"Table 79" 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）数据集：本研究针对包含衰变至电子对或缪子对的Z玻色子（Z-boson）的单举事件样本，开展了敏感反映underlying事件（underlying event）性质的带电粒子分布测量。本次测量基于大型强子对撞机（LHC）上ATLAS探测器（ATLAS）采集的数据，数据对应质心系能量为7 TeV的质子-质子碰撞，积分亮度为4.6 fb⁻¹。

本测量针对相对于Z玻色子方向定义的方位角差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动量分布，具体区域划分如下：
- 前向区域：|Δφ| < 60°
- 横向区域：60° < |Δφ| < 120°
- 背向区域：|Δφ| > 120°
- 最大横向区域：按单次事件统计，两个横向扇区中带电粒子横动量标量和最大的扇区
- 最小横向区域：按单次事件统计，两个横向扇区中带电粒子横动量标量和最小的扇区

本研究定义的fiducial相空间区域（fiducial volume）如下：
- Z衰变产生的两个带异号电荷的轻子需满足横动量p_T > 20 GeV，赝快度|η| < 2.4，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-质子碰撞的粒子，或是寿命小于τ的瞬生粒子的衰变产物），横动量p_T > 0.5 GeV，赝快度|η| < 2.5

本次测量的可观测量包括：
- p_T(Z)：Z玻色子的横动量
- N_ch/(ΔηΔφ)：单位η-φ区间内的稳定带电粒子数目，在-2.5 < η < 2.5且0 < Δφ < π的范围内取平均。该可观测量已校正探测器接收度、重建与选择效率、轻子识别效率以及Z玻色子动量分辨能力，并扣除了堆集本底与产生与Z→μ⁺μ⁻、Z→e⁺e⁻信号具有相同实验特征的末态带来的背景。

已发布的分布可直接与粒子级蒙特卡洛（MC）发生器的输出结果进行对比，对比时采用两种Z→轻子对末态的定义（如表中所示）：
- 玻恩近似：Z玻色子的动量定义为轻子与末态辐射光子（FSR）的动量之和，忽略轻子的光子辐射与过程中其他带电粒子线之间的干涉。粒子级fiducial相空间区域可视为不存在末态辐射光子的假想实验中的区域，例如Z→νν̅末态且两个轻子满足p_T>20 GeV、|η|<2.5的情况。
- 缀饰轻子（dressed lepton）：缀饰轻子的动量定义为轻子自身的动量与其运动方向周围ΔR<0.1锥区内所有非强相互作用起源光子的动量之和。粒子级fiducial相空间区域采用缀饰轻子的动量进行定义。

表格中标记为‘辅助材料’的内容可从以下网址获取：https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2011-42/.