mn>0</mn></msub></math> <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi></math> channel allows for the existence of a near-threshold scalar structure, which may correspond to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>6200</mn><mo stretchy="false">)</mo></math>. In the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>2</mn><mrow><mo>+</mo><mo>+</mo></mrow></msup></math> channel, while the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mo>​</mo><mn>5</mn></msup><msub><mi>S</mi><mn>2</mn></msub></math> <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi><mi>J</mi><mo stretchy="false">/</mo><mi>ψ</mi></math> system exhibits a repulsive interaction near threshold, the scattering amplitude has a Castillejo-Dalitz-Dyson zero at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>6.45</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> and a resonance pole at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>R</mi></mrow></msub></mrow></msqrt><mo>=</mo><mrow><mo stretchy="false">[</mo><mn>6.543</mn><mo stretchy="false">(</mo><mn>10</mn><mo stretchy="false">)</mo><mo>−</mo><mi>i</mi><mn>0.548</mn><mo stretchy="false">(</mo><mn>34</mn><mo stretchy="false">)</mo><mo>/</mo><mn>2</mn><mo stretchy="false">]</mo></mrow><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>π</mi></msub><mo>≈</mo><mn>420</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>R</mi></mrow></msub></mrow></msqrt><mo>=</mo><mrow><mo stretchy="false">[</mo><mn>6.538</mn><mo stretchy="false">(</mo><mn>13</mn><mo stretchy="false">)</mo><mo>−</mo><mi>i</mi><mn>0.537</mn><mo stretchy="false">(</mo><mn>56</mn><mo stretchy="false">)</mo><mo>/</mo><mn>2</mn><mo stretchy="false">]</mo></mrow><mtext> </mtext><mi>GeV</mi></mrow></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>π</mi></msub><mo>≈</mo><mn>250</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, where the uncertainties are statistical. This resonance may correspond to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>6600</mn><mo stretchy="false">)</mo></math> (or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>X</mi><mo stretchy="false">(</mo><mn>6400</mn><mo stretchy="false">)</mo></math>) reported by the ATLAS and CMS Collaborations. Our result supports its <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>2</mn><mrow><mo>+</mo><mo>+</mo></mrow></msup></math> assignment, in agreement with the latest spin-parity determination by CMS. Despite the observed dominance of the quark rearrangement effect, the light-hadron dynamics underlying dicharmonium scattering need to be explored at lighter pion masses. Furthermore, since our lattices are coarse and the lattice volumes are small, the associated systematic uncertainties should be controlled in future studies using more sophisticated lattice setups.

Geng Li

Chunjiang Shi

Ying Chen

Wei Sun

<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi><mi>J</mi><mo>/</mo><mi>ψ</mi></math> scattering from lattice QCD

We report the first searches for charged-lepton-flavor violation in decays of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>b</mi><mi>J</mi></mrow></msub><mo stretchy="false">(</mo><mn>1</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, and 2) to a pair of charged leptons using 158 million <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">ϒ</mi><mo stretchy="false">(</mo><mn>2</mn><mi>S</mi><mo stretchy="false">)</mo></math> decays collected with the Belle detector 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 KEKB collider. No significant signal is observed, and we set upper limits on the branching fractions for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>b</mi><mi>J</mi></mrow></msub><mo stretchy="false">(</mo><mn>1</mn><mi>P</mi><mo stretchy="false">)</mo></math> decays to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>±</mo></msup><msup><mi>μ</mi><mo>∓</mo></msup></math> at the level of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>6</mn></mrow></msup></math> and to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>±</mo></msup><msup><mi>τ</mi><mo>∓</mo></msup></math> or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>μ</mi><mo>±</mo></msup><msup><mi>τ</mi><mo>∓</mo></msup></math> at the level of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>. Limits on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>b</mi><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mn>1</mn><mi>P</mi><mo stretchy="false">)</mo></math> decays are translated into bounds on the corresponding Wilson coefficients of scalar operators that mediate charged-lepton-flavor violation.

