Charge-changing Reactions Research Articles

A new approach for deducing rms proton radii from charge-changing reactions of neutron-rich nuclei and the reaction-target dependence

We report the charge-changing cross sections (σcc) of 24 p-shell nuclides on both hydrogen and carbon at about 900A MeV, of which 8,9Li, 10–12Be, 10,14,15B, 14,15,17–22N and 16O on hydrogen and 8,9Li on carbon are for the first time. Benefiting from the data set, we found a new and robust relationship between the scaling factor of the Glauber model calculations and the separation energies of the nuclei of interest on both targets. This allows us to deduce proton radii (Rp) for the first time from the cross sections on hydrogen. Nearly identical Rp values are deduced from both target data for the neutron-rich carbon isotopes; however, the Rp from the hydrogen target is systematically smaller in the neutron-rich nitrogen isotopes. This calls for further experimental and theoretical investigations.

High-Energy Lepton Scattering and Nuclear Structure Issues

High-energy lepton scattering constitutes the focus of this study. Developments are provided to motivate the basic choices of kinematic variables for the particular case of semi-inclusive electron scattering where these variables are devised to match well with the underlying dynamics to be expected for the general “nuclear landscape”. Various nuclear structure issues and other issues related to the nature of the electroweak currents at high energies are then discussed, as are some of the issues related to the different conditions occurring for electron scattering versus what is typically the case for charge-changing neutrino reactions.

Neutrino-nucleus scattering in the SuSA model

The super-scaling approach (SuSA) model, based on the analogies between electron and neutrino interactions with nuclei, is reviewed and its application to the description of neutrino-nucleus scattering is presented. The contribution of both one- and two-body relativistic currents is considered. The model is validated with the (e,e') data, including also inelastic contributions for the inclusive reaction. A discussion of semi-inclusive reactions and their implications for charge-changing reactions of neutrinos is also presented. A selection of results for the inclusive neutrino reactions with change of charge is presented where theoretical predictions are compared with cross-section measurements from the main ongoing neutrino oscillation experiments.

Solar wind charge exchange in cometary atmospheres

Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. To understand the role of these reactions in the evolution of the solar wind plasma, and interpret the complex in-situ measurements made by Rosetta, numerical or analytical models are necessary. We use an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyzer (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as charge-changing cross sections of hydrogen and helium particles in a water gas. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms, with fluxes expected to rival those of H+ and He2+ ions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements, and match ROSINA's estimates very well. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop of solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take into account the relative ion dynamics and, to a lesser extent, ignore the formation of bow shock-like structures upstream of the nucleus. This work also shows that the ionization by solar EUV radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

Neutral-current neutrino scattering from the deuteron

Neutral-current neutrino scattering from the deuteron leading to proton-neutron final states is considered using an approach that incorporates relativistic dynamics and consequently provides robust modeling at relatively high energies and momenta. In this work the focus is placed on the fully exclusive reaction where both the proton and neutron in the final state are assumed to be detected. Accordingly, the incident neutrino energy, the neutrino scattering angle and the scattered neutrino's energy can all be reconstructed. It is shown that for specific choices of kinematics the reaction proceeds mainly via scattering from the proton, while for other choices of kinematics it proceeds mainly from the neutron. Specific asymmetries are introduced to focus on these attributes. Measurements in both regions have the potential to yield valuable information on the nucleon's electroweak form factors at momentum transfers up to a (GeV/c)$^2$. In particular, the cross sections are shown to be very sensitive to the isoscalar axial-vector form factor, and sensitive but less so to the magnetic strangeness form factor. Comparisons with other reactions, specifically charge-changing neutrino reactions and both parity-conserving and -violating electron scattering, have the potential to provide new ways to test the Standard Model.

Nuclear theory and event generators for charge-changing neutrino reactions

Semi-inclusive $\mathrm{CC}\ensuremath{\nu}$ cross sections based on factorized cross sections are studied for a selection of spectral function models with the objective of facilitating the choice of models for use as input into event generators. The basic formalism for such cross sections is presented along with an introduction to constructing spectral functions for simple models based on the independent-particle shell model, the relativistic Fermi gas model (RFG), and a local density approximation (LDA) based on the RFG. Spectral functions for these models are shown for $^{16}\mathrm{O}$ along with a more sophisticated model which includes nucleon-nucleon interactions [Alvarez-Ruso et al., Prog. Part. Nucl. Phys. 100, 1 (2018)]. Inclusive and semi-inclusive cross sections are calculated for these models. Although the inclusive cross sections are all of similar size and shape, the semi-inclusive cross sections are substantially different depending upon whether the spectral functions contain some features associated with the nuclear shell model or are based on the RFG and LDA models. Calculations of average values and standard deviations of the initial neutrino energy using the semi-inclusive cross section for the various models are presented and indicate that there may be simple kinematical descriptions of the average neutrino energy which is common to all of these models.

