State-selective single-electron capture in He+ + Ne collisions was studied at laboratory He+ projectile kinetic energies of 30-100 keV (corresponding to 7.5-25 keV/u) using a reaction microscope. Q-value spectra were obtained through recoil-ion momentum reconstruction, enabling the decomposition of the capture yield into three distinct contributions: (i) capture into excited states of the projectile without target excitation, (ii) capture into the projectile ground state accompanied by excitation of the residual Ne+ ion, and (iii) capture involving simultaneous excitation of both He and Ne+. Across the studied energy range, capture into the projectile ground state accompanied by target excitation is the dominant pathway. With increasing impact energy, the fraction of joint projectile-target excitation increases markedly, whereas the target-excitation-only contribution decreases; the projectile-excitation-only fraction remains at a low, nearly constant level. These findings underscore the significance of multi-electron dynamics in intermediate-energy collisions involving many-electron targets.

State-selective single electron capture has been investigated in collisions between He^2+ ions and Ar atoms at energies of 30, 62.5, and 100 keV/u, using high resolution reaction microscope (ReMi). The Q-value spectra, state-selective cross sections, and scattering angle distributions are obtained. The results show that pure single electron capture (PSEC) into the n = 2 and n ≥ 3 states is dominant at low impact energy, while the transfer target excitation (TTE) process becomes dominant at high impact energy. The total cross sections of TTE are found to be comparable to those of PSEC. A comparison of the experimental scattering angle distributions with theoretical results calculated by molecular Coulombic over-barrier model (MCBM) shows that correlated two-electron transitions play a vital role at high impact energies.

Based on 6.1  fb^{-1} of e^{+}e^{-} annihilation data collected at center-of-mass energies from 4.600 to 4.843 GeV with the BESIII detector at the BEPCII collider, a partial wave analysis of Λ_{c}^{+}→Λπ^{+}η is performed, and branching fractions and decay asymmetry parameters of intermediate processes are determined. The process Λ_{c}^{+}→Λa_{0}(980)^{+} is observed for the first time, and evidence for the pentaquark candidate Σ(1380)^{+} decaying into Λπ^{+} is found with statistical significance larger than 3σ with mass and width fixed to theoretical predictions. The branching fraction product B[Λ_{c}^{+}→Λa_{0}(980)^{+}]B[a_{0}(980)^{+}→π^{+}η] is determined to be (1.05±0.16_{stat}±0.05_{syst}±0.07_{ext})%, which is larger than theoretical calculations by 1-2 orders of magnitude. Here the third (external) systematic is from B(Λ_{c}^{+}→Λπ^{+}η). Finally, we precisely obtain the absolute branching fraction B(Λ_{c}^{+}→Λπ^{+}η)=(1.94±0.07_{stat}±0.11_{syst})%.

State-selective single-and double-electron capture in collisions of N4+ ions with He atoms have been studied at projectile energies in the range of 20-80 keV. The state-selective single-and double-electron capture cross sections and projectile scattering angle distributions were obtained using cold-target recoil-ion momentum spectroscopy. For single-electron capture, the experimentally obtained state-selective cross sections show an obvious discrepancy with the calculated results by molecular orbital close-coupling methods and are in good agreement at a projectile energy of 20 keV with other experiments. The angular distributions are compared with calculations from the multichannel Landau-Zener model. For double-electron capture, electrons captured into 2l2l' states of the N4+ projectile are dominant. The angular distributions are explained by a two-step model combining the classical deflection function.

The line ratios in X-ray emission resulting from charge exchange between highly charged ions (HCIs) and neutral atoms are not only crucial for accurately modeling astrophysical X-ray emissions but also offer a unique perspective on the charge exchange processes happening during collisions. The K X-ray spectra following charge exchange between Mg11+ and He are presented for a collision velocity of 1489 km/s (11.5 keV/amu). The spectra were measured by two Silicon Drift Detectors capable of resolving the Mg10+ Kα, Kβ, Kγ, and Kδ+ lines. The line intensity ratios of Kβ, Kγ, and Kδ+ relative to the Kα line, as well as the hardness ratio, were obtained. The experimental results were compared with the theoretical results from a cascade model that utilizes the state cross-sections produced by multichannel Landau–Zener (MCLZ) calculation. It was discovered that the K X-ray spectrum features can be reproduced well by MCLZ theory when the contributions of both single electron capture (SEC) and autoionizing double capture (ADC) processes are included. This finding implies that the ADC feeding mechanism is significant and should be taken into account for the X-ray emission during charge exchange between highly charged ions and multielectron atoms.

