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arXiv 1408.4342hep-ex
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用ATLAS探测器测量$\sqrt{s_{NN}}=2.76$ TeV中Pb + Pb碰撞中多粒子累积流谐波

Measurement of flow harmonics with multi-particle cumulants in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV with the ATLAS detector

ATLAS Collaboration

摘要:

ATLAS测量的方位角各向异性在铅铅碰撞在$\sqrt{s_{NN}}=2.76$ TeV显示使用数据集的约7 $μ$ b $^{-1}$在2010年收集的大型强子对撞机。测量的带电粒子的横向动量$0.5<p_T<20$ GeV和在伪快度范围$|η|<2.5$。各向异性由n = 2 - 4的带电粒子方位角分布的傅里叶系数$v_n$来表征。傅立叶系数的计算使用多粒子累积量与生成函数方法。给出了$v_n$系数的横动量、赝快度和中心度依赖关系的结果。椭圆流,$v_2$,从两个,四个,六个和八个粒子的累积量,而高阶系数,$v_3$和$v_4$,确定与两个和四个粒子的累积量。与涉及两个粒子累积量的测量相比,用四粒子累积量测量的流谐波$v_n$显著减少。使用不同的分析方法获得的$v_n$测量和以前报告的大型强子对撞机实验的比较也显示。多粒子累积量的流量波动的测量结果进行评估显示为横向动量和碰撞中心的函数。初始空间几何形状及其波动的模型不能描述流动波动测量。

英文摘要:

ATLAS measurements of the azimuthal anisotropy in lead-lead collisions at $\sqrt{s_{NN}}=2.76$ TeV are shown using a dataset of approximately 7 $μ$b$^{-1}$ collected at the LHC in 2010. The measurements are performed for charged particles with transverse momenta $0.5<p_T<20$ GeV and in the pseudorapidity range $|η|<2.5$. The anisotropy is characterized by the Fourier coefficients, $v_n$, of the charged-particle azimuthal angle distribution for n = 2-4. The Fourier coefficients are evaluated using multi-particle cumulants calculated with the generating function method. Results on the transverse momentum, pseudorapidity and centrality dependence of the $v_n$ coefficients are presented. The elliptic flow, $v_2$, is obtained from the two-, four-, six- and eight-particle cumulants while higher-order coefficients, $v_3$ and $v_4$, are determined with two- and four-particle cumulants. Flow harmonics $v_n$ measured with four-particle cumulants are significantly reduced compared to the measurement involving two-particle cumulants. A comparison to $v_n$ measurements obtained using different analysis methods and previously reported by the LHC experiments is also shown. Results of measurements of flow fluctuations evaluated with multi-particle cumulants are shown as a function of transverse momentum and the collision centrality. Models of the initial spatial geometry and its fluctuations fail to describe the flow fluctuations measurements.

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