Solar wind charge exchange in cometary atmospheres

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet, mass-loading the solar wind through an effective conversion of fast light solar wind ions into slow heavy cometary ions. Aims. To understand these processes and place them in the context of a solar wind plasma interacting with a neutral atmosphere, numerical or analytical models are necessary. Inputs of these models, such as collision cross sections and chemistry, are crucial. Methods. Book-keeping and fitting of experimentally measured charge-changing and ionization cross sections of hydrogen and helium particles in a water gas are discussed, with emphasis on the low-energy/low-velocity range that is characteristic of solar wind bulk speeds (<20 keV u−1/2000 km s−1). Results. We provide polynomial fits for cross sections of charge-changing and ionization reactions, and list the experimental needs for future studies. To take into account the energy distribution of the solar wind, we calculated Maxwellian-averaged cross sections and fitted them with bivariate polynomials for solar wind temperatures ranging from 105 to 106 K (12–130 eV). Conclusions. Single- and double-electron captures by He2+ dominate at typical solar wind speeds. Correspondingly, single-electron capture by H+ and single-electron loss by H− dominate at these speeds, resulting in the production of energetic neutral atoms (ENAs). Ionization cross sections all peak at energies above 20 keV and are expected to play a moderate role in the total ion production. However, the effect of solar wind Maxwellian temperatures is found to be maximum for cross sections peaking at higher energies, suggesting that local heating at shock structures in cometary and planetary environments may favor processes previously thought to be negligible. This study is the first part in a series of three on charge exchange and ionization processes at comets, with a specific application to comet 67P/Churyumov-Gerasimenko and the Rosetta mission.

Solar wind charge exchange in cometary atmospheres

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet because they mass-load the solar wind through an effective conversion of fast, light solar wind ions into slow, heavy cometary ions. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provided a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of charge-changing reactions in the evolution of the solar wind plasma and to interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary. Methods. An extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines is presented. It is based on a thorough book-keeping of available charge-changing cross sections of hydrogen and helium particles in a water gas. Results. After presenting a general 1D solution of charge exchange at comets, we study the theoretical dependence of charge-state distributions of (He2+, He+, He0) and (H+, H0, H−) on solar wind parameters at comet 67P. We show that double charge exchange for the He2+−H2O system plays an important role below a solar wind bulk speed of 200 km s−1, resulting in the production of He energetic neutral atoms, whereas stripping reactions can in general be neglected. Retrievals of outgassing rates and solar wind upstream fluxes from local Rosetta measurements deep in the coma are discussed. Solar wind ion temperature effects at 400 km s−1 solar wind speed are well contained during the Rosetta mission. Conclusions. As the comet approaches perihelion, the model predicts a sharp decrease of solar wind ion fluxes by almost one order of magnitude at the location of Rosetta, forming in effect a solar wind ion cavity. This study is the second part of a series of three on solar wind charge-exchange and ionization processes at comets, with a specific application to comet 67P and the Rosetta mission.

Solar wind charge exchange in cometary atmospheres

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary. Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas. Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions. Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

Coincidence charged-current neutrino-induced deuteron disintegration for H22O16

Semi-inclusive charge-changing neutrino reactions on targets of heavy water are investigated with the goal of determining the relative contributions to the total cross section of deuterium and oxygen in kinematics chosen to emphasize the former. The study is undertaken for conditions where the typical neutrino beam energies are in the few GeV region, and hence relativistic modeling is essential. For this, the previous relativistic approach for the deuteron is employed, together with a spectral function approach for the case of oxygen. Upon optimizing the kinematics of the final-state particles assumed to be detected (typically a muon and a proton) it is shown that the oxygen contribution to the total cross section is suppressed by roughly an order of magnitude compared with the deuterium cross section, thereby confirming that CC$\nu$ studies of heavy water can effectively yield the cross sections for deuterium, with acceptable backgrounds from oxygen. This opens the possibility of using deuterium to determine the incident neutrino flux distribution, to have it serve as a target for which the nuclear structure issues are minimal, and possibly to use deuterium to provide improved knowledge of specific aspects of hadronic structure, such as to explore the momentum transfer dependence of the isovector axial-vector form factor of the nucleon.

