Measurements of azimuthal anisotropies at forward and backward rapidity with muons in high-multiplicity p-Pb collisions at $\sqrt{s_{\rm NN}} = 8.16$ TeV

The collaboration
CERN-EP-2022-209, 2022.

Abstract (data abstract)
The azimuthal anisotropy of inclusive muons produced in p--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV is measured by using the ALICE detector at the LHC. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, $v_2$, is performed as a function of transverse momentum $p_{\rm T}$ in the 0$-$20% high-multiplicity interval at both forward ($2.03 < y_{\mathrm{cms}} < 3.53$) and backward ($-4.46 < y_{\mathrm{cms}} < -2.96$) rapidities over a wide $p_{\rm T}$ range, $0.5 < p_{\rm T} < 10$ GeV/$c$, in which a dominant contribution of muons from heavy-flavour hadron decays is expected at $p_{\rm T} > 2$ GeV/$c$. The $v_2$ coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward--central two-particle correlations. A positive $v_2$ is measured at both forward and backward rapidities with a significance larger than 4.7$\sigma$ and 7.6$\sigma$, respectively, in the interval $2<p_{\rm T}<6$ GeV/$c$. The comparisons between the results and theoretical calculations can impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.