Testing the handedness of a heavy W' at future hadron colliders.

We show that the associated production pp → W W , and the rare decay pp → W ′ → l̄lW are useful tests of W ′ couplings to fermions at future hadron colliders. For MW ′ ∼ (1− 3) TeV they would allow a clean determination on whether the W ′ couples to V − A or V + A currents. As an illustration a model in which the W ′± couples only to V −A currents is contrasted to the left-right symmetric models which involve V + A currents. PACS # 12.15, 12.10, 11.15 Many types of new physics, including some grand unified and superstring theories, predict the existence of additional charged and neutral gauge bosons (W , Z ). While their masses are a priori arbitrary, it is at least possible that they may be in the experimentally accessible range of a few TeV [1]. The present direct and indirect limits on additional gauge bosons are very model dependent. The bounds on the mass of a new Z ′ are 160−400 GeV [2, 3, 4, 5], although the limits are stronger, e.g., 500 − 1000 GeV, in some models in which the Z ′ mass and the Z − Z ′ mixing are related. In the version of left-right symmetric models [6] with equal leftand right-handed gauge couplings and magnitudes of quark-mixing matrix elements one has the stringent limit MW ′ > 1.4 TeV from the KL −KS mass difference [7]. In general left-right models, however, one has the weaker limit [8] gLMW ′/gR > 300 GeV. Stronger limits follow from CP violation unless there is fine tuning [9]. Heavy Z ′ and W ′ can be produced and detected by their leptonic decays at the Large Hadron Collider (LHC) and Superconducting Super Collider (SSC) for masses up to ∼ 5 TeV [1], [10]-[17]. To identify the origin of such bosons, more detailed diagnostic probes of their couplings will be needed. Recent detailed studies [18]-[24] have demonstrated that the rare decay process [18, 19] Z ′ → f̄1f2V (V = W,Z), where f1,2 are ordinary fermions, the associated production [23] pp → Z V , and the rapidity distribution in pp → Z ′ → ll [24] are useful diagnostics of the Z ′ couplings to the ordinary fermions. Another clean probe for the gauge couplings of Z ′ and W ′ is the forward-backward asymmetry [25]. For pp → Z ′ → ll (l = e or μ) and pp → W ′± → lνl the asymmetries can distinguish between different models for MZ′(W ) up to a few TeV, and test some combinations of the couplings of Z ′ and W ′ to quarks and leptons. However, the forward-backward asymmetry for W ′± does not distinguish V + A couplings from V − A. Although the most likely extension of the standard model involving a W ′ is the left-right symmetric model [6] with V +A couplings, it is possible to construct viable models with V −A couplings as well [26]. It is therefore important to be able to distinguish V + A from V −A. Possibilities for distinguishing the handedness of W ′ have been recently pointed out