Incoming Pion Research Articles

A relativistic description of the [formula omitted] reaction

We investigate the A ( π + , K + ) Λ A reaction within a covariant model. We consider those amplitudes which are described by creation, propagation and decay into the relevant channel of N ∗ (1650), N ∗ (1710), and N ∗ (1720) intermediate baryonic resonance states in the initial collision of the incoming pion with one of the target nucleons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Expressions for the reaction amplitudes are derived taking continuum particle wave function in the plane wave approximation. Numerical calculations are presented for reactions on 12C, 40Ca, 51V and 89Y target nuclei. The predictions of our model are in reasonable agreement with the available experimental data.

Prospects of the COMPASS hadron program with charged kaonic final states

The COMPASS experiment at CERN took data with a 190 GeV/c negative hadron beam on a fixed proton target in 2008. These data provide an opportunity to search for mesons with exotic J P C and for glueballs. A first glance on the ongoing analyses is presented. This includes the discussion of kaonic final states produced by incoming pions or kaons. The available statistics of the 2008 data allow an improved study of centrally produced resonances compared to previous experiments. Preliminary results on resonances in the kaonic final states are shown and discussed. The analysis of charged kaonic final states serves as an important cross-check of the ongoing neutral kaonic final state studies. In particular, we discuss prominent KKπ resonances which preferentially decay via K*(890) and the exclusive ϕπ production. Partial wave analyses of these final states are planned.

Low energy analyzing powers in pion–proton elastic scattering

Analyzing powers of pion–proton elastic scattering have been measured at PSI with the Low Energy Pion Spectrometer LEPS and a novel polarized scintillator target. Angular distributions between 40 and 120 deg (c.m.) were taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic energy for π+p scattering, and at 67.3 and 87.2 MeV for π−p scattering. These new measurements constitute a substantial extension of the polarization data base at low energies. Predictions from phase shift analyses are compared with the experimental results, and deviations are observed at low energies.

The reaction πN → ππN above threshold in chiral perturbation theory

Single pion production off nucleons is studied in the framework of relativistic baryon chiral perturbation theory at tree level with the inclusion of the terms from the dimension two effective pion-nucleon Lagrangian. The five appearing low-energy constants are fixed from pion-nucleon scattering data. Despite the simplicity of the approach, most of the existing data for total and differential cross sections as well as for the angular correlation functions for incoming pion kinetic energies up to 400 MeV can be satisfactorily described.

Estimates of hypernuclear production via the exclusive (p, K+) reaction

We investigate the possibility of producing hypernuclei with proton beams via (p, K +) reaction. We present differential cross sections calculations utilizing the distorted wave impulse approximation in momentum space. We consider the reactions12C(p,K +) 13 and16O(p,K +) 17 within the energy region 0.8 GeV1.2 GeV. We study both the case of formation ofΛ in S-state (12C) and P-state (16O). We take into account the contribution of both one-step and two-step processes when ΛK pair is produced directly by incoming proton and intermediate pion, respectively. It is found that practically in all cases the two-step processes give significant contribution.

Dynamics in skyrmions

Time-dependent solutions of the SU(2) Skyrme model in the hedgehog approximation are determined for classical pion-nucleon scattering at energies where the amplitude of the pion fluctuating field is large, and analysis in terms of normal modes no longer possible. The response by a skyrmion to incoming pions is determined for initial conditions of interest in relativistic heavy-ion collisions. There is no evidence for dramatic signals, such as an emerging pionic shock front, in the physical observables.

Pi pi -angular correlations for pi -p--> pi + pi -n in the region of the Delta dominance.

The reaction ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$n was studied at a total c.m. energy of 1301 MeV. The incoming pion beam was focused on a liquid hydrogen target. For the ${\mathrm{\ensuremath{\pi}}}^{+}$ detection a large acceptance spectrometer was used whereas the outgoing ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ was measured in a 4 sr detector arrangement. A collected set of 32 000 kinematical complete ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$n events delivered invariant mass distribution and double differential cross sections as well as angular correlation functions and triple differential cross sections, respectively. The observables, showing a characteristic deviation from phase space, are compared with model calculations based on Weinberg's Lagrangian. The dynamics of the reaction is well described. In addition, there are clear indications for the need of relativistic corrections, whereas the data do not justify strong contributions of \ensuremath{\sigma}- and \ensuremath{\rho}-propagation diagrams.

Pion absorption on polarized nuclear targets.