Solar and nuclear physics uncertainties in cosmic-ray propagation

Recent data released by the AMS experiment on the primary spectra and secondary-to-primary ratios in cosmic rays (CRs) can pose tight constraints to astrophysical models of CR acceleration and transport in the Galaxy, thereby providing a robust baseline of the astrophysical background for dark matter search via antimatter. However, models of CR propagation are affected by other important sources of uncertainties, notably from solar modulation and nuclear fragmentation, that cannot be improved with the sole use of the AMS data. The present work is aimed at assessing these uncertainties and their relevance in the interpretation of the new AMS data on the boron-to-carbon (B/C) ratio. Uncertainties from solar modulation are estimated using improved models of CR transport in the Heliosphere constrained against various type of measurements: monthly-resolved CR data collected by balloon-born or space missions, interstellar flux data from the Voyager-1 spacecraft, and counting rates from ground-based neutron monitor detectors. Uncertainties from nuclear fragmentation are estimated using semiempirical cross-section formulae constrained by measurements on isotopically-resolved and charge-changing reactions. We found that a proper data-driven treatment of solar modulation can guarantee the desired level of precision, in comparison with the improved accuracy of the recent data on the B/C ratio. On the other hand, nuclear uncertainties represent a serious limiting factor over a wide energy range. We therefore stress the need for establishing a dedicated program of cross-section measurements at the $\mathcal{O}$(100 GeV) energy scale.

Meson-Exchange Currents and Quasielastic Antineutrino Cross Sections in the Superscaling Approximation

We evaluate quasielastic double-differential antineutrino cross sections obtained in a phenomenological model based on the superscaling behavior of electron scattering data and estimate the contribution of the vector meson-exchange currents in the two-particle-two-hole sector. We show that the impact of meson-exchange currents for charge-changing antineutrino reactions is much larger than in the neutrino case.

Scaling and isospin effects in quasielastic lepton–nucleus scattering in the relativistic mean field approach

The role of isospin in quasielastic electron scattering and charge-changing neutrino reactions is investigated in the relativistic impulse approximation. We analyze proton and neutron scaling functions making use of various theoretical descriptions for the final-state interactions, focusing on the effects introduced by the presence of strong scalar and vector terms in the relativistic mean field approach. An explanation for the differences observed in the scaling functions evaluated from ( e , e ′ ) and ( ν , μ ) reactions is provided by invoking the differences in isoscalar and isovector contributions.

Neutrino-nucleus interactions

Inclusive electron scattering cross-sections in the quasielastic and resonance regions for few GeV electrons are well represented in terms of scaling functions and scaling variables, the so-called superscaling analysis (SuSA). The concepts of scaling of the first and second kinds and superscaling are discussed, as are several mechanisms which are known to yield scaling violations. Given the high quality of scaling for cross-sections at appropriate kinematics, it is shown how the ideas can be turned around to provide predictions for both charge-changing and neutral current neutrino reactions with nuclei at comparable kinematics.

Using electron scattering superscaling to predict charge-changing neutrino cross sections in nuclei

Superscaling analyses of few-GeV inclusive electron scattering from nuclei are extended to include not only quasielastic processes, but also the region where $\ensuremath{\Delta}$ excitation dominates. With reasonable assumptions about the basic nuclear scaling function extracted from data and information from other studies of the relative roles played by correlation and meson-exchange-current effects, it is shown that the residual strength in the resonance region can be accounted for through an extended scaling analysis. One observes scaling upon assuming that the elementary cross section by which one divides the residual to obtain a new scaling function is dominated by the $N\ensuremath{\rightarrow}\ensuremath{\Delta}$ transition and employing a new scaling variable suited to the resonance region. This yields a good representation of the electromagnetic response in both the quasielastic and $\ensuremath{\Delta}$ regions. The scaling approach is then inverted and predictions are made for charge-changing neutrino reactions at energies of a few GeV, with focus placed on nuclei that are relevant to neutrino oscillation measurements. For this, a relativistic treatment of the required weak interaction vector and axial-vector currents for both quasielastic and $\ensuremath{\Delta}$-excitation processes is presented.

