The production yields of the orbitally excited charm-strange mesons $\mathrm{D_{s1}(1^{+})(2536)^+}$ and $\mathrm{D_{s2}^{*}(2^{+})(2573)^+}$were measured for the first time in proton-proton (pp) collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV with the ALICE experiment at the LHC. The $\mathrm{D_{s1}^+}$ and $\mathrm{D_{s2}^{*+}}$ mesons were measured at midrapidity ($|y|<0.5$) in minimum-bias and high-multiplicity pp collisions in the transverse-momentum interval $2<p_{\rm T}<24$ GeV/$c$. Their production yields relative to the $\mathrm{D_{s}^{+}}$ ground-state yield were found to be compatible between minimum-bias and high-multiplicity collisions, as well as with previous measurements in ${\rm e}^{\pm}$p and ${\rm e^+ e^-}$ collisions. The measured $\mathrm{D_{s1}^+/D_{s}^{+}}$ and $\mathrm{D_{s2}^{*+}/D_{s}^{+}}$ yield ratios are described by statistical hadronization models and can be used to tune the parameters governing the production of excited charm-strange hadrons in Monte Carlo generators, such as PYTHIA 8.

The ALICE Collaboration reports measurements of the large relative transverse momentum ($k_{\text{T}}$) component of jet substructure in pp and Pb$-$Pb collisions at center-of-mass energy per nucleon pair $\sqrt{s_{\text{NN}}}=5.02$ TeV. Enhancement in the yield of such large-$k_{\text{T}}$ emissions in head-on Pb$-$Pb collisions is predicted to arise from partonic scattering with quasi-particles of the quark-gluon plasma. The analysis utilizes charged-particle jets reconstructed by the anti-$k_{\text{T}}$ algorithm with resolution parameter $R=0.2$ in the transverse-momentum interval $60 < p_{\text{T,ch jet}} < 80$ GeV/$c$. The soft drop and dynamical grooming algorithms are used to identify high transverse momentum splittings in the jet shower. Comparison of measurements in Pb$-$Pb and pp collisions shows medium-induced narrowing, corresponding to yield suppression of high-$k_{\text{T}}$ splittings, in contrast to the expectation of yield enhancement due to quasi-particle scattering. The measurements are compared to theoretical model calculations incorporating jet modification due to jet-medium interactions ("jet quenching"), both with and without quasi-particle scattering effects. These measurements provide new insight into the underlying mechanisms and theoretical modeling of jet quenching.

The ALICE Collaboration at the CERN LHC has measured the inclusive production cross section of isolated photons at midrapidity as a function of the photon transverse momentum ($p_{\rm T}^{\gamma}$), in Pb$-$Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=5.02$ TeV. The photon transverse momentum range is between 10-14 and 40-140 GeV/$c$, depending on the collision system and on the Pb$-$Pb centrality class. The result extends to lower $p_{\rm T}^{\gamma}$ than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is $|\eta^{\gamma}| <0.67$. The isolation selection is based on a charged particle isolation momentum threshold $p_{\rm T}^{\rm iso,~ch} = 1.5$ GeV/$c$ within a cone of radii $R=0.2$ and $0.4$. The nuclear modification factor is calculated and found to be consistent with unity in all centrality classes, and also consistent with the HG-PYTHIA model, which describes the event selection and geometry biases that affect the centrality determination in peripheral Pb$-$Pb collisions. The measurement is compared to next-to-leading order perturbative QCD calculations and to the measurements of isolated photons and Z$^0$ bosons from the CMS experiment, which are all found to be in agreement.

ALICE is a large experiment at the CERN Large Hadron Collider. Located 52 meters underground, its detectors are suitable to measure muons produced by cosmic-ray interactions in the atmosphere. In this paper, the studies of the cosmic muons registered by ALICE during Run 2 (2015--2018) are described. The analysis is limited to multimuon events defined as events with more than four detected muons ($N_\mu>4$) and in the zenith angle range $0^{\circ}<\theta<50^{\circ}$. The results are compared with Monte Carlo simulations using three of the main hadronic interaction models describing the air shower development in the atmosphere: QGSJET-II-04, EPOS-LHC, and SIBYLL 2.3d. The interval of the primary cosmic-ray energy involved in the measured muon multiplicity distribution is about $ 4 \times 10^{15}<E_\mathrm{prim}< 6 \times 10^{16}$~eV. In this interval none of the three models is able to describe precisely the trend of the composition of cosmic rays as the energy increases. However, QGSJET-II-04 is found to be the only model capable of reproducing reasonably well the muon multiplicity distribution, assuming a heavy composition of the primary cosmic rays over the whole energy range, while SIBYLL 2.3d and EPOS-LHC underpredict the number of muons in a large interval of multiplicity by more than $20\%$ and $30\%$, respectively. The rate of high muon multiplicity events ($N_\mu>100$) obtained with QGSJET-II-04 and SIBYLL 2.3d is compatible with the data, while EPOS-LHC produces a significantly lower rate ($55\%$ of the measured rate). For both QGSJET-II-04 and SIBYLL 2.3d, the rate is close to the data when the composition is assumed to be dominated by heavy elements, an outcome compatible with the average energy $E_\mathrm{prim} \sim 10^{17}$ eV of these events. This result places significant constraints on more exotic production mechanisms.

