First Observation of Top Quark Production in the Forward Region

Top quark production in the forward region in proton-proton collisions is observed for the first time. The $W+b$ final state with $W\to \mu \nu$ is reconstructed using muons with a transverse momentum, $p_T$, larger than 25 GeV in the pseudorapidity range $2.0<\eta <4.5$. The $b$ jets are required to have $50<p_T<100\mathrm{GeV}$ and $2.2<\eta <4.2$, while the transverse component of the sum of the muon and $b$-jet momenta must satisfy $p_T>20\mathrm{GeV}$. The results are based on data corresponding to integrated luminosities of 1.0 and $2.0{\mathrm{fb}}^{-1}$ collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross sections in the fiducial region are $$\begin{gathered} \sigma (\text{top})[7\mathrm{TeV}]=239\pm 53(\text{stat})\pm 33(\text{syst})\pm 24(\text{theory})\mathrm{fb}, \\ \sigma (\text{top})[8\mathrm{TeV}]=289\pm 43(\text{stat})\pm 40(\text{syst})\pm 29(\text{theory})\mathrm{fb}. \end{gathered}$$These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order standard model predictions.

Figure 1

Distribution of $p_T(\mu )/p_T(j_{\mu })$ with fit overlaid for all $W+\text{jet}$ candidates.

Figure 2

Results for the inclusive $W+\text{jet}$ yield (left) and charge asymmetry (right) versus $p_T(\mu +j)$ compared to SM predictions at NLO obtained using MCFM. The data error bars are smaller than the marker size; the SM uncertainties are highly correlated across $p_T(\mu +j)$ bins.

Figure 3

Results for $W+c$ compared to SM predictions at NLO obtained using MCFM.

Figure 4

Distribution of $p_T(\mu )/p_T(j_{\mu })$ with fit overlaid for all $W+b$ candidates.

Figure 5

Results for the $W+b$ yield (left) and charge asymmetry (right) versus $p_T(\mu +b)$ compared to SM predictions obtained at NLO using MCFM.