Antiproton-proton cross sections at 200 and 900 GeV c.m. energy

Data on antiproton-proton cross sections at the c.m. energies 200 and 900 GeV are presented. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode in which the same beams were accelerated and decelerated between beam energies of 450 and 100 GeV. The properties of the machine determine the ratio of the luminosities at the two energies to about 1% and thus an accurate measurement of the ratioR of the inelastic cross sections could be made. We findR (=σ ⁹⁰⁰/σ ²⁰⁰)=1.20±0.01±0.02, where the first error is statistical and the second systematic. Interpolating existing data to estimateσ _ine1(200 GeV) this measurement ofR leads toσ _ine1(900 GeV)=50.3+0.4+1.0 mb. Using an extrapolated value ofσ _e1/σ _tot we estimate the total cross section at 900 GeV to be 65.3±0.7±1.5 mb. Both the inelastic and total cross sections are compatible with a ln² s dependence. Comparisons are made with different fits to the total cross section energy dependence.     

Muon spin relaxation as a probe of molecular dynamics of organometallic compounds

LF‐Muon Spin Relaxation data are reported for the organometallic compounds Pb(C₆H₅)₄, (C₆H₆)Cr(CO)₃ and (C₅H₅)₂Ru. In each case the change in relaxation rate with temperature shows a peak analogous to the T_1 minimum in NMR. The activation parameters were calculated, and the mechanism of muon spin relaxation in the case of (C₆H₆)Cr(CO)₃ is shown to be the reorientation motion of the benzene ring. This revised version was published online in August 2006 with corrections to the Cover Date.     

SSRF前端区锯齿墙束流孔洞中子屏蔽的蒙特卡罗估算

主要关于上海同步辐射装置(SSRF)储存环电子引发产生的韧致辐射和中子辐射的研究.中子和光子经多种组合材料(厚度在5cm-115cm之间)屏蔽后的剂量特征由蒙特卡罗代码McNP和EGSnrc估算得到;蒙特卡罗计算表明,单一的材料如铅,铁和聚乙烯对高能中子是无效的生物屏蔽材料,而组合材料如铅或者铁加聚乙烯和铅或者铁加混凝土被认为是屏蔽高能中子很好的组合材料.铅铁等高Z材料加点包含有氢的低Z材料如聚乙烯是同时屏蔽高能中子和韧致辐射的一种比较好的组合材料选择.     

Molecular sensors using a resonance Raman template

The potential use of resonance Raman spectroscopy as a molecular sensing tool is illustrated using a metalloporphyrin template and pyridine as an analyte. The equilibrium binding constant for the axial binding of pyridine to zinc tetraphenylporphyrin has been measured using resonance Raman spectroscopy. Although no new peaks are observed and the porphyrin peaks do not shift position, the quantification is made possible by the selective resonance enhancement of the template vibrations. The value for log k was determined by resonance Raman to be 3.65 +/- 0.32, which compares well with previously published values estimated using absorption data. Values for log k were determined for a series of related compounds, the picolines, and these also compare favourably with those previously reported.     

Muon implantation of metallocenes: ferrocene

Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17 T, for the low-temperature phase at 18 K. The high-temperature phase at 295 K shows that only the last feature shifted down to about 0.49 T and a muon spin relaxation peak at about 0.106 T which approaches zero field when reaching the phase transition temperature of 164 K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe-Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the muSR spectra of ferrocene was estimated to be 584 K. Correlation time for the ring rotation dynamics of the Fe-Mu radical at this temperature is 3.2 ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported.     

Longitudinal optical-transverse optical (L.O.-T.O.) splitting on internal modes in the Raman spectra of noncentric crystals

A qualitative, but detailed, account of the phenomenon of L.O.-T.O. splitting in the Raman spectroscopy of noncentrosymmetric crystals is given. Tables are provided which give predictions for 45°, 90°, and 180° scattering geometries for all such crystals.     

A pyridine ring-containing ecdysteroid from Diploclisia glaucescens

A novel pyridine ring-containing ecdysteroid, named diploclidine, was isolated from the methanol extract of the leaves of Diploclisia glaucescens, and its structure was determined by spectral means.     

Photon production at c.m. energies of 200 and 900 GeV

We present data on photon production in non single-diffractivep \(\bar p\) -collisions at c.m. energies of 200 and 900 GeV. Besides the general properties of photon production, i.e. pseudorapidity distribution and average multiplicity, we also investigate photon-charged two-particle pseudorapidity and multiplicity correlations. We find for the average number of photons in non single-diffractivep \(\bar p\) -collisions 22.2±1.4±2.0 at 200 GeV and 41.4±2.1±3.5 at 900 GeV, where the first error is statistical and the second systematic. The analysis of photon-charged particle multiplicity correlations reveals strong positive correlations between the average number of photons and the number of simultaneously produced charged particles, as expected from FNAL and ISR studies and from our result at 546 GeV. We obtain for the correlation slope 0.95±0.08±0.11 at 200 GeV and 1.09±0.09±0.13 at 900 GeV (first error is statistical and the second systematic). The investigation of photon-charged two-particle pseudorapidity correlations shows that these correlations are of short range and compatible with the observed charged two-particle pseudorapidity correlations. These correlations and the results for the average number of photons as a function of the produced number of charged particles favour the conclusion that photon sources other than π⁰ s contribute significantly to the observed photon yield in non single-diffractivep \(\bar p\) -collisions. For example, if all photons are assumed to come from π⁰ s and η mesons, a η/π⁰ ratio of about 20% is inferred.     

Scaling of pseudorapidity distributions at c.m. energies up to 0.9 TeV

New data are presented on charged particle pseudorapidity distributions for inelastic events produced at c.m. energies \(\sqrt s \) =200 and 900 GeV. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode. The rise of the central density ρ(0) at energies up to \(\sqrt s \) =900 GeV has been studied. A new form of central region scaling is found involving the densityρ _n (0) for charged multiplicityn, namely that the scaled central densityρ _n (0)/ρ(0) expressed as a function ofz=n/〈n〉 is independent ofs. Scaling in the fragmentation region holds to 10–20%, and the small amount of scalebreaking observed here could be accommodated within the framework suggested by Wdowcyk and Wolfendale to account for both accelerator and cosmic ray data.