Tue·May 7, 2024Tuesday·May 7, 2024

1. 01*

   Girth and groomed radius of jets recoiling against isolated photons in lead-lead and proton-proton collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   CMS Collaboration

   This Letter presents the first measurements of the groomed jet radius $R_{\mathrm{g}}$ and the jet girth $g$ in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables $R_{\mathrm{g}}$ and $g$ provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7 nb${}^{-1}$ and 301 pb${}^{-1}$, respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentum $p_{\mathrm{T}}^{\gamma }$ $>$ 100 GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum $p_{\mathrm{T}}^{\text{jet}}$ such that $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma }$ $>$ 0.4. The measured $R_{\mathrm{g}}$ and $g$ distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma }$ $>$ 0.8, i.e., those that closely balance the photon $p_{\mathrm{T}}^{\gamma }$, are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma }$ $>$ 0.4 reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements.

   nucl-exhep-exPLB(2025)·42 citations
2. 02*

   Analog-antianalog isospin mixing in ${}^{47}$K ${\beta }^{-}$ decay

   Brian Kootte · H. Gallop · C. Luktuke · J.C. McNeil · A. Gorelov · D.G. Melconian · J. Klimo · B.M. Vargas-Calderon. J.A. Behr

   We have measured the isospin mixing of the I${}^{\pi }$= 1/2${}^{+}$ E${}_x$=2.599 MeV state in nearly-doubly-magic ${}^{47}$Ca with the isobaric analog 1/2${}^{+}$ state of ${}^{47}$K. Using the TRIUMF atom trap for $\beta$ decay, we have measured a nonzero asymmetry of the progeny ${}^{47}$Ca with respect to the initial ${}^{47}$K spin polarization, which together with the $\beta$ asymmetry implies a nonzero ratio of Fermi to Gamow-Teller matrix elements $y$= 0.098$\pm$0.037 for the $1/2^{+}\to 1/2^{+}$ transition. Interpreting $y$ as mixing between this state and the isobaric analog state implies a Coulomb matrix element magnitude 101 $\pm$ 37 keV. This relatively large matrix element supports a model from the literature of analog-antianalog isospin mixing, which predicts large matrix elements in cases involving excess neutrons over protons occupying more than one major shell. The result supports pursuing a search for time-reversal odd, parity-even, isovector interactions using a correlation in ${}^{47}$K $\beta$ decay.

   nucl-exhep-exPRC(2024)·0 citations
3. 03*

   Study of the ${}^7$Be($d$,${}^3$He)${}^6$Li* reaction at 5 MeV/u

   Sk M. Ali🇮🇳 · D. Gupta🇮🇳 · K. Kundalia🇮🇳 · S. Maity🇨🇳 · Swapan K Saha🇮🇳 · O. Tengblad🇪🇸 · J.D. Ovejas🇪🇸 · A. Perea🇪🇸 · I. Martel🇪🇸 · J. Cederkall🇸🇪 · J. Park🇰🇷 · A. M. Moro🇪🇸

   The measurement of the ${}^7$Be($d$,${}^3$He)${}^6$Li* transfer cross section at 5 MeV/u is carried out. The population of the 2.186 MeV excited state of ${}^6$Li in this reaction channel is observed for the first time. The experimental angular distributions have been analyzed in the finite range DWBA and coupled-channel frameworks. The effect of the ${}^7$Be($d$,${}^3$He)${}^6$Li reaction on both the ${}^6$Li and ${}^7$Li abundances are investigated at the relevant big-bang nucleosynthesis energies. The excitation function is calculated by TALYS and normalized to the experimental data. The $S$ factor of the ($d$,${}^3$He) channel from the present work is about 50$\%$ lower than existing data at nearby energies. At big-bang energies, the $S$ factor is about three orders of magnitude smaller than that of the ($d,p$) channel. The ($d$,${}^3$He) reaction rate is found to have a less than 0.1$\%$ effect on the ${}^{6,7}$Li abundances.

   nucl-exPLB(2024)·1 citation
4. 04*

   K+K- photoproduction in ultra$-$peripheral Pb$--$Pb collisions

   Minjung Kim (for the ALICE Collaboration)🇺🇸

   In ultra-peripheral collisions (UPCs) of relativistic heavy ions, photoproduction occurs when a photon emitted from one nucleus interacts with the other nucleus from the opposing beam, producing particles in the final state. Measurements of \KK photoproduction probe interactions and couplings between the $\varphi (1020)$ and charged kaons with photons and nuclear targets. We report exclusive \KK photoproduction cross section at midrapidity in \PbPb collisions at \snn = 5.02 TeV, which is measured for the first time in UPCs.

