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Abstract Threebody nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the threenucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the threebody forces. In this work, we present the first direct measurement of the p–p–p and p–p– $$\Lambda $$ Λ systems in terms of threeparticle correlation functions carried out for pp collisions at $$\sqrt{s} = 13$$ s = 13 TeV. Threeparticle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the threeparticle interaction contribution to these correlations can be isolated after subtracting the known twobody interaction terms. A negative cumulant is found for the p–p–p system, hinting to the presence of a residual threebody effect while for p–p– $$\Lambda $$ Λ the cumulant is consistent with zero. This measurement demonstrates the accessibility of threebaryon correlations at the LHC.more » « lessFree, publiclyaccessible full text available July 1, 2024

Abstract A newly developed observable for correlations between symmetry planes, which characterize the direction of the anisotropic emission of produced particles, is measured in Pb–Pb collisions at $$\sqrt{s_\text {NN}}$$ s NN = 2.76 TeV with ALICE. This socalled Gaussian Estimator allows for the first time the study of these quantities without the influence of correlations between different flow amplitudes. The centrality dependence of various correlations between two, three and four symmetry planes is presented. The ordering of magnitude between these symmetry plane correlations is discussed and the results of the Gaussian Estimator are compared with measurements of previously used estimators. The results utilizing the new estimator lead to significantly smaller correlations than reported by studies using the Scalar Product method. Furthermore, the obtained symmetry plane correlations are compared to stateoftheart hydrodynamic model calculations for the evolution of heavyion collisions. While the model predictions provide a qualitative description of the data, quantitative agreement is not always observed, particularly for correlators with significant nonlinear response of the medium to initial state anisotropies of the collision system. As these results provide unique and independent information, their usage in future Bayesian analysis can further constrain our knowledge on the properties of the QCD matter produced in ultrarelativistic heavyion collisions.more » « lessFree, publiclyaccessible full text available July 1, 2024

A bstract The production of π ± , K ± , and $$ \left(\overline{\textrm{p}}\right)\textrm{p} $$ p ¯ p is measured in pp collisions at $$ \sqrt{s} $$ s = 13 TeV in different topological regions of the events. Particle transverse momentum ( p 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 nearside and awayside jets, respectively, the transverse region is dominated by particles from the Underlying Event (UE). The relative transverse activity classifier, R T = N T /〈 N T 〉, is used to group events according to their UE activity, where N T is the measured chargedparticle multiplicity per event in the transverse region and 〈 N T 〉 is the mean value over all the analysed events. The first measurements of identified particle p T spectra as a function of R T in the three topological regions are reported. It is found that the yield of high transverse momentum particles relative to the R T integrated measurement decreases with increasing R T in both the toward and the away regions, indicating that the softer UE dominates particle production as R T increases and validating that R T can be used to control the magnitude of the UE. Conversely, the spectral shapes in the transverse region harden significantly with increasing R T . This hardening follows a mass ordering, being more significant for heavier particles. Finally, it is observed that the p T differential particle ratios $$ \left(\textrm{p}+\overline{\textrm{p}}\right)/\left({\uppi}^{+}+{\uppi}^{}\right) $$ p + p ¯ / π + + π − and (K + + K − ) / ( π + + π − ) in the low UE limit ( R T → 0) approach expectations from Monte Carlo generators such as PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jetfragmentation models have been tuned to reproduce e + e − results.more » « lessFree, publiclyaccessible full text available June 1, 2024

Free, publiclyaccessible full text available June 1, 2024

Free, publiclyaccessible full text available June 1, 2024

A bstract The first measurements of elliptic flow of π ± , K ± , $$ \textrm{p}+\overline{\textrm{p}} $$ p + p ¯ , $$ {\textrm{K}}_{\textrm{S}}^0 $$ K S 0 , $$ \Lambda +\overline{\Lambda} $$ Λ + Λ ¯ , ϕ , $$ {\Xi}^{}+{\overline{\Xi}}^{+} $$ Ξ − + Ξ ¯ + , and $$ {\varOmega}^{}+{\overline{\varOmega}}^{+} $$ Ω − + Ω ¯ + using multiparticle cumulants in Pb–Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV are resented. Results obtained with two ( v 2 {2}) and fourparticle cumulants ( v 2 {4}) are shown as a function of transverse momentum, p 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 eventbyevent 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 T differential anisotropic flow measurements for identified hadrons with twoparticle correlations, namely the mass ordering at low p T and the approximate scaling with the number of constituent quarks at intermediate p T , are similarly present in the fourparticle 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 T range.more » « lessFree, publiclyaccessible full text available June 1, 2024

Free, publiclyaccessible full text available June 1, 2024

Abstract Twoparticle correlations with $$\textrm{K}^{0}_\mathrm{{S}}$$ K S 0 , $$\Lambda $$ Λ / $$\overline{\Lambda }$$ Λ ¯ , and charged hadrons as trigger particles in the transverse momentum range $$8{<}p_{{\textrm{T}},{\textrm{trig}}}{<}16$$ 8 < p T , trig < 16 GeV/ $$c$$ c , and associated charged particles within $$1{<}p_{{\textrm{T}},{\textrm{assoc}}}{<}8$$ 1 < p T , assoc < 8 GeV/ $$c$$ c , are studied at midrapidity in pp and central Pb–Pb collisions at a centreofmass energy per nucleon–nucleon collision $$\sqrt{s_{\textrm{NN}}}~=~5.02$$ s NN = 5.02 TeV with the ALICE detector at the LHC. After subtracting the contributions of the flow background, the pertrigger yields are extracted on both the near and away sides, and the ratio in Pb–Pb collisions with respect to pp collisions ( $$I_{\textrm{AA}}$$ I AA ) is computed. The pertrigger yield in Pb–Pb collisions on the away side is strongly suppressed to the level of $$I_{\textrm{AA}}$$ I AA $$\approx 0.6$$ ≈ 0.6 for $$p_{{\textrm{T}},{\textrm{assoc}}}>3$$ p T , assoc > 3 GeV/ $$c$$ c as expected from strong inmedium energy loss, while an enhancement develops at low $$p_{{\textrm{T}},{\textrm{assoc}}}$$ p T , assoc on both the near and away sides, reaching $$I_{\textrm{AA}}$$ I AA $$\approx 1.8$$ ≈ 1.8 and 2.7 respectively. These findings are in good agreement with previous ALICE measurements from twoparticle correlations triggered by neutral pions ( $$\pi ^{0}$$ π 0 –h) and charged hadrons (h–h) in Pb–Pb collisions at $$\sqrt{s_{\textrm{NN}}}~=~2.76$$ s NN = 2.76 TeV. Moreover, the correlations with $$\textrm{K}^{0}_\mathrm{{S}}$$ K S 0 mesons and $$\Lambda $$ Λ / $$\overline{\Lambda }$$ Λ ¯ baryons as trigger particles are compared to those of inclusive charged hadrons. The results are compared with the predictions of Monte Carlo models.more » « lessFree, publiclyaccessible full text available June 1, 2024

Free, publiclyaccessible full text available May 1, 2024

Free, publiclyaccessible full text available May 1, 2024