The study of the azimuthal anisotropy of inclusive muons produced in p-Pb collisions at $\sqrt{s_{\rm NN}} = 8.16$ TeV, using the ALICE detector at the LHC is reported. 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 ($2.03 <~ y_{\rm CMS} <~ 3.53$) and backward ($-4.46 <~ y_{\rm CMS} <~ -2.96$) 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. Both techniques give compatible results. 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/$c$. Comparisons with previous measurements in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.
Phys. Lett. B 846 (2023) 137782
HEP Data
e-Print: arXiv:2210.08980 | PDF | inSPIRE
CERN-EP-2022-209
Figure group
Figure 1
Left: associated yield per trigger particle as a function of $\Delta \eta$ and $\Delta \varphi$ between inclusive muons with $ 2 < \pT < 2.5$ GeV/$c$ and SPD tracklets, $Y_{\rm sub}$, in high-multiplicity (0$-$20%) p--Pb collisions at $\sNN =$ 8.16 TeV after the subtraction of the unscaled (top) and scaled (bottom) muon--tracklet correlation in low-multiplicity (60$-$90%) events. Right: fit of the corresponding correlation distributions in $-5 < \Delta\eta < -1.5$ projected onto $\Delta\varphi$ with a Fourier decomposition, see Eq. (3). The three first harmonics are also presented. |     |
Figure 2
Comparison of the two-particle second-order $\pT$-differential muon cumulant before and after the subtraction of the $\pT$-differential cumulant in low-multiplicity collisions and remaining long-range jet correlations at forward (left) and backward (right) rapidities in high-multiplicity p--Pb collisions at $\sNN =$ 8.16 TeV. The comparison is presented with the V0M estimator. Only statistical uncertainties are shown. |   |
Figure 3
Inclusive muon $v_2^{\rm \mu}$ as a function of $\pT$ at forward (left) and backward (right) rapidities in high-multiplicity p--Pb collisions at $\sNN =$ 8.16 TeV. The event activity is estimated with the V0M estimator. Open and full symbols refer to the measurements with two-particle correlations and two-particle cumulants, respectively. |   |
Figure 4
Inclusive muon $v_2^{\rm \mu}$ as a function of $\pT$ at forward (left) and backward (right) rapidity in high-multiplicity p--Pb collisions at $\sNN =$ 8.16 TeV, extracted with two-particle cumulants (top) and two-particle correlations (bottom). The results are obtained with three different estimators of the event activity: V0M, CL1 and ZN. |     |
Figure 5
Comparison of the $\pT$-differential $v_2\lbrace {\rm 2PC} \rbrace$ of inclusive muons at forward (left) and backward (right) rapidity in high-multiplicity p--Pb collisions at $\sNN =$ 8.16 TeV, extracted with the two-particle correlation method with previous measurements performed in p--Pb collisions at $\sNN =$ 5.02 TeV for inclusive muons and electrons from heavy-flavour hadron decays . |   |
Figure 6
Comparison of the $\pT$-differential $v_2^{\rm \mu} \lbrace {\rm 2PC} \rbrace$ of inclusive muons at forward (left) and backward (right) rapidities in high-multiplicity p--Pb collisions at $\sNN =$ 8.16 TeV with AMPT calculations . The predictions are shown for muons from charm-hadron decays and beauty-hadron decays, separately, muons from charged-pion and kaon decays, and for muons from the combination of the various sources. The contribution of muons from both charm- and beauty-hadron decays is also displayed. |   |
Figure 7
Left: comparison of the $\pT$-differential $v_2^{\rm \mu} \lbrace {\rm 2PC} \rbrace$ of inclusive muons at forward rapidity in high-multiplicity p--Pb collisions at $\sNN =$ 8.16 TeV with CGC-based calculations . The predictions are shown for muons from charm-hadron decays and beauty-hadron decays, separately, and for muons from the combination of the two sources. Right: comparison of the $\pT$-differential $v_2$ of muons from heavy-flavour hadron decays as obtained with CGC and AMPT calculations with the measured inclusive muon $v_2$. |   |