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arXiv 1208.0563hep-ex
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用ATLAS探测器在sqrt(s)= 7 TeV的pp碰撞中带电粒子喷流事件的基本事件特征及其对喷流尺寸的依赖性

Underlying event characteristics and their dependence on jet size of charged-particle jet events in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

ATLAS Collaboration

摘要:

在大型强子对撞机(LHC)的ATLAS探测器在sqrt(s)= 7 TeV的pp碰撞中产生的一个或多个带电粒子喷流的事件中,研究了对潜在事件敏感的分布。这些测量反映了2010年期间采集的800个反向微仓的数据。使用半径参数R在0.2和1.0之间变化的antikt算法重建射流。带电粒子多重数的分布,带电粒子的横向动量的标量和,以及平均带电粒子pT测量为pT^JET的函数,在区域横向和相对于领先的射流为4 GeV < pT^JET < 100 GeV。此外,这些观测值的平均值的R-依赖性进行了研究。在横向区域,固定pT^JET时的多重数和横向动量的标量和都随R显著变化,而平均带电粒子横向动量对R的依赖性极小。从几个蒙特卡洛曲调的预测已经与数据进行了比较; Pythia 6的预测,基于已经使用LHC数据确定的曲调,显示出与数据的合理一致性,包括对R的依赖性。与其他发电机的比较表明,额外的软QCD参数的调整是必要的,这些发电机。这里提出的测量提供了一个测试场的进一步发展的蒙特卡罗模型。

英文摘要:

Distributions sensitive to the underlying event are studied in events containing one or more charged-particle jets produced in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). These measurements reflect 800 inverse microbarns of data taken during 2010. Jets are reconstructed using the antikt algorithm with radius parameter R varying between 0.2 and 1.0. Distributions of the charged-particle multiplicity, the scalar sum of the transverse momentum of charged particles, and the average charged-particle pT are measured as functions of pT^JET in regions transverse to and opposite the leading jet for 4 GeV < pT^JET < 100 GeV. In addition, the R-dependence of the mean values of these observables is studied. In the transverse region, both the multiplicity and the scalar sum of the transverse momentum at fixed pT^JET vary significantly with R, while the average charged-particle transverse momentum has a minimal dependence on R. Predictions from several Monte Carlo tunes have been compared to the data; the predictions from Pythia 6, based on tunes that have been determined using LHC data, show reasonable agreement with the data, including the dependence on R. Comparisons with other generators indicate that additional tuning of soft-QCD parameters is necessary for these generators. The measurements presented here provide a testing ground for further development of the Monte Carlo models.

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