Tue·Jun 3, 2025Tuesday·June 3, 2025

1. 01*

   Charge Separation Measurements in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7--200 GeV in Search of the Chiral Magnetic Effect

   The STAR Collaboration

   The chiral magnetic effect in heavy-ion collisions predicts a charge separation signal along a magnetic field, which indicates local $P$ and $CP$ violations in the quark-gluon plasma. We report measurements of electric charge separation signals perpendicular to the spectator event plane in Au+Au collisions using high-statistics data from RHIC Beam Energy Scan II and top-energy runs. A novel event shape selection method is employed to suppress the flow-induced background. The residual charge separation signals near the zero-flow limit are positive in Au+Au collisions within the 20\%--50\% centrality range, with significance levels of $2.6\sigma$, $3.1\sigma$, and $3.3\sigma$ at $\sqrt{s_{NN}}=$ 11.5, 14.6, and 19.6 GeV, respectively. At other beam energies, the signals are either statistically limited or consistent with zero.

   nucl-exhep-ex15 citations
2. 02*

   Search for the chiral magnetic effect through beam energy dependence of charge separation using event shape selection

   The STAR Collaboration

   High-energy, heavy-ion collisions can create local domains of chirality-imbalanced quarks, reflecting the topological features of quantum chromodynamics. The chiral magnetic effect (CME) predicts an electric charge separation of quarks in such topological domains along the magnetic field ($\vec{B}$) generated by the passing of two high-$Z$ nuclei. We use a correlation observable $\Delta {\gamma }^{112}$ between charged meson pairs to detect the CME-induced charge separation and a novel event shape selection (ESS) method to mitigate the background effects related to elliptic flow ($v_2$). The ESS method classifies events based on the emission pattern of final-state particles and determines $\Delta {\gamma }_{\mathrm{ESS}}^{112}$ from the zero-flow limit. We reconstruct the $\vec{B}$ field direction from the spectator nucleons, which minimizes backgrounds unrelated to the collective motion of the system. In this work, we report the measurements of $\Delta {\gamma }^{112}$ and a background indicator $\Delta {\gamma }^{132}$ in Au+Au collisions from the RHIC Beam Energy Scan phase II and at the top RHIC energy. After background suppression, $\Delta {\gamma }_{\mathrm{ESS}}^{132}$ aligns with zero, and $\Delta {\gamma }_{\mathrm{ESS}}^{112}$ is reduced to no more than 20\% of $\Delta {\gamma }^{112}$. We observe a finite residual charge separation with $2.6\sigma$, $3.1\sigma$, and $3.3\sigma$ significance in the 20\%--50\% centrality range of Au+Au collisions at 11.5, 14.6, and 19.6 GeV. The results at 17.3 and 27 GeV also show positive values but with a lower significance of $1.3\sigma$ and $1.1\sigma$, respectively. The corresponding $\Delta {\gamma }_{\mathrm{ESS}}^{112}$ values at 7.7, 9.2, and 200 GeV are consistent with zero within uncertainties.

   nucl-exhep-exPRC(2026)·14 citations
3. 03*

   First systematic experimental 2D mapping of linearly polarized $\gamma$-ray polarimetric distribution in relativistic Compton scattering

   Kaijie Chen · Xiangfei Wang · Hanghua Xu · Gongtao Fan · Zirui Hao · Longxiang Liu · Yue Zhang · Sheng Jin · Zhicai Li · Pu Jiao · Qiankun Sun · Zhenwei Wang and 5 other authors

   The interaction of photons with relativistic electrons constitutes a fundamental electromagnetic process whose polarization transfer mechanics remain incompletely characterized. We report the first systematic measurement of spatial polarization distribution for $\gamma$-rays generated via \SI{45}{\degree} slant inverse Compton scattering (ICS) between linearly polarized \SI{0.117}{\eV} photons and \SI{3.5}{\GeV} electrons, performing full 2D mapping of intensity, polarization angle (AOP), and degree of polarization (DOP). Measurements reveal an asymmetric beam profile along the laser's polarization direction that resembles \SI{180}{\degree} backward ICS observations. The central beam region exhibits DOP $\approx$ 1.0 with AOP rigidly aligned at \SI{45}{\degree}, while peripheral regions display complex non-uniform polarization distributions. These findings confirm quantum electrodynamics predictions of near-complete polarization transfer along the beam axis in slant geometries, thus establishing slant scattering as a viable alternative to head-on configurations for generating high DOP $\gamma$-rays.

