Single Stop Production at Hadron Colliders

We analyze the production of a single top squark at hadron colliders: pp̄/pp → t̃1 + X. The total cross sections and the transverse momentum distributions are presented in next-toleading order QCD. The higher-order corrections render the predictions theoretically stable with respect to variations of the factorization and renormalization scales. The transverse momentum distribution is resummed to estimate effects of the small transverse momentum regime on possible analyses. Since the corrections increase the cross sections and reduce the theoretical uncertainty, the discovery range for these particles is extended in the refined analysis. Hadron colliders like the Tevatron and the LHC will soon be able to either discover or strongly constrain physics at scales well above the Standard Model masses. From an aesthetic point of view, the most attractive realization of supersymmetry could be the minimal supersymmetric model (MSSM). However, R parity conservation is an ad hoc assumption, invoked to bypass problems with flavor–changing neutral currents, proton decay, atomic parity violation and other experimental constraints. From a more general point of view, these observables put tight limits on some, but not on all, R parity violating couplings. For collider searches, exact R parity predicts that supersymmetric particles can only be pair-produced. Limited by the beam energy, the Tevatron tends to run out of supersymmetry discovery reach if the strongly interacting squarks and gluinos become too heavy to be produced in pairs. But many models based on unification scenarios at some high scale prefer exactly this kind of mass spectra. If, in contrast, R parity is not an exact symmetry, the signals from single superpartner production can be nicely extracted in the low background environment at the Tevatron [1–3] or even at the LHC [4]. In the case of a light scalar top squark, the baryon number violating coupling λ ijk induces the production process d̄jd̄k → t̃ [2]. It stems from the superpotential contribution [5] W = λ ijkU c i D jD k, (1) where D and U c denote charge conjugate right handed quark superfields. The couplings including at least one third generation flavor index {i, j, k} are currently only constrained in the combination |λ′′ 313λ′′ 323∗| [6,7]. The relevant Lagrangean reads Lλ′′ = −2ελ 3jk [ t̃RαdjβPRdkγ + h.c. ]