Quantification of backgrounds in the high-q2 region of R(Λ)

Bouma, Sander (2024) Quantification of backgrounds in the high-q2 region of R(Λ). Master's Thesis / Essay, Physics.

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Abstract

This analysis aims to investigate the background modes present in the measurement of R(Λ) in the high-q 2 region. This is the ratio of B(Λ0b → Λ0 µ+ µ−) and B(Λ0b → Λ0 e+ e−) in the region of 14.3 GeV2 /c4 < q 2 <20.0 GeV2 /c4 , where q2 is the invariant mass of the dilepton pair of the decay. The R(Λ) analysis uses the Run 1 and Run 2 LHCb datasets and aims to test Lepton Flavour Universality as well as performing the first measurement of the Λ0b → Λ0 e+ e− branching fraction. R(Λ) suffers from low statistics; therefore, it is vital to know which backgrounds are present in the data, how much they contribute and how they can be modeled. In this analysis, the backgrounds in both the muon and electron modes are investigated. An estimation of the yields of each background is made from efficiencies (from MC data) and branching fractions to determine which backgrounds are most likely to be significant. A study of the combinatorial background is not performed here, as it is a separate study on its own. It was estimated that the Λ0b → Λ+c (→ Λ ℓ νℓ )ℓ ν ℓ decay has the highest background yield, but by employing an Λc-veto on the data it was shown that there was no significant contribution in the high-q2 region. The contribution of the B0 → KS0 (→ π + π − )ℓ+ ℓ− background was shown to be in agreement with its expectation; a yield of around 2.0% relative to the signal yield. Further research should investigate the contribution of partially reconstructed backgrounds.

Item Type:	Thesis (Master's Thesis / Essay)
Supervisor name:	Mulder, M. and Jones, S.A.
Degree programme:	Physics
Thesis type:	Master's Thesis / Essay
Language:	English
Date Deposited:	02 Aug 2024 12:46
Last Modified:	02 Aug 2024 12:46
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/33830

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