Nucleon Energy Correlators as a Probe of Light-Quark Dipole Operators at the Electron-Ion Collider

Abstract

We propose nucleon energy correlators (NECs) as a novel framework to probe electroweak light-quark dipole operators in deep inelastic scattering with an unpolarized nucleon. These operators encode chirality-flipping interactions, whose effects are usually quadratically suppressed in unpolarized cross sections. We construct a chiral-odd quark NEC that accesses quark transverse spin via azimuthal angle asymmetries in the energy flow of the target fragmentation region. These asymmetries serve as clean and powerful observables, enabling linear constraints on the quark dipole couplings. Unlike existing methods, our approach requires neither polarized nucleon beams nor final-state hadron identification, relying instead on fully inclusive calorimetric measurements. This work establishes one of the first applications of energy correlator observables to new physics searches and opens a promising direction for precision studies of chirality-flipping effects at electron-ion colliders.

Figures (13)

• Figure 1: Illustration of the NEC mechanism for probing the SMEFT quark dipole operator in DIS. The blue transverse plate highlights the role of the transversity NEC, which selects the quark transverse spin $S_T^q$ in an unpolarized nucleon by measuring an energy flux from the target remnants. The magenta blob denotes the dipole interaction mediated by $\gamma$ or $Z$. The interference with the SM amplitude is implied.
• Figure 2: Projected $68\,\%$ C.L. constraints at the EIC on the two Wilson coefficients ${\rm Re}[C_{uB}]$ and ${\rm Re}[C_{uW}]$, assuming $\Lambda=1$ TeV. The limits are derived from the azimuthal asymmetries $A^{\sin\phi}_{UU}$ (purple), $A^{\sin\phi}_{LU}$ (blue), and their combination (red). The shaded regions represent the simultaneous two-coefficient constraints, while dashed lines show the limits for a single coefficient.
• Figure 3: Comparison of projected $68\,\%$ C.L. constraints on $\text{Re}[C_{uB}]$ and $\text{Re}[C_{uW}]$ from HERA (green), the EIC (red), and the LHeC (blue), assuming $\Lambda=1$ TeV. The LHeC limits are scaled by a factor of $10$ for visibility. A detailed description of our analysis setup is provided in appendix.
• Figure 4: The factorized structure of the DIS energy pattern in the TFR with the inclusion of the light-quark dipole interactions. The blue blob denotes the dipole interactions.
• Figure 5: $|A_{UU}^{\sin \phi}|$ ($\textbf{Left}$) and $|A_{LU}^{\sin \phi}|$ ($\textbf{Right}$) as a function of the Bjorken variable $x_B$ for the up-quark dipole operators with different $Q$ at the EIC. The solid (dashed) lines correspond to setting $c_{u\gamma}\,(c_{uZ})=v/(\sqrt{2}\,{\rm TeV}^2)$. The center-of-mass energy is set to be $105\ \mathrm{GeV}$, and the inelasticity $y$ is limited to $[0.1,0.9]$.