The production yields of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ resonances are measured in pp collisions at $\sqrt{s}=13$ TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle$, which is related to the energy density produced in the collision. The results include transverse momentum ($p_{\rm T}$) distributions, $p_{\rm T}$-integrated yields, mean transverse momenta of $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$, as well as ratios of the $p_{\rm T}$-integrated resonance yields relative to yields of other hadron species. The $\Sigma(1385)^{\pm}/\pi^{\pm}$ and $\Xi(1530)^{0}/\pi^{\pm}$ yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the $\Sigma(1385)^{\pm}$ and $\Xi(1530)^{0}$ production in pp collisions at $\sqrt{s}=13$ TeV.

The study of nuclei and antinuclei production has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. The first measurement of the production of ${\rm ^{3}_{\Lambda}\rm H}$ in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV is presented in this Letter. Its production yield measured in the rapidity interval $-1 < y < 0$ for the 40% highest multiplicity p-Pb collisions is ${\rm d} N /{\rm d} y =[\mathrm{6.3 \pm 1.8 (stat.) \pm 1.2 (syst.) ] \times 10^{-7}}$. The measurement is compared with the expectations of statistical hadronisation and coalescence models, which describe the nucleosynthesis in hadronic collisions. These two models predict very different yields of the hypertriton in charged particle multiplicity environments relevant to small collision systems such as p-Pb and therefore the measurement of ${\rm d} N /{\rm d} y$ is crucial to distinguish between them. The precision of this measurement leads to the exclusion with a significance larger than 6.9$\sigma$ of some configurations of the statistical hadronization model, thus constraining the theory behind the production of loosely bound states at hadron colliders.

Understanding the production mechanism of light (anti)nuclei is one of the key challenges of nuclear physics and has important consequences for astrophysics, since it provides an input for indirect dark-matter searches in space. In this paper, the latest results about the production of light (anti)nuclei in pp collisions at $\sqrt{s} = 13$ TeV are presented, focusing on the comparison with the predictions of coalescence and thermal models. For the first time, the coalescence parameters $B_2$ for deuterons and $B_3$ for helions are compared with parameter-free theoretical predictions that are directly constrained by the femtoscopic measurement of the source radius in the same event class. A fair description of the data with a Gaussian wave function is observed for both deuteron and helion, supporting the coalescence mechanism for the production of light (anti)nuclei in pp collisions. This method paves the way for future investigations of the internal structure of more complex nuclear clusters, including the hypertriton.

The production of prompt $D^{0}$, $D^{+}_{\rm s}$, and $\Lambda_{\rm c}^{+}$ hadrons, and their ratios, $D^{+}_{\rm s}$/$D^{0}$ and $\Lambda_{\rm c}^{+}$/$D^{0}$, 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 $D^{+}_{\rm s}$/$D^{0}$ ratio indicates no significant multiplicity dependence, the baryon-to-meson $p_{\rm T}$-differential $\Lambda_{\rm c}^{+}$/$D^{0}$ 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 $\Lambda_{\rm c}^{+}$/$D^{0}$ ratios as a function of $p_{\rm T}$ present a similar shape and magnitude as the $\Lambda/K^{0}_{s}$ 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.

The transverse momentum ($p_{\rm T}$) differential production cross section of the promptly produced charm-strange baryon $\Xi_{\rm c}^{0}$ (and its charge conjugate $\overline{\Xi_{\rm c}^{0}}$) is measured at midrapidity via its hadronic decay into ${\rm \pi^{+}}\Xi^{-}$ in p$-$Pb collisions at a centre-of-mass energy per nucleon$-$nucleon collision $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV with the ALICE detector at the LHC. The $\Xi_{\rm c}^{0}$ nuclear modification factor ($R_{\rm pPb}$), calculated from the cross sections in pp and p$-$Pb collisions, is presented and compared with the $R_{\rm pPb}$ of $\Lambda_{\rm c}^{+}$ baryons. The ratios between the $p_{\rm T}$-differential production cross section of $\Xi_{\rm c}^{0}$ baryons and those of $\mathrm {D^0}$ mesons and $\Lambda_{\rm c}^{+}$ baryons are also reported and compared with results at forward and backward rapidity from the LHCb Collaboration. The measurements of the production cross section of prompt $\Xi^0_{\rm c}$ baryons are compared with a model based on perturbative QCD calculations of charm-quark production cross sections, which includes only cold nuclear matter effects in p$-$Pb collisions, and underestimates the measurement by a factor of about 50. This discrepancy is reduced when the data is compared with a model that includes string formation beyond leading-colour approximation or in which hadronisation is implemented via quark coalescence. The $p_{\rm T}$-integrated cross section of prompt $\Xi^0_{\rm c}$-baryon production at midrapidity extrapolated down to $p_{\rm T}$ = 0 is also reported. These measurements offer insights and constraints for theoretical calculations of the hadronisation process. Additionally, they provide inputs for the calculation of the charm production cross section in p$-$Pb collisions at midrapidity.