   nucl-exphysics.class-phNatl.Sci.Rev.(2026)·2 citations
4. 04*

   Potential absence of observed ${\pi }^2$ linear-chain structures in ${}^{14}$O via ${}^{10}$C($\alpha ,\alpha$) resonant scattering

   J. Bishop🇬🇧 · A. Hollands🇬🇧 · Tz. Kokolova🇬🇧 · G.V. Rogachev🇺🇸 · C. Wheldon🇬🇧 · E. Aboud🇺🇸 · S. Ahn🇺🇸 · M. Barbui🇺🇸 · N. Curtis🇬🇧 · J. Hooker🇺🇸 · C. Hunt🇺🇸 · H. Jayatissa🇺🇸 and 5 other authors

   Background: The preference for light nuclear systems to coagulate into $\alpha$-particle clusters has been well-studied. The possibility of a linear chain configuration of $\alpha$-particles would allow for a new way to study this phenomenon. Purpose: A rotational band of states in ${}^{14}$C has been claimed showing a ${\pi }^2$ linear chain structure. The mirror system, ${}^{14}$O, has been studied here to examine how this linear chain structure is affected by replacing the valence neutrons with protons. Method: A beam of ${}^{10}$C was incident into a chamber filled with He:CO${}_2$ gas with the tracks recorded inside the TexAT Time Projection Chamber and the recoil $\alpha$-particles detected by a silicon detector array to measure the ${}^{10}\mathrm{C}(\alpha ,\alpha )$ cross section. Results: The experimental cross section was compared with previous studies and fit using R-Matrix theory with the previously-observed ${}^{14}$O states being transformed to the ${}^{14}$C using mirror symmetry. The measured cross section does not replicate the claimed states, with the predicted cross section exceeding that observed at several energies and angles. Conclusion: A series of possibilities are highlighted with the most likely being that the originally-seen ${}^{14}$C states did not constitute a ${\pi }^2$ rotational band with a potentially incorrect spin assignment due to the limitations of the angular correlation method with non-zero spin particles. The work highlights the difficulties in measuring broad resonances corresponding to a linear chain state in a high level density.

   nucl-exPRC(2025)·0 citations
5. 05*

   Detection of molecular hydrogen in a neutron beam lifetime experiment

   J. Caylor (1)🇺🇸 · R. Biswas (2) · B. Crawford (3) · M. S. Dewey (4)🇺🇸 · N. Fomin (5)🇺🇸 · G. L. Greene (5 and 2)🇺🇸 · S. F. Hoogerheide (4)🇺🇸 · J. Hungria-Negron (3) · H. P. Mumm (4)🇺🇸 · J. S. Nico (4)🇺🇸 · F. E. Wietfeldt (2)🇺🇸 · D. O. Valete (3) · J. Zuchegno (2) ((1) Thomas Jefferson National Accelerator Facility, Newport News USA, (2) Tulane University, New Orleans USA, (3) Gettysburg College, Gettysburg USA, (4) National Institute of Standards and Technology, Gaithersburg USA, (5) University of Tennessee, Knoxville USA)

   One method of determining the free neutron lifetime involves the absolute counting of neutrons and trapped decay protons. In such experiments, a cold neutron beam traverses a segmented proton trap inside a superconducting solenoid while the neutron flux is continuously monitored. Protons that are born within the fiducial volume of the trap are confined radially by the magnetic field and axially by the electrostatic potential supplied by trap electrodes. They are periodically released and counted, and the ratio of the absolute number of neutrons to protons is proportional to the neutron lifetime. Systematic error can be introduced if protons in the trap are lost, gained, or misidentified. The influence of molecular hydrogen interactions is of particular interest because of its ubiquitous presence in ultrahigh vacuum systems. To understand how it could affect the neutron lifetime, measurements were performed on the production and detection of molecular hydrogen in an apparatus used to measure the neutron lifetime. We demonstrate that charge exchange with molecular hydrogen can occur with trapped protons, and we determine the efficiency with which the molecular hydrogen ions in the trap are detected. Finally, we comment on the potential impact on a neutron lifetime experiment using this beam technique. We find that the result of the beam neutron lifetime performed at NIST is unlikely to have been significantly affected by charge exchange with molecular hydrogen.

