Physics Motivation
Inside a nucleon, quarks interact by exchanging 'gluons'. A unique feature of Quantum Chromodynamics (QCD)—unlike electromagnetism—is that gluons themselves carry color charge and can interact with each other (its non-Abelian nature). Usually, gluons act merely as the force-carrying 'glue'. However, QCD predicts that this glue can vibrate and become excited, acting as a structural constituent of a particle. A baryon with an explicitly excited gluonic degree of freedom is called a 'hybrid baryon' (qqqg). Recent Lattice QCD calculations predict their existence around a mass of 2 GeV. Finding a hybrid baryon would be a monumental discovery, directly proving that the strong force field itself can be excited to form matter, providing deep insights into non-perturbative QCD and the origin of hadronic mass.
Nucleon resonances calculated on the Lattice QCD, where conventional qqq states are shown by the grey boxes and hybrid baryons are shown by the blue boxes.
Ref: J.J. Dudek and R.G. Edwards, Phys. Rev. D 85, 054016 (2012)
The Experiment
Hybrid baryons are difficult to find because they are broad and overlap with many other standard baryon resonances. Using the K1.8 beamline at J-PARC and the large-acceptance HypTPC spectrometer, we will measure the πN → ππN and πN → KY reactions with unprecedented precision. By scanning a wide range of center-of-mass energies and applying rigorous Partial-Wave Analysis (PWA), we aim to disentangle these overlapping resonances and isolate the signature of hybrid baryons.