arXiv subjects

D. Yan

Publications and source records attributed to D. Yan.

At least 19 recordsLinked to original sources

arXiv2026

Probing the Size of Neutron and Proton Single-Particle Orbitals from Nucleon Knockout Reactions

The size of neutron and proton single-particle orbitals of $^{52}$Ca, $^{53}$Ca, $^{54}$Ca, and $^{55}$Sc were investigated via nucleon knockout reactions at $\sim$ 230 MeV/nucleon. The determination method is based on the measured fragment momentum distributions in $(p,pn)$ and $(p,2p)$ reactions, which are shown to be sensitive to the spatial extension of the wave function of the knocked-out nucleon, interpreted within the distorted wave impulse approximation (DWIA) framework. A systematic sensitivity study is carried out for the $(p,pn)$ recoil-momentum distribution method and is presented in this work. The experimental momentum distributions are compared to state-of-the-art mean field and $ab$ $initio$ in-medium similarity renormalization group and self-consistent Green's function calculations in combination with DWIA reaction theory calculations. Based on this work, the 1$p$ neutron orbitals are consistently found $0.48-0.78$ fm larger than the $0f_{7/2}$ neutron orbitals in $^{52-54}$Ca, while the size evolution of the valence proton orbitals remains inconclusive due to the large associated statistical uncertainties.

nucl-ex↗

arXiv2026

Engineering the non-Hermitian Su-Schrieffer-Heeger model with skin effects in Rydberg atom arrays

We propose and systematically analyze a practical scheme for implementing a one-dimensional non-Hermitian (NH) Su-Schrieffer-Heeger model using individually addressable Rydberg atom arrays. Our setup consists of an atomic chain with three-atom unit cells, in which a synthetic gauge field is generated by applying multicolor laser fields. By engineering fast dissipative channels for one auxiliary atom in each unit cell, adiabatic elimination effectively gives rise to a NH skin effect. We examine how fluctuations in the experimental parameters influence both the skin effect and the topological invariant in real space and find that both features remain highly robust. This work establishes a versatile, controllable, and programmable open-system quantum simulator with neutral atoms, providing a clear route for exploring rich NH topological phenomena.

quant-ph↗

arXiv2024

Spectroscopy of $^{52}$K

The first spectroscopy of $^{52}$K was investigated via in-beam $\gamma$-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory after one-proton and one-neutron knockout from $^{53}$Ca and $^{53}$K beams impinging on a 15-cm liquid hydrogen target at $\approx$ 230~MeV/nucleon. The energy level scheme of $^{52}$K was built using single $\gamma$ and $\gamma$-$\gamma$ coincidence spectra. The spins and parities of the excited states were established based on momentum distributions of the fragment after the knockout reaction and based on exclusive cross sections. The results were compared to state-of-the-art shell model calculations with the SDPF-Umod interaction and ab initio IMSRG calculations with chiral effective field theory nucleon-nucleon and three-nucleon forces.

nucl-ex↗

arXiv2024

Spectroscopy of deeply bound orbitals in neutron-rich Ca isotopes

The calcium isotopes are an ideal system to investigate the evolution of shell structure and magic numbers. Although the properties of surface nucleons in calcium have been well studied, probing the structure of deeply bound nucleons remains a challenge. Here, we report on the first measurement of unbound states in $^{53}$Ca and $^{55}$Ca, populated from \ts{54,56}Ca($p,pn$) reactions at a beam energy of around 216 MeV/nucleon at the RIKEN Radioactive Isotopes Beam Factory. The resonance properties, partial cross sections, and momentum distributions of these unbound states were analyzed. Orbital angular momentum $l$ assignments were extracted from momentum distributions based on calculations using the distorted wave impulse approximation (DWIA) reaction model. The resonances at excitation energies of 5516(41)\,keV in $^{53}$Ca and 6000(250)\,keV in $^{55}$Ca indicate a significant $l$\, =\,3 component, providing the first experimental evidence for the $\nu 0f_{7/2}$ single-particle strength of unbound hole states in the neutron-rich Ca isotopes. The observed excitation energies and cross-sections point towards extremely localized and well separated strength distributions, with some fragmentation for the $\nu 0f_{7/2}$ orbital in $^{55}$Ca. These results are in good agreement with predictions from shell-model calculations using the effective GXPF1Bs interaction and \textit{ab initio} calculations and diverge markedly from the experimental distributions in the nickel isotones at $Z=28$.

nucl-ex↗

arXiv2023

A Configurable Ultra-Low Noise Current Source for Transition-Edge Sensor Characterization

