The two-particle momentum correlation functions between charm mesons (${\mathrm{D}}^{*\pm }$ and ${\mathrm{D}}^{\pm }$) and charged light-flavor mesons (${\pi }^{\pm }$ and ${\mathrm{K}}^{\pm }$) in all charge combinations are measured for the first time by the ALICE Collaboration in high-multiplicity proton–proton collisions at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$. For DK and ${\mathrm{D}}^{*}\mathrm{K}$ pairs, the experimental results are in agreement with theoretical predictions of the residual strong interaction based on quantum chromodynamics calculations on the lattice and chiral effective field theory. In the case of $\mathrm{D}\pi$ and ${\mathrm{D}}^{*}\pi$ pairs, tension between the calculations including strong interactions and the measurement is observed. For all particle pairs, the data can be adequately described by Coulomb interaction only, indicating a shallow interaction between charm and light-flavor mesons. Finally, the scattering lengths governing the residual strong interaction of the $\mathrm{D}\pi$ and ${\mathrm{D}}^{*}\pi$ systems are determined by fitting the experimental correlation functions with a model that employs a Gaussian potential. The extracted values are small and compatible with zero.

Deuterons are atomic nuclei composed of a neutron and a proton held together by the strong interaction. Unbound ensembles composed of a deuteron and a third nucleon have been investigated in the past using scattering experiments, and they constitute a fundamental reference in nuclear physics to constrain nuclear interactions and the properties of nuclei. In this work, $K^{+}\text{−}d$ and $p\text{−}d$ femtoscopic correlations measured by the ALICE Collaboration in proton-proton ($pp$) collisions at $\sqrt{s}=13\mathrm{TeV}$ at the Large Hadron Collider (LHC) are presented. It is demonstrated that correlations in momentum space between deuterons and kaons or protons allow us to study three-hadron systems at distances comparable with the proton radius. The analysis of the $K^{+}\text{−}d$ correlation shows that the relative distances at which deuterons and protons or kaons are produced are around 2 fm. The analysis of the $p\text{−}d$ correlation shows that only a full three-body calculation that accounts for the internal structure of the deuteron can explain the data. In particular, the sensitivity of the observable to the short-range part of the interaction is demonstrated. These results indicate that correlations involving light nuclei in $pp$ collisions at the LHC will also provide access to any three-body system in the strange and charm sectors.

The femtoscopic study of pairs of identical pions is particularly suited to investigate the effective source function of particle emission, due to the resulting Bose–Einstein correlation signal. In small collision systems at the LHC, pp in particular, the majority of the pions are produced in resonance decays, which significantly affect the profile and size of the source. In this work, we explicitly model this effect in order to extract the primordial source in pp collisions at $$\sqrt{s}~=~13$$ s = 13 TeV from charged $$\uppi $$ π – $$\uppi $$ π correlations measured by ALICE. We demonstrate that the assumption of a Gaussian primordial source is compatible with the data and that the effective source, resulting from modifications due to resonances, is approximately exponential, as found in previous measurements at the LHC. The universality of hadron emission in pp collisions is further investigated by applying the same methodology to characterize the primordial source of $$\textrm{K}$$ K – $$\textrm{p}$$ p pairs. The size of the primordial source is evaluated as a function of the transverse mass ( $$m_{\textrm{T}}$$ m T ) of the pairs, leading to the observation of a common scaling for both $$\uppi $$ π – $$\uppi $$ π and $$\textrm{K}$$ K – $$\textrm{p}$$ p , suggesting a collective effect. Further, the present results are compatible with the $$m_{\textrm{T}}$$ m T scaling of the $$\textrm{p}$$ p – $$\textrm{p}$$ p and p $$-\Lambda $$ - Λ primordial source measured by ALICE in high multiplicity pp collisions, providing additional evidence for the presence of a common emission source for all hadrons in small collision systems at the LHC. This will allow the determination of the source function for any hadron–hadron pairs with high precision, granting access to the properties of the possible final-state interaction among pairs of less abundantly produced hadrons, such as strange or charmed particles.