Measurement of the low-energy antitriton inelastic cross section

In this Letter, the first measurement of the inelastic cross section for antitriton–nucleus interactions is reported, covering the momentum range of 0.8 ≤ p < 2.4 GeV/c. The measurement is carried out using data recorded with the ALICE detector in pp and Pb–Pb collisions at a centre-of-mass energy per nucleon of 13 TeV and 5.02 TeV, respectively. The detector material serves as an absorber for antitriton nuclei. The raw yield of (anti)triton nuclei measured with the ALICE apparatus is compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of (anti)particles through matter, allowing one to quantify the inelastic interaction probability in the detector material. This analysis complements the measurement of the inelastic cross section of antinuclei up to A=3 carried out by the ALICE Collaboration, and demonstrates the feasibility of the study of the isospin dependence of inelastic interaction cross section with the analysis techniques presented in this Letter

First Measurement of the |t| Dependence of Incoherent J/ψ Photonuclear Production

The first measurement of the cross section for incoherent photonuclear production of J/ψ vector mesons as a function of the Mandelstam |t| variable is presented. The measurement was carried out with the ALICE detector at midrapidity, |y|&lt;0.8, using ultraperipheral collisions of Pb nuclei at a center-of-mass energy per nucleon pair of sNN=5.02 TeV. This rapidity interval corresponds to a Bjorken-x range (0.3-1.4)×10-3. Cross sections are given in five |t| intervals in the range 0.04&lt;|t|&lt;1 GeV2 and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a |t| dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data

Investigating strangeness enhancement in jet and medium via φ(1020) production in p−Pb collisions at √sNN = 5.02 TeV

This work aims to differentiate strangeness produced from hard processes (jet-like) and softer processes (underlying event) by measuring the angular correlation between a high-momentum trigger hadron (h) acting as a jet-proxy and a produced strange hadron (φ(1020) meson). Measuring h−φ correlations at midrapidity in p−Pb collisions at √sNN = 5.02 TeV as a function of event multiplicity provides insight into the microscopic origin of strangeness enhancement in small collision systems. The jet-like and the underlying-event-like strangeness production are investigated as a function of event multiplicity. They are also compared between a lower and higher momentum region. The evolutions of the per-trigger yields within the near-side (aligned with the trigger hadron) and away-side (in the opposite direction of the trigger hadron) jets are studied separately, allowing for the characterization of two distinct jet-like production regimes. Furthermore, the h−φ correlations within the underlying event give access to a production regime dominated by soft production processes, which can be compared directly to the in-jet production. Comparisons between h−φ and dihadron correlations show that the observed strangeness enhancement is largely driven by the underlying event, where the φ/h ratio is significantly larger than within the jet regions. As multiplicity increases, the fraction of the total φ(1020) yield coming from jets decreases compared to the underlying event production, leading to high-multiplicity events being dominated by the increased strangeness production from the underlying event

Modification of charged-particle jets in event-shape engineered Pb-Pb collisions at √SNN=5.02 TeV

Charged-particle jet yields have been measured in semicentral Pb–Pb collisions at center-of-mass energy per nucleon–nucleon collision sNN=5.02 TeV with the ALICE detector at the LHC. These yields are reported as a function of the jet transverse momentum, and further classified by their angle with respect to the event plane and the event shape, characterized by ellipticity, in an effort to study the path-length dependence of jet quenching. Jets were reconstructed at midrapidity from charged-particle tracks using the anti-kT algorithm with resolution parameters R = 0.2 and 0.4, with event-plane angle and event-shape values determined using information from forward scintillating detectors. The results presented in this letter show that, in semicentral Pb–Pb collisions, there is no significant difference between jet yields in predominantly isotropic and elliptical events. However, out-of-plane jets are observed to be more suppressed than in-plane jets. Further, this relative suppression is greater for low transverse momentum (&lt; 50 GeV/c) R = 0.2 jets produced in elliptical events, with out-of-plane to in-plane jet-yield ratios varying up to 5.2σ between different event-shape classes. These results agree with previous studies indicating that jets experience azimuthally anisotropic suppression when traversing the QGP medium, and can provide additional constraints on the path-length dependence of jet energy loss

Observation of abnormal suppression of f0(980) production in p-Pb collisions at √sNN=5.02 TeV

The dependence of f0(980) production on the final-state charged-particle multiplicity in p–Pb collisions at sNN=5.02 TeV is reported. The production of f0(980) is measured with the ALICE detector via the f0(980)→π+π− decay channel in a midrapidity region of −0.5&lt;0. Particle yield ratios of f0(980) to π and K⁎(892)0 are found to be decreasing with increasing charged-particle multiplicity. The magnitude of the suppression of the f0(980)/π and f0(980)/K⁎(892)0 yield ratios is found to be dependent on the transverse momentum pT, suggesting different mechanisms responsible for the measured effects. Furthermore, the nuclear modification factor QpPb of f0(980) is measured in various multiplicity ranges. The QpPb shows a strong suppression of the f0(980) production in the pT region up to about 4 GeV/c. The results on the particle yield ratios and QpPb for f0(980) may help to understand the late hadronic phase in p–Pb collisions and the nature of the internal structure of f0(980) particle

Accessing the strong interaction between Λ baryons and charged kaons with the femtoscopy technique at the LHC

