Pion Production Processes Research Articles

Neutrino Induced Charged Current [formula omitted] Production From 12C At Intermediate Energies

The charged current one pion production induced by ν μ in 12C has been studied. The calculations have been done for the incoherent and the coherent pion production processes assuming Δ dominance and take into account the effects of the Pauli blocking, Fermi motion, renormalization of the Δ properties in a nuclear medium and the final state interaction effects of pions with the residual nucleus. The numerical results have been compared with the preliminary experimental results of the MiniBooNE collaboration in 12C.

Study of the single neutral top pion production process atγγcollider

$\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\Pi}}_{t}^{0}$ is the major production mechanism of the neutral top pion at the linear colliders. In this paper, we calculate the cross section of the process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\Pi}}_{t}^{0}$ and discuss the potential to observe the neutral top pion via its various decay modes at the planned International Linear Collider. The study shows that, among the various neutral top-pion production processes at the linear colliders, the cross section of $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\Pi}}_{t}^{0}$ is the largest one which can reach the level of ${10}^{1}\ensuremath{-}{10}^{2}\text{ }\text{ }\mathrm{fb}$. Because of the existence of the tree-level flavor-changing coupling ${\ensuremath{\Pi}}_{t}^{0}t\overline{c}$, $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\Pi}}_{t}^{0}\ensuremath{\rightarrow}t\overline{c}$ can provide enough number of typical signals to identify the neutral top pion with the clean SM background. Therefore, the process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\Pi}}_{t}^{0}$ plays an important role in searching for the neutral top pion and tests the TC2 model.

A New Neutrino Cross Section Data Resource

We describe a new web based data resource being developed to provide access to accurate and validated cross sections of low energy neutrino and antineutrino interactions. The proposed content of this database are outlined which cover total and differential cross from inclusive, quasi-elastic and exclusive pion production processes from charged and neutral current interactions. Efforts to obtain these data, which come mainly from old bubble chamber experiments, are described as well as the implementation of an embryonic web site to make the resource generally accessible.

Energy dependence of the single spin asymmetries in inclusive pion production processes

Recent data from the E925 Collaboration at Brookheaven National Laboratory show a significant energy dependence of the single-spin left-right asymmetry in inclusive hadron production in hadron-hadron collisions. We analyze the experimental results and show that the observed energy dependence can be reproduced naturally in the picture proposed in a previous Letter. We fix all the parameters at the Fermilab E704 energy and calculate the asymmetry at the BNL E925 energy. We compare the results with the data and make predictions for experiments at even higher energies.

Pion production in deeply virtual Compton scattering

Using a soft pion theorem based on chiral symmetry and a $\Delta(1232)$ resonance model we propose an estimate for the production cross section of low energy pions in the deeply virtual Compton scattering (DVCS) process. In particular, we express the $e p \to e \gamma \pi N$ processes in terms of generalized parton distributions. We provide estimates of the contamination of the $e p \to e \gamma p$ DVCS observables due to this associated pion production processes when the experimental data are not fully exclusive, for a set of kinematical conditions representative of present or planned experiments at JLab, HERMES and COMPASS.

New Results for Bremsstrahlung and Pion Production in the Neutron–Proton System

Differential cross sections for the neutron-proton bremsstrahlung (np → npγ) and pion production (np → npπ0 and np → ppπ-) processes have been measured for the first time at the Los Alamos Neutron Science Center. A pulsed neutron beam, produced by 800 MeV protons incident on a tungsten spallation target, bombarded a liquid hydrogen target. The outgoing neutrons and protons (in the first two reactions) or pairs of protons (in the third reaction) were observed in coincidence in organic liquid or plastic and CsI(pure) detectors at angles between 12° and 32° on opposite sides of the beam. For each pair of nucleon angles, the angular distribution of the unobserved photons or pions was deduced from the data.

