The production yields of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ resonances are measured in pp collisions at $\sqrt{s}=13$ TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$, which is related to the energy density produced in the collision. The results include transverse momentum ($p_{\rm T}$) distributions, $p_{\rm T}$-integrated yields, mean transverse momenta of $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$, as well as ratios of the $p_{\rm T}$-integrated resonance yields relative to yields of other hadron species. The $\Sigma(1385)^{\pm}/\pi^{\pm}$ and $\Xi(1530)^{0}/\pi^{\pm}$ yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ production in pp collisions at $\sqrt{s}=13$ TeV.
JHEP 05 (2024) 317
HEP Data
e-Print: arXiv:2308.16116 | PDF | inSPIRE
CERN-EP-2023-172
Figure group
Figure 1
Sketch of the decay modes of $\Sigma(1385)^\pm$ and $\Xi(1530)^0$ and depiction of the relevant variables employed for the selection of displaced decay topologies. The distance between the decay vertex (black circle) of the resonances and the PV (red circle) is inflated for clarity, that is, to separate such vertices normally just a few dozen femtometers away from one another. |   |
Figure 2
The invariant mass distribution of $\Lambda\pi^{+} + \overline{\Lambda}\pi^{-}$ pairs (a) and the charge conjugates (c) in $|y|<0.5$ produced in pp collisions at $\sqrt{s} = 13$ TeV for $1.8 < p_{\rm T,\Lambda\pi} < 2.0$ GeV/$c$ and the I+II+III multiplicity class (full black circles). The combinatorial background estimated with the event mixing technique is shown as open red squares in the (a) and (c) panels, whereas the invariant mass distributions after combinatorial background subtraction are shown in the (b) and (d) panels together with the fits to the signal and the residual background contributions. The solid red curves are the results of the combined fit and the dashed black lines represent the residual background. |     |
Figure 3
The invariant mass distribution of $\Xi^-\pi^+ + \Xi^+\pi^-$ pairs in $|y|<0.5$ produced in pp collisions at $\sqrt{s} = 13$ TeV for $1.6 < < p_{\rm T,\Lambda\pi} < 2.0$ GeV/$c$ and the I+II+III multiplicity class (full black circles). The combinatorial background estimated with the event mixing technique is shown as open red squares in panel (a), whereas the invariant mass distribution after combinatorial background subtraction is shown in panel (b) together with the fits to the signal and the residual background contributions. The solid red curve is the result of the combined fit and the dashed black line represents the residual background. |   |
Figure 4
The product of geometrical acceptance ($A$), reconstruction efficiency of the detector ($\epsilon_{\rm{rec}}$) and branching ratio (B.R.) for $\Sigma(1385)^\pm$ and $\Xi(1530)^0$ resonances as a function of $\pt$ in $|y|<0.5$ obtained with simulations based on event generation with PYTHIA 8 Monash 2013 and particle transported with GEANT 3. |  |
Figure 5
Transverse momentum spectra of $\Sigma(1385)^+$ (a), $\Sigma(1385)^-$ (b) and $\Xi(1530)^0$ (c) in pp collisions at $\sqrt{s}$ = 13 TeV in multiplicity classes and for the inclusive case (INEL $>$ 0). Statistical and total systematic uncertainties are shown by error bars and boxes, respectively. The bottom panels show the ratios of the multiplicity-dependent spectra to the INEL $>$ 0 distributions. The systematic uncertainties on the ratios are obtained by considering only contributions of multiplicity-uncorrelated uncertainties described in Table 5. The dashed lines represent the fits to the spectra with the Levi-Tsallis function. |    |
Figure 6
Ratios of transverse momentum spectra of $\Sigma(1385)^\pm$ (a) and $\Xi(1530)^0$ (b) in inelastic pp collisions at $\sqrt{s}$ = 13 TeV to the ones in inelastic pp collisions $\sqrt{s}$ = 7 TeV compared with those of $\Xi^{-}$, $\Lambda$ and $\pi^{\pm}$. The statistical and systematic uncertainties are shown as vertical error bars and boxes, respectively. In the present measurement, the shaded boxes represent the multiplicity-uncorrelated uncertainties. |   |
Figure 7
The $\pt$-integrated yields as a function of charged-particle pseudorapidity density $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle_{|\eta|<0.5}$ for $\Sigma(1385)^\pm$ (left) and $\Xi(1530)^0$ (right) compared with the measurements in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared with predictions from different event generators, namely EPOS-LHC, PYTHIA 8 with Monash 2013 tuning, and PYTHIA 8 with Rope shoving. (Appendix B). The predictions are obtained for pp collisions at $\sqrt{s}$ = 13 TeV on INEL $>$ 0 events. |  |
Figure 8
The $\langle \pt \rangle$ as a function of charged-particle pseudorapidity density for $\Sigma(1385)^\pm$ (left) and $\Xi(1530)^0$ (right) compared with the measurements in at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared with predictions from different event generators, namely EPOS-LHC, PYTHIA 8 with Monash 2013 tuning, and PYTHIA 8 with Rope shoving. (Appendix B). The predictions are obtained for pp collisions at $\sqrt{s}$ = 13 TeV on INEL $>$ 0 events. |  |
Figure 9
Ratio of the resonance to pion $\pt$-integrated yield as a function of the charged-particle pseudorapidity density for $\Sigma(1385)^\pm$ (left) and $\Xi(1530)^0$ (right). The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared with predictions from different event generators, namely EPOS-LHC, PYTHIA 8 with Monash 2013 tuning, and PYTHIA 8 with Rope shoving. (Appendix B). The predictions are obtained for pp collisions at $\sqrt{s}$ = 13 TeV on INEL $>$ 0 events. |  |
Figure 10
Yield ratio of the resonances to the ground states having the same quark content as a function of the charged-particle pseudorapidity density for $\Sigma(1385)^\pm$ (left) and $\Xi(1530)^0$ (right). The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared with predictions from different event generators, namely EPOS-LHC, PYTHIA 8 with Monash 2013 tuning, and PYTHIA 8 with Rope shoving. (Appendix B). The predictions are obtained for pp collisions at $\sqrt{s}$ = 13 TeV on INEL $>$ 0 events. |  |