arXiv subjects

W. Xiong

Publications and source records attributed to W. Xiong.

17 recordsLinked to original sources

arXiv2026

Precision Neutron Skins of $^{208}$Pb and $^{48}$Ca from Parity-Violating Electron Scattering

We have measured the parity-violating elastic electron scattering asymmetry in the PREX and CREX experiments on ${}^{208}$Pb and ${}^{48}$Ca respectively; these are both doubly-magic nuclei whose excited states can be discriminated from the ground state by the high resolution spectrometers in Hall A at Jefferson Lab. This asymmetry provides a precise determination of the weak charge form factor at one $Q^2$ and pins down the neutron radius in these two nuclei in a relatively clean and model-independent way. This is because the $Z^0$ boson of the weak interaction couples primarily to neutrons. The heavier lead nucleus, with a neutron excess, provides an interpretation of the neutron skin thickness in terms of properties of bulk neutron matter. For the lighter ${}^{48}$Ca nucleus, which is also rich in neutrons, comparisons to microscopic nuclear theory calculations are sensitive to poorly constrained 3-neutron forces. The weak neutral form factors $F_W(Q^2)$ were extracted to be $0.368 \pm 0.013$ at $Q = 0.3977 {\rm\ fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.1304 \pm 0.0055$ at $Q = 0.8733 {\rm\ fm}^{-1}$ for $^{48}$Ca. The form factor differences $(F_{ch}-F_W)(Q^2)$ were calculated to be $0.041 \pm 0.013$ at $Q = 0.3977 {\rm fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.0277 \pm 0.0055$ at $Q = 0.8733 {\rm fm}^{-1}$ for $^{48}$Ca. Correcting for Coulomb distortions and using nuclear model information, we find the neutron skin thicknesses to be $R^{208}_{\rm skin} = 0.283 \pm 0.071$ fm combining PREX-1 and PREX-2 and $R^{48}_{\rm skin} = 0.121 \pm 0.035$ fm. This paper provides a full description of the special experimental and data analysis techniques employed for precisely measuring these small asymmetries.

nucl-ex↗

arXiv2025

Evolution of the rippled inner-interface-initiated ablative Rayleigh-Taylor instability in laser-ablating high-Z doped targets

Rippled interface between the ablator and DT ice can feedout and form the perturbation seeds for the ablative Rayleigh-Taylor (ART) instability, which negatively affects direct-drive inertial confinement fusion (ICF). However, the evolution of instability remains insufficiently studied, and the effect of high-Z dopant on it remains unclear. In this paper, we develop a theoretical model to calculate the feedout seeds and describe this instability. Our theory suggests that the feedout seeds are determined by the ablation pressure and the adiabatic index, while the subsequent growth mainly depends on the ablation velocity. Two-dimensional radiation hydrodynamic simulations confirm our theory. It is shown that high-Z doped targets exhibit more severe feedout seeds, because of their higher ionization compared to undoped targets. However, the X-ray pre-ablation in high-Z doped targets significantly suppresses the subsequent growth, leading to the suppression of short-wavelength perturbations. But for long-wavelength perturbations, this suppression weakens, resulting in an increased instability in the high-Z doped targets. The results are helpful for understanding the inner-interface-initiated instability and the influence of high-Z dopant on it, providing valuable insights for target design and instability control in ICF.

physics.plasm-ph↗

arXiv2023

A new direct detection electron scattering experiment to search for the X17 particle

