Pion Energy Spectra Research Articles

Spectra and multiplicities of n, p, d, t, K±, π± from antiproton annihilation in Cu and U

Inclusive energy spectra of neutrons, protons, deuterons, tritons, charged kaons and pions following antiproton annihilation at rest in copper and uranium have been measured. The determined multiplicity charged kaons is compared to recent measurements and indicates an enhancement of strangeness production. Ratios of directly emitted neutrons and protons have been determined for copper and uranium to 3.0±0.6 and 3.2±0.5, respectively.

Temperatures of negative pions in inelastic (d, alpha,C)+ (C,Ta) collisions at 4.2A GeV/c.

The slopes of the noninvariant center-of-mass energy spectrum of negative pions in inelastic collisions of d, \ensuremath{\alpha}, C nuclei with C and Ta targets at 4.2A GeV/c are studied. The temperatures of the negative pion are obtained using the Boltzmann distribution. The two-temperature shape of c.m. energy spectra is observed. The values of temperature do not depend significantly both on collision ``centrality'' and on atomic weight of the projectile nuclei. The experimental results are compared with the quark-gluon string model. The influence of resonances and directly produced pions on temperature values is studied.

Pion production in intermediate energy nucleus-nucleus collisions

Pion production in heavy-ion collisions is reviewed while placing emphasis on recent subthreshold experiments. The data are compared with predictions of NN collision and statistical models. The study of collision dynamics together with pion energy spectra suggests that the roduction mechanism at energies above 60 A MeV can be understood by either a microscopic description such as BUU, or by a statistical picture reflecting centrality. As for below 60 A MeV, importance of high momentum components in the momentum distribution and of the limiting temperature of hot nuclear matter are discussed from respective points of view.

Neutral pion production in the reactions 16O+ 27Al, 58Ni, 208Pb at Elab=95 MeV/nucleon

The production of neutral pions has been studied in the 16O+ 27Al, 58Ni, 208Pb reactions at 95 MeV/nucleon. Inclusive pion differential distributions dσ dp t , dσ dT π , and dσ dΩ have been measured by detecting the two-pion decay γ-rays in a setup of 8 lead glass Cherenkov detector telescopes. The data are discussed in the framework of a moving thermal source model. It is shown that the shape of the pion energy spectra is better described if mean field effects on the primary pion-production cross section and pion reabsorption are included in the calculation.

Pion production with radioactive nuclei

The possibility to study the coordinate and momentum space structure of exotic nuclei via pion production with radioactive beams is investigated. Exploratory calculations for 11Li are presented. A strong sensitivity of the pion energy spectra to the momentum distribution of the halo neutrons is found.

Coincidence measurements of the (π+,π0p) reaction atTπ+=165 MeV

We report coincidence measurements of the ({pi}{sup +},{pi}{sup 0}{ital p}) reaction at a beam energy of {ital T}{sub {pi}}{sup +}=165 MeV. The neutral pions were detected by the LAMPF {pi}{sup 0} spectrometer and the protons by an array of plastic-scintillator telescopes. The resulting energy resolution for the determination of the excitation energy of the residual nucleus was about 10 MeV. Measurements were performed on {sup 16}O at laboratory angles {theta}{sub {pi}}{sup 0}=70{degree}, 80{degree}, 110{degree}, and 130{degree}. The cross section is predominantly quasifree. Its angular dependence follows the trend of the free single-charge-exchange cross section at back angles and is somewhat suppressed relative to this at more forward angles. Events corresponding to removal of {ital p}-shell nucleons were identified by their {pi}{sup 0} and {ital p} energies. The {pi}{sup 0} energy spectra for such events are compared to similar pion energy spectra for the {sup 16}O({pi}{sup {plus minus}},{pi}{sup {plus minus}}{ital p}) reactions; the cross-section ratios are consistent with ratios calculated from isospin coupling alone. {pi}{sup 0} energy spectra are also compared to predictions of {Delta}-hole model calculations; the calculations for events in which protons are detected at the conjugate quasifree angle underestimate the ({pi}{sup +},{pi}{sup 0}{ital p}) cross sections by 30--55more » %. At {theta}{sub {pi}}{sup 0}=110{degree} the ({pi}{sup +},{pi}{sup 0}{ital p}) reaction was also studied on Fe, Sn, and Pb. No significant {ital A} dependence of the cross section was observed.« less

Subthreshold production of pions in coincidence with light particles

He ions have been detected in coincidence with charged pions in the reactions 16O on 27Al at E lab = 94 MeV/u. We analyse velocity spectra and cross-sections of He ions emitted in the angular range 4 0 ÷ 150 0 in coincidence with charged pions detected at 90 0. A two source emission mechanism of the helium particles and a pion statistical production from an equilibrated participant zone is stressed. The absolute yields at different angles are compared with results of a theoretical model for medium energy heavy ion reactions in the frame f a participant-spectator picture. A comparison of the pion energy spectra with Boltzmann-Nordheim-Vlasov calculations and a discussion on the time scale for pion emission is also presented.

