Mon·Oct 23, 2023Monday·October 23, 2023

1. 01*

   Estimate of Background Baseline and Upper Limit on the Chiral Magnetic Effect in Isobar Collisions at $\sqrt{s_{\text{NN}}}=200$ GeV at the Relativistic Heavy-Ion Collider

   STAR Collaboration: M. I. Abdulhamid · B. E. Aboona · J. Adam · J. R. Adams · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · A. Aitbaev · I. Alekseev · E. Alpatov · A. Aparin and 345 other authors

   For the search of the chiral magnetic effect (CME), STAR previously presented the results from isobar collisions (${}_{44}^{96}\text{Ru}+{}_{44}^{96}\text{Ru}$, ${}_{40}^{96}\text{Zr}+{}_{40}^{96}\text{Zr}$) obtained through a blind analysis. The ratio of results in Ru+Ru to Zr+Zr collisions for the CME-sensitive charge-dependent azimuthal correlator ($\Delta \gamma$), normalized by elliptic anisotropy ($v_2$), was observed to be close to but systematically larger than the inverse multiplicity ratio. The background baseline for the isobar ratio, $Y=\frac{(\Delta \gamma /v_2{)}^{\text{Ru}}}{(\Delta \gamma /v_2{)}^{\text{Zr}}}$, is naively expected to be $\frac{(1/N{)}^{\text{Ru}}}{(1/N{)}^{\text{Zr}}}$; however, genuine two- and three-particle correlations are expected to alter it. We estimate the contributions to $Y$ from those correlations, utilizing both the isobar data and HIJING simulations. After including those contributions, we arrive at a final background baseline for $Y$, which is consistent with the isobar data. We extract an upper limit for the CME fraction in the $\Delta \gamma$ measurement of approximately $10\%$ at a $95\%$ confidence level on in isobar collisions at $\sqrt{s_{\text{NN}}}=200$ GeV, with an expected $15\%$ difference in their squared magnetic fields.

   nucl-exnucl-thPRC(2024)·23 citations
2. 02*

   Amplitude analysis of vector-pseudoscalar final states at GlueX

   Amy M. Schertz (Indiana University, for the GlueX Collaboration)🇺🇸

   Excited vector mesons, some of which are predicted to include gluonic excitation in their wavefunctions, and certain classes of axial vector mesons, some of which are implicated in the decay of spin-exotic mesons, decay dominantly to vector-pseudoscalar final states. In particular, the axial vector $b_1(1235)$ decays dominantly to $\omega \pi$, and is produced copiously at the GlueX experiment. It provides a testing ground to explore strategies for amplitude analysis of further vector-pseudoscalar channels where the intermediate resonances may be harder to isolate. The formalism for amplitude analysis of $b_1^{-}$ production via charge exchange with a recoiling ${\Delta }^{++}$ is presented here, and compared with the proton recoil case. A strategy for a systematic analysis of reactions involving ${\Delta }^{++}$ recoil is outlined.

   nucl-exhep-exhep-phNuovo Cim.C(2024)·0 citations
3. 03*

   Collective Enhancement of Nuclear Level Density and its fade-out in ${}^{161}$Dy

   T. Santhosh · P.C. Rout · S. Santra🇮🇳 · A. Pal🇮🇳 · G. Mohanto · Ramandeep Gandhi · A. Baishya

   The nuclear level density is a fundamental quantity in nuclear physics, governing various nuclear reactions and astrophysical processes. In this study, we report on the collective enhancement of nuclear level density and its fade-out with excitation energy in the deformed ${}^{161}$Dy, obtained through an exclusive measurement of neutron evaporation spectra. The ${}^{162}$Dy nucleus was populated via the transfer of a triton in a ${}^7$Li-induced reaction on ${}^{159}$Tb. Statistical model analysis of the neutron spectra revealed a large collective enhancement factor of 42$\pm$2, consistent with microscopic calculations. This enhancement factor is similar to the one obtained for mass A$\sim$170 in our previous measurement. The energy-dependent collective enhancement over a wide range of excitation energies was inferred by combining the present results with the available Oslo level density below the neutron binding energy.