A new electron scattering experiment (E12-21-003) to verify and understand the nature of hidden sector particles, with particular emphasis on the so-called X17 particle, has been approved at Jefferson Lab. The search for these particles is motivated by new hidden sector models introduced to account for a variety of experimental and observational puzzles: excess in $e^+e^-$ pairs observed in multiple nuclear transitions, the 4.2$σ$ disagreement between experiments and the standard model prediction for the muon anomalous magnetic moment, and the small-scale structure puzzle in cosmological simulations. The aforementioned X17 particle has been hypothesized to account for the excess in $e^+e^-$ pairs observed from the $^8$Be M1, $^4$He M0, and, most recently, $^{12}$C E1 nuclear transitions to their ground states observed by the ATOMKI group. This experiment will use a high resolution electromagnetic calorimeter to search for or set new limits on the production rate of the X17 and other hidden sector particles in the $3 - 60$ MeV mass range via their $e^+e^-$ decay (or $γγ$ decay with limited tracking). In these models, the $1 - 100$ MeV mass range is particularly well-motivated and the lower part of this range still remains unexplored. Our proposed direct detection experiment will use a magnetic-spectrometer-free setup (the PRad apparatus) to detect all three final state particles in the visible decay of a hidden sector particle for an effective control of the background and will cover the proposed mass range in a single setting. The use of the well-demonstrated PRad setup allows for an essentially ready-to-run and uniquely cost-effective search for hidden sector particles in the $3 - 60$ MeV mass range with a sensitivity of 8.9$\times$10$^{-8}$ - 5.8$\times$10$^{-9}$ to $ε^2$, the square of the kinetic mixing interaction constant between hidden and visible sectors.

nucl-ex↗

arXiv2022

A Direct Detection Search for Hidden Sector New Particles in the 3-60 MeV Mass Range

In our quest to understand the nature of dark matter and discover its non-gravitational interactions with ordinary matter, we propose an experiment using a \pbo ~calorimeter to search for or set new limits on the production rate of i) hidden sector particles in the $3 - 60$ MeV mass range via their $e^+e^-$ decay (or $γγ$ decay with limited tracking), and ii) the hypothetical X17 particle, claimed in multiple recent experiments. The search for these particles is motivated by new hidden sector models and dark matter candidates introduced to account for a variety of experimental and observational puzzles: the small-scale structure puzzle in cosmological simulations, anomalies such as the 4.2$σ$ disagreement between experiments and the standard model prediction for the muon anomalous magnetic moment, and the excess of $e^+e^-$ pairs from the $^8$Be M1 and $^4$He nuclear transitions to their ground states observed by the ATOMKI group. In these models, the $1 - 100$ MeV mass range is particularly well-motivated and the lower part of this range still remains unexplored. Our proposed direct detection experiment will use a magnetic-spectrometer-free setup (the PRad apparatus) to detect all three final state particles in the visible decay of a hidden sector particle allowing for an effective control of the background and will cover the proposed mass range in a single setting. The use of the well-demonstrated PRad setup allows for an essentially ready-to-run and uniquely cost-effective search for hidden sector particles in the $3 - 60$ MeV mass range with a sensitivity of 8.9$\times$10$^{-8}$ - 5.8$\times$10$^{-9}$ to $ε^2$, the square of the kinetic mixing interaction constant between hidden and visible sectors. This updated proposal includes our response to the PAC49 comments.

nucl-ex↗

arXiv2022

Precision Determination of the Neutral Weak Form Factor of $^{48}$Ca

We report a precise measurement of the parity-violating asymmetry $A_{\rm PV}$ in the elastic scattering of longitudinally polarized electrons from $^{48}{\rm Ca}$. We measure $A_{\rm PV} =2668\pm 106\ {\rm (stat)}\pm 40\ {\rm (syst)}$ parts per billion, leading to an extraction of the neutral weak form factor $F_{\rm W} (q=0.8733$ fm$^{-1}) = 0.1304 \pm 0.0052 \ {\rm (stat)}\pm 0.0020\ {\rm (syst)}$ and the charge minus the weak form factor $F_{\rm ch} - F_{\rm W} = 0.0277\pm 0.0055$. The resulting neutron skin thickness $R_n-R_p=0.121 \pm 0.026\ {\rm (exp)} \pm 0.024\ {\rm (model)}$~fm is relatively thin yet consistent with many model calculations. The combined CREX and PREX results will have implications for future energy density functional calculations and on the density dependence of the symmetry energy of nuclear matter.

