arXiv subjects

C. Weiss

Publications and source records attributed to C. Weiss.

At least 19 recordsLinked to original sources

arXiv2026

Exploring chiral dynamics with low-energy electron- and positron-nucleon scattering

Low-energy lepton-nucleon scattering probes various expressions of the long-distance dynamics in the baryon sector of QCD, governed by chiral symmetry breaking and the $\Delta$ resonance. We discuss some specific studies that could be performed with combined electron- and positron-nucleon scattering at lab energies $E_{e\pm} \lesssim$ 500 MeV. They include: (a) chiral dynamics in the low-$Q^2$ nucleon elastic form factors (peripheral charge and current densities); (b) two-photon exchange effects in the target normal single-spin asymmetry and beam charge asymmetry in elastic and inclusive scattering ($\Delta$ excitation); (c) nucleon generalized polarizabilities in virtual Compton scattering with beam charge asymmetry measurements.

hep-ph↗

arXiv2026

Semi-inclusive deep-inelastic scattering on a polarized spin-1 target. I. Cross section and spin observables

We develop the theoretical framework for semi-inclusive deep-inelastic scattering on a polarized spin-1 target and apply it to scattering on the polarized deuteron with spectator nucleon tagging. In Part I (this article) we present the general form of the semi-inclusive cross section and polarization observables for the spin-1 target. A relativistically covariant formulation in terms of 4-vectors and invariant polarization parameters is employed. The target polarization is described by a spin density matrix with vector and tensor polarization. The spin and azimuthal angle dependence of the semi-inclusive cross section is derived and parametrized in terms of invariant structure functions. To validate the result, the structure functions are expressed as photon-target helicity amplitudes with known symmetry properties. The expressions presented here are kinematic (no assumptions about particle production dynamics) and valid in all regions of the deep-inelastic final state (current and target fragmentation regions). In Part II (following article), we consider deep-inelastic scattering on the polarized deuteron with spectator nucleon tagging as a special case of target fragmentation. The semi-inclusive structure functions are computed by separating nuclear and hadronic structure, and the polarization observables are explored as functions of the tagged nucleon momentum.

hep-ph↗

arXiv2026

Semi-inclusive deep-inelastic scattering on a polarized spin-1 target. II. Deuteron and spectator nucleon tagging

We develop the theoretical framework for semi-inclusive deep-inelastic scattering on a polarized spin-1 target and apply it to scattering on the polarized deuteron with spectator nucleon tagging. In Part I (previous article) we present the general form of the semi-inclusive cross section and polarization observables for the spin-1 target. In Part II (this article) we consider deep-inelastic scattering on the polarized deuteron with spectator nucleon tagging as a special case of target fragmentation. Methods of light-front quantization are employed to separate nuclear and hadronic structure in the high-energy process and achieve a composite description. The light-front wave function of the polarized deuteron is obtained from a rotationally covariant 3-dimensional wave function in the center-of-mass frame of the proton-neutron system. The tagged structure functions are computed in the impulse approximation. The momentum and spin distribution of the active nucleon are controlled by the deuteron polarization and the detected spectator momentum ($D/S$ wave ratio). The cross section and spin asymmetries are evaluated for general deuteron polarization (vector and tensor, longitudinal and transverse) as functions of the spectator momentum. Tensor-polarized spin asymmetries of order unity are achieved for spectator momenta $\sim$ 300 MeV, which select configurations with large $D$-wave. Sum rules for the tagged spin structure functions are derived. The results can be used for simulations of spectator tagging in future polarized fixed-target experiments (Jefferson Lab) or at the Electron-Ion Collider.

hep-ph↗

arXiv2025

Single-event neutron time-of-flight spectroscopy with a petawatt-laser-driven neutron source