Three-nucleon mechanisms in photoreactions

The 12C(γ,ppn) reaction has been measured for Eγ=150–800 MeV in the first study of this reaction in a target heavier than 3He. The experimental data are compared to a microscopic many body calculation. The model, which predicts that the largest contribution to the reaction arises from final state interactions following an initial pion production process, overestimates the measured cross sections and there are strong indications that the overestimate arises in this two-step process. The selection of suitable kinematic conditions strongly suppresses this two-step contribution leaving cross sections in which up to half the yield is predicted to arise from the absorption of the photon on three interacting nucleons and which agree with the model. The results indicate (γ,3N) measurements on nuclei may be a valuable tool for obtaining information on the nuclear three-body interaction.

Electromagnetically induced nuclear-charge pickup observed in ultrarelativistic Pb collisions.

A strong increase of inclusive nuclear-charge pickup cross sections, forming 83Bi from 158A GeV 82Pb ions, is observed in comparison to similar measurements at 10.6A GeV. From the dependence of these cross sections on target atomic number, this increase is attributed to the electromagnetic process of pion production by equivalent photons. The observed cross sections can be reproduced quantitatively using the recently developed RELDIS code.

Pion production at low energies

Intense muon beams are needed both for neutrino oscillation experiments of a new generation and for muon colliders. A detailed knowledge of pion production processes in proton–nucleus collisions is important for the optimization of the pion collection. Comparison of particle generations at low proton kinetic energy (2GeV) using different codes on a thin target are presented. The physical considerations underlying the models are also discussed. Results from simulations of a thick Hg-target will be given and some conclusions for the construction of a pion collector are shown.

Neutrino anomaly and ν-nucleus interactions

A review of various calculations of the inclusive quasi-elastic reactions and pion production processes in neutrino reactions for various nuclei at intermediate energies relevant to solar, atmospheric and accelerator neutrinos is presented

Estimating the particle-antiparticle correlation effect for pion production in heavy-ion collisions

Estimation of the back-to-back pi-pi correlations arising due to evolution of the pionic field in the course of pion production process is given for central heavy nucleus collisions at moderate energies.

Pion photo- and electroproduction and the partially conserved axial current

The relevance of the axial current for pion production processes off the nucleon with real or virtual photons is revisited. Employing the hypothesis of a partially conserved axial current (PCAC), it is shown that, when all of the relevant contributions are taken into account, PCAC does not provide any additional constraint for threshold production processes that goes beyond the Goldberger-Treiman relation. In particular, it is shown that pion electroproduction processes at threshold cannot be used to extract any information regarding the weak axial form factor. The relationships found in previous investigations are seen to be an accident of the approximations usually made in this context.

Large basis shell model analysis of 14N( gamma, pi +)14Cg.s. reaction.

The {sup 14}N({gamma},{pi}{sup +}){sup 14}C{sub g.s.} cross section at {ital E}{sub {gamma}}=173 MeV has been calculated using shell model wave functions determined in complete (0+2){h_bar}{omega} and (0+2+4){h_bar}{omega} shell model spaces. Using the (0+2+4){h_bar}{omega} shell model wave functions yields an improvement over older results obtained with Cohen-Kurath wave functions by a factor of 2, but still overpredicts the back-angle data. When correlated with analyses of inelastic electron and proton scattering from {sup 14}N, the present results indicate the need for an improved shell model calculation and possibly an improved description of the elementary pion production process in nuclei. {copyright} {ital 1996 The American Physical Society.}

