Mon·Apr 7, 2025Monday·April 7, 2025

1. 01*

   Azimuthal anisotropy of direct photons in Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

   PHENIX Collaboration: N.J. Abdulameer · U. Acharya · A. Adare · C. Aidala · N.N. Ajitanand · Y. Akiba · M. Alfred · S. Antsupov · N. Apadula · H. Asano · B. Azmoun · V. Babintsev and 314 other authors

   The PHENIX experiment at the Relativistic Heavy Ion Collider measured the second Fourier component $v_2$ of the direct-photon azimuthal anisotropy at midrapidity in Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV. The results are presented in 10\% wide bins of collision centrality and cover the transverse-momentum range of $1<p_T<20$ GeV/$c$, and are in quantitative agreement with findings published earlier, but provide better granularity and higher $p_T$ reach. Above a $p_T$ of 8--10 GeV/$c$, where hard scattering dominates the direct-photon production, $v_2$ is consistent with zero. Below that in each centrality bin $v_2$ as a function of $p_T$ is comparable to the ${\pi }^0$ anisotropy albeit with a tendency of being somewhat smaller. The results are compared to recent theory calculations that include, in addition to thermal radiation from the quark-gluon plasma and hadron gas, sources of photons from pre-equilibrium, strong magnetic fields, or radiative hadronization. While the newer theoretical calculations describe the data better than previous models, none of them alone can fully explain the results, particularly in the region of $p_T=4$--8 GeV/$c$.

   nucl-exPRC(2026)·8 citations
2. 02*

   Calculation and comparison of sensitivities in $0\nu \beta \beta$ experiments based on key parameters

   X. Yu🇨🇳 · L. T. Yang🇨🇳 · Q. Yue🇨🇳 · H. Ma🇨🇳 · H. T. Wong🇹🇼

   Worldwide efforts are underway to detect neutrinoless double beta ($0\nu \beta \beta$) decay using experiments based on various technologies and target isotopes. Future experiments in this regard aim to exclude the inverted order (IO) condition or explore the normal order (NO) band. Consequently, comparing the sensitivities of proposed $0\nu \beta \beta$ decay experiments with promising prospects is essential. The current study adopts sensitivity metrics, including exclusion and discovery sensitivities, half-life sensitivities, and $m_{\beta \beta }$ sensitivities, to provide a comprehensive evaluation of ten typical promising experiments: LEGEND, CDEX, nEXO, XLZD, PandaX, NEXT, KamLAND-Zen, JUNO, SNO+, and CUPID, and highlight their unique features. Based on reported experimental parameters, the concept of a ``technical line'' is introduced to determine the location that each experiment may realize in the $\xi$ and ${\lambda }_b$ space, where $\xi$ represents the sensitive exposure per year, and ${\lambda }_b$ denotes the expected annual rate of background events. Half-life sensitivities for the selected experiments are calculated, some of them in multiple phases and others in conservative or aggressive condition. The results indicate that increasing the operation time is more beneficial for zero-background experiments, which also demonstrate greater competitiveness in discovery sensitivity. $m_{\beta \beta }$ sensitivities are presented as uncertainty bands arising from the nuclear matrix element uncertainties. Additionally, half-life and $m_{\beta \beta }$ sensitivities are estimated under ideal conditions also in the form of uncertainty bands, where only irreducible $2\nu \beta \beta$ and solar B-8 neutrino induced background remain.

   nucl-exhep-exphysics.ins-detPRD(2025)·2 citations
3. 03*

   A unified algorithm for multi-particle correlations between azimuthal angle and transverse momentum in ultra-relativistic nuclear collisions

   Emil Gorm Dahlbæk Nielsen🇩🇰 · Nina Nathanson🇩🇰 · Kristjan Gulbrandsen🇩🇰 · You Zhou🇩🇰

   Multi-particle correlations between azimuthal angle and mean transverse momentum are a powerful tool for probing size and shape correlations in the initial conditions of heavy-ion collisions. These correlations have also been employed to investigate nuclear structure, including potential nuclear shape phase transitions at the energy frontier. However, their implementation is highly nontrivial, and prior studies have been mostly limited to lower-order correlations, such as the modified Pearson correlation coefficient, $\rho (v_{\mathrm{n}}^2,[p_{\mathrm{T}}])$. This paper presents a unified framework that employs a recursive algorithm, enabling the efficient evaluation of arbitrary-order correlations while maintaining computational efficiency. This framework is demonstrated using widely adopted transport models, including AMPT and HIJING. The proposed unified algorithm for multi-particle correlations between azimuthal angle and transverse momentum provides a systematic and efficient approach for multi-particle correlation analyses. Its application in experiments at the Relativistic Heavy Ion Collider and the Large Hadron Collider facilitates the exploration of nuclear structure at ultra-relativistic energies.

