Suppression of $\mathrm{\Lambda }\left(1520\right)$ resonance production in central Pb-Pb collisions at $\sqrt{s_{\mathit{NN}}}=2.76$ TeV

The production yield of the $\mathrm{\Lambda }\left(1520\right)$ baryon resonance is measured at midrapidity in Pb-Pb collisions at $\sqrt{s_{\mathit{NN}}}$ = 2.76 TeV with the ALICE detector at the Large Hadron Collider (LHC). The measurement is performed in the $\mathrm{\Lambda }\left(1520\right)\to \mathrm{p}{\mathrm{K}}^{-}$ (and charge conjugate) hadronic decay channel as a function of the transverse momentum ($p_{\mathrm{T}}$) and collision centrality. The ratio of the $p_{\mathrm{T}}$-integrated production of $\mathrm{\Lambda }\left(1520\right)$ baryons relative to $\mathrm{\Lambda }$ baryons in central collisions is suppressed by about a factor of 2 with respect to peripheral collisions. This is the first observation of the suppression of a baryonic resonance at the LHC and the first $3\sigma$ evidence of $\mathrm{\Lambda }\left(1520\right)$ suppression within a single collision system. The measured $\mathrm{\Lambda }\left(1520\right)/\mathrm{\Lambda }$ ratio in central collisions is smaller than the value predicted by the statistical hadronization model calculations. The shape of the measured $p_{\mathrm{T}}$ distribution and the centrality dependence of the suppression are reproduced by the EPOS3 Monte Carlo event generator. The measurement adds further support to the formation of a dense hadronic phase in the final stages of the evolution of the fireball created in heavy-ion collisions, lasting long enough to cause a significant reduction in the observable yield of short-lived resonances.

Figure 1

Example invariant-mass distributions of the $\mathrm{\Lambda }\left(1520\right)\to \mathrm{p}{\mathrm{K}}^{-}$ (and charged conjugate) reconstruction after subtraction of the mixed-event background. The solid line represents the global fit (signal + residual background) to the data while the dashed line indicates the estimated residual background. The error bars indicate the statistical uncertainties of the data.

Figure 2

(Left) $p_{\mathrm{T}}$-differential yields of $\mathrm{\Lambda }\left(1520\right)$ at midrapidity, $\left|y\right|<0.5$, in the centrality classes 0–20%, 20–50%, and 50–80%. The solid and dashed curves represent predictions from the blast-wave model (normalization fitted to the data) and EPOS3, respectively. The horizontal error bars represents the width of the measured $p_{\mathrm{T}}$ interval. (Right) Ratio of the data to the blast-wave and EPOS3 predictions.

Figure 3

$\langle p_{\mathrm{T}}\rangle$ of $\mathrm{\Lambda }\left(1520\right)$ as a function of ${\langle d{N}_{\mathrm{ch}}/d\eta \rangle }^{1/3}$. Statistical and systematic uncertainties are shown as bars and boxes, respectively. The solid line shows the blast-wave predictions. The dashed lines show the predictions from EPOS3 with and without the hadronic phase (UrQMD off).

Figure 4

$p_{\mathrm{T}}$-integrated ratio of $\mathrm{\Lambda }\left(1520\right)/\mathrm{\Lambda }$ production as a function of ${\langle d{N}_{\mathrm{ch}}/d\eta \rangle }^{1/3}$. Predictions from several SHMs and from EPOS3 are also shown.