Measurement of $Λ$(1520) production in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV

The production of the $\Lambda$(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at $\sqrt{s}$ = 7 TeV and in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel $\Lambda$(1520) $\rightarrow$ pK$^{-}$ and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p-Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons ($\pi$, K, K$_{\rm{S}}^0$, p, $\Lambda$) describes the shape of the $\Lambda$(1520) transverse momentum distribution up to 3.5 GeV/$c$ in p-Pb collisions. In the framework of this model, this observation suggests that the $\Lambda(1520)$ resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of $\Lambda(1520)$ to the yield of the ground state particle $\Lambda$ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p-Pb collisions on the $\Lambda$(1520) yield.

 

Eur. Phys. J. C 80 (2020) 160
HEP Data
e-Print: arXiv:1909.00486 | PDF | inSPIRE
CERN-EP-2019-178

Figure 1

Invariant-mass distributions of pK pairs for MB pp collisions at $\sqrt{s}$ $=$ 7 TeV (left panels) and for p--Pb collisions in the 0--20\% multiplicity interval at $\sn$ $\mathrm{=}$ 5.02 TeV (right panels) for the momentum interval 1.0 $\leq \pt

Figure 2

The geometrical acceptances times reconstruction efficiency (A $\times \ \epsilon$) for $\Ls$ in minimum bias pp and p--Pb events. Uncertainties (bars) are statistical only.

Figure 4

The $\mpt$ of $\Ls$ compared with previously measured $\mpt$ values of K$^{*0}$, ${\rm \phi}$, ${\rm \Sigma^{*\pm}}$, ${\rm\Xi^{*0}}$ and ${\rm\Omega^-}$ in p--Pb collisions at $\sn$ $\mathrm{=}$ 5.02 TeV as a function of the mean charged-particle multiplicity density $\dnchdeta$, measured in the pseudorapidity range $|\eta_{\rm lab}|

Figure 5

Mass dependence of the $\mpt$ of identified particles measured in inelastic pp collisions at \mbox{$\s$ $\mathrm{=}$ 7 TeV}  and in p--Pb collisions at $\sn$ $\mathrm{=}$ 5.02 TeV for the 0--20\% multiplicity intervals . Statistical uncertainties are represented as bars, square brackets indicate total systematic uncertainties.

Figure 6

The upper panel shows the $\pt$ distribution of $\Ls$ in p--Pb collisions at \mbox{$\sn$ $\mathrm{=}$ 5.02 TeV} in the 0--20\% (red) and 40--60\% (blue) multiplicity intervals. The dashed curves represent predictions from the Blast-Wave model , where the parameters are obtained from simultaneous fits to $\pi^{\pm}$, K$^{\pm}$, K$_{\rm{S}}^{0}$, p($\overline{\rm p}$) and $\Lam$($\overline{\Lam}$) $\pt$ spectra and the shapes are normalized to the data. The lower panel shows the ratios of the measured distributions to the values from the respective Blast-Wave functions. The statistical uncertainties are shown as bars and the systematic uncertainties are shown as boxes.

Figure 7

Ratio of $\Ls$, K$^{*0}$, ${\rm \Xi^{*0}}$ and ${\rm \phi}$ to charged $\pi$ (left) and K$^-$ (right) in p--Pb collisions at $\sn$ $\mathrm{=}$ 5.02 TeV as a function of the average charged-particle density $\dnchdeta$ measured at midrapidity . Statistical uncertainties (bars) are shown together with total (hollow boxes) and multiplicity-uncorrelated (shaded boxes) systematic uncertainties. The EPOS3 model predictions  with statistical uncertainties are shown as horizontal bars (pp collisions at $\s$ $\mathrm{=}$ 7 TeV) and shaded bands (p--Pb collisions at $\sn$ $\mathrm{=}$ 5.02 TeV).

Figure 8

Ratio of $\Ls$ to $\Lam$ in inelastic pp collisions at $\s$ $\mathrm{=}$ 7 TeV, p--Pb collisions at \mbox{$\sn$ $\mathrm{=}$ 5.02 TeV}  and in NSD pp collisions at $\s$ $\mathrm{=}$ 200 GeV . Statistical uncertainties (bars) are shown together with total (hollow boxes) and multiplicity-uncorrelated (shaded boxes) systematic uncertainties. The results are compared with several model calculations (see text for details).