Pion Proton Research Articles

Total pion\u2013proton cross section from the new LHCf data on leading neutrons spectra

In the light of the latest data by the LHCf collaboration of the LHC on leading neutrons spectra it is possible to obtain total pion–proton cross sections in the TeV energy region. In this work the exact extraction procedure is shown. Final results for the pion–proton cross section are collected at several different values of the colliding energy and compared with some popular theoretical predictions. The errors of the results are estimated.

Higher-twist mechanism and inclusive gluon production in pion–proton collisions

We calculate the contribution of the higher-twist Feynman diagrams to the large-[Formula: see text] inclusive gluon production cross-section in [Formula: see text] collisions in case of the running coupling and frozen coupling approaches within perturbative and holographic QCD. The structure of infrared renormalon singularities of the higher-twist subprocess cross-section is obtained and the resummed higher-twist cross-sections (Borel sum) with the ones obtained in the framework of the frozen coupling approach and leading-twist cross-section are compared and analyzed.

Neutron detection using a crystal ball calorimeter

The program of experiments of the A2 Collaboration performed on a beam of tagged photons of the MAMI electron microtron in Mainz (Germany) includes precision measurements of the total and differential cross sections of the pion photoproduction on neutrons of a deuterium target. The determination of the detector ability to detect neutrons is undoubtedly one of the important problems of the experiment. The calorimetric system of the detector contains a segmented NaI Crystal Ball detector, which gives information about the position, energy, and detection time of neutral and charged particles in a wide angular range. In this work, we describe the measurement of the neutron detection efficiency in the energy range from 20 to 400MeV. The results are compared with BNL data obtained on a pion beam and proton target.

Proton–proton, pion–proton and pion–pion diffractive collisions at ultrahigh energies

The LHC energies are those at which the asymptotic regime in hadron–hadron diffractive collisions (pp, πp, ππ) might be switched on. Based on results of the Dakhno–Nikonov eikonal model which is a generalization of the Good–Walker eikonal approach for a continuous set of channels, we present a picture for transformation of the constituent quark mode to the black disk one. In the black disk mode [Formula: see text], we have a growth of the logarithm squared type for total and elastic cross-sections, σ tot ~ ln 2 s and σ el ~ ln 2 s and [Formula: see text]-scaling for diffractive scattering and diffractive dissociation of hadrons. The diffractive dissociation cross-section grows as σD ~ ln s, σDD ~ ln s, and their relative contribution tends to zero: σD/σ tot → 0, σDD/σ tot → 0. Asymptotic characteristics of diffractive and total cross-sections are universal, and this results in the asymptotical equality of cross-sections for all types of hadrons (the Gribov universality). The energy scale for switching on the asymptotic mode is estimated for different processes.

High precision measurements of the pion proton elastic scattering and kaon-lambda production in the EPECUR experiment

Study of the pion-nucleon scattering can produce a rich information on the dynamics of the strong interaction and baryon spectroscopy. The EPECUR collaboration is aimed at the research of baryon resonances in the second resonance region in s-channel via pion-proton elastic scattering and kaon-lambda production.

John Riley Holt. 15 February 1918 — 6 January 2009

John Riley Holt was an experimental physicist who dedicated his working life to research in nuclear and particle physics at the University of Liverpool. He was born in 1918 in Runcorn, Cheshire, and in 1938 was awarded a first-class honours degree in physics at Liverpool University. He obtained his PhD in 1941 and became a member of Sir James Chadwick’s team working on the UK atomic weapon project. After the war he developed several new experimental techniques, which he used to make a systematic study of the deuteron stripping process with the use of the Liverpool cyclotron. After the Liverpool synchro-cyclotron became operational in 1954 he initiated a programme of precision measurements of cross-sections for proton–proton and pion–proton scattering. After the first observation of parity violation in 1957, his group completed an important experiment that observed parity violation in muon decay. When the construction of an electron synchrotron (NIN A, at the Daresbury Laboratory) was proposed, he became leader of the magnet design team. As NIN A became operational in 1966, John established a group to measure the cross-sections for the photoproduction of neutral and charged pions. The group then developed a collaboration with colleagues in other universities to measure the spin dependence of cross-sections for meson photoproduction by using a polarized photon beam and a polarized proton target. Before his retirement he contributed to the design of the experiment to determine the spin structure of the proton, performed by the European Muon Collaboration.