The availability of polarized nuclear targets for nuclear reaction studies offers new research directions. In this paper we present the distorted wave impulse approximation formalism and calculations for two-nucleon pion absorption on polarized nuclear targets. We assume that the pion absorbs on a $^{3}$${\mathit{S}}_{1}$ n-p pair and use phenomenological amplitudes to describe the \ensuremath{\pi}NN vertex. The effects of the distortions on the incoming pion and outgoing protons, in contrast to the elementary \ensuremath{\pi}NN vertex, are delineated for certain special cases in which the formalism simplifies. Predictions of cross sections and vector and tensor analyzing powers are made for polarized target nuclei $^{6}\mathrm{Li}$, $^{7}\mathrm{Li}$, $^{13}\mathrm{C}$, and $^{14}\mathrm{N}$ at pion incident energies of 115, 165, and 255 MeV.

Muons as a probe in solid state and surface physics and in materials research

Facilities providing muons are coming up more and more. Correspondingly, muons, positive (μ+) as well as negative (μ−), are increasingly being used as tools in pure and applied research. μ+ are needed for muon spin rotation (μsr) where one measures mainly internal magnetic fields, but also for channeling; in both cases the site where the muon or pion decays is of interest. In chemistry the μ+ acts as a marked light “proton”. μsr with μ− is also of some importance. Muonic X-rays, emitted when the μ− cascades down the atomic ladder, provide the unique opportunity to investigate quantitatively the elemental composition of a sample in a fully nondestructive way. Imaging with μ+ and μ− using the incoming pion or muon track and the outgoing decay electron track is possible and has been demonstrated. Slow muons (μ+ and μ−) are stopped in the surface layer (down to monomolecular layers) of a sample and are, hence, excellent thin-film and surface probes. Muonic hydrogen transfers the μ− to heavier atoms; this transfer can be used to study surfaces and the spatial structure of gaseous molecules. Present techniques and techniques envisaged for the future are reviewed; emphasis will be put on phase space compression of μ beams.

Use of a high-resolution, scintillating-fibre, tracking detector in recording π−-nucleon interactions at √ s ≈ 26 GeV

A scintillating-microfibre, tracking detector has been used at the CERN Omega spectrometer to record the interactions of 340 GeV/ cπ − particles incident on a fixed target. The detector - based on coherent bundles of ∼36 μm diameter, PMP-doped plastic fibres - was oriented so as to give views of interactions in the plane perpendicular to the incoming pions. Additional event information was provided by a series of 20 and 50 μm pitch silicon-microstrip detectors, placed near to the fibres, and by the spectrometer. An account is given of the contribution of the scintillating-fibre device in obtaining full event reconstruction.

Role of pion absorption on quasi-deuterons inC12(π+,2p)

Data by Altman et al. for exclusive pion absorption on /sup 12/C are reexamined using an impulse approximation formalism which treats pion absorption as proceeding only through absorption on a deuteronlike structure within the target nucleus. The results indicate that previous estimates of the strength of this quasi-deuteron absorption component of the reaction mechanism by Altman et al. are probably too low. Reasonable agreement with the shape and magnitude of the observed angular distribution is achieved by ignoring distortions for both the incoming pion and outgoing nucleons, with somewhat poorer agreement with inclusion of distortions.

The three dose components of negative pion beam and their role in pion radiotherapy.

A new method has been developed for analyzing therapeutic negative pion beams into three LET (linear energy transfer) dose components inherent in such a beam. The technique utilizes thin silicon detectors to obtain pulse height spectra produced by the various particles in the beam traversing the detectors. It is shown that a low LET group is correlated with the incoming pions, muons and electrons; a medium LET group corresponds to protons, deuterons, tritons, and high energy alpha particles; and a high LET group is due to low energy alpha particles, 3He and recoil particles. Several beams used clinically have been studied.

A binary encoded position-sensitive scintillation hodoscope

A position-sensitive scintillation hodoscope with reduced photomultiplier use has been built and used in experiments. This device is a fast, economical counter which has good timing characteristics and spatial resolution. Isolated strips of plastic scintillator (NE102) form a single layer (per coordinate) detecting surface, and are coupled by adiabatic light guides to photomultiplier tubes (RCA 8575). The light guides are encoded into a binary readout pattern, termed “error-free”, because the code identifies inefficient and multiple track events or the valid position measurement. These counters were successfully used to measure the incoming pion trajectories in a small angle scattering experiment.