Study of sigma (750) and rho 0(770) production in measurements of pi N

We present a new and improved model-independent amplitude analysis of the reactions ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathit{n}}_{\mathrm{\ensuremath{\uparrow}}}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p at 5.98 and 11.85 GeV/c and ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathit{p}}_{\mathrm{\ensuremath{\uparrow}}}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{+}$n at 17.2 GeV/c measured with transversely polarized targets at the CERN Proton Synchrotron. For dipion masses below 1000 MeV the pion production process is described by two S-wave and six P-wave production amplitudes. Previous analyses suffered from the presence of unphysical solutions for moduli of amplitudes or cosines of their relative phases, causing uncertainties regarding the signal for the scalar state I=0 ${0}^{++}$(750). To remove the unphysical solutions we use a Monte Carlo approach to amplitude analysis. In each (m,t) bin we randomly varied the input spin-density-matrix elements 30 000 times within their experimental errors and performed an amplitude analysis for each selection. Unphysical solutions were rejected and the physical solutions produced a continuous range of values for moduli, cosines of relative phases, and for partial wave intensities. A clear signal for \ensuremath{\sigma}(750) resonance emerges in all four solutions for an S-wave intensity ${\mathit{I}}_{\mathit{S}}$ at 5.98 and 11.85 GeV/c and in both solutions for an S-wave amplitude \ensuremath{\Vert}S\ifmmode\bar\else\textasciimacron\fi{}${\mathrm{\ensuremath{\Vert}}}^{2}$\ensuremath{\Sigma} at 17.2 GeV/c. Its ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ decay width is estimated to be in the range 200--300 MeV. We find a significant suppression of ${\mathrm{\ensuremath{\rho}}}^{0}$ production in the amplitudes \ensuremath{\Vert}U${\mathrm{\ensuremath{\Vert}}}^{2}$\ensuremath{\Sigma}, \ensuremath{\Vert}N\ifmmode\bar\else\textasciimacron\fi{}${\mathrm{\ensuremath{\Vert}}}^{2}$\ensuremath{\Sigma} and at 17.2 GeV/c in \ensuremath{\Vert}L${\mathrm{\ensuremath{\Vert}}}^{2}$\ensuremath{\Sigma}. The mass dependence of the amplitudes \ensuremath{\Vert}L\ifmmode\bar\else\textasciimacron\fi{}${\mathrm{\ensuremath{\Vert}}}^{2}$\ensuremath{\Sigma} and \ensuremath{\Vert}L${\mathrm{\ensuremath{\Vert}}}^{2}$\ensuremath{\Sigma} shows unexpected structures within the ${\mathrm{\ensuremath{\rho}}}^{0}$ mass region which correlate the mass spectra corresponding to opposite nucleon spins. These features of the P-wave moduli reveal the essential role of nucleon spin in the pion production process and contradict the factorization hypothesis. Our results emphasize the need for a systematic study of pion production on the level of amplitudes in a new generation of dedicated experiments with spin at the recently proposed high-intensity hadron facilities. \textcopyright{} 1996 The American Physical Society.

η → π0γγtoO( p6) in chiral perturbation theory

The decay η → π 0 γγis discussed in the framework of SU(3) chiral perturbation theory. The process is dominated by the O( p 6) in the momentum expansion where tree-level amplitudes from the effective Lagrangian G6 enter together with one-loop contributions from λ 4 and twoloop contributions from L 6. We estimate the six independent L 6 coupling constants by resonance saturation consistent with the pion production process γγ → π 0 π 0 and calculate the pion-loop part of the one- and two-loop amplitude. Predictions for the total rate and spectrum of η → π 0 γγ are given together with a discussion of the uncertainties involved.

Pion production in proton-deuteron disintegration

Abstract The reaction pd → π − ppp has been investigated in a line-reversed hydrogen bubble chamber experiment using 3.3 GeV / c deuteron beam. The present work appears to be the first account of this reaction in the GeV region. The observed spectra are very well reproduced by a parameter-free calculational scheme based on the impulse approximation and one-pion-exchange model of pion production. Our approach is fully relativistic and special care has been taken to ensure the proper antisymmetry of the three-proton states. When kinematical cuts are introduced to suppress the dominant quasi-free pion-production processes, the effective mass distributions exhibit narrow enhancements which are not accounted for by our model and might be considered as candidates for dibaryonic resonances.