The process e^+e^-→K_S^0K_S^0ψ (3686) is studied by analyzing e+e− collision data samples collected at eight center-of-mass energies ranging from 4.682 to 4.951 GeV with the BESIII detector operating at the BEPCII collider, corresponding to an integrated luminosity of 4.1 fb−1. Observation of the e^+e^-→K_S^0K_S^0ψ (3686) process is found for the first time with a statistical significance of 6.3σ, and the cross sections at each center-of-mass energy are measured. The ratio of cross sections of e^+e^-→K_S^0K_S^0ψ (3686) relative to e+e− → K+K−ψ(3686) is determined to be σ(e^+e^-→K_S^0K_S^0ψ (3686))/σ(e^+e^-→K^+K^-ψ (3686))=0.45± 0.25 , which is consistent with the prediction based on isospin symmetry. The uncertainty includes both statistical and systematic contributions. Additionally, the K_S^0ψ (3686) invariant mass distribution is found to be consistent with three-body phase space. The significance of a contribution beyond three-body phase space is only 0.8σ.

We study the fragmentation of NOq+(q=2,3)molecular ions produced by collisions between 96 keV O6+ions and neutral nitric oxide(NO)molecules,using the cold target recoil ion momentum spectrometer(COLTRIMS).The kinetic energy release(KER)for various dissociation channels is obtained.For the channel NO2+→ N++O+,double-electron capture followed by autoionization of the projectile ions is the dominant process,which can be explained by the recapture of loosely bound electrons into highly excited states of the target.For NO3+trication,two dissociation channels,i.e.,(a)N++O2+and(b)N2++O+,are observed,where channel(b)is the dominant channel.Moreover,for dissociation channels originating from the same parent molecular ion,the dissociation channel with a higher charge for the oxygen ion fragment exhibits a higher most probable KER,which is consistent with studies of CO fragmentation by Rajput et al.Additionally,it is observed that as capture stability increases,the average KER shifts to higher values.

As a fundamental process in atomic physics,charge exchange relies on quantum state-resolved data that is crucial for various fields such as astrophysics and plasma physics.However,there remains a gap in the research on multi-electron target systems.This study aims to investigate the dynamic mechanisms of single/double electron capture in collisions between Ar2+ions and Ar atoms or N2 molecules at an energy of 40 keV,thereby supplementing high-precision experimental data in this field.The experiment is conducted on the electron beam ion source(EBIS)platform at the Institute of Modern Physics,Chinese Academy of Sciences,using the cold target recoil ion momentum spectroscopy(COLTRIMS)technique.An ion beam containing ground-state Ar2+(3s23p4 3P)and metastable Ar2+(3s23p4 1D,1S)is used as the projectile,colliding with a supersonic Ar/N2 mixed gas target.Three-dimensional momentum of recoil ions is reconstructed through coincidence measurements of recoil ions and scattered ions,and the Q-value and scattering angle distribution are calculated.Theoretical comparisons are performed using the molecular Coulombic over barrier model(MCBM). The results show that there are similarities in the populations of single-electron captured states between the two systems,but the contribution ratios are different:the Q-value spectrum of the Ar2+-Ar system contains an additional characteristic peak,which corresponds to the process where the projectile ion captures an electron from the 3s orbital of the target while its own 3s electron is excited to the 3p orbital.In contrast,this characteristic peak is absent in the Ar2+-N2 system due to the easy dissociation of excited N2+ions.For double-electron capture,both systems are dominated by capturing electrons to the ground state,but only the Ar2+-N2 system shows a significant contribution from excited state populations.The comparison of scattering angles reveals that the higher the capture state of the product ion,the larger the corresponding scattering angle is and the smaller the impact parameter is.This is presumably because electron interactions become more complex at smaller impact parameters,leading to a higher probability of capturing electrons to high-energy levels.In the double-electron capture of the Ar2+-N2 system,only the ground-state channel is populated at small angles(0-1.2 mrad).Additionally,electron capture exhibits dependence on impact parameter:as the angle increases(i.e.the impact parameter decreases),the Q-value of the capture reaction decreases,indicating that the reaction tends to be more endothermic.