The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of $\sqrt{s}=13$ TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of $|\eta^{\gamma}|<0.67$ and a transverse momentum range of $7<p_{\rm T}^{\gamma}<200$ GeV/$c$. The result extends to lower $p_{\rm T}^{\gamma}$ and $x_{\rm T}^{\gamma} = 2p_{\rm T}^{\gamma}/\sqrt{s}$ ranges, the lowest $x_{\rm T}^{\gamma}$ of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower $p_{\rm T}^{\gamma}$ at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties.

This Letter presents the first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced $\rho^0$ mesons. The $\rho^0$ mesons are reconstructed through their decay into pion pairs. The measured anisotropy corresponds to the amplitude of the $\cos(2\phi)$ modulation, where $\phi$ is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb$-$Pb collisions at a center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the $\cos(2\phi)$ modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations describe the measured $\cos(2\phi)$ anisotropy and its impact-parameter dependence as the result of a quantum interference effect at the femtometer scale, arising from the ambiguity regarding which of the nuclei is the photon source in the interaction.

First measurements of balance functions (BFs) of all combinations of identified charged hadron $(\pi,\rm K,\rm p)$ pairs in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV recorded by the ALICE detector are presented. The BF measurements are carried out as two-dimensional differential correlators versus the relative rapidity ($\Delta y$) and azimuthal angle ($\Delta\varphi$) of hadron pairs, and studied as a function of collision centrality. The $\Delta\varphi$ dependence of BFs is expected to be sensitive to the light quark diffusivity in the quark$-$gluon plasma. While the BF azimuthal widths of all pairs substantially decrease from peripheral to central collisions, the longitudinal widths exhibit mixed behaviors: BFs of $\pi\pi$ and cross-species pairs narrow significantly in more central collisions, whereas those of $\rm KK$ and $\rm pp$ are found to be independent of collision centrality. This dichotomy is qualitatively consistent with the presence of strong radial flow effects and the existence of two stages of quark production in relativistic heavy-ion collisions. Finally, the first measurements of the collision centrality evolution of BF integrals are presented, with the observation that charge balancing fractions are nearly independent of collision centrality in Pb$-$Pb collisions. Overall, the results presented provide new and challenging constraints for theoretical models of hadron production and transport in relativistic heavy-ion collisions.

The measurement of the production of deuterons, tritons and $^{3}\mathrm{He}$ and their antiparticles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV is presented in this article. The measurements are carried out at midrapidity ($|y| < $ 0.5) as a function of collision centrality using the ALICE detector. The $p_{\rm T}$-integrated yields, the coalescence parameters and the ratios to protons and antiprotons are reported and compared with nucleosynthesis models. The comparison of these results in different collision systems at different centre-of-mass collision energies reveals a suppression of nucleus production in small systems. In the Statistical Hadronisation Model framework, this can be explained by a small correlation volume where the baryon number is conserved, as already shown in previous fluctuation analyses. However, a different size of the correlation volume is required to describe the proton yields in the same data sets. The coalescence model can describe this suppression by the fact that the wave functions of the nuclei are large and the fireball size starts to become comparable and even much smaller than the actual nucleus at low multiplicities.

The study of the production of nuclei and antinuclei in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper, the production of protons, deuterons and $^3$He and their charge conjugates at midrapidity is studied as a function of the charged-particle multiplicity in inelastic pp collisions at $\sqrt{s}=5.02$ TeV using the ALICE detector. Within the uncertainties, the yields of nuclei in pp collisions at $\sqrt{s}=5.02$ TeV are compatible with those in pp collisions at different energies and to those in p-Pb collisions when compared at similar multiplicities. The measurements are compared with the expectations of coalescence and Statistical Hadronisation Models. The results suggest a common formation mechanism behind the production of light nuclei in hadronic interactions and confirm that they do not depend on the collision energy but on the number of produced particles.