{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/267824"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/267824","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Measurements of $B \\to \\mu^+ \\mu^-$ decays using the LHCb experiment","abstract":"This dissertation documents a study of very rare $B$-meson decays at the LHCb experiment, using data taken during the first experiment run of the Large Hadron Collider (LHC) and during the second experiment run until September 2016. The LHCb experiment was designed to test the Standard Model of particle physics and to search for New Physics effects that go beyond the scope of the Standard Model through the decay of $b$ hadrons produced in high energy proton-proton collisions at the LHC. The measurements described in this dissertation are made using data samples of proton-proton collisions with integrated luminosities of 1.0, 2.0 and 1.4fb$^{-1}$, collected at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The branching fractions of the very rare $B^{0} \\to \\mu^{+} \\mu^{-}$ and $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decays and the effective lifetime of $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decays are precisely predicted by the Standard Model and are sensitive to effects from New Physics. New Physics processes could influence the $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ branching fraction and effective lifetime independently, and therefore the two observables are complementary. The $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decay is observed with a statistical significance of 7.8$\\sigma$ and the branching fraction is measured to be $\\mathcal{B}(B_{s}^{0} \\to \\mu^{+} \\mu^{-}) = (3.0 \\pm 0.6^{ +0.3}_{ -0.2}) \\times 10^{-9}$. The $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ effective lifetime is measured for the first time as 2.04 $\\pm$ 0.44 $\\pm$ 0.05 \\ps. The $B^{0} \\to \\mu^{+} \\mu^{-}$ branching fraction is measured as $\\mathcal{B}(B^{0} \\to \\mu^{+} \\mu^{-})$ = $(1.5\\frac{+1.2+0.2}{-1.0-0.1})\\times 10^{-10}$ with a statistical significance of 1.6$\\sigma$. An upper limit is set for the branching fraction of $\\mathcal{B}(B^{0} \\to \\mu^{+} \\mu^{-})< 3.4 \\times 10^{-10}$ at the 95$\\%$ confidence level. All results are consistent with the predictions of the Standard Model.","abstract_html":"This dissertation documents a study of very rare $B$-meson decays at the LHCb experiment, using data taken during the first experiment run of the Large Hadron Collider (LHC) and during the second experiment run until September 2016. The LHCb experiment was designed to test the Standard Model of particle physics and to search for New Physics effects that go beyond the scope of the Standard Model through the decay of $b$ hadrons produced in high energy proton-proton collisions at the LHC. The measurements described in this dissertation are made using data samples of proton-proton collisions with integrated luminosities of 1.0, 2.0 and 1.4fb<span class=\"etd-inline-math\"><sup>-1</sup></span>, collected at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The branching fractions of the very rare <span class=\"etd-inline-math\">B<sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> and <span class=\"etd-inline-math\">B<sub>s</sub><sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> decays and the effective lifetime of <span class=\"etd-inline-math\">B<sub>s</sub><sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> decays are precisely predicted by the Standard Model and are sensitive to effects from New Physics. New Physics processes could influence the <span class=\"etd-inline-math\">B<sub>s</sub><sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> branching fraction and effective lifetime independently, and therefore the two observables are complementary. The <span class=\"etd-inline-math\">B<sub>s</sub><sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> decay is observed with a statistical significance of 7.8<span class=\"etd-inline-math\">&sigma;</span> and the branching fraction is measured to be <span class=\"etd-inline-math\">\\mathcal{B}(B<sub>s</sub><sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup>) = (3.0 \\pm 0.6<sup> +0.3</sup><sub> -0.2</sub>) \\times 10<sup>-9</sup></span>. The <span class=\"etd-inline-math\">B<sub>s</sub><sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> effective lifetime is measured for the first time as 2.04 $\\pm$ 0.44 $\\pm$ 0.05 \\ps. The <span class=\"etd-inline-math\">B<sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup></span> branching fraction is measured as <span class=\"etd-inline-math\">\\mathcal{B}(B<sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup>)</span> = <span class=\"etd-inline-math\">(1.5\\frac{+1.2+0.2}{-1.0-0.1})\\times 10<sup>-10</sup></span> with a statistical significance of 1.6<span class=\"etd-inline-math\">&sigma;</span>. An upper limit is set for the branching fraction of <span class=\"etd-inline-math\">\\mathcal{B}(B<sup>0</sup> \\to &mu;<sup>+</sup> &mu;<sup>-</sup>)&lt; 3.4 \\times 10<sup>-10</sup></span> at the 95$\\%$ confidence level. All results are consistent with the predictions of the Standard Model.","abstract_has_math":true,"creators":["Evans, Hannah Mary"],"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":2017,"date_issued":"2017-10-04","date_published":"2017-10-04","updated_at":"2026-07-22T22:24:23Z","subjects":["Large hadron collider","Particle physics","Rare decays","LHCb experiment"],"languages":["en"],"rights":[],"rights_urls":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/d020eaa5-5722-42e0-aa57-25d5a839709e/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.13748","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":["PhD funded by the Science and Technology Facilities Council (STFC)"]},{"key":"dc:creator","label":"Author","values":["Evans, Hannah