Separation of theΔΔandNNcomponents of the deuteron by the kinematics of high energyπDreactions

The kinematics of the reaction $\ensuremath{\pi}+d\ensuremath{\rightarrow}\ensuremath{\pi}+N+\mathrm{anything}$ is analyzed for 15 GeV incoming pions. It is shown that by observing both the invariant mass and the angular correlations of backward $\ensuremath{\pi}N$ events one can insure that the observed particles arise from the decay of a spectator $\ensuremath{\Delta}$ in a quasifree scattering event, i.e., they give a quantitative estimate of the $\ensuremath{\Delta}\ensuremath{\Delta}$ admixture of the deuteron. Failure of experimental observation of such events would indicate a failure of the effective Lagrangian formalism.NUCLEAR REACTIONS Quasifree scattering, $\ensuremath{\Delta}$ admixture.

(π +,p) Reaction in12C

Hartree-Fock wave functions obtained from realistic nucleon-nucleon interaction are employed to calculate cross-sections for the reaction12 C(π +,p)11 C(g.s.). These wave functions take into account central correlations between nucleons inside the nucleus. This itself is found to change the cross-section by more than an order of magnitude. The incoming pion is represented by a plane wave while proton-distortion is taken into account in the high-energy or semi-classical approximation, thereby determining the proton optical well parameters. These values agree well with those obtained by more conventional methods. Variation of the cross-section with the oscillator well parameter is also studied. Calculations have been made using the one-nucleon mechanism for the pion-absorption process.

Single-particle distributions in inclusiveπ−preactions at 10.0 and 15.5 GeV/c

Single-particle distributions have been measured at the Stanford Linear Accelerator Center for the inclusive processes ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}X$ and ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}X$ at 10.0 and 15.5 GeV/c. The kinematic range for secondary pions was ${p}_{T}=0.15$ GeV/c to 0.9 GeV/c and $x=0 \mathrm{to} 0.5$. The differential cross sections have been assumed to be slowly varying and have been fitted to smooth functions of $x$ and ${p}_{T}$. Cross sections have been obtained for all incoming and outgoing pion charges. The cross sections for the reactions with incident and outgoing pions of like charge are higher than those for unlike charge, but have similar shape. The cross section as a function of the rapidity is plotted together with that of $pp$ inclusive scattering at CERN ISR energies, for the purpose of comparing pion and proton fragmentation.

Search forμ→e+e+e

We have made a search for the neutrinoless decay mode $\ensuremath{\mu}\ensuremath{\rightarrow}e+e+e$. Positive poins from the Berkeley 184-in. synchrocyclotron were stopped in a lithium target. The detection of three decay particles not in coincidence with an incoming pion served to trigger two thin-plate spark chambers viewing the decays. The energy of the decay particles was measured with a combination of NaI counters and range telescopes. The spark chamber pictures were first scanned for events with three tracks meeting at a common point in the target. A requirement that no angle between any of the three tracks could be greater than 160\ifmmode^\circ\else\textdegree\fi{} eliminated essentially all of the main source of background, namely, knock-on collisions of electrons passing through the target. Further requirements for the three tracks to be coplanar and for each particle to have at least 16 MeV eliminated all but one ambiguous event. For this event insufficient energy information was available. If we assume that one event to be $\ensuremath{\mu}\ensuremath{\rightarrow}e+e+e$, and with a calculated detection efficiency of 0.0083, an upper limit for the branching ratio for this mode can be set at 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ with a 90% confidence level.

Dispersion Relations for Virtual Pion-Nucleon Scattering

In connection with a proposed calculation of single pion production in nucleon-nucleon collisions, the process of pion-nucleon scattering in which the incoming pion is virtual is investigated by means of the dispersion theoretic method developed by Chew, Goldberger, Low and Nambu. The static limit is studied in detail and the Chew-Low amplitude for virtual scattering is shown to result for small virtual pion masses. More generally, it is proposed that the Blankenbecler-Gantenhaus solution, which is recorded, may provide a useful approach in applications in which large virtual pion masses play an essential role. (auth)

π−-Nucleon Interactions at 4.5 Bev

An emulsion study has been made of ${\ensuremath{\pi}}^{\ensuremath{-}}$-nucleon interactions at a pion energy of 4.5 Bev. The percentage of elastic scattering at this energy seems slightly smaller than at energies slightly above 1.0 Bev. One can deduce from this that the range of interaction between ${\ensuremath{\pi}}^{\ensuremath{-}}$ and proton is greater than 1.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm.The inelastic interactions resulting in two prongs have been considered in some detail. The angular distributions are suggestive of a direct knock out of a pion by the incoming pion. The momentum distributions obtained recently from diffusion chamber work at Berkeley also seem to support such a model. The four- and six-prong events are more complicated. The data from all inelastic interactions indicate the nucleons seem to go strongly in the backward direction in the c.m. system. Thus none of the interactions seem consistent with the statistical model of pion production.