   nucl-ex0 citations
4. 04*

   Reactor antineutrino flux and anomaly

   Chao Zhang🇺🇸 · Xin Qian🇺🇸 · Muriel Fallot🇫🇷

   Reactor antineutrinos have played a significant role in establishing the standard model of particle physics and the theory of neutrino oscillations. In this article, we review the reactor antineutrino flux and in particular the reactor antineutrino anomaly (RAA) coined over a decade ago. RAA refers to a deficit of the measured antineutrino inverse beta decay rates at very short-baseline reactor experiments compared to the theoretically improved predictions (i.e. the Huber-Mueller model). Since the resolution of several previous experimental anomalies have led to the discovery of non-zero neutrino mass and mixing, many efforts have been invested to study the origin of RAA both experimentally and theoretically. The progress includes the observation of discrepancies in antineutrino energy spectrum between data and the Huber-Mueller model, the re-evaluation of the Huber-Mueller model uncertainties, the potential isotope-dependent rate deficits, and the better agreement between data and new model predictions using the improved summation method. These developments disfavor the hypothesis of a light sterile neutrino as the explanation of RAA and supports the deficiencies of Huber-Mueller model as the origin. Looking forward, more effort from both the theoretical and experimental sides is needed to fully understand the root of RAA and to make accurate predictions of reactor antineutrino flux and energy spectrum for future discoveries.

   ↳ hep-phhep-exnucl-exPPNP(2024)·33 citations
5. 05*

   Light Meson Spectroscopy with GlueX and Beyond

   Alexander Austregesilo (for the GlueX Collaboration)🇺🇸

   The GlueX experiment at Jefferson Lab was specifically designed for precision studies of the light-meson spectrum. For this purpose, a photon beam with energies up to 12 GeV is directed onto a liquid hydrogen target contained within a hermetic detector with near-complete neutral and charged particle coverage. Linear polarization of the photon beam with a maximum around 9 GeV provides additional information about the production process. In 2018, the experiment completed its first phase, recording data with a total integrated luminosity above 400 pb${}^{-1}$. We highlight a selection of results from this world-leading data set with emphasis on the search for light hybrid mesons. In the mean time, the detector underwent significant upgrades and is currently recording data with an even higher luminosity. The future plans of the GlueX experiment to explore the meson spectrum with unprecedented precision are summarized.

   ↳ hep-exnucl-exNuovo Cim.C(2024)·0 citations
6. 06*

   Alpha-decay from ${}^{44}$Ti: A study of the microscopic clusterization

   Alan C. Dassie🇫🇷 · Rodolfo M. Id Betan🇦🇷

   Microscopic determination of alpha-decay half-lives requires structure and reaction calculations. The structure part is given by the microscopic distribution of the constituent nucleons, while the relative motion of the product's decay provides the reaction part. This paper studies the clusterization of the $0^{+}$ excited states of ${}^{44}$Ti arising from the nucleonic degrees of freedom. The continuum spectra of proton and neutron are incorporated through the Gamow Shell Model formalism. The alpha-like wave function is calculated in the weak-coupling approximation. Gaussian effective interaction in each pair of nucleons is included. The $0^{+}$ ground and excited states are compared with experiment and shell model calculations. The wave function amplitudes are obtained and discriminated by their resonant and non-resonant contributions. The influence of a four-body truncated basis is analyzed. Inclusion of the continuum spectra produces a gain in the excited states of a few hundred keV of energy. One candidate for alpha decay was identified near the experimental unresolved state $(0,2{)}^{+}$ of 6.8 MeV excitation energy, with a lower limit for the half-life of $\approx 0.8$ ns.

   ↳ nucl-thnucl-exPRC(2023)·2 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.