Particle acceleration through multiple conversions from a charged into a neutral state and back

We propose a new means for a quick and efficient acceleration of protons and/or electrons in relativistic bulk flows. The maximum attainable particle energies are limited either by radiative losses or by the condition of confinement in the magnetic field. The new mechanism takes advantage of a conversion of particles from the charged state (protons, electrons or positrons) into a neutral state (neutrons or photons) and back. In most cases, the conversion is photon induced and requires the presence of intense radiation fields, but under special circumstances the converter acceleration mechanism may operate via other charge-changing reactions, for example, inelastic nucleon-nucleon collisions. As in the traditional, ``stochastic'' (or diffusive) acceleration models, the acceleration cycle in the proposed scenario consists of the escape of particles from the relativistic flow followed by their return back after deflection from the ambient magnetic field. The difference is that the charge-changing reactions, which occur during the cycle, allow accelerated particles to increase their energies in each cycle by a factor much larger than 2 and usually roughly equal to the bulk Lorentz factor squared. The emerging spectra of accelerated particles can be very hard and their maximum energy in some cases is larger than in the standard mechanism. This significantly reduces the required energy budget of the sources of the highest-energy particles observed in cosmic rays. The proposed acceleration mechanism has a distinctive feature---it unavoidably creates neutral beams, consisting of photons, neutrinos, or neutrons, whose beam pattern may be much broader than the inverse Lorentz factor of the relativistic flow. Also, the new mechanism may serve as an efficient means of transferring the energy of bulk motion to gamma radiation and, if the accelerated particles are nucleons, inevitably produces high-energy neutrinos at a relative efficiency approaching $\ensuremath{\gtrsim}50%.$

Charge state studies of low energy heavy ions passing through hydrogen and helium gas

Studies of the charge state distribution of low energy (<1.5 MeV/u), low Z (<13) heavy ions passing through hydrogen and helium gas of varying target pressure have been performed using separate windowless gas target systems at TRIUMF and the University of Naples. Semi-empirical relationships have been deduced to estimate the equilibrium charge state distributions as a function of beam energy. From these distributions, cross-sections for the relevant charge changing reactions have been deduced.

Charge permutation reactions in beam type mass spectrometers

This is a review of the gas-phase reactions, in beam type mass spectrometers, that change the charge states of ions. The Cooks research group has been a leader in both the understanding and use of these charge-changing reactions. The charge of ions can be manipulated in beam type instruments via collisions with neutral gas atoms or molecules in the high ion kinetic energy regime. The two major processes, charge inversion and charge stripping due to high energy ion/neutral collisions, are discussed. Charge permutation reactions often result in the formation of unique ion structures that aid in the differentiation of isomers. The products of charge permutation reactions may possess excess internal energy that cause the ions to fragment, and these fragment ions may provide complementary information to that obtained from high energy collision-induced dissociation. The charge of ions also can be changed as a result of a collision with a surface in the low ion kinetic energy regime. Charge exchange and charge inversion processes that occur as a result of low energy ion/surface collisions are presented.

Introduction to special section: Proton precipitation into the atmosphere

Energetic protons, precipitating into the atmosphere, interact with the ambient neutrals, leading to excitation, ionization, elastic scattering, and, for MeV protons, dissociation. In addition, a proton can capture an electron, producing an energetic H atom, which has enough energy to interact, in turn, with the ambient neutrals. This H atom can also get stripped of its electron, becoming a proton again. Because of these charge‐changing reactions, the incident proton beam penetrating the atmosphere becomes a mixture of protons and H atoms [see, e.g., Rets, 1989].

Charge-changing nuclear reactions of relativistic light-ion beams (5 ≤ Z ≤ 10) passing through thick absorbers

Light-ion beams of 20Ne, 19Ne, 18F, 16O, 15O, 14N, 12C and 10B in the energy range between 200 and 670 MeV/u were fragmented in thick targets of water, carbon, lucite, polyethylene, and aluminum. The nuclear charge composition of the fragmented beam was measured via energy loss in a large-area ionisation chamber. Using a water absorber of variable thickness up to 25 cm the elemental fragment yields were measured down to Z = 5. Their build-up and decay characteristics are described by a system of differential equations. From an analysis of the depth distributions of the surviving projectiles and the lower- Z projectile fragments, both total and partial charge-changing cross sections were obtained.