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2025 No.8
2025, 49(8): 085102.
doi:10.1088/1674-1137/add9fb
Abstract:
The rotational metric provides an exact solution to Einstein's clock-rate problem in curved spacetime, specifically, whether time flows more slowly at the equator of a compact object such as a neutron star than at its poles. It features a curvature singularity, an event horizon, a potentially evolving ergosphere, a rigidly-rotating normal space, and two stationary limit surfaces. Although derived from the Schwarzschild metric through rotational transformations, it includes an additional ergosphere. Given the equivalence of inertia and gravity, this demonstrates how non-inertial transformations, such as rotational transformations, can introduce new spacetime structures into a gravitational system. In particular, the additional physical degrees of freedom carried by rotational transformations are eaten by the gravitational system to form an additional ergosphere. Furthermore, the rotational metric effectively models a rigidly-rotating gravitational system and is applicable for describing rotationally-induced gravitational effects in various rotating magnetospheres.
The rotational metric provides an exact solution to Einstein's clock-rate problem in curved spacetime, specifically, whether time flows more slowly at the equator of a compact object such as a neutron star than at its poles. It features a curvature singularity, an event horizon, a potentially evolving ergosphere, a rigidly-rotating normal space, and two stationary limit surfaces. Although derived from the Schwarzschild metric through rotational transformations, it includes an additional ergosphere. Given the equivalence of inertia and gravity, this demonstrates how non-inertial transformations, such as rotational transformations, can introduce new spacetime structures into a gravitational system. In particular, the additional physical degrees of freedom carried by rotational transformations are eaten by the gravitational system to form an additional ergosphere. Furthermore, the rotational metric effectively models a rigidly-rotating gravitational system and is applicable for describing rotationally-induced gravitational effects in various rotating magnetospheres.
2025, 49(8): 1-5.
doi:10.1088/1674-1137/adcc00
Abstract:
Non-destructive Schottky detectors are indispensable devices widely used in experiments at heavy-ion storage rings. In particular, they can be used to accurately determine the masses and lifetimes of short-lived exotic nuclear species. Single-ion sensitivity – which is the highest level of sensitivity – has been regularly achieved in the past by utilizing resonant cavity detectors. Recent designs and analysis methods aim to push the limits of measurement accuracy by increasing the dimensionality of the acquired data, namely, the position of the particle as well as the phase difference between several detectors. This paper describes current methods and future perspectives for Schottky detection techniques, with a focus on their application to mass and lifetime measurements of the most rare and simultaneously short-lived radio nuclides.
Non-destructive Schottky detectors are indispensable devices widely used in experiments at heavy-ion storage rings. In particular, they can be used to accurately determine the masses and lifetimes of short-lived exotic nuclear species. Single-ion sensitivity – which is the highest level of sensitivity – has been regularly achieved in the past by utilizing resonant cavity detectors. Recent designs and analysis methods aim to push the limits of measurement accuracy by increasing the dimensionality of the acquired data, namely, the position of the particle as well as the phase difference between several detectors. This paper describes current methods and future perspectives for Schottky detection techniques, with a focus on their application to mass and lifetime measurements of the most rare and simultaneously short-lived radio nuclides.
2025, 49(8): 084001.
doi:10.1088/1674-1137/add10c
Abstract:
Invariant-mass spectroscopy has been performed to search for possible resonance states in the loosely bound neutron-rich15C nucleus. By detecting alpha and11Be in coincidence, we reconstruct the excitation energy spectrum for15C. To estimate the physical background from non-resonant prompt alpha particles, we employ a recently proposed weighted event-mixing method with phenomenological reduced weighting at around the alpha-decay threshold to account for the depletion in the prompt alpha's contribution owing likely to the Coulomb final-state interactions. A new weighted mixed-event method that focuses on a robust treatment of the Coulomb effect is also proposed. Through fitting the spectrum using the background estimated with these two methods, up to two resonance state candidates are proposed. Further experiments with improved statistics and theoretical calculations are called for to confirm these resonance states.