The $p_{\rm T}$-differential production cross sections of non-prompt ${\rm D^0}$, ${\rm D^+}$, and ${\rm D_s^+}$ mesons originating from beauty-hadron decays are measured in proton$-$proton collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV. The measurements are performed at midrapidity, $|y| < 0.5$, with the data sample collected by ALICE from 2016 to 2018. The results are in agreement with predictions from several perturbative QCD calculations. The fragmentation fraction of beauty quarks to strange mesons divided by the one to non-strange mesons, $f_{\rm{s}}/(f_{\rm{u}} + f_{\rm{d}})$, is found to be $0.114 \pm 0.016~{\rm (stat.)} \pm 0.006~{\rm (syst.)} \pm 0.003~{\rm (BR)} \pm 0.003~{\rm (extrap.)}$. This value is compatible with previous measurements at lower centre-of-mass energies and in different collision systems in agreement with the assumption of universality of fragmentation functions. In addition, the dependence of the non-prompt D meson production on the centre-of-mass energy is investigated by comparing the results obtained at $\sqrt{s} = 5.02$ and 13 TeV, showing a hardening of the non-prompt D-meson $p_{\rm T}$-differential production cross section at higher $\sqrt{s}$. Finally, the ${\rm b\overline{b}}$ production cross section per unit of rapidity at midrapidity is calculated from the non-prompt ${\rm D^0}$, ${\rm D^+}$, ${\rm D_s^+}$, and $\Lambda_{\rm c}^+$ hadron measurements, obtaining ${\rm d}\sigma/{\rm d}y = 75.2\pm 3.2~(\mathrm{stat.}) \pm 5.2~(\mathrm{syst.})^{+12.3}_{-3.2} ~(\mathrm{extrap.})\text{ } \rm \mu b \;.$

We report on the measurement of inclusive, non-prompt, and prompt J/$ψ$-hadron correlations by the ALICE Collaboration at the CERN Large Hadron Collider in pp collisions at a center-of-mass energy of $13~\text{TeV}$. The correlations are studied at midrapidity ($|y| < 0.9$) in the transverse momentum ranges $p_{\rm T} < 40~\text{GeV}/c$ for the J/$ψ$ and $0.15 < p_{\rm T} < 10~\text{GeV}/c$ and $|η|<0.9$ for the associated hadrons. The measurement is based on minimum bias and high multiplicity data samples corresponding to integrated luminosities of $L_{\text{int}} = 34~\text{nb}^{-1}$ and $L_{\text{int}} = 6.9~\text{pb}^{-1}$, respectively. In addition, two more data samples are employed, requiring, on top of the minimum bias condition, a threshold on the tower energy of $E = 4$ and $9~\text{GeV}$ in the ALICE electromagnetic calorimeters, which correspond to integrated luminosities of $L_{\text{int}} = 0.9~\text{pb}^{-1}$ and $L_{\text{int}} = 8.4~\text{pb}^{-1}$, respectively. The azimuthally integrated near and away side yields of associated charged hadrons per J/$ψ$ trigger are presented as a function of the J/$ψ$ and associated hadron transverse momentum. The measurements are discussed in comparison to PYTHIA calculations.

The multiplicity dependence of jet production in pp collisions at the centre-of-mass energy of $\sqrt{s} = 13\ \mathrm{TeV}$ is studied for the first time. Jets are reconstructed from charged particles using the anti-$k_\mathrm{T}$ algorithm with resolution parameters $R$ varying from $0.2$ to $0.7$. The jets are measured in the pseudorapidity range $|\eta_{\rm jet}|< 0.9-R$ and in the transverse momentum range $5<p_\mathrm{T,jet}^{\rm ch}<140\ \mathrm{GeV}/c$. The multiplicity intervals are categorised by the ALICE forward detector V0. The $p_{\mathrm{T}}$ differential cross section of charged-particle jets are compared to leading order (LO) and next-to-leading order (NLO) perturbative quantum chromodynamics (pQCD) calculations. It is found that the data are better described by the NLO calculation, although the NLO prediction overestimates the jet cross section below $20\ \mathrm{GeV}/c$. The cross section ratios for different $R$ are also measured and compared to model calculations. These measurements provide insights into the angular dependence of jet fragmentation. The jet yield increases with increasing self-normalised charged-particle multiplicity. This increase shows only a weak dependence on jet transverse momentum and resolution parameter at the highest multiplicity. While such behaviour is qualitatively described by the present version of PYTHIA, quantitative description may require implementing new mechanisms for multi-particle production in hadronic collisions.

