and from the Tevatron 8 (from the DØ analysis of Ref. [4] using 5 . 4 fb − 1 and the CDF analysis of Ref. [5] using 4 . 6 fb − 1 of data, respectively for electrons and muons in the final state). The Tevatron limits for the Z ′ B − L boson are shown in table II (for selected masses and couplings). In the same figure we also include for comparison the Tevatron discovery potential at the pp → e $^{+}$e − pp → µ $^{+}$µ − g ′ 1 M$_{Z}$ ′ (GeV) g ′ 1 M$_{Z}$ ′ (GeV) 0.0197 300 0.0179 300 0.0193 400 0.0189 400 0.0281 500 0.0456 500 0.0351 600 0.0380 600 0.0587 700 0.0544 700 0.0880 800 0.0830 800 0.1350 900 0.1360 900 0.2411 1000 0.2220 1000 0.3880 1100 0.3380 1100 TABLE II: Lower bounds on the Z ′ boson mass for selected g ′ 1 values in the B − L model, at 95% C.L., by comparing the collected data of Refs. [4, 5] with our theoretical prediction for pp → Z ′ B − L → e $^{+}$e $^{−}$( µ $^{+}$µ $^{−}$) at the Tevatron. integrated luminosities used for the latest published analyses [4, 5] (5 . 4 fb − 1 and 4 . 6 fb − 1 for electrons and muons, respectively) as well as the expected reaches at L = 10 fb − $^{1}$. Notice that the Tevatron excluded area are based on the actual data, while the dot-dashed 2 σ curves are our theoretical curves. Thus, if from the one side theory cannot reproduce experiments, from the other side we are comparing two methods of extracting the results. As mentioned previously, figure 3 shows that the procedures used in experimental analyses for the electron channel [4, 6] are not quite optimised for maximizing the signal significance. The alternative analysis described in this work has the potential to improve sensitivities and can be easily developed even further. 8 Notice that these are the most conservative limits, as they are evaluated for decoupled heavy neutrinos, i.e., with masses bigger than M Z ′ / 2. 12