Invariant-mass spectroscopy has been performed to search for possible resonance states in the loosely bound neutron-rich15C nucleus. By detecting alpha and11Be in coincidence, we reconstruct the excitation energy spectrum for15C. To estimate the physical background from non-resonant prompt alpha particles, we employ a recently proposed weighted event-mixing method with phenomenological reduced weighting at around the alpha-decay threshold to account for the depletion in the prompt alpha's contribution owing likely to the Coulomb final-state interactions. A new weighted mixed-event method that focuses on a robust treatment of the Coulomb effect is also proposed. Through fitting the spectrum using the background estimated with these two methods, up to two resonance state candidates are proposed. Further experiments with improved statistics and theoretical calculations are called for to confirm these resonance states.
2025, 49(8): 084005.
doi:10.1088/1674-1137/adcc90
Abstract:
In this study, neutron activation experiments were performed to measure the (n, 2n) reaction cross section for80Kr at five neutron energies, 13.59±0.12, 13.86±0.15, 14.13±0.16, 14.70±0.13, and 14.94±0.02 MeV, using a highly enriched gaseous sample. The neutron energies and their uncertainties were determined using theQ-value equation for the3H(d,n)4He reaction, accounting for the solid angle of the sample. The93Nb(n, 2n)92mNb reaction was employed to monitor the neutron flux. Eight characteristic gamma rays of the produced nucleus were selected to determine the activity of the generated nuclei. The final cross sections were obtained using a weighted average method. The self-absorption and cascade of rays, as well as the geometry and solid angles of the sample, were corrected. The80Kr(n, 2n)79Kr reaction cross sections obtained in this work exhibited the smallest uncertainty than the values in existing literature, which provided improved experimental constraints for the prediction of excitation curves, thereby enhancing the quality of the corresponding database. The measured results were compared with previously reported experimental values, empirical and systematic formula predictions, theoretical calculations from TALYS-1.96 with six adjustable energy level densities, and evaluated database results. Our experimental results demonstrated high precision and extended the energy range appropriately, offering valuable insights for future studies.
In this study, neutron activation experiments were performed to measure the (n, 2n) reaction cross section for80Kr at five neutron energies, 13.59±0.12, 13.86±0.15, 14.13±0.16, 14.70±0.13, and 14.94±0.02 MeV, using a highly enriched gaseous sample. The neutron energies and their uncertainties were determined using theQ-value equation for the3H(d,n)4He reaction, accounting for the solid angle of the sample. The93Nb(n, 2n)92mNb reaction was employed to monitor the neutron flux. Eight characteristic gamma rays of the produced nucleus were selected to determine the activity of the generated nuclei. The final cross sections were obtained using a weighted average method. The self-absorption and cascade of rays, as well as the geometry and solid angles of the sample, were corrected. The80Kr(n, 2n)79Kr reaction cross sections obtained in this work exhibited the smallest uncertainty than the values in existing literature, which provided improved experimental constraints for the prediction of excitation curves, thereby enhancing the quality of the corresponding database. The measured results were compared with previously reported experimental values, empirical and systematic formula predictions, theoretical calculations from TALYS-1.96 with six adjustable energy level densities, and evaluated database results. Our experimental results demonstrated high precision and extended the energy range appropriately, offering valuable insights for future studies.
2025, 49(8): 084104.
doi:10.1088/1674-1137/add70f
Abstract:
In this study, we employ the maximum likelihood estimator (MLE) to investigate the relationship between initial-state fluctuations and final-state anisotropies in relativistic heavy-ion collisions. The granularity of the initial state, reflecting fluctuations in the initial conditions (ICs), is modeled using a peripheral tube model. In addition to differential flow, our analysis focuses on a class of more sensitive observables known as flow factorization. Specifically, we evaluate these observables using the MLE, an asymptotically normal and unbiased tool in standard statistical inference. Our findings show that the resulting differential flow remains essentially unchanged for different ICs defined by the peripheral tube model. The resulting harmonic coefficients obtained using the MLE and multi-particle cumulants are found to be consistent. However, the calculated flow factorizations show significant variations depending on both the IC and estimators, which is attributed to their sensitivity to initial-state fluctuations. Thus, we argue that the MLE offers a compelling alternative to standard methods, such as multi-particle correlators, particularly for sensitive observables constructed from higher moments of the azimuthal distribution.
