共查询到20条相似文献,搜索用时 156 毫秒
1.
大角度巴巴散射和双μ产生的研究与亮度测量 总被引:1,自引:0,他引:1
利用北京谱仪(BES)在S=4.03GeV下正负电子对撞数据,研究了巴巴和双μ事例的QED过程.结果表明,实验数据在误差范围内同QED预言较好地一致,且从e+e-和μ+μ-末态测出的两亮度值在4%范围内相互一致.计算给出:BES在该能区获取数据的总积分亮度为23.1pb-1. 相似文献
2.
3.
4.
5.
6.
在TC2理论框架下,计算了在高能正负电子对撞机(LC)上,TC2动力学对味改变中性流过程e+e-→tc产生截面的修正和TC2理论预言的中性top–pionπ0t对该过程产生截面的贡献.计算结果表明:TC2理论对LC实验中tc夸克联合产生的贡献主要来自中性top-pion π0t.在TC2理论的绝大部分参数空间内,可达10-2ph.若假设LC的积分亮度为500fb-1,则每年可产生数千个tc事例.因此,将来的LC实验可作为检验TC2理论的重要工具. 相似文献
7.
8.
9.
10.
利用北京谱仪(BES)在北京正负电子对撞机(BEPC)e+e-对撞质心系能量为4.03GeV处收集的积分亮度为22.3pb-1的数据,测量了带电及中性D介子的单举半轻子(电子)衰变的分支比.分析中采用了“联合D0和D+单双标记”的方法,测得D-和D0单举半轻子(电子)衰变的分支比分别为BF(D-→e-X)=(21.8±8.5±4.2)%,BF(D0→e-X)=(8.9±3.0±1.6)%,其相对比值为BF(D-→e-X)BF(D0→e-X)=2.4±1.7±0.8. 相似文献
11.
12.
Measurement of integrated luminosities at BESIII for data samples at center-of-mass energies between 4.0 and 4.6 GeV 下载免费PDF全文
《中国物理C(英文版)》2022,46(11):113002-113002-11
The integrated luminosities of data samples collected in the BESIII experiment in 2016–2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010–2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur. 相似文献
13.
XUE Zhen XU Zi-Zong WANG Xiao-Lian HU Tao WANG Zhi-Yong FU Cheng-Dong YAN Wen-Biao L Jun-Guang ZHOU Li CAI Xiao YU Bo-Xiang FANG Jian SUN Xi-Lei SHI Feng WANG Zhi-Gang AN Zheng-Hua SUN Li-Jun LIU Hong-Bang ZHANG Ai-Wu WANG Xiao-Dong 《中国物理C(英文版)》2011,35(1)
The BEPCⅡLuminosity Monitor(BLM)monitors relative luminosity per bunch.The counting rates of gamma photons,which are proportional to the luminosities from the BLM at the center of mass system energy of the ψ(3770)resonance,are obtained with a statistical error of 0.01% and a systematic error of 4.1%.Absolute luminosities are also determined by the BESⅢ End-cap Electro-Magnetic Calorimeter(EEMC)using Bhabha events with a statistical error of 2.3% and a systematic error of 3.5%.The calibration constant between the luminosities obtained with the EEMC and the counting rates of the BLM are found to be 0.84±0.03(x1026 cm-2·count-1).With the calibration constant,the counting rates of the BLM can be scaled up to absolute luminosities. 相似文献
14.
The production of single photons has been studied in the reaction at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of events with multi-photon final states
accompanied by missing energy has been updated with 189 GeV data. The data were collected with the DELPHI detector and correspond
to integrated luminosities of about 51 pb and 158 pb at the two energies. The number of light neutrino families is measured to be . The absence of an excess of events beyond that expected from Standard Model processes is used to set limits on new physics
as described by supersymmetric and composite models. A limit on the gravitational scale is also determined.
Received: 28 January 2000 / Revised version: 27 April 2000 / Published online: 26 July 2000 相似文献
15.