Fast neutron-induced nuclear reactions are crucial for advancing our understanding of fundamental nuclear processes, stellar nucleosynthesis, and applications, including reactor safety, medical isotope production, and materials research. With many research reactors being phased out, compact accelerator-based neutron sources are becoming increasingly important. Laser-driven neutron sources (LDNSs) offer unique advantages -- ultrashort neutron pulsees for superior energy resolution, high per-pulse flux, and a drastically reduced footprint. However, their use in single-event fast neutron spectroscopy remains unproven, requiring stable multi-shot operation and detectors capable of functioning in the extreme environment of petawatt-class laser-plasma interactions. Here, we present a proof-of-concept experiment at the DRACO~PW laser in a pitcher-catcher configuration, stably producing 6-7e7 neutrons/shot with energies above 1 MeV, over more than 200 shots delivered at a shot-per-minute rate. Neutron time-of-flight measurements were performed using a single-crystal diamond detector, which is located only 1.5 m away from the source and capable of resolving individual neutron-induced reactions. Observed reaction rates are consistent with Monte Carlo simulations inferred by real-time diagnostics of accompanying gamma, ion, and electron fluxes. With the recent advances in repetition rate, targetry, and ion acceleration efficiency, this work establishes LDNSs as a promising, scalable platform for future fast neutron-induced reaction studies, particularly for measurements involving short-lived isotopes or requiring high instantaneous neutron flux.

nucl-ex↗

arXiv2023

Proton charge radius extraction from muon scattering at MUSE using dispersively improved chiral effective field theory

The MUSE experiment at Paul Scherrer Institute will perform the first measurement of low-energy muon-proton elastic scattering (muon lab momenta 115-210 MeV) with the aim of determining the proton charge radius. We study the prospects for the proton radius extraction using the theoretical framework of Dispersively Improved Chiral Effective Field Theory (DI$\chi$EFT). It connects the proton radii with the finite-$Q^2$ behavior of the form factors through complex analyticity and enables the use of data up to $Q^2 \sim$ 0.1 GeV$^2$ for radius extraction. We quantify the sensitivity of the $\mu p$ cross section to the proton charge radius, the theoretical uncertainty of the cross section predictions, and the size of two-photon exchange corrections. We find that the optimal kinematics for radius extraction at MUSE is at momenta 210 MeV and $Q^2 \sim$ 0.05-0.08 GeV$^2$. We compare the performance of electron and muon scattering in the same kinematics. As a byproduct, we obtain explicit predictions for the $\mu p$ and $ep$ cross sections at MUSE as functions of the assumed value of the proton radius.

hep-ph↗

arXiv2022

Target normal single-spin asymmetry in inclusive electron-nucleon scattering with two-photon exchange: Analysis using $1/N_c$ expansion

We calculate the target normal single-spin asymmetry caused by two-photon exchange in inclusive electron-nucleon scattering in the resonance region. Our analysis uses the $1/N_c$ expansion of low-energy QCD and combines $N$ and $\Delta$ intermediate and final states using the contracted $SU(4)$ spin-flavor symmetry. The normal spin asymmetry obtained in leading-order accuracy in $1/N_c$ has magnitude $\sim 10^{-2}$ and different sign in $ep$ and $en$ scattering. It can be measured in electron scattering at lab energies $\sim$ 0.5-1.5 GeV and provides a clean probe of two-photon exchange dynamics.

hep-ph↗

arXiv2022

Transverse charge and current densities in the nucleon from dispersively improved chiral effective field theory

Background: The transverse densities $\rho_{1, 2}(b)$ describe the distributions of electric charge and magnetic moment at fixed light-front time and connect the nucleon's elastic form factors with its partonic structure. The dispersive representation of the form factors $F_{1, 2}(t)$ expresses the densities in terms of exchanges of hadronic states in the $t$-channel and permits their analysis using hadronic physics methods. Purpose: Compute the densities at peripheral distances $b = \mathcal{O}(M_\pi^{-1})$, where they are generated predominantly by the two-pion states in the dispersive representation. Quantify the uncertainties. Methods: Dispersively improved chiral effective field theory (DI$\chi$EFT) is used to calculate the isovector spectral functions $\textrm{Im}\, F_{1, 2}(t)$ on the two-pion cut. The method includes $\pi\pi$ interactions ($\rho$ resonance) through elastic unitarity and provides realistic spectral functions up to $t \approx$ 1 GeV$^2$. Higher-mass states are parametrized by effective poles and constrained by sum rules (charges, radii, superconvergence relations). The densities $\rho_{1, 2}(b)$ are obtained from their dispersive representation. Uncertainties are quantified by varying the spectral functions. The method respects analyticity and ensures the correct $b \rightarrow \infty$ asymptotic behavior of the densities. Results: Accurate densities are obtained at all distances $b \gtrsim 0.5$ fm, with correct behavior down to $b \rightarrow 0$. The region of distances is quantified where transverse nucleon structure is governed by the two-pion state. The light-front current distributions in the polarized nucleon are computed and discussed. Conclusions: Peripheral nucleon structure can be computed from first principles using DI$\chi$EFT. The method can be extended to generalized parton distributions and other nucleon form factors.

