Proton Knockout Research Articles

Final-state interactions in neutrino-induced proton knockout from argon in MicroBooNE

Final-state interactions in neutrino-induced proton knockout from argon in MicroBooNE

Response of commercial Si-IGBT to neutrons and direction dependency

Silicon-insulated gate bipolar transistors (Si-IGBTs) are widely used for power control. In this study, we measured the energy deposited inside a commercial device with neutrons irradiation from 252Cf. We irradiated the device from the sealing and heat sink sides to evaluate the directional characteristics. A radiation simulation analysis was performed to understand the measurement results. The experiment and simulation showed that energy deposition in the device occurs through elastic scattering of neutrons and nuclear reactions. In particular, protons were generated by elastic scattering in the sealing material when the device was irradiated from the sealing side. Thus, the effect of neutrons on commercial Si-IGBTs is due to not only reactions inside the device but also secondary particles from the sealing material. When irradiated with high-energy neutrons, the knocked-out protons from sealing possibly cause single-event burnout (SEB). Therefore, the probability of SEB may depend on the direction of neutron incidence.

Mass, Spectroscopy, and Two-Neutron Decay of ^{16}Be.

The structure and decay of the most neutron-rich beryllium isotope, ^{16}Be, has been investigated following proton knockout from a high-energy ^{17}B beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5)MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15)MeV, respectively. These were assigned to be the ground (J^{π}=0^{+}) and first excited (2^{+}) state, with E_{x}=1.31(6) MeV. The mass excess of ^{16}Be was thus deduced to be 56.93(13)MeV, some 0.5MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2^{+} level presents a far more diffuse neutron-neutron distribution.

Diverse mechanisms in proton knockout reactions from the Borromean nucleus ^{17}text {Ne}

Nucleon knockout experiments using beryllium or carbon targets reveal a strong dependence of the quenching factors, i.e., the ratio (hbox {R}_{textrm{s}}) of theoretical to the experimental spectroscopic factors (hbox {C}^2{textrm{S}}), on the proton-neutron asymmetry in the nucleus under study. However, this dependence is greatly reduced when a hydrogen target is used. To understand this phenomenon, exclusive ^{1}text {H}(^{17}text {Ne},2hbox {p}~^{16}text {F}) and inclusive ^{12}text {C}(^{17}text {Ne},2hbox {p}~^{16}text {F})hbox {X}, ^{12}text {C}(^{17}text {Ne},^{16}text {F})hbox {X} as well as ^{1}text {H}(^{17}text {Ne},^{16}text {F})hbox {X} (X-denotes undetected reaction products) reactions with ^{16}text {F} in the ground and excited states were analysed. The longitudinal momentum distribution of ^{16}{textrm{F}} and the correlations between the detached protons were studied. In the case of the carbon target, there is a significant deviation from the predictions of the eikonal model. The eikonal approximation was used to extract spectroscopic factor values hbox {C}^2{textrm{S}}. The experimental hbox {C}^2hbox {S} value obtained with C target is markedly lower than that for H target. This is interpreted as rescattering due to simultaneous nucleon knockout from both reaction partners, ^{17}text {Ne} and ^{12}text {C}.

Effective polarization in proton-induced α knockout reactions

The effective polarization of the residual nucleus in the proton-induced $\alpha$ knockout reaction is investigated within the distorted wave impulse approximation framework. The strong absorption of the emitted $\alpha$ particle results in strong selectivity on the reaction "position" depending on the third component of the single-particle orbital angular momentum of the $\alpha$ particle inside a nucleus, hence on the spin direction of the reaction residue. This is caused by a mechanism that is similar to the Maris effect, the effective polarization in the proton-induced proton knockout reactions. However, as a distinct feature of the effective polarization in the $\alpha$ knockout process, the spin degrees of freedom of the reacting particles play no role. The $\alpha$ knockout process with complete kinematics can be a useful polarization technique for the residual nucleus, without actively controlling the spin of the proton.

Investigation of Single Proton Knockout from 26P Nucleus on 9Be Target at 65 MeV/n Beam Energy

Investigation of Single Proton Knockout from 26P Nucleus on 9Be Target at 65 MeV/n Beam Energy

