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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.

 

Submitted to: EPJC
e-Print: arXiv:1909.00486 | PDF | inSPIRE
CERN-EP-2019-178

Figures

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 20--40\% multiplicity interval at $\sn$ $\mathrm{=}$ 5.02 TeV (right panels) for the momentum interval 1.0 $\leq \pt < $ 1.2 GeV/$c$. Panels (a) and (b) show the unlike-sign pK invariant-mass distribution from the same event and normalized combinatorial background for pp and p--Pb collisions, respectively. Panels (c) and (d) show the invariant-mass distribution after subtraction of the combinatorial background. The solid curve represents the Voigtian fit, while the dashed line describes the residual background. The statistical uncertainties are shown as bars.
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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.
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Figure 3

$\pt$ spectra of $\Ls$ measured with ALICE in the rapidity range $|y| < $ 0.5 in pp collisions at $\s$ $\mathrm{=}$ 7 TeV and in the rapidity range $-0.5 < y < 0$ in p--Pb collisions at \mbox{$\sn$ $\mathrm{=}$ 5.02 TeV} for minimum bias and different multiplicity intervals (V0A estimator). The multiplicity-dependent spectra are normalized to the visible cross-section, whereas the minimum bias spectrum is normalized to the fraction of NSD events. The minimum bias spectrum in pp collisions is normalized to the number of inelastic events. Statistical and systematic uncertainties ($\pt$-uncorrelated) are indicated as bars and boxes, respectively. Dashed lines represent L\'{e}vy-Tsallis fits.
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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 $|\eta_{\rm lab}| < 0.5$~. The ${\rm\Xi^{*0}}$ points are slightly displaced along the abscissa for clarity. Statistical uncertainties are represented as bars, whereas boxes indicate systematic uncertainties.
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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.
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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.
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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).
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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).
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