A. Heister et al. 《The European Physical Journal C - Particles and Fields》2001,21(3):423-441
The triple gauge-boson couplings involving the W are determined using data samples collected with the ALEPH detector at mean centre-of-mass energies of 183 GeV and 189 GeV,
corresponding to integrated luminosities of 57 pb and 174 pb, respectively. The couplings, , and , are measured using W-pair events, single-{\it W} production and single- production. Each coupling is measured individually with the other two couplings fixed at their standard model value. Including
ALEPH results from lower energies, the 95% confidence level intervals for the deviation to the standard model are
, , and .
Fits are also presented where two or all three couplings are allowed to vary. In addition, W-pair events are used to set limits on the C- or P-violating couplings , , , and , where V denotes either or Z. No deviations from the standard model expectations are observed.
Received: 28 February 2001 / Published online: 24 August 2001 相似文献
16.
A. N. Dmitrieva R. P. Kokoulin K. G. Kompaniets G. Mannocchi A. A. Petrukhin O. Saavedra D. A. Timashkov G. Trinchero D. V. Chernov V. V. Shutenko I. I. Yashin 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(4):552-555
Precision measurements of the zenith-angle distributions of muons in the range 61°–89° are performed using the DECOR coordinate detector. The total number of selected events is more than 20 million. The dependence of the integrated muon intensity on the zenith angle is determined for several threshold energies in the range from 1.7 to 7.2. GeV. The experimental results in these ranges of zenith angles and threshold energies are obtained for the first time. It is demonstrated that the dependence of the integrated muon intensity on the zenith angle is adequately described by a simple analytical relationship. 相似文献
17.
Hadron production and lepton-pair production in e+e- collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies
. Using a total integrated luminosity of 453 pb-1, 36057 hadronic events and 12863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair
production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted
prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally,
the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle.
An overall good agreement is found with Standard Model predictions. 相似文献
18.
The forward GEM tracker of the P?ANDA detector at the future FAIR facility will track the particles produced in antiproton-proton annihilations and emitted in the polar angle range 5° –22°. Position resolution at the level of 100 μ m and good time resolution are critical to work under luminosities up to 2×1032 c m ?2 s ?1. The simulations performed with Garfield program compared several detector layouts and determined the optimal granularity of readout electronics. The time resolution for two possible gas mixtures was also estimated. 相似文献
19.
In this study, all available data on the largest solar proton events (SPEs), or extreme solar energetic particle (SEP) events, for the period from 1561 up to now are analyzed. Under consideration are the observational, methodological and physical problems of energy-spectrum presentation for SEP fluxes (fluences) near the Earth's orbit. Special attention is paid to the study of the distribution function for extreme fluences of SEPs by their sizes. The authors present advances in at least three aspects: 1) a form of the distribution function that was previously obtained from the data for three cycles of solar activity has been completely confirmed by the data for 41 solar cycles; 2) early estimates of extremely large fluences in the past have been critically revised, and their values were found to be overestimated; and 3) extremely large SEP fluxes are shown to obey a probabilistic distribution, so the concept of an “upper limit flux” does not carry any strict physical sense although it serves as an important empirical restriction. SEP fluxes may only be characterized by the relative probabilities of their appearance, and there is a sharp break in the spectrum in the range of large fluences (or low probabilities). It is emphasized that modern observational data and methods of investigation do not allow, for the present, the precise resolution of the problem of the spectrum break or the estimation of the maximum potentialities of solar accelerator(s). This limitation considerably restricts the extrapolation of the obtained results to the past and future for application to the epochs with different levels of solar activity. 相似文献
20.
《中国科学:物理学 力学 天文学(英文版)》2010,(6)
Combining the 12CO(1-0),13CO(1-0),and C18O(1-0) data with IRAS four band data,we here estimate the physical parameters such as size,viral mass,and CO J=1-0 isotopic and infrared luminosities for 29 dense molecular clouds from two published CO samples. We further analyze the various correlations between CO J=1-0 isotopic luminosities and infrared luminosity(star formation rate,SFR) and discuss the relationships between the molecular gas tracers and SFR. The results show that 12CO(1-0),13CO(1-0) and C18O(1-0) luminosities have tight correlations with each other. CO J=1-0 isotopic luminosities and SFR show weak correlations with larger scatter than the HCN-IR correlations of 47 dense cores in the Galaxy and 65 external star-forming galaxies. This might be interpreted as that both the SFR and star formation efficiency are mainly determined by the molecular gas at high volume density rather than high column density. 相似文献