Transition-edge sensors (TESs) are sensitive devices for detecting photons from millimeter radiation to gamma rays. Their photon counting efficiency and collecting area benefit from large-array multiplexing scheme, and therefore the development of multiplexing readout system has been an important topic in this field. Among the many multiplex techniques, time-division multiplexing (TDM) superconducting quantum interference device (SQUID) has been used most widely for TES readout. In this work, we design a Configurable Ultra-Low Noise Current Source (CLCS) for TES characterization and as a part of a whole TDM-TES bias control system. The CLCS is based on the feedback structure of ultra-low noise instrumentation amplifiers and low-noise, high-resolution (20 bits) digital-to-analog converter (DAC). CLCS has an ultra-high resolution of 10 nA in the 0 to 5 mA current output range, and can perform current-voltage (IV) sweep and bias-step tests to measure key TES parameters on board. The feedback structure of the CLCS also avoids the issue of impedance mismatch.

astro-ph.IM↗

arXiv2023

Level Structures of $^{56,58}$Ca Cast Doubt on a doubly magic $^{60}$Ca

Gamma decays were observed in $^{56}$Ca and $^{58}$Ca following quasi-free one-proton knockout reactions from $^{57,59}$Sc beams at $\approx 200$ MeV/nucleon. For $^{56}$Ca, a $\gamma$ ray transition was measured to be 1456(12) keV, while for $^{58}$Ca an indication for a transition was observed at 1115(34) keV. Both transitions were tentatively assigned as the $2^+_1 \rightarrow 0^+_{gs}$ decays, and were compared to results from ab initio and conventional shell-model approaches. A shell-model calculation in a wide model space with a marginally modified effective nucleon-nucleon interaction depicts excellent agreement with experiment for $2^+_1$ level energies, two-neutron separation energies, and reaction cross sections, corroborating the formation of a new nuclear shell above the $N$ = 34 shell. Its constituents, the $0f_{5/2}$ and $0g_{9/2}$ orbitals, are almost degenerate. This degeneracy precludes the possibility for a doubly magic $^{60}$Ca and potentially drives the dripline of Ca isotopes to $^{70}$Ca or even beyond.

nucl-ex↗

arXiv2022

A First Glimpse at the Shell Structure beyond $^{54}$Ca: Spectroscopy of $^{55}$K, $^{55}$Ca, and $^{57}$Ca

States in the $N=35$ and 37 isotopes $^{55,57}$Ca have been populated by direct proton-induced nucleon removal reactions from $^{56,58}$Sc and $^{56}$Ca beams at the RIBF. In addition, the $(p,2p)$ quasi-free single-proton removal reaction from $^{56}$Ca was studied. Excited states in $^{55}$K, $^{55}$Ca, and $^{57}$Ca were established for the first time via in-beam $\gamma$-ray spectroscopy. Results for the proton and neutron removal reactions from $^{56}$Ca to states in $^{55}$K and $^{55}$Ca for the level energies, excited state lifetimes, and exclusive cross sections agree well with state-of-the-art theoretical calculations using different approaches. The observation of a short-lived state in $^{57}$Ca suggests a transition in the calcium isotopic chain from single-particle dominated states at $N=35$ to collective excitations at $N=37$.

nucl-ex↗

arXiv2021

H$\alpha$ and He I absorption in HAT-P-32 b observed with CARMENES -- Detection of Roche lobe overflow and mass loss

We analyze two high-resolution spectral transit time series of the hot Jupiter HAT-P-32 b obtained with the CARMENES spectrograph. Our new XMM-Newton X-ray observations of the system show that the fast-rotating F-type host star exhibits a high X-ray luminosity of 2.3e29~erg/s (5-100 A), corresponding to a flux of 6.9e4 erg/cm**2/s at the planetary orbit, which results in an energy-limited escape estimate of about 1e13 g/s for the planetary mass-loss rate. The spectral time series show significant, time-dependent absorption in the Halpha and He I triplet lines with maximum depths of about 3.3% and 5.3%. The mid-transit absorption signals in the Halpha and He I lines are consistent with results from one-dimensional hydrodynamic modeling, which also yields mass-loss rates on the order of 1e13 g/s. We observe an early ingress of a redshifted component of the transmission signal, which extends into a redshifted absorption component, persisting until about the middle of the optical transit. While a super-rotating wind can explain redshifted ingress absorption, we find that an up-orbit stream, transporting planetary mass in the direction of the star, also provides a plausible explanation for the pre-transit signal. This makes HAT-P-32 a benchmark system for exploring atmospheric dynamics via transmission spectroscopy.

astro-ph.EP↗

arXiv2021

Investigation of the ground-state spin inversion in the neutron-rich 47,49Cl isotopes

