Tue·Mar 1, 2022Tuesday·March 1, 2022

1. 01*

   Differential cross sections and photon beam asymmetries of $\eta$ photoproduction on the proton at $E_{\gamma }$ = 1.3-2.4 GeV

   T. Hashimoto🇯🇵 · T. Nam🇯🇵 · N. Muramatsu🇯🇵 · J.K. Ahn🇰🇷 · W.C. Chang🇹🇼 · J.Y. Chen🇹🇼 · M.L. Chu🇹🇼 · S. Date🇯🇵 · T. Gogami🇯🇵 · H. Goto🇯🇵 · H. Hamano🇯🇵 · Q.H. He🇨🇳 and 48 other authors

   We have carried out exclusive measurements for the photoproduction of an $\eta$ meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the $\gamma p\to \eta p$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0<\cos {\theta }_{c.m.}^{\eta }<0.6$. The reaction is identified by selecting a proton and two $\gamma$'s produced by an $\eta$-meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than $1$\%. A bump structure at $W$ = $2.0$-$2.3$ GeV in the differential cross section is confirmed at extremely backward $\eta$ polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with $s\bar{s}$ quarks. The results of the photon beam asymmetries in a wide $\eta$ polar angle range are new for the photon beam energies exceeding $2.1$ GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies.

   nucl-exPRC(2022)·11 citations
2. 02*

   Experimental study of the ${}^{40,48}$Ca+ ${}^{40,48}$Ca reactions at 35 MeV/nucleon

   Q. Fable (GANIL, LPCC, L2IT)🇫🇷 · A. Chbihi (GANIL)🇫🇷 · M. Boisjoli (ULaval)🇨🇦 · J.D. Frankland (GANIL)🇫🇷 · A. Le Fèvre (GSI)🇩🇪 · N. Le Neindre (LPCC)🇫🇷 · P. Marini (CENBG)🇫🇷 · G. Verde (L2IT, INFN)🇮🇹 · G. Ademard (IJCLab)🇫🇷 · L. Bardelli (INFN, Sezione di Firenze)🇮🇹 · C. Bhattacharya🇮🇳 · S. Bhattacharya🇮🇳 and 32 other authors

   In this article we investigate ${}^{40,48}$Ca+${}^{40,48}$Ca peripheral and semi-peripheral reactions at 35 MeV/nucleon. Data were obtained using the unique coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector.The spectrometer allowed high resolution measurement of charge, mass and velocity of the cold projectile-like fragment (PLF), while the INDRA detector recorded coincident charged particles with nearly $4\pi$ acceptance.The measured isotopic composition of the PLF identified in VAMOS and the average light charged particle (LCP) multiplicities are promising observables to study the isospin diffusion.The detection of the PLF in coincidence with LCP allows the reconstruction of the mass, charge and excitation energy of the associated initial quasi-projectile nuclei (QP), as well as the extraction of apparent temperatures.We investigate the suitability of the isoscaling method with the PLF and the experimental reconstructed QP.The extracted $\alpha$ and $\Delta$ isoscaling parameters present a dependence on the considered system combination that could justify their use as a surrogate for isospin asymmetry in isospin transport studies.The reconstruction of the QP allows to observe an evolution of the $\alpha /\Delta$ with the size of the QP, the latter being consistent with a strong surface contribution to the symmetry energy term in finite nuclei. This leads to the conclusion that the reconstruction of the primary source is mandatory for the study of the symmetry energy term based on the isoscaling method for such reactions.

   nucl-exphysics.atom-phPRC(2022)·11 citations
3. 03*

   Effective field theory of pairing rotations

   T. Papenbrock🇺🇸

   Pairing rotations are the low-energy excitations of finite superfluid systems, connecting systems that differ in their number of Cooper pairs. This paper presents a model-independent derivation of pairing rotations within an effective theory that exploits the emergent breaking of U(1) phase symmetries. The symmetries are realized nonlinearly and the Nambu-Goldstone modes depend only on time because the system is finite. Semi-magic nuclei exhibit pairing rotational bands while the pairing spectrum becomes an elliptical paraboloid for open-shell nuclei. Model-independent relations between double charge-exchange reactions and alpha particle capture or knockout in open-shell nuclei are in analogy to the pair transfer reactions in a single superfluid. Odd semi-magic nuclei are described by coupling a fermion to the superfluid. The leading-order theories reproduce data for pairing rotational bands within uncertainty estimates.