Mary"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2017-10-04"]},{"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/1810/267824"]},{"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":["Large hadron collider","Particle physics","Rare decays","LHCb experiment"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/d020eaa5-5722-42e0-aa57-25d5a839709e/download","https://www.rioxx.net/licenses/all-rights-reserved/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["10.17863/CAM.13748"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b6c5aebe-c573-466c-89d9-83d7c1a1dfbe/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["This dissertation documents a study of very rare $B$-meson decays at the LHCb experiment, using data taken during the first experiment run of the Large Hadron Collider (LHC) and during the second experiment run until September 2016. The LHCb experiment was designed to test the Standard Model of particle physics and to search for New Physics effects that go beyond the scope of the Standard Model through the decay of $b$ hadrons produced in high energy proton-proton collisions at the LHC. The measurements described in this dissertation are made using data samples of proton-proton collisions with integrated luminosities of 1.0, 2.0 and 1.4fb$^{-1}$, collected at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The branching fractions of the very rare $B^{0} \\to \\mu^{+} \\mu^{-}$ and $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decays and the effective lifetime of $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decays are precisely predicted by the Standard Model and are sensitive to effects from New Physics. New Physics processes could influence the $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ branching fraction and effective lifetime independently, and therefore the two observables are complementary. The $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decay is observed with a statistical significance of 7.8$\\sigma$ and the branching fraction is measured to be $\\mathcal{B}(B_{s}^{0} \\to \\mu^{+} \\mu^{-}) = (3.0 \\pm 0.6^{ +0.3}_{ -0.2}) \\times 10^{-9}$. The $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ effective lifetime is measured for the first time as 2.04 $\\pm$ 0.44 $\\pm$ 0.05 \\ps. The $B^{0} \\to \\mu^{+} \\mu^{-}$ branching fraction is measured as $\\mathcal{B}(B^{0} \\to \\mu^{+} \\mu^{-})$ = $(1.5\\frac{+1.2+0.2}{-1.0-0.1})\\times 10^{-10}$ with a statistical significance of 1.6$\\sigma$. An upper limit is set for the branching fraction of $\\mathcal{B}(B^{0} \\to \\mu^{+} \\mu^{-})< 3.4 \\times 10^{-10}$ at the 95$\\%$ confidence level. All results are consistent with the predictions of the Standard Model."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["87eda9de84448d1f82354d60eee3eb5f","8770f6f970687eac7132f390df5e4309"]},{"key":"dc:title","label":"Title","values":["Measurements of $B \\to \\mu^+ \\mu^-$ decays using the LHCb experiment"]}]}],"canonical_facts":{"dc:contributor.advisor":["Gibson, Valerie"],"dc:contributor.sponsor":["PhD funded by the Science and Technology Facilities Council (STFC)"],"dc:creator":["Evans, Hannah Mary"],"dc:date.issued":["2017-10-04"],"dc:description.abstract":["This dissertation documents a study of very rare $B$-meson decays at the LHCb experiment, using data taken during the first experiment run of the Large Hadron Collider (LHC) and during the second experiment run until September 2016. The LHCb experiment was designed to test the Standard Model of particle physics and to search for New Physics effects that go beyond the scope of the Standard Model through the decay of $b$ hadrons produced in high energy proton-proton collisions at the LHC. The measurements described in this dissertation are made using data samples of proton-proton collisions with integrated luminosities of 1.0, 2.0 and 1.4fb$^{-1}$, collected at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The branching fractions of the very rare $B^{0} \\to \\mu^{+} \\mu^{-}$ and $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decays and the effective lifetime of $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decays are precisely predicted by the Standard Model and are sensitive to effects from New Physics. New Physics processes could influence the $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ branching fraction and effective lifetime independently, and therefore the two observables are complementary. The $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ decay is observed with a statistical significance of 7.8$\\sigma$ and the branching fraction is measured to be $\\mathcal{B}(B_{s}^{0} \\to \\mu^{+} \\mu^{-}) = (3.0 \\pm 0.6^{ +0.3}_{ -0.2}) \\times 10^{-9}$. The $B_{s}^{0} \\to \\mu^{+} \\mu^{-}$ effective lifetime is measured for the first time as 2.04 $\\pm$ 0.44 $\\pm$ 0.05 \\ps. The $B^{0} \\to \\mu^{+} \\mu^{-}$ branching fraction is measured as $\\mathcal{B}(B^{0} \\to \\mu^{+} \\mu^{-})$ = $(1.5\\frac{+1.2+0.2}{-1.0-0.1})\\times 10^{-10}$ with a statistical significance of 1.6$\\sigma$. An upper limit is set for the branching fraction of $\\mathcal{B}(B^{0} \\to \\mu^{+} \\mu^{-})< 3.4 \\times 10^{-10}$ at the 95$\\%$ confidence level. All results are consistent with the predictions of the Standard Model."],"dc:format.checksum.md5":["87eda9de84448d1f82354d60eee3eb5f","8770f6f970687eac7132f390df5e4309"],"dc:identifier.doi":["10.17863/CAM.13748"],"dc:identifier.uri":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b6c5aebe-c573-466c-89d9-83d7c1a1dfbe/download"],"dc:language":["en"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/267824"],"dc:rights":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/d020eaa5-5722-42e0-aa57-25d5a839709e/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"dc:subject":["Large hadron collider","Particle physics","Rare decays","LHCb experiment"],"dc:title":["Measurements of $B \\to \\mu^+ \\mu^-$ decays using the LHCb experiment"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:23Z"}