In this study, we employ the maximum likelihood estimator (MLE) to investigate the relationship between initial-state fluctuations and final-state anisotropies in relativistic heavy-ion collisions. The granularity of the initial state, reflecting fluctuations in the initial conditions (ICs), is modeled using a peripheral tube model. In addition to differential flow, our analysis focuses on a class of more sensitive observables known as flow factorization. Specifically, we evaluate these observables using the MLE, an asymptotically normal and unbiased tool in standard statistical inference. Our findings show that the resulting differential flow remains essentially unchanged for different ICs defined by the peripheral tube model. The resulting harmonic coefficients obtained using the MLE and multi-particle cumulants are found to be consistent. However, the calculated flow factorizations show significant variations depending on both the IC and estimators, which is attributed to their sensitivity to initial-state fluctuations. Thus, we argue that the MLE offers a compelling alternative to standard methods, such as multi-particle correlators, particularly for sensitive observables constructed from higher moments of the azimuthal distribution.
2025, 49(8): 084006.
doi:10.1088/1674-1137/add8fb
Abstract:
The deformation driving tendency of various single particle orbitals near the Fermi surface has been investigated with the lifetime measurements of high spin states in the non-yrast bands of
$^{177}{\rm Re}$
nucleus. For this study, the
$^{165}{\rm{Ho}}$
(
$^{16}{\rm{O}}$
,4n)
$^{177}{\rm{Re}}$
reaction at a beam energy of 84 MeV was used. Lifetimes of four lowest levels in the
$\pi i_{13/2}[660]1/2^+$
band and four levels in the
$\pi d_{5/2}[402]5/2^+$
(α= –1/2) band were measured. The extracted transition quadrupole moments for the
$\pi i_{13/2}$
intruder band showed a sharp increase with increasing level spin, indicating a significant shape transition in the nucleus. The average transitional quadrupole moment (
$Q_t$
), a measure of deformation, for the
$\pi i_{13/2}$
band was significantly larger (
$Q_t$
~ 8.7 (6) eb) compared with the
$\pi d_{5/2}$
(
$Q_t$
~ 6.3 (5) eb) band. To interpret the observed shape changes in the two bands, the experimental transition probabilities for these bands were compared with the results obtained from Projected Shell Model (PSM) calculations.
The deformation driving tendency of various single particle orbitals near the Fermi surface has been investigated with the lifetime measurements of high spin states in the non-yrast bands of
2025, 49(8): 084103.
doi:10.1088/1674-1137/add872
Abstract:
The effects of nucleon-nucleon short-range correlations leading to the high-momentum tail (HMT) in the nucleon momentum distribution are studied using the isospin- and momentum-dependent Lanzhou quantum molecular dynamics (LQMD) transport model. Based on the transport model, we study the effects of the HMT of the nucleon momentum distribution on initialization in isotopic nuclear reactions at a beam energy of 120 MeV/u. The single and double ratios of gas-phase neutron and proton spectra are analyzed and compared with experimental data in central
$ ^{112} {\rm{Sn}}$
+
$ ^{112} {\rm{Sn}}$
and
$ ^{124} {\rm{Sn}}$
+
$ ^{124} {\rm{Sn}}$
collisions. The HMT affects the single ratios but not the double ratios, which can be employed to study other isospin effects more effectively. The ratio of triton to
$ ^3 {\rm{He}}$
of light clusters contained in the gas-phase nucleons is also influenced by the HMT. Combining the QMD transport model that can describe multi-fragmentation and the production of fragments in intermediate-energy heavy-ion collisions, we study the short-range correlation effect on fragment generation. We find that the isospin-dependent HMT significantly affects the fragment multiplicity distribution and average neutron-to-proton ratio of produced isobars.