   ↳ nucl-thnucl-exPRC(2022)·12 citations
4. 04*

   Insights into the equation of state of neutron-rich matter since GW170817

   J. Piekarewicz🇺🇸

   The historical detection of gravitational waves emitted from the binary neutron star merger GW170817 has opened the new era of multi-messenger astronomy. Since then, many other significant discoveries -- both on heaven and earth -- are providing new clues into the behavior of neutron-rich matter. It is the goal of this article to illustrate how the remarkable progress made during the last few years is spearheading the field into the golden age of neutron-star physics.

   ↳ nucl-thgr-qcnucl-exJ.Phys.Conf.Ser.(2022)·0 citations
5. 05*

   Non-iterative finite amplitude methods for E1 and M1 giant resonances

   Hirokazu Sasaki🇺🇸 · Toshihiko Kawano🇺🇸 · Ionel Stetcu🇺🇸

   The finite amplitude method (FAM) is a very efficient approach for solving the fully self-consistent random-phase approximation (RPA) equations. We use FAM to rederive the RPA matrices for general Skyrme-like functionals, calculate the electric dipole (E1) and the magnetic dipole (M1) giant resonances, and compare the results with available experimental and evaluated data. For the E1 transitions in heavy nuclei, the calculations reproduce well the resonance energy of the photoabsorption cross sections. In the case of M1 transitions, we show that the residual interaction does not affect the transition strength of double-magic nuclei, which suggests that the spin terms in the Skyrme force currently neglected in the present computation could improve the agreement between FAM and experimental data.

   ↳ nucl-thastro-ph.HEnucl-exPRC(2022)·10 citations
6. 06*

   Onset of color transparency in holographic light-front QCD

   Stanley J. Brodsky🇺🇸 · Guy F. de Teramond🇨🇷

   The color transparency (CT) of a hadron, propagating with reduced absorption in a nucleus, is a fundamental property of QCD (quantum chromodynamics) reflecting its internal structure and effective size when it is produced at high transverse momentum, $Q$. CT has been confirmed in many experiments, such as semi-exclusive hard electroproduction, $eA\to e^{\prime }\pi X$ for mesons produced at $Q^2>3{\mathrm{GeV}}^2$. However, a recent JLab (Jefferson Laboratory) measurement for a proton electroproduced in carbon $e\mathrm{C}\to e^{\prime }pX$, where $X$ stands for the inclusive sum of all produced final states, fails to observe CT at $Q^2$ up to 14.2 GeV${}^2$. In this paper, the onset of CT is determined by comparing the $Q^2$-dependence of the hadronic cross sections for the initial formation of a small color-singlet configuration using the generalized parton distributions from holographic light-front QCD. A critical dependence on the hadron's twist, $\tau$, the number of hadron constituents, is found for the onset of CT, with no significant effects from the nuclear medium. This effect can explain the absence of proton CT in the present kinematic range of the JLab experiment. The proton is predicted to have a "two-stage" color transparency with the onset of CT differing for the spin-conserving (twist-3, $\tau =3$) Dirac form factor with a higher onset in $Q^2$ for the spin-flip Pauli (twist-4) form factor. In contrast, the neutron is predicted to have a "one-stage" color transparency with the onset at higher $Q^2$ because of the dominance of its Pauli form factor. The model also predicts a strong dependence at low energies on the flavor of the quark current coupling to the hadron.

