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Published byMathilde Bonnet Modified 5年之前
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Measurement of the continuum Ruds, Ruds(c)+Ψ(3770) and Rhad values in the range from to GeV 张达华 (for BES Collaboration) Institute of High Energy Physics, Beijing 第7届全国高能物理会议,桂林 October ,2006
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Cross section scan experiment Data analysis Radiative corrections
Outline Introduction Cross section scan experiment Data analysis Radiative corrections Results -- – R values
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Introduction R definition & measurements
pQCD calculates the R ratio in continuum region Experimentally, one measures : # of hadronic events : Luminosity : Effs. : radiative correction factor Have to be determined precisely !
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Introduction Why are we interested in R(s) ? Evaluate
affects the determination of the mass of Higgs boson from the measurement of indirectly. For the evaluation of the electromagnetic coupling at the Z mass scale, For determination of of the muon. The R values at all energies is needed to calculate the effects of vacuum polarization on the parameters of Standard Model. [ for example, and ]. A large uncertainty in this calculation arises from the uncertainties in the measured R values in the open charm threshold region (3.7 GeV to 5.0 GeV). Evaluate Non-DD decays of psi(3770)
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R measured by BES and other experiments
Introduction R measured by BES and other experiments
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Introduction
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Introduction Precision measurement of the cross sections in this region
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Cross section experiment
Cross section scan experiment The data were collected at 67 energy points from to GeV, which begin from off-resonance, mainly cover (3770) and stop at DD* production threshold . Separated beam collision data at 3 energy points were collected to study beam associated background.
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Cross section experiment
快速数据重建,快速物理分析,快速信息反馈 监测探测器状况 监测物理信号 动量 p GeV/c 能量 E GeV “快速”重建数据信息质量的监测结果
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Data analysis
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Data analysis Events collected at BESII 初态辐射修正可以删除高阶过程的影响 实验观测的强子事例
Events Recorded by BESII Distributions of the averaged Z of events Cosmic-ray and beam associated background could be estimated based on cross sections, luminosity and acceptance
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Data analysis 强子事例筛选 径迹筛选 事例级筛选 好的螺旋度拟合 径迹来源于原初顶点 立体角范围
Beam gas associate background, cosmic-ray
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Data analysis 数据和Monte Carlo 事例的对比
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Data analysis 强子事例选择条件的系统误差 Phys. Lett. B641 (2006)145
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Data analysis 亮度测量 径迹筛选 好的螺旋度拟合 径迹来源于原初顶点 立体角范围 去除加强筋区域 Z向灵敏区
Number of events Δφ=|φ1-φ2|-1800 Luminosity of the precision scan data sets determined by
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Data analysis 数据和Monte Carlo 事例的对比 DATA M.C. P1(GeV) P2(GeV)
EBSC1(GeV) EBSC2(GeV) ZBSC Number of events 数据和Monte Carlo 事例的对比
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Data analysis 数据和Monte Carlo 事例的对比 污染率: ~0.35% Number of events
Track 1 Track 1 数据和Monte Carlo 事例的对比 Accepted e+e- events are then examined for background contaminations by man visual scan. Number of events Track 2 Track 2 污染率: ~0.35% P [GeV] Table. Systematic uncertainties due to Bhabha event selection Sources ΔSYS (%) VXY <= m 0.18 |VXY| <= 0.15 m 0.48 |cos(θ)| <= 0.70 0.65 EBSC >= 1.1 GeV 0.27 P+(or P-) >= 0.9·Eb 1.33 0.10 m <= |ZBSC| <= 0.77 m or |ZBSC| >= 1.04 m 0.89 Total 1.83 Track 1 Track 1 Number of events Track 2 Track 2 EBSC [GeV]
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Data analysis 背景减除 The background from two-photon-exchange processes are also subtracted (<0.3%) in this analysis.
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Data analysis 触发效率
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Data analysis 强子效率 Full simulation Monte Carlo generator
High order ISR inclusive hadronic generator was developed to determine had in the all energy region A wide region ISR return generator ISRAD drives a set of sub-generators to generate the physics processes in the energy region from 0.28 GeV to 4.0 GeV with Lorentz boost due to initial state photon emission. DD-bar and D*D-bar productions are simulated by DDGEN and DsDGEN. In the radiative return region, the decays of (2S) and J/ resonances are simulated byLUND_CRM (see PRD V62, ). One photon inclusive hadron prodution is simulated by LUND modified for BES energy region.
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Data analysis 强子效率
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Radiative corrections
初态辐射修正 (Kuraev and Fadin)
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Radiative corrections
Vacuum polarization correction 真空极化改变光子传播子 从而导致 蔡永士(SLAC)公式 Berands, et al. have another approach to deal with the vacuum polarization.
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Ψ(3770) resonance parameters
Results -R values R values Table. Systematic uncertainties in the determination of R values Sources ΔSYS (%) Luminosity 1.8 Hadron selection 2.5 M.C. modeling 2.0 ISR 1.5 Ψ(3770) resonance parameters 2.7 Total (off Ψ(3770) region) 3.9 (within Ψ(3770) region) 4.9
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Results -R values a(M2Z) aμ=(g-2)/2 Ruds = 2.134±0.025±0.085 Ruds
above cc-bar threshold below cc-bar threshold hadrons Ruds = 2.134±0.025±0.085 RpQCDuds = 2.15±0.03 Ruds Rtot(s)=Rhad(s)+ΣRres,i(s), Rres,i(s) is R values due to all 1-- resonances decay to hadrons except Ψ(3770). a(M2Z) aμ=(g-2)/2 hadrons calculate Rtot
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continuum Rudsc + RΨ(3770)hadrons
R values (This work) Dec data set BES-II Preliminary ! continuum Rudsc + RΨ(3770)hadrons
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Thank You
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Introduction
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Introduction
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