G. Abbiendi et al., Search for anomalous production of acoplanar di-lepton events in e(+)e(-) collisions at root s=183 and 189 GeV, EUR PHY J C, 14(1), 2000, pp. 51-71
A selection of di-lepton events with significant missing transverse momentu
m has been performed using a total data sample of 237.4 pb(-1) at e(+)e(-)
centre-of-mass energies of approximately 183 GeV and 189 GeV. The observed
numbers of events - 78 at 183 GeV and 301 at 189 GeV are consistent with th
e numbers expected from Standard Model processes, which arise predominantly
from W+W- production with both W bosons decaying leptonically. This topolo
gy is also an experimental signature for the pair production of new particl
es that decay to a charged lepton accompanied by one or more invisible part
icles. Discrimination techniques are described that optimise the sensitivit
y to particular new physics channels. No evidence for new phenomena is appa
rent. Upper limits on the production cross-section times branching ratio sq
uared for sleptons and for leptonically decaying charginos and charged Higg
s are presented in a manner intended to minimise the number of model assump
tions. Assuming a 100% branching ratio for the decay (l)over tilde(R)(+/-)
--> l(+/-)(chi)over tilde(1)(0), where (chi)over tilde>(0)(1) is the lighte
st neutralino, we exclude at 95% CL: right-handed smuons with masses below
82.3 GeV for m((mu)over tilde) - m((chi)over tilde)(1)(0) > 3 GeV and right
-handed staus with masses below 81.0 GeV for m((tau)over tilde>) - m((chi)o
ver tilde)(1)(0) > 8 GeV. Right-handed selectruns are excluded at 95% CL fo
r masses below 87.1 GeV for m(e)(over tilde)(-) - m(chi)(over tilde>)(0)(1)
> 5 GeV, within the framework of the Minimal Supersymmetric Standard Model
assuming mu < -100 GeV and tan beta = 1.5. Charged Higgs bosons, H+/- are
excluded at 95% CL for masses below 82.8 GeV, assuming a 100% branching rat
io for the decay H+/- --> tau(+/-)nu(tau).