Inclusive $\mathrm{\Lambda }$ production in proton-proton collisions at 3.5 GeV

The inclusive production of $\mathrm{\Lambda }$ hyperons in proton-proton collisions at $\sqrt{s}=3.18\mathrm{GeV}$ was measured with HADES at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. The experimental data are compared to a data-based model for individual exclusive $\mathrm{\Lambda }$ production channels in the same reaction. The contributions of intermediate resonances such as $\mathrm{\Sigma }\left(1385\right)$, ${\mathrm{\Delta }}^{++}$, or ${\text{N}}^{*}$ are considered in detail. In particular, the result of a partial-wave analysis accounts for the abundant $p{\mathrm{K}}^{+}\mathrm{\Lambda }$ final state. Model and data show a reasonable agreement at midrapidities, while a difference is found for larger rapidities. A total $\mathrm{\Lambda }$ production cross section in $p+p$ collisions at $\sqrt{s}=3.18\mathrm{GeV}$ of $\sigma (p+p\to \mathrm{\Lambda }+X)=207.3\pm 1.3{}_{-7.3}^{+6.0}(\mathrm{stat}.)\pm 8.4(\mathrm{syst}.){}_{-0.5}^{+0.4}(\mathrm{model}.)\mu \mathrm{b}$ is found.

Figure 1

Energy loss $dE/dx$ as a function of the momentum multiplied by the charge for all particle candidates. The two-dimensional graphical cuts (white curves) are used for the particle identification.

Figure 2

Invariant mass spectrum for proton-pion pairs for three different $y_{\mathrm{c}}.\mathrm{m}.$ bins. The red solid line shows the signal+background fit, and the black dashed line shows the background component of the fit.

Figure 3

Phase space distributions of $\mathrm{\Lambda }$ candidates prior to efficiency corrections: (a) $\mathrm{\Lambda }$ momentum in the $p+p$ c.m. as a function of the polar angle $cos{\theta }_{\mathrm{c}}.\mathrm{m}.$; (b) transverse $\mathrm{\Lambda }$ momentum as a function of the c.m. rapidity $y_{\mathrm{c}}.\mathrm{m}.$.

Figure 4

Corrected experimental data and production model of the differential cross section $d\sigma /d{p}_{\mathrm{c}}.\mathrm{m}.$ for different bins of $cos{\theta }_{\mathrm{c}}.\mathrm{m}.$. Statistical and systematic errors are depicted by crosses and boxes, respectively. The solid black and red dashed curves represent the original and refitted production model, respectively. The contribution by the different channels to the original model are depicted by the different curves labeled in the figure legend.

Figure 5

Same as Fig. 4 for $d\sigma /d{p}_{\mathrm{t}}$ for different bins of $y_{\mathrm{c}}.\mathrm{m}.$.

Figure 6

Differential cross section distribution (a) $d\sigma /dcos{\theta }_{\mathrm{c}}.\mathrm{m}.$ and (b) $d\sigma /d{y}_{\mathrm{c}}.\mathrm{m}.$, extrapolated to the whole phase space and integrated over the $p_{\mathrm{c}}.\mathrm{m}.$ and $p_{\mathrm{t}}$ variables, respectively. The full square symbols represent measured data, the empty squares refer to mirrored data, and the full triangles correspond to average between mirrored and measured data.

Figure 7

Compilation of the total $pp\to \mathrm{\Lambda }+X$ production cross section measurements. The empty symbols refer to the measurements of the exclusive channel $pp\to p{\mathrm{K}}^{+}\mathrm{\Lambda }$, the full symbols show the measurements of the inclusive $\mathrm{\Lambda }$ production, and the dashed curve depicts a phase space fit for the $p{\mathrm{K}}^{+}\mathrm{\Lambda }$ exclusive channel in Ref. [20].