Observation of a multiplicity dependence in the $p_{\rm T}$-differential charm baryon-to-meson ratios in proton-proton collisions at $\sqrt{s} = 13$ TeV

The collaboration
Phys.Lett.B 829 (2022) 137065, 2022.

Abstract (data abstract)
The production of prompt $\rm D^{0}$, $\rm D^{+}_{s}$, and $\rm \Lambda_{c}^{+}$ hadrons, and their ratios, $\rm D^{+}_{s} / D^{0}$ and $\rm \Lambda_{c}^{+} / D^{0}$, are measured in proton--proton collisions at $\sqrt{s}=13$~TeV at midrapidity ($|y|<0.5$) with the ALICE detector at the LHC. The measurements are performed as a function of the charm-hadron transverse momentum ($p_{\rm T}$) in intervals of charged-particle multiplicity, measured with two multiplicity estimators covering different pseudorapidity regions. While the strange to non-strange $\rm D^{+}_{s} / D^{0}$ ratio indicates no significant multiplicity dependence, the baryon-to-meson $p_{\rm T}$-differential $\rm \Lambda_{c}^{+} / D^{0}$ ratio shows a multiplicity-dependent enhancement, with a significance of 5.3$\sigma$ for $1 < p_{\rm T} < 12$~GeV/$c$, comparing the highest multiplicity interval with respect to the lowest one. The measurements are compared with a theoretical model that explains the multiplicity dependence by a canonical treatment of quantum charges in the statistical hadronisation approach, and with predictions from event generators that implement colour reconnection mechanisms beyond the leading colour approximation to model the hadronisation process. The $\rm \Lambda_{c}^{+} / D^{0}$ ratios as a function of $p_{\rm T}$ present a similar shape and magnitude as the $\rm \Lambda/K^{0}_{S}$ ratios in comparable multiplicity intervals, suggesting a potential common mechanism for light- and charm-hadron formation, with analogous multiplicity dependence. The $p_{\rm T}$-integrated ratios, extrapolated down to $p_{\rm T}=0$, do not show a significant dependence on multiplicity within the uncertainties.

• #### Table 1a

Data from Figure 1, top left panel

10.17182/hepdata.128718.v1/t1

Transverse-momentum spectra of $\mathrm{D^0}$ hadrons measured in pp collisions at $\sqrt{{s}} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 1b

Data from Figure 1, top middle panel

10.17182/hepdata.128718.v1/t2

Transverse-momentum spectra of $\mathrm{D_s^+}$ hadrons measured in pp collisions at $\sqrt{{s}} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 1c

Data from Figure 1, top right panel

10.17182/hepdata.128718.v1/t3

Transverse-momentum spectra of $\mathrm{\Lambda_c^+}$ hadrons measured in pp collisions at $\sqrt{{s}} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 1aR

Data from Figure 1, bottom left panel

10.17182/hepdata.128718.v1/t4

Transverse-momentum spectra ratios of $\mathrm{D^0}$ hadrons measured in pp collisions at $\sqrt{{s}} = 13$~TeV for different multiplicity classes selected with...

• #### Table 1bR

Data from Figure 1, bottom middle panel

10.17182/hepdata.128718.v1/t5

Transverse-momentum spectra ratios of $\mathrm{D_s^+}$ hadrons measured in pp collisions at $\sqrt{{s}} = 13$~TeV for different multiplicity classes selected with...

• #### Table 1cR

Data from Figure 1, bottom right panel

10.17182/hepdata.128718.v1/t6

Transverse-momentum spectra ratios of $\mathrm{\Lambda_c^+}$ hadrons measured in pp collisions at $\sqrt{{s}} = 13$~TeV for different multiplicity classes selected with...

• #### Table 2a

Data from Figure 2, top left panel

10.17182/hepdata.128718.v1/t7

The $\mathrm{D_s^+ / D^0}$ ratio measured in pp collisions at $\sqrt{s} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 2b

Data from Figure 2, top right panel

10.17182/hepdata.128718.v1/t8

The $\mathrm{D_s^+ / D^0}$ ratio measured in pp collisions at $\sqrt{s} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 2c

Data from Figure 2, bottom left panel

10.17182/hepdata.128718.v1/t9

The $\mathrm{\Lambda_c^+ / D^0}$ ratio measured in pp collisions at $\sqrt{s} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 2d

Data from Figure 2, bottom right panel

10.17182/hepdata.128718.v1/t10

The $\mathrm{\Lambda_c^+ / D^0}$ ratio measured in pp collisions at $\sqrt{s} = 13$~TeV for different multiplicity classes selected with the...

• #### Table 5

Data from Figure 5

10.17182/hepdata.128718.v1/t11

• #### Table sup6b

Data from Figure 6 (suppl. material), right panel

10.17182/hepdata.128718.v1/t19