Tue·Sep 7, 2021Tuesday·September 7, 2021

1. 01*

   Observation of B${}_s^0$ mesons and measurement of the B${}_s^0$ / B${}^{+}$ yield ratio in PbPb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV

   CMS Collaboration

   The B${}_s^0$ and B${}^{+}$ production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb${}^{-1}$. The mesons are reconstructed in the exclusive decay channels B${}_s^0$ $\to$ J/$\psi ({\mu }^{+}{\mu }^{-})\varphi ($K${}^{+}$K${}^{-})$ and B${}^{+}$ $\to$ J/$\psi ({\mu }^{+}{\mu }^{-})$K${}^{+}$, in the transverse momentum range 7-50 GeV/c and absolute rapidity 0-2.4. The B${}_s^0$ meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of B${}_s^0$ and B${}^{+}$ is measured and compared to theoretical models that include quark recombination effects.

   ↳ hep-exnucl-exPLB(2022)·30 citations
2. 02*

   Deeply virtual Compton scattering off the neutron

   M. Benali🇹🇳 · C. Desnault🇫🇷 · M. Mazouz🇹🇳 · Z. Ahmed🇺🇸 · H. Albataineh🇺🇸 · K. Allada🇺🇸 · K. A. Aniol🇺🇸 · V. Bellini🇮🇹 · W. Boeglin🇺🇸 · P. Bertin🇫🇷 · M. Brossard🇫🇷 · A. Camsonne🇺🇸 and 87 other authors

   The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly-energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark's transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasi-free neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton's internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle.

   ↳ hep-phhep-exnucl-exNat.Phys.(2020)·39 citations
3. 03*

   Tensor force role in $\beta$ decays analyzed within the Gogny-interaction shell model

   B. Dai🇨🇳 · B. S. Hu🇨🇳 · Y. Z. Ma🇨🇳 · J. G. Li🇨🇳 · S. M. Wang🇨🇳 · C. W. Johnson🇺🇸 · F. R. Xu🇨🇳

   Background: The half-life of the famous ${}^{14}$C $\beta$ decay is anomalously long, with different mechanisms: the tensor force, cross-shell mixing, and three-body forces, proposed to explain the cancellations that lead to a small transition matrix element. Purpose: We revisit and analyze the role of the tensor force for the $\beta$ decay of ${}^{14}$C as well as of neighboring isotopes. Methods: We add a tensor force to the Gogny interaction, and derive an effective Hamiltonian for shell-model calculations. The calculations were carried out in a $p$-$sd$ model space to investigate cross-shell effects. Furthermore, we decompose the wave functions according to the total orbital angular momentum $L$ in order to analyze the effects of the tensor force and cross-shell mixing. Results: The inclusion of the tensor force significantly improves the shell-model calculations of the $\beta$-decay properties of carbon isotopes. In particular, the anomalously slow $\beta$ decay of ${}^{14}$C can be explained by the isospin $T=0$ part of the tensor force, which changes the components of ${}^{14}$N with the orbital angular momentum $L=0,1$, and results in a dramatic suppression of the Gamow-Teller transition strength. At the same time, the description of other nearby $\beta$ decays are improved. Conclusions: Decomposition of wave function into $L$ components illuminates how the tensor force modifies nuclear wave functions, in particular suppression of $\beta$-decay matrix elements. Cross-shell mixing also has a visible impact on the $\beta$-decay strength. Inclusion of the tensor force does not seem to significantly change, however, binding energies of the nuclei within the phenomenological interaction.

   ↳ nucl-thnucl-exPRC(2021)·7 citations
4. 04*

   First application of dispersive optical model to ($p$,$2p$) analysis within distorted wave impulse approximation framework