Color coherence effects in the reaction H2(p,2p)n

The hard proton knock-out by the proton from the deuteron at relativistic energies is considered with a focus on the color transparency (CT) effect which influences the initial- and final-state interactions. The calculations are performed in the framework of the generalized eikonal approximation supplemented by the quantum diffusion model of CT. The main results of the previous calculations [Frankfurt et al., Phys. Rev. C 56, 2752 (1997)] at the beam momentum below 20 $\mathrm{GeV}/\mathrm{c}$ are confirmed, including the dependence of the nuclear transparency on the transverse momentum of the spectator neutron, ${p}_{st}$, and on the relative azimuthal angle $\ensuremath{\phi}$ between proton and neutron: absorption at ${p}_{st}<0.2\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\mathrm{c}$ and enhancement at ${p}_{st}>0.3\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\mathrm{c}$ due to rescattering on the neutron, the change of $\ensuremath{\phi}$ dependence between these two regions, and the enhancement of CT effects with ${p}_{\mathrm{lab}}$. The study is then generalized to higher beam momenta, up to 75 $\mathrm{GeV}/\mathrm{c}$. It is shown that such behavior of the transparency is mainly preserved up to ${p}_{\mathrm{lab}}\ensuremath{\simeq}50\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\mathrm{c}$, but changes significantly at higher beam momenta due to the interference of valence quark configurations of small and large sizes. As a result, the transparency at small ${p}_{st}$ exhibits oscillations as a function of the beam momentum (the nuclear filtering effect). The tensor analyzing power due to the longitudinal polarization of the deuteron is calculated. The event rate at Nuclotron-based Ion Collider fAcility (NICA) is estimated.

Study of final-state interactions of protons in neutrino-nucleus scattering with INCL and NuWro cascade models

The modeling of neutrino-nucleus interactions constitutes a challenging source of systematic uncertainty for the extraction of precise values of neutrino oscillation parameters in long-baseline accelerator neutrino experiments. To improve such modeling and minimize the corresponding uncertainties, a new generation of detectors is being developed, which aim to measure the complete final state of particles resulting from neutrino interactions. In order to fully benefit from the improved detector capabilities, precise simulations of the nuclear effects on the final-state nucleons are needed. This article presents the study of the in-medium propagation of knocked-out protons, i.e., final-state interactions (FSI), comparing the NuWro and INCL cascade models. The INCL model is used here for the first time to predict exclusive final states in measured neutrino interaction cross sections. This study of INCL in the framework of neutrino interactions features various novelties, including the production of nuclear clusters (e.g., deuterons, $\ensuremath{\alpha}$ particles) in the final state. The paper includes a complete characterization of the final state after FSI, comparisons to available measurements of single transverse variables, and an assessment of the observability of nuclear clusters.

Measurements of the electron-helicity asymmetry in the quasi-elastic [formula omitted] process

We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from 2H and 12C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle ϕpq, with a polar angle θpq coverage up to about 8°. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual 11B system. We find that the helicity asymmetry for p-shell knockout from 12C depends on the final state of the residual system and is relatively large (up to ≈0.16), especially at low missing momentum. It is considerably smaller (up to ≈0.01) for s-shell knockout from both 12C and 2H. The data for 2H are in very good agreement with theoretical calculations, while the predictions for 12C exhibit differences with respect to the data.

Extracting Hypernuclear Properties from the (e, e′K+) Cross Section

Experimental studies of hypernuclear dynamics, besides being essential for the understanding of strong interactions in the strange sector, have important astrophysical implications. The observation of neutron stars with masses exceeding two solar masses poses a serious challenge to the models of hyperon dynamics in dense nuclear matter, many of which predict a maximum mass incompatible with the data. In this paper, it is argued that valuable new insight can be gained from the forthcoming extension of the experimental studies of kaon electro production from nuclei to include the 208Pb(e,e′K+)Λ208Tl process. A comprehensive framework for the description of kaon electro production, based on factorization of the nuclear cross section and the formalism of the nuclear many-body theory, is outlined. This approach highlights the connection between the kaon production and proton knockout reactions, which will allow us to exploit the available 208Pb(e,e′p)207Tl data to achieve a largely model-independent analysis of the measured cross section.

Proton Knockout of Nucleon Clusters with Allowance for Excited States of the Fragments

Proton Knockout of Nucleon Clusters with Allowance for Excited States of the Fragments

How Different is the Core of ^{25}F from ^{24}O_{g.s.} ?

The structure of a neutron-rich ^{25}F nucleus is investigated by a quasifree (p,2p) knockout reaction at 270A MeV in inverse kinematics. The sum of spectroscopic factors of π0d_{5/2} orbital is found to be 1.0±0.3. However, the spectroscopic factor with residual ^{24}O nucleus being in the ground state is found to be only 0.36±0.13, while those in the excited state is 0.65±0.25. The result shows that the ^{24}O core of ^{25}F nucleus significantly differs from a free ^{24}O nucleus, and the core consists of ∼35% ^{24}O_{g.s.}. and ∼65% excited ^{24}O. The result may infer that the addition of the 0d_{5/2} proton considerably changes neutron structure in ^{25}F from that in ^{24}O, which could be a possible mechanism responsible for the oxygen dripline anomaly.