   nucl-exhep-exPhys.Proc.UPC(2024)·0 citations
5. 05*

   Wobbling motion in triaxial nuclei

   Stefan Frauendorf

   The experimental evidence for the collective wobbling motion of triaxial nuclei is reviewed. The classification into transverse and longitudinal in the presence of quasiparticle excitations is discussed. The description by means of the quasiparticle+triaxial rotor model is discussed in detail. The structure of the states is analyzed using the spin-coherent-state and spin-squeezed-state representations of the reduced density matrices of the total and particle angular momenta, which distill the corresponding classical precessional motions. Various approximate solutions of the quasiparticle+triaxial rotor model are evaluated. The microscopic studies of wobbling in the small-amplitude random phase approximation are discussed. Selected studies of wobbling by means of the triaxial projected shell model are presented, which focus on how this microscopic approach removes certain deficiencies of the semi-microscopic quasiparticle+triaxial rotor model.

   ↳ nucl-thnucl-ex4 citations
6. 06*

   A Bayesian mixture model approach to quantifying the empirical nuclear saturation point

   C. Drischler🇺🇸 · P. G. Giuliani🇺🇸 · S. Bezoui · J. Piekarewicz🇺🇸 · F. Viens🇺🇸

   The equation of state (EOS) in the limit of infinite symmetric nuclear matter exhibits an equilibrium density, $n_0\approx 0.16{\mathrm{fm}}^{-3}$, at which the pressure vanishes and the energy per particle attains its minimum, $E_0\approx -16\mathrm{MeV}$. Although not directly measurable, the saturation point $(n_0,E_0)$ can be extrapolated by density functional theory (DFT), providing tight constraints for microscopic interactions derived from chiral effective field theory (EFT). However, when considering several DFT predictions for $(n_0,E_0)$ from Skyrme and Relativistic Mean Field models together, a discrepancy between these model classes emerges at high confidence levels that each model prediction's uncertainty cannot explain. How can we leverage these DFT constraints to rigorously benchmark saturation properties of chiral interactions? To address this question, we present a Bayesian mixture model that combines multiple DFT predictions for $(n_0,E_0)$ using an efficient conjugate prior approach. The inferred posterior for the saturation point's mean and covariance matrix follows a Normal-inverse-Wishart class, resulting in posterior predictives in the form of correlated, bivariate $t$-distributions. The DFT uncertainty reports are then used to mix these posteriors using an ordinary Monte Carlo approach. At the 95\% credibility level, we estimate $n_0\approx 0.157\pm 0.010{\mathrm{fm}}^{-3}$ and $E_0\approx -15.97\pm 0.40\mathrm{MeV}$ for the marginal (univariate) $t$-distributions. Combined with chiral EFT calculations of the pure neutron matter EOS, we obtain bivariate normal distributions for the symmetry energy and its slope parameter at $n_0$: $S_v\approx 32.0\pm 1.1\mathrm{MeV}$ and $L\approx 52.6\pm 8.1\mathrm{MeV}$ (95\%), respectively. Our Bayesian framework is publicly available, so practitioners can readily use and extend our results.

   ↳ nucl-thnucl-exphysics.data-anPRC(2024)·26 citations
7. 07*

   Observation of Universal Expansion Anisotropy from Cold Atoms to Hot Quark-Gluon Plasma

   Ke Li🇺🇸 · Hong-Fang Song🇨🇳 · Hao-Jie Xu🇨🇳 · Yu-Liang Sun🇨🇳 · Fuqiang Wang🇺🇸

   Azimuthal anisotropy has been ubiquitously observed in high-energy proton-proton, proton-nucleus, and nucleus-nucleus (heavy-ion) collisions, shaking the early belief that those anisotropies require an intense phase of multiple interactions between the created particles. This work reports a study of anisotropic expansion of cold ${}^6$Li Fermi gases, initially trapped in an anisotropic potential, as a function of the interaction strength that can be readily tuned by an external magnetic field. It is found that the expansion anisotropy builds up quickly at small interaction strength, without the need of a large amount of interactions. An unexpected and quantitative universal scaling of the expansion anisotropy is observed for the first time between cold atom and heavy-ion systems as a function of the number of collisions per particle or opacity ($n_{\mathrm{coll}}$), despite their vast differences in scale and physics. The expansion isotropy in both the cold atom gases and heavy-ion collisions increases smoothly and shows no sign of saturation in the observed opacity range, with an approximate power-law dependence of $\sqrt{n_{\mathrm{coll}}}$, characteristic of random walks. This universality potentially unifies a variety of vastly different physical systems, from weakly interacting dilute gases to the strongly interacting quark-gluon plasma of the early universe.

   ↳ cond-mat.quant-gasnucl-exnucl-thNewton 1 (2025) 100237·4 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.