Comprehensive results on the production of unidentified charged particles, ${\pi }^{\pm }, {\mathrm{K}}^{\pm }, {\mathrm{K}}_{\mathrm{S}}^0, {\mathrm{K}}^{*}{\left(892\right)}^0, p, \overline{p}, \varphi$(1020), $\mathrm{\Lambda }, \overline{\mathrm{\Lambda }}, {\mathrm{\Xi }}^{-}, {\overline{\mathrm{\Xi }}}^{+}, {\mathrm{\Omega }}^{-}$, and ${\overline{\mathrm{\Omega }}}^{+}$ hadrons in proton-proton ($pp$) collisions at $\sqrt{s}=7$ TeV at midrapidity ($\left|y\right|<0.5$) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum ($p_{\mathrm{T}}$) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in $p$-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained $p_{\mathrm{T}}$ distributions and yields are compared to expectations from QCD-based $pp$ event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity $pp$ collisions.

Measurements of anisotropic flow coefficients ($v_n$) and their cross-correlations using two- and multiparticle cumulant methods are reported in collisions of $pp$ at $\sqrt{s}=13\mathrm{TeV}$, $p\text{−}\mathrm{Pb}$ at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$, Xe-Xe at $\sqrt{s_{\mathrm{NN}}}=5.44\mathrm{TeV}$, and Pb-Pb at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ recorded with the ALICE detector. The multiplicity dependence of $v_n$ is studied in a very wide range from 20 to 3000 particles produced in the midrapidity region $|\eta |<0.8$ for the transverse momentum range $0.2<p_T<3.0\mathrm{GeV}/c$. An ordering of the coefficients $v_2>v_3>v_4$ is found in $pp$ and $p\text{−}\mathrm{Pb}$ collisions, similar to that seen in large collision systems, while a weak $v_2$ multiplicity dependence is observed relative to nucleus-nucleus collisions in the same multiplicity range. Using a novel subevent method, $v_2$ measured with four-particle cumulants is found to be compatible with that from six-particle cumulants in $pp$ and $p\text{−}\mathrm{Pb}$ collisions. The magnitude of the correlation between $v_n^2$ and $v_m^2$, evaluated with the symmetric cumulants $\mathrm{SC}(m,n)$ is observed to be positive at all multiplicities for $v_2$ and $v_4$, while for $v_2$ and $v_3$ it is negative and changes sign for multiplicities below 100, which may indicate a different $v_n$ fluctuation pattern in this multiplicity range. The observed long-range multiparticle azimuthal correlations in high multiplicity $pp$ and $p\text{−}\mathrm{Pb}$ collisions can neither be described by pythia 8 nor by impact-parameter-Glasma, music, and ultrarelativistic quantum molecular dynamics model calculations, and hence, provide new insights into the understanding of collective effects in small collision systems.

We report on the first femtoscopic measurement of baryon pairs, such as $p-p, p-\mathrm{\Lambda }$, and $\mathrm{\Lambda }-\mathrm{\Lambda }$, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$. This study demonstrates the feasibility of such measurements in $pp$ collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The $p-p, p-\mathrm{\Lambda }$, and $\mathrm{\Lambda }-\mathrm{\Lambda }$ correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems: Correlation Analysis Tool using the Schrödinger equation (CATS). Within the assumption that in $pp$ collisions the three particle pairs originate from a common source, its radius is found to be equal to $r_0=1.125\pm 0.018\left(\mathrm{stat}\right){}_{-0.035}^{+0.058}\left(\mathrm{syst}\right)$ fm. The sensitivity of the measured $p-\mathrm{\Lambda }$ correlation is tested against different scattering parameters, which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the $\mathrm{\Lambda }-\mathrm{\Lambda }$ correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models.