Differential two-particle normalized cumulants ($R_2$) and transverse momentum correlations ($P_2$) are measured as a function of the relative pseudorapidity and azimuthal angle difference $( Δη, Δφ)$ of charged particle pairs in minimum bias pp collisions at $\sqrt{\textit{s}}$ = 13 TeV. The measurements use charged hadrons in the pseudorapidity region of $|η| < 0.8$ and the transverse momentum range \mbox{0.2 $< \textit{p}_{\mathrm T} < $ 2.0 $\mathrm{GeV}/\textit{c}$} in order to focus on soft multiparticle interactions and to complement prior measurements of these correlation functions in p-Pb and Pb-Pb collisions. The correlation functions are reported for both unlike-sign and like-sign pairs and their charge-independent and charge-dependent combinations. Both the $R_2$ and $P_2$ measured in pp collisions exhibit features qualitatively similar to those observed in p--Pb and Pb--Pb collisions. The $Δη$ and $Δφ$ root mean square widths of the near-side peak of the correlation functions are evaluated and compared with those observed in p-Pb and Pb-Pb collisions and show smooth evolution with the multiplicity of charged particles produced in the collision. The comparison of the measured correlation functions with predictions from PYTHIA8 shows that this model qualitatively captures their basic structure and characteristics but feature important differences. In addition, the $R_2^{\rm CD}$ is used to determine the charge balance function of hadrons produced within the detector acceptance of the measurements. The integral of the balance function is found to be compatible with those reported by a previous measurement in Pb--Pb collisions.

Ultrarelativistic heavy-ion collisions create a quark-gluon plasma (QGP), a hot and dense state of strongly interacting QCD matter. In ultracentral collisions, the QGP volume remains nearly constant event-by-event, while its total entropy can fluctuate due to quantum effects, leading to temperature variations. These features allow the correlation between the mean transverse momentum $(\langle p_{\mathrm{T}} \rangle)$ of charged hadrons and their multiplicity to serve as a probe of the QGP's speed of sound, $c_{s}$. This study extracts $c_{s}$ by analyzing the relative increase in $\langle p_{\mathrm{T}} \rangle$ with respect to the charged-particle density $(\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta \rangle)$ at midrapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$, using data from the ALICE detector. Centrality is determined with estimators based on multiplicity and transverse energy, applying a pseudorapidity gap to reduce selection biases. The extracted value of $c_{s}^{2}$ is found to strongly depend on the employed centrality estimator and ranges between $0.1146 \pm 0.0028 \,\mathrm{(stat.)} \pm 0.0065 \,\mathrm{(syst.)}$ and $0.4374 \pm 0.0006 \mathrm{(stat.)} \pm 0.0184 \mathrm{(syst.)}$ in natural units. Additionally, the event-by-event $[p_{\mathrm{T}}]$ distribution is studied through its variance, skewness, and kurtosis. A pronounced decrease in the self-normalized variance and a peak followed by a drop in skewness suggest the suppression of impact-parameter fluctuations in ultracentral collisions. These observations provide new insights into the thermodynamic properties and initial-state fluctuations of the QGP.

The coherent J/$\psi$ photoproduction cross section is measured for the first time at midrapidity in peripheral to semicentral Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. The centrality differential cross section ${\rm d} \sigma/ {\rm d}y$ is reported for the centrality range 40-90%, together with the doubly-differential cross section ${\rm d}^2 \sigma /{\rm d}y {\rm d} p_{\rm T}$, extracted in two peripheral centrality classes. The J/$\psi$ mesons are reconstructed in the dielectron channel, in the rapidity interval $|y| <$ 0.9 using the ALICE central barrel detectors. The J/$\psi$ cross section at midrapidity is statistically compatible to the earlier ALICE measurement at forward rapidity and at the same centre-of-mass energy, and shows only a mild centrality dependence over the covered range. Several sets of theoretical calculations taking into account the hadronic overlap in the collisions but ignoring possible final-state effects from a hot expanding medium are found to give a fairly good description of the current measurements within uncertainties.