   ↳ hep-phnucl-exnucl-thMDPI Physics(2022)·19 citations
7. 07*

   Pulse shape analysis in GERDA Phase II

   The GERDA collaboration: M. Agostini🇬🇧 · G. Araujo🇨🇭 · A.M. Bakalyarov🇷🇺 · M. Balata🇮🇹 · I. Barabanov🇷🇺 · L. Baudis🇨🇭 · C. Bauer🇩🇪 · E. Bellotti🇮🇹 · S. Belogurov🇷🇺 · A. Bettini🇮🇹 · L. Bezrukov🇷🇺 · V. Biancacci🇮🇹 and 103 other authors

   The GERmanium Detector Array (GERDA) collaboration searched for neutrinoless double-$\beta$ decay in ${}^{76}$Ge using isotopically enriched high purity germanium detectors at the Laboratori Nazionali del Gran Sasso of INFN. After Phase I (2011-2013), the experiment benefited from several upgrades, including an additional active veto based on LAr instrumentation and a significant increase of mass by point-contact germanium detectors that improved the half-life sensitivity of Phase II (2015-2019) by an order of magnitude. At the core of the background mitigation strategy, the analysis of the time profile of individual pulses provides a powerful topological discrimination of signal-like and background-like events. Data from regular ${}^{228}$Th calibrations and physics data were both considered in the evaluation of the pulse shape discrimination performance. In this work, we describe the various methods applied to the data collected in GERDA Phase II corresponding to an exposure of 103.7 kg$\cdot$yr. These methods suppress the background by a factor of about 5 in the region of interest around Q${}_{\beta \beta }$ = 2039 keV, while preserving (81$\pm$3)% of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis.

   ↳ physics.ins-detnucl-exEPJC(2022)·35 citations
8. 08*

   Emergent geometry and duality in the carbon nucleus

   Shihang Shen🇩🇪 · Serdar Elhatisari🇹🇷 · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Bing-Nan Lu🇨🇳 · Ulf-G. Meißner🇩🇪

   The carbon atom provides the backbone for the complex organic chemistry composing the building blocks of life. The physics of the carbon nucleus in its predominant isotope, ${}^{12}$C, is similarly full of multifaceted complexity. Some nuclear states of ${}^{12}$C can be preferentially treated as a collection of independent particles held by the mean field of the nucleus, while other states behave more as a collection of three alpha-particle clusters. But these two pictures are not mutually exclusive, and some states can be described in either fashion${}^{1,2}$. In this work, we provide the first model-independent tomographic scan of the three-dimensional geometry of the nuclear states of ${}^{12}$C using the {\it ab initio} framework of nuclear lattice effective field theory. We find that the well-known but enigmatic Hoyle state is composed of a "bent-arm" or obtuse triangular arrangement of alpha clusters. We identify all of the low-lying nuclear states of ${}^{12}$C as having an intrinsic shape composed of three alpha clusters forming either an equilateral triangle or an obtuse triangle. From these basic structural formations, the various nuclear states correspond to different rotational and vibrational excitations as well as either distortions or large-amplitude displacements of the alpha clusters. The states with the equilateral triangle formation also have a dual description in terms of particle-hole excitations in the mean-field picture. We compare our theoretical calculations with experimental data for binding energies, quadrupole moments, electromagnetic transitions, charge densities, and form factors. The overall agreement is good, and further studies using higher-fidelity interactions are planned.

   ↳ nucl-thhep-latnucl-exNature Commun.(2023)·77 citations
9. 09*

   Time-dependent generator coordinate method study of fission: dissipation effects

   Jie Zhao🇨🇳 · Tamara Nikšić🇭🇷 · Dario Vretenar🇭🇷

   Starting from a quantum theory of dissipation for nuclear collective motion, the time-dependent generator coordinate method (TDGCM) is extended to allow for dissipation effects in the description of induced fission dynamics. The extension is based on a generalization of the GCM generating functions that includes excited states, and the resulting equation of motion in the collective coordinates and excitation energy. With the assumption of a narrow hamiltonian kernel, an expansion in a power series in collective momenta leads to a Schrödinger-like equation that explicitly includes a dissipation term, proportional to the momentum of the statistical wave function. An illustrative calculation is performed for induced fission of ${}^{228}$Th. The three-dimensional model space includes the axially-symmetric quadrupole and octupole shape variables, and the nuclear temperature. When compared to data for photo-induced fission of ${}^{228}$Th, the calculated fission yields demonstrate the important role of the additional term in the hamiltonian that explicitly takes into account the dissipation of energy of collective motion into intrinsic degrees of freedom.

   ↳ nucl-thnucl-exPRC(2022)·28 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.