The production of strange hadrons (K$^{0}_{\rm S}$, $\Lambda$, $\Xi^{\pm}$, and $\Omega^{\pm}$), baryon-to-meson ratios ($\Lambda/{\rm K}^0_{\rm S}$, $\Xi/{\rm K}^0_{\rm S }$, and $\Omega/{\rm K}^0_{\rm S}$), and baryon-to-baryon ratios ($\Xi/\Lambda$, $\Omega/\Lambda$, and $\Omega/\Xi$) associated with jets and the underlying event were measured as a function of transverse momentum ($p_{\rm T}$) in pp collisions at $\sqrt{s} = 13$ TeV and p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector at the LHC. The inclusive production of the same particle species and the corresponding ratios are also reported. The production of multi-strange hadrons, $\Xi^{\pm}$ and $\Omega^{\pm}$, and their associated particle ratios in jets and in the underlying event are measured for the first time. In both pp and p-Pb collisions, the baryon-to-meson and baryon-to-baryon yield ratios measured in jets differ from the inclusive particle production for low and intermediate hadron $p_{\rm T}$ (0.6$-$6 GeV/$c$). Ratios measured in the underlying event are in turn similar to those measured for inclusive particle production. In pp collisions, the particle production in jets is compared with PYTHIA 8 predictions with three colour-reconnection implementation modes. None of them fully reproduces the data in the measured hadron $p_{\rm T}$ region. The maximum deviation is observed for $\Xi^{\pm}$ and $\Omega^{\pm}$, which reaches a factor of about six. In p-Pb collisions, there is no significant event-multiplicity dependence for particle production in jets, in contrast to what is observed in the underlying event. The presented measurements provide novel constraints on hadronisation and its Monte Carlo description. In particular, they demonstrate that the fragmentation of jets alone is insufficient to describe the strange and multi-strange particle production in hadronic collisions at LHC energies.
JHEP 07 (2023) 136
HEP Data
e-Print: arXiv:2211.08936 | PDF | inSPIRE
CERN-EP-2022-218
Figure group
Figure 1
Invariant mass distribution for ${\rm K_S^0}$, $\Lambda$, $\Xi^-$, and $\Omega^-$ in different $\pT$ intervals in MB p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The candidates are reconstructed in $|\eta|<0.75$. The grey areas are used to determine the background (red dashed lines), see text for details. |     |
Figure 2
Strange particle reconstruction efficiency in pp collisions at $\sqrt{s}$ = 13 TeV (left) and in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV (right) for two selections: inside the jet cone ($R({\rm par, jet}) < 0.4$) and for the inclusive case The vertical bars represent the statistical uncertainties. |   |
Figure 3
Fraction of $\Lambda$ yield removed due to the subtraction of feed-down contributions from charged and neutral $\Xi$ baryons decays in pp collisions at $\sqrt{s}$ = 13 TeV (left) and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV (right) The vertical bars represent the statistical uncertainties. |   |
Figure 4
$\pT$-differential density, ${\rm d}\rho/{\rm d}\pT$, of ${\rm K_S^0}$ (top left panel), $\Lambda$ (top right panel), $\Xi$ (bottom left panel), and $\Omega$ (bottom right panel) in pp collisions at $\sqrt{s}$ = 13 TeV. The spectra of JE particles (red triangles), associated with hard scatterings, are compared with that of JC (green squares) and UE (blue open circles) selections The results from inclusive measurements (black closed circles) are presented as well The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure 5
$\pT$-dependent strange baryon-to-meson (top) and baryon-to-baryon (bottom) yield ratios in pp collisions at $\sqrt{s}$ = 13 TeV. For each case, the results of JE particles (red triangles) are compared with that of inclusive (black closed circles) and UE (blue open circles) particles The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure 6
$\pT$-differential density distributions for inclusive (left) and within jets (right) ${\rm K_S^0}$ (black closed circles), $\Lambda$ (red open circles), $\Xi$ (blue squares), and $\Omega$ (green inverted triangles) in pp collisions at $\sqrt{s}$ = 13 TeV. The spectra in data are compared with PYTHIA 8 CR-BLC simulations Three modes, labeled as mode $0$ (solid line), $2$ (dashed line), and $3$ (dash-dotted line) are adopted in the simulations The PYTHIA-to-data ratios are shown in the four bottom panels where the spread of the three PYTHIA 8 CR-BLC implementation modes are presented as bands For clarity, some of the spectra were scaled with the factors indicated in the legends The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |   |