The effects of nucleon-nucleon short-range correlations leading to the high-momentum tail (HMT) in the nucleon momentum distribution are studied using the isospin- and momentum-dependent Lanzhou quantum molecular dynamics (LQMD) transport model. Based on the transport model, we study the effects of the HMT of the nucleon momentum distribution on initialization in isotopic nuclear reactions at a beam energy of 120 MeV/u. The single and double ratios of gas-phase neutron and proton spectra are analyzed and compared with experimental data in central
2025, 49(8): 084101.
doi:10.1088/1674-1137/adc4cb
Abstract:
A method for the treatment of the neutron-proton (np) isovector pairing correlations at finite temperature is developed within the path integral formalism. It generalizes the recently proposed model using a similar approach for pairing between like-particles. The pairing terms in the total Hamiltonian are expressed in a square form to facilitate the use of the Hubbard-Stratonovitch transformation. The expression for the partition function of the system is then established. The gap equations, as well as the expressions for the energy, entropy, and heat capacity of the system are deduced. In a first step, the formalism is numerically applied to the schematic Richardson model. In a second step, the method is applied to nuclei with
$ N=Z $
using the single-particle energies of a deformed Woods-Saxon mean-field. The variations in the gap parameters, excitation energy, and heat capacity are studied as functions of the temperature. We show that the overall behavior of these quantities is similar to their homologues in the standard FTBCS model. We note in particular the existence of critical temperatures beyond which the pairing vanishes. Moreover, in the framework of the present approach, the pairing effects appear to persist beyond the critical temperatures predicted by the FTBCS model for pairing between like-particles or its generalization fornppairing.
A method for the treatment of the neutron-proton (np) isovector pairing correlations at finite temperature is developed within the path integral formalism. It generalizes the recently proposed model using a similar approach for pairing between like-particles. The pairing terms in the total Hamiltonian are expressed in a square form to facilitate the use of the Hubbard-Stratonovitch transformation. The expression for the partition function of the system is then established. The gap equations, as well as the expressions for the energy, entropy, and heat capacity of the system are deduced. In a first step, the formalism is numerically applied to the schematic Richardson model. In a second step, the method is applied to nuclei with
2025, 49(8): 1-7.
doi:10.1088/1674-1137/add10e
Abstract:
Recent high-resolution observations have established a strong link between black hole jets and accretion disk structures, particularly in the 3.5 mm wavelength band [Nature. 616,686 (2023)]. In this work, we propose a "jet-modified Novikov-Thorne disk model" that explicitly incorporates jet luminosity into the accretion disk radiation framework. By integrating synchrotron radiation from relativistic electrons in the jet, we derive a modified luminosity function that accounts for both the accretion disk and jet contributions. Our analysis demonstrates that the inclusion of jet luminosity enhances the total accretion disk luminosity by approximately 33.5%, as derived from the integration of radiative flux. Furthermore, we compare our modified model with the standard Novikov-Thorne model and find that the jet contribution remains significant across different observational inclinations. These results highlight the necessity of incorporating jet effects when estimating the observable flux of black hole accretion systems, which has direct implications for future astronomical observations.
Recent high-resolution observations have established a strong link between black hole jets and accretion disk structures, particularly in the 3.5 mm wavelength band [Nature. 616,686 (2023)]. In this work, we propose a "jet-modified Novikov-Thorne disk model" that explicitly incorporates jet luminosity into the accretion disk radiation framework. By integrating synchrotron radiation from relativistic electrons in the jet, we derive a modified luminosity function that accounts for both the accretion disk and jet contributions. Our analysis demonstrates that the inclusion of jet luminosity enhances the total accretion disk luminosity by approximately 33.5%, as derived from the integration of radiative flux. Furthermore, we compare our modified model with the standard Novikov-Thorne model and find that the jet contribution remains significant across different observational inclinations. These results highlight the necessity of incorporating jet effects when estimating the observable flux of black hole accretion systems, which has direct implications for future astronomical observations.