nucl-ex↗

arXiv2022

PRad-II: A New Upgraded High Precision Measurement of the Proton Charge Radius

The PRad experiment has credibly demonstrated the advantages of the calorimetric method in e-p scattering experiments to measure the proton root-mean-square (RMS) charge radius with high accuracy. The PRad result, within its experimental uncertainties, is in agreement with the small radius measured in muonic hydrogen spectroscopy experiments and it was a critical input in the recent revision of the CODATA recommendation for the proton charge radius. Consequently, the PRad result is in direct conflict with all modern electron scattering experiments. Most importantly, it is 5.8% smaller than the value from the most precise electron scattering experiment to date, and this difference is about three standard deviations given the precision of the PRad experiment. As the first experiment of its kind, PRad did not reach the highest precision allowed by the calorimetric technique. Here we propose a new (and) upgraded experiment -- PRad-II, which will reduce the overall experimental uncertainties by a factor of 3.8 compared to PRad and address this as yet unsettled controversy in subatomic physics. In addition, PRad-II will be the first lepton scattering experiment to reach the Q^2 range of 10^{-5} GeV^2 allowing a more accurate and robust extraction of the proton charge radius. The muonic hydrogen result with its unprecedented precision (~0.05%) determines the CODATA value of the proton charge radius, hence, it is critical to evaluate possible systematic uncertainties of those experiments, such as the laser frequency calibration that was raised in recent review articles. The PRad-II experiment with its projected total uncertainty of 0.43% could demonstrate whether there is any systematic difference between $e-p$ scattering and muonic hydrogen results. PRad-II will establish a new precision frontier in electron scattering and open doors for future physics opportunities.

nucl-ex↗

arXiv2021

2-bit topological-encoded acoustic multifunctional device

Valley degree of freedom, an excellent information carrier in valleytronics, has been further introduced into advanced microstructure systems for achieving the acoustic valley-Hall topological insulators (VHTIs), which host valley-projected edge states suppressing the undesired sound backscattering under certain perturbations. Therein, the majority of previous literatures focused on single frequency region, and the lack of capability of simultaneous multi-band operation with individual control radically impedes their potential applications. Here, a binary topological-encoded acoustic VHTI is investigated both theoretically and experimentally to manipulate each of the dual-band valley-projected edge states. Through arranging different coding elements derived from the combined valley-Chern numbers, the existence and propagation directions of the frequency selective edge states can be configured in corresponding frequency regions individually. On this basis, three types of proof-of-concept acoustic topological-encoded functional devices are designed, including frequency beam splitter, anti-interference demultiplex topological sensing and composite topological whispering gallery. Our proposal may provide versatile possibilities for achieving the integrated multifunctional systems in multi-channel signal processing and memorizing with high efficiency and high capacity.

physics.app-ph↗

arXiv2021

The PRad Windowless Gas Flow Target

We report on a windowless, high-density, gas flow target at Jefferson Lab that was used to measure $r_p$, the root-mean-square charge radius of the proton. To our knowledge, this is the first such system used in a fixed-target experiment at a (non-storage ring) electron accelerator. The target achieved its design goal of an areal density of 2$\times$10$^{18}$ atoms/cm$^2$, with the gas uniformly distributed over the 4 cm length of the cell and less than 1% residual gas outside the cell. This design eliminated scattering from the end caps of the target cell, a problem endemic to previous measurements of the proton charge radius in electron scattering experiments, and permitted a precise, model-independent extraction of $r_p$ by reaching unprecedentedly low values of $Q^2$, the square of the electron's transfer of four-momentum to the proton.

physics.ins-det↗

arXiv2021

Time- and energy-resolved effects in the boron-10 based Multi-Grid and helium-3 based thermal neutron detectors

