Thu·Feb 13, 2025Thursday·February 13, 2025

1. 01*

   Observation of $\Lambda$ hyperon local polarization in pPb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 8.16 TeV

   CMS Collaboration

   The polarization of the $\Lambda$ and $\overline{\Lambda }$ hyperons along the beam direction has been measured in proton-lead (pPb) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of 186.0 $\pm$ 6.5 nb${}^{-1}$. A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient $P_{z,s2}$, is observed. The $P_{z,s2}$ values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed $P_{z,s2}$ values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the pPb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.

   nucl-exhep-exPRL(2025)·22 citations
2. 02*

   Benchmarking nuclear matrix elements of $0\nu \beta \beta$ decay with high-energy nuclear collisions

   Yi Li🇨🇳 · Xin Zhang🇨🇳 · Giuliano Giacalone🇨🇭 · Jiangming Yao🇨🇳

   Reducing uncertainties in the nuclear matrix elements (NMEs) remains a critical challenge in designing and interpreting experiments aimed at discovering neutrinoless double beta ($0\nu \beta \beta$) decay. Here, we identify a class of observables, distinct from those employed in low-energy nuclear structure applications, that are strongly correlated with the NMEs: momentum correlations among hadrons produced in high-energy nuclear collisions. Focusing on the ${}^{150}$Nd$\to$${}^{150}$Sm transition, we combine a Bayesian analysis of the structure of ${}^{150}$Nd with simulations of high-energy ${}^{150}$Nd+${}^{150}$Nd collisions. We reveal prominent correlations between the NMEs and features of the quark-gluon plasma (QGP) formed in these processes, such as spatial gradients and anisotropies, which are accessible via collective flow measurements. Our findings demonstrate collider experiments involving $0\nu \beta \beta$ decay candidates as a platform for benchmarking theoretical predictions of the NMEs.

   ↳ nucl-thhep-phnucl-exPRL(2025)·17 citations
3. 03*

   Directly probing existence of $\alpha$-cluster structure in ${}^{20}$Ne by relativistic heavy-ion collisions

   Lu-Meng Liu🇨🇳 · Hai-Cheng Wang🇨🇳 · Song-Jie Li🇨🇳 · Chunjian Zhang🇨🇳 · Jun Xu🇨🇳 · Zhong-Zhou Ren🇨🇳 · Jiangyong Jia🇺🇸 · Xu-Guang Huang🇨🇳

   Can relativistic heavy-ion collisions only probe the global shape of colliding nuclei, or their detailed internal structure as well? Taking ${}^{20}$Ne as an example, we attempt to directly probe its internal $\alpha$-cluster structure, by comparing experimentally measured observables in collisions at relativistic energies from density distributions of ${}^{20}$Ne with and without $\alpha$-cluster structure. Since the two density distributions give the same nucleus size and deformation, they lead to similar mid-rapidity observables. However, the $\alpha$-cluster structure may considerably reduce the free spectator nucleon yield and enhance the spectator light nuclei yield, as a result of more compact initial phase-space distribution of nucleons inside $\alpha$ clusters. We propose to measure the scaled yield ratio of free spectator neutrons to charged particles with mass-to-charge ratio $A/Z=3$, 3/2, and 2 in ultra-central ${}^{20}$Ne+${}^{20}$Ne collisions, which is found to be reduced by about $25\%$ at $\sqrt{s_{\mathrm{NN}}}=7$ TeV and about $20\%$ at $\sqrt{s_{\mathrm{NN}}}=200$ GeV with $\alpha$-cluster structure in ${}^{20}$Ne. This scaled yield ratio thus serves as a robust and direct probe of the existence of $\alpha$-cluster structure in ${}^{20}$Ne free from the uncertainty of mid-rapidity dynamics.

   ↳ nucl-thhep-exnucl-exPRC(2025)·15 citations
4. 04*

   Fixing effective range parameters in elastic $\alpha$-${}^{12}$C scattering: an impact on resonant $2_4^{+}$ state of ${}^{16}$O and $S_{E2}$ factor of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O

   Shing-Ichi Ando🇰🇷

   Elastic $\alpha$-${}^{12}$C scattering for $l=2$ and $E2$ transition of radiative $\alpha$ capture on ${}^{12}$C, ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O, are studied in cluster effective field theory. Due to the problem in fixing the asymptotic normalization coefficient (ANC) of the subthreshold $2_1^{+}$ state of ${}^{16}$O, equivalently, the effective range parameters of the $2_1^{+}$ state, from the elastic scattering data, we introduce the conditions that lead to a large value of the ANC. In addition, $d$-wave phase shift data of the elastic scattering up to the $\alpha$ energy, $E_{\alpha }=10$~MeV, which contain resonant $2_4^{+}$ state of ${}^{16}$O, are also introduced in the study. Applying the conditions, the parameters of the $S$ matrix of the elastic scattering for $l=2$ are fitted to the phase shift data, and the fitted parameters are employed in the calculation of astrophysical $S_{E2}$ factor of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O; we extrapolate the $S_{E2}$ factor to the Gamow-peak energy, $E_G=0.3$~MeV. We find that the conditions lead to significant effects in the observables of the $2_4^{+}$ state of ${}^{16}$O and the estimate of the $S_{E2}$ factor at $E_G$ and confirm that the ANC of the $2_1^{+}$ of ${}^{16}$O cannot be determined by the phase shift data for $l=2$.

   ↳ nucl-thnucl-exCPC(2025)·6 citations
5. 05*

   Complete set of observables in pseudo-scalar meson photoproduction -- Controversy solved

   A. Švarc🇭🇷

   The long-standing debate over whether the complete set of observables in pseudo-scalar meson photoproduction consists of eight or merely four elements continues to persist. From the perspective of amplitude analysis, it is argued that all eight observables are necessary to completely determine the others. On the other hand, proponents of partial-wave analysis, working with theoretically precise data of infinite accuracy, claim that only four observables are needed. However, this claim is not acceptable from an experimental viewpoint, as all data in the real world contain some uncertainty. This paper illustrates that the controversy is artificial and is due to additional mathematical assumptions used in partial-wave analysis. Our research advances this discussion by moving from exact synthetic numerical data to also synthetic, but more realistic data in partial-wave analysis and shows that the claimed reduction in observables is unjustified. Consequently, the final conclusion is that the complete set of observables in pseudo-scalar meson photoproduction, whether using amplitude analysis or partial-wave analysis with practical data, must consist of eight observables.

   ↳ nucl-thnucl-exActa Phys.Polon.B(2026)·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.