低能高电荷态离子与H原子电荷交换X射线的实验和理论研究为天体环境中非平衡态等离子体的诊断和建模提供了重要原子数据。本工作利用半经典多通道Landau-Zener（MCLZ）方法计算了全裸和类氢的C、N、O离子与H原子电荷交换截面并与已报道实验结果进行了比较。我们发现，对于C 5+ +H碰撞体系，理论计算的总截面和实验测量相差较大。同时，也对比了太阳风离子速度（或能量）区间MCLZ方法和全量子分子轨道紧耦合（QMOCC）方法计算的态选择截面。发现，对于俘获到n=3壳层，MCLZ方法计算的态选择截面随碰撞能量升高而增加；对于俘获到n=4壳层，MCLZ方法计算的态选择截面随碰撞能量升高而减小；在低能端比QMOCC方法计算的截面小两个量级之多。最后，采用天文领域发展的Kronos程序包，通过Janev推荐的截面数据[Atomic Data and Nuclear Data Tables, 1999, 55（2）:201]计算了1 keV·u -1 O 8+ +H电荷交换X射线谱、线强比及硬度比，并与MCLZ计算结果比较。我们认为，MCLZ计算方法结合l分布模型具有较大的不确定性，会影响天体环境建模的准确性。亟需发展更加准确的全量子理论。

State-selective single-and double-electron capture processes in collisions of S 5+ ions with helium at energies ranging from 50.8 keV to 100 keV were investigated using cold target recoil ion momentum spectroscopy（COLTRIMS）.Q-value spectra and projectile scattering angle distributions were obtained.For single-electron capture,single electron capture into n=3 states of the projectile ion is dominant.As the projectile energy increases,the contribution of single electron capture into n=4 states is observed.Experimental relative cross-sections for single-electron capture into different projectile final states were compared with theoretical predictions based on the molecular orbital close-coupling（MOCC） method.In double-electron capture,two-electron populating into the 3s 2 3p and 3s3p 2 states of projectile dominates.The reaction window calculated from the classical molecular Coulombic barrier model can qualitatively explain the experimental results.The scattering angle distribution of the multi-peak structure of the double-electron capture process is observed.The database is openly available in Science Data Bank at https://doi.org/10.57760/sciencedb.j00113.00233.

We report a comprehensive study of charge-exchange dynamics in collisions of He+ and He2+ ions with Ne and Ar targets at velocities ranging from 0.63 to 1.41 a.u. (atomic units). Using a high-voltage cylindrical mirror analyzer, we analyzed scattered ions at a fixed large scattering angle of 14 degrees, achieving sub-K-shell penetration where projectile-target separations fall below the K-shell radius of the target atoms. This work bridges the gap between low-velocity quasimolecular-orbital models and high-velocity perturbative approaches. The measured He2+/He+ ratios exhibit a strong dependence on both velocity and target species, which are quantitatively reproduced by a modified classical overbarrier model incorporating empirical corrections for screening effects. Our analysis reveals that K-shell electrons dominate charge exchange at intermediate velocities due to their ultrashort orbital periods, particularly in heavy targets like Ar. Our study advances the understanding of electron dynamics in deeply penetrating ion-atom collisions and provides a valuable reference for modeling charge transfer in asymmetric systems.

A combined experimental and theoretical study is carried out on the single-electron capture process in He+–He collisions at energies ranging from 0.5 keV/u to 5 keV/u. Using cold target recoil ion momentum spectroscopy, we obtain state-selective cross sections and angular differential cross sections. Within the entire studied energy range, the dominant channel is the electron captured into the ground-state, and the relative contribution of the dominant channel shows a decreasing trend with increasing energy. The angular differential cross sections of ground-state capture exhibit obvious oscillatory structures. To understand the oscillatory structures of the differential cross sections, we also performed theoretical calculations using the two-center atomic orbital close-coupling method, which well reproduced the oscillatory structures. The results indicate that these structures are strongly correlated to the oscillatory structures of the impact parameter dependence of electron probability.

