Flavor physics at the EIC with b-jet tagging

TL;DR

The paper proposes using the approximate bottomness symmetry via $b$-Parity, $b_P=(-1)^n$, to search for TeV-scale flavor-changing interactions involving the 3rd generation at the EIC. Within the SMEFT framework, it analyzes dim-6 operators that mediate $b\to u$ transitions, focusing on charged-current processes that yield single- and di-jet final states with a $b$-jet, and defines the sensitivity in terms of the effective scale $\Lambda_{\text{eff}}=\Lambda/\sqrt{\alpha}$. It demonstrates that, with high $b$-tag purity and potential electron-beam polarization, the EIC can probe $\Lambda_{\text{eff}}$ in the $\sim 1$–$5$ TeV range—significantly beyond its center-of-mass energy—thereby providing a powerful, clean probe of TeV-scale flavor structure and guiding UV-model interpretations. The results show that single-$b$-jet channels are more sensitive than di-jet channels, and that polarization enhances discrimination of chiral NP, offering valuable guidance for future EIC experiments and SMEFT-based flavor studies.

Abstract

We employ an approximate conserved quantum number (defined as "$b$-Parity" in [1]) of the Standard Model (SM): $b_P=(-1)^n$, where $n$ is the number of produced $b$-jets in the reaction $e + p/A \to n \cdot j_b +X$, to explore new TeV-scale flavor-changing interactions involving the 3rd generation quarks at the EIC; simply by counting the number of $b$-jets in the final state. In particular, the SM single and di-jet production at the EIC which occur through charge current interactions, $e + p/A \to j + \!\not\!E_T$ and $e + p/A \to 2\cdot j + \!\not\!E_T$, are $b_P$-even since the $b_P$-violating (i.e, $b_P=-1$) SM signals for these processes are necessarily CKM suppressed and, therefore, have a vanishingly small production rate. In contrast, new flavor physics can generate $b_P=-1$ signals at the EIC whose only significant SM background is due to $b$-jet misidentification. We thus show that $b_P$ can be used as a simple and sensitive probe of new flavor violating physics; specifically, we find that counting single $b$-jet events in $e + p/A \to j + \!\not\!E_T$ at the EIC with a center-of-mass (CM) energy of $\sqrt{s} \sim 140$ GeV, can probe scales of new physics up to $Λ\sim {\cal O}(5)$ TeV for a certain type of new chiral flavor-changing physics in 3rd generation interactions. This is remarkably more than 30 times larger than the assumed EIC CM energy and it critically depends on the $b$-tagging efficiency and purity as well as the feasibility of electron-beam polarization. The sensitivity of the di-jet process, $e + p/A \to 2j + \!\not\!E_T$, to these type of new physics is reduced compared to the single-jet channel.

Figures (4)

• Figure 1: Expected 95% CL bounds on $\Lambda_{\tt eff}$ [TeV] from the CC singel-jet signal, $e + p/A \to j + {\not\!\! E_T}$, for the Tensor operator $Q_{\ell e q u}^{(3)}(1131)$, as a function of the light-jet mis-tagging purity factor $t_j$, for three values of the $b$-tagging efficiency $\epsilon_b=0.6,0.7,0.8$. On left: without electron beam polarization and on right: with $P_e=0.7$, i.e, $+70\%$ right-handed electron beam polarization.
• Figure 2: Expected 95% CL bounds on $\Lambda_{\tt eff}$ [TeV] from the CC single-jet signal, $e + p/A \to j + {\not\!\! E_T}$, as a function of the electron beam polarization, $P_e$, for the "loose", "medium" and "tight" $b$-tagging scenarios. Results are shown for the tensor operator $Q_{\ell e q u}^{(3)}(1131)$ (left) and the vector operator $Q_{\ell q}^{(3)}(1113)$ (right).
• Figure 3: The polarization asymmetry ${\cal A}_{P_e}^{CC}(\epsilon_b,t_j,\Lambda_{\tt eff})$ of Eq.\ref{['pol_asym']} when the tensor operator $Q_{\ell e q u}^{(3)}(1131)$ is turned on with $\Lambda_{\tt eff}=1$ TeV, as a function of the electron beam polarization $P_e$. The asymmetry is plotted for the "loose", "medium" and "tight" $b$-tagging scenarios and also for the SM case. See also text.
• Figure 4: Expected 95% CL bounds on $\Lambda_{\tt eff}$ [TeV] from the CC di-jet production process, $e + p/A \to 2 \cdot j + {\not\!\! E_T}$, as a function of the electron beam polarization, $P_e$, for the "loose", "medium" and "tight" $b$-tagging scenarios, for the tensor operator $Q_{\ell e q u}^{(3)}(1131)$.