The interaction between Λ baryons and kaons/antikaons is a crucial ingredient for the strangeness S=0 and S=-2 sector of the meson–baryon interaction at low energies. In particular, the Lambda-Kbar might help in understanding the origin of states such as the Csi(1620), whose nature and properties are still under debate. Experimental data on Lambda-K and Lambda-Kbar systems are scarce, leading to large uncertainties and tension between the available theoretical predictions constrained by such data. In this Letter we present the measurements of Λ–KK− and Λ–KK+ correlations obtained in the high-multiplicity triggered data sample in pp collisions at sqrt(s) = 13 TeV recorded by ALICE at the LHC. The correlation function for both pairs is modeled using the Lednický–Lyuboshits analytical formula and the corresponding scattering parameters are extracted. The Λ–KK+ correlations show the presence of several structures at relative momenta k* above 200 MeV/c, compatible with the Ω baryon, the , and resonances decaying into Λ–K− pairs. The low k* region in the Λ–KK+ also exhibits the presence of the state, expected to strongly couple to the measured pair. The presented data allow to access the ΛK+ and ΛK− strong interaction with an unprecedented precision and deliver the first experimental observation of the decaying into ΛK−

Common femtoscopic hadron-emission source in pp collisions at the LHC

The femtoscopic study of pairs of identical pions is particularly suited to investigate the effective source function of particle emission, due to the resulting Bose-Einstein correlation signal. In small collision systems at the LHC, pp in particular, the majority of the pions are produced in resonance decays, which significantly affect the profile and size of the source. In this work, we explicitly model this effect in order to extract the primordial source in pp collisions at root s = 13 TeV from charged pi-pi correlations measured by ALICE. We demonstrate that the assumption of a Gaussian primordial source is compatible with the data and that the effective source, resulting from modifications due to resonances, is approximately exponential, as found in previous measurements at the LHC. The universality of hadron emission in pp collisions is further investigated by applying the same methodology to characterize the primordial source of K-p pairs. The size of the primordial source is evaluated as a function of the transverse mass (m(T)) of the pairs, leading to the observation of a common scaling for both pi-pi and K-p, suggesting a collective effect. Further, the present results are compatible with the mT scaling of the p-p and p-Lambda primordial source measured by ALICE in high multiplicity pp collisions, providing additional evidence for the presence of a common emission source for all hadrons in small collision systems at the LHC. This will allow the determination of the source function for any hadron-hadron pairs with high precision, granting access to the properties of the possible final-state interaction among pairs of less abundantly produced hadrons, such as strange or charmed particles

Emergence of Long-Range Angular Correlations in Low-Multiplicity Proton-Proton Collisions

This Letter presents the measurement of near-side associated per-trigger yields, denoted ridge yields, from the analysis of angular correlations of charged hadrons in proton-proton collisions at s=13 TeV. Long-range ridge yields are extracted for pairs of charged particles with a pseudorapidity difference of 1.4&lt;|Δη|&lt;1.8 and a transverse momentum of 1&lt;2 GeV/c, as a function of the charged-particle multiplicity measured at midrapidity. This Letter extends the measurements of the ridge yield to the low multiplicity region, where in hadronic collisions it is typically conjectured that a strongly interacting medium is unlikely to be formed. The precision of the new low multiplicity results allows for the first direct quantitative comparison with the results obtained in e+e- collisions at s=91 GeV and s=183-209 GeV, where initial-state effects such as preequilibrium dynamics and collision geometry are not expected to play a role. In the multiplicity range

Charged-particle production as a function of the relative transverse activity classifier in pp, p-Pb, and Pb-Pb collisions at the LHC

Measurements of charged-particle production in pp, p–Pb, and Pb–Pb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum pTtrig in the range 8 &lt; 15 GeV/c. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier, RT=NchT/NchT, is used to group events according to their UE activity, where NchT is the charged-particle multiplicity per event in the transverse region and NchT is the mean value over the whole analysed sample. The energy dependence of the RT distributions in pp collisions at s = 2.76, 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particle pT spectra as a function of RT in the three azimuthal regions in pp, p–Pb, and Pb–Pb collisions at sNN = 5.02 TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and p–Pb)

Exploring the Strong Interaction of Three-Body Systems at the LHC

Deuterons are atomic nuclei composed of a neutron and a proton held together by the strong interaction. Unbound ensembles composed of a deuteron and a third nucleon have been investigated in the past using scattering experiments, and they constitute a fundamental reference in nuclear physics to constrain nuclear interactions and the properties of nuclei. In this work, \u1d43e+−\u1d451 and \u1d45d−\u1d451 femtoscopic correlations measured by the ALICE Collaboration in proton-proton (\u1d45d⁢\u1d45d) collisions at √\u1d460=13  TeV at the Large Hadron Collider (LHC) are presented. It is demonstrated that correlations in momentum space between deuterons and kaons or protons allow us to study three-hadron systems at distances comparable with the proton radius. The analysis of the \u1d43e+−\u1d451 correlation shows that the relative distances at which deuterons and protons or kaons are produced are around 2 fm. The analysis of the \u1d45d−\u1d451 correlation shows that only a full three-body calculation that accounts for the internal structure of the deuteron can explain the data. In particular, the sensitivity of the observable to the short-range part of the interaction is demonstrated. These results indicate that correlations involving light nuclei in \u1d45d⁢\u1d45d collisions at the LHC will also provide access to any three-body system in the strange and charm sectors