hep-ph↗

arXiv2021

Progress and Opportunities in Backward angle (u-channel) Physics

Backward angle (u-channel) scattering provides complementary information for studies of hadron spectroscopy and structure, but has been less comprehensively studied than the corresponding forward angle case. As a result, the physics of u-channel scattering poses a range of new experimental and theoretical opportunities and questions. We summarize recent progress in measuring and understanding high energy reactions with baryon charge exchange in the u-channel, as discussed in the first backward angle (u-channel) Physics Workshop. In particular, we discuss backward angle measurements and their theoretical description via both hadronic models and the collinear factorization approach, and discuss planned future measurements of u-channel physics. Finally, we propose outstanding questions and challenges for u-channel physics.

hep-ph↗

arXiv2021

Design concept for the second interaction region for Electron-Ion Collider

The possibility of two interaction regions (IRs) is a design requirement for the Electron Ion Collider (the EIC). There is also a significant interest from the nuclear physics community in a 2nd IR with measurements capabilities complementary to those of the first IR. While the 2nd IR will be in operation over the entire energy range of ~20GeV to ~140GeV center of mass (CM). The 2nd IR can also provide an acceptance coverage complementary to that of the first. We present a brief overview and the current progress of the 2nd IR design in terms of the parameters, magnet layout, and beam dynamics.

physics.acc-ph↗

arXiv2021

Nucleon matrix element of Weinberg's CP-odd gluon operator from the instanton vacuum

We calculate the nucleon matrix element of Weinberg's dimension-6 CP-odd gluon operator $f^{abc} (\tilde F_{\mu\nu})^a (F^{\mu\rho})^b (F^{\nu}_{\;\;\rho})^c$ in the instanton vacuum. In leading order of the instanton packing fraction, the dimension-6 operator is effectively proportional to the topological charge density $(\tilde F_{\mu\nu})^a (F^{\mu\nu})^a$, whose nucleon matrix element is given by the flavor-singlet axial charge and constrained by the $U(1)_A$ anomaly. The nucleon matrix element of the dimension-6 operator is obtained substantially larger than in other estimates, because of the strong localization of the nonperturbative gluon fields in the instanton vacuum. We argue that the neutron electric dipole moment induced by the dimension-6 operator is nevertheless of conventional size.

hep-ph↗

arXiv2020

Polarized electron-deuteron deep-inelastic scattering with spectator nucleon tagging

Background: DIS on the polarized deuteron with detection of a proton in the nuclear breakup region (spectator tagging) represents a unique method for extracting the neutron spin structure functions and studying nuclear modifications. The tagged proton momentum controls the nuclear configuration during the DIS process and enables a differential analysis of nuclear effects. Such measurements could be performed with the future electron-ion collider (EIC) and forward proton detectors if deuteron beam polarization could be achieved. Purpose: Develop theoretical framework for polarized deuteron DIS with spectator tagging. Formulate procedures for neutron spin structure extraction. Methods: A covariant spin density matrix formalism is used to describe general deuteron polarization in collider experiments (vector/tensor, pure/mixed). Light-front (LF) quantum mechanics is employed to factorize nuclear and nucleonic structure in the DIS process. A 4-dimensional representation of LF spin structure is used to construct the polarized deuteron LF wave function and efficiently evaluate the spin sums. Free neutron structure is extracted using the impulse approximation and analyticity in the tagged proton momentum (pole extrapolation). Results: General expressions of the polarized tagged DIS observables in collider experiments. Analytic and numerical study of the polarized deuteron LF spectral function and nucleon momentum distributions. Practical procedures for neutron spin structure extraction from the tagged deuteron spin asymmetries. Conclusions: Spectator tagging provides new tools for precise neutron spin structure measurements. D-wave depolarization and nuclear binding effects can be eliminated through the tagged proton momentum dependence. The methods can be extended to tensor-polarized observables, spin-orbit effects, and diffractive processes.

