Unveiling the strong interaction among hadrons at the LHC

One of the key challenges for nuclear physics today is to understand from first principles the effective interaction between hadrons with different quark content. First successes have been achieved using techniques that solve the dynamics of quarks and gluons on discrete space-time lattices. Experimentally, the dynamics of the strong interaction have been studied by scattering hadrons off each other. Such scattering experiments are difficult or impossible for unstable hadrons and so high-quality measurements exist only for hadrons containing up and down quarks. Here we demonstrate that measuring correlations in the momentum space between hadron pairs produced in ultrarelativistic proton-proton collisions at the CERN Large Hadron Collider (LHC) provides a precise method with which to obtain the missing information on the interaction dynamics between any pair of unstable hadrons. Specifically, we discuss the case of the interaction of baryons containing strange quarks (hyperons). We demonstrate how, using precision measurements of p-omega baryon correlations, the effect of the strong interaction for this hadron-hadron pair can be studied with precision similar to, and compared with, predictions from lattice calculations. The large number of hyperons identified in proton-proton collisions at the LHC, together with an accurate modelling of the small (approximately one femtometre) inter-particle distance and exact predictions for the correlation functions, enables a detailed determination of the short-range part of the nucleon-hyperon interaction.

 

Nature 588 (2020) 232–238
HEP Data
e-Print: arXiv:2005.11495 | PDF | inSPIRE
CERN-EP-2020-091

Figure 1

Schematic representation of the correlation method. a, A collision of two protons generates a particle source $S(\rs)$ from which a hadron--hadron pair with momenta $\bm{p}\bf{_1}$ and $\bm{p}\bf{_2}$ emerges at a relative distance $r^*$ and can undergo final-state interaction before being detected Consequently, the relative momentum \ks is either reduced or increased via an attractive or a repulsive interaction, respectively b, Example of attractive (green) and repulsive (dotted red) interaction potentials, V(\rs), between two hadrons, as a function of their relative distance Given a certain potential, a non-relativistic Schr\"odinger equation is used to obtain the corresponding two-particle wave function, $\psi(\bm{k}^*,\bm{r}^*)$ c, The equation of the calculated (second term) and measured (third term) correlation function < em>C< /em>(\ks), where $N_{\mathrm{same}}(\ks)$ and $N_{\mathrm{mixed}}(\ks)$ represent the \ks distributions of hadron--hadron pairs produced in the same and in different collisions, respectively, and $\xi(\ks)$ denotes the corrections for experimental effects d, Sketch of the resulting shape of < em>C< /em>(\ks) The value of the correlation function is proportional to the interaction strength It is above unity for an attractive (green) potential, and between zero and unity for a repulsive (dotted red) potential