The HaSP Network
The spectrum of hadrons is composed of bound states of quarks and gluons. The distinctive property of confinement in strong interactions, which are described by Quantum Chromo-Dynamics (QCD), prevents quarks and gluons from appearing as free particles. A new generation of dedicated experiments in hadron physics has been proposed with the aim of uncovering properties of strong interactions and specifically the mysteries of confinement. Some of these experiments are already in operation and several more are planned for the near future in the main EU laboratories (CERN, Mainz, Bonn, GSI) and abroad (TJNAF/US, BESIII/China, J-PARC/Japan, Belle/Japan). These new experiments will produce an unprecedented amount of high-precision data that requires a level of sophistication in analysis never before achieved. The challenge for the hadron physics community is to synergize the theoretical and experimental efforts to develop best practices for analyzing and interpreting the complex experimental data, developing a sound analysis framework that incorporates latest advances in theory and phenomenology and a set of tools to manipulate, analyze, and preserve the data. Thus, the most advanced and innovative theoretical techniques (effective theories, analyticity constraints, unitarity re-summations and dispersion relations, Lattice-QCD (LQCD) simulations and analysis, etc.) need to be fully developed and applied for a solid interpretation of the experimental results. Observables need to be interpreted using robust methods that rely only on the basic theoretical principles, and compared to the best solutions provided by the fundamental theory of the strong interaction via LQCD or systematic effective field theory expansions. These goals can only be achieved through a large-scale collaborative effort that takes full advantage of the expertise in hadron physics communities in Europe and in the rest of the world. The HaSP network activity aims to coordinate the leading European institutions active in hadron spectroscopy with the objective of making progress in: development of theoretical, phenomenological and computational foundations for amplitude; establishment of best practices for accessing systematic uncertainties in analysis of hadron reaction data and interpretation of physics results.
The networking activity of HS-HPH is divided in four main tasks:
QCD symmetries at the hadron level can be used to construct EFT's able to describe the low energy hadronic phenomenology. Dispersion relations provide rigorous constraints to theoretical predictions that can be used to obtain accurate properties of excited states. Especially when combined with EFT’s, they provide a very powerful connection between the Hadronic and QCD realms. Theoretical tools developed here will be employed/tested to analyze the data used in Tasks 3 and 4.
EFT techniques complement very efficiently LQCD simulations, allowing to better control the needed extrapolations to physical kinematics and covering regions of parameter space not yet reachable in the lattice. Concerning systems made of two heavy quarks (generically called quarkonia) their study has witnessed an enormous theoretical progress due to the use of EFTs (non-relativistic QCD, NRQCD, potential NRQCD, pNRQCD, Born-Oppenheimer EFT, BOEFT, ...) combined with significant advancements in LQCD calculations of hadronic observables allowing precision spectroscopy of exotic and excited states and the treatment of states above thresholds in coupled-channel scattering analyses. Heavy quarkonia provide also a clear signature in heavy-ion experiments and their suppressed production is a hard-probe of the medium formed therein (e.g..bottomonium suppression has been already observed in heavy-ion collisions at the LHC). Further progress will crucially depend on accurate LQCD determinations of the relevant low-energy matrix elements.
Task 3: Meson Spectroscopy analysis of new and exotic states
A large number of “exotic” experimental discoveries, which did not fit the expectations of the quark model, as well as the unprecedented statistical precision have been obtained by COMPASS, LHCb, BESIII, Belle and other experiments. These discoveries occur especially in the open and hidden charm and bottom sectors, but some of them also correspond to the light quark sector. We propose to perform combined Partial Wave Analyses (PWAs) of the same final state measured in different experiments, making use of the theoretical tools developed in Task1 (all sub-tasks) and Task2 (in particular T2.1 and T2.2).
Baryon resonance parameters (e.g. mass, width, pole position) have been extracted so far by partial-wave analyses of scattering data. An intense effort has started to add information from photon-induced meson production at ELSA, JLAB and MAMI, from charmonium decays at BESIII and diffractive pp reactions at COMPASS. The recent strong indications for a resonance around 2.4GeV in the 6-quark system are an important advance in the quest for a deeper understanding of QCD and bound quark systems beyond the usual 3q and systems. Other experiments are providing evidence for the existence of 4q (Belle, BaBar, BESIII, LHCb) and 5q (LHCb) systems. The same analysis framework developed for Task3 will be used to extract resonance parameters adopting the state-of-the-art calculations developed in Task1 (e.g Laurent-Pietarinen method).