Rescattering effects in antiproton-induced exclusive J/$ \psi$ and $ \psi^{{\prime}}_{}$ production on the deuteron

On the basis of the generalized eikonal approximation we study the exclusive reactions $\bar p d \to J/\psi\, n$ and $\bar p d \to \psi^\prime\, n$ in vicinity of the thresholds for charmonium production on a free proton target. It is shown that the rescattering of the incoming antiproton and outgoing charmonium on the spectator neutron leads to a depletion of the charmonium production at low- and to an enhancement at high transverse momenta. This is in qualitative agreement with previous studies of hard proton knockout in proton-deuteron collisions. We analyze different physical sources of uncertainty which may influence the extraction of the total charmonium-neutron cross section. The color transparency effect for the incoming $\bar p$ largely compensates the influence of charmonium rescattering both at low and high transverse momenta. Different choices of the deuteron wave function lead to significant uncertainties at high transverse momenta. As an outcome of the calculations of charmonium production, we also provide predictions on the production of open charm hadrons due to the dissociation of the charmonium on the neutron. It is shown that the open charm production cross section is proportional to the total charmonium-nucleon cross section and quite stable with respect to the variation of other parameters of the model. We thus suggest that open charm channels are most suited for future studies of charmonium-nucleon interactions at PANDA with a deuteron target.

Quasi-free proton knockout from 12C on carbon target at 398 MeV/u

The proton-removal mechanism of the 12C→11B reaction induced on a carbon target via elementary nucleon-nucleon scattering is investigated in exclusive triple-coincidence measurements. The observed two-nucleon angular correlations are found to be consistent with quasi-free scattering of a projectile-like proton off a target-like nucleon. Exclusive cross sections for one-step pp and pn interactions are determined as σpp=17.2(12) mb and σpn=18.2(18), respectively. The extracted quasi-free component amounts up to 58(4)% of the total proton-removal cross section. The results are compared to total proton-removal cross sections obtained from the experiment and eikonal reaction theory.

Quasi-free neutron and proton knockout reactions from light nuclei in a wide neutron-to-proton asymmetry range

The quasi-free scattering reactions 11C(p,2p) and 10,11,12C(p,pn) have been studied in inverse kinematics at beam energies of 300–400 MeV/u at the R3B-LAND setup. The outgoing proton-proton and proton-neutron pairs were detected in coincidence with the reaction fragments in kinematically complete measurements. The efficiency to detect these pairs has been obtained from GEANT4 simulations which were tested using the 12C(p,2p) and 12C(p,pn) reactions. Experimental cross sections and momentum distributions have been obtained and compared to DWIA calculations based on eikonal theory. The new results reported here are combined with previously published cross sections for quasi-free scattering from oxygen and nitrogen isotopes and together they enable a systematic study of the reduction of single-particle strength compared to predictions of the shell model over a wide neutron-to-proton asymmetry range. The combined reduction factors show a weak or no dependence on isospin asymmetry, in contrast to the strong dependency reported in nucleon-removal reactions induced by nuclear targets at lower energies. However, the reduction factors for (p,2p) are found to be 'significantly smaller than for (p,pn) reactions for all investigated nuclei.

Energy and momentum dependence of nuclear short-range correlations - Spectral function, exclusive scattering experiments and the contact formalism

Results of electron-induced one- and two-nucleon hard knockout reactions, A(e,e′p) and A(e,e′pN), in kinematics sensitive to nuclear short-range correlations, are studied using the nuclear contact formalism. A relation between the spectral function and the nuclear contacts is derived and used to analyze the dependence of the data on the initial energy and momentum of the knocked-out proton. The ratio between the number of emitted proton-proton pairs and proton-neutron pairs is shown to depend predominantly on a single ratio of contacts. This ratio is expected to present deep minima in the initial energy and momentum plane, associated with the node in the proton-proton wave function.The formalism is applied to analyze data from recent 4He and 12C electron-scattering experiments performed at Jefferson laboratory. Different nucleon-nucleon potentials were used to assess the model-dependence of the results. For the ratio of proton-proton to proton-neutron pairs in 4He, a fair agreement with the experimental data is obtained using the two potentials, whereas for the ratio of proton-proton pairs to the total knocked-out protons in 12C, some of the features of the theory are not seen in the experimental data. Several possible explanations for this disagreement are discussed. It is also observed that the spectral function at specific domains of the momentum-energy plane is sensitive to the nucleon-nucleon interaction. Based on this sensitivity, it might be possible to constrain the short range part of the nuclear potential using such experimental data.

