Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab

TL;DR

The white paper argues that the 12 GeV CEBAF upgrade furnishes a versatile platform for exploring nonperturbative QCD and confinement through meson spectroscopy and 3D nucleon imaging via GPDs and TMDs, while also enabling nuclear QCD studies and high-precision tests of the Standard Model at low energy. It outlines a coordinated program: GlueX in Hall D for light-quark hybrids, CLAS12 and Hall A/C for multi-dimensional nucleon and nuclear structure measurements, and DVCS/DVMP for GPD/TMD extractions, all supported by lattice QCD. It emphasizes strong international context and synergy with other facilities, including opportunities to test quark-gluon dynamics, short-range nuclear phenomena, and potential new physics through parity violation and heavy-photon searches. The impact is a comprehensive pathway to elucidate how confinement emerges from QCD, how nucleon spin and structure arise from quark and gluon dynamics, and how new physics might appear at low energies, leveraging Jefferson Lab’s high-luminosity, highly polarized beams and diverse detectors.

Abstract

This white paper summarizes the scientific opportunities for utilization of the upgraded 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and associated experimental equipment at Jefferson Lab. It is based on the 52 proposals recommended for approval by the Jefferson Lab Program Advisory Committee.The upgraded facility will enable a new experimental program with substantial discovery potential to address important topics in nuclear, hadronic, and electroweak physics.

Figures (66)

• Figure 1: The experimental spectrum of isovector mesons as summarized by the Particle Data Group [2-1]. The vertical height of each box indicates the hadronic decay width of each state. The rightmost column shows the controversial exotic candidate state,$\pi_{1}(1600)$.
• Figure 2: The spectrum of isovector mesons extracted from a lattice QCD calculation [2-4, 2-5, 2-6, 2-7] with light quark masses corresponding to$m_{\pi} \sim \mathbf{4 0 0 ~ M e V}$. A clear spectrum of q $\bar{q}$ excitations (red) is supplemented with a spectrum of exotic and non-exotic hybrid mesons (blue). The vertical height of each box indicates the statistical uncertainty on the mass within the calculations - the hadronic widths are not determined. Inset: the quark mass dependence of the exotic meson spectrum demonstrating the robustness of the calculated observables.
• Figure 3: Partial spectrum of isoscalar mesons extracted from a lattice QCD calculation [2-7] with light quark masses corresponding to$\boldsymbol{m}_{\boldsymbol{\pi}} \sim \mathbf{4 0 0 ~ M e V}$. Green/Black boxes show isoscalar states with green indicating $\boldsymbol{s} \overline{\boldsymbol{s}}$ and black indicating $u \bar{u}+d \bar{d}$ content. Grey boxes show the isovector spectrum for comparison. The experimentally determined mixing pattern is reproduced for conventional states with $J^{P C}=0^{-+}, 1^{--}, 1^{++}, 2^{++}$and the mixing pattern for exotic states, to be measured in GlueX, is predicted.
• Figure 4: An amplitude analysis carried out using the full GlueX software suite showing a small exotic signal being cleanly extracted from the much stronger conventional signals in the data. The top plot shows the total cross section (solid curve) and the extracted intensities of several partial waves. Of note is the reproduction of a very small signal for an exotic$\pi_{1}(1600)$. The strength of this wave, which may be large in actual photoproduction, is chosen to be small in the simulation to test the sensitivity of the analysis methodology. The bottom plot shows the weak exotic signal on a large scale as well as the observed phase motion between the signal and one of the stronger waves. Such an extracted phase motion would be clear evidence for resonant behavior of the signal.
• Figure 5: Values of the quark mass ratio$\mathcal{R}$ defined in the text: the red line denotes the result for $\mathcal{R}$ using leading order Chiral Perturbation Theory with electromagnetic corrections to Kaon masses from Dashen's Theorem. The green box represents the corresponding result at next to leading order, which requires model inputs --- the size of the band delineates the uncertainties [2-18]. The purple box gives the result from Lattice QCD with the electromagnetic corrections to Kaon masses from Ref. [2-15]. These are to be compared with data on the right. These data result from the extractions of $\mathcal{R}$ from experimental information on $\boldsymbol{\eta} \rightarrow 3 \boldsymbol{\pi}$ from the Cornell Primakoff measurement and from electron-positron colliders as analyzed in Refs. [2-16]. The uncertainty expected from the proposed experiment at Jefferson Lab is E12-10-011 [2-17] is indicated by the red datapoint.