Tue·May 13, 2025Tuesday·May 13, 2025

1. 01*

   Dielectron measurements in Au+Au collisions at BES-II energies with the STAR experiment

   Chenliang Jin (for the STAR Collaboration)🇺🇸

   Dielectrons, emitted during the evolution of the hot and dense QCD medium created in relativistic heavy-ion collisions, offer an effective probe of the hot medium properties, as they do not involve strong interactions. The dielectron emission rate is proportional to the medium's electromagnetic spectral function. In the dielectron mass range from 400 to 800 MeV/$c^2$, the spectral function probes the in-medium $\rho$ meson propagator which is sensitive to the medium's properties including the total baryon density and the temperature. By measuring thermal dielectron production, we can study the microscopic interactions between the electromagnetic current and the medium. The RHIC Beam Energy Scan (BES) program provides a unique opportunity to systematically study dielectron production in a collision energy range where the total baryon density and temperatures are varying substantially. In these proceedings, STAR measurements of thermal electrons produced in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 9.2, 11.5, 14.6 and 19.6 GeV will be reported. The results will include the thermal dielectron spectra, differential/total excess yield, and the temperature extracted from the low invariant mass range, as well as their collision energy dependence.

   nucl-exhep-exEPJ Web Conf.(2025)·1 citation
2. 02*

   The 76Cu conundrum remains unsolved

   B. Olaizola · A. Illana · J. Benito · D.P. Suárez-Bustamante · G. Del Piccolo · A. Algora · B. Andel · A.N. Andreyev · M. Araszkiewicz · Y. Ayyad · R.A. Bark · T. Berry and 71 other authors

   Near the doubly-magic nucleus \nuc{Ni}{78} ($Z=28$, $N=50$), there has been a decades-long debate on the existence of a long-lived isomer in \nuc{Cu}{76}. A recent mass measurement claimed to have settled the debate, by measuring the energy of the isomer and shedding light on the structure of the nucleus. In this work, we present new, more accurate, and precise values of the half-lives of the isomeric and ground states in \nuc{Cu}{76}. Our findings suggest that both states have very similar half-lives, in the 600-700 ms range, in disagreement with the literature values, implying that they cannot be differentiated by their decay curves. These results raise more questions than they answer, reopening the debate and showing that the structures in \nuc{Cu}{76} are still not fully understood.

   nucl-exPLB(2025)·0 citations
3. 03*

   Extraction of the non-spin- and spin-transfer isovector responses via the ${}^{12}\mathrm{C}{(}^{10}\mathrm{Be},{}^{10}\mathrm{B}+\gamma {)}^{12}\mathrm{B}$ reaction

   Sk M. Ali🇺🇸 · C. Maher🇺🇸 · R. G. T. Zegers🇺🇸 · M. Scott🇺🇸 · D. Bazin🇺🇸 · M. Bowry🇺🇸 · B. A. Brown🇺🇸 · C. M. Campbell🇺🇸 · A. Gade🇺🇸 · S. Gales🇫🇷 · U. Garg🇺🇸 · M. N. Harakeh🇳🇱 and 10 other authors