2025, 49(8): 084105.
doi:10.1088/1674-1137/adcc8c
Abstract:
The spin alignment of
$ J/\psi $
with respect to the event plane in relativistic heavy ion collisions exhibits a significant signal. We propose a possible mechanism for spin alignment through the spin-dependent dissociation of quarkonia in vortical quark-gluon plasma. The spin-dependent dissociation is realized through inelastic scattering between constituents of quarkonium and those of quark-gluon plasma polarized by vorticity. The spin-dependent dissociation rate is found to depend on the directions of vorticity, quantization axis, and quark momentum. We implement our results in a dissociation-dominated evolution model for quarkonia in the Bjorken flow, finding that the spin 0 state is slightly suppressed compared with the average of the other two, which is consistent with the sign observed in experiments. We also observe the absence of logarithmic enhancement in the binding energy in the vortical correction to the dissociation rate, which is understood from the requirement that a spin-dependent dissociation can only result from quark coupling to a pair of chromomagnetic and chromoelectric fields.
The spin alignment of
2025, 49(8): 083105.
doi:10.1088/1674-1137/add674
Abstract:
Holographic models that consider classical vector fields in a 5-d background provide effective descriptions for heavy vector meson spectra. This is true both in vacuum and a thermal medium, such as quark gluon plasma. However, the manner in which these phenomenological models work is unclear. In particular, what is the role of the fifth dimension, and what is the relation between the holographic 5-d background and physical (4-d) heavy mesons? Hadrons, in contrast to leptons, are composite particles with some internal structure that depends on the energy at which they are observed. In this study, a static meson is represented by a heavy quark-antiquark pair with an interaction described by a Nambu Goto string existing in the same 5-d background that provides field solutions leading to masses and decay constants of charmonium states. The resulting interaction potential is linear for large distances, with a string tension consistent with the effective Cornell potential. Introducing temperatureTin the background, it is found for the
$J/\psi$
case that there is a deconfining transition at some critical value ofT. The obtained results indicate that the 5-d background effectively represents the internal structure of the (static) charmonium (quasi) states.
Holographic models that consider classical vector fields in a 5-d background provide effective descriptions for heavy vector meson spectra. This is true both in vacuum and a thermal medium, such as quark gluon plasma. However, the manner in which these phenomenological models work is unclear. In particular, what is the role of the fifth dimension, and what is the relation between the holographic 5-d background and physical (4-d) heavy mesons? Hadrons, in contrast to leptons, are composite particles with some internal structure that depends on the energy at which they are observed. In this study, a static meson is represented by a heavy quark-antiquark pair with an interaction described by a Nambu Goto string existing in the same 5-d background that provides field solutions leading to masses and decay constants of charmonium states. The resulting interaction potential is linear for large distances, with a string tension consistent with the effective Cornell potential. Introducing temperatureTin the background, it is found for the
2025, 49(8): 083107.
doi:10.1088/1674-1137/add873
Abstract:
We study flavor-changing bottom quark radiative decay
$ b {\rightarrow} s \gamma $
induced at the one-loop level within the minimal gauged two-Higgs-doublet model (G2HDM). Among the three new contributions to this rare process in G2HDM, we find that only the charged Higgs
$ {\cal{H}}^\pm $
contribution can be constrained by the current global fit data inB-physics. The other two contributions from complex vectorial dark matter
$ {\cal{W}} $
and dark Higgs
$ {\cal{D}} $
are not sensitive to the current data. Incorporating theoretical constraints imposed on the scalar potential and electroweak precision data for the oblique parameters, we exclude mass regions
$ m_{\cal{H}}^\pm \lesssim 250 $
GeV and
$ m_{\cal{D}} \lesssim 100 $
GeV at the 95% confidence level.