hep-ph↗

arXiv2020

Structural and optical properties of silicon nanocrystals embedded in silicon carbide

The outstanding demonstration of quantum confinement in Si nanocrystals (Si NC) in a SiC matrix requires the fabrication of Si NC with a narrow size distribution. It is understood without controversy that this fabrication is a difficult exercise and that a multilayer (ML) structure is suitable for such fabrication only in a narrow parameter range. This parameter range is sought by varying both the stoichiometric SiC barrier thickness and the Si-rich SiC well thickness between 3 and 9 nm and comparing them to single layers (SL). The samples processed for this investigation were deposited by plasma-enhanced chemical vapor deposition (PECVD) and subsequently subjected to thermal annealing at 1000-1100${\deg}$C for crystal formation. Bulk information about the entire sample area and depth were obtained by structural and optical characterization methods: information about the mean Si NC size was determined from grazing incidence X-ray diffraction (GIXRD) measurements. Fourier-transform infrared spectroscopy (FTIR) was applied to gain insight into the structure of the Si-C network, and spectrophotometry measurements were performed to investigate the absorption coefficient and to estimate the bandgap $E_{04}$. All measurements showed that the influence of the ML structure on the Si NC size, on the Si-C network and on the absorption properties is subordinate to the influence of the overall Si content in the samples, which we identified as the key parameter for the structural and optical properties. We attribute this behavior to interdiffusion of the barrier and well layers. Because the produced Si NC are within the target size range of 2-4 nm for all layer thickness variations, we propose to use the Si content to adjust the Si NC size in future experiments.

physics.app-ph↗

arXiv2020

Electron and proton irradiation effect on the minority carrier lifetime in SiC passivated p-doped Ge wafers for space photovoltaics

We report on the effect of electron and proton irradiation on effective minority carrier lifetimes (${\tau}_{eff}$) in p-type Ge wafers. Minority carrier lifetimes are assessed using the microwave-detected photoconductance decay (${\mu}$W-PCD) method. We examine the dependence of ${\tau}_{eff}$ on the p-type doping level and on electron and proton radiation fluences at 1 MeV. The measured ${\tau}_{eff}$ before and after irradiation are used to estimate the minority carriers diffusion lengths, which is an important parameter for solar cell operation. We observe ${\tau}_{eff}$ ranging from 50 to 230 ${\mu}$s for Ge doping levels between 1E17 and 1E16 at.cm$^{-3}$, corresponding to diffusion lengths of 500-1400 ${\mu}$m. A separation of ${\tau}_{eff}$ in Ge bulk lifetime and surface recombination velocity is conducted by irradiating Ge lifetime samples of different thicknesses. The possible radiation-induced defects are discussed on the basis of literature.

physics.app-ph↗

arXiv2020

Formation of silicon nanocrystals in silicon carbide using flash lamp annealing

During the formation of Si nanocrystals (Si NC) in Si$_x$C$_{1-x}$ layers via solid-phase crystallization, the unintended formation of nanocrystalline SiC reduces the minority carrier lifetime and therefore the performance of Si$_x$C$_{1-x}$ as an absorber layer in solar cells. A significant reduction in the annealing time may suppress the crystallization of the SiC matrix while maintaining the formation of Si NC. In this study, we investigated the crystallization of stoichiometric SiC and Si-rich SiC using conventional rapid thermal annealing (RTA) and nonequilibrium millisecond range flash lamp annealing (FLA). The investigated Si$_x$C$_{1-x}$ films were prepared by plasma-enhanced chemical vapor deposition and annealed at temperatures from 700${\deg}$C to 1100${\deg}$C for RTA and at flash energies between 34 J/cm$^2$ and 62 J/cm$^2$ for FLA. GIXRD and FTIR were conducted to investigate hydrogen effusion, Si and SiC NC growth, and SiC crystallinity. Both the Si content and the choice of the annealing process affect the crystallization behavior. It is shown that under certain conditions, FLA can be successfully utilized for the formation of Si NC in a SiC matrix, which closely resembles Si NC in a SiC matrix achieved by RTA. The samples must have excess Si, and the flash energy should not exceed 40 J/cm$^2$ and 47 J/cm$^2$ for Si$_{0.63}$C$_{0.37}$ and Si$_{0.77}$C$_{0.23}$ samples, respectively. Under these conditions, FLA succeeds in producing Si NC of a given size in less crystalline SiC than RTA does. This result is discussed in terms of nucleation and crystal growth using classical crystallization theory. For FLA and RTA samples, an opposite relationship between NC size and Si content was observed and attributed either to the dependence of H effusion on Si content or to the optical absorption properties of the materials, which also depend on the Si content.