Spin-isospin excitation in 12C(γ, π +) 12B ∗ using tagged photons

The energy spectra of positive pions from the reaction 12C(γ, π +) 12B ∗ were measured at five angles, using quasi-monochromatic, tagged photons in the energy range from 176 to 182 MeV. Strong transitions to the isovector nuclear states in 12B at 0–1, 4.5, and 7.5 MeV were observed. The differential cross sections to these states have been obtained for the momentum transfers 0.5 < q < 1.2 fm −1. DWIA calculations have been carried out in momentum space for each observed state or group of states. Comparisons are made between the present data, previous data from bremsstrahlung experiments, and various DWIA calculations.

Unified calculation of photon and pion spectra in intermediate energy heavy ion reactions.

We calculate the energy spectra of high energy photons and pions produced in heavy ion collisions at intermediate energies of around 75 MeV/nucleon. We use a unified approach based on the Boltzmann-Uehling-Uhlenbeck theory and the assumption that both pions and high energy gamma rays are produced in individual nucleon-nucleon collisions during the course of the heavy ion reaction. A comparison to existing data for energy spectra of neutral pions and high energy photons shows good agreement.

The effect of nuclear binding energy on pion yields in relativistic nuclear collisions

An alternative way for including the nuclear binding energy in intranuclear cascade calculations of relativistic heavy-ion collisions is presented. The present model strictly conserves the total energy and momentum of the system. Pions are produced only via the formation of Δ resonances and the pion absorption is taken into account through the delta recombination reaction. This simple treatment leads to a correct description of the pion multiplicity in the ArKCl reaction case. The proton and pion energy spectra calculated within this model agree with the data.

Thermal Model Analysis of Pion Energy Spectrum after p-p Annihilation

We have studied the pion energy spectrum after p-p annihilation at low energy with the experimental knowledge of various meson multiplicities in the thermal model. Assuming the Boltzmann distribution for various mesons with a common temperature, we obtain the temperature of T∼80MeV. If we would assume that this temperature is the hadronization temperature of quark phase, we deduce the size of the hot matter of radius ∼1.9fm. The correlation function measurement of identical particles is suggested to determine the radius of the hot matter under the Hunbury-Brown/Twiss effct.

Pion-reabsorption effect on pion spectra in high-energy heavy-ion collisions.

Cascade-model calculations are extended to study the pion energy spectra in high-energy heavy-ion collisions of heavy systems. It is found that pion reabsorption (\ensuremath{\pi}+N\ensuremath{\rightarrow}\ensuremath{\Delta}) is essential in explaining the difference between the energy slopes for pions and protons. This pion-reabsorption effect becomes more and more important as the mass number increases and reproduces even the observed falloff of the energy slopes (temperatures) for pions in the collisions of heavier nuclei. We show also the average pion multiplicities with mass number.

Majorana neutrinos and photinos from kaon decay.

We discuss the suggestion by Deshpande and Eilam of putting bounds on the ..nu../sub tau/ mass from the decay K/sup +/..--> pi../sup +/..nu..nu-bar. We show that the Dirac or Majorana nature of the ..nu../sub tau/ can make a significant difference in the pion energy spectrum. We also discuss the relative importance of the K/sup +/..--> pi../sup +/lambda/sub ..gamma../lambda/sub ..gamma../ mode, lambda/sub ..gamma../ being the photino.

Cascade-Model Analysis of Pion Production in Relativistic Nuclear Collisions

A nuclear mean field cascade(NMC) model is applied to the analysis of pion production mechanism in high energy heavy-ion collisions. The cascade process is described by using the experimental data of nucleon-nucleon and pion-nucleon collisions, and the reciprocal theorem for the collision N + Δ→N + N. The NMC model can well reproduce 1) the inelastic cross sections in EL=730 MeV proton-nucleus collisions, 2) the pion multiplicity in Ar+KCl central collisions, and 3) the different slopes between proton and pion energy spectra in EL=800 MeV/ nucleon Ne+NaF collisions, which have been discussed extensively.

Measurement of pion-induced deuteron breakup at 150 MeV.

