Searching for the rules that govern hadron construction

Scalar and Tensor Charmonium Resonances in Coupled-Channel Scattering from Lattice QCD

We determine J^{PC}=0^{++} and 2^{++} hadron-hadron scattering amplitudes in the charmonium energy region up to 4100 MeV using lattice QCD, a first-principles approach to QCD. Working at m_{π}≈391  MeV, more than 200 finite-volume energy levels are computed and these are used in extensions of the Lüscher formalism to determine infinite-volume coupled-channel scattering amplitudes. We find that this energy region contains a single χ_{c0} and a single χ_{c2} resonance. Both are found as pole singularities on the closest unphysical Riemann sheet, just below 4000 MeV with widths around 70 MeV. The largest couplings are to kinematically closed D^{*}D[over ¯]^{*} channels in S-wave, and couplings to several decay channels consisting of pairs of open-charm mesons are found to be large and significant in both cases. Above the ground state χ_{c0}, no other scalar bound states or near-DD[over ¯] threshold resonances are found, in contrast to several theoretical and experimental studies.

Deciphering the Nature of X(3872) in Heavy Ion Collisions

Exploring the nature of exotic multiquark candidates such as the X(3872) plays a pivotal role in understanding quantum chromodynamics (QCD). Despite significant efforts, consensus on their internal structures is still lacking. As a prime example, it remains a pressing open question to decipher the X(3872) state between two popular exotic configurations: a loose hadronic molecule or a compact tetraquark. We demonstrate a novel approach to help address this problem by studying the X(3872) production in heavy ion collisions, where a hot fireball with ample light as well as charm (anti-)quarks is available for producing the exotics. Adopting a multiphase transport model (AMPT) for describing such collisions and implementing appropriate production mechanism of either molecule or tetraquark picture, we compute and compare a series of observables for X(3872) in Pb-Pb collisions at the Large Hadron Collider. We find the fireball volume plays a crucial role, leading to a 2-order-of-magnitude difference in the X(3872) yield and a markedly different centrality dependence between hadronic molecules and compact tetraquarks, thus offering a unique opportunity for distinguishing the two scenarios. We also make the first prediction of X(3872) elliptic flow coefficient to be tested by future experimental measurements.

Recent dibaryon studies at ANKE

The recent results of dibaryon studies at ANKE are being presented, along with our plans concerning further studies on the topic. TheD03resonance has been observed at ANKE in the coherentpd→pd+(ππ)0channel, accompanied by the ABC effect. An explanation of the ABC effect has been proposed, suggesting to to explain it as a kinematic cumulation of the pion pairs in theD03→D12+π→d+ (π+π)I=0cascade decay channel due to the predominantly collinearD12decay. Based on this hypothesis, a search for aD21signal in thepp→ {pp}sππreaction is suggested. Thep-wave dibaryon resonances3P2and3P0have been observed at ANKE; for3P0it is a first experimental observation. Preliminary results for a resonance peak in thepp→ {pp}sπ0reaction with the massm= 2646 ± 5 MeV and the widthΓ= 132 ± 14 MeV are being presented. Also we propose to search for the narrowNN*(1535) resonance in thepd→pdηreaction.