Measurement of the fraction of jet longitudinal momentum carried by ${\mathrm{\Lambda }}_c^{+}$ baryons in $pp$ collisions

Recent measurements of charm-baryon production in hadronic collisions have questioned the universality of charm-quark fragmentation across different collision systems. In this work the fragmentation of charm quarks into charm baryons is probed, by presenting the first measurement of the longitudinal jet momentum fraction carried by ${\mathrm{\Lambda }}_c^{+}$ baryons, $z_{\parallel }^{\mathrm{ch}}$, in hadronic collisions. The results are obtained in proton-proton ($pp$) collisions at $\sqrt{s}=13\mathrm{TeV}$ at the LHC, with ${\mathrm{\Lambda }}_c^{+}$ baryons and charged (track-based) jets reconstructed in the transverse momentum intervals of $3\le p_T^{{\mathrm{\Lambda }}_c^{+}}<15\mathrm{GeV}/c$ and $7\le p_T^{\text{jet ch}}<15\mathrm{GeV}/c$, respectively. The $z_{\parallel }^{\mathrm{ch}}$ distribution is compared to a measurement of ${\mathrm{D}}^0$-tagged charged jets in $pp$ collisions as well as to pythia 8 simulations. The data hints that the fragmentation of charm quarks into charm baryons is softer with respect to charm mesons, in the measured kinematic interval, as predicted by hadronization models which include color correlations beyond leading-color in the string formation.

Figure 1

Left: fully corrected normalized $z_{\parallel }^{\mathrm{ch}}$ distribution of ${\mathrm{\Lambda }}_c^{+}$-tagged charged jets (black open circles) measured in the $7\le p_T^{\text{jet ch}}<15\mathrm{GeV}/c$ and $3\le p_T^{{\mathrm{\Lambda }}_c^{+}}<15\mathrm{GeV}/c$ intervals in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$, compared with predictions from different pythia 8 tunes [20, 21, 23] (red-dotted and green-dashed lines). The ratios of the MC simulations to the data are shown in the bottom panel. Right: comparison of the measured $z_{\parallel }^{\mathrm{ch}}$ distribution of ${\mathrm{\Lambda }}_c^{+}$-tagged jets and the previously measured $z_{\parallel }^{\mathrm{ch}}$ distribution of ${\mathrm{D}}^0$-tagged jets [7], obtained in the same kinematic interval. The ratio of the $z_{\parallel }^{\mathrm{ch}}$ distribution of ${\mathrm{\Lambda }}_c^{+}$-tagged and ${\mathrm{D}}^0$-tagged jets is shown in the bottom panel for both the data and the different pythia tunes.