Multiplicity-dependent production of $Σ(1385)^{\pm}$ and $Ξ(1530)^{0}$ in pp collisions at $\sqrt{s}=13$ TeV

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 to 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.

 

Submitted to: JHEP
e-Print: arXiv:2308.16116 | PDF | inSPIRE
CERN-EP-2023-172
Figure group

Figure 1

$\sigmapm$. $\xizero$. Sketch of the decay modes of $\sigmapm$ and $\xizero$ and depiction of the relevant variables employed for the selection of displaced decay topologies. The position of the decay vertex of the resonances is inflated to separate it from the PV for clarity.

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_ gev="" and="" the="" i="" multiplicity="" class="" black="" circles="" combinatorial="" background="" estimated="" with="" event="" mixing="" technique="" is="" shown="" as="" open="" red="" squares="" in="" panels="" whereas="" invariant="" mass="" distributions="" after="" subtraction="" are="" together="" fits="" to="" signal="" residual="" contributions.="" solid="" curves="" results="" of="" combined="" fit="" dashed="" lines="" represent="" background.="">< /p_>

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_ gev="" and="" the="" i="" multiplicity="" class="" black="" circles="" combinatorial="" background="" estimated="" with="" event="" mixing="" technique="" is="" shown="" as="" open="" red="" squares="" in="" panel="" whereas="" invariant="" mass="" distribution="" after="" subtraction="" together="" fits="" to="" signal="" residual="" contributions.="" solid="" curve="" result="" of="" combined="" fit="" dashed="" line="" represents="" background.="">< /p_>

Figure 4

The product of geometrical acceptance ($A$), reconstruction efficiency of the detector ($\epsilon_{\rm{rec}}$) and branching ratio (B.R.) for $\sigmapm$ and $\xizero$ resonances as a function of $\pt$ in $|y|<0.5$ obtained with simulations based on event generation with $\pythiaDef$ Monash 2013  and particle transported with GEANT 3 .

Figure 5

. . . Transverse momentum spectra of $\sigmap$ (a), $\sigmam$ (b) and $\xizero$ (c) in pp collisions at $\cms$ = 13 TeV in multiplicity classes and for the inclusive case ($\inelg$). 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 $\inelg$ distributions. The systematic uncertainties on the ratios are obtained by considering only contributions of multiplicity-uncorrelated uncertainties described in Table \ref{table:systable}. The dashed lines represent the fits to the spectra with the \levi function.

Figure 6

. . Ratios of transverse momentum spectra of $\sigmapm$ (a) and $\xizero$ (b) in inelastic \pp collisions at $\cms$ = 13 TeV to the ones in inelastic \pp collisions $\cms$ = 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 $\avdndeta_{|\eta|<0.5}$ for $\sigmapm$ (left) and $\xizero$ (right) compared with the measurements in \pp collisions at \seven  and \pPb collisions at \fivenn . The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared to predictions from different event generators, namely EPOS-LHC , $\pythiaDef$ with Monash 2013 tuning , and $\pythiaDef$ with Rope shoving  . (Appendix \ref{sec:ropetune}). The predictions are obtained for pp collisions at \thirteen on $\inelg$ events.

Figure 8

The \meanpt as a function of charged-particle pseudorapidity density for $\sigmapm$ (left) and $\xizero$ (right) compared with the measurements in \pp collisions at \seven  and \pPb collisions at \fivenn . The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared to predictions from different event generators, namely EPOS-LHC , $\pythiaDef$ with Monash 2013 tuning , and $\pythiaDef$ with Rope shoving  . (Appendix \ref{sec:ropetune}). The predictions are obtained for pp collisions at \thirteen, based on $\inelg$ events.

Figure 9

Ratio of the resonance to pion $\pt$-integrated yield as a function of the charged-particle pseudorapidity density for $\sigmapm$ (left) and $\xizero$ (right). The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared to predictions from different event generators, namely EPOS-LHC , $\pythiaDef$ with Monash 2013 tuning , and $\pythiaDef$ with Rope shoving  . (Appendix \ref{sec:ropetune}). The predictions are obtained for pp collisions at \thirteen, based on $\inelg$ 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 $\sigmapm$ (left) and $\xizero$ (right). The open and shaded boxes represent the total and multiplicity-uncorrelated systematic uncertainties, respectively. The measured points are compared to predictions from different event generators, namely EPOS-LHC , $\pythiaDef$ with Monash 2013 tuning , and $\pythiaDef$ with Rope shoving  . (Appendix \ref{sec:ropetune}). The predictions are obtained for pp collisions at \thirteen, based on $\inelg$ events.