   The isovector response in ${}^{12}$B was investigated via the ${}^{12}$C(${}^{10}\mathrm{Be}$,${}^{10}\mathrm{B}$+$\gamma$)${}^{12}$B${}^{\ast }$ reaction at $100A\mathrm{MeV}$. By utilizing the $\gamma$-decay properties of the 1.74 MeV $0^{+}$ and 0.718 MeV $1^{+}$ states in ${}^{10}\mathrm{B}$, the separate extraction of the non-spin-transfer ($\Delta S=0$) and spin-transfer ($\Delta S=1$) isovector responses up to an excitation energy of 50 MeV in ${}^{12}$B in a single measurement is demonstrated. The experimental setup employed the S800 spectrometer to detect and analyze the ${}^{10}\mathrm{B}$ ejectiles and the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) for obtaining the Doppler-reconstructed spectrum for $\gamma$-rays emitted in-flight by ${}^{10}\mathrm{B}$. A ${}^{12}$C foil was placed at the pivot point of the spectrograph. The ${}^{12}$B reaction product was not detected. Contributions from transitions associated with the transfer of different units of angular momentum in the non-spin- and spin-transfer responses were analyzed using a multipole decomposition analysis. The extracted non-spin-dipole ($\Delta S=0$, $\Delta L=1$) and spin-dipole ($\Delta S=1$, $\Delta L=1$) responses were found to be consistent with available data from other charge-exchange probes, validating the non-spin- and spin-transfer filters used. While statistical uncertainties and experimental resolutions were relatively large due to the modest intensity of the ${}^{10}\mathrm{Be}$ secondary beam, the results show that, with the much higher intensities that will be available at new rare-isotope beam facilities, the (${}^{10}\mathrm{Be}$,${}^{10}\mathrm{B}$+$\gamma$) reaction and its $\Delta T_z=-1$ partner, the (${}^{10}$C,${}^{10}\mathrm{B}$+$\gamma$) reaction, are powerful tools for elucidating the isovector non-spin- and spin-transfer responses in nuclei.

   nucl-exPRC(2025)·0 citations
4. 04*

   Phenomenology of baryon dynamics with directed flow in relativistic heavy-ion collisions

   Tribhuban Parida🇮🇳

   This thesis aims to elucidate the role of initial baryon stopping and its diffusion in heavy-ion collisions (HIC) using hydrodynamic model. In this regard, we have studied the observable-directed flow ($v_1$) of identified hadrons, particularly the $v_1$ of baryons and antibaryons, as well as the splitting observed between them in detail. We propose a new ansatz for the initial baryon distribution. By employing this initial baryon deposition model alongside a tilted energy distribution as inputs to a hybrid framework, we successfully describe the rapidity-odd $v_1$ of identified hadrons, including the elusive baryon-antibaryon splitting of $v_1$ across a wide range of $\sqrt{s_{NN}}$. Our model, incorporating baryon stopping and it's subsequent diffusion within a relativistic hydrodynamic framework and employing a crossover equation of state derived from lattice QCD calculations, establishes a non-critical baryonic baseline. Moreover, we demonstrate that recent STAR measurements of the centrality and system-size dependence of $v_1$ splitting between oppositely charged hadrons-attributed to electromagnetic field effects-are significantly influenced by background contributions from baryon stopping and its diffusion. Furthermore, we show that the rapidity dependence of the splitting of the rapidity-even component of $v_1$ between $p$ and $\bar{p}$ is highly sensitive to the initial baryon deposition scheme. If measured experimentally, this could constraint the rapidity dependence of the initial baryon deposition profile. Moreover, it could offer valuable phenomenological insights into the baryon junction picture and help refine constraints on the baryon diffusion coefficient of the medium. Notably, utilizing this phenomenologically successful baryon deposition model, we present the first estimation of the baryon diffusion coefficient for the strongly interacting QCD matter created in HIC.

   ↳ nucl-thhep-exhep-phnucl-ex4 citations
5. 05*

   Continuum Lambda spectra for a 6Li_Lambda hypernucleus in the 6Li(K-, pi-) reaction

   Toru Harada🇯🇵 · Yoshiharu Hirabayashi🇯🇵

   We theoretically investigate Lambda production via a (K-, pi-) reaction on a 6Li target, using the distorted-wave impulse approximation (DWIA) with a Fermi-averaged K-n --> pi-Lambda amplitude. We calculate Lambda production spectra using the Green's function method for a 5Li nuclear core + Lambda system, employing a Lambda folding-model potential based on the 5Li nuclear density, which is constructed from alpha-p and 3He-d cluster wave functions. The results show that the calculated spectrum, which includes Lambda bound, resonance, and continuum states, agrees well with the experimental data from the (K-, pi-) reaction at p_K- = 790 MeV/c (0 deg.), where substitutional (0p_Lambda, 0p^{-1}_n) and (0s_Lambda, 0s^{-1}_n) configurations dominate in the near-recoilless reactions. A narrow peak corresponds to a high-lying excited state with spin-parity J^P= 1+ at E_Lambda= 13.8 MeV near the 3He + d + Lambda threshold, arising from interference effects between 5Li(3/2+)x(0s1/2)_Lambda and 5Li(1/2+)x(0s1/2)_Lambda components. This study offers a valuable framework for extracting essential information on the structure and production mechanisms of hypernuclear states from experimental data.

