北京谱仪Ⅲ飞行时间计数器系统刻度中的关联分析

[5] [6]
generator, and sub-
jected to a Geant4
based detector simulation pro-
gram BOOST , in which the generation and transport of optical photons in TOF counter are taken into account. The simulated data are processed in the BES Offline Software System (BOSS) . 2.1 The time-of-flight calibration The calibration of TOF is proceeded by comparing the measured time tmea = traw − t0 − tcor against the predicted time texp = L/βc, where traw is the TDC value recorded by electronics, t0 the event start time, tcor the correction term; c is the velocity of √ light in vacuum, β = p/ p2 + m2 , the flight velocity of charged particle, m the particle mass, L and p are the corresponding flight path and momentum measured by the MDC(Main Drift Chamber). The correction term (tcor ) is a function of pulse height Q and hit position z , we take the following empirical form
Abstract The errors and correlations of BESIII TOF measurements are carefully checked in hit position at z partitions with the electron-pair events. The measured time-of-flight’s and their covariance matrices are subjected to a correlation analysis algorithm which is developed for BESIII to combine the independent measurements with common errors. Monte Carlo studies show that the correlated analysis can provide more reliable TOF information on particle identification.
893 — 899
894
( HEP & NP )
31
The PID ability depends on the time resolution of TOF system. There are many factors which affect the TOF measurements . They can be classified into two major categories: the un-correlated parts and the correlated parts. The un-correlated uncertainty is dominated by the detector resolution. The correlated uncertainty of TOF measurements is mainly caused by the beam bunch spread (∼40ps for BES ), which must be taken into account. In this bration/reconstruction software system
31 2007
10 10 HIGH ENERGY PHYSICS AND NUCLEAR PHYSICS
Vol. 31, No. 10 Oct., 2007
Correlation Analysis in Time-of-Flight Calibration of BES
HU Ji-Feng1,2;1) HE Miao2,3 LIU Huai-Min2 HE Kang-Lin2;2) HUANG Bin2,3 Ya-Jun5 YANG Ming
2,3
MAO Ze-Pu2
SUN Sheng-Sen2 WU Ling-Hui
SUN Yong-Zhao2,3 XIE Yu-Guang
WANG Ji-Ke2,3
WANG Liang-Liang2,3 YOU Zheng-Yun
WEN Shuo-Pin2 YU Guo-Wei2
[3] [1]
etc.; the correction function of time walk effect is represented by the terms containing P1 to P3 , then a polynomial containing P4 to P6 is used to describe the saturation of PMTs, etc.; while the polynomial containing P7 to P9 describes the correction to the effective velocity of light in the scintillator; the term with P10 is used to correct the effect caused by different depths of charged track traversing in scintillator. The toffset is an additional term to correct the t0 off0 sets run-by-run, which is set to be zero at present. A χ2 minimization method is applied by defining a set of
2,3
*
ZHANG Zi-Ping1 JI Xiao-Bin2
BIAN Jian-Ming2,3 LI Hai-Bo2
CAO Guo-Fu2,3 LI Wei-Dong2 MO Xiao-Hu2
5
DENG Zi-Yan2 QIU Jin-Fa2
LI Gang2,4
LIU Chun-Xiu2
MA Xiang2,3
[1, 2]
sists of a beryllium beam pipe, a helium-based smallcelled drift chamber, Time-of-Flight (TOF) counters for particle identification, a CsI(Tl) crystal calorime-
1 (Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China) 2 (Institute of High Energy Physics, CAS, Beijing 100049, China) 3 (Graduate University of Chinese Academy of Sciences, Beijing 100049, China) 4 (CCAST(World Laboratory), Beijing 100080, China) 5 (Peking University, Beijing 100871, China) 6 (Hunan University, Changsha 410082, China) 7 (Shandong University, Ji’nan 250100, China)
dant τ −charm physics. The BES
con-
Received 31 December 2006 * Supported by CAS Knowledge Innovation Project (U-602, U-34), National Natural Science Foundation of China (10491300, 10605030) and 100 Talents Program of CAS (U-54, U-25) 1) E-mail: hujf@ 2) E-mail: hekl@
Key words time-of-flight, particle identification, offline calibration, time resolution, errors and correlations
1
Introduction
The BEPC(Beijing Electron Positron Collider)
YUAN Chang-Zheng2 ZHANG Jian-Yong2,4
YUAN Ye2
ZANG Shi-Lei2,4
ZHANG Chang-Chun2 ZHANG Yao7
ZHANG Ling6
ZHANG Xue-Yao7
ZHENG Zhi-Peng2
ZHU Yong-Sheng2
ZOU Jia-Heng7
is a double-ring, multi-bunch collider with the designed luminosity approximately 100 times higher than that of BEPC. The Beijing Spectrometer (BES) will operate at BEPC and denote the abundetector