Azimuthal anisotropy of jet particles in p-Pb and Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The azimuthal anisotropy of particles associated with jets (jet particles) at midrapidity is measured for the first time in p-Pb and Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV down to transverse momentum ($p_{\rm T}$) of 0.5 GeV/$c$ and 2 GeV/$c$, respectively, with ALICE. The second-order Fourier coefficient of the jet-particle azimuthal distribution ($v_2$) in high-multiplicity p-Pb collisions is positive, with a significance reaching 6.8$\sigma$ at low $p_{\rm T}$. Comparisons with the inclusive charged-particle $v_2$ and with AMPT calculations are discussed. The model describes qualitatively the main features of the jet-particle $v_2$ in high-multiplicity p-Pb collisions and indicates that the positive jet-particle $v_2$ is generated by parton interactions.


Submitted to: PRL
e-Print: arXiv:2212.12609 | PDF | inSPIRE
Figure group

Figure 1

Raw associated yield per trigger particle $Y$ (left) and $v_{2}$ of trigger charged particles (right) as a function of $\Delta \eta$ and $\Delta \varphi$ for pairs of charged particles measured in $\vert \eta \vert < 0.8$ with $3 < \pT^{\rm trig} < 5$ GeV/$c$ and $1 < \pT^{\rm assoc} < \pT^{\rm trig}$ GeV/$c$ in high-multiplicity (0--10\%) p--Pb collisions at $\snn = 5.02$ TeV.

Figure 2

Top: Jet-particle $v_2$ as a function of \pt of trigger particles for several $\pt^{\rm assoc}$ intervals in 0--10\% \pPb and 20--60\% \PbPb collisions at $\snn = 5.02$ TeV, compared with the inclusive charged-particle $v_2$ in both systems. The values of the jet-particle $v_2$ are horizontally shifted around the centre of the bin for better visibility. The statistical uncertainties, shown as vertical bars, are determined using the sub-sample technique. The systematic uncertainties are represented as filled boxes. Horizontal bars indicate the bin width. The previous results published by ALICE for reconstructed jet $v_2$ measured in 30--50\% \PbPb collisions at $\snn = 2.76$ TeV are also shown . The \PbPb measurements are downscaled by a factor of 0.6. Middle: Comparison of the jet-particle and inclusive charged-particle $v_2$ obtained in \pPb collisions with AMPT calculations . Bottom: Comparison of the nuclear modification factor $Q_{\rm pPb}$ of inclusive charged particles obtained in \pPb collisions with AMPT calculations .