Events with Isolated Leptons and Missing Transverse Momentum at Hera

Events with isolated leptons and missing transverse momentum are searched for in electron– or positron–proton collisions at HERA by the H1 and ZEUS experiments. Such events may be explained within the Standard Model by W boson production, followed by leptonic decay. The analysis performed including HERA I and the recently collected data at HERA II results in clear evidence ofW production. However, H1 collaboration observes an excess of events in ep collisions, not supported so far by ZEUS. If the difference between the H1 and ZEUS observations is attributed to a statistical fluctuation, the combined result exceeds the Standard Model prediction at 2.6σ level. A search for events with τ leptons and missing transverse momentum is also presented.