Mass and lifetime limits on new long-lived particles in 300 GeV/c π− interactions

A sensitive search has been done for the production of new long-lived and penetrating particles by 300 GeV/c negative pions. No new state —decaying into at least two charged known particles —has been detected with mass above 1 GeV/c² and lifetime in the range 5·10^?11 s to 5·10^?7s. We give upper limits on production cross sections, and consequences on the existence of heavy “axion-like” particles, heavy neutrinos and supersymmetric particles. In particular, this experiment excludes the existence of light gluinos with lifetime in the range 5·10^?11 to 10^?8s: this closes the last “window of opportunity” for gluinos withM<2 GeV/c² and lifetime measurable in particle physics experiments.     

CaMoO_4:Tb~(3+)发光材料的制备和发光性质的研究

用共沉淀法制备了样品CaMoO_4:Tb~(3+)的前驱物,经TG-DTA测试表明:样品在850℃时有能量吸收峰,即达到样品反应的活化点。XRD谱图分析显示,焙烧后样品CaMoO_4:Tb~(3+)为CaMoO_4的白钨矿结构,但峰位发生了右移,说明晶体内部产生了微小的晶体缺陷,推测该缺陷可能是由晶胞内2个Tb~(3+)取代了3个Ca~(2+)形成空穴而引发的。通过对激发谱图的测试发现,此种缺陷结构有利于使MoO_4~(2-)发射特征峰(488 nm)的能量有效地传递给Tb~(3+),使Tb~(3+)的4f电子发生跃迁,特别使Tb~(3+)的~7F_6→~5D_4(488 nm)电子跃迁大大加强,因而在样品CaMoO_4:Tb~(3+)的发射谱图(λ_(ex)=488 nm)中,自激活荧光体MoO_4~(2-)的发射强度被大大减弱,而Tb~(3+)的~5D_4→~7F_5(544 nm)跃迁的绿光发光强度被大大增强,使该材料成为有潜在应用价值的发光材料。     

The Influence of Au-Doping on Morphology and Visible-Light Reflectivity of TiN Thin Films Deposited by Direct-Current Reactive Magnetron Sputtering

Ti, TiN and Au-TiN （Au content： from 0.5%to 7.7%） thin films were deposited on stainless steel substrates by dc reactive magnetron sputtering with a metal Ti target. The crystal structure, surface morphology and visiblelight reflectivity of the films for different film compositions are studied in detail. Distinctly different surface morphologies appear for the Ti, TiN and Au-TiN thin films. It can be observed that the surface morphology of the TiN film is affected by the Au-doping, when the Au content increases from 0% to 7.7%, surface roughness enlarges from 62.4 to 82.8 nm. Moreover, visible-light reflectivity varies significantly with increasing A u contents in the TiN films. However, the rettectivity of the TiN thin film at 550-800 nm is higher than that of the Au-TiN thin film. The present work illustrates the dependence of metal elements on the surface morphology and on the reflectivity of Au-TiN thin films. It is speculated that the addition of Au can suppress the formation and growth of TiN grains so that it changes the surface morphology and the Au-TiN thin film has potential applications in spectral selective coating.     

A new measurement of $J/\psi$ suppression in Pb-Pb collisions at 158 GeV per nucleon

We present a new measurement of production in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that the cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that the cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions. Received: 25 August 2004, Revised: 15 December 2004, Published online: 21 January 2005     

Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS

We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.     

过氧化氢和磷酸对以亚磷酸作磷源合成SAPO-41和AIPO-41的影响

考察了以亚磷酸作为磷源合成SAPO-41和AlPO-41时加入过氧化氢或磷酸对生成SAPO-41和AlPO-41的影响.结果表明,向反应体系中加入过氧化氢或者使用磷酸部分替代亚磷酸,都能明显缩短SAPO-41和AlPO-41的晶化时间.此外,使用混合磷源还能够降低模板剂的用量,获得小晶粒晶化产物.     

基于LED光源痕量二氧化氮气体的检测

随着现代化工业的发展,大气污染越来越严重,吸收光谱法是检测大气污染的重要手段.NO2是大气污染的主要污染物之一,文章将发光二极管作为光源,选择发光光谱范围处于NO2强吸收峰位置的发光二极管,通过测虽含有NO2污染物的吸收光谱,利用最小二乘法,将实验得到的吸收光谱与标准谱作拟合运算,反演计算出污染物浓度.分析了检测的幕本原理,研究了光谱分析过程,包括实验光谱与标准光谱的拟合、浓度的反演计算等数据处理过程.具体利用NO2在300～500 nm光谱范围内有强吸收的特点,测量了样品中NO2的浓度.实验使用发光二极管作为光源,使检测变得方便快捷,实验装置便于携带,可以随时对待测场所实现高精度的实时在线检测.