The photoproduction of neutral pions from protons between 0.7 GeV and 1.7 GeV

Measurements of differential cross sections for pi-zero photoproduction from protons have been made at angles between 60° and 140° c.m. in the photon energy range 0.7 GeV to 1.7 GeV. The data are compared with the rits provided by three recent partial-wave analyses of pion photoproduction and some significant discrepancies observed.     

Correlations between neutral and charged pions in multiparticle production

We make a theoretical and phenomenological study of correlations between neutral and charged pions in multiparticle production in the framework of the so-called σ, π, ? and ?-? models. Following the method of Drijard and Pokorski, we express the predictions of various models in terms of the negative multiplicity distribution, which is known experimentally. In particular we compute the average number of $\text{π}{}^0\text{,}\text{n}{}_0\text{(n\_)}$, and the integral of π⁰?π⁰ correlations, f₀²(n_), as a function of the number of negative pions; we study also the total multiplicity distribution P(N) and its first two moments $\text{N}\text{and}\text{D}{}_{\mathrm{<mtext>tot</mtext>}}{}^2$. We show that with the present experimental accuracy neither $\text{n}{}_0\text{(n\_)}$ allow us to discriminate between the different models.     

Multiplicity of charged particles in 800 GeV p-p interactions

Results are reported concerning the charged-particle multiplicity distribution obtained in an exposure of the high-resolution hydrogen bubble chamber LEBC to a beam of 800 GeV protons at the Fermilab MPS. This is the first time that such data have been available at this energy. The distribution of the number n_ch of charged particles produced in inelastic interactions obeys KNO-scaling. The average multiplicity is 〈n_ch〉 = 10.26±0.15. For n_ch⩾8 the data can be well fitted to a negative binomial. The difference between the overall experimental multiplicity distribution and that resulting from the latter fit is in agreement with the contribution expected from diffractive processes.     

γ production and multiplicity correlations between neutral and charged pions in pp interactions at 69 GeV/c

From 3500 γ's observed in the 4.7 m HBC MIRABELLE at Sepukhov, we obtain the dependence on n_? of the average number of produced π^0,s, 〈n₀〉, and the π⁰π⁰ correlation parameter, $\text{?}{}_2{}^{00}$. We present also the $\text{?}{}_2{}^{\mathrm{??}}$ and $\text{?}{}_2{}^{\mathrm{+0}}$ parameters and information concerning KNO scaling. Various momentum distributions are given. The invariant γ cross sections distributions are compared with corresponding data at other energies.     

Photoproduction of neutral pions on hydrogen below 500 MeV

At the Bonn 500 MeV electron synchrotron differential cross sections of the reactionγ+p→Π ⁰+p were measured in the kinematical region of photon energies between 340 and 420 MeV and pionCM angles from 10° to 70° by means of detecting the two photons from the pion decay by two Cherenkov counters.     

Multiplicity of charged secondaries emitted in association with neutral strange particles in antiproton-nucleus collisions at 40 GeV/c

In collisions of 40-GeV/c antiprotons with D, Li, C, S, Cu, and Pb nuclei, mean multiplicities of various secondary particles are investigated as functions of the mass number A. The mass-number dependence of the mean multiplicities of positively charged particles suggests that the effect of intranuclear cascades is strong for the emission of Λ hyperons, but that it is relatively weak for the emission of either K ⁰ or $\bar \Lambda $ . Also measured are the yields of various neutral strange particles with respect to those of charged secondaries.     

A study of fluctuations and correlations in deep-inelastic muon-nucleon scattering at 280 GeV

Using data of the European Muon Collaboration on muon-proton and muon-deuteron scattering at 280 GeV, an intermittency analysis in one, two and three phase space dimensions is carried out. In addition, a factorial correlator analysis and a multifractal analysis, both in one dimension (rapidity), are presented.     

Photoproduction of neutral pions off hydrogen at photonenergies between 0.55 and 2.2 GeV at a cm-angle of 120°

The differential cross section has been measured for the reaction γ+p→π^o + p at the Bonn 2.5 GeV electron synchrotron in the energy range from 0.55 to 2.2 GeV at a c.m.angle of 120 degrees.     

