LIMITS ON THE MASS OF LIGHT (PSEUDO)SCALAR PARTICLES FROM BETHE-HEITLER e⁺e− and μ⁺μ⁻ PAIR PRODUCTION IN A PROTON-IRON BEAM DUMP EXPERIMENT

A search has been performed for weakly interacting neutral light scalar and pseudoscalar particles in a proton-iron beam dump experiment via the Bethe-Heitler process. No positive signal was observed. Limits are derived on the masses of these particles in the framework of the Standard Model and its minimal supersymmetric extension (MSSM) comparing the experimental results with expectations for Bethe-Heitler e + e − and μ + μ − pair production. The Higgs particle of the SU 2L ×U 1 Standard Theory is excluded for masses in the range m H <0.9 MeV at 95% CL. Limits on light Higgs particles of the MSSM and Peccei-Quinn like axions are derived.