Garra Ticó, JordiGraugés Pous, EugeniBABAR Collaboration2019-07-252019-07-252009-10-150031-9007https://hdl.handle.net/2445/138338We have performed a search for the η b ( 1 S ) meson in the radiative decay of the Υ ( 2 S ) resonance using a sample of 91.6 × 10 6 Υ ( 2 S ) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E γ = 609.3 + 4.6 − 4.5 ( stat ) ± 1.9 ( syst )     MeV , corresponding to an η b ( 1 S ) mass of 9394.2 + 4.8 − 4.9 ( stat ) ± 2.0 ( syst )     MeV / c 2 . The branching fraction for the decay Υ ( 2 S ) → γ η b ( 1 S ) is determined to be [ 3.9 ± 1.1 ( stat ) + 1.1 − 0.9 ( syst ) ] × 10 − 4 . We find the ratio of branching fractions B [ Υ ( 2 S ) → γ η b ( 1 S ) ] / B [ Υ ( 3 S ) → γ η b ( 1 S ) ] = 0.82 ± 0.24 ( stat ) + 0.20 − 0.19 ( syst ) .7 p.application/pdfeng(c) American Physical Society, 2009Física de partículesExperimentsParticle physicsExperimentsinfo:eu-repo/semantics/article5777362019-07-25info:eu-repo/semantics/openAccess