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arXiv 1603.04775nucl-exhep-ex
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在$\sqrt{s_{\rm NN}} = 2.76$ TeV上测量Pb-Pb碰撞中快度横能

Measurement of transverse energy at midrapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV

ALICE Collaboration

摘要:

本文报道了用ALICE测量的${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV的Pb-Pb碰撞中快度横向能量($E_{\mathrm T}$)随中心性的变化。使用确定的单粒子轨道的横向能量进行测量。用电磁量热计和ALICE先前报道的已识别粒子的横向动量分布对测量结果进行了交叉检验。的结果进行了比较,理论模型以及从其他实验的结果。在0-5%的中心碰撞中,每单位伪快度的平均$E_{\mathrm T}$($η$),$\langle $ d $E_{\mathrm T}/$ d $η\rangle$为1737 $\pm$ 6(统计)。$\pm$ 97(系统)GeV。我们发现一个类似的中心依赖性的形状的$\langle $ d $E_{\mathrm T}/$ d $η\rangle$作为一个功能的参与核子的数量,看到在较低的能量。在大型强子对撞机${\sqrt{s_{\mathrm {NN}}}}$上,$\langle $、$E_{\mathrm T}/$、$η\rangle$的增长超过了低能数据的外推。我们观察到$\langle $ d $E_{\mathrm T}/$ d $η\rangle$与夸克参与者的数量近似线性标度。在1 fm/ $c$形成时间的规范假设下,我们估计在${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV的0-5%中心Pb-Pb碰撞中的能量密度为12.3 $\pm$ 1.0 GeV/fm $^3$ \xspace,并且在碰撞的最中心80 fm $^2$处的能量密度至少为21.5 $\pm$ 1.7 GeV/fm $^3$。这大约是在${\sqrt{s_{\mathrm {NN}}}}$ = 200 GeV的0-5%中心Au-Au碰撞中观察到的2.3倍。

英文摘要:

We report the transverse energy ($E_{\mathrm T}$) measured with ALICE at midrapidity in Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean $E_{\mathrm T}$ per unit pseudorapidity ($η$), $\langle $d$E_{\mathrm T}/$d$η\rangle$, in 0-5% central collisions is 1737 $\pm$ 6(stat.) $\pm$ 97(sys.) GeV. We find a similar centrality dependence of the shape of $\langle $d$E_{\mathrm T}/$d$η\rangle$ as a function of the number of participating nucleons to that seen at lower energies. The growth in $\langle $d$E_{\mathrm T}/$d$η\rangle$ at the LHC ${\sqrt{s_{\mathrm {NN}}}}$ exceeds extrapolations of low energy data. We observe a nearly linear scaling of $\langle $d$E_{\mathrm T}/$d$η\rangle$ with the number of quark participants. With the canonical assumption of a 1 fm/$c$ formation time, we estimate that the energy density in 0-5% central Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV is 12.3 $\pm$ 1.0 GeV/fm$^3$\xspace and that the energy density at the most central 80 fm$^2$ of the collision is at least 21.5 $\pm$ 1.7 GeV/fm$^3$. This is roughly 2.3 times that observed in 0-5% central Au-Au collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 200 GeV.

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