physics.app-ph↗

arXiv2020

Precise determination of proton magnetic radius from electron scattering data

We extract the proton magnetic radius from the high-precision electron-proton elastic scattering cross section data. Our theoretical framework combines dispersion analysis and chiral effective field theory and implements the dynamics governing the shape of the low-$Q^2$ form factors. It allows us to use data up to $Q^2\sim$ 0.5 GeV$^2$ for constraining the radii and overcomes the difficulties of empirical fits and $Q^2 \rightarrow 0$ extrapolation. We obtain a magnetic radius $r_M^p$ = 0.850 $\pm$0.001 (fit 68%) $\pm$0.010 (theory full range) fm, significantly different from earlier results obtained from the same data, and close to the extracted electric radius $r_E^p$ = 0.842 $\pm$0.002 (fit) $\pm$0.010 (theory) fm.

hep-ph↗

arXiv2019

Neutron spin structure from polarized deuteron DIS with proton tagging

Polarized electron-deuteron deep-inelastic scattering (DIS) with detection of the spectator proton ("tagged DIS") enables measurements of neutron spin structure with maximal control of nuclear effects. We calculate the longitudinal spin asymmetries in polarized tagged DIS using methods of light-front nuclear structure and study their dependence on the measured proton momentum. Asymmetries can be formed with all three deuteron spin states ($\pm 1, 0$) or the two maximum-spin states only ($\pm 1$, involving tensor polarization). The proton momentum dependence can be used to select pure S-wave configurations in the deuteron and eliminate D-wave depolarization (transverse momenta $p_{pT} \lesssim$ 100 MeV). Free neutron spin structure can be extracted model-independently through pole extrapolation of the tagged asymmetries. Such measurements could be performed at a future electron-ion collider (EIC) with polarized deuteron beams and forward proton detectors.

hep-ph↗

arXiv2019

Longitudinal spin asymmetries in polarized deuteron DIS with spectator tagging

Polarized electron-deuteron DIS with spectator proton tagging offers a way of measuring the neutron spin structure functions with maximal theoretical control of nuclear effects. We calculate the nuclear structure factors in the longitudinal double-spin asymmetries using methods of light-front nuclear structure. A unique feature of the spin-1 system is that spin asymmetries can be formed either relative to the cross section in all three spin states ($\lambda_d = \pm 1, 0$) or in the two maximum-spin states only ($\pm 1$, involving tensor polarization). We find that the two-state deuteron spin asymmetry at small spectator proton momenta permits accurate extraction of the neutron structure function $g_{1n}$. Such measurements could be performed at a future electron-ion collider (EIC) with polarized deuteron beams and suitable forward detectors.

hep-ph↗

arXiv2018

Proton charge radius extraction from electron scattering data using dispersively improved chiral effective field theory

We extract the proton charge radius from the elastic form factor (FF) data using a novel theoretical framework combining chiral effective field theory and dispersion analysis. Complex analyticity in the momentum transfer correlates the behavior of the spacelike FF at finite $Q^2$ with the derivative at $Q^2 = 0$. The FF calculated in the predictive theory contains the radius as a free parameter. We determine its value by comparing the predictions with a descriptive global fit of the spacelike FF data, taking into account the theoretical and experimental uncertainties. Our method allows us to use the finite-$Q^2$ FF data for constraining the radius (up to $Q^2\sim$ 0.5 GeV$^2$ and larger) and avoids the difficulties arising in methods relying on the $Q^2 \rightarrow 0$ extrapolation. We obtain a radius of 0.844(7) fm, consistent with the high-precision muonic hydrogen results.

hep-ph↗