Proton-neutron Collisions Research Articles

Simulation of proton–neutron collisions in inverse kinematics and its possible application

Neutrons have played a vital role in many nuclear physics fields. In some cases, the inverse kinematics of neutrons colliding with other nuclei are also worth studying. In this study, the inverse kinematics of thermal neutrons colliding with high-energy protons is simulated by using the Monte Carlo method. Thermal neutrons are taken as target particles, whereas protons are incident particles. The simulation implies that, after collision, the energy of the output neutron at $$0^{\circ }$$ equals the energy of the incident proton. A possible application of the result is proposed that might yield single-energy neutrons. Some key parameters of the conceptual design were evaluated, demonstrating that the design may reach high-neutron-energy resolution.

Measuring baryon radiative decays in timelike region with HADES

Radiative transition of excited baryon to a nucleon with emission of a virtual massive photon decaying to dielectron pair (Dalitz decay) provides important information about baryon-photon coupling at low q 2 in timelike region. First measurements of such decays in proton-proton and quasi-free neutron-proton collisions have been conducted with the HADES detector at GSI/FAIR. The results for the Δ(1232) and higher mass resonances are presented. The extension of this program to pion induced reactions is outlined and illustrated with performance reached in the first pilot experiment.

Analysis of the exclusive final state npe+e- in the quasi-free np reaction

.We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25GeV/u impinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of e^{+}e^{-} pairs above the pi^{0} mass in the exclusive channel dp rightarrow npe^{+}e^{-}(p_{spect}) as compared to the exclusive channel ppe^{+}e^{-} measured in proton-proton collisions at the same energy. That excess points to different bremsstrahlung production mechanisms. Two models were evaluated for the role of the charged pion exchange between nucleons and double- Delta excitation combined with intermediate rho-meson production. Differential cross sections as a function of the e^{+}e^{-} invariant mass and of the angles of the virtual photon, proton and electrons provide valuable constraints and encourage further investigations on both experimental and theoretical sides.

Near threshold production of η-mesons in proton neutron collisions at ANKE

The interaction between hadrons and η-mesons is an intensively studied topic. Due to its stength it might lead to the formation of η-mesic nuclei. In order to study the characteristics of this interaction a measurement of the reaction p + d → d + η + p sp has been performed at the ANKE spectrometer at the COSY accelerator of the Forschungszentrum Julich. The two different beam momenta ( p 1 = 2.09 GeV/c and p 2 = 2.25 GeV/c) in combination with the Fermi motion inside the target deuteron grant access to the determination of total and differential cross sections in an excess energy range from threshold up to Q = 90 MeV. While the course of the total cross section, especially near threshold, will allow to extract the scattering length a dη via an s-wave final state interaction ansatz, the differential cross sections permit to verify the legitimacy of the s-wave assumption.

Signatures of volatiles in the lunar proton albedo

We find evidence for hydrated material in the lunar regolith using “albedo protons” measured with the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO). Fluxes of these albedo protons, which are emitted from the regolith due to steady bombardment by high energy radiation (Galactic Cosmic Rays), are observed to peak near the poles, and are inconsistent with the latitude trends of heavy element enrichment (e.g., enhanced Fe abundance). The latitudinal distribution of albedo protons anti-correlates with that of epithermal or high energy neutrons. The high latitude enhancement may be due to the conversion of upward directed secondary neutrons from the lunar regolith into tertiary protons due to neutron–proton collisions in hydrated regolith that is more prevalent near the poles. The CRaTER instrument may thus provide important measurements of volatile distributions within regolith at the Moon and potentially, with similar sensors and observations, at other bodies within the Solar System.

Formula omitted] bosons production in the quantum statistical parton distributions approach

We consider W± gauge bosons production in connection with recent results from BNL-RHIC and FNAL-Tevatron and interesting predictions from the statistical parton distributions. They concern relevant aspects of the structure of the nucleon sea and the high-x region of the valence quark distributions. We also give predictions in view of future proton–neutron collisions experiments at BNL-RHIC.

High Energy Hadronic Collisions Using Neural Network and Genetic Programming Techniques

 Abstract—Artificial Intelligence (AI) techniques of artificial neural networks (ANN) and evolutionary computation of genetic programming (GP) have recently been used to design and implement more effective models. The artificial neural network (ANN) model has been used to study the charged particles multiplicity distributions for antiproton-neutron ( n p   ) and proton-neutron ( n p  ) collisions at different lab momenta. The neural network model performance was also tested at non-trained space (predicted) and matched them effectively. The trained NN shows a good fitting with the available experimental data. The NN simulation results prove a solid existence in modeling hadronic collisions. Genetic Programming (GP) model is a flexible and powerful technique that can be used for solving the same problem. In this paper, genetic programming (GP) has been used to discover a function that calculates the charged particles multiplicity distribution of created pions for the same interactions at high energies. The predicted distributions from the GP-based model are compared with the available experimental data. The discovered function of GP model has proven an excellent matching with the corresponding experimental data.