A first gamma-ray study of 47,49Cl spectroscopy was performed at the Radioactive Isotope Beam Factory with 50Ar projectiles at 217 MeV/nucleon, impinging on the liquid hydrogen target of the MINOS device. Prompt de-excitation gamma-rays were measured with the NaI(Tl) array DALI2+. Through the one-proton knockout reaction 50Ar(p,2p), a spin assignment could be determined for the low-lying states of 49Cl from the momentum distribution obtained with the SAMURAI spectrometer. A spin-parity J = 3/2+ is deduced for the ground state of 49Cl, similar to the recently studied N = 32 isotope 51K.

nucl-ex↗

arXiv2020

$\boldsymbol{N=32}$ shell closure below calcium: Low-lying structure of $^{50}$Ar

Low-lying excited states in the $N=32$ isotope $^{50}$Ar were investigated by in-beam $\gamma$-ray spectroscopy following proton- and neutron-knockout, multi-nucleon removal, and proton inelastic scattering at the RIKEN Radioactive Isotope Beam Factory. The energies of the two previously reported transitions have been confirmed, and five additional states are presented for the first time, including a candidate for a 3$^-$ state. The level scheme built using $\gamma\gamma$ coincidences was compared to shell-model calculations in the $sd-pf$ model space, and to ab initio predictions based on chiral two- and three-nucleon interactions. Theoretical proton- and neutron-knockout cross sections suggest that two of the new transitions correspond to $2^+$ states, while the previously proposed $4^+$ state could also correspond to a $2^+$ state.

nucl-ex↗

arXiv2019

Shell evolution of $N=40$ isotones towards $^{60}$Ca: First spectroscopy of $^{62}$Ti

Excited states in the $N=40$ isotone $^{62}$Ti were populated via the $^{63}$V$(p,2p)$$^{62}$Ti reaction at $\sim$200~MeV/u at the Radioactive Isotope Beam Factory and studied using $\gamma$-ray spectroscopy. The energies of the $2^+_1 \rightarrow 0^{+}_{\mathrm{gs}}$ and $4^+_1 \rightarrow 2^+_1$ transitions, observed here for the first time, indicate a deformed $^{62}$Ti ground state. These energies are increased compared to the neighboring $^{64}$Cr and $^{66}$Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for $^{62}$Ti show a dominant configuration with four neutrons excited across the $N=40$ gap. Likewise, they indicate that the $N=40$ island of inversion extends down to $Z=20$, disfavoring a possible doubly magic character of the elusive $^{60}$Ca.

nucl-ex↗

arXiv2019

Development of Transition-Edge Sensor X-ray Microcalorimeter Linear Array for Compton Scattering and Energy Dispersive Diffraction Imaging

We present a strip transition-edge sensor microcalorimeter linear array detector developed for energy dispersive X-ray diffraction imaging and Compton scattering applications. The prototype detector is an array of 20 transition-edge-sensors with absorbers in strip geometry arranged in a linear array. We discuss the fabrication steps needed to develop this array including Mo/Cu bilayer, Au electroplating, and proof-of-principle fabrication of long strips of SiNx membranes. We demonstrate minimal unwanted effect of strip geometry on X-ray pulse response, and show linear relationship of 1/pulse height and pulse decay times with absorber length. For the absorber lengths studied, preliminary measurements show energy resolutions of 40 eV to 180 eV near 17 keV. Furthermore, we show that the heat flow to the cold bath is nearly independent of the absorber area and depends on the SiNx membrane geometry.

physics.ins-det↗

arXiv2019

A Study of the Numerical Stability of an ImEx Scheme with Application to the Poisson-Nernst-Planck Equations

The Poisson-Nernst-Planck equations with generalized Frumkin-Butler-Volmer boundary conditions (PNP-FBV) describe ion transport with Faradaic reactions and have applications in a wide variety of fields. Using an adaptive time-stepper based on a second-order variable step-size, semi-implicit, backward differentiation formula (VSSBDF2), we observe that when the underlying dynamics is one that would have the solutions converge to a steady state solution, the adaptive time-stepper produces solutions that "nearly" converge to the steady state and that, simultaneously, the time-step sizes stabilize at a limiting size $dt_\infty$. Linearizing the SBDF2 scheme about the steady state solution, we demonstrate that the linearized scheme is conditionally stable and that this is the cause of the adaptive time-stepper's behaviour. Mesh-refinement, as well as a study of the eigenvectors corresponding to the critical eigenvalues, demonstrate that the conditional stability is not due to a time-step constraint caused by high-frequency contributions. We study the stability domain of the linearized scheme and find that it can have corners as well as jump discontinuities.