We study flavor-changing bottom quark radiative decay
2025, 49(8): 083001.
doi:10.1088/1674-1137/adcdf3
Abstract:
Using 20.3 fb–1of
$e^+e^-$
annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we report on an improved search for the radiative leptonic decay
$D^+\to\gamma e^+\nu_e$
. An upper limit on its partial branching fraction for photon energies
$E_\gamma>10 $
MeV was determined to be
$1.2\times10^{-5}$
at a 90% confidence level; this excludes most current theoretical predictions. A sophisticated deep learning approach, which includes thorough validation and is based on the Transformer architecture, was implemented to efficiently distinguish the signal from massive backgrounds.
Using 20.3 fb–1of
2025, 49(8): 083109.
doi:10.1088/1674-1137/add09f
Abstract:
The
$ \gamma p \to \pi^0 \eta p $
reaction has been investigated by the CBELSA/TAPS collaboration, revealing a narrow structure in the
$ \eta p $
invariant mass distributions at a mass of 1700 MeV. In this study, we explore the possibility of the narrow structure being caused by a decay cascade via an intermediate nucleon resonance decaying to
$ \eta p $
final states. The candidates for the intermediate nucleon resonances are
$ N(1700)3/2^{-} $
and
$ N(1710)1/2^{+} $
, with masses near the observed structure. We considered thet-channelρ- andω-exchange diagrams,u-channel nucleon-pole exchange diagram, contact term, ands-channel pole diagrams of the nucleon, Δ, along with the nucleon resonances when constructing the reaction amplitudes, to reproduce the stripped individual contribution of the narrow structure. Our analysis indicates that the signature strength of the decay cascade
$ \gamma p \to \pi^{0}N(1700)3/2^{-} \to \pi^{0}\eta p $
is too weak to reach the experimental curve of the narrow structure due to the small decay branching ratio of
$ N(1700)3/2^{-} $
to
$ \eta p $
. Although the decay cascade
$ \gamma p \to \pi^{0}N(1710)1/2^{+} \to \pi^{0}\eta p $
can qualitatively reproduce the experimental curve of the invariant mass distributions, its cross-section width is much larger than that of the corresponding experimental curve. Therefore, we conclude that the decay cascade via an intermediate nucleon resonance cannot be the reason for the narrow structure in the
$ \eta p $
invariant mass distributions of the
$ \gamma p \to \pi^0 \eta p $
reaction.
The
2025, 49(8): 083102.
doi:10.1088/1674-1137/adcd4b
Abstract:
In this study, we present several improvements of the non-relativistic Friedrichs-Lee model with multiple discrete and continuous states while retaining its solvability. Our findings establish a solid theoretical basis for the exploration of resonance phenomena in scenarios involving multiple interfering states across various channels. The scattering amplitudes associated with the continuum states naturally adhere to coupled-channel unitarity, rendering this framework particularly valuable for investigating hadronic resonant states appearing in multiple coupled channels. Moreover, this generalized framework exhibits a wide-range applicability, enabling investigations into resonance phenomena across diverse physical domains, including hadron physics, nuclear physics, optics, cold atom physics, etc.
In this study, we present several improvements of the non-relativistic Friedrichs-Lee model with multiple discrete and continuous states while retaining its solvability. Our findings establish a solid theoretical basis for the exploration of resonance phenomena in scenarios involving multiple interfering states across various channels. The scattering amplitudes associated with the continuum states naturally adhere to coupled-channel unitarity, rendering this framework particularly valuable for investigating hadronic resonant states appearing in multiple coupled channels. Moreover, this generalized framework exhibits a wide-range applicability, enabling investigations into resonance phenomena across diverse physical domains, including hadron physics, nuclear physics, optics, cold atom physics, etc.
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