Higgsophilic $s$-channel $Z^{\prime }$ and the CDF $W+2J$ anomaly

The CDF Collaboration recently presented evidence for an excess in the dijet invariant mass distribution coming from events in a $W+2j$ exclusive sample. Here we show that this excess can be explained by the $s$-channel production of a weakly coupled Higgsophilic $Z^{\prime }$ near $M_{Z^{\prime }}\sim 270\mathrm{GeV}$ which decays into a $W^{\pm }$ and a charged Higgs at $M_{H^{\pm }}\sim 150\mathrm{GeV}$. While the simplest implementations of a general leptophobic $Z^{\prime }$ model quickly run into tensions with electroweak observables, a more specific Higgsophilic model evades these constraints without resorting to any fine-tuning. We discuss the distinctive features of this model, focusing on its particular signatures at the Tevatron.

Figure 1

The production and decay topology considered in this paper to explain the excess observed by the CDF collaboration.

Figure 2

The different branching ratios of the charged Higgs with $M_{H^{+}}=150\mathrm{GeV}$ as a function of $\tan \beta$. The general behavior of these curves is not greatly affected by the mass of the charged Higgs in the range relevant for the CDF anomalous excess.

Figure 3

Limits on the cross section times branching ratio into dijets for a $Z^{\prime }$ produced at the Tevatron. The low mass limits come from UA2, while those at high mass come from CDF.

Figure 4

The invariant mass of the $W+2j$ system for both $\mu$ and $e$ samples using the $4.3{\mathrm{fb}}^{-1}$ CDF data. Preliminary figures showing the distributions from the $7.3{\mathrm{fb}}^{-1}$ data set are available at 48.

Figure 5

The $p_T(jj)\sim p_T(W)$ distribution for an $s$-channel $Z^{\prime }$ ($M_{Z^{\prime }}=270\mathrm{GeV}$, $M_{H^{\pm }}=150\mathrm{GeV}$) and a $Z^{\prime }$ produced in association with a $W$ ($M_{Z^{\prime }}=150\mathrm{GeV}$). These distributions were generated using the Fastjet [51] implementation of JETCLU, operating on events generated by Madgraph 5 [52] and showered in Pythia6 [53]. The cuts applied were those used by CDF in their $W+jj$ analysis.

Figure 6

Cross section for the different decay modes of the $Z^{\prime }$ from Sec. (5a) taken as a function of $\tan \beta$. The coupling, $g_2$, is normalized to yield a signal cross section of 4 pb. The other parameters were chosen to be $M_{Z^{\prime }}=270\mathrm{GeV}$, $M_{H^{\pm }}=150\mathrm{GeV}$, $Q_d=-Q_{H_d}=1$ with all other charges zero.

Figure 7

Cross section for the different decay modes of the $Z^{\prime }$ as a function of $\tan \beta$. The coupling, $g_2$, is normalized to yield a signal cross section of 4 pb. The other parameters were chosen to be $M_{Z^{\prime }}=270\mathrm{GeV}$, $M_{H^{\pm }}=150\mathrm{GeV}$, $Q_{H_d}=1$, $Q_u=0.1$ with all other charges zero.

Figure 8

The upper curves in blue show $\delta \rho$ vs $\tan \beta$ for the Higgsophilic model discussed in the text, where the coupling, $g_2$, is normalized to yield a signal cross section of 4 pb for $M_{Z^{\prime }}=240\mathrm{GeV}$ (dot-dashed), $M_{Z^{\prime }}=270\mathrm{GeV}$ (thick), and $M_{Z^{\prime }}=300\mathrm{GeV}$ (dashed). The other parameters were $M_{H^{\pm }}=150\mathrm{GeV}$, $Q_{H_d}=1$, and an effective up-type quark coupling of $Q_u=0.1$ with all other charges zero. The lower red curves depict the same thing with $g_2$ now normalized for a 2 pb signal cross section.

Figure 9

The upper curves in blue show ${\chi }^2$ vs $\tan \beta$ for the Higgsophilic model discussed in the text, where the coupling, $g_2$, is normalized to yield a signal cross section of 4 pb for $M_{Z^{\prime }}=240\mathrm{GeV}$ (dot-dashed), $M_{Z^{\prime }}=270\mathrm{GeV}$ (thick), and $M_{Z^{\prime }}=300\mathrm{GeV}$ (dashed). The other parameters were $M_{H^{\pm }}=150\mathrm{GeV}$, $Q_{H_d}=1$, and an effective up-type quark coupling of $Q_u=0.1$ with all other charges zero. The lower red curves depict the same thing with $g_2$ now normalized for a 2 pb signal cross section.

Figure 10

The lower curves in blue show the predicted $\sigma (p\overline{p}\to Z^{\prime })\times \mathrm{BR}(Z^{\prime }\to l^{+}{l}^{-})$ at the Tevatron, for $M_{Z^{\prime }}=240$, 270, 300 GeV (dot-dashed, solid, dashed). The upper curves show the corresponding rates for $pp$ at the LHC with $\sqrt{s}=7\mathrm{TeV}$.