2026-09-21T15:48:45Zhttps://api.repository.cam.ac.uk/server/oai/request

oai:www.repository.cam.ac.uk:1810/3900962025-12-20T02:22:54Zcom_1810_198332com_1810_256064col_1810_214775

Search for the B+ → π+e+e− decay with the LHCb experiment https://doi.org/10.17863/CAM.121769 Williams, Richard Alvarez Cartelle, Paula The B+ → π+e+e− decay is strongly suppressed in the Standard Model, and therefore a highly sensitive probe for new physics. Previous experimental searches have not observed this decay and have only set weak constraints on the upper limit of the branching ratio. This thesis presents the most precise search to date, using data collected by the LHCb detector from 2011-2018 , corresponding to 9 fb−1 of pp collisions. The B+ → π+e+e− signal is observed with a significance of 3.2σ, constituting the first evidence for this decay. The branching ratio is measured to be B(B+ → π+e+e−) = ( 2.44 +0.92−0.83 (stat.) +0.39−0.24 (syst.) ) × 10−8 which is in good agreement with the Standard Model prediction. In addition, this thesis reports the branching ratio in bins of the dielectron invariant mass. University of Cambridge 2025-05-30 Thesis Doctoral Doctor of Philosophy (PhD) eng STFC Training Grant Start Date: 01/10/2021 End Data: 31/03/2025 Ref: KGZA/160.01.G113387 https://www.repository.cam.ac.uk/handle/1810/390096 https://www.repository.cam.ac.uk/bitstreams/fc58ee82-6305-4250-8726-ff9c2ece2b5c/download 8ba8991ff076814ef55dfc28cd1c3686 https://www.repository.cam.ac.uk/bitstreams/98e0ff9f-277b-45e0-a90a-d10f0cabdb30/download 87eda9de84448d1f82354d60eee3eb5f http://purl.org/NET/rdflicense/allrightsreserved High Energy Physics LHCb Particle Physics Physics