Experimental Setup for Measuring P Asymmetry in the Resonance Region of Elastic Pion–Proton Scattering

The SPIN-P experimental setup was designed for measuring the P asymmetry during pion scattering into the backward hemisphere at a minimum differential cross section of elastic πpscattering. The physical grounds of the experiment and the results of its simulation by the Monte Carlo method are presented. The setup is composed of a polarized proton target in a superconducting solenoid with vertical polarization of free protons, wire track detectors, scintillation counters, electronics for data readout and processing, and an appropriate computer network. The experimental program has been under way since 2002 on the pion beam of the proton synchrotron at the Institute of Theoretical and Experimental Physics (Moscow).

Non-identical particle correlations in 130 and 200 A GeV collisions at STAR

STAR has performed correlation analyses of pion–kaon and pion–proton pairs for and and kaon–proton, proton–Lambda and pion–Cascade pairs for AuAu collisions . They show that average emission spacetime points of pions, kaons and protons are not the same. These asymmetries are interpreted as a consequence of transverse radial expansion of the system; emission time differences explain only part of the asymmetry. Therefore our measurements independently confirm the existence of transverse radial flow. Furthermore, correlations of strange hyperons are investigated by performing proton–Lambda and pion–Cascade analyses, giving estimates of source size at high mT. The strong interaction potential between (anti-)proton and lambda as well as kaon and proton is investigated.

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.

Hadron–hadron interactions at high energy via Rademacher functions

Charged particles multiplicity distributions for hadron–hadron interactions at high energy have been studied. Two cases are considered: the proton–proton (p–p) and the pion–proton (π–p) interactions. The parton two-fireball model based on an impact parameter is adopted. The overlapping functions, known to be complicated and nonlinear, are approximated employing a series of Rademacher functions. The analysis has been facilitated, since Rademacher functions are linear, analytic and mathematically simple. The accuracy of the approximation is tunable through the order of the employed Rademacher functions. Theoretical expressions for inelastic cross-sections and the charged multiplicity distributions have been derived employing the proposed representation. Figures are provided to demonstrate good agreement between theoretical calculations and experimental data at different energies. Formulae for the change of some important parameters with the variation of high energy have been derived employing least square curve fitting techniques.

Asymmetries between strange and antistrange particle production in pion–proton interactions

Recent measurements of the asymmetries between Feynman x distributions of strange and antistrange hadrons in π − A interactions show a strong effect as a function of x F . We calculate strange hadron production in the context of the intrinsic model and make predictions for particle/antiparticle asymmetries in these interactions.

Testbeam results on particle identification with aerogel used as RICH radiator

We present the results obtained by testing in a beam sample of silica aerogel which is foreseen as one of the radiators for the Ring Imaging Cherenkov counter of LHCb. Pion and proton beams with momenta ranging from 6 to 10 GeV/ c traversed different thickness of aerogel. Two large diameter (12 cm) Hybrid Photodiodes with 2048 channels, produced at CERN, were used as photodetectors. The number of photoelectrons and the radius of the Cherenkov rings allowed pion–proton separation over the whole considered momentum range.

The modified additive quark model applied to the elastic and charge exchange pion proton reaction

The modified additive quark model (MAQM) successfully used in pp and p p elastic scattering and also in pion proton total cross section is applied to the description of differential cross section in pion proton scattering (elastic and charge exchange). The spin-flip components of pomeron and secondary reggeons are included permitting to describe polarization.

