Evgeny Andronov

Measurements of the production of the W $$^{\pm }$$ ± and Z $$^0$$ 0 bosons at midrapidity in pp collisions at $$\sqrt{s} = 13$$ s = 13 TeV with ALICE at the Large Hadron Collider (LHC) are presented. The W $$^{\pm }$$ ± and Z $$^0$$ 0 bosons are detected via their (di)electronic decay channels, with the electron reconstruction performed in the midrapidity region $$(|y|< 0.6).$$ ( | y | < 0.6 ) . The $$p_{{\text {T}}}$$ p T -integrated and $$p_{\textrm{T}}$$ p T -differential production cross sections of electrons from W $$^{\pm }$$ ± decays in the interval $$30<p_{{\text {T}}}< 60$$ 30 < p T < 60 GeV/ c , as well as the $$p_{{\text {T}}}$$ p T -integrated production cross section of Z $$^0$$ 0 bosons, are measured. The results are described by perturbative QCD calculations using different sets of parton distribution functions. The production of W $$^{\pm }$$ ± bosons and azimuthally correlated associated hadrons is also measured as a function of the charged-particle multiplicity for the first time at the LHC. The former increases approximately linearly with the charged-particle multiplicity, while for the latter, there are hints of a faster-than-linear increase. These observations are compared with theoretical calculations .

Studies of the phase diagram of strongly interacting matter created in nuclear collisions are typically carried out using event-by-event fluctuations. Well-known way to disentangle statistical and dynamical fluctuations is to construct special observables named strongly intensive which are free from trivial volume fluctuations. Within the color string model behavior of the second-order strongly intensive quantity \(\Sigma \) is completely determined by the two-particle correlation function from a single string and the string fusion mechanism. In this paper, we analyze third-order strongly intensive observable for forward-backward rapidity correlations and test its behavior within the PYTHIA8 model.

Particle identification (PID) is a fundamental aspect of the ALICE detector system, central to its heavy-ion and proton–proton physics programs. Among the different PID strategies, ALICE uses the time-of-flight (TOF) detector to identify particles at intermediate momenta ( $$0.5< p_{\mathrm{T}} <4\ {\,{\textrm{GeV}}/c} $$ 0.5 < p T < 4 GeV / c ). The ALICE TOF detector performed successfully during the first 10 years of LHC operations. During the Long Shutdown 2, many ALICE sub-detectors, including TOF, were upgraded to fully leverage the targeted 50 kHz interaction rate of Pb–Pb collisions, which required the implementation of a continuous readout scheme. The TOF detector electronics were upgraded and refurbished, while processing algorithms for data quality control, reconstruction, calibration, and analysis were rewritten. This paper presents the upgraded TOF detector operation and calibration procedures and its performance in terms of timing resolution, a key factor for particle separation in ALICE analyses. Using 2022 pp collision data at $$\sqrt{s} = 13.6\,\textrm{TeV}$$ s = 13.6 TeV from Run 3, the time resolution of the detector was estimated with two independent methods, both yielding consistent results, better than 80 ps. Despite the excellent performance already achieved, further improvements are expected after additional detector commissioning and refined calibration procedures, thus enhancing the ALICE PID capabilities for Run 3 and beyond.

Two-particle angular correlations probe particle production mechanisms and the underlying event-wide phenomena present in hadronic collisions. The correlations are examined as a function of rapidity and azimuthal-angle differences ( $$\Delta y, \Delta \varphi $$ Δ y , Δ φ ) for pairs of like- and unlike-sign pions, kaons, and (anti-)protons produced in pp collisions at $$\sqrt{s}$$ s = 13 TeV, measured by the ALICE experiment. Two-particle correlation functions are provided together with $$\Delta y$$ Δ y and $$\Delta \varphi $$ Δ φ projections and compared to Monte Carlo (MC) model predictions. For the first time, the measurement is performed as a function of the event’s charged-particle density. Previous studies conducted for pp collisions at $$\sqrt{s}$$ s = 7 TeV at ALICE revealed a near-side anticorrelation for baryon–baryon and antibaryon–antibaryon pairs, whose origin remains unresolved. Here, an additional approach is introduced to study the multiplicity dependence and the expected inverse multiplicity scaling of the correlation function. This method highlights qualitative differences in the underlying sources of correlations, such as quantum-statistics effects, final-state interactions, and resonance decays. The puzzling near-side anticorrelation in baryon baryon measurements is observed across all multiplicity classes and continues to challenge current particle-production models. Furthermore, the multiplicity dependence of the correlations between mesons provides an independent probe of the sensitivity of current MC models to soft-QCD effects and hadronization dynamics. The presented measurements, together with the baryon results, enrich the experimental picture of two-particle correlations in pp collisions and serve as valuable input for ongoing theoretical developments.

