A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV, and Cu+Cu collisions sqrt(s_NN) = 22.5, 62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for non-dynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon p+p data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. An analysis of Negative Binomial Distribution fits to the multiplicity distributions demonstrates that the heavy ion data exhibit weak clustering properties.

We have studied ω photoproduction using 7.5- to 10.5-GeV tagged photons. Cross sections from hydrogen lie 22% below the bubble chamber results of Ballam et al., but have a similar slope. Density matrices indicate approximate s-channel helicity conservation. The proton-neutron cross-section difference is midway between zero and the value suggested by the γp−γn total-cross-section difference. Fits to the cross sections for D, Be, and Cu and those for Be, C, Al, Cu, and Pb from a previous experiment yield σωN=25.4±2.7 mb and γω24π=7.6±1.2.

We report the measurement of direct photons at midrapidity in Au+Au collisions at sqrt{s_NN} = 200 GeV. The direct photon signal was extracted for the transverse-momentum range of 4 GeV/c < p_T < 22 GeV/c, using a statistical method to subtract decay photons from the inclusive-photon sample. The direct-photon nuclear-modification factor R_AA was calculated as a function of p_T for different Au+Au collision centralities using the measured p+p direct-photon spectrum and compared to theoretical predictions. R_AA was found to be consistent with unity for all centralities over the entire measured p_T range. Theoretical models that account for modifications of initial-direct-photon production due to modified-parton-distribution functions in Au and the different isospin composition of the nuclei, predict a modest change of R_AA from unity and are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.

The first measurements of elliptic flow of $\pi^\pm$, ${\rm K}^\pm$, p+$\overline{\rm p}$, ${\rm K_{S}^0}$, $\Lambda$+$\overline{\Lambda}$, $\phi$, $\Xi^-$+$\Xi^+$, and $\Omega^-$+$\Omega^+$ using multiparticle cumulants in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. Results obtained with two- ($v_2\{2\}$) and four-particle cumulants ($v_2\{4\}$) are shown as a function of transverse momentum, $p_{\rm T}$, for various collision centrality intervals. Combining the data for both $v_2\{2\}$ and $v_2\{4\}$ also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark-gluon plasma. The characteristic features observed in previous $p_{\rm T}$-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low $p_{\rm T}$ and the approximate scaling with the number of constituent quarks at intermediate $p_{\rm T}$, are similarly present in the four-particle correlations and the combinations of $v_2\{2\}$ and $v_2\{4\}$. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide $p_{\rm T}$ range.

The interaction of $\rm{K}^{-}$ with protons is characterised by the presence of several coupled channels, systems like ${\rm \overline{K}^0}$n and $\pi\Sigma$ with a similar mass and the same quantum numbers as the $\rm{K}^{-}$p state. The strengths of these couplings to the $\rm{K}^{-}$p system are of crucial importance for the understanding of the nature of the $\Lambda(1405)$ resonance and of the attractive $\rm{K}^{-}$p strong interaction. In this article, we present measurements of the $\rm{K}^{-}$p correlation functions in relative momentum space obtained in pp collisions at $\sqrt{s}~=~13$ TeV, in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV, and (semi)peripheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV. The emitting source size, composed of a core radius anchored to the $\rm{K}^{+}$p correlation and of a resonance halo specific to each particle pair, varies between 1 and 2 fm in these collision systems. The strength and the effects of the ${\rm \overline{K}^0}$n and $\pi\Sigma$ inelastic channels on the measured $\rm{K}^{-}$p correlation function are investigated in the different colliding systems by comparing the data with state-of-the-art models of chiral potentials. A novel approach to determine the conversion weights $\omega$, necessary to quantify the amount of produced inelastic channels in the correlation function, is presented. In this method, particle yields are estimated from thermal model predictions, and their kinematic distribution from blast-wave fits to measured data. The comparison of chiral potentials to the measured $\rm{K}^{-}$p interaction indicates that, while the $\pi\Sigma-\rm{K}^{-}$p dynamics is well reproduced by the model, the coupling to the ${\rm \overline{K}^0}$n channel in the model is currently underestimated.

The transverse-momentum ($p_{\rm T}$) spectra of ${\rm K}^*(892)^0$ and $\phi(1020)$ measured with the ALICE detector up to $p_{\rm T}$ = 16 GeV/$c$ in the rapidity range $-1.2 < y < 0.3$, in p-Pb collisions at the center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented as a function of charged particle multiplicity and rapidity. The measured $p_{\rm T}$ distributions show a dependence on both multiplicity and rapidity at low $p_{\rm T}$ whereas no significant dependence is observed at high $p_{\rm T}$. A rapidity dependence is observed in the $p_{\rm T}$-integrated yield (d$N$/d$y$), whereas the mean transverse momentum ($\left< p_{\rm T} \right>$) shows a flat behavior as a function of rapidity. The rapidity asymmetry ($Y_{\rm asym}$) at low $p_{\rm T}$ ( < 5 GeV/$c$) is more significant for higher multiplicity classes. At high $p_{\rm T}$, no significant rapidity asymmetry is observed in any of the multiplicity classes. Both ${\rm K}^*(892)^0$ and $\phi(1020)$ show similar $Y_{\rm asym}$. The nuclear modification factor ($Q_{\rm CP}$) as a function of $p_{\rm T}$ shows a Cronin-like enhancement at intermediate $p_{\rm T}$, which is more prominent at higher rapidities (Pb-going direction) and in higher multiplicity classes. At high $p_{\rm T}$ (> 5 GeV/$c$), the $Q_{\rm CP}$ values are greater than unity and no significant rapidity dependence is observed.

