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

Abstract

The study of the strength and behavior of the antikaon-nucleon (KN) 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 þ p ⊕ K −p) and (K − p ⊕ K þp) pairs measured in pp collisions at ffiffi ffi s p ¼ 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 þp) with a significance of 4.4σ constitutes the first experimental evidence for the opening of the ðK 0 n ⊕ K 0n Þ 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 theKN threshold for low-energy QCD chiral models.

Strangeness in nuclei and neutron stars

“…For antikaons, the behaviour above threshold is only scarcely constrained by scattering experiments due to the low available statistics close to theKN threshold. But of late, new measurements above threshold have been made available exploiting correlation techniques to K − -p pairs [35], that are measured in pp collisions at the LHC by the ALICE collaboration.…”

“…The particle emitting source is found to be very small in pp and p+Pb collisions at the LHC [38,39], that is of the order of 1 fm. These values are evaluated by using known interactions, with pp and K + p as benchmarks [35]. and 13 TeV (right).…”

“…and 13 TeV (right). Three different potentials were considered: Coulomb potential (blue band), Kyoto model and Jülich model [35]. In the bottom panels, differences between the data and the model are shown.…”

“…In the bottom panels, differences between the data and the model are shown. Figure 1 shows the correlation functions measured for K − p pairs in pp collisions at 5, 7 and 13 TeV by the ALICE collaboration [35]. The fact that the correlation function is larger than one indicates the overall attractive nature of the interaction.…”

First Observation of an Attractive Interaction between a Proton and a Cascade Baryon

“…Recently it has been shown that hyperon-nucleon, hyperon-hyperon [18,19], and kaon-nucleon [20] interactions can be more precisely measured in proton-proton (pp) and proton-lead (p-Pb) collisions at the LHC. Indeed, small colliding systems at LHC energies lead to particleemitting sources with sizes of about 1 fm, allowing a precise test of the short-range strong interaction.…”