Figure 7
$\pT$-dependent strange baryon-to-meson (top) and baryon-to-baryon (bottom) ratios in pp collisions at $\sqrt{s}$ = 13 TeV. For each case, the results of JE (red triangles) and inclusive (black closed circles) particles are compared with PYTHIA 8 CR-BLC simulations The bands correspond to the spread of simulations of the three different CR-BLC implementation modes The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure 8
$\pT$-differential density, ${\rm d}\rho/{\rm d}\pT$, of ${\rm K_S^0}$ (top left panel), $\Lambda$ (top right panel), $\Xi$ (bottom left panel), and $\Omega$ (bottom right panel) in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The spectra of JE particles (red triangles), associated with hard scatterings, are compared with that of JC (green squares) and UE (blue open circles) selections The results from inclusive measurements (black closed circles) are presented as well. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure 9
$\pT$-dependent strange baryon-to-meson (top) and baryon-to-baryon (bottom) ratios for particles produced within jets in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. For each case, the results for different event multiplicity classes are compared with that in pp collisions at $\sqrt{s}$ = 13 TeV. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes See the text for details. |  |
Figure B.1
$\pT$-dependent $\Xi$/$\Lambda$ (left panel) and $\Omega$/$\Lambda$ (right panel) ratios in pp collisions at $\sqrt{s}$ = 13 TeV. For each case, the results of JE particles (red inverted-triangle) are compared with that of inclusive (black closed circles) The corresponding colour-rope predictions implemented in the PYTHIA 8 event generator are compared to data as well. |   |
Figure C.1
$\pT$-differential density, ${\rm d}\rho/{\rm d}\pT$, of ${\rm K_S^0}$ (left panel), $\Lambda$ (middle panel) and $\Xi$ (right panel) for the 0$-$10% event multiplicity class in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The spectra of JE particles (red inverted-triangle), associated with hard scatterings, are compared with that of JC (green squares) and UE (blue open circles) selections. The results from inclusive measurements (black closed circles) are presented as well. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure C.2
$\pT$-differential density, ${\rm d}\rho/{\rm d}\pT$, of ${\rm K_S^0}$ (left panel), $\Lambda$ (middle panel) and $\Xi$ (right panel) for the 10$-$40% event multiplicity class in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The spectra of JE particles (red inverted-triangle), associated with hard scatterings, are compared with that of JC (green squares) and UE (blue open circles) selections. The results from inclusive measurements (black closed circles) are presented as well. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure C.3
$\pT$-differential density, ${\rm d}\rho/{\rm d}\pT$, of ${\rm K_S^0}$ (left panel), $\Lambda$ (middle panel) and $\Xi$ (right panel) for the 40$-$100% event multiplicity class in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The spectra of JE particles (red inverted-triangle), associated with hard scatterings, are compared with that of JC (green squares) and UE (blue open circles) selections. The results from inclusive measurements (black closed circles) are presented as well. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure C.4
$\pT$-dependent $\Lambda$/${\rm K_S^0}$ ratio for 0$-$10% (left panel), 10$-$40% (middle panel) and 40$-$100% (right panel) event multiplicity classes. For each case, the results of JE particles (red inverted-triangle) are compared with that of inclusive (black closed circles) and UE (blue open circles) particles. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure C.5
$\pT$-dependent $\Xi$/${\rm K_S^0}$ ratio for 0$-$10% (left panel), 10$-$40% (middle panel) and 40$-$100% (right panel) event multiplicity classes. For each case, the results of JE particles (red inverted-triangle) are compared with that of inclusive (black closed circles) and UE (blue open circles) particles. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |
Figure C.6
$\pT$-dependent $\Xi$/$\Lambda$ ratio for 0$-$10% (left panel), 10$-$40% (middle panel) and 40$-$100% (right panel) event multiplicity classes. For each case, the results of JE particles (red inverted-triangle) are compared with that of inclusive (black closed circles) and UE (blue open circles) particles. The statistical uncertainties are represented by the vertical error bars and the systematic uncertainties by the boxes. |  |