Volume 245, number 2 PHYSICS LETTERS B 9 August 1990 CP-violating scattering processes in the minimal supersymmetric standard model A. Pilaftsis Institut J~r Physik, Universitdt Dortmund, D-4600 Dortmund 50, FRG and M. Nowakowski lnstitut far TheoretischeKernphysik, UniversitiitKarlsruhe, Postfach 6980, D-7500 Karlsruhe I, FRG Received 13 February 1990; revised manuscript received 14 May 1990 We examine the possibility to find new CP violating signals in the supersymmetric extension of the standard model. We focus our investigation on high energy scattering processes suitable for the new generation of coUiders. We point out that certain super- symmetric scenarios can account for quite large CP asymmetries due to the scalar quark-quark mixing. The new generation of high energy colliders (LEP, SSC, UNK, etc. ) will hopefully provide us with some hints to decide whether certain scenarios ofsupersymmetric theories [ 1 ] are realized by nature. If nature should make use of such a fundamental theory, it is of interest to investigate if effects which are preferably small in the standard model (SM) can be enhanced by imposing supersymmetry. Certainly one field of investigations here which deserves attention is CP violation [2]. Indeed, the supersymmetric SM possesses some appealing prop- erties, which give rise to the hope that CP violation can also be detected outside the standard K°-I( ° system [ 3 ]. For instance the appearance of a new supersymmetric phase makes the theory CP violating already at the two- generation level, which is in strict contrast to the SM. Furthermore the scalar quark-quark mixing goes hand in hand with the strong coupling constant as, together with the elements of the super Kobayashi-Maskawa (KM) matrix. Until now the implications of this new SUSY source for CP violation have been studied in refs. [4,5 ] for the K°-I( ° system and e.g. in ref. [ 6 ] for CP-odd phenomena in chargino or neutralino decays. In this note we will argue that SUSY offers also an opportunity to study CP violation in scattering processes. To be specific, we consider the reaction gluino (g) quark scattering. Hereby our emphasis will be on sizeable CP violating phenomena in total rates. In spite of the difficulty of tagging different quarks in the final state, it is desirable to separate true CP-odd observables at high energies. An example of CP violating scattering processes in supersymmetry has been given in ref. [ 6 ]. However, in this particular reaction, e+e-~ff+~¢ -, the CP violation is based on CP-odd triple product correlation s.p×k, where s is the spin of one of the winos (if). We also mention that in the SM with the minimal content of particles the possibility to find CP-nonconserving phenomena in scattering processes is rather remote [ 7 ]. Since it can be shown that this is mainly due to the relative smallness of the quark masses involved, only the contribution of fourth generation heavy quarks can lead to measurable effects [ 7 ]. Provided that the hypothetical four genera- tion neutrino v4 is lighter than/Mz this possibility seems to be excluded by recent LEP measurements [ 8 ]. This is another motivation for us to look for new CP sources. We proceed by introducing some theoretical concepts which we will need for our discussion. More details can 0370-2693/90/$ 03.50 © 1990 - Elsevier Science Publishers B.V. ( North-Holland ) 185