${\mathrm{\Lambda }}_c^{+}$ production in $pp$ and in $p$-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV

The production cross section of prompt ${\mathrm{\Lambda }}_c^{+}$ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton ($pp$) and proton-lead ($p\text{–Pb}$) collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. The ${\mathrm{\Lambda }}_c^{+}$ and $\overline{\mathrm{\Lambda }}{}_c^{-}$ baryons were reconstructed in the hadronic decay channels ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to p{K}_S^0$ and respective charge conjugates. The measured differential cross sections as a function of transverse momentum ($p_T$) and the $p_T$-integrated ${\mathrm{\Lambda }}_c^{+}$ production cross section in $pp$ and in $p\text{–Pb}$ collisions are presented. The ${\mathrm{\Lambda }}_c^{+}$ nuclear modification factor ($R_{p\mathrm{Pb}}$), calculated from the cross sections in $pp$ and in $p\text{–Pb}$ collisions, is presented and compared with the $R_{p\mathrm{Pb}}$ of $D$ mesons. The ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio is also presented and compared with the light-flavor baryon-to-meson ratios $p/\pi$ and $\mathrm{\Lambda }/K_S^0$, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators.

Figure 1

Invariant mass distributions of ${\mathrm{\Lambda }}_c^{+}$ candidates in different $p_T$ intervals, collision systems, and decay channels, with the corresponding fit functions. Top-left: ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ for $3<p_T<4\mathrm{GeV}/c$ in $\mathit{pp}$ collisions; top-right: ${\mathrm{\Lambda }}_c^{+}\to p{K}_S^0$ for $8<p_T<12\mathrm{GeV}/c$ in $\mathit{pp}$ collisions; bottom-left: ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ for $5<p_T<6\mathrm{GeV}/c$ in $p\text{–Pb}$ collisions; bottom-right: ${\mathrm{\Lambda }}_c^{+}\to p{K}_S^0$ with BDT analysis in $12<p_T<24\mathrm{GeV}/c$ in $p\text{–Pb}$ collisions. The dashed lines represent the fit to the background and the solid lines represent the total fit function.

Figure 2

Product of detector acceptance and efficiency for ${\mathrm{\Lambda }}_c^{+}$ baryons in $\mathit{pp}$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$, as a function of $p_T$. From left to right: ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to p{K}_S^0$. The solid lines correspond to the $(A\times \varepsilon )$ for prompt ${\mathrm{\Lambda }}_c^{+}$, while the dotted lines represent $(A\times \epsilon )$ for ${\mathrm{\Lambda }}_c^{+}$ baryons originating from beauty-hadron decays. The statistical uncertainties are smaller than the marker size.

Figure 3

Product of detector acceptance and efficiency for ${\mathrm{\Lambda }}_c^{+}$ baryons in $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$, as a function of $p_T$. From left to right: ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to p{K}_S^0$. The solid lines correspond to the $(A\times \varepsilon )$ for prompt ${\mathrm{\Lambda }}_c^{+}$, while the dotted lines represent $(A\times \epsilon )$ for ${\mathrm{\Lambda }}_c^{+}$ baryons originating from beauty-hadron decays. The statistical uncertainties are smaller than the marker size.

Figure 4

Left: $p_T$-differential prompt ${\mathrm{\Lambda }}_c^{+}$-baryon cross section in $pp$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ in the interval $1<p_T<12 \mathrm{GeV}/c$. Right: $p_T$-differential prompt ${\mathrm{\Lambda }}_c^{+}$-baryon cross section in $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ in the interval $1<p_T<24 \mathrm{GeV}/c$. The statistical uncertainties are shown as vertical bars and the systematic uncertainties are shown as boxes. Horizontal position of points are shifted to provide better visibility.