The boron-10 based Multi-Grid detector is being developed as an alternative to helium-3 based neutron detectors. At the European Spallation Source, the detector will be used for time-of-flight neutron spectroscopy at cold to thermal neutron energies. The objective of this work is to investigate fine time- and energy-resolved effects of the Multi-Grid detector, down to a few $μ$eV, while comparing it to the performance of a typical helium-3 tube. Furthermore, it is to characterize differences between the detector technologies in terms of internal scattering, as well as the time reconstruction of ~ $μ$s short neutron pulses. The data were taken at the Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube were installed at the ESS test beamline, V20. Using a Fermi-chopper, the neutron beam of the reactor was chopped into a few tens of $μ$s wide pulses before reaching the detector, located a few tens of cm downstream. The data of the measurements show an agreement between the derived and calculated neutron detection efficiency curve. The data also provide fine details on the effect of internal scattering, and how it can be reduced. For the first time, the chopper resolution was comparable to the timing resolution of the Multi-Grid detector. This allowed a detailed study of time- and energy resolved effects, as well as a comparison with a typical helium-3 tube.

physics.ins-det↗

arXiv2019

Extra-factorial sum: a graph-theoretic parameter in Hamiltonian cycles of complete weighted graphs

A graph-theoretic parameter, in a form of a function, called the extra-factorial sum is discussed. The main results are presented in ref. [1] (Nastou et al., Optim Lett, 10, 1203-1220, 2016) and the reader is strongly advised to study the aforementioned paper. The current work presents subject matter in a tutorial form with proofs and some newer unpublished results towards the end (lemma six extension and lemma seven). The extra-factorial sum is relevant to Hamiltonian cycles of complete weighted graphs $WH_n$ with $n$ vertices and is obtained for each edge of $WH_n$. If this sum is multiplied by $1 / (n - 2)$ then it gives directly the arithmetic mean of the sum of lengths $l_i$ of all Hamiltonian cycles that traverse a selected edge $e_q$. The number of terms in this sum is a factorial proven to be $(n - 2)!$ which signifies that its value depends on $n$. Using the extra-factorial sum, the arithmetic mean of the sum of the squared lengths of $(n - 1)! / 2$ Hamiltonian cycles of $WH_{n}$ can be obtained as well.

math.CO↗

arXiv2018

Statistical Description of Transport in Multimode Fibers with Mode-Dependent Loss

We analyze coherent wave transport in a new physical setting associated with multimode wave systems where reflection is completely suppressed and mode-dependent losses together with mode-mixing are dictating the wave propagation. An additional physical constraint is the fact that in realistic circumstances the access to the scattering (or transmission) matrix is incomplete. We have addressed all these challenges by providing a statistical description of wave transport which fuses together a free probability theory approach with a Filtered Random Matrix ensemble. Our theoretical predictions have been tested successfully against experimental data of light transport in multimode fibers.

physics.optics↗

arXiv2017

The Microsoft 2017 Conversational Speech Recognition System

We describe the 2017 version of Microsoft's conversational speech recognition system, in which we update our 2016 system with recent developments in neural-network-based acoustic and language modeling to further advance the state of the art on the Switchboard speech recognition task. The system adds a CNN-BLSTM acoustic model to the set of model architectures we combined previously, and includes character-based and dialog session aware LSTM language models in rescoring. For system combination we adopt a two-stage approach, whereby subsets of acoustic models are first combined at the senone/frame level, followed by a word-level voting via confusion networks. We also added a confusion network rescoring step after system combination. The resulting system yields a 5.1\% word error rate on the 2000 Switchboard evaluation set.

cs.CL↗

arXiv2017

Achieving Human Parity in Conversational Speech Recognition

Conversational speech recognition has served as a flagship speech recognition task since the release of the Switchboard corpus in the 1990s. In this paper, we measure the human error rate on the widely used NIST 2000 test set, and find that our latest automated system has reached human parity. The error rate of professional transcribers is 5.9% for the Switchboard portion of the data, in which newly acquainted pairs of people discuss an assigned topic, and 11.3% for the CallHome portion where friends and family members have open-ended conversations. In both cases, our automated system establishes a new state of the art, and edges past the human benchmark, achieving error rates of 5.8% and 11.0%, respectively. The key to our system's performance is the use of various convolutional and LSTM acoustic model architectures, combined with a novel spatial smoothing method and lattice-free MMI acoustic training, multiple recurrent neural network language modeling approaches, and a systematic use of system combination.