Comparison of inclusiveK+production in proton-proton and proton-neutron collisions

The momentum spectra of ${K}^{+}$ produced at small angles in proton-proton and proton-deuteron collisions have been measured at four beam energies, 1.826, 1.920, 2.020, and 2.650 GeV, using the ANKE spectrometer at COSY-J\"ulich. After making corrections for Fermi motion and shadowing, the data indicate that ${K}^{+}$ production near threshold is stronger in $pp$- than in $pn$-induced reactions. However, most of this difference could be made up by the unobserved ${K}^{0}$ production in the $pn$ case.

GAMMA-RAY BURSTS FROM MAGNETIZED COLLISIONALLY HEATED JETS

Jets producing gamma-ray bursts (GRBs) are likely to carry a neutron component that drifts with respect to the proton component. The neutron-proton collisions strongly heat the jet and generate electron-positron pairs. We investigate radiation produced by this heating using a new numerical code. Our results confirm the recent claim that collisional heating generates the observed Band-type spectrum of GRBs. We extend the model to study the effects of magnetic fields on the emitted spectrum. We find that the spectrum peak remains near 1 MeV for the entire range of the magnetization parameter $0<\epsilon_B<2$ that is explored in our simulations. The low-energy part of the spectrum softens with increasing $\epsilon_B$, and a visible soft excess appears in the keV band. The high-energy part of the spectrum extends well above the GeV range and can contribute to the prompt emission observed by Fermi/LAT. Overall, the radiation spectrum created by the collisional mechanism appears to agree with observations, with no fine-tuning of parameters.

Investigation of the production of electron-positron pairs in nucleon-nucleon interactions with the HADES detector

The inclusive production of electron-positron pairs in proton-proton and deuteron-proton collisions at a beam kinetic energy of 1.25 GeV per nucleon was studied with the HADES (High Acceptance Dielectron Spectrometer) detector. The main objective of the deuteron-proton experiment was to investigate pair production in quasifree neutron-proton collisions. In the invariant-mass region M > 140 MeV/c 2, the invariant-mass spectrum determined in this channel shows a significant enhancement of the pair yield in relation to that in the case of proton-proton collisions.

The study of the negative pion production in neutron-proton collisions at beam momenta below 1.8 GeV/c

A detailed investigation of the reaction np $ \rightarrow$ pp $ \pi^{{-}}_{}$ has been carried out using the data obtained with the continuous neutron beam produced by charge exchange scattering of protons off the deuterium target. Partial-wave event-by-event analysis based on the maximum likelihood method was applied to determine contributions of different partial waves to the pion production process. A combined analysis of the np $ \rightarrow$ pp $ \pi^{{-}}_{}$ and pp $ \rightarrow$ pp $ \pi^{{0}}_{}$ data measured in the same energy region allows us to determine the contribution of isoscalar partial waves (I = 0 in the momentum range from 1.1 up to 1.8GeV/c . The decay of isoscalar partial waves into the (1 S 0)pp $ \pi$ channel provides us with a good tool for the determination of the pp S -wave scalar scattering length in the final state which was found to be a pp = - 7.5±0.3 fm.

ISOSPIN DEPENDENCE OF THE η' MESON PRODUCTION IN NUCLEON-NUCLEON COLLISIONS

A comparison of the close–to–threshold total cross section for the η' production in pp → ppη' and pn → pnη' reactions constitutes a tool to investigate the η' meson structure and the reaction mechanism in the channels of isospin I = 0 and I = 1 and may provide insight into the flavour-singlet (perhaps also into gluonium) content of the η' meson. In this contribution we present preliminary results of measurement of the quasi-free production of the η' meson in the proton-neutron collisions conducted using the COSY-11 facility.

Neutron-rich gamma-ray burst flows: dynamics and particle creation in neutron-proton collisions

We consider gamma-ray burst outflows with a substantial neutron component that are either dominated by thermal energy (fireballs) or by magnetic energy. In the latter case, we focus on the recently introduced “AC” model which relies on magnetic reconnection to accelerate the flow and power the prompt emission. For both the fireball and the AC model, we investigate the dynamical importance of neutrons on the outflow. We study particle creation in inelastic neutron-proton collisions and find that in both models the resulting neutrino emission is too weak to be detectable. The inelastic collisions also produce γ-rays, which create pairs in interactions with soft photons carried with the flow. In magnetically driven outflows, the energy of these pairs is radiated away as synchrotron emission. The bulk of the emission takes place at a few hundred keV, which makes it difficult to disentangle this signal from the prompt emission. In fireballs, however, pair cascading leads to the emission of γ-rays with observer energy in the range of 2–20 GeV and a fluence well above the GLAST threshold. Therefore this emission can be a useful diagnostic of the nature of the outflow.

