Jet modification in heavy-ion collisions provides microscopic access to the properties of the quark-gluon plasma. However, conventional approaches based on traditional global observables, such as <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>R</mi><mrow><mi>A</mi><mi>A</mi></mrow></msub></math>, capture limited information about the complex dynamics of parton-medium interactions during hard scatterings. In this work, we apply sequential machine-learning architectures to the jet declustering history tree, achieving improved classification performance compared with static models that learn only from a single stage of the jet evolution. We find that models trained on different medium implementations exhibit meaningful performance modification under cross-domain validation, indicating that machine learning is sensitive to implementation-specific features that traditional observables may not resolve. These results suggest new opportunities for using machine learning as an analysis tool to overcome some of the limitations of traditional jet-modification studies.

Brazil

Leonardo Lima da Silva

Marcelo Gameiro Munhoz

Jet quenching identification via supervised learning in simulated heavy-ion collisions

We investigate how the temperature influences the threshold cusps in meson-meson scatterings, i.e., <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi>π</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>D</mi><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mo>*</mo></msup></mrow></math> (or <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>D</mi><mo>*</mo></msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover></mrow></math>) scatterings, using the production rates and propagators obtained at finite temperature. The line shape of production rate of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi>π</mi></mrow></math> at different temperatures demonstrates that the cusp structure in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi>π</mi></mrow></math> scattering is mildly enhanced as the temperature increases. For the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi>π</mi></mrow></math> propagator, which includes isospin symmetry breaking, the line shape displays a unique plateaulike structure, and this structure will also be enhanced as the temperature increases. For comparison, the line shape of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>D</mi><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mo>*</mo></msup></mrow></math> propagator including isospin symmetry breaking is also investigated at different temperatures. As the temperature increases, its line shape shows a similar plateaulike structure but with some different properties when the temperature modifications to the masses and widths of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>D</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mo>*</mo></msup></math> are considered.

China

Japan

Ying Zhang

Atsushi Hosaka

Qian Wang

Shigehiro Yasui

Finite-temperature effects on the threshold cusps in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi>π</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>D</mi><msup><mover accent="true"><mi>D</mi><mo>¯</mo></mover><mo>*</mo></msup></mrow></math> scatterings from relativistic heavy-ion collisions

This study constrains the range of in-medium mass modification through a comparison of theoretical calculations with experimental transverse momentum spectra and the yield ratio <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mover accent="true"><mi>p</mi><mo>¯</mo></mover><mo>/</mo><mi>p</mi></mrow></math> of protons and antiprotons. Based on the constrained range and a Gaussian source model with radial flow, the theoretical predictions for the fermion back-to-back correlation (fBBC) of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mover accent="true"><mi>p</mi><mo>¯</mo></mover></mrow></math> pairs at BNL Relativistic Heavy Ion Collider energies are presented. The results reveal a strong sensitivity of the fBBC signal to the assumed source time distribution: a Lorentzian form generates a pronounced high-momentum signal, whereas an <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>α</mi></math>-stable Lévy form leads to a marked low-momentum signal. Moreover, the in-medium mass modification is shown to enhance the yield ratio <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mover accent="true"><mi>p</mi><mo>¯</mo></mover><mo>/</mo><mi>p</mi></mrow></math>. Therefore, events characterized by a larger <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mover accent="true"><mi>p</mi><mo>¯</mo></mover><mo>/</mo><mi>p</mi></mrow></math> ratio are predicted to have a significantly higher probability of exhibiting a detectable fBBC signal. This study may propose a promising new direction for the experimental observation of this phenomenon.

Yong Zhang

Squeezed spectra and back-to-back correlations of protons and antiprotons at energies available at the BNL Relativistic Heavy Ion Collider

