Gravity localization on hybrid branes

Abstract

The NA60 experiment studied low-mass muon pair production in proton–nucleus (p–A) collisions using a 400 GeV proton beam at the CERN SPS. The low-mass dimuon spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons η, ρ, ω, η' and φ, and no evidence of in-medium effects is found. A new high-precision measurement of the electromagnetic transition form factors of the η and ω was performed, profiting from a 10 times larger data sample than the peripheral In–In sample previously collected by NA60. Using the pole-parameterisation |F(M)|²=(1 - M²/Λ²)^-2 we find Λ^-2_η = 1.934 ± 0.067 (stat.) ±0.050(syst.) (GeV/c²)^-2 and Λ^-2_ω = 2.223 ± 0.026(stat.) ± 0.037(syst.) (GeV/c²)^-2. An improved value of the branching ratio of the Dalitz decay ω → μ⁺μ^-π⁰ is also obtained, with BR(ω → μ⁺μ^-π⁰) = [1.41 ± 0.09(stat.) ± 0.15(syst.)] ×10^-4. Finally, further results refer to the ρ line shape and a new limit on ρ/ω interference in hadron interactions.