math.NA↗

arXiv2018

How Robust is the N = 34 Subshell Closure? First Spectroscopy of $^{52}$Ar

The first $\gamma$-ray spectroscopy of $^{52}$Ar, with the neutron number N = 34, was measured using the $^{53}$K(p,2p) one-proton removal reaction at $\sim$210 MeV/u at the RIBF facility. The 2$^{+}_{1}$ excitation energy is found at 1656(18) keV, the highest among the Ar isotopes with N $>$ 20. This result is the first experimental signature of the persistence of the N = 34 subshell closure beyond $^{54}$Ca, i.e., below the magic proton number Z = 20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2$^{+}_{1}$ systematics of neutron-rich Ar isotopes, and support a N = 34 subshell closure in $^{52}$Ar.

nucl-ex↗

arXiv2015

Design and construction of a multi-layer CsI(Tl) telescope for high-energy reaction studies

A prototype of a new CsI(Tl) telescope, which will be used in the reaction studies of light isotopes with energy of several hundred AMeV, has been constructed and tested at the Institute of Modern Physics, Chinese Academy of Sciences. The telescope has a multi-layer structure and the range information will be obtained to improve the particle identification performance. This prototype has seven layers of different thickness. A 5.0% (FWHM) energy resolution has been extracted for one of the layers in a beam test experiment. Obvious improvement for the identification of $^{14}$O and $^{15}$O isotopes was achieved by using the range information.

physics.ins-det↗

arXiv2015

New measurement of the excited states in $^{11}$B via the elastic resonance scattering of $^{10}$Be + p

The elastic resonance scattering protons decayed from $^{11}$B to the ground state of $^{10}$Be were measured using the thick-target technique in inverse kinematics at the Heavy Ion Research Facility in Lanzhou (HIRFL). The obtained excitation functions were well described by a multichannel R-matrix procedure under the kinematics process assumption of resonant elastic scattering. The excitation energy of the resonant states ranges from 13.0 to 17.0 MeV, and their resonant parameters such as the resonant energy E$_{x}$, the spin-parity J$^\pi$, and the proton-decay partial width $\Gamma_p$ were determined from R-matrix fits to the data. Two of these states around E$_{x}$ = 14.55 MeV [J$^\pi$ = (3/2$^+$, 5/2$^+$), $\Gamma_p$ = 475 $\pm$ 80 keV] and E$_{x}$ = 14.74 MeV [J$^\pi$ = 3/2$^-$, $\Gamma_p$ = 830 $\pm$ 145 keV], and a probably populated state at E$_x$ = 16.18 MeV [J$^\pi$ =(1/2$^-$, 3/2$^-$), $\Gamma_p$ $<$ 60 keV], are respectively assigned to the well-known states in $^{11}$B at 14.34 MeV, 15.29 MeV, and 16.43 MeV. The isospin of these three states were previously determined to be T = 3/2, but discrepancies exist in widths and energies due to the current counting statistics and energy resolution. We have compared these states with previous measurements, and the observation of the possibly populated resonance is discussed.

nucl-ex↗

arXiv2014

Dark-bright Solitons and their Lattices in Atomic Bose-Einstein Condensates

In the present contribution, we explore a host of different stationary states, namely dark-bright solitons and their lattices, that arise in the context of multi-component atomic Bose-Einstein condensates. The latter, are modeled by systems of coupled Gross-Pitaevskii equations with general interaction (nonlinearity) coefficients $g_{ij}$. It is found that in some particular parameter ranges such solutions can be obtained in analytical form, however, numerically they are computed as existing in a far wider parametric range. Many features of the solutions under study, such as their analytical form without the trap or the stability/dynamical properties of one dark-bright soliton even in the presence of the trap are obtained analytically and corroborated numerically. Additional features, such as the stability of soliton lattice homogeneous states or their existence/stability in the presence of the trap, are examined numerically.

cond-mat.quant-gas↗

arXiv2013

Exploring Rigidly Rotating Vortex Configurations and their Bifurcations in Atomic Bose-Einstein Condensates

In the present work, we consider the problem of a system of few vortices $N \leq 5$ as it emerges from its experimental realization in the field of atomic Bose-Einstein condensates. Starting from the corresponding equations of motion, we use a two-pronged approach in order to reveal the configuration space of the system's preferred dynamical states. On the one hand, we use a Monte-Carlo method parametrizing the vortex "particles" by means of hyperspherical coordinates and identifying the minimal energy ground states thereof for $N=2, ..., 5$ and different vortex particle angular momenta. We then complement this picture with a dynamical systems analysis of the possible rigidly rotating states. The latter reveals all the supercritical and subcritical pitchfork, as well as saddle-center bifurcations that arise exposing the full wealth of the problem even at such low dimensional cases. By corroborating the results of the two methods, it becomes fairly transparent which branch the Monte-Carlo approach selects for different values of the angular momentum which is used as a bifurcation parameter.

nlin.PS↗