   K. Yoshida🇯🇵 · M. C. Atkinson🇨🇦 · K. Ogata🇯🇵 · W. H. Dickhoff🇺🇸

   Both ($e$,$e^{\prime }p$) and ($p$,$2p$) reactions have been performed to study the proton single-particle character of nuclear states with its related spectroscopic factor. Recently, the dispersive optical model (DOM) was applied to the ($e$,$e^{\prime }p$) analysis revealing that the traditional treatment of the single-particle overlap function, distorted waves, and nonlocality must be further improved to achieve quantitative nuclear spectroscopy. We apply the DOM wave functions to the traditional ($p$,$2p$) analysis and investigate the consistency of the DOM spectroscopic factor that describes the ($e$,$e^{\prime }p$) cross section with the result of the ($p$,$2p$) analysis. Additionally, we make a comparison with a phenomenological single-particle wave function and optical potential. Uncertainty arising from a choice of $p$-$p$ interaction is also investigated. We implement the DOM wave functions to the distorted wave impulse approximation (DWIA) framework for ($p$,$2p$) reactions. DOM + DWIA analysis on ${}^{40}$Ca($p$,$2p$)${}^{39}$K data generates a proton $0d_{3/2}$ spectroscopic factor of 0.560, which is meaningfully smaller than the DOM value of 0.71 shown to be consistent with the ($e$,$e^{\prime }p$) analysis. Uncertainties arising from choices of single-particle wave function, optical potential, and $p$-$p$ interaction do not explain this inconsistency. The inconsistency in the spectroscopic factor suggests there is urgent need for improving the description of $p$-$p$ scattering in a nucleus and the resulting in-medium interaction with corresponding implications for the analysis of this reaction in inverse kinematics.

   ↳ nucl-thnucl-exPRC(2022)·3 citations
5. 05*

   Collapse of N$=$28 magicity in exotic ${}^{40}$Mg -- Probe of deformed halo and 2n-radioactivity at Mg neutron drip-line

   G. Saxena · M. Kumawat · R. Sharma🇮🇳 · Mamta Aggarwal🇮🇳

   The exotic phenomenon of two-neutron halos and 2n-radioactivity are explored in the neutron-rich ${}^{40,42,44}$Mg by employing various variants of the relativistic mean-field approach. The extended tail of spatial density distributions including the enhanced neutron radii and skin thickness, pairing correlations, single-particle spectrum and wave functions predict ${}^{40,42,44}$Mg to be strong candidates for deformed neutron halos. Weakening of magicity at N$=$28 plays a significant role in the existence of a weakly bound halo in ${}^{40}$Mg which is currently the heaviest isotope of Mg accessible experimentally. Large deformation, mixing of f-p shell Nilsson orbitals and the valence neutron occupancy of p-states leads to a reduced centrifugal barrier and broader spatial density distributions that favour 2n-radioactivity in ${}^{42,44}$Mg.

   ↳ nucl-thnucl-exJ.Phys.G(2021)·5 citations
6. 06*

   Deblurring for Nuclei: 3D Characteristics of Heavy-Ion Collisions

   Pawel Danielewicz (FRIB-MSU)🇺🇸 · Mizuki Kurata-Nishimura (RIKEN)🇯🇵

   Observables from nuclear and high-energy experiments can be degraded by detector performance and/or methodology in extracting the observables, such as of the final-state characteristics of heavy-ion collisions in relation to a coarsely estimated reaction-plane direction. We propose the use of deblurring methods, such as in optics, to correct for observable degradation. Our main focus is the restoration of triple-differential particle distributions in heavy-ion collisions. We demonstrate that these could be extracted from collision measurements following the Richardson-Lucy deblurring method from optics. We illustrate basic features of the restoration methodology in a schematic model assuming either ideal or more realistic particle detection. The inferred three-dimensional (3D) distributions for collisions may easier to interpret in terms of collision dynamics and sought properties of bulk matter than the currently employed Fourier coefficients, that combine information from different azimuthal angles relative to the reaction plane.

   ↳ nucl-thnucl-exPRC(2022)·26 citations
7. 07*

   Searching for Exotic Spin-Dependent Interactions Using Rotationally Modulated Source Masses and an Atomic Magnetometer Array

   K.Y. Wu🇨🇳 · S.Y. Chen🇨🇳 · J. Gong🇨🇳 · M. Peng🇨🇳 · H. Yan🇨🇳

   We describe a proposed experimental search for exotic spin-dependent interactions using rotationally modulated source masses and an atomic magnetometer array. Rather than further improving the magnetometer sensitivity, noise reduction can be another way to reach higher measurement precision. In this work, we propose to use modulating techniques of the source masses to reduce the noise of the experiment. Better precision can be achieved if the fundamental frequency and harmonics of the rotating source masses are used to detect the new interactions. Furthermore, if an array of magnetometers are applied, the statistic precision can be improved, and some common noises can be canceled. Our analysis and simulations indicate that the proposed experiment scheme can improve the detection precisions of three types of spin-dependent interactions by as much as $\sim$5 orders in the force range of $\sim$cm to $\sim$10m.

   ↳ hep-exnucl-exPRD(2022)·10 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.