The production of $\pi^\pm$, ${\rm K}^\pm$, and $(\overline{\rm p})$p is measured in pp collisions at $\sqrt{s}=13$ TeV in different topological regions. Particle transverse momentum ($p_{\rm T}$) spectra are measured in the ``toward'', ``transverse'', and ``away'' angular regions defined with respect to the direction of the leading particle in the event. While the toward and away regions contain the fragmentation products of the near-side and away-side jets, respectively, the transverse region is dominated by particles from the Underlying Event (UE). The relative transverse activity classifier, $R_{\rm T}=N_{\rm T}/\langle N_{\rm T}\rangle$, is used to group events according to their UE activity, where $N_{\rm T}$ is the measured charged-particle multiplicity per event in the transverse region and $\langle N_{\rm T}\rangle$ is the mean value over all the analysed events. The first measurements of identified particle $p_{\rm T}$ spectra as a function of $R_{\rm T}$ in the three topological regions are reported. The yield of high transverse momentum particles relative to the $R_{\rm T}$-integrated measurement decreases with increasing $R_{\rm T}$ in both the toward and away regions, indicating that the softer UE dominates particle production as $R_{\rm T}$ increases and validating that $R_{\rm T}$ can be used to control the magnitude of the UE. Conversely, the spectral shapes in the transverse region harden significantly with increasing $R_{\rm T}$. This hardening follows a mass ordering, being more significant for heavier particles. The $p_{\rm T}$-differential particle ratios $({\rm p+\overline{p}})/(\pi^+ +\pi^-)$ and $({\rm K^+ +K^-})/(\pi^+ +\pi^-)$ in the low UE limit $(R_{\rm T}\rightarrow 0)$ approach expectations from Monte Carlo generators such as PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jet-fragmentation models have been tuned to reproduce ${\rm e^+ e^-}$ results.

This article reports measurements of the angle between differently defined jet axes in pp collisions at $\sqrt{s} = 5.02$ TeV carried out by the ALICE Collaboration. Charged particles at midrapidity are clustered into jets with resolution parameters $R=0.2$ and 0.4. The jet axis, before and after Soft Drop grooming, is compared to the jet axis from the Winner-Takes-All (WTA) recombination scheme. The angle between these axes, $\Delta R_{\mathrm{axis}}$, probes a wide phase space of the jet formation and evolution, ranging from the initial high-momentum-transfer scattering to the hadronization process. The $\Delta R_{\mathrm{axis}}$ observable is presented for $20 < {p_{\mathrm{T}}^{\mathrm{ch\; jet}}}< 100$ GeV/$c$, and compared to predictions from the PYTHIA 8 and Herwig 7 event generators. The distributions can also be calculated analytically with a leading hadronization correction related to the non-perturbative component of the Collins$-$Soper$-$Sterman (CSS) evolution kernel. Comparisons to analytical predictions at next-to-leading-logarithmic accuracy with leading hadronization correction implemented from experimental extractions of the CSS kernel in Drell$-$Yan measurements are presented. The analytical predictions describe the measured data within 20% in the perturbative regime, with surprising agreement in the non-perturbative regime as well. These results are compatible with the universality of the CSS kernel in the context of jet substructure.

Measurements of the midrapidity transverse energy distribution, $d\Et/d\eta$, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and additionally for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 130 GeV. The $d\Et/d\eta$ distributions are first compared with the number of nucleon participants $N_{\rm part}$, number of binary collisions $N_{\rm coll}$, and number of constituent-quark participants $N_{qp}$ calculated from a Glauber model based on the nuclear geometry. For Au$+$Au, $\mean{d\Et/d\eta}/N_{\rm part}$ increases with $N_{\rm part}$, while $\mean{d\Et/d\eta}/N_{qp}$ is approximately constant for all three energies. This indicates that the two component ansatz, $dE_{T}/d\eta \propto (1-x) N_{\rm part}/2 + x N_{\rm coll}$, which has been used to represent $E_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in $E_T$ distributions. The $dE_{T}/d\eta$ distributions of Au$+$Au and $d$$+$Au are then calculated from the measured $p$$+$$p$ $E_T$ distribution using two models that both reproduce the Au$+$Au data. However, while the number-of-constituent-quark-participant model agrees well with the $d$$+$Au data, the additive-quark model does not.

ω photoproduction off hydrogen and deuterium has been studied with the tagged photon beam of the ELSA accelerator in Bonn for photon energies up to 2.0 GeV. The ω meson has been identified via the ω → π$^{0}$ γ → γγγ decay mode, using the combined setup of the Crystal Barrel/TAPS detector systems. Both inclusive and exclusive analyses have been carried out. Differential and total cross-sections have been derived for ω mesons produced off free protons and off protons and neutrons bound in deuterium. The cross-section for the production off the bound neutron is found to be a factor of ≈ 1.3 larger than the one off the bound proton in the incident beam energy region 1.2 GeV < E$_{γ}$ < 1.6 GeV. For higher incident beam energies this factor goes down to ≈ 1.1 at 2.0 GeV. The cross-sections of this work have been used as normalization for transparency ratio measurements.