Hidden GeV-Scale Interactions of Quarks

We explore quark interactions mediated by new gauge bosons of masses in the 0.3–50 GeV range. A tight upper limit on the gauge coupling of light $Z^{\prime }$ bosons is imposed by the anomaly cancellation conditions in conjunction with collider bounds on new charged fermions. Limits from quarkonium decays are model dependent, while electroweak constraints are mild. We derive the limits for a $Z^{\prime }$ boson coupled to baryon number and then construct a $Z^{\prime }$ model with relaxed constraints, allowing quark couplings as large as 0.2 for a mass of a few GeV.

Figure 1

Limits in the gauge coupling versus mass plane for $Z_B^{\prime }$. Values of $g_z$ above the straight lines are excluded by the anomaly cancellation conditions in conjunction with collider searches for new fermions; for $N_f=1$ or 3, $m_f>90\mathrm{GeV}$, and for $N_f=1$, $m_f>450\mathrm{GeV}$. The top regions are excluded by quarkonium and hadronic $Z$ decays.

Figure 2

Limits in the $g_z$ versus $M_{Z^{\prime }}$ plane for $Z_{ds}^{\prime }$. The shaded regions are excluded (see the caption of Fig. 1).