Anna Rita Altamura

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.

The transverse momentum spectra and integrated yields of anti- $$\Sigma $$ Σ hyperons ( $$\overline{\Sigma }^{\pm } $$ Σ ¯ ± ) have been measured in $$\text {pp}$$ pp and $$\text {p}{-}\text {Pb}$$ p - Pb collisions at $$\sqrt{s_{\textrm{NN}}}=5.02$$ s NN = 5.02 TeV with the ALICE experiment. Measurements are performed via the newly accessed decay channel $$\overline{\Sigma }^{\pm } \!\!\rightarrow \mathrm{\overline{n}} \pi ^{\pm }$$ Σ ¯ ± → n ¯ π ± . A new method of antineutron reconstruction with the PHOS electromagnetic spectrometer is developed and applied to this analysis. The $$p_{\textrm{T}}$$ p T spectra of $$\overline{\Sigma }^{\pm } $$ Σ ¯ ± are measured in the range $$0.5<p_{\textrm{T}} <3$$ 0.5 < p T < 3 GeV/ $$c$$ c and compared to predictions of the PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4 models. The EPOS LHC and EPOS4 models provide the best descriptions of the measured spectra both in $$\text {pp}$$ pp and $$\text {p}{-}\text {Pb}$$ p - Pb collisions, while models which do not account for multiparton interactions provide a considerably worse description at high $$p_{\textrm{T}}$$ p T . The total yields of $$\overline{\Sigma }^{\pm } $$ Σ ¯ ± in both $$\text {pp}$$ pp and $$\text {p}{-}\text {Pb}$$ p - Pb collisions are compared to predictions of the Thermal-FIST model and dynamical models PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4. All models reproduce the total yields in both colliding systems within uncertainties. The nuclear modification factors $$R_\textrm{pPb}$$ R pPb for both $$\overline{\Sigma }^{+} $$ Σ ¯ + and $$\overline{\Sigma }^{-} $$ Σ ¯ - are evaluated and compared to those of protons, $$\Lambda $$ Λ and $$\Xi $$ Ξ hyperons, and predictions of EPOS LHC and EPOS4 models. No deviations of $$R_\textrm{pPb}$$ R pPb for $$\overline{\Sigma }^{\pm } $$ Σ ¯ ± from the model predictions or measurements for other hadrons are found within uncertainties.

The measurement of $$\Sigma ^{+}$$ Σ + production in pp collisions at $$\sqrt{s}=13$$ s = 13 TeV is presented. The measurement is performed at midrapidity in both minimum-bias and high-multiplicity pp collisions at $$\sqrt{s} =13$$ s = 13 TeV. The $$\Sigma ^{+}$$ Σ + is reconstructed via its weak-decay topology in the decay channel $$\Sigma ^{+} \rightarrow \mathrm{{p}} + \pi ^{0}$$ Σ + → p + π 0 with $$\pi ^{0} \rightarrow \gamma + \gamma .$$ π 0 → γ + γ . In a novel approach, the neutral pion is reconstructed by combining photons that convert in the detector material with photons measured in the calorimeters. The transverse-momentum $$(p_{\textrm{T}})$$ ( p T ) distributions of the $$\Sigma ^{+}$$ Σ + and its rapidity densities $${\textrm{d}}N$$ d N / $${\textrm{d}}y$$ d y in both event classes are reported. The $$p_{\textrm{T}}$$ p T spectrum in minimum-bias collisions is compared to QCD-inspired event generators. The ratio of $$\Sigma ^{+}$$ Σ + to previously measured $$\Lambda $$ Λ baryons is in good agreement with calculations from the Statistical Hadronization Model. The high efficiency and purity of the novel reconstruction method for $$\Sigma ^{+}$$ Σ + presented here will enable future studies of the interaction of $$\Sigma ^{+}$$ Σ + with protons in the context of femtoscopic measurements, which could be crucial for understanding the equation of state of neutron stars.