   ↳ nucl-thnucl-exPRC(2025)·1 citation
6. 06*

   Enhancement of photon emission rate near QCD critical point

   Yukinao Akamatsu🇯🇵 · Masayuki Asakawa🇯🇵 · Masaru Hongo🇯🇵 · Mikhail Stephanov🇺🇸 · Ho-Ung Yee🇺🇸

   We compute photon emission rate enhancement near the QCD critical point using an effective theory of dynamic critical phenomena and derive a universal photon spectrum. The emission rate scales similarly to conductivity, increasing with the correlation length ($\xi$), diverging at the critical point. The spectrum exhibits $\omega d{N}_{\gamma }/d^{3}k\propto {\omega }^{-1/2}$ in the scaling regime, with the transition occurring at a frequency comparable to shear damping rate $\omega \sim {\gamma }_{\eta }/{\xi }^2$, reflecting the nonequilibrium properties of the near-critical liquid.

   ↳ hep-phcond-mat.stat-mechhep-thnucl-ex+1PRD(2026)·4 citations
7. 07*

   Violation of NCQ scaling in hadron elliptic flow in Au+Au collisions at $\sqrt{s_{NN}}=3.0-7.7GeV

   Xun Zhu🇨🇳 · Gao-Chan Yong🇨🇳

   We investigate the number-of-constituent-quark (NCQ) scaling of elliptic flow for various hadrons in non-central Au+Au collisions at \(\sqrt{s_{NN}} = 3.0\text{--}7.7\,\mathrm{GeV}\) using the AMPT model with string melting (SM) and pure hadron cascade (HC) modes. For the SM case, NCQ scaling is absent at \(\sqrt{s_{NN}} =3.0\,\mathrm{GeV}\) but is largely restored by \(\sqrt{s_{NN}} =3.9\,\mathrm{GeV}\). Although quark coalescence occurs at \(\sqrt{s_{NN}} =3.0\,\mathrm{GeV}\), the lack of NCQ scaling is attributed to the insufficient development of quark elliptic flow and the limited production of strange quarks and antiquarks. This finding suggests that NCQ scaling could not be considered a definitive signature of quark-gluon plasma (QGP) formation in the RHIC fixed-target energy region. For the HC case, as expected, no NCQ scaling is observed. However, a mass ordering in the elliptic flow emerges at \(\sqrt{s_{NN}} =4.5\,\mathrm{GeV}\), indicating that full thermalization may not be a prerequisite for mass ordering.

   ↳ nucl-thhep-phnucl-exPLB(2025)·4 citations
8. 08*

   A two-stage time-stretching TDC with discrete components

   Yanbo Chu🇨🇳 · Zhicai Zhang🇨🇳

   This paper presents the design and testing of a time-stretching-based time-to-digital converter (TDC) implemented with discrete components. The TDC utilizes capacitor charging and discharging to achieve a time resolution of under 100 ps using a 100 MHz clock counter on a low-power, low-cost FPGA, achieving a time amplification factor of over 100. A two-stage time-stretching architecture is employed to reduce the conversion time to below 300 ns for a 10 ns input range. An onboard calibration system, including a pulse generation circuit, is implemented, and calibration results are presented. This system serves as a proof-of-concept platform for circuit optimization toward an ASIC implementation of a front-end TDC targeting future 4D pixel detectors at hadron colliders, with goals of sub-50 ps resolution and power consumption at the $\mu$W/channel level. Additionally, the design offers a modular, low-cost solution for extracting signal arrival times with 100 ps precision in particle physics experiments, such as photoelectron timing extraction for photodetector readout in neutrino experiments.

   ↳ physics.ins-dethep-exnucl-exJINST(2025)·0 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.