Evidence for a high mass enhancement in K+K− photoproduction

The reaction γp → K⁺K^? p has been investigated with tagged photons in the energy range of 20 < E_γ < 70 GeV. A structure in the 1.7 GeV mass region is observed and interpreted in terms of a recurrence of the ø.     

Investigating the mechanisms of diamond polishing using Raman spectroscopy

Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe₃O₄) and haematite (α-Fe₂O₃), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides.     

Testing heteroscedasticity by wavelets in a nonparametric regression model

In the nonparametric regression models, a homoscedastic structure is usually assumed. However, the homoscedasticity cannot be guaranteed a priori. Hence, testing the heteroscedasticity is needed. In this paper we propose a consistent nonparametric test for heteroscedasticity, based on wavelets. The empirical wavelet coefficients of the conditional variance in a regression model are defined first. Then they are shown to be asymptotically normal, based on which a test statistic for the heteroscedasticity is constructed by using Fan's wavelet thresholding idea. Simulations show that our test is superior to the traditional nonparametric test.     

Testing coeffcients of AR and bilinear time series models by a graphical approach

AR and bilinear time series models are expressed as time series chain graphical models, based on which, it is shown that the coefficients of AR and bilinear models are the conditional correlation coefficients conditioned on the other components of the time series. Then a graphically based procedure is proposed to test the significance of the coeffcients of AR and bilinear time series. Simulations show that our procedure performs well both in sizes and powers.     

The reaction γp → pπ+π−π+π− for photon energies from 25 to 70 GeV

Measurements of the reaction γp → pπ⁺π^?π⁺π^? are presented, in which π⁺π^?π⁺π^? systems with masses up to 3 GeV are produced from fragmentation of the incident photon. The reaction is dominated by production of the large peak of the ?′(1600) meson and, at higher masses ?2 GeV, y production of jet-like 4π systems. The ?′(1600) meson is produced by a predominantly s-channel helicity conserving mechanism. At higher masses there are also indications of ?π peaks, of masses 1.3 GeV (the A₂ meson) and 1.75 GeV, produced with a recoiling π meson by a mechanism consistent with the Deck effect.     

Proton-antiproton states in high energy photoproduction

Exclusive and inclusive $\text{p}\text{p}$ photoproduction (with ? 2 accompanying charged particles) have been measured in the photon energy range 44–70 GeV. The exclusive process shows no prominent features; the inclusive process shows evidence for S(1936) production as a resonant-like structure with mass 1930 ± 2 MeV and width 12 ± 7 MeV.     

Inclusive photoproduction of φ-mesons at photon energies of 25–70 GeV

Results are presented on inclusive φ photoproduction for incident energies between 25 and 70 GeV. Distributions in Feynman x, p_T and decay angles are presented and interpreted in terms of quark fusion models. We demonstrate a similarity with the corresponding pion-induced reaction and obtain information on the hadronic nature of the photon.     

Photoproduction of ϱ0 and ω on hydrogen at photon energies of 20 to 70 GeV

We present results on photoproduction of ?⁰ and ω in the reactions γp→π⁺π^?p and γp→π⁺π^?π⁰p by tagged photons in the energy ranges 20 to 70 GeV and 20 to 45 GeV, respectively. The production of the ?⁰ shows dominantly the characteristics of a diffractive process with respect to the E_γ and t dependence of the cross section and the spin density matrix. The ?⁰ photoproduction yields on average over the photon energy range a total cross section of σ(γp→?⁰p) = 9.4±0.1 μb with an additional systematic error of ±1 μb, and average slope parameters of the t distribution dσ/dt≈exp(?b|t| + ct²), of b=9.1±0.1 GeV^?2 and c = 3.1 ±±0.2 GeV^?4. The shape of the ?⁰ peak in the π⁺π^? invariant spectra shows a skewing similar to that observed at lower energies. The photoproduction of ω is also consistent with a diffractive process and has a cross section of σ(γp→ωp) = 1.2± 0.1 μb with an additional systematic error of ±0.2 μb. The average slope parameters of the t distribution are b=8.3 ± 1.3 GeV^?2 and c = 3.4±2.6 GeV^?4.