Tue·Dec 19, 2023Tuesday·December 19, 2023

1. 01*

   Measurement of the Isolated Nuclear Two-Photon Decay in ${}^{72}\mathrm{Ge}$

   D. Freire-Fernández🇩🇪 · W. Korten🇫🇷 · R. J. Chen🇩🇪 · S. Litvinov🇩🇪 · Yu. A. Litvinov🇩🇪 · M. S. Sanjari🇩🇪 · H. Weick🇩🇪 · F. C. Akinci🇹🇷 · H. M. Albers🇩🇪 · M. Armstrong🇩🇪 · A. Banerjee🇩🇪 · K. Blaum🇩🇪 and 48 other authors

   The nuclear two-photon or double-gamma ($2\gamma$) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the $2\gamma$ decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to $\sim 100$\,keV and half-lives as short as $\sim 10$\,ms. The half-life for the $2\gamma$ decay of the first-excited $0^{+}$ state in bare ${}^{72}\mathrm{Ge}$ ions was determined to be $23.9\left(6\right)$\,ms, which strongly deviates from expectations.

   nucl-exnucl-thPRL(2024)·15 citations
2. 02*

   Baryon-to-Meson Ratios in Jets from Au+Au and p+p Collisions at \sqrt{s_{NN}} = 200 GeV

   Gabriel Dale-Gau (on behalf of the STAR collaboration)🇺🇸

   Measurements at RHIC and the LHC show strongly enhanced baryon-to-meson yield ratios at intermediate transverse momenta ($p_{\mathrm{T}}$) in high-energy nuclear collisions compared to $p$+$p$ baseline. This enhancement is attributed to the following QGP effects: strong hydrodynamic flow and parton recombination. Jet probes have been used extensively to gain insights into QGP properties, with substantial modifications to jet yields and internal structures seen across multiple measurements. Despite apparent medium-induced changes to jet fragmentation patterns, the LHC results indicate that in-jet baryon-to-meson ratios remain similar to that of $p$+$p$ measurements and are significantly different from that of the QGP bulk. To explore this behavior at RHIC, we employ particle identification through time-of-flight and TPC $dE/dx$ information alongside jet-track correlations to measure in-jet particle ratios for $p_{\mathrm{T}}<5.0$ GeV/$c$. We present the first in-cone baryon-to-meson yield ratios associated with fully reconstructed jets from Au+Au and $p$+$p$ collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV using the STAR detector at RHIC.

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

   Precision Mass Measurement of Proton-Dripline Halo Candidate ${}^{22}$Al

   S. E. Campbell🇺🇸 · G. Bollen🇺🇸 · B. A. Brown🇺🇸 · A. Dockery🇺🇸 · K. Fossez🇺🇸 · C. M. Ireland🇺🇸 · K. Minamisono🇺🇸 · D. Puentes🇺🇸 · A. Ortiz-Cortez · B. J. Rickey🇺🇸 · R. Ringle🇺🇸 · S. Schwarz🇺🇸 and 3 other authors

   We report the first mass measurement of the proton-halo candidate ${}^{22}$Al performed with the LEBIT facility's 9.4~T Penning trap mass spectrometer at FRIB. This measurement completes the mass information for the lightest remaining proton-dripline nucleus achievable with Penning traps. ${}^{22}$Al has been the subject of recent interest regarding a possible halo structure from the observation of an exceptionally large isospin asymmetry [Phys. Rev. Lett. \textbf{125} 192503 (2020)]. The measured mass excess value of $\text{ME}=18093.6(7)$~keV, corresponding to an exceptionally small proton separation energy of $S_p=99.2(1.0)$~keV, is compatible with the suggested halo structure. Our result agrees well with predictions from \textit{sd}-shell USD Hamiltonians. While USD Hamiltonians predict deformation in ${}^{22}$Al ground-state with minimal $1s_{1/2}$ occupation in the proton shell, a particle-plus-rotor model in the continuum suggests that a proton halo could form at large quadrupole deformation. These results emphasize the need for a charge radius measurement to conclusively determine the halo nature.