   ↳ nucl-thnucl-exEPJC(2025)·4 citations
4. 04*

   Evaluation of the Response to Electrons and Pions in the Scintillating Fiber and Lead Calorimeter for the Future Electron-Ion Collider

   Henry Klest🇺🇸 · Maria Żurek🇺🇸 · Tegan D. Beattie🇨🇦 · Manoj Jadhav🇺🇸 · Sylvester Joosten🇺🇸 · Maggie Kerr🇺🇸 · Bobae Kim🇺🇸 · Minho Kim🇺🇸 · Jessica Metcalfe🇺🇸 · Zisis Papandreou🇨🇦 · Jared Richards🇺🇸 · Jonathan Zarling🇨🇦

   The performance of the Baby Barrel Electromagnetic Calorimeter (Baby BCAL) - a small-scale lead-scintillating-fiber (Pb/ScFi) prototype of the GlueX Barrel Electromagnetic Calorimeter (BCAL) - was tested in a dedicated beam campaign at the Fermilab Test Beam Facility (FTBF). This study provides a benchmark for the Pb/ScFi component of the future Barrel Imaging Calorimeter (BIC) in the ePIC detector at the Electron-Ion Collider (EIC). The detector response to electrons and pions was studied at beam energies between 4 and 10 GeV, extending previous GlueX tests [NIM A 596 (2008) 327-337 and arXiv:1801.03088] to a higher energy regime. The calibrated detector exhibits good linearity within uncertainties, and its electron energy resolution meets EIC requirements. The data further constrain the constant term in the energy resolution to below 1.9%, improving upon previous constraints at lower energies. Simulations reproduce key features of the electron and pion data within the limitations of the collected dataset and the FTBF test environment. Electron-pion separation in the test beam setup was analyzed using multiple methods, incorporating varying degrees of beam-related effects. The inclusion of longitudinal shower profile information enhanced the separation performance, underscoring its relevance for the full-scale BIC in ePIC. These results provide essential benchmarks for the Pb/ScFi section of the future BIC, validating detector simulations and guiding optimization strategies for electron-pion discrimination.

   ↳ physics.ins-dethep-exnucl-exJINST(2025)·5 citations
5. 05*

   Optimal Observables for the Chiral Magnetic Effect from Machine Learning

   Yuji Hirono🇯🇵 · Kazuki Ikeda🇺🇸 · Dmitri E. Kharzeev🇺🇸 · Ziyi Liu🇨🇳 · Shuzhe Shi🇨🇳

   The detection of the Chiral Magnetic Effect (CME) in relativistic heavy-ion collisions remains challenging due to substantial background contributions that obscure the expected signal. In this Letter, we present a novel machine learning approach for constructing optimized observables that significantly enhance CME detection capabilities. By parameterizing generic observables constructed from flow harmonics and optimizing them to maximize the signal-to-background ratio, we systematically develop CME-sensitive measures that outperform conventional methods. Using simulated data from the Anomalous Viscous Fluid Dynamics framework, our machine learning observables demonstrate up to 90\% higher sensitivity to CME signals compared to traditional $\gamma$ and $\delta$ correlators, while maintaining minimal background contamination. The constructed observables provide physical insight into optimal CME detection strategies, and offer a promising path forward for experimental searches of CME at RHIC and the LHC.

   ↳ hep-phnucl-exnucl-thPRC(2025)·1 citation
6. 06*

   Energy-energy correlators in charm-tagged jets in proton-proton collisions at $\sqrt{\mathbf{s}}=13$ TeV

   ALICE Collaboration

   In this letter, we present the first measurement of the energy-energy correlator (EEC) in charm-tagged jets from proton-proton (pp) collisions at $\sqrt{s}=13$ TeV. EECs probe the structure of QCD radiation, providing a unique test of mass-dependent effects in parton showers involving a charm quark and offering a distinct view into non-perturbative phenomena, including the hadronization process. The EEC is measured for charm-tagged jets and flavor-untagged (inclusive) jets with transverse momenta of $10<p_{\mathrm{T}}<30$ GeV/$c$, where charm-quark mass effects are significant. We observe a significant suppression of the EEC amplitude in charm jets compared to inclusive ones, consistent with the expected suppression of radiation from massive quarks -- a fundamental prediction of QCD. Despite the significant amplitude difference, the observed peak positions of the charm and inclusive-jet EEC are similar, indicating a complex interplay between Casimir factor (differentiating quark and gluon jets), and quark-mass (dead-cone) effects in the QCD parton shower as well as subsequent hadronization effects. Comparisons with next-to-leading order calculations and various Monte Carlo event generators reveal the sensitivity of this observable to both mass effects in the parton shower and hadronization process. These results provide new constraints on theoretical models of heavy-quark jets and offer insights into the parton-to-hadron transition in QCD.

   ↳ hep-exnucl-ex35 citations
7. 07*

   Supercooled Goldstone Bosons at the QCD Chiral Phase Transition

   Adrien Florio🇩🇪 · Eduardo Grossi🇮🇹 · Aleksas Mazeliauskas🇩🇪 · Alexander Soloviev🇸🇮 · Derek Teaney🇺🇸

   We discuss a universal non-equilibrium enhancement of long-wavelength Goldstone bosons induced by quenches to the broken phase in Model G -- the dynamical universality class of an $O(4)$-antiferromagnet and the chiral phase transition in QCD. Scaling arguments for the coarsening dynamics describing the formation of the chiral condensate predict a parametric enhancement in the infrared spectra of Goldstones, a prediction confirmed by stochastic simulations of the transition. The details of the enhancement are determined by the non-linear dynamics of a superfluid effective theory, which is a limit of Model G reflecting the broken $O(4)$ symmetry. Our results translate to a parametric enhancement of low-momentum pions in heavy-ion collisions at the LHC, which are underpredicted in current hydrodynamic models without critical dynamics.

   ↳ hep-phhep-latnucl-exnucl-thPRL(2025)·14 citations

* 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.