康普顿背散射技术对贮存环电子束诊断及其应用 II贮存环电子束的极化度测量

简单介绍以激光 电子康普顿背散射原理为基础建立的康普顿背散射极化仪,采用它能实时、非破坏性地监测电子束的极化.该项工作可作为上海激光电子γ源(SLEGS)低能γ束应用研究的内容之一.     

A precision measurement of pp elastic scattering cross-sections at intermediate energies

We have measured differential cross-sections for elastic scattering with internal fiber targets in the recirculating beam of the proton synchrotron COSY. Measurements were made continuously during acceleration for projectile kinetic energies between 0.23 and 2.59 GeV in the angular range . Details of the apparatus and the data analysis are given and the resulting excitation functions and angular distributions presented. The precision of each data point is typically better than 4%, and a relative normalization uncertainty of only 2.5% within an excitation function has been reached. The impact on phase shift analysis as well as upper bounds on possible resonant contributions in lower partial waves are discussed.Received: 24 March 2004, Published online: 19 October 2004PACS: 25.40.Cm Elastic proton scattering - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 13.85.Dz Elastic scattering - 21.30.-x Nuclear forces     

Measurement of dijet production at low <Emphasis Type="Italic">Q</Emphasis><Superscript>2</Superscript> at HERA

Triple differential dijet cross sections in interactions are presented in the region of photon virtualities 2 < Q ² < 80 GeV², inelasticities 0.1 < y < 0.85, jet transverse energies E ^* _{T 1} > 7 GeV, E ^* _{T 2} > 5 GeV, and pseudorapidities . The measurements are made in the centre-of-mass frame, using an integrated luminosity of 57 pb^-1. The data are compared with NLO QCD calculations and LO Monte Carlo programs with and without a resolved virtual photon contribution. NLO QCD calculations fail to describe the region of low Q ² and low jet transverse energies, in contrast to a LO Monte Carlo generator which includes direct and resolved photon interactions with both transversely and longitudinally polarised photons. Initial and final state parton showers are tested as a mechanism for including higher order QCD effects in low E _T jet production.Received: 13 January 2004, Revised: 21 July 2004, Published online: 18 August 2004     

Searches for neutral Higgs bosons in extended models

Searches for neutral Higgs bosons produced at LEP in association with Z bosons, in pairs and in the Yukawa process are presented in this paper. Higgs boson decays into b quarks, leptons, or other Higgs bosons are considered, giving rise to four-b, four-b + jets, six-b and four- final states, as well as mixed modes with b quarks and leptons. The whole mass domain kinematically accessible at LEP in these topologies is searched. The analysed data set covers both the LEP1 and LEP2 energy ranges and exploits most of the luminosity recorded by the DELPHI experiment. No convincing evidence for a signal is found, and results are presented in the form of mass-dependent upper bounds on coupling factors (in units of model-independent reference cross-sections) for all processes, allowing interpretation of the data in a large class of models.Received: 26 October 2003, Revised: 1 September 2004, Published online: 28 October 2004     

Search for chargino and neutralino productionat $\sqrt{s} = 192$-209 GeV at LEP

Approximately 438 pb^-1 of e ⁺ e^- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 GeV, are analyzed to search for evidence of chargino pair production, , or neutralino associated production, . Limits are set at the 95% confidence level on the product of the cross-section for the process and its branching ratios to topologies containing jets and missing energy, or jets with a lepton and missing energy, and on the product of the cross-section for and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the and , and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on with the assumption that each chargino decays via a W boson, and on with the assumed to decay via a Z⁰.Received: 15 December 2003, Revised: 16 February 2004, Published online: 23 April 2004     

Small-<Emphasis Type="Italic">x</Emphasis> phenomenology - summary and status 2002

A second workshop on small-x physics, within the Small-x Collaboration, was held in Lund in June 2002 with the aim of over-viewing recent theoretical progress in this area and summarizing the experimental status.Received: 23 December 2003, Published online: 30 April 2004This paper is dedicated to the memory of Jan Kwieciski, who died unexpectedly on August 29, 2003.     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 189-209 GeV at LEP

Cross-sections and angular distributions for hadronic and lepton-pair final states in e ⁺ e^- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant at LEP 2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the -Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.Received: 28 August 2003, Published online: 18 February 2004     

Search for a narrow charmed baryonic state decaying to $D^{\ast \pm} p^\mp$in ep collisions at HERA

A resonance search has been made in the invariant-mass spectrum with the ZEUS detector at HERA using an integrated luminosity of . The decay channels and (and the corresponding antiparticle decays) were used to identify mesons. No resonance structure was observed in the mass spectrum from more than 60 000 reconstructed mesons. The results are not compatible with a report of the H1 Collaboration of a charmed pentaquark, .Received: 14 September 2004, Revised: 29 September 2004, Published online: 9 November 2004     

Homology classes that can be represented by embedded spheres in rational surfaces

The problem of embedding spheres in rational surfaces CP~2#nCP~2 is studied.For homology classes u=(b_1+k, b_2,…, b_n) with positive self-intersection numbers, anecessary and sufficient condition to detect its representability is given when k≤5.     

265Bh(Z=107)同位素的首次观测

在兰州的重离子加速器上用²⁶Mg离子束轰击²⁴³Am靶,产生了新同位素²⁶⁵Bh.通过观测新同位素²⁶⁵Bh和它的已知子核²⁶¹Db和²⁵⁷Lr之间的α衰变的关联,实现了对新核素的鉴别.实验中使用了一套新建立的具有数个探测器对的转轮收集探测系统.将该系统用于特殊的母–子核搜索模式,从而大大减少了本底.共测得了8个²⁶⁵Bh的α衰变关联事件;同时4个已知核²⁶⁴Bh的衰变关联事件也被鉴别出来.实验测得²⁶⁵Bh的α衰变能量为(9.24±0.05)MeV,半衰期为0.94+0.70–0.31s.