   nucl-exPRL(2024)·27 citations
4. 04*

   Transverse momentum fluctuation in ultra-central Pb+Pb collision at the LHC

   Rupam Samanta🇵🇱 · Somadutta Bhatta🇺🇸 · Jiangyon Jia🇺🇸 · Matthew Luzum🇧🇷 · Jean-Yves Ollitrault🇫🇷

   The ATLAS collaboration has recently observed that the variance of the transverse momentum per particle ($[p_t]$), when measured as a function of the collision multiplicity ($N_{ch}$) in Pb+Pb collisions, decreases by a factor $2$ for the largest values of $N_{ch}$, corresponding to ultra-central collisions. We show that this phenomenon is naturally explained by invoking impact parameter ($b$) fluctuations, which contribute to the variance, and gradually disappear in ultra-central collisions. It implies that $N_{ch}$ and $[p_t]$ are strongly correlated at fixed $b$, which is explained by the local thermalization of the QGP medium.

   ↳ nucl-thnucl-exEPJ Web Conf.(2024)·0 citations
5. 05*

   Symmetry-restored Skyrme-Random-Phase-Approximation calculations of the monopole strength in deformed nuclei

   A. Porro🇩🇪 · G. Colò🇮🇹 · T. Duguet🇫🇷 · D. Gambacurta🇮🇹 · V. Somà🇫🇷

   Within the Energy Density Functional (EDF) approach, the use of mean-field wave-functions deliberately breaking (some) symmetries of the underlying Hamiltonian is an efficient and largely utilized way to incorporate static correlations. However, the restoration of broken symmetries is eventually mandatory to recover the corresponding quantum numbers and to achieve a more precise description of nuclear properties. While symmetry-restored calculations are routinely performed to study ground-state properties and low-lying excitations, similar applications to the nuclear response are essentially limited to either formal studies or to schematic models. In the present paper, the effect of angular momentum restoration on the monopole and quadrupole responses of doubly open-shell nuclei is investigated. Based on deformed Skyrme-Random Phase Approximation (RPA) calculations, the exact Angular Momentum Projection (AMP) is implemented in the calculation of the multipole strength functions, thus defining a projection after variation (PAV-RPA) scheme. The method is employed for the first time in a realistic study to investigate the effect of AMP on the coupling of monopole and quadrupole modes in ${}^{24}$Mg resulting from its intrinsic deformation.

   ↳ nucl-thnucl-exPRC(2024)·8 citations
6. 06*

   About the magnitude of the ${\gamma }^{\ast }N\to N(1520)$ transverse amplitudes near $Q^2=0$

   G. Ramalho🇰🇷

   The ${\gamma }^{\ast }N\to N(1520)$ transition has a property that differs from the other low-lying nucleon resonance amplitudes: the magnitude of the transverse helicity amplitudes.The transition helicity amplitudes are defined in terms of square-transfer momentum $q^2$, or $Q^2=-q^2$. Near the photon point ($Q^2=0$) there is a significant difference in the magnitude of the transverse amplitudes: $A_{3/2}$ is very large and $A_{1/2}$ is very small. This atypical behavior contrasts with the relation between the amplitudes at the pseudothreshold [the limit where the nucleon and the $N(1520)$ are both at rest and $Q^2<0$], where $A_{3/2}=A_{1/2}/\sqrt{3}$, and also in the large-$Q^2$ region, where theory and data suggest that $A_{3/2}$ is suppressed relative to $A_{1/2}$. In the present work, we look for the source of the suppression of the $A_{1/2}$ amplitude at $Q^2=0$. The result is easy to understand in first approximation, when we look into the relation between the transverse amplitudes and the elementary form factors, defined by a gauge-invariant parametrization of the ${\gamma }^{\ast }N\to N(1520)$ transition current, near $Q^2=0$. There is a partial cancellation between contributions of two elementary form factors near $Q^2=0$. We conclude, however, that the correlation between the two elementary form factors at $Q^2=0$ is not sufficient to explain the transverse amplitude data below $Q^2=1$ GeV${}^2$. The description of the dependence of the transverse amplitudes on $Q^2$ requires the determination of the scale of variation of the elementary form factors in the range $Q^2=0$...0.5 GeV${}^2$,a region with almost non existent data. We conclude at the end that the low-$Q^2$ data for the transverse amplitudes can be well described when we relate the scale of variation of the elementary form factors with the nucleon dipole form factor.