   nucl-exPRC(2025)·2 citations
6. 06*

   Comparing effective temperatures in standard and Tsallis distributions from transverse momentum spectra in small collision systems

   Peng-Cheng Zhang🇨🇳 · Pei-Pin Yang🇨🇳 · Ting-Ting Duan🇨🇳 · Hailong Zhu🇨🇳 · Fu-Hu Liu🇨🇳 · Khusniddin K. Olimov🇺🇿

   The transverse momentum ($p_T$) spectra of identified light charged hadrons, specifically bosons (${\pi }^{\pm }$ and $K^{\pm }$) as well as fermions [$p(\bar{p})$], produced in small collision systems, namely deuteron-gold (d+Au) and proton-proton (p+p) collisions at the top energy of the Relativistic Heavy Ion Collider (RHIC) with a center-of-mass energy of $\sqrt{s_{NN}}=200$ GeV, are investigated in this paper. In present study, d+Au collisions are categorized into three centrality classes: central (0--20\%), semi-central (20--40\%), and peripheral (40--100\%) collisions. Various types of distributions, including standard [Bose-Einstein (Fermi-Dirac) and Boltzmann] and Tsallis distributions, are employed to fit the same $p_T$ spectra to derive different effective temperatures denoted as $T_{eff}$. The results indicate that $T_{eff}$ values obtained from Bose-Einstein, Boltzmann, Fermi-Dirac, and Tsallis distributions exhibit systematically a decreasing trend. Meanwhile, these $T_{eff}$ values also show a decreasing trend with a decrease in collision centrality. Furthermore, based on the spectra of given particles, a perfect linear relationship is observed between different pairwise combinations of $T_{eff}$ derived from both Boltzmann and Bose-Einstein (Fermi-Dirac) distributions as well as between Tsallis and Bose-Einstein (Fermi-Dirac) distributions.

   ↳ hep-phhep-exnucl-exnucl-thIndian J.Phys.(2026)·2 citations
7. 07*

   Regularization Prescription for the Mixing Between Nonlocal Gluon and Quark Operators

   Yao Ji🇨🇳 · Zhuoyi Pang🇨🇳 · Fei Yao🇺🇸 · Jian-Hui Zhang🇨🇳

   It is well-known that in the study of mixing between nonlocal gluon and quark bilinear operators there exists an ambiguity when relating coordinate space and momentum space results, which can be conveniently resolved through Mellin moments matching in both spaces. In this work, we show that this ambiguity is due to the lack of a proper regularization prescription of the singularity that arises when the separation between the gluon/quark fields approaches zero. We then demonstrate that dimensional regularization resolves this issue and yields consistent results in both coordinate and momentum space. This prescription is also compatible with lattice extractions of parton distributions from nonlocal operators.

   ↳ hep-phhep-latnucl-exnucl-thPRD(2026)·0 citations
8. 08*

   Unwinding the rare $\Omega$ sector: Fragmentation of fully charmed baryons from HL-LHC to FCC

   Francesco Giovanni Celiberto🇪🇸

   By adopting a hadron-structure-oriented approach, we present and discuss the release of the novel OMG3Q1.0 set of collinear fragmentation functions for fully charmed, rare $\Omega$ baryons. Our methodology combines diquark-like proxy model inputs for both charm-quark and gluon channels, calculated at the initial energy scales, with a DGLAP evolution that ensures a consistent treatment of heavy-quark thresholds, following directly from the HF-NRevo scheme. We complement our work with a phenomenological study of NLL/NLO${}^{+}$ resummed ${\Omega }_{3c}$ plus jet distributions using (sym)JETHAD at the HL-LHC and the future FCC. Unraveling the production mechanisms of rare, yet-unobserved hadrons, as provided by the OMG3Q1.0 functions, stands as a key asset for deepening our understanding of QCD at future high-energy hadron colliders.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2025)·15 citations
9. 09*

   Perspectives for hyperon and hypernuclei physics

   Jin-Hui Chen🇨🇳 · Li-Sheng Geng🇨🇳 · Emiko Hiyama🇯🇵 · Zhi-Wei Liu🇨🇳 · Josef Pochodzalla🇩🇪