Abstract The process e + e − → K S 0 K S 0 ψ 3686 $$ {e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686) $$ is studied by analyzing e + e − collision data samples collected at eight center-of-mass energies ranging from 4.682 to 4.951 GeV with the BESIII detector operating at the BEPCII collider, corresponding to an integrated luminosity of 4.1 fb −1. Observation of the e + e − → K S 0 K S 0 ψ 3686 $$ {e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686) $$ process is found for the first time with a statistical significance of 6.3σ, and the cross sections at each center-of-mass energy are measured. The ratio of cross sections of e + e − → K S 0 K S 0 ψ 3686 $$ {e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686) $$ relative to e + e − → K + K − ψ(3686) is determined to be σ e + e − → K S 0 K S 0 ψ 3686 σ e + e − → K + K − ψ 3686 = 0.45 ± 0.25 $$ \frac{\sigma \left({e}^{+}{e}^{-}\to {K}_S^0{K}_S^0\psi (3686)\right)}{\sigma \left({e}^{+}{e}^{-}\to {K}^{+}{K}^{-}\psi (3686)\right)}=0.45\pm 0.25 $$ , which is consistent with the prediction based on isospin symmetry. The uncertainty includes both statistical and systematic contributions. Additionally, the K S 0 ψ 3686 $$ {K}_S^0\psi (3686) $$ invariant mass distribution is found to be consistent with three-body phase space. The significance of a contribution beyond three-body phase space is only 0.8σ.

利用反应显微成像谱仪,采用二重符合方法,实验测量了0.64 keV/u N + 与He单电子俘获产生的反冲离子He + 三维动量,获得了电子俘获到炮弹离子不同量子态的态选择截面和角分布。实验结果表明:基态的炮弹离子N + （1s 2 2s 2 2p 2 ～3P）俘获He靶的一个1s电子主要布居到2p壳层,也可以看到布居到更高壳层的贡献;亚稳态的炮弹离子N + （1s 2 2s2p 3 ～5S）俘获He靶的一个1s电子主要布居到2s壳层,几乎看不到布居到更高壳层的贡献。利用NHe + 准分子离子的势能曲线定性地解释了实验结果,但分子库仑过垒模型的反应窗预测与实验存在较大差别。在亚稳态炮弹离子N + （1s 2 2s2p 3 ～5S）俘获靶电子到2s轨道的过程中,角微分截面出现了明显的振荡结构,这很可能来自Demkov型跃迁。

Intermolecular Coulombic decay (ICD) is considered a general phenomenon that plays a key role in many fundamental and applied fields related to biological environments. In many cases, however, the mechanisms and efficiency of ICD have yet to be uncovered. A prominent example is heavy-ion cancer therapy. Here, we report the first detection of a damaging intermolecular relaxation cascade initiated by heavy-ion bombardment of hydrated pyrimidine clusters. The process can significantly contribute to the high biological effectiveness of heavy-ion irradiation and thus might play an essential role in many radiotherapy techniques. Inner-valence ionization of the cluster initiates ICD and triggers proton transfer between water molecules, producing destructive low-energy electrons, HO^{•} radicals, and hydrated protons. Notably, the efficiency of ICD was found to increase dramatically with the number of water molecules, making ICD the dominant decay mechanism after inner-valence ionization. These findings indicate that the biological damage, caused by ICD in aqueous environments, is much more severe than was previously recognized.

One of the main goals of studying semileptonic decays in flavor physics is to gain a better understanding of hadronic transitions in the nonperturbative region of Quantum Chromodynamics. This involves measuring Cabibbo-Kobayashi-Maskawa matrix elements, understanding form factors, and comparing them with theoretical predictions. We report a first study of the semileptonic decay D^{0}→K^{-}π^{0}μ^{+}ν_{μ} by analyzing an e^{+}e^{-} annihilation data sample of 7.93  fb^{-1} collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The absolute branching fraction of D^{0}→K^{-}π^{0}μ^{+}ν_{μ} is measured for the first time, providing necessary input for extracting the c→s Cabibbo-Kobayashi-Maskawa matrix element through this process. This measurement allows us to test lepton flavor universality, with no indication of violation found. Furthermore, a series of hadronic form factors have been determined and compared with theoretical predictions, which will impose stricter constraints on theoretical models.