The reactions $^{2}\mathrm{H}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{p})\mathrm{n}$ and $^{2}\mathrm{H}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{n})\mathrm{p}$ have been observed in a kinematically complete experiment at 150 MeV for two pairs of pion and nucleon angles corresponding to quasifree scattering. The general features of the pion energy spectrum are reproduced by the simple impulse approximation. However, both the ratio of neutron to proton production and the lower energy side of the pion energy spectra show significant departures from this model.

Composition and spectra of cosmic-ray hadrons at sea level

Energy spectra of neutrons, protons and pions were measured at sea level using a cosmic-ray hadron spectrometer consisting of a double neutron monitor and scintillation counters. All the hadron spectra were determined simultaneously. The analysis of the observed neutron multiplicity distributions was based on computer simulations of hadron cascades in the spectrometer. The neutron spectrum was determined in the range 0.05-1000 GeV. The proton-to-neutron ratio was estimated below 2 GeV, where the contribution of pions is of minor importance. Assuming a smooth rise of the p/n ratio above 2 GeV to a constant value at 5 GeV, the pion spectrum was determined between 2 and 50 GeV. At higher energies, where accompanied hadrons distort the measured spectra, upper bounds of the pion intensities were estimated. The composition of the hadron flux at sea level is discussed on the basis of the present and previous experimental and theoretical results.

Theoretical Study of Pion Spectra after Antiproton Annihilation at Rest in Nuclei

We study the role of the nuclear medium on the pion spectra after the antiproton annihilation at rest in nuclei. The nuclear medium acts as a scatterer and an absorber of outgoing pions and modifies the pion energy spectra. The pion spectra seem to be reproduced by assuming that half of the pions moving outward go out freely, while the other half moving inward to the nucleus are absorbed by nucleons according to the π-nucleus absorption cross sections. We propose a coincidence experiment to verify this picture.

Evidence for a resonant structure in inclusive Cu(p,π +)X reactions between 300 and 400 MeV

The energy spectra of positive pions between 23 and 122 MeV produced by protons of 300 to 400 MeV on copper have been measured at 90° in the laboratory frame. A surprisingly narrow structure (FWHM ⪅ 10 MeV) is observed for low energy pions at T p lab =350 MeV.

Characterization of the radiation environment at a new proposed irradiation facility at LAMPF

A new irradiation facility is being planned at the Clinton P. Anderson Meson Physics Facility (LAMPF). Irradiations will be possible both in the direct proton beam (∼760 MeV) and in a spallation neutron flux generated at the LAMPF beam stop area. As an aid in the design of the facility and an aid to potential experimenters, the radiation environment expected in this area was characterized by calculation. The Monte Carlo Code for the Transport of Neutrons and Photons (MCNP) and the High-Energy Transport Code (HETC) were employed to calculate the flux and energy spectrum of neutrons, protons, pions, muons, and photons generated by 760-MeV protons incident on components along the beam line in the Target Station A-6 area. In the direct proton beam a current density of 20 μA/cm 2 can be realized. The maximum total neutron flux outside the beam line between 1 eV and 800 MeV was determined as 4.9 × 10 13 neutrons cm −2 s −1 (± 2.2%). The calculated spallation neutron spectrum resembles a fission spectrum with the addition of substantial numbers of higher energy (⩾ 1 MeV) neutrons. The maximum secondary proton flux was calculated as 1.18 × 10 12 protons cm −2 s −1 (± 3.2%). The maximum pion, muon, and photon fluxes along the beam line were calculated to be 5.68 × 10 10 π + cm −2s −1 (± 14.4% ), 8.21 × 10 8μ + cm −2s −1 (± 51.5%) , and 1.4 × 10 13 photons cm −2s −1 (± 8%), respectively. Additionally, calculations were done that predict transmutation product generation in a variety of materials including a ferritic stainless steel. These products, most notably He, have been identified as being effective in determining microstructural evolution of materials under high-energy neutron (14-MeV) irradiation as is present in fusion reactors. It is felt that this new facility will be useful in the study of material for fusion applications.

Spectra of cosmic-ray hadrons in the range 0.1–1000 GeV

The energy spectra of cosmic-ray neutrons, protons, and pions were determined at sea level in the range 0.1 – 1000 GeV. The results are based on the measurements of the neutron-multiplicity distributions produced by cosmic hadrons in the Turku spectrometer. Below 0.5 GeV, the values γ = 1.47 ± 0.04 and 0.8 ± 0.1 were obtained for the slopes of the neutron and proton spectra. At 1000 GeV, the nucleon spectra are much steeper with γ = 2.79 ± 0.06. The pion spectrum was found to obey the power law with γ = 1.41 ± 0.05 in the low-energy region up to 30 GeV. Above 500 GeV, the spectrum of pions, containing an admixture of accompanied particles, was found to reach the high energy limit with γ = 2.92 ± 0.06.