Comparison of electron and neutron compton scattering from entangled protons in a solid polymer.

We present, for the first time, a direct comparison between electron (ECS) and neutron (NCS) Compton scattering results from protons of a solid polymer. The momentum distributions of hydrogen obtained from ECS and NCS are in excellent agreement. In both experiments, a strong "anomalous" shortfall in the scattering intensity of protons [first detected in liquid water with NCS [Phys. Rev. Lett. 79, 2839 (1997)]]] is found ranging from about 20% up to 50%, depending on the momentum transfer applied. The characteristic times of electron- and neutron-proton collisions lie in the subfemtosecond range. The presented ECS and NCS results provide further direct evidence for this striking effect, which has been ascribed to attosecond quantum entanglement of the protons.

Role of baryonic resonances in the dilepton emission in nucleon-nucleon collisions

Within an effective Lagrangian model, we present calculations for cross sections of the dilepton production in proton-proton and proton-neutron collisions at laboratory kinetic energies in 1-5 GeV range. Production amplitudes include contributions from the nucleon-nucleon bremsstrahlung as well as from the mechanism of excitation, propagation, and radiative decay of Delta(1232) and N*(1520) intermediate baryonic resonances. It is found that the delta isobar terms dominate the cross sections in the entire considered beam energy range. Our calculations are able to explain the data of the DLS collaboration on the dilepton production in proton-proton collisions for beam energies below 1.3 GeV. However, for incident energies higher than this the inclusion of contributions from other dilepton sources like Dalitz decay of pi0 and eta mesons, and direct decay of rho and omega mesons is necessary to describe the data.

η meson production inNNcollisions

Eta meson production in both proton-proton and proton-neutron collisions is investigated within a relativistic meson exchange model of hadronic interactions. It is found that the available cross section data can be described equally well by either the vector or pseudoscalar meson exchange mechanism for exciting the S_{11}(1535) resonance. It is shown that the analyzing power data can potentially be very useful in distinguishing these two scenarios for the excitaion of the S_{11}(1535) resonance.

Nucleon-nucleon bremsstrahlung of axions and pseudoscalar particles from neutron-star matter

The energy-loss rates of degenerate neutron-star matter due to thermal bremsstrahlung of pseudoscalar particles and axions via neutron-proton collisions together with the mean-free path and the energy spectrum from neutron-neutron, neutron-proton, and neutron-neutron processes are calculated. Analytic expressions for these quantities are obtained in the general case where the pseudoscalar particle couples to the proton and neutron with different strengths and the protons and the neutrons have different Fermi momenta. These rates are compared with those of other authors.

Thermal hard-photons probing multifragmentation in nuclear collisions around the fermi energy

Hard-photon (E$_{\gamma} >$ 30 MeV) emission issuing from proton-neutron bremsstrahlung collisions is investigated in four different heavy-ion reactions at intermediate bombarding energies ($^{36}$Ar+$^{197}$Au, $^{107}$Ag, $^{58}$Ni, $^{12}$C at 60{\it A} MeV) coupling the TAPS photon spectrometer with two charged-particle multidetectors covering more than 80% of the solid angle. The hard-photon spectra of the three heavier targets result from the combination of two distinct exponential distributions with different slope parameters, a result which deviates from the behaviour expected for hard-photon production just in first-chance proton-neutron collisions. The thermal origin of the steeper bremsstrahlung component is confirmed by the characteristics of its slope and angular distribution. Such thermal hard-photons convey undisturbed information of the thermodynamical state of hot and excited nuclear systems undergoing multifragmentation.

Instantons and η meson production near threshold in NN collisions

An enhancement for the η production in proton–neutron collisions as compared with that in proton–proton scattering has been recently observed. We present a calculation for the production cross section, in proton–neutron collisions near threshold, within instanton model for the QCD vacuum and show that a specific flavor dependent nonperturbative quark–gluon interaction related to instantons is able to explain the observed enhancement.

Polarization Phenomena for Vector-Meson Production Induced by Neutron-Proton Collisions in Collinear Kinematics

Polarization phenomena for vector meson production in neutron-proton collisions, \(\), with \(\), are studied for collinear kinematics when the vector mesons are produced at angles \(\) or 180° with respect to the momentum of the incoming beam. It is shown that the spin structure of the matrix elements can be parametrized in terms of five independent complex scalar amplitudes whose symmetry properties follow from the isotopic invariance of the strong interaction and from which specific polarization properties can be deduced. The polarization structure functions, calculated in terms of these five independent scalar amplitudes, allow to analyze one and two spin polarization observables in a model independent way.