Figure 5

Prompt ${\mathrm{\Lambda }}_c^{+}$-baryon $p_T$-differential production cross section in $pp$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ in the interval $1<p_T<12\mathrm{GeV}/c$. The statistical uncertainties are shown as vertical bars and the systematic uncertainties are shown as boxes. Left: Comparison to predictions from different tunes of the PYTHIA 8 event generator [23, 24]. The vertical bars on the PYTHIA 8 predictions represent the statistical uncertainty from the simulation, and the vertical bars on the ratios in the bottom panel also include the statistical uncertainties from the data. Right: Comparison to predictions from the POWHEG event generator [96] and GM-VFNS calculations [98]. The orange(blue) boxes represent the uncertainties of POWHEG(GM-VFNS) due to the choice of pQCD scales. See text for details on the PYTHIA 8 and POWHEG event generator settings.

Figure 6

Comparison between the $p_T$-differential production cross section of prompt ${\mathrm{\Lambda }}_c^{+}$ baryons in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ [14] and $\sqrt{s}=5.02\mathrm{TeV}$. The ratio between the cross sections is shown in the lower panel. The statistical uncertainties are shown as vertical bars and the systematic uncertainties are shown as boxes.

Figure 7

$p_T$-differential prompt ${\mathrm{\Lambda }}_c^{+}$-baryon production cross section in $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ in the interval $1<p_T<24\mathrm{GeV}/c$ compared to predictions from the POWHEG event generator [96]. The statistical uncertainties are shown as vertical bars and the systematic uncertainties are shown as boxes. The orange boxes represent the uncertainties of POWHEG due to the choice of pQCD scales. See text for details on the POWHEG event generator settings.

Figure 8

The nuclear modification factor $R_{p\mathrm{Pb}}$ of prompt ${\mathrm{\Lambda }}_c^{+}$ baryons in $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ as a function of $p_T$, compared to the $R_{p\mathrm{Pb}}$ of $D$ mesons [101] (average of $D^0, D^{+}$, and $D^{*+}$ in the range $1<p_T<12 \mathrm{GeV}/c$ and $D^0$ in $0<p_T<1 \mathrm{GeV}/c$) (left), as well as to $\text{POWHEG}+\text{PYTHIA}$ 6 [96] with EPPS16 [48] simulations, and POWLANG [60] predictions (right). The black-filled box at $R_{p\mathrm{Pb}}=1$ represents the normalization uncertainty.

Figure 9

The ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio as a function of $p_T$ measured in $\mathit{pp}$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ and in $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$.

Figure 10

The ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio measured in $\mathit{pp}$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$, compared to theoretical predictions. The measurement is compared with predictions from MC generators (PYTHIA 8 [23, 24], HERWIG 7 [27], POWHEG [96]), GM-VFNS [98], a statistical hadronization model [72] (“SH model” in the legend) and a model which implements hadronization via coalescence and fragmentation [104]. See text for model details.

Figure 11

Left: The ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio measured in $\mathit{pp}$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$, compared to the measurement at $\sqrt{s}=7\mathrm{TeV}$ [14]. PYTHIA 8 predictions are shown at both energies, for the Monash tune (solid lines) and with the Mode 2 CR tune (dotted lines). Right: the ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio at $\sqrt{s}=5.02\mathrm{TeV}$ compared with the measurement by the CMS Collaboration at $\left|y\right|<1$ [28].

Figure 12

The ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio measured in $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$, compared with the measurement at forward and backward rapidity [71] by the LHCb collaboration. The measurements are shown as a function of $p_T$ (left) and as a function of $y$ (right).

Figure 13

The baryon-to-meson ratios in the light-flavor and charm sector; p/$\pi$ in $\mathit{pp}$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ and $7\mathrm{TeV}$ and $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ [68] (left), $\mathrm{\Lambda }/K_S^0$ in $\mathit{pp}$ collisions at $\sqrt{s}=7\mathrm{TeV}$ and $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ [107, 108] (middle), and ${\mathrm{\Lambda }}_c^{+}/D^0$ in $pp$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ and $p\text{–Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ (right). The data are compared to predictions from PYTHIA 8 [23, 24]. See text for model details.