Search for $Z^{\prime }\to e^{+}{e}^{-}$ Using Dielectron Mass and Angular Distribution

We search for $Z^{\prime }$ bosons in dielectron events produced in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$, using $0.45{\mathrm{fb}}^{-1}$ of data accumulated with the Collider Detector at Fermilab II detector at the Fermilab Tevatron. To identify the $Z^{\prime }\to e^{+}{e}^{-}$ signal, both the dielectron invariant mass distribution and the angular distribution of the electron pair are used. No evidence of a signal is found, and 95% confidence level lower limits are set on the $Z^{\prime }$ mass for several models. Limits are also placed on the mass and gauge coupling of a generic $Z^{\prime }$, as well as on the contact-interaction mass scales for different helicity structure scenarios.

Figure 1

$M_{ee}$ distribution of the data (points) compared to the prediction for SM Drell-Yan and backgrounds. The individual contributions are stacked as follows: other backgrounds (dark gray), dijet background (light gray), and SM Drell-Yan (open). The inset shows the $M_{ee}$ distribution of high-mass data events using a bin size of $10\mathrm{GeV}/c^2$. There are no events in the sample with $M_{ee}>500\mathrm{GeV}/c^2$.

Figure 2

Left: Distributions of $\cos {\theta }^{*}$ for the high-mass region $M_{ee}>200\mathrm{GeV}/c^2$. The points are the data, the open histograms are the predictions from Drell-Yan Monte Carlo simulation, and the shaded histograms are the background predictions. The individual contributions are stacked. Right: distributions of the forward-backward asymmetry $A_{\mathrm{FB}}^{\mathrm{raw}}$ for the data (points) and predicted SM processes (histogram).

Figure 3

Exclusion contours for the $B-xL$, $10+x\overline{5}$, $d-xu$, and $q+xu$ $Z^{\prime }$ families. The dotted lines represent the exclusion boundaries derived in Ref. [2] from the LEP II results [24]. The region below each curve is excluded by our data at 95% C.L. Only models with $M_{Z^{\prime }}>200\mathrm{GeV}/c^2$ are tested, which explains the gap at small $|x|$ for some models.