{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/341247"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/341247","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Tests of lepton universality in $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ decays at the LHCb experiment","abstract":"The decays $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ - where $l^{+} l^{-}$ represents an electron-positron or muon-antimuon pair - are examples of $b \\to s l^{+} l^{-}$ processes. Numerous analyses of such decays have found tensions with predictions under the Standard Model (SM) of particle physics. These tensions form a coherent pattern, which could be caused by a novel physical effect. Ratios of branching fractions for muon-mode and electron-mode $b \\to s l^{+} l^{-}$ processes can be predicted with O(1%) precision under the SM, and can provide stringent experimental tests for novel physical processes which violate lepton universality. This dissertation presents new measurements of such ratios using $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ decays, denoted $R^{-1}_{K_{S}^{0}}$ and $R^{-1}_{K^{*+}}$. These measurements used data from pp collisions collected using the LHCb detector between 2011 and 2018, with a total sample size of $9 fb^{-1}$ . The results are: $R^{-1}_{K_{S}^{0}} = 1.51\\,^{+0.40}_{-0.35} (\\text{stat.}) ^{+0.09}_{-0.04} (\\text{syst.})$ $R^{-1}_{K^{*+}} = 1.44\\,^{+0.32}_{-0.29} (\\text{stat.}) ^{+0.09}_{-0.06} (\\text{syst.})$ Here, the first uncertainties are statistical, and the second systematic. Both $R^{-1}_{K_{S}^{0}}$ and $R^{-1}_{K^{*+}}$ consistent with SM expectations, at significances of 1.5σ and 1.4σ , respectively. In addition, differential branching fractions for the decays $B^{0} \\to K_{S}^{0} e^{+} e^{-}$ and $B^{+} \\to K^{*+} e^{+} e^{-}$ are measured in bins of the dilepton invariant mass squared. The first ever observations of these decays are reported.","abstract_html":"The decays <span class=\"etd-inline-math\">B<sup>0</sup> \\to K<sub>S</sub><sup>0</sup> l<sup>+</sup> l<sup>-</sup></span> and <span class=\"etd-inline-math\">B<sup>+</sup> \\to K<sup>*+</sup> l<sup>+</sup> l<sup>-</sup></span> - where <span class=\"etd-inline-math\">l<sup>+</sup> l<sup>-</sup></span> represents an electron-positron or muon-antimuon pair - are examples of <span class=\"etd-inline-math\">b \\to s l<sup>+</sup> l<sup>-</sup></span> processes. Numerous analyses of such decays have found tensions with predictions under the Standard Model (SM) of particle physics. These tensions form a coherent pattern, which could be caused by a novel physical effect. Ratios of branching fractions for muon-mode and electron-mode <span class=\"etd-inline-math\">b \\to s l<sup>+</sup> l<sup>-</sup></span> processes can be predicted with O(1%) precision under the SM, and can provide stringent experimental tests for novel physical processes which violate lepton universality. This dissertation presents new measurements of such ratios using <span class=\"etd-inline-math\">B<sup>0</sup> \\to K<sub>S</sub><sup>0</sup> l<sup>+</sup> l<sup>-</sup></span> and <span class=\"etd-inline-math\">B<sup>+</sup> \\to K<sup>*+</sup> l<sup>+</sup> l<sup>-</sup></span> decays, denoted <span class=\"etd-inline-math\">R<sup>-1</sup><sub>K<sub>S</sub><sup>0</sup></sub></span> and <span class=\"etd-inline-math\">R<sup>-1</sup><sub>K<sup>*+</sup></sub></span>. These measurements used data from pp collisions collected using the LHCb detector between 2011 and 2018, with a total sample size of <span class=\"etd-inline-math\">9 fb<sup>-1</sup></span> . The results are: <span class=\"etd-inline-math\">R<sup>-1</sup><sub>K<sub>S</sub><sup>0</sup></sub> = 1.51 <sup>+0.40</sup><sub>-0.35</sub> (\\text{stat.}) <sup>+0.09</sup><sub>-0.04</sub> (\\text{syst.})</span> <span class=\"etd-inline-math\">R<sup>-1</sup><sub>K<sup>*+</sup></sub> = 1.44 <sup>+0.32</sup><sub>-0.29</sub> (\\text{stat.}) <sup>+0.09</sup><sub>-0.06</sub> (\\text{syst.})</span> Here, the first uncertainties are statistical, and the second systematic. Both <span class=\"etd-inline-math\">R<sup>-1</sup><sub>K<sub>S</sub><sup>0</sup></sub></span> and <span class=\"etd-inline-math\">R<sup>-1</sup><sub>K<sup>*+</sup></sub></span> consistent with SM expectations, at significances of 1.5σ and 1.4σ , respectively. In addition, differential branching fractions for the decays <span class=\"etd-inline-math\">B<sup>0</sup> \\to K<sub>S</sub><sup>0</sup> e<sup>+</sup> e<sup>-</sup></span> and <span class=\"etd-inline-math\">B<sup>+</sup> \\to K<sup>*+</sup> e<sup>+</sup> e<sup>-</sup></span> are measured in bins of the dilepton invariant mass squared. The first ever observations of these decays are reported.","abstract_has_math":true,"creators":["Smeaton, John"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Gibson, Valerie"],"committee_chairs":[],"committee_members":[],"year":2022,"date_issued":"2022-03-01","date_published":"2022-03-01","updated_at":"2026-07-22T22:24:17Z","subjects":["B Physics","CERN","Flavour Physics","High-Energy Physics","Large Hadron Collider","LHCb Experiment","Particle Physics"],"languages":["eng"],"rights":[],"rights_urls":["http://purl.org/NET/rdflicense/allrightsreserved"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.88673","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Gibson, Valerie"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["Science