Hadron Experiments at J-PARC using HypTPC
Our group conducts experimental research at the J-PARC Hadron Hall, aiming to uncover the mechanisms by which matter is formed from quarks.
Quarks, the fundamental building blocks of matter, cannot exist in isolation and are always confined within hadrons. Normal hadrons consist of either three quarks (baryons) or a quark-antiquark pair (mesons).
However, Quantum Chromodynamics (QCD)—the fundamental theory of strong interactions—predicts more complex structures known as exotic hadrons. These include tetraquarks (two quarks and two antiquarks) and pentaquarks (four quarks and one antiquark).
Recently, candidate particles for these exotic hadrons have been discovered by international collaborations such as Belle (Japan) and LHCb (Europe), adding new perspectives to our understanding of matter.
By systematically studying the properties of exotic hadrons, we aim to reach the core of the "hadronization mechanism"—how quarks are bound together to form hadrons.
The HypTPC Group utilizes the custom-developed 3D tracking detector, HypTPC (Time Projection Chamber), at J-PARC's Hadron Hall to search for exotic hadrons and elucidate their properties through state-of-the-art experimental techniques.
We are currently promoting five major experiments (E42, E45, E72, E90, and E104) using the HypTPC detector at J-PARC. All these experiments are closely related to the study of exotic hadrons.
For more details on each experiment, please refer to the experimental proposals below:
- E42: Search for H-Dibaryon (Do 6-quark states exist?) Details ➔
- E45: Hadron Spectroscopy (N*, Δ* Spectroscopy, Hybrid Baryon Search) Details ➔
- E72: Λ* Spectroscopy (Strong candidate for exotic states) Details ➔
- E90: ΣN Cusp Spectroscopy (Does a deuteron-like ΣN dibaryon exist?) Details ➔
- E104: Double-φ Production (Related to glueballs?) Details ➔
- LOI (to be submitted): Θ+ Search (Does the uudds̄ pentaquark exist?) Details ➔
Fig: Structure of HypTPC and overview of the experimental programs.
Heavy-Ion Collision Experiments
While J-PARC currently operates as a proton accelerator, plans are underway to realize heavy-ion beam acceleration. This is the J-PARC-HI (Heavy Ion) project.
In heavy-ion collisions at CERN (ALICE) or BNL (RHIC), a Quark-Gluon Plasma (QGP)—where quarks are liberated from hadrons—has been observed under extreme temperature conditions. This suggests a phase transition between quarks and hadrons.
This state change can be intuitively understood through the phase transition of water (ice → liquid → steam). Similarly, at high densities (high chemical potential μb), quarks are expected to be released from confinement into the QGP phase.
While transitions at ultra-high temperatures are crossover (continuous), a first-order phase transition is predicted in the high-density region. The transition point is called the QCD Critical Point.
The J-PARC-HI project will conduct heavy-ion collisions at energy ranges of 1–19 AGeV to create high-density states (5-10 times that of normal nuclei) and precisely study hadron properties within this environment.
Is the quark-to-hadron transition really a first-order transition? Does the QCD Critical Point truly exist? These remain fundamental unanswered questions. A definitive confirmation would bring a revolution to our understanding of strong interactions.
We also conduct research on hadron-hadron interactions using particle correlations (Femtoscopy). In line with this, we are participating in the STAR experiment at BNL (USA) and the FAIR-CBM experiment at GSI (Germany).
- Exploring High-Density Nuclear Matter via Femtoscopy (J-PARC E88 / STAR BES / J-PARC-HI) Details ➔
Learn more about J-PARC-HI Femtoscopy measurements → Link
Learn more about the J-PARC-HI Project → Project Page
Fig: Conceptual QCD phase diagram.