Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.798891
Title: Determining the weak couplings |Vub|/|Vcb| using semileptonic decays
Author: Smith, Iwan Thomas
ISNI:       0000 0004 8508 9496
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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Abstract:
This thesis will present the first observation of the decay B s 0 →K − μ + ν μ and the determination of |V ub |/|V cb |. Using 2 fb −1 of data with a centre of mass energy √s = 8 TeV provided by the Large Hadron Collider and collected using the LHCb experiment, a measurement of the ratio of branching fractions of the decays Bs →Kμν and Bs→Dsμν is performed. This is the first observation of the decay B s 0 → K μ + ν μ which is found to have the branching fraction, B(B s 0 → K μ + ν μ )/B(B s 0 → D s − μ + ν μ )= (3.70 ± 0.29 ± 0.51) × 10 −3 , where the first uncertainty is statistical and the second is systematic. A second set of branching fraction measurements are made, restricted to high and low regions of q 2 . The experimental ratio of branching fractions is combined with form factor calculations allowing for measurements of |V ub |/|V cb | to be performed. There is a long standing discrepancy of ≈ 3.5σ between exclusive and inclusive measurements of |V ub | and a new measurement of this parameter provides some clarity on this discrepancy. Form factors from lattice QCD in the high q 2 region give, |V ub |/|V cb | = 0.0719 ± 0.0056 ± 0.0086, and form factors from light-cone sum rules in the low q 2 region give |V ub |/|V cb | = 0.0625 ± 0.0090 ± 0.0039, where the first uncertainty is experimental and the second is theoretical. The two measurements are in agreement and differ by 1σ. This high precision measurement of |V ub |/|V cb | provides an essential constraint for global fits to the CKM sector, and these results confirm the long-standing tension between inclusive and exclusive determinations of |V ub |.
Supervisor: Muheim, Franz ; Needham, Matthew Sponsor: Science and Technology Facilities Council (STFC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.798891  DOI: Not available
Keywords: Vub ; Large Hadron Collider ; semileptonic decay ; |V ub |/|V cb |
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