   ↳ hep-phhep-exhep-latnucl-ex+1PRD(2024)·1 citation
7. 07*

   Status of direct detection searches of heavy dark matter

   Marcin Kuźniak🇵🇱

   Dark matter accounts for 26% of the mass-energy density of the Universe, however, its nature and origins remain the most important open questions in physics. The search for Weakly Interacting Massive Particles (WIMPs), one of the leading dark matter particle candidates, is now in a decisive phase, with experiments targeting both the high-mass and the low-mass (1-10 GeV/$c^2$) WIMP scenarios. The status of the leading experimental searches is discussed, together with their prospects and challenges they are facing. Searches of heavy non-WIMP dark matter candidates are also briefly summarized.

   ↳ hep-phastro-ph.COastro-ph.IMhep-ex+1PoS(2023)·3 citations
8. 08*

   Multi-parton interactions in pp collisions using charged-particle flattenicity with ALICE

   Gyula Bencédi (on behalf of the ALICE Collaboration)🇭🇺

   Event classifiers based either on the charged-particle multiplicity or on event topologies, such as spherocity and underlying event, became very useful tools to study collective-like behaviors in small collision systems. However, multiplicity-based event classifiers were shown to bias the data sample in a way that can obscure the effects of multi-parton interactions, and, this way, make it difficult to pin down the origins of small-system collectivity. In this proceedings, the measurement of the transverse momentum ($p_{\mathrm{T}}$) spectra of primary charged pions, kaons, (anti)protons and unidentified hadrons in inelastic pp collisions at $\sqrt{s}=13\mathrm{TeV}$ are reported. Events are classified using a novel event shape observable, flattenicity, that was proposed to select minijet-enhanced pp collisions. Particle production is studied as a function of flattenicity and double-differentially as a function of flattenicity and charged-particle multiplicity. The results are compared with theoretical predictions from the PYTHIA 8 and EPOS LHC Monte Carlo models.

   ↳ hep-exnucl-exPoS(2024)·4 citations
9. 09*

   Directed flow and hyperon polarization at RHIC BES from multi-fluid dynamics

   Iurii Karpenko🇨🇿 · Jakub Cimerman🇨🇿

   We present directed flow of protons and pions, as well as mean polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons computed for Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}=\mathrm{5...19.6}$ GeV in MUFFIN model. MUlti Fluid simulation for Fast IoN collisions, or MUFFIN, is a state-of-the-art 3-fluid dynamic model for simulating heavy-ion collisions in the region from a few to a hundred GeV center-of-mass energy. Whereas MUFFIN succeeds to reproduce basic observables in the collision energy range of interest, the slope of the directed flow at mid-rapidity is much steeper as compared to the data, it has unclear EoS dependence and final-state hadronic cascade affects this observable significantly. The excitation function of the $\Lambda$ polarization shows a significant splitting between polarizations of $\Lambda$ and $\bar{\Lambda }$, which challenges a widespread interpretation that the splitting is affected mainly by the late-stage magnetic field.

   ↳ nucl-thnucl-exEPJ Web Conf.(2024)·3 citations
10. 10*

    Holographic transport coefficients and jet energy loss for the hot and dense quark-gluon plasma

    Joaquin Grefa🇺🇸 · Mauricio Hippert🇺🇸 · Raghav Kunnawalkam Elayavalli🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸 · Israel Portillo🇺🇸 · Claudia Ratti🇺🇸 · Romulo Rougemont🇧🇷

    We employ an Einstein-Maxwell-dilaton model, based on the gauge/gravity correspondence, to obtain the thermodynamics and transport properties for the hot and dense quark-gluon plasma. The model, which is constrained to reproduce lattice QCD thermodynamics at zero density, predicts a critical point and a first order line at finite temperature and density, is used to quantify jet energy loss through simulations of high-energy collision events.

    ↳ nucl-thhep-phhep-thnucl-exEPJ Web Conf.(2024)·3 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.