The distribution of angular correlations between prompt charm hadrons and primary charged particles in pp collisions is sensitive to the charm-quark hadronisation process. In this letter, charm-baryon correlations are measured for the first time by studying the azimuthal-angle difference between charged particles and prompt $\Lambda_{\rm c}^+$ baryons produced in pp collisions at a centre-of-mass energy $\sqrt{s} = 13$ TeV, with the ALICE detector. $\Lambda_{\rm c}^+$ baryons are reconstructed at midrapidity ($|y| <~ 0.5$) in the transverse-momentum interval $3 <~ p_{\rm T} <~ 16$ GeV/$c$, and correlated with charged particles with $p_{\rm T} > 0.3$ GeV/$c$ and pseudorapidity $|\eta| <~ 0.8$. For $3 <~ p_{\rm T}^{\Lambda_{\rm c}^+,{\rm D}} <~ 5$ GeV/$c$, the comparison with published measurements of D-meson and charged-particle correlations in the same collision system hints at a larger number of low-momentum particles associated with $\Lambda_{\rm c}^+$-baryon triggers than with D-meson triggers, both in the collinear and opposite directions with respect to the trigger particle. These differences can be quantified by the comparison of the properties of the near- and away-side correlation peaks, and are not reproduced by predictions of various Monte Carlo event generators, generally underpredicting the associated particle yields at $p_{\rm T}^{\rm assoc} <~ 1$ GeV/$c$. This tension between $\Lambda_{\rm c}^+$-baryon and D-meson associated peak yields could suggest a modified fragmentation of the charm quark, or a different hadronisation process, when a charm baryon is produced in the final state.
Submitted to: PLB
e-Print: arXiv:2411.10104 | PDF | inSPIRE
CERN-EP-2024-302
Figure group
Figure 1
Examples of azimuthal-correlation distributions of $\Lambda_\mathrm{c}^{+}$-baryons with associated particles (red markers) after the baseline subtraction in pp collisions at $\sqrt{s}$ = 13 TeV, compared to the average of the azimuthal-correlation distributions of D$^0$, D$^+$, and D$^{*+}$ mesons with associated particles measured by ALICE (blue markers) , for the $p_\mathrm{T}$ intervals 3 $< p_\mathrm{T}^\mathrm{D,\Lambda_{c}^{+}} < $ 5 GeV/$c$ and 0.3 $< p_\mathrm{T}^\mathrm{assoc}< $ 1 GeV/$c$, 5 $ < p_\mathrm{T}^\mathrm{D,\Lambda_{c}^{+}} < $ 8 GeV/$c$ and 0.3 $< p_\mathrm{T}^\mathrm{assoc}< $ 1 GeV/$c$, and 8 $< p_\mathrm{T}^\mathrm{D,\Lambda_{c}^{+}} < $ 16 GeV/$c$ and $p_\mathrm{T}^\mathrm{assoc}>$ 1 GeV/$c$(from left to right). Statistical and $\Delta \varphi$-dependent systematic uncertainties are shown as vertical error bars and boxes, respectively, and $\Delta \varphi$-independent uncertainties are written as text. The uncertainties from the subtraction of the baseline are displayed as boxes at $\Delta \varphi>\pi$. |  |
Figure 2
Near-side peak yields (first row) and widths (third row) obtained from the fit to the azimuthal correlation distributions of $\Lambda_\mathrm{c}^{+}$ with charged particles after the baseline subtraction in pp collisions at $\sqrt{s}=13$ TeV. The measurements are compared to D-meson average results by ALICE in the same collision system . The ratios of $\Lambda_\mathrm{c}^{+}$-baryon to D-meson near-side peak observables are shown in the second and fourth rows for yields and widths, respectively. |  |
Figure 3
Away-side peak yields (first row) obtained from the fit to the azimuthal correlation distributions of $\mathrm{\Lambda_{c}^{+}}$ and charged particles after the baseline subtraction in pp collisions at $\sqrt{s}=13$ TeV. The measurements are compared to D-meson average results by ALICE in the same collision system . The ratios of $\mathrm{\Lambda_{c}^{+}}$-baryon to D-meson away-side peak yields are shown in the second row. |  |
Figure 4
Near-side peak yields (first row) and widths (third row) from the fit to the $\mathrm{\Lambda_{c}^{+}}$-charged particle azimuthal correlation distributions after the baseline subtraction, compared to simulations from PYTHIA 8 with Monash tune , POWHEG+PYTHIA 8 , PYTHIA 8 with CR-BLC mode 2 , and JETSCAPE with hybrid hadronisation . The ratios of model predictions to data measurements for the yield (width) values are shown in the second (fourth) row. In these rows, model statistical and systematic uncertainties are shown as vertical error bars and boxes, respectively, while data total uncertainties are displayed as a solid grey band. |  |
Figure 5
Away-side peak yields (first row) from the fit to the $\mathrm{\Lambda_{c}^{+}}$-charged particle azimuthal-correlation distributions after the baseline subtraction, compared to simulations from PYTHIA 8 with Monash tune , POWHEG+PYTHIA 8 , PYTHIA 8 with CR-BLC mode 2 , and JETSCAPE with hybrid hadronisation . The ratios of model predictions to data measurements for yield values are shown in the second row. In this row, model statistical and systematic uncertainties are shown as vertical error bars and boxes, respectively, while data total uncertainties are displayed as a solid grey band. |  |
Figure 6
Left: comparison between the measured $\mathrm{\Lambda_{c}^{+}}$-charged particle azimuthal correlation function and the Monte Carlo correlation templates obtained from PYTHIA 8, Monash tune and by including SHM+RQM charm baryon states (see text for details) for $3 < p_\mathrm{T}^\mathrm{\Lambda_{c}^{+}}< 5 $ GeV/$c$ and for 0.3 $< p_\mathrm{T}^\mathrm{assoc}< $ 1 GeV/$c$. Right: the near-side yields from data compared to the same model predictions for 0.3 $< p_\mathrm{T}^\mathrm{assoc}< $ 1 GeV/$c$. |   |