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151.
Virkus T Thomsen HD Uggerhøj E Uggerhøj UI Ballestrero S Sona P Mangiarotti A Ketel TJ Dizdar A Kartal S Pagliarone C;CERN NA Collaboration 《Physical review letters》2008,100(16):164802
Experimental results for the restricted energy loss of pairs created from 1-178 GeV photons in a thin Au target and subsequently passing a CCD detector are presented. It is shown that pairs--when detected close to the creation vertex--suffer a reduced energy loss due to the internal screening of the charges constituting the pair. Furthermore, the ability to measure directly the energy of the pair by calorimetry enables a comparison with theory as a function of energy. The observed phenomenon is in good qualitative agreement with general expectations from the Chudakov effect but indicates a quantitative disagreement with either of two mutually disagreeing theories. 相似文献
152.
J. Badier C. Bemporad J. Boucrot O. Callot P. Charpentier A. M. Cnops M. Crozon P. Delpierre J. F. Detoeuf G. R. Giannini R. Hammarstr?m P. Lariccia R. Lorenzi J. Mas A. Michelini A. Tilquin J. K. Walker NA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1986,31(1):21-32
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. 相似文献
153.
Adamová D Agakichiev G Appelshäuser H Belaga V Braun-Munzinger P Cherlin A Damjanović S Dietel T Dietrich L Drees A Esumi SI Filimonov K Fomenko K Fraenkel Z Garabatos C Glässel P Hering G Holeczek J Kushpil V Lenkeit B Maas A Marín A Milosević J Milov A Miśkowiec D Panebrattsev Y Petchenova O Petrácek V Pfeiffer A Rak J Ravinovich I Rehak P Richter M Sako H Schmitz W Sedykh S Seipp W Sharma A Shimansky S Slívová J Specht HJ Stachel J Sumbera M Tilsner H Tserruya I Wessels JP Wienold T 《Physical review letters》2003,91(4):042301
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. 相似文献
154.
J. Badier M. Bardadin-Otwinowska C. Bemporad U. Berthon H. Bienvenu J. Boucrot J. Bourotte O. Callot P. Charpentier A. M. Cnops M. Cohen F. Costantini M. Crozon D. Décamp P. Delpierre J. F. Detoeuf P. Espigat G. R. Giannini Y. Karyotakis P. Lariccia J. Mas A. Michelini G. C. Moneti M. Moniez E. Paré G. Rahal-Callot M. Rumpf A. Tilquin NA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1986,30(1):45-50
We have measured the inclusive cross-section for π0 production at large transverse momentum by 200 GeV/c positive and negative hadron beams on Carbon targets (2.9<P T <6 GeV/c; ?0.4<y *<1.2). We used the NA3 spectrometer at the CERNSPS. 相似文献
155.
The NA50 experiment at CERN SPS studies charmonia and Drell-Yan production in the μ+ μ? decay channel at 158A GeV. The data collected in Pb?Pb collisions during 1995, 1996 and 1998 run periods show that the J/ψ is anomalously suppressed in central collisions. This observed suppression pattern can be considered as a strong indication of the production of Quark-Gluon Plasma. 相似文献
156.
157.
WANG De-Wu SHEN Gui-Lin NA Shu-Zhen LI Yun-Shan LI Cheng-Ze LI Zhi-Gang CHEN Kun CHEN Yuan-Bo CHEN Zhi-Ping MA Mei SHEN Miao-He ZHAO Mei LOU Jia-Shu XU Rong-Fen 《中国物理C(英文版)》1988,12(3):289-297
A positron CT camera system using multiwire proportional chambers as detectors is reported.This system is composed of two high density MWPC γ-ray detectors,an electronic readout system and a computer for data processing.The tomography of three dimensions is obtained.The imaging matrix 64×64×16. 相似文献
158.
The algebras of meromorphic vector fields and the bases of meromorphic λ-differentials with multipoles are constructed explicitly on general genus Riemann surfaces. For Riemann sphere the central extension of the algebra is also given. 相似文献
159.
160.
CaO对Cu-ZnO-ZrO催化CO加H合成甲醇性能影响 《燃料化学学报》2016,44(4):437-448
用CaO作为改性助剂,采用并流共沉淀法制备了CuO∶ZnO∶ZrO_2为5∶4∶1(物质的量比),CaO添加量为0、1%、2%、4%、8%、16%(摩尔分数)的六组催化剂。用X射线衍射(XRD)、微商热重(TG-DTG)、傅里叶红外(FT-IR)、N2吸附脱附(BET)、X射线光电子能谱(XPS)、氢气程序升温还原(H_2-TPR)、CO_2程序升温脱附(CO_2-TPD)、NH_3程序升温脱附(NH_3-TPD)对催化剂进行了表征。用自制固定床评价了催化剂活性。结果表明,添加CaO后,催化剂路易斯酸性和表面碱性增强;催化剂母体中高温碳酸盐含量增加,热稳定性增强,CuO颗粒粒径变小,Cu-Zn协同作用增强,Cu比表面积增大,分散性变好。催化剂活性受到表面酸碱性、铜比表面积、Cu-Zn协同作用和铜分散性共同影响。当CaO为2%时,铜比表面积为79.3 m2/g、铜分散度为34.8%、CO_2转化率为24.55%、甲醇选择性为19.01%、甲醇收率为0.044 g/(gcat·h),催化剂活性最好。过量CaO占据催化剂孔道和覆盖表面活性位,使催化剂路易斯酸性和表面碱性过强,CuO与H_2有效接触减少,CO_2难以脱附,催化活性下降。因此,适量CaO(2%)添加可促进CO_2加氢反应合成甲醇。 相似文献