Mass dependence of π 0-production in heavy ion collisions at 1 A GeV

The production of neutral pions has been studied in the reactions 40 Ar+ nat Ca , 86 Kr+ nat Zr and 197 Au+ 197 Au at 1 A GeV. For high energy pions emitted from the heavier systems a steeper than linear rise of the pion multiplicity with the centrality of the reaction is observed, indicating a pion production process other than binary nucleon-nucleon collisions. At low transverse momenta an enhancement of the π 0-multiplicity increasing with the mass of the collision system is found. Systematic discrepancies between the experimental results and recent BUU, QMD and Cascade calculations are discussed.

Mass dependence of pion production in heavy ion collisions near, but below threshold

We have measured the inclusive cross section for production of negative pions near mid-rapidity in 20 Ne + NaF, 139 La + 139 La and 197 Au + 197 Au collisions at E = 183 and 236 MeV/u. Au + Au is the heaviest system from which subthreshold pion production has been measured to date. The dependence of the pion cross section on pion energy, beam energy and associated charged particle multiplicity is consistent with previous results both above and below threshold. The dependence of the cross section on the mass of the colliding system varies only slightly as the beam energy is reduced below threshold, in contrast to some previous measurements. Comparison with theory suggests that at these energies the pion production process is still dominated by nucleon-nucleon collisions.

Threshold behaviour of the π+π− invariant mass in nuclei

We present π + π − invariant-mass distributions between 300 and 380 MeV for the 2H, 4He, 16O, 208 Pb(π +, π +π −) reaction at an incident π + energy of 280 MeV. A prominent feature is the shift of their maximum downward to the 2m π threshold as A increases. This behaviour finds a qualitative explanation in the framework of a model that investigates the modification of the strength function for an interacting ( ππ) I = L = 0 system embedded in the nuclear medium. Also, the π + π − invariant-mass cross sections are compared with the predictions of an A( π +, π + π −) model that uses a microscopical approach for the elementary process of pion production, πN → ππ N. Four-fold differential cross sections as a function of the energy of outgoing π + and p, and missing-mass distributions for the A( π +, pπ −) reaction are also presented for some of the examined nuclei. The experimental results are discussed within the framework of the two available models.

Amplitude analysis of reaction K+n

We present a model-independent amplitude analysis of the reaction {ital K}{sup +}{ital n}{sub {up arrow}}{r arrow}{ital K}{sup +}{pi}{sup {minus}}{ital p} at 5.98 GeV/{ital c} using Saclay data obtained with a transversely polarized deuteron target at the CERN Proton Synchrotron. The analysis makes use of the data in two sets of binnings to examine the dependence of amplitudes on momentum transfer {ital t} ({minus}{ital t}{le}1.0 (GeV/{ital c}){sup 2}) in the {ital K}{sup *0} mass region, and their dependence on {ital K}{sup +}{pi}{sup {minus}} invariant mass below 1000 MeV for momentum transfers {minus}{ital t}=0.2--0.4 (GeV/{ital c}){sup 2}. The analysis is performed in both {ital t}-channel and {ital s}-channel helicity frames of the dimeson state. The data yield two solutions for 8 moduli and 6 cosines of relative phases of nucleon transversity amplitudes with dimeson spins {ital J}=0 ({ital S} wave) and {ital J}=1 ({ital P} wave). The two solutions differ mainly in the contributions of the {ital S} wave. Both solutions require nonzero nucleon helicity-flip amplitudes. The differences in the moduli of the amplitudes with a recoil nucleon transversity up'' and down'' reveal the essential role of nucleon spin in the pion production process. The {ital P}-wave moduli show unexpected structures withinmore » the {ital K}{sup *0} mass range which provide new information on {ital K}{sup *0} production. The mass dependence of solution 2 suggests the possible existence of a scalar state {ital I}=1/2 0{sup +} (887) with a width of about 20 MeV. We comment on its possible constituent structure. Our results emphasize the need for a systematic study of pion production on the level of amplitudes in a new generation of dedicated experiments with spin at the recently proposed advanced hadron facilities.« less