Energy dependence of the reduced single-particle strength for strongly-bound proton removal on 16C

Experimental data on the strongly-bound one-proton knockout from 16C at intermediate and high energies have recently been measured at NSCL and GSI, respectively. This is the first case that strongly-bound valence-nucleon knockout from weakly-bound nuclei was measured at both intermediate and high energies on composite nuclear targets. Based on these data, the eikonal model is employed to study the energy dependence of the reduction factor Rs, defined as the ratio of the experimental and theoretical cross sections, for the strongly-bound proton knockout from 16C. The Rs deduced at high energy [Rs = 0.40(1)] is larger than that extracted at intermediate energy [Rs = 0.30(3)], but is relatively small compared to the Rs's obtained for weakly-bound nucleon knockout(Rs ∼ 1) and well-bound nucleon knockout(Rs ∼ 0.6). A scaled Rs value of 0.32(1) for the high energy case is obtained after considering the possible uncertainties in the experimental data. It suggests that, if the scaled Rs is reliable, measurements using high-energy beams could not resolve the spectroscopic strength reduction problem and the strong isospin asymmetry dependence of the Rs persists at high energies.

Structure of Be13 studied in proton knockout from B14

The neutron-unbound isotope Be-13 has been studied in several experiments using different reactions, different projectile energies, and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the Be-13 structure, is a challenge, particularly in light of its bridging role between Be-12, where the N = 8 neutron shell breaks down, and the Borromean halo nucleus Be-14. The purpose of the present study is to investigate the role of bound excited states in the reaction product Be-12 after proton knockout from B-14, by measuring coincidences between Be-12, neutrons, and gamma rays originating from de-excitation of states fed by neutron decay of Be-13. The Be-13 isotopes were produced in proton knockout from a 400 MeV/nucleon B-14 beam impinging on a CH2 target. The Be-12-n relative-energy spectrum d sigma/dE(fn) was obtained from coincidences between Be-12(g.s.) and a neutron, and also as threefold coincidences by adding gamma rays, from the de-excitation of excited states in Be-12. Neutron decay from the first 5/2(+) state in Be-13 to the 2(+) state in Be-12 at 2.11 MeV is confirmed. An energy independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/nucleon B-14 beam. A low-lying p-wave resonance in Be-13(1/2(-)) is confirmed by comparing proton- and neutron-knockout data from B-14 and Be-14.

Probing high-momentum protons and neutrons in neutron-rich nuclei

The atomic nucleus is one of the densest and most complex quantum-mechanical systems in nature. Nuclei account for nearly all the mass of the visible Universe. The properties of individual nucleons (protons and neutrons) in nuclei can be probed by scattering a high-energy particle from the nucleus and detecting this particle after it scatters, often also detecting an additional knocked-out proton. Analysis of electron- and proton-scattering experiments suggests that some nucleons in nuclei form close-proximity neutron-proton pairs1-12 with high nucleon momentum, greater than the nuclear Fermi momentum. However, how excess neutrons in neutron-rich nuclei form such close-proximity pairs remains unclear. Here we measure protons and, for the first time, neutrons knocked out of medium-to-heavy nuclei by high-energy electrons and show that the fraction of high-momentum protons increases markedly with the neutron excess in the nucleus, whereas the fraction of high-momentum neutrons decreases slightly. This effect is surprising because in the classical nuclear shell model, protons and neutrons obey Fermi statistics, have little correlation and mostly fill independent energy shells. These high-momentum nucleons in neutron-rich nuclei are important for understanding nuclear parton distribution functions(the partial momentum distribution of the constituents of the nucleon) and changes in the quark distributions of nucleons bound in nuclei (the EMC effect)1,13,14. They are also relevant for the interpretation of neutrino-oscillation measurements15 and understanding of neutron-rich systems such as neutron stars3,16.

Exclusive quasi-free proton knockout from oxygen isotopes at intermediate energies

The dependence of the single-particle strength on the difference between proton and neutron separation energies is studied for oxygen isotopes in a wide range of isospins. The cross sections of the quasi-free (⁠|$p,2p$|⁠) reaction on |$^{14,16,18,22,24}$|O were measured at intermediate energies. The measured cross sections are compared to predictions based on the distorted wave impulse approximation and shell-model |$psd$| valence-space spectroscopic factors. The reduction factors, which are the ratio of the experimental cross sections to the theoretical predictions, show no apparent dependence on the proton–neutron separation energy difference. The result is compatible with the result of the (⁠|$e,e^{\prime}p$|⁠) reaction on stable targets and with the predictions of recent ab initio calculations.