Using <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>(</mo><mn>10087</mn><mo>±</mo><mn>44</mn><mo>)</mo></mrow><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> events collected with the BESIII detector operating at the BEPCII storage ring in 2009, 2012, 2018, and 2019, we perform a search for the reaction <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup><mi>n</mi><mo>→</mo><mi mathvariant="normal">Λ</mi><mi mathvariant="normal">Λ</mi><mi>X</mi></mrow></math>, where <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>X</mi></math> denotes any additional final particles. Given the highly suppressed phase space for producing extra pions, the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>X</mi></math> consists of either nothing or a photon, corresponding to the processes <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup><mi>n</mi><mo>→</mo><mi mathvariant="normal">Λ</mi><mi mathvariant="normal">Λ</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup><mi>n</mi><mo>→</mo><mi mathvariant="normal">Λ</mi><msup><mi mathvariant="normal">Σ</mi><mn>0</mn></msup><mo>→</mo><mi mathvariant="normal">Λ</mi><mi mathvariant="normal">Λ</mi><mi>γ</mi></mrow></math>. The <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup></math> comes from the decay of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>→</mo><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup><msup><mover accent="true"><mi mathvariant="normal">Ξ</mi><mo>¯</mo></mover><mn>0</mn></msup></mrow></math>, while the neutron originates from material of the beam pipe. A signal is observed for the first time with a statistical significance of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>6.4</mn><mi>σ</mi></mrow></math>. The cross section for the reaction <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup><mo>+</mo><mmultiscripts><mi>Be</mi><mprescripts></mprescripts><none></none><mn>9</mn></mmultiscripts><mo>→</mo><mi mathvariant="normal">Λ</mi><mo>+</mo><mi mathvariant="normal">Λ</mi><mo>+</mo><mi>X</mi></mrow></math> is measured to be <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>(</mo><mn>43.6</mn><mo>±</mo><mn>10</mn><mo>.</mo><msub><mn>5</mn><mtext>stat</mtext></msub><mo>±</mo><mn>11</mn><mo>.</mo><msub><mn>1</mn><mtext>syst</mtext></msub><mo>)</mo><mspace width="0.28em"></mspace><mi>mb</mi></mrow></math> at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>P</mi><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup></msub><mo>≈</mo><mn>0.818</mn><mspace width="0.28em"></mspace><mi>GeV</mi><mo>/</mo><mi>c</mi></mrow></math>, where the first uncertainty is statistical and the second systematic. No significant <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>H</mi></math>-dibaryon signal is observed in the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Λ</mi><mi mathvariant="normal">Λ</mi></mrow></math> final state.

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

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

X.Y. Chen

Y.B. Chen

Y.Q. Chen

Z. Chen

Z.J. Chen

Z.K. Chen

J.C. Cheng

South Korea

S.K. Choi

X. Chu

G. Cibinetto

F. Cossio

United Kingdom

J. Cottee-Meldrum

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

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

L. Feng

Q.X. Feng

Experimental study of the reaction <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup><mi>n</mi><mo>→</mo><mi mathvariant="normal">Λ</mi><mi mathvariant="normal">Λ</mi><mi>X</mi></mrow></math> using <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi mathvariant="normal">Ξ</mi><mn>0</mn></msup></math>-nucleus scattering

In this article, the surface tension and stability of quark matter modified by the vector interaction in a strong magnetic field are investigated in the quasiparticle model with the multiple reflection expansion. The self-consistent thermodynamic treatment of the chemical-potential-dependent quark mass is maintained by the effective bag function, which depends on both the chemical potential and the magnetic field. It is found that the vector interaction could enlarge the surface tension in both the parallel and transverse directions with respect to the magnetic field. In a stronger magnetic field region, the presence of the vector repulsive interaction leads to an increase in transverse surface tension with the magnetic field strength, which is opposite to the vanishing value without repulsive interaction in the previous work. Consequently, it is concluded that a moderate-intensity magnetic field is required for the formation of a quark-matter bubble with the vector interaction. Finally, it is demonstrated that the vector interaction slightly reduces the stability of quark matter.

Yu-Ying He

Xin-Jian Wen

Anisotropic surface tension and stability of quark matter modified by the vector interaction

Measurement of particle emission source is a fundamental objective of femtoscopy in high-energy nuclear collisions. Conventional analyses rely on Gaussian parametrizations of pair emission sources, which makes the extraction of single-particle emission sources challenging, particularly for rare particles. Here, we introduce a novel statistical reconstruction method that allows extracting information of the target source relative to a data-constrained reference source instead of the Gaussian assumption. The correlation function is expressed as an ensemble average over the single-particle-conditioned correlation kernel, defined as the particle-by-particle contribution to the correlation function conditioned by the target particles. For particles with rare yields, the particle-by-particle distribution of this kernel can be transformed into event-by-event extraction and becomes experimentally accessible, enabling a direct statistical reconstruction of the emission source of single particles, instead of inferring a pair source. We apply this method to reconstruct <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> source via <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mtext>−</mtext><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> correlations, using HAL QCD-derived <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>N</mi><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> potentials in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13.6</mn></mrow></math> TeV <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions simulated with EPOS4HQ. The reconstructed source reproduces the key characteristics and this new approach achieves a systematic uncertainty of approximately <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>13</mn><mo>%</mo></mrow></math> based on EPOS4 simulation.

