$K_S^0$ and ${\Lambda }^0$ production studies in $p\overline{p}$ collisions at $\sqrt{s}=1800$ and 630 GeV

We present a study of the production of $K_S^0$ and ${\Lambda }^0$ in inelastic $p\overline{p}$ collisions at $\sqrt{s}=1800$ and 630 GeV using data collected by the CDF experiment at the Fermilab Tevatron. Analyses of $K_S^0$ and ${\Lambda }^0$ multiplicity and transverse momentum distributions, as well as of the dependencies of the average number and $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ on charged particle multiplicity, are reported. Systematic comparisons are performed for the full sample of inelastic collisions, and for the low and high momentum transfer subsamples, at the two energies. The $p_T$ distributions extend above $8\mathrm{GeV}/c$, showing a $⟨p_T⟩$ higher than previous measurements. The dependence of the mean $K_S^0({\Lambda }^0)$ $p_T$ on the charged particle multiplicity for the three samples shows a behavior analogous to that of charged primary tracks.

Figure 1

Invariant mass with a $\pi$-$\pi$ and $\pi$-$p$ mass assignment for oppositely signed track pairs passing all selection requirements but allowing the mass to be within $10\sigma$ from the nominal mass. The background includes the contamination by $K_S^0$ in the ${\Lambda }^0$ sample and vice versa. 1800 GeV data are shown.

Figure 2

Overall correction factors at 1800 GeV for $K_S^0({\Lambda }^0)$ as a function of the transverse momentum. The correction factors are defined in the text.

Figure 3

Raw and corrected $K_S^0$ and ${\Lambda }^0$ proper lifetime distributions for 1800 GeV data. The line represents the best exponential fit to the data.

Figure 4

The mean $p_T$ of $K_S^0$ and ${\Lambda }^0$ as a function of proper lifetime ($t$) at 1800 GeV. Raw and corrected data are shown.

Figure 5

Distribution of the multiplicity of $K_S^0$ at 1800 (full symbols) and 630 GeV (open symbols).$P(N_K)=(\mathrm{\text{number of events with}}{N}_K{K}_S^0)/(\mathrm{\text{total number of events}})$. MB, soft (divided by 100), and hard data (multiplied by 100) are shown.

Figure 6

Distribution of the multiplicity of ${\Lambda }^0$ at 1800 (full symbols) and 630 GeV (open symbols). $P(N_{\Lambda })=(\mathrm{\text{number of events with}}{N}_{\Lambda }{\Lambda }^0)/(\mathrm{\text{total number of events}})$. MB, soft (divided by 100), and hard data (multiplied by 100) are shown.

Figure 7

$K_S^0$ inclusive invariant $p_T$ distributions at 1800 GeV. MB, soft, and hard data are shown, normalized to the number of events in each sample. $E$ is the particle energy and $N_{\mathrm{event}}$ is the total number of events which contribute to the distribution. To separate the curves, hard data points are multiplied by 10 and soft data points by 0.1. The solid lines represent the best fits to Eq. (2) of the text.

Figure 8

$K_S^0$ inclusive invariant $p_T$ distributions at 630 GeV MB, soft, and hard data are shown, normalized to the number of events in each sample. $E$ is the particle energy and $N_{\mathrm{event}}$ is the total number of events which contribute to the distribution. To separate the curves, hard data points are multiplied by 10 and soft data points by 0.1. The solid lines represent the best fits to Eq. (2) of the text.

Figure 9

${\Lambda }^0$ inclusive invariant $p_T$ distributions at 1800 GeV. MB, soft, and hard data are shown, normalized to the number of events in each sample. $E$ is the particle energy and $N_{\mathrm{event}}$ is the total number of events which contribute to the distribution. To separate the curves, hard data points are multiplied by 10 and soft data points by 0.1. The solid lines represent the best fits to Eq. (2) of the text.

Figure 10

${\Lambda }^0$ inclusive invariant $p_T$ distributions at 630 GeV. MB, soft, and hard data are shown, normalized to the number of events in each sample. $E$ is the particle energy and $N_{\mathrm{event}}$ is the total number of events which contribute to the distribution. To separate the curves, hard data points are multiplied by 10 and soft data points by 0.1. The solid lines represent the best fits to Eq. (2) of the text.

Figure 11

Average transverse momentum $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ at 1800 GeV as a function of the event charged multiplicity ($N_{\mathrm{ch}}^{\star }$). MB data are shown. For comparison, the mean $p_T$ of charged particles measured in the same phase space region is also plotted [4]. The filled squares around the points delimit the systematic uncertainties.

Figure 12

Average transverse momentum $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ at 1800 GeV as a function of the event charged multiplicity ($N_{\mathrm{ch}}^{\star }$). Soft data are shown. For comparison, the mean $p_T$ of charged particles measured in the same phase space region is also plotted [4]. The filled squares around the points delimit the systematic uncertainties.

Figure 13

Average transverse momentum $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ at 1800 GeV as a function of the event charged multiplicity ($N_{\mathrm{ch}}^{\star }$). Hard data are shown. For comparison, the mean $p_T$ of charged particles measured in the same phase space region is also plotted [4]. The filled squares around the points delimit the systematic uncertainties.

Figure 14

Average transverse momentum $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ at 630 GeV as a function of the event charged multiplicity ($N_{\mathrm{ch}}^{\star }$). MB data are shown. For comparison, the mean $p_T$ of charged particles measured in the same phase space region is also plotted [4]. The filled squares around the points delimit the systematic uncertainties.

Figure 15

Average transverse momentum $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ at 630 GeV as a function of the event charged multiplicity ($N_{\mathrm{ch}}^{\star }$). Soft data are shown. For comparison, the mean $p_T$ of charged particles measured in the same phase space region is also plotted [4]. The filled squares around the points delimit the systematic uncertainties.

Figure 16

Average transverse momentum $⟨p_T⟩$ of $K_S^0$ and ${\Lambda }^0$ at 630 GeV as a function of the event charged multiplicity ($N_{\mathrm{ch}}^{\star }$). Hard data are shown. For comparison, the mean $p_T$ of charged particles measured in the same phase space region is also plotted [4]. The filled squares around the points delimit the systematic uncertainties.

Figure 17

Mean number of $K_S^0$ per event divided by the charged multiplicity ($N_{\mathrm{ch}}^{\star }$) and plotted as a function of $N_{\mathrm{ch}}^{\star }$. The MB, soft and hard data at 1800 GeV are shown.

Figure 18

Mean number of $K_S^0$ per event divided by the charged multiplicity ($N_{\mathrm{ch}}^{\star }$) and plotted as a function of $N_{\mathrm{ch}}^{\star }$. The MB, soft, and hard data at 1800 GeV are shown.

Figure 19

Mean number of ${\Lambda }^0$ per event divided by the charged multiplicity ($N_{\mathrm{ch}}^{\star }$) and plotted as a function of $N_{\mathrm{ch}}^{\star }$. The MB, soft, and hard data at 1800 GeV are shown.

Figure 20

Mean number of ${\Lambda }^0$ per event divided by the charged multiplicity ($N_{\mathrm{ch}}^{\star }$) and plotted as a function of $N_{\mathrm{ch}}^{\star }$. The MB, soft, and hard data at 630 GeV are shown.

Figure 21

$K_S^0$ invariant $p_T$ distribution in pythia and data.

Figure 22

${\Lambda }^0$ invariant $p_T$ distribution in pythia and data.

Figure 23

Correlation of the average $p_T$ of $K_S^0$ with multiplicity in pythia and data.

Figure 24

Correlation of the average $p_T$ of ${\Lambda }^0$ with multiplicity in pythia and data.