Measurement of the continuum Ruds, Ruds(c)＋Ψ(3770) and Rhad values in the range from 3.660 to 3.872 GeV 张达华 (for BES Collaboration) Institute of High Energy Physics, Beijing 100049 第7届全国高能物理会议，桂林 October 27--31，2006

Cross section scan experiment Data analysis Radiative corrections Outline Introduction Cross section scan experiment Data analysis Radiative corrections Results -- – R values

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 !

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)

R measured by BES and other experiments Introduction R measured by BES and other experiments

Introduction

Introduction Precision measurement of the cross sections in this region

Cross section experiment Cross section scan experiment The data were collected at 67 energy points from 3.660 to 3.872 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.

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

Data analysis

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

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

Data analysis 数据和Monte Carlo 事例的对比

Data analysis 强子事例选择条件的系统误差 Phys. Lett. B641 (2006)145

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

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

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 <= 0.015 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]

Data analysis 背景减除 The background from two-photon-exchange processes are also subtracted (<0.3%) in this analysis.

Data analysis 触发效率

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, 034003). One photon inclusive hadron prodution is simulated by LUND modified for BES energy region.

Data analysis 强子效率

Radiative corrections 初态辐射修正 (Kuraev and Fadin)

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.

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

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

continuum Rudsc + RΨ(3770)hadrons R values (This work) Dec. 2003 data set BES-II Preliminary ! continuum Rudsc + RΨ(3770)hadrons

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Introduction

Introduction