Based on (10.09 +/- 0.04) x 10(9) J/psi events collected with the BESIII detector operating at the BEPCII collider, a partial wave analysis of the decay J/psi -> phi pi(0 eta). is performed. We observe for the first time two new structures on the phi eta invariant mass distribution, with significances exceeding 27 sigma and 13 sigma; the first with J(PC) = 1(+-), mass M = (1908 +/- 6(stat)(-4)(+8) (sys)) MeV/c(2), and width Gamma = (175 +/- 13(stat)(-16)(+7) (sys)) MeV, the second with J(PC) = 1(--), mass M = (1992 +/- 12 (stat)(-6)(+15) (sys)) MeV/c(2), and width Gamma = (132 +/- 22(stat)(-4)(+17) (sys)) MeV. These measurements provide important input for the strangeonium spectrum. In addition, the f(0) (980) - a(0)(980)(0) mixing signal in J/psi -> phi f(0)(980) -> phi a(0)(980)(0) and the corresponding electromagnetic decay J/psi -> phi a(0)(980)(0) are measured with improved precision, providing crucial information to understand the nature of a(0)(980)(0) and f(0)(980).

Based on (2712.4±14.3)×106 e+e−→ψ(3686) events collected with the BESIII detector operating at the BEPCII Collider, we report the first evidence of χc0→ΛΛ¯ϕ decays and the first observation of χc1,2→ΛΛ¯ϕ decays, with significances of 4.1σ, 11.3σ and 13.0σ, respectively. The decay branching fractions of χc0,1,2→ΛΛ¯ϕ are measured to be (2.99±1.24±0.19)×10−5, (6.01±0.90±0.40)×10−5, and (7.13±0.81±0.36)×10−5, where the first uncertainties are statistical and the second systematic. No obvious enhancement near the ΛΛ¯ production threshold or excited Λ state is found in the Λϕ (or Λ¯ϕ) system. Published by the American Physical Society 2024

We present cross sections for the reaction e(+)e(-) -> (KSKL0)-K-0 at center-of-mass energies ranging from 3.51 to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb(-1). The ratio of neutral-to-charged kaon form factors at large momentum transfers (12 < Q(2) < 25 GeV2) is determined to be 0.21 +/- 0.01, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and, consequently, excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction vertical bar F(pi(+/-))vertical bar/vertical bar F(K-+/-)vertical bar = f(pi)(2)/f(K)(2), where F(pi(+/-)) and F(K-+/-) are the form factors, and f(pi) and f(K) are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay psi(3770)->(KSKL0)-K-0 for the first time. Within a 1 sigma contour of the likelihood value, the branching fraction for psi(3770)-> K K-0(S)L(0) is determined to be B=(2.63(-1.59)(+1.40)) x 10(-5), and the relative phase between the continuum and psi(3770) amplitudes is phi = (-0.39(-0.10)(+0.05))pi. The branching fraction is in good agreement with the S- and D-wave charmonia mixing scheme proposed in the interpretation of the "rho pi puzzle" between J/psi and psi(3686) decays.

Using e(+)e(-) annihilation data sets corresponding to an integrated luminosity of 4.5 fb(-1), collected with the BESIII detector at center-of-mass energies between 4.600 and 4.699 GeV, we report the first measurements of the absolute branching fractions B(Lambda(+)(c)-> pK(L)(0) = (1.67 +/- 0.06 +/- 0.04)%, B(Lambda(+)(c)-> pK(L)(0) pi(+)pi(-) = (1.69 +/- 0.10 +/- 0.05)%, and B(Lambda(+)(c)-> pK(L)(0)pi(0) = (2.02 +/- 0.13 +/- 0.05)%, where the first uncertainties are statistical and the second systematic. Combining with the known branching fractions of Lambda(+)(c)-> pK(S)(0), Lambda(+)(c)-> pK(S)(0) pi(+)pi(-), and Lambda(+)(c)-> pK(S)(0)pi(0), we present the first measurements of the K-S(0)-K-L(0) asymmetries R(Lambda K-+(c)S,L(0) X) = B(Lambda(+)(c) -> (KSX)-X-0-B (Lambda(+)(c)-> K-L(0) X/B(Lambda(+)(c)->(KSX)-X-0)+B(Lambda(+)(c)->(KLX)-X-0) in charmed baryon decays: R(Lambda(+)(c)pK(S,L)(0)) = -0.025 +/- 0.031, R(Lambda(+)(c)pK(S,L)(0) pi(+)pi(-)) = -0.027 +/- 0.048 and R(Lambda(+)(c)pK(S,L)(0)pi(0) = -0.015 +/- 0.046. No significant asymmetries with statistical significance are observed.