The production of $\Lambda$ baryons and ${\rm K}^{0}_{\rm S}$ mesons (${\rm V}^{0}$ particles) was measured in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and pp collisions at $\sqrt{s} = 7$ TeV with ALICE at the LHC. The production of these strange particles is studied separately for particles associated with hard scatterings and the underlying event to shed light on the baryon-to-meson ratio enhancement observed at intermediate transverse momentum ($p_{\rm T}$) in high multiplicity pp and p-Pb collisions. Hard scatterings are selected on an event-by-event basis with jets reconstructed with the anti-$k_{\rm T}$ algorithm using charged particles. The production of strange particles associated with jets $p_{\rm T,\;jet}^{\rm ch}>10$ and $p_{\rm T,\;jet}^{\rm ch}>20$ GeV/$c$ in p-Pb collisions, and with jet $p_{\rm T,\;jet}^{\rm ch}>10$ GeV/$c$ in pp collisions is reported as a function of $p_{\rm T}$. Its dependence on angular distance from the jet axis, $R({\rm V}^{0},\;{\rm jet})$, for jets with $p_{\rm T,\;jet}^{\rm ch}>10$ GeV/$c$ in p-Pb collisions is reported as well. The $p_{\rm T}$-differential production spectra of strange particles associated with jets are found to be harder compared to that in the underlying event and both differ from the inclusive measurements. In events containing a jet, the density of the ${\rm V}^{0}$ particles in the underlying event is found to be larger than the density in the minimum bias events. The $\Lambda/{\rm K}^{0}_{\rm S}$ ratio associated with jets in p-Pb collisions is consistent with the ratio in pp collisions and follows the expectation of jets fragmenting in vacuum. On the other hand, this ratio within jets is consistently lower than the one obtained in the underlying event and it does not show the characteristic enhancement of baryons at intermediate $p_{\rm T}$ often referred to as "baryon anomaly" in the inclusive measurements.
Phys. Lett. B 827 (2022) 136984
HEP Data
e-Print: arXiv:2105.04890 | PDF | inSPIRE
CERN-EP-2021-048
Figure group
Figure 1
Reconstruction efficiency of \Vzero\ particles in \pPb\ collisions at \fivenn (left panel) and in pp collisions at \seven (right panel) for three selection criteria: inclusive, within $\Rvj<0.4$ and \Vzero{}s in UE (upper panels) and the ratio relative to inclusive selection (lower panels) UE \Vzero{}s are estimated with the OC estimator ($\Rvj>0.6$) in \pPb collisions and with the PC estimator in pp collisions. |  |
Figure 2
The $\pT$-differential density of particles $\drhoVdpT$ (see Eq. \eqref{eq:defv0rho}) in \pPb collisions at \fivenn for \kzero\ (upper panel) and the sum of \lmb\ and \almb\ (lower panel) The density is shown for three selection criteria: inclusive particles from minimum bias events (black full circle), particles associated with the underlying event production estimated with PC selection (blue open circle, labelled as ``Perp. cone" in the figure), JC $\Vzero$s with $\Rvj < 0.4$ (green full square) The density distribution of $\Vzero$s in jets with UE background subtracted (defined by Eq. (\ref{eq:defJEV0s})) is shown as the red full triangle Statistical uncertainties and systematic uncertainties are shown as vertical bars and open boxes, respectively. |   |
Figure 3
The $\pt$-differential density of particles $\drhoVdpT$ (see Eq. \eqref{eq:defv0rho}) in pp collisions at \seven for \kzero\ (upper), and the sum of \lmb\ and \almb\ (lower) The density is shown for four selection criteria with the same definitions as Fig. \ref{fig:rhov0pPb}. |   |
Figure 4
The $\rLK$ ratio in \pPb collisions at \fivenn as a function of $\Rvj$ for three different \Vzero{}-particle $\pT$ intervals associated with charged jets with $\pTjch>10$ \GeVc The data points of the ratios in $0.6<\pTv <1.8$ \GeVc and in $4.2<\pTv <12$ \GeVc are shifted to the left and right sides from the centre, along the $\Rvj$-axis for better visibility Statistical uncertainties (vertical bars) and systematic uncertainties (open boxes) are shown The sources of the systematic uncertainty are summarized in table \ref{tab:systR} The uncertainty on $\Vzero$ yield extraction is uncorrelated with $\Vzero$ $\pT$ but correlated with $\Rvj$, the uncertainties on jet $\pT$ scale and on UE subtraction are uncorrelated on both $\Vzero$ $\pT$ and $\Rvj$. |  |
Figure 5
The $\rLK$ ratio in \pPb collisions at \fivenn (upper panel) and pp collisions at \seven (lower panel) as a function of \Vzero{}-particle $\pT$, associated with charged jets with $\pTjch>10$ \GeVc (for both pp and p--Pb collisions) and $20$ \GeVc (for p--Pb collisions only) together with that in inclusive and PC selection, and JC selection in case of pp collisions The systematic uncertainties (open boxes) are fully uncorrelated with $\pT$ In both upper and lower panels, the black dashed curves are the results for inclusive $\Vzero$s from \Pythia $8$ simulations The jet selection within \Pythia $8$ is made using the generator level information with $\pTjch>10$ \GeVc shown as the red curves. |   |
Figure 6
The $\rLK$ ratio in pp collisions at \seven and in \pPb\ collisions at \fivenn as a function of \Vzero{}-particle $\pT$ associated with charged particle jets with $\pTjch>10$ \GeVc reconstructed using the \akT\ jet finder with resolution parameter $R=0.4$ The ratio is shown for the same selection of the matching radius $\Rvj<0.4$ in both systems The systematic uncertainties (open boxes) are uncorrelated between the systems. |  |