# $φ$ meson production at forward rapidity in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=2.76$ TeV

$\phi$ meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured $\phi$ production through its decay in muon pairs in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76 TeV in the intermediate transverse momentum range $2 <~ p_{\rm T} <~ 5$ GeV/$c$ and in the rapidity interval $2.5<~y<~4$. The $\phi$ yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same $p_{\rm T}$ range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties.

Submitted to: EPJC
e-Print: arXiv:1804.08906 | PDF | inSPIRE
CERN-EP-2018-082

Figures

## Figure 1

 Invariant mass spectra for opposite-sign muon pairs in different centrality classes, in the range $2 < \pt < 5$ GeV/\textit{c}. The combinatorial background, evaluated from opposite-sign pairs in mixed events, is also shown.

## Figure 2

 Ratio between the mass spectra of correlated and uncorrelated pairs for different centralities, in the range 2~$< p_\mathrm{T} <$~5~GeV/\textit{c} in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76~TeV.

## Figure 3

 Invariant mass spectra in different centrality classes for 2~$< p_\mathrm{T} <$~5~GeV/\textit{c} in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76~TeV. The solid red line represents the result of the fit to the hadronic cocktail; the green dashed line represents the correlated background, given by the sum of all the MC sources other than $\phi$, $\rho$ and $\omega$ mesons.

## Figure 4

 Invariant mass spectra for $2.5 < \pt < 3$ GeV/$c$ and $3.6 < \pt < 4.2$ GeV/$c$ in 0--90\% Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 2.76~TeV. The solid red line represents the result of the fit to the hadronic cocktail; the green dashed line represents the correlated background, given by the sum of all the MC sources other than $\phi$, $\rho$ and $\omega$ mesons.

## Figure 5

 $\phi$ yield as a function of $\pt$ at forward rapidity in pp~ and Pb--Pb collisions for different centralities The distributions have been scaled differently for better visibility.

## Figure 6

 Top panel: comparison between the $\phi$ yield as a function of $\pt$ with the EPOS~3.101~and HIJING~2.0~ event generators, at forward and midrapidity~ The distributions have been scaled differently for better visibility. The same scale factorsapplied to data were also used for the models. The transparent boxes represent the uncorrelated systematic uncertaintiesat forward rapidity and the total systematic uncertainties (including correlated and uncorrelated components) at midrapidity Lower panels: ratios between the measured yields and the calculations by EPOS and HIJING.

## Figure 7

 Top panel: comparison between $(\mathrm{d}N_{\phi}/\mathrm{d}y)/\npart$ as afunction of $\npart$ measured in the muon decay channel at forward rapidity and in the kaon decay channel at midrapidity, in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}}= 2.76$~TeV, for $2 < p_\mathrm{T} < 5$~GeV/\textit{c} The corresponding points in pp collisions at $\npart = 2$ are also shown Transparent boxes represent the uncorrelated systematic uncertainties at forward rapidity and the total systematic uncertainties (including correlated and uncorrelated components) at midrapidity The shaded red box represents the correlated systematic uncertainties at forward rapidity, the shaded blue box represents the normalization uncertainty at midrapidity Results from the EPOS~3.101 and HIJING~2.0 event generators are shown for comparison The rapidity density per participant for pions at midrapidity is also reported, scaled to 0.1 Bottom panel: ratio between $\phi$ rapidity densities per participant at mid- and forward rapidity, in pp (open circle) and Pb--Pb collisions (full circles).

## Figure 8

 $R_{\mathrm{AA}}$ of the $\phi$ meson as a function of $\langle N_{\mathrm{part}} \rangle$ for $2.5< y< 4$, compared with theALICE measurement for $|y|< 0.5$. All the midrapidity points have been displaced by $\npart$ = 10 for better visibility Transparent boxes represent the uncorrelated systematic uncertainties at forward rapidity and the total systematic uncertainties (including correlated and uncorrelated components) at midrapidity The shaded red box represents the correlated systematic uncertainties at forward rapidity, the shaded blue box represents the normalization uncertainty at midrapidity. Results from PHENIX in Au-Au and Cu-Cu collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV are also shown for comparison.