Liang Zhang

Song Zhang

Kai-Jia Sun

Yu-Gang Ma

Reconstructing sources of rare particles by femtoscopic correlations

In this work, we investigate the interaction between the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Ω</mi></math> baryon and the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>s</mi><mover accent="true"><mi>s</mi><mo>¯</mo></mover></mrow></math> meson within the framework of the quark delocalization color-screening model. The spectra calculations show that no bound state is formed in any of the considered channels, while the scattering indicates that the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Ω</mi><mi>ϕ</mi></mrow></math> interaction with <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>J</mi><mi>P</mi></msup><mo>=</mo><mn>1</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> is weakly attractive. As for the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Ω</mi><mi>ϕ</mi></mrow></math> interactions with <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>J</mi><mi>P</mi></msup><mo>=</mo><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>5</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math>, as well as the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Ω</mi><msup><mi>η</mi><mo>′</mo></msup></mrow></math> interaction with <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>J</mi><mi>P</mi></msup><mo>=</mo><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>−</mo></msup></mrow></math>, they are all repulsive. After an investigation on the femtoscopic correlation functions, we find that, due to the spin-averaging effect, the overall <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Ω</mi><mi>ϕ</mi></mrow></math> correlation function exhibits a weak dependence on the source size, which provides a crucial significance of our model for future experimental examinations in relativistic heavy-ion collisions.

Ye Yan

Yuheng Wu

Yue Tan

Xiaohuang Hu

Qi Huang

Hongxia Huang

Jialun Ping

Investigating the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Ω</mi><mi>ϕ</mi></mrow></math> interaction and correlation functions

We study open-charm hadrons production in pp and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV using an improved multiphase transport (AMPT) model. Specifically, we show the transverse-momentum spectra and nuclear modification factors <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>R</mi><mi>AA</mi></msub></math> of <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>D</mi><mn>0</mn></msup></math> mesons and <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup></math> baryons, as well as the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> ratio in pp and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions. The results obtained from the AMPT model simulations are compared with the STAR experimental data and found to be consistent. We further investigate the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> ratio by evaluating contributions from coalescence, fragmentation, and the combined <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>coalescence</mi><mo>+</mo><mi>fragmentation</mi></mrow></math> mechanisms, and we find that fragmentation alone underestimates the pronounced enhancement in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> relative to pp at low and intermediate <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math>, whereas the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>coalescence</mi><mo>+</mo><mi>fragmentation</mi></mrow></math> mechanism reproduces the observed trend significantly better. These results indicate that coalescence plays a key role in charm-baryon productions and helps constrain the relative importance of different hadronization mechanisms in the ultrarelativistic nuclear collisions.

Bijun Fan

Shusu Shi

Chao Zhang

Liang Zheng

Open charm production and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> ratio in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn><mo> </mo><mi>GeV</mi></mrow></math>

We present measurements of the total and differential cross sections for near-threshold <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction obtained with the CLAS12 detector at the Thomas Jefferson National Accelerator Facility. The results are based on data collected during the fall 2018 and spring 2019 running periods, using electron beams with energies of 10.6 and 10.2 GeV, respectively, scattered off a liquid-hydrogen target. Near-threshold <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction offers a unique sensitivity to the strong interaction in the nonperturbative regime of quantum chromodynamics (QCD). The energy dependence of the cross section constrains the underlying <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> production mechanisms, including multigluon exchange and potential baryonic excitations. Additionally, the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>t</mi></math> dependence of the differential cross section can be related to the transverse spatial distribution of gluons in the proton, providing critical input for theoretical descriptions of the gluonic structure of the proton. An interpretation of the results in terms of the gluon content of the proton is presented, providing new experimental constraints on QCD-inspired models of the proton structure and the role of gluonic degrees of freedom in hadronic mass generation.

France

P. Chatagnon

V. Kubarovsky

R. Paremuzyan

S. Stepanyan

M. Tenorio

R. Tyson

A.G. Acar

P. Achenbach

J.S. Alvarado

M.J. Amaryan

W.R. Armstrong

H. Avakian

N.A. Baltzell

L. Barion

M. Bashkanov

M. Battaglieri

F. Benmokhtar

A. Bianconi

A.S. Biselli

S. Boiarinov

M. Bondi

F. Bossù

K.-Th. Brinkmann

W.J. Briscoe

S. Bueltmann

V.D. Burkert

T. Cao

D.S. Carman

A. Celentano

H. Chinchay

G. Ciullo

P.L. Cole

A. D'Angelo

Armenia

N. Dashyan

M. Defurne

R. De Vita

A. Deur

S. Diehl

C. Dilks

C. Djalali

M. Dugger

R. Dupré

H. Egiyan

M. Ehrhart

Chile

A. El Alaoui

L. El Fassi

Measurement of the near-threshold <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction cross section with the CLAS12 experiment