Multiplicity structure of the hadronic final state in diffractive deep-inelastic scattering at HERA

The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type , where Y is a hadronic system with mass GeV and where the squared momentum transfer at the pY vertex, t, is limited to , is studied as a function of the invariant mass of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-of-mass system of X. The data are compared to results in annihilation, fixed-target lepton-nucleon collisions, hadro-produced diffractive final states and to non-diffractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a significant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the diffractive structure function, which assumes a large hard gluonic component of the colourless exchange at low . A model with soft colour interactions is also successful. Received: 27 April 1998 / Published online: 3 September 1998     

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.     

Elastic backward scattering of negative pions on neutrons at 23 and 40 GeV/c

The differential cross sections of the elastic backward scattering reaction π⁻n→nπ⁻ has been measured at 23 and 40 GeV/c in the u-interval −0.07 ? u ? 0.01 (GeV/c)².     

Millimeter-wave scattering from neutral and charged water droplets

We investigated 94 GHz millimeter-wave (MMW) scattering from neutral and charged water mist produced in the laboratory with an ultrasonic atomizer. Diffusion charging of the mist was accomplished with a negative ion generator (NIG). We observed increased forward- and backscattering of MMW from charged mist, as compared to MMW scattering from an uncharged mist. In order to interpret the experimental results, we developed a model based on classical electrodynamics theory of scattering from a dielectric sphere with diffusion-deposited mobile surface charge. In this approach, scattering and extinction cross-sections are calculated for a charged Rayleigh particle with effective dielectric constant consisting of the volume dielectric function of the neutral sphere and surface dielectric function due to the oscillation of the surface charge in the presence of applied electric field. For small droplets with radius smaller than 100 nm, this model predicts increased MMW scattering from charged mist, which is qualitatively consistent with the experimental observations. The objective of this work is to develop indirect remote sensing of radioactive gases via their charging action on atmospheric humid air.     

Photoproduction of neutral pions on hydrogen at photon energies between 200 and 440 MeV

At the Bonn 500 MeV electron synchrotron the differential cross section of the reaction γ+p → π⁰+p has been measured detecting the recoil proton by a magnetic spectrometer. Angular distributions between pion c.m. angles of 50 ° and 160 ° were taken at photon energies between 220 and 420 MeV.     

Fluctuations of the number of neutral pions at high multiplicity in pp interactions at 50 GeV

Results obtained by measuring fluctuations of the number of neutral pions in the SERP-E-190 Experiment (Thermalization Project) upon irradiating a liquid-hydrogen target of the SVD-2 setup with a beam of 50-GeV protons are presented. A simulation of the detection of photons from the decay of neutral pions with the aid of an electromagnetic calorimeter revealed a linear relation between the number of detected photons and the mean number of neutral pions in an event. After the introduction of corrections for the loss of charged tracks because of a limited acceptance of the setup, trigger operation, and the efficiency of the data-treatment system, distributions of the number of neutral pions, N ₀, were obtained for each value of the total number of particles in an event, N _tot = N _ch + N ₀. The fluctuation parameter ?? = D/??N ₀?? was measured. In the region N _tot > 22, fluctuations of the number of neutral pions increase, which, within statistical models (GCE, CE, MCE), indicates that the system involving a large number of pions approaches the pion-condensate state. This effect was observed for the first time.     

Multiplicity distributions and double scattering effects in π−d interactions at 205 GeV

Multiplicity distributions of charged secondaries, σ_N(π^?d) are obtained. The effective multiplicities σ_N(π^?n) and σ_N(π^?p) are extracted using the measured spectator momentum. The probability of double scattering P_N is found to be independent of multiplicity.     

Elastic backward scattering of negative pions on protons at 25 and 38 GeV/c

The backward elastic scattering reaction π^?p → pπ^? at momenta 25 and 38 GeV/c have been measured using a magnetic spectrometer with hybrid chambers. The experimental data on the dependence of the cross section dσ/du on the momentum transfer u as well as the energy dependence dσ/du at u = 0 are given.     

Production of neutral strange particles in muon-nucleon scattering at 490 GeV

The production ofK ⁰, and particles is studied in the E665 muon-nucleon experiment at Fermilab. The average multiplicities and squared transverse momenta are measured as a function ofx _F andW ². Most features of the data can be well described by the Lund model. Within this model, the data on the K⁰/^± ratios and on the averageK ⁰ multiplicity in the forward region favor a strangeness suppression factors/u in the fragmentation process near 0.20. Clear evidence for QCD effects is seen in the average squared transverse momentum ofK ⁰ and particles.Deceased