A bstract: The probability to observe a specific number of strange and multi-strange hadrons ( n _S ), denoted as P( n _S ), is measured by ALICE at midrapidity (| y | < 0 . 5) in $$\sqrt{s}=5.02$$ TeV proton-proton (pp) collisions, dividing events into several multiplicity-density classes. Exploiting, for the first time, a technique based on counting the number of strange-particle candidates event-by-event, this measurement allows one to extend the study of strangeness production beyond the mean of the distribution. This constitutes a new test bench for production mechanisms, probing events with a large imbalance between strange and non-strange content. The analysis of a large-statistics data sample makes it possible to extract P( n _S ) up to a maximum n _S of 7 for $${\text{K}}_{\text{S}}^{0}$$ , 5 for Λ and $$\overline{\Lambda }$$ , 4 for Ξ ⁻ and $${\overline{\Xi } }^{+}$$ , and 2 for Ω ⁻ and $${\overline{\Omega } }^{+}$$ . From this, the probability of producing strange hadron multiplets per event is calculated, thereby enabling the extension of the study of strangeness enhancement to extreme situations where several strange quarks hadronize in a single event at midrapidity. Moreover, comparing hadron combinations with different u and d quark compositions and equal overall s quark content, the contribution to the enhancement pattern coming from non-strangeness related mechanisms is isolated. The results are compared with state-of-the-art phenomenological models implemented in commonly used Monte Carlo event generators, including PYTHIA 8 Monash 2013, PYTHIA 8 with QCD-based Color Reconnection and Rope Hadronization (QCD-CR + Ropes), and EPOS LHC, which incorporates both partonic interactions and hydrodynamic evolution. These comparisons show that the new approach dramatically enhances the sensitivity to the different underlying physics mechanisms modeled by each generator.

The azimuthal-correlation distributions between electrons from the decays of heavy-flavor hadrons and associated charged particles in Pb–Pb collisions at $$\sqrt{s_{\textrm{NN}}} = 5.02$$ s NN = 5.02 TeV are reported for the 0–10% and 30–50% centrality classes. This measurement provides access to the jet-like correlation observables in the heavy-flavor sector in Pb–Pb collisions. The analysis is performed for trigger electrons from heavy-flavor hadron decays with transverse momentum $$4< p_\textrm{T}^\textrm{e} < 16~\textrm{GeV}/c$$ 4 < p T e < 16 GeV / c , considering associated particles within the transverse-momentum range $$1< p_\textrm{T}^\textrm{assoc} < 7$$ 1 < p T assoc < 7 $$\textrm{GeV}/c$$ GeV / c , and a pseudorapidity difference of $$|\Delta \eta |<1$$ | Δ η | < 1 between the trigger electron and associated particles. The per-trigger nuclear modification factor ( $$I_\textrm{AA}$$ I AA ) is calculated to compare the near- and away-side peak yields to those in pp collisions at $$\sqrt{s} = 5.02$$ s = 5.02 TeV. In 0–10% central collisions, the $$I_\textrm{AA}$$ I AA indicates a hint of enhancement of associated-particle yields with $$p_\textrm{T}<3$$ p T < 3 GeV/ c on the near side, and a suppression of yields with $$p_\textrm{T}>4$$ p T > 4 GeV/ c on the away side. The $$I_\textrm{AA}$$ I AA for electron triggers from heavy-flavor hadron decays is compared with that for light-flavor and strange-particle triggers to investigate the dependence on different fragmentation processes and parton-medium dynamics, and is found to be the same within uncertainties.

A bstract: The measurement of three-dimensional femtoscopic correlations between identical charged kaons (K ^± K ^± ) produced in p–Pb collisions at center-of-mass energy per nucleon pair $$\sqrt{{s}_{\text{NN}}}=5.02$$ TeV with ALICE at the LHC is presented for the first time. This measurement, supplementary to those in pp and Pb–Pb collisions, allows understanding the particle-production mechanisms at different charged-particle multiplicities and provides information on the dynamics of the source of particles created in p–Pb collisions, for which a general consensus does not yet exist. It is shown that the measured source sizes increase with charged-particle multiplicity and decrease with increasing pair transverse momentum. These trends for K ^± K ^± are similar to the ones observed earlier in identical charged-pion and $${\text{K}}_{\text{s}}^{0}{\text{K}}_{\text{s}}^{0}$$ correlations in Pb–Pb collisions at various energies and in π ^± π ^± correlations in p–Pb collisions at $$\sqrt{{s}_{\text{NN}}}=5.02$$ TeV. At comparable multiplicity, the source sizes measured in p–Pb collisions agree within uncertainties with those observed in pp collisions, and there is an indication that they are smaller than those observed in Pb–Pb collisions. The obtained results are also compared with predictions from the hadronic interaction model EPOS 3, which tends to underestimate the source size for the most central collisions and agrees with the data for semicentral and peripheral events. Furthermore, the time of maximal emission for kaons is extracted. It turns out to be comparable with the value obtained in highly peripheral Pb–Pb collisions at the same energy, indicating that the kaon emission evolution is similar to that in p–Pb collisions.