A UNIVERSAL NEURAL NETWORK REPRESENTATION FOR HADRON–HADRON INTERACTIONS AT HIGH ENERGY

An efficient neural network (NN) has been designed to simulate the hadron–hadron interaction at high energy. Two cases have been considered simultaneously, the proton–proton (p–p) and the pion–proton (π-p) interactions. The neural network has been trained to produce the charged multiplicity distribution for both cases based on samples from the overlapping functions. The trained NN shows a good performance in matching the trained distributions. The NN is then used to predict the distributions that are not present in the training set and matched them effectively. The robustness of the designed NN in the presence of uncertainties, in the overlapping functions has been demonstrated.

A low-energy π/μ identifier

The design and testing of a π/μ identifier suitable for use in pion–proton elastic scattering experiments in the momentum range 65–160 MeV/ c is described. A neural network technique is used for particle identification. The apparatus (a multilayer scintillator stack) was found to have a particle identification efficiency of better than 98%.

Low-energy differential cross sections of pion-proton ( pi +/-p) scattering. I. The isospin-even forward scattering amplitude at T pi =32.2 and 44.6 MeV.

The values of the pion nucleon (\ensuremath{\pi}N) \ensuremath{\sigma} term, as determined, on the one hand, from experimental pion nucleon scattering by means of dispersion relations and, on the other hand, from baryon masses by means of chiral perturbation theory, differ by 10 to 15 MeV. The origin of this discrepancy is not yet understood. If the difference between the two values is attributed to the scalar current of strange sea quark pairs within the proton, the contribution to the proton mass would be of the order of 120 MeV. The discrepancy may hint at either theoretical deficiencies or an inadequate \ensuremath{\pi}N database. In order to provide reliable experimental data we have measured angular distributions of elastic pion proton scattering at pion energies ${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}$=32.2 and 44.6 MeV using the magnet spectrometer LEPS located at the Paul-Scherrer-Institute (PSI) in Villigen, Switzerland. From the data covering the region of the Coulomb nuclear interference, the real parts of the isospin-even forward scattering amplitude Re${\mathit{D}}^{+}$(t=0), have been determined as a function of energy. The results have been compared with the predictions of the Karlsruhe-Helsinki phase shift analysis KH80, revealing discrepancies most pronounced for the ${\mathrm{\ensuremath{\pi}}}^{+}$p data. The experimentally determined values for Re${\mathit{D}}^{+}$(t=0), however, support the KH80 prediction (which is based on \ensuremath{\pi}N data available in 1979).

Pion and fast proton production in $$\bar p$$ A annihilation at rest

We consider annihilation pions scattering and absorption inside the nucleus to analyse fast proton production in $$\bar p$$ A annihilation. The method suggested allows description of both pion and proton spectra, particularly high energy proton tail. New experimental data obtained at LEAR are analysed and we have found an extraordinary behaviour of pion scattering and absorption probabilities depending on atomic number.

Intermediate energy bremsstrahlung and the structure of free and bound hadrons: Radiative pion proton scattering, pion decay and muon capture

Experimental data on pion-proton bremsstrahlung, radiative pion decay and radiative muon capture are reviewed to demonstrate that the study of intermediate energy bremsstrahlung processes can reveal additional information on hadron structure inaccessible in their non-radiative counterparts.

Breit–Wigner resonance and the delta++

Pion–proton cross-section data from the literature are used to illustrate how the delta++ resonance is analyzed to obtain the rest mass energy of 1232 MeV and the width of 112 MeV. This example illustrates the approximate nature of the Breit–Wigner resonance formula with its corresponding Lorentzian shape. Also, the way in which the wavelength of the bombarding particle, which appears in the resonance formula, should be determined for a relativistic situation such as this is discussed.

Experiments at TRIUMF on radiative processes

The current program of nucleon and pion radiative capture and proton–proton bremsstrahlung measurements at TRIUMF is described. Neutron radiative capture with polarized beam and target is suggested as a possible future experiment.