cs.CL↗

arXiv2017

The Microsoft 2016 Conversational Speech Recognition System

We describe Microsoft's conversational speech recognition system, in which we combine recent developments in neural-network-based acoustic and language modeling to advance the state of the art on the Switchboard recognition task. Inspired by machine learning ensemble techniques, the system uses a range of convolutional and recurrent neural networks. I-vector modeling and lattice-free MMI training provide significant gains for all acoustic model architectures. Language model rescoring with multiple forward and backward running RNNLMs, and word posterior-based system combination provide a 20% boost. The best single system uses a ResNet architecture acoustic model with RNNLM rescoring, and achieves a word error rate of 6.9% on the NIST 2000 Switchboard task. The combined system has an error rate of 6.2%, representing an improvement over previously reported results on this benchmark task.

cs.CL↗

arXiv2016

A Search for the LHCb Charmed 'Pentaquark' using Photo-Production of $J/ψ$ at Threshold in Hall C at Jefferson Lab

We propose to measure the photo-production cross section of $J/ψ$ near threshold, in search of the recently observed LHCb hidden-charm resonances $P_c$(4380) and $P_c$(4450) consistent with 'pentaquarks'. The observation of these resonances in photo-production will provide strong evidence of the true resonance nature of the LHCb states, distinguishing them from kinematic enhancements. A bremsstrahlung photon beam produced with an 11 GeV electron beam at CEBAF covers the energy range of $J/ψ$ production from the threshold photo-production energy of 8.2 GeV, to an energy beyond the presumed $P_c$(4450) resonance. The experiment will be carried out in Hall C at Jefferson Lab using a 50μA electron beam incident on a 9% copper radiator. The resulting photon beam passes through a 15 cm liquid hydrogen target, producing $J/ψ$ mesons through a diffractive process in the $t$-channel, or through a resonant process in the $s$- and $u$-channel. The decay $e^+e^-$ pair of the $J/ψ$ will be detected in coincidence using the two high-momentum spectrometers of Hall C. The spectrometer settings have been optimized to distinguish the resonant $s$- and $u$-channel production from the diffractive $t$-channel $J/ψ$ production. The $s$- and $u$-channel production of the charmed 5-quark resonance dominates the $t$-distribution at large $t$. The momentum and angular resolution of the spectrometers is sufficient to observe a clear resonance enhancement in the total cross section and $t$-distribution. We request a total of 11 days of beam time with 9 days to carry the main experiment and 2 days to acquire the needed $t$-channel elastic $J/ψ$ production data for a calibration measurement. This calibration measurement in itself will greatly enhance our knowledge of $t$-channel elastic $J/ψ$ production near threshold.

hep-ex↗

arXiv2015

Measurement of the Doubly-Polarized $\vec{{^3}He}(\vecγ,n)pp$ Reaction at 16.5 MeV and Its Implications for the GDH Sum Rule

We report new measurements of the doubly-polarized photodisintegration of $^3$He at an incident photon energy of 16.5 MeV, carried out at the High Intensity $γ$-ray Source (HI$γ$S) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contribution from the three--body channel to the Gerasimov-Drell-Hearn (GDH) integrand were extracted and compared with the state-of-the-art three--body calculations. The calculations, which include the Coulomb interaction and are in good agreement with the results of previous measurements at 12.8 and 14.7 MeV, can no longer describe the cross section results at 16.5 MeV. The GDH integrand was found to be about one standard deviation larger than the maximum value predicted by the theories.

nucl-ex↗

arXiv2012

Heavy doped ABA stacked trilayer graphene: triple splitting of its Raman G peak

For the first time, we have observed the obvious triple G peak splitting of ABA stacked trilayer graphene. The G peak splitting can be quantatively understood through the different electron-phonon coupling strength of Ea', Eb' and Ea" modes. In addition, the fluctuation of G peak position at different sample locations can also be understood from the view of the varied interaction strength among graphene layers of TLG, which is induced by nonuniform hole doping at the microscopic level.

cond-mat.mes-hall↗