"Table 107" of "Measurement of distributions sensitive to the underlying event in inclusive Z-boson production in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector"

CERN-LHC. A measurement of charged-particle distributions sensitive to the properties of the underlying event is presented for an inclusive sample of events containing a Z-boson, decaying to an electron or muon pair. The measurement is based on data collected using the ATLAS detector at the LHC in proton--proton collisions at a centre-of-mass energy of 7 TeV with an integrated luminosity of 4.6/fb. Distributions of the charged particle (excluding the two leptons from Z decay) multiplicity and of the charged particle transverse momentum are measured in regions of azimuthal angle delta(phi) = |phi - phi(Z)| defined with respect to the Z-boson direction: - the toward region: |delta(phi)| < 60 degrees - the transverse region: 60 < |delta(phi)| < 120 degrees - the away region: |delta(phi)| > 120 degrees - the trans-max region: one of the two transverse sectors having a maximum scalar sum of transverse momenta of charged particles on event-by-event basis - the trans-min region: one of the two transverse sectors having a minimum scalar sum of transverse momenta of charged particles on event-by-event basis The fiducial volume is defined as follows: - the two oppositely charged leptons from Z decay are required to have pT > 20 GeV, |eta| < 2.4 and 66 < M(ll) < 116 GeV - charged particles are required to have a proper lifetime tau > 0.3*10**-10 sec, be primary (i.e. produced directly in pp interaction or being decay products of prompt particles with the lifetime less than tau), have pT > 0.5 GeV and |eta| < 2.5 The observables: - pT(Z): transverse momentum of the Z-boson - N(ch)/delta(eta)/delta(delta(phi)): number of stable charged particles per eta-phi unit, averaged over eta-phi range, where -2.5 mu+ mu-, e+ e- identification efficiency and Z momentum resolution; background from pileup and final states yielding the same experimental signature as the Z -> mu+ mu-, e+ e- signal. - Published distributions can be directly compared to a particle level MC generator output with the two definitions of Z -> lepton+ lepton- final state (as indicated in the tables): - Born approximation: Z momentum is defined as the sum of leptons' and FSR photons' momenta, in neglect of interference between photon radiation off the leptons and other charged legs in the process. The particle level fiducial volume can be viewed as the one obtained in an imaginary experiment without FSR, e.g., with Z -> nu nubar final state where both leptons have pT>20 GeV and |eta|<2.5. - Dressed leptons: dressed lepton momentum is defined as a sum of the lepton's momentum and the momenta of all photons of non-hadronic origin within DeltaR<0.1 cone around the direction of the lepton. The particle level fiducial volume is defined using dressed lepton momenta. Material referenced as `auxiliary' in the tables is available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2011-42/.

欧洲核子研究中心大型强子对撞机（CERN-LHC）。针对包含衰变至电子或缪子对的Z玻色子的全包含事件样本，我们展示了一项对敏感于本底相互作用（underlying event）的带电粒子分布的测量结果。
本次测量基于大型强子对撞机（LHC）上的ATLAS探测器采集的数据，数据来自质心系能量为7 TeV的质子-质子碰撞事件，积分亮度为4.6 fb⁻¹。
我们针对以Z玻色子方向为基准定义的方位角差Δφ = |φ - φ_Z|的不同区域，测量了（扣除Z衰变产生的两个轻子后的）带电粒子多重数分布以及带电粒子横向动量分布：
- 前向区域（toward region）：|Δφ| < 60°
- 横向区域（transverse region）：60° < |Δφ| < 120°
- 对向区域（away region）：|Δφ| > 120°
- 最大横向子区域（trans-max region）：基于逐个事件选取的两个横向扇区中，带电粒子横向动量标量和最大的那个扇区
- 最小横向子区域（trans-min region）：基于逐个事件选取的两个横向扇区中，带电粒子横向动量标量和最小的那个扇区

本征体积（fiducial volume）定义如下：
- Z衰变产生的两个带异种电荷的轻子需满足横向动量p_T > 20 GeV、赝快度|η| < 2.4，且双轻子不变质量66 GeV < M_ll < 116 GeV
- 带电粒子需满足固有寿命τ > 0.3×10⁻¹⁰ s，为原初粒子（即直接产生于质子-质子相互作用，或是寿命小于τ的瞬态粒子的衰变产物），且p_T > 0.5 GeV、|η| < 2.5

可观测物理量如下：
- p_T(Z)：Z玻色子的横向动量
- N_ch/(ΔηΔφ)：单位η-φ空间内的稳定带电粒子数，在-2.5 < η < 2.5且0 < Δφ < π的范围内取平均。测量中已针对探测效率、e⁺e⁻/μ⁺μ⁻鉴别效率以及Z玻色子动量分辨率进行修正，并扣除了叠加事件（pileup）以及与Z→μ⁺μ⁻、Z→e⁺e⁻信号具有相同实验特征的末态背景。

已发布的分布结果可直接与两种Z→轻子+轻子末态定义下的粒子级蒙特卡洛（MC）发生器输出结果进行比对（详见表格）：
- 玻恩近似（Born approximation）：Z玻色子动量定义为轻子与末态辐射光子（FSR，final state radiation）的动量之和，忽略轻子上的光子辐射与过程中其他带电支腿之间的干涉效应。粒子级本征体积可视为在无末态辐射的假想实验中得到的体积，例如Z→νν̄末态且两个轻子满足p_T>20 GeV、|η|<2.5的情况。
- 缀饰轻子（dressed leptons）：缀饰轻子动量定义为轻子自身动量与以轻子方向为中心、ΔR<0.1锥区内所有非强作用起源光子的动量之和。粒子级本征体积通过缀饰轻子动量进行定义。

表格中标记为“辅助材料”的内容可访问以下链接获取：https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2011-42/