Search for New Physics via Single Top Production at the LHC

Abstract

We consider single-top production as a probe for new physics effects at the Large Hadron Collider (LHC). We argue that for natural theories a small deviation from the Standard Model tree-level couplings in this reaction can be parameterized by 3 higher dimension operators. Precision measurement of these effective couplings in the single-top events, via studying their interference effects with the SM contributions, can discriminate several new physics models. In particular, combining the production rate of three single-top production modes will provide a severe test of the Little Higgs model with T-parity. We find that at the LHC, a 5% accuracy in the measurement of the single-top cross sections would probe the new physics scale up to about $3 {\rm TeV}$.

Figures (4)

• Figure 1: Examples of new physics that can induce the effective vertices listed in Eqs. (\ref{['eq:fl-defin']}) and (\ref{['eq:operator-4f-2']}). (a) and (b) generate a $Wtb$ vertex through mixing with a heavy $W'$ gauge boson or a heavy $T$ quark (top-quark partner), while (c) and (d) induce effective four fermion operators through exchanging a heavy $W'$ gauge boson or a heavy charged Higgs boson $\phi^{+}$. Although (a) and (c) are both induced by $W'$, they originate from different new physics effects: the former is related to the gauge boson mixing, while the latter to the $W'$ couplings to quarks.
• Figure 2: Regions corresponding to $|\delta\sigma_{i}|\leq5\%$ for various single-top production processes, in the plane of $\mathcal{F}_{L}$ and $\mathcal{G}_{4f}$. Predictions for two different models, LHT (circle) and NP with heavy $W'$ (box), are also given. (See the main text for its details.)
• Figure 3: The expected statistical accuracy on measuring $\mathcal{F}_{L}$ and $\mathcal{G}_{4f}$ at the ATLAS with an integrated luminosity of $30\,{\rm fb}^{-1}$ at the LHC.
• Figure 4: Normalized distributions of $p_{T}^{b}$, $p_{T}^{q}$ and $\eta_{q}$ of the $t$-channel process for $\mathcal{G}_{4f}=-0.01$ (first row) and of $p_{T}^{b}$, $p_{T}^{\bar{b}}$ and $m_{t\bar{b}}$ of the $s$-channel process for $\mathcal{G}_{4f}=0.01$ (second row) at the LHC. $p_{T}^{z}$ and $\eta_{z}$ denote the transverse momentum and rapidity of particle $z$; $m_{X}$ denotes the invariant mass of the set of particles $X$.