and Technology Facilities Council (STFC)"]},{"key":"dc:creator","label":"Author","values":["Smeaton, John"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2022-03-01"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/341247"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["B Physics","CERN","Flavour Physics","High-Energy Physics","Large Hadron Collider","LHCb Experiment","Particle Physics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["http://purl.org/NET/rdflicense/allrightsreserved"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["10.17863/CAM.88673"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/e3907c62-d827-46f5-b66a-9ed1dbc09d11/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The decays $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ - where $l^{+} l^{-}$ represents an electron-positron or muon-antimuon pair - are examples of $b \\to s l^{+} l^{-}$ processes. Numerous analyses of such decays have found tensions with predictions under the Standard Model (SM) of particle physics. These tensions form a coherent pattern, which could be caused by a novel physical effect. Ratios of branching fractions for muon-mode and electron-mode $b \\to s l^{+} l^{-}$ processes can be predicted with O(1%) precision under the SM, and can provide stringent experimental tests for novel physical processes which violate lepton universality. This dissertation presents new measurements of such ratios using $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ decays, denoted $R^{-1}_{K_{S}^{0}}$ and $R^{-1}_{K^{*+}}$. These measurements used data from pp collisions collected using the LHCb detector between 2011 and 2018, with a total sample size of $9 fb^{-1}$ . The results are: $R^{-1}_{K_{S}^{0}} = 1.51\\,^{+0.40}_{-0.35} (\\text{stat.}) ^{+0.09}_{-0.04} (\\text{syst.})$ $R^{-1}_{K^{*+}} = 1.44\\,^{+0.32}_{-0.29} (\\text{stat.}) ^{+0.09}_{-0.06} (\\text{syst.})$ Here, the first uncertainties are statistical, and the second systematic. Both $R^{-1}_{K_{S}^{0}}$ and $R^{-1}_{K^{*+}}$ consistent with SM expectations, at significances of 1.5σ and 1.4σ , respectively. In addition, differential branching fractions for the decays $B^{0} \\to K_{S}^{0} e^{+} e^{-}$ and $B^{+} \\to K^{*+} e^{+} e^{-}$ are measured in bins of the dilepton invariant mass squared. The first ever observations of these decays are reported."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["21f4feb9eb937e6e9a5189da20cfc484"]},{"key":"dc:title","label":"Title","values":["Tests of lepton universality in $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ decays at the LHCb experiment"]}]}],"canonical_facts":{"dc:contributor.advisor":["Gibson, Valerie"],"dc:contributor.sponsor":["Science and Technology Facilities Council (STFC)"],"dc:creator":["Smeaton, John"],"dc:date.issued":["2022-03-01"],"dc:description.abstract":["The decays $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ - where $l^{+} l^{-}$ represents an electron-positron or muon-antimuon pair - are examples of $b \\to s l^{+} l^{-}$ processes. Numerous analyses of such decays have found tensions with predictions under the Standard Model (SM) of particle physics. These tensions form a coherent pattern, which could be caused by a novel physical effect. Ratios of branching fractions for muon-mode and electron-mode $b \\to s l^{+} l^{-}$ processes can be predicted with O(1%) precision under the SM, and can provide stringent experimental tests for novel physical processes which violate lepton universality. This dissertation presents new measurements of such ratios using $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ decays, denoted $R^{-1}_{K_{S}^{0}}$ and $R^{-1}_{K^{*+}}$. These measurements used data from pp collisions collected using the LHCb detector between 2011 and 2018, with a total sample size of $9 fb^{-1}$ . The results are: $R^{-1}_{K_{S}^{0}} = 1.51\\,^{+0.40}_{-0.35} (\\text{stat.}) ^{+0.09}_{-0.04} (\\text{syst.})$ $R^{-1}_{K^{*+}} = 1.44\\,^{+0.32}_{-0.29} (\\text{stat.}) ^{+0.09}_{-0.06} (\\text{syst.})$ Here, the first uncertainties are statistical, and the second systematic. Both $R^{-1}_{K_{S}^{0}}$ and $R^{-1}_{K^{*+}}$ consistent with SM expectations, at significances of 1.5σ and 1.4σ , respectively. In addition, differential branching fractions for the decays $B^{0} \\to K_{S}^{0} e^{+} e^{-}$ and $B^{+} \\to K^{*+} e^{+} e^{-}$ are measured in bins of the dilepton invariant mass squared. The first ever observations of these decays are reported."],"dc:format.checksum.md5":["21f4feb9eb937e6e9a5189da20cfc484"],"dc:identifier.doi":["10.17863/CAM.88673"],"dc:identifier.uri":["https://www.repository.cam.ac.uk/bitstreams/e3907c62-d827-46f5-b66a-9ed1dbc09d11/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/341247"],"dc:rights":["http://purl.org/NET/rdflicense/allrightsreserved"],"dc:subject":["B Physics","CERN","Flavour Physics","High-Energy Physics","Large Hadron Collider","LHCb Experiment","Particle Physics"],"dc:title":["Tests of lepton universality in $B^{0} \\to K_{S}^{0} l^{+} l^{-}$ and $B^{+} \\to K^{*+} l^{+} l^{-}$ decays at the LHCb experiment"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:17Z"}