Report of the 1997 LEP2 Phenomenology Working Group on `Searches' (Oxford)

. The Searches Working Group discussed a variety of topics relating to present and future measurements of searches at LEP 2 . The individual contributions are included separately. Abstract. A reassessment of the luminosity and centre-of-mass energy conditions needed to exclude/discover a Higgs boson signal at LEP 2 is presented, both for the neutral Higgs boson predicted in the context of the Standard Model and for the lightest neutral Higgs boson of the Minimal Supersymmetric Standard Model. This reconsideration is based on the results prepared before the start of LEP 2 and on recent studies incorporating more up-to-date knowledge of the performance of the four LEP experiments at LEP 2 energies. Results are presented in terms of the two relevant collider parameters, the average integrated luminosity delivered to the experiments, L and the centre-of-mass energy, √ s . We first examine the case of the SM Higgs boson and then consider the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM). Abstract. Here, we review constraints that may be placed upon the parameters of the MSSM by requiring that the vacuum lies in a bounded colour and charge conserving global minimum of the scalar potential. The weakening of these constraints originating from the possibility of a meta-stable charge and colour conserving minimum are also presented. Abstract. We present preliminary results on the possible effects of a particular, possibly large, R-parity violating (RPV) coupling in the MSSM. We focus on the effects upon the unification predictions of tan β and α S ( M Z ), as compared to the R-parity conserving (RPC) case. We find that α 3 ( M Z ) can be lowered by ∼ 3%, bringing the prediction more in line with data. Bottom-tau Yukawa unification becomes possible for any value of tan β , rather than the restricted ranges allowed in the RPC model. Abstract. When searching for massive, pair-produced, new particles close to the kinematic limit at LEP , achieving the maximum possible centre-of-mass energy E CM has the benefit of giving the highest possible production cross-section. However, because of, e.g., operational instabilities when running at the highest possible energy, a larger integrated luminosity ( L ) may be achieved when running at a somewhat lower E CM . It therefore becomes interesting to consider the possible trade-off between E CM and L . Abstract. We propose a new method of detecting supersymmetry at LEP 2 when R-parity is violated by an LLE operator. We present the matrix element for the process γe → ˜ ν j e k and calculate the cross-section in e + e − collisions. A preliminary Monte-Carlo analysis is undertaken to investigate the possible sensitivity to this signal and we present the 5 σ discovery contours in the m ˜ ν j vs. coupling plane. Abstract. The recent observations by the HERA experiments have revived interest in the phenomenology of particles with leptoquark like couplings. Leptoquarks or searches reviewed and summarized, with particular emphasis on the gains from running LEP at 200 GeV, and on alternative paradigms for supersymmetric phenomenology, such as models with violation of R parity.