在质心能量\(\sqrt{s_{NN}} = 5.02\) TeV的铅-铅碰撞中，来自重味强子衰变的电子椭圆流

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Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata, India.

Nuclear Physics Institute of the Czech Academy of Sciences, Řež u Prahy, Czech Republic.

Phys Rev Lett. 2021 Apr 23;126(16):162001. doi: 10.1103/PhysRevLett.126.162001.

The elliptic flow of electrons from beauty hadron decays at midrapidity (|y|<0.8) is measured in Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV with the ALICE detector at the LHC. The azimuthal distribution of the particles produced in the collisions can be parametrized with a Fourier expansion, in which the second harmonic coefficient represents the elliptic flow, v_{2}. The v_{2} coefficient of electrons from beauty hadron decays is measured for the first time in the transverse momentum (p_{T}) range 1.3-6 GeV/c in the centrality class 30%-50%. The measurement of electrons from beauty-hadron decays exploits their larger mean proper decay length cτ≈500 μm compared to that of charm hadrons and most of the other background sources. The v_{2} of electrons from beauty hadron decays at midrapidity is found to be positive with a significance of 3.75 σ. The results provide insights into the degree of thermalization of beauty quarks in the medium. A model assuming full thermalization of beauty quarks is strongly disfavored by the measurement at high p_{T}, but is in agreement with the results at low p_{T}. Transport models including substantial interactions of beauty quarks with an expanding strongly interacting medium describe the measurement within uncertainties.

利用大型强子对撞机（LHC）上的ALICE探测器，在质心能量(\sqrt{s_{NN}} = 5.02) TeV的铅-铅碰撞中，测量了在中快度（(\vert y \vert < 0.8)）下美强子衰变产生的电子的椭圆流。碰撞中产生的粒子的方位角分布可以用傅里叶展开来参数化，其中二次谐波系数代表椭圆流(v_2)。首次在中心度为30%-50%的情况下，在横向动量（(p_T)）范围1.3 - 6 GeV/c内测量了美强子衰变产生的电子的(v_2)系数。对美强子衰变产生的电子的测量利用了它们与粲强子及大多数其他背景源相比更大的平均固有衰变长度(c\tau\approx500) (\mu)m。发现在中快度下美强子衰变产生的电子的(v_2)为正，显著性为3.75 (\sigma)。这些结果为介质中美夸克的热化程度提供了见解。一个假设美夸克完全热化的模型在高(p_T)测量中受到强烈质疑，但与低(p_T)的结果一致。包括美夸克与膨胀的强相互作用介质大量相互作用的输运模型在不确定性范围内描述了该测量结果。