Exploring the N Lambda-N Sigma coupled system with high precision correlation techniques at the LHC

The interaction of Lambda and Sigma hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel dynamics. Due to the small mass difference of the N Lambda and N Sigma systems, the sizable coupling strength of the N Sigma N Lambda processes constitutes a crucial element in the determination of the N Lambda interaction. In this letter we present the most precise measurements on the interaction of p Lambda pairs, from zero relative momentum up to the opening of the N Sigma channel. The correlation function in the relative momentum space for p Lambda circle plus (p) over bar(Lambda) over bar pairs measured in high-multiplicity triggered pp collisions at root s = 13 TeV at the LHC is reported. The opening of the inelastic N Sigma channels is visible in the extracted correlation function as a cusp-like structure occurring at relative momentum k* = 289 MeV/c. This represents the first direct experimental observation of the N Sigma N Lambda coupled channel in the p Lambda system. The correlation function is compared with recent chiral effective field theory calculations, based on different strengths of the N Sigma N Lambda transition potential. A weaker coupling, as possibly supported by the present measurement, would require a more repulsive three-body NN Lambda interaction for a proper description of the Lambda in-medium properties, which has implications on the nuclear equation of state and for the presence of hyperons inside neutron stars. (C) 2022 European Organization for Nuclear Research, ALICE. Published by Elsevier B.V.Peer reviewe

Exploring the NΛ–NΣ coupled system with high precision correlation techniques at the LHC

The interaction of Λ and Σ hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel dynamics. Due to the small mass difference of the NΛ and NΣ systems, the sizable coupling strength of the NΣ ↔ NΛ processes constitutes a crucial element in the determination of the NΛ interaction. In this letter we present the most precise measurements on the interaction of pΛ pairs, from zero relative momentum up to the opening of the NΣ channel. The correlation function in the relative momentum space for pΛ ⊕ pΛ-- pairs measured in high-multiplicity triggered pp collisions at √s = 13 TeV at the LHC is reported. The opening of the inelastic NΣ channels is visible in the extracted correlation function as a cusp-like structure occurring at relative momentum k∗ = 289 MeV/c. This represents the first direct experimental observation of the NΣ ↔ NΛ coupled channel in the pΛ system. The correlation function is compared with recent chiral effective field theory calculations, based on different strengths of the NΣ ↔ NΛ transition potential. A weaker coupling, as possibly supported by the present measurement, would require a more repulsive three-body NNΛ interaction for a proper description of the Λ in-medium properties, which has implications on the nuclear equation of state and for the presence of hyperons inside neutron stars

Investigating the role of strangeness in baryon–antibaryon annihilation at the LHC

Annihilation dynamics plays a fundamental role in the baryon–antibaryon interaction (B–B) at lowenergy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the p–p system but not in the low relative momentum region. Data regarding the B–B interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon– antinucleon (N–N) results, when available. In this letter we present a measurement of the p–p, p–⊕p– and – interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at √s = 13 TeV recorded by ALICE at the LHC. In the p–p system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent χEFT potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednický–Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental p–⊕p– and – correlations. The model describes the – data and underestimates the p–⊕p– data in the region of momenta below 200 MeV/c. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons

Measurement of the Lifetime and Λ Separation Energy of 3ΛH

The most precise measurements to date of the HΛ3 lifetime τ and Λ separation energy BΛ are obtained using the data sample of Pb-Pb collisions at sNN=5.02 TeV collected by ALICE at the LHC. The HΛ3 is reconstructed via its charged two-body mesonic decay channel (HΛ3→He3+π- and the charge-conjugate process). The measured values τ=[253±11(stat)±6(syst)] ps and BΛ=[102±63(stat)±67(syst)] keV are compatible with predictions from effective field theories and confirm that the HΛ3 structure is consistent with a weakly bound system

Investigating the role of strangeness in baryon-antibaryon annihilation at the LHC

Annihilation dynamics plays a fundamental role in the baryon-antibaryon interaction (B-(B) over bar) at low-energy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the p-(p) over bar system but not in the low relative momentum region. Data regarding the B-(B) over bar interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon-antinucleon (N-(N) over bar) results, when available. In this letter we present a measurement of the p-(p) over bar, p-(Lambda) over bar circle plus(p) over bar-Lambda and Lambda-(Lambda) over bar interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at root s = 13 TeV recorded by ALICE at the LHC. In the p-(p) over bar system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent chi EFT potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednicky-Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental p-(Lambda) over bar circle plus(p) over bar-Lambda and Lambda-(Lambda) over bar correlations. The model describes the Lambda-(Lambda) over bar data and underestimates the p-(Lambda) over bar circle plus(p) over bar-Lambda data in the region of momenta below 200 MeV/c. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons. (C) 2022 European Organization for Nuclear Research. Published by Elsevier B.V.Peer reviewe

Measurement of the Lifetime and Λ Separation Energy of _{Λ}^{3}H

The most precise measurements to date of the _{Λ}^{3}H lifetime τ and Λ separation energy B_{Λ} are obtained using the data sample of Pb-Pb collisions at sqrt[s_{NN}]=5.02  TeV collected by ALICE at the LHC. The _{Λ}^{3}H is reconstructed via its charged two-body mesonic decay channel (_{Λ}^{3}H→^{3}He+π^{-} and the charge-conjugate process). The measured values τ=[253±11(stat)±6(syst)]  ps and B_{Λ}=[102±63(stat)±67(syst)]  keV are compatible with predictions from effective field theories and confirm that the _{Λ}^{3}H structure is consistent with a weakly bound system

Scattering Studies with Low-Energy Kaon-Proton Femtoscopy in Proton-Proton Collisions at the LHC

The study of the strength and behavior of the antikaon-nucleon ((K) over bar N) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of (K+ p circle plus K- (p) over bar) and (K- p circle plus K+ (p) over bar) pairs measured in pp collisions at root s = 5, 7, and 13 TeV are reported. A structure observed around a relative momentum of 58 MeV/c in the measured correlation function of (K- p circle plus K+ (p) over bar) with a significance of 4.4 sigma constitutes the first experimental evidence for the opening of the ((K) over bar (0)(n) circle plus K-0 (n) over bar) breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to Julich and Kyoto models in addition to the Coulomb potential. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the (K) over barN threshold for low-energy QCD chiral models.Peer reviewe

Scattering Studies with Low-Energy Kaon-Proton Femtoscopy in Proton-Proton Collisions at the LHC

The study of the strength and behavior of the antikaon-nucleon (K̄N) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of (K+p⊕K-p) and (K-p⊕K+p) pairs measured in pp collisions at s=5, 7, and 13 TeV are reported. A structure observed around a relative momentum of 58 MeV/c in the measured correlation function of (K-p⊕K+p) with a significance of 4.4σ constitutes the first experimental evidence for the opening of the (K̄0n.K0n) isospin breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to Jülich and Kyoto models in addition to the Coulomb potential. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the K̄N threshold for low-energy QCD chiral models