M. Abumusabh

I. Adachi

A. Aggarwal

L. Aggarwal

H. Ahmed

Y. Ahn

H. Aihara

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

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

V. Bhardwaj

F. Bianchi

T. Bilka

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. Chang

P. Cheema

L. Chen

B.G. Cheon

C. Cheshta

H. Chetri

K. Chilikin

K. Chirapatpimol

H.E. Cho

K. Cho

S.J. Cho

S.K. Choi

S. Choudhury

S. Chutia

J. Cochran

J.A. Colorado-Caicedo

I. Consigny

L. Corona

J.X. Cui

E. De La Cruz-Burelo

S.A. De La Motte

G. De Nardo

G. De Pietro

R. de Sangro

M. Destefanis

S. Dey

R. Dhayal

A. Di Canto

J. Dingfelder

Z. Doležal

I. Domínguez Jiménez

T.V. Dong

X. Dong

G. Dujany

P. Ecker

D. Epifanov

J. Eppelt

Searches for Charged-Lepton-Flavor Violation in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>χ</mi><mrow><mi>b</mi><mi>J</mi></mrow></msub><mo stretchy="false">(</mo><mn>1</mn><mi>P</mi><mo stretchy="false">)</mo></math> Decays

We investigate the modification of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> meson mass in asymmetric nuclear matter at zero and finite temperatures employing an effective Lagrangian approach that considers the contributions of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mi>D</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><msup><mi>D</mi><mo>*</mo></msup></math> meson loops. The medium dependence of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math> meson masses is determined using the hadronic chiral SU(3) model, where scalar condensates are calculated and subsequently utilized in the QCD sum rules approach. Our findings indicate that an increase in baryonic density results in a negative mass shift of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> meson. This suggests that the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> meson is attracted to nuclear mean fields indicating the possibility of the formation of meson-nucleus bound states. Moreover, we have also determined the binding energy and absorption decay width of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> meson for both the ground and excited states of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="normal">O</mi><mn>16</mn></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Ca</mi><mn>40</mn></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Zr</mi><mn>90</mn></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Pb</mi><mn>208</mn></msup></math> nuclei. These results are expected to contribute to the understanding of experimental data from upcoming studies at Jefferson lab and the facility for antiproton and ion research, where low-momentum charmed mesons can be produced and examined within nuclei.

India

Manpreet Kaur

Arvind Kumar

Study of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> mass shift and bound states: Impact of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mi>D</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><msup><mi>D</mi><mo>*</mo></msup></math> meson loops

We report on a blinded search for dark matter (DM) using ionization-only (S2-only) signals in XENONnT with a total exposure of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>7.83</mn><mtext> </mtext><mtext> </mtext><mtext>Tonne-year</mtext></mrow></math> over 579 days in three science runs. Dedicated background suppression techniques and the first complete S2-only background model in XENONnT provide sensitivity to nuclear recoils of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">[</mo><mn>0.5</mn><mo>,</mo><mn>5.0</mn><mo stretchy="false">]</mo><mtext> </mtext><mtext> </mtext><msub><mrow><mi>keV</mi></mrow><mrow><mi>nr</mi></mrow></msub></mrow></math> and electronic recoils of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">[</mo><mn>0.04</mn><mo>,</mo><mn>0.7</mn><mo stretchy="false">]</mo><mtext> </mtext><mtext> </mtext><msub><mrow><mi>keV</mi></mrow><mrow><mi>ee</mi></mrow></msub></mrow></math>. No significant excess over the expected background is observed, and we set 90% confidence level upper limits on spin-independent DM-nucleon and spin-dependent DM-neutron scattering for DM masses between 3 and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>8</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></math>, as well as on DM-electron scattering, axionlike particles, and dark photons, improving on previous constraints. For spin-independent DM-nucleon scattering, we exclude cross sections above <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>6.0</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>45</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></math> at a DM mass of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>5</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></math>, pushing the XENONnT sensitivity closer to the region where coherent elastic neutrino-nucleus scattering becomes an irreducible background.