   Hypernuclei, nuclei containing one or more hyperons, serve as unique laboratories for probing the non-perturbative quantum chromodynamics (QCD). Recent progress in hypernuclear physics, driven by advanced experimental techniques and theoretical innovations, is briefly reviewed with a focus on key findings and unresolved challenges, such as the precise determination of the hypertriton binding energy, investigations of charge symmetry breaking in mirror hypernuclei, and the search for exotic systems, including the neutral nn$\Lambda$ state. Experimental breakthroughs, including invariant-mass analyses and femtoscopy studies in heavy-ion collisions, as well as high-resolution $\gamma$-spectroscopy, have enabled precise studies of light hypernuclei and offered critical insights into the hyperon-nucleon interaction. Theoretical progress, including ab initio calculations based on chiral effective field theory and lattice QCD, has further enhanced our understanding of hyperon-nucleon and hyperon-hyperon interactions.

   ↳ nucl-thnucl-exChin.Phys.Lett.(2025)·18 citations
10. 10*

    Photon-induced production of the exotic charged charmonium-like state $Z_c(3900)$ off nuclear targets and its internal structure

    E. Ya. Paryev🇷🇺

    In this paper, we investigate the possibility to study the famous charged charmonium-like state $Z_c(3900)$ production off nuclear targets and its properties in inclusive photon-induced reactions near the kinematic threshold within the collision model based on the nuclear spectral function. The model accounts for its charged components $Z_c(3900{)}^{\pm }$ production in direct photon-nucleon interactions as well as three different popular scenarios for their internal structures: compact tetraquarks, molecules of the two open-charm mesons and mixtures of both of them. We calculate the absolute and relative excitation functions for production of $Z_c(3900{)}^{\pm }$ mesons on ${}^{12}$C and ${}^{184}$W target nuclei at initial photon energies of 9.0-17.5 GeV, the absolute momentum differential cross sections and their ratios for the $Z_c(3900{)}^{\pm }$ production off these target nuclei at laboratory polar angles of 0${}^{\circ }$-10${}^{\circ }$ and at photon energy of 14 GeV as well as the A-dependences of the ratios of the total cross sections for $Z_c(3900{)}^{\pm }$ production at photon energy of 14 GeV within the adopted scenarios for the $Z_c(3900{)}^{\pm }$ internal structures. We demonstrate that the absolute and relative observables considered show a certain sensitivity to the $Z_c(3900{)}^{\pm }$ internal structures which are by far the best known. Hence, they might be useful for the determination of these structures -- the issue which has attracted much attention in the hadron physics community -- from the comparison of them with the experimental data from the future high-precision experiments at the CEBAF facility.

    ↳ hep-phhep-exnucl-exnucl-thNPA(2025)·2 citations
11. 11*

    The Electron-Gamma Coincidence Setup DAGOBERT

    B. Hesbacher · G. Steinhilber · J. Isaak · N. Pietralla · J. Birkhan · M. L. Cortés · D. H. Jakubassa-Amundsen · I. Jurosevic · P. von Neumann-Cosel · M. Rech · X. Roca-Maza · D. Schneider

    The QCLAM electron spectrometer at the S-DALINAC electron accelerator at Technische Universität Darmstadt has been extended by the DAGOBERT $\gamma$-detector array consisting of fast timing and high efficiency LaBr${}_3$:Ce detectors to perform electron-gamma coincidence measurements. The functionality of the setup and data acquisition system was demonstrated in a commissioning measurement on ${}^{12}\text{C}$ observing the $4.44$MeV and $15.11$MeV states. A medium-heavy nucleus, ${}^{96}\text{Ru}$, has been studied for the first time up to excitation energies of $15$MeV using the $(e,e^{\prime }\gamma )$ reaction. In particular, the angular distribution of the $2_1^{+}$ state and the $\gamma$-decay branching ratios of the mixed-symmetric $2_3^{+}$ state were observed. DAGOBERT@QCLAM is a new and worldwide unique setup for nuclear structure studies of excitation and decay using purely electromagnetic probes, with a significantly improved sensitivity compared to previous experiments.

    ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2025)·1 citation

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.