Tests of lepton universality in the rates of inclusive semileptonic B-meson decays at Belle II
Tests of lepton universality in the rates of inclusive semileptonic B-meson decays at Belle II
View/Type of Scholarly Publication
DissertationDate of Exam
28.06.2024Date of Publication
23.07.2024Advisor
Dingfelder, JochenCo-Referee
Desch, KlausMetadata
Show full item record
Citable Links 
Abstract
This thesis presents two precision tests of lepton universality: the first measurement of the ratio of light-lepton branching fractions of inclusive semileptonic B-meson decays, R(Xe/μ) = ℬ(B → Xeν) / ℬ(B → Xμν), and the first successful measurement of inclusive B → Xτν decays, measured in a ratio relative to B → Xℓν decays (ℓ = e, μ), R(Xτ/ℓ) = ℬ(B → Xτν) / ℬ(B → Xℓν).
Experimental data from electron-positron collisions at the ϒ(4S) resonance collected with the Belle II detector is used, that corresponds to an integrated luminosity of 189 fb−1. Continuum e+e− → qq events are constrained using 18 fb−1 of off-resonance data, collected 60 MeV below the ϒ(4S) resonance. One B meson from the ϒ(4S) → BB decay is fully reconstructed in a hadronic decay mode. In the signal or normalization decay of the second B meson, B → X[τ→ℓνν]ν or B → Xℓν, a charged lepton candidate is required. The hadronic system X is left unconstrained, rendering this analysis sensitive to all possible hadronic final states.
The light-lepton ratio R(Xe/μ) is extracted in a binned maximum-likelihood fit to the lepton-momentum spectra above 1.3 GeV. The fit is performed simultaneously for both lepton flavors, resulting in a substantial cancellation of correlated systematic uncertainties. The yields from BB backgrounds are constrained in a fit to control-sample data defined by the presence of two B-meson candidates with the same flavor. The value of
R(Xe/μ) = 1.007 ± 0.009 (stat.) ± 0.019 (syst.)
is obtained, which aligns with the Standard-Model expectation. This is the most precise branching fraction-based test of lepton universality in semileptonic B-meson decays to date.
For the measurement of R(Xτ/ℓ), significant discrepancies between experimental data and simulation, mostly attributed to the modeling of D-meson decays within the hadronic system X, are revealed. A new data-driven method to identify, quantify, and correct these modeling inaccuracies is developed, which simultaneously ameliorates the modeling of several observables that are associated with the hadronic system. This technique enables the extraction of R(Xτ/ℓ) in a two-dimensional binned maximum-likelihood fit to the lepton-momentum spectra and the squared missing mass in the event.
The resulting R(Xτ/ℓ) values for electrons and muons are R(Xτ/e) = 0.232 ± 0.020 (stat.) ± 0.037 (syst.), and R(Xτ/μ) = 0.222 ± 0.027 (stat.) ± 0.050 (syst.), respectively. The combination of lepton flavors in a weighted average of correlated values yields
R(Xτ/ℓ) = 0.228 ± 0.016 (stat.) ± 0.036 (syst.).
The results are in agreement with the Standard-Model predictions and represent a complementary test of the longstanding flavor anomaly observed in the exclusive ratios R(D(*)).
Experimental data from electron-positron collisions at the ϒ(4S) resonance collected with the Belle II detector is used, that corresponds to an integrated luminosity of 189 fb−1. Continuum e+e− → qq events are constrained using 18 fb−1 of off-resonance data, collected 60 MeV below the ϒ(4S) resonance. One B meson from the ϒ(4S) → BB decay is fully reconstructed in a hadronic decay mode. In the signal or normalization decay of the second B meson, B → X[τ→ℓνν]ν or B → Xℓν, a charged lepton candidate is required. The hadronic system X is left unconstrained, rendering this analysis sensitive to all possible hadronic final states.
The light-lepton ratio R(Xe/μ) is extracted in a binned maximum-likelihood fit to the lepton-momentum spectra above 1.3 GeV. The fit is performed simultaneously for both lepton flavors, resulting in a substantial cancellation of correlated systematic uncertainties. The yields from BB backgrounds are constrained in a fit to control-sample data defined by the presence of two B-meson candidates with the same flavor. The value of
R(Xe/μ) = 1.007 ± 0.009 (stat.) ± 0.019 (syst.)
is obtained, which aligns with the Standard-Model expectation. This is the most precise branching fraction-based test of lepton universality in semileptonic B-meson decays to date.
For the measurement of R(Xτ/ℓ), significant discrepancies between experimental data and simulation, mostly attributed to the modeling of D-meson decays within the hadronic system X, are revealed. A new data-driven method to identify, quantify, and correct these modeling inaccuracies is developed, which simultaneously ameliorates the modeling of several observables that are associated with the hadronic system. This technique enables the extraction of R(Xτ/ℓ) in a two-dimensional binned maximum-likelihood fit to the lepton-momentum spectra and the squared missing mass in the event.
The resulting R(Xτ/ℓ) values for electrons and muons are R(Xτ/e) = 0.232 ± 0.020 (stat.) ± 0.037 (syst.), and R(Xτ/μ) = 0.222 ± 0.027 (stat.) ± 0.050 (syst.), respectively. The combination of lepton flavors in a weighted average of correlated values yields
R(Xτ/ℓ) = 0.228 ± 0.016 (stat.) ± 0.036 (syst.).
The results are in agreement with the Standard-Model predictions and represent a complementary test of the longstanding flavor anomaly observed in the exclusive ratios R(D(*)).
Subjects
Hochenergiephysik, Belle II Experiment, Semileptonische B-Meson Zerfälle, Lepton-Universalität, high energy physics, semileptonic B-meson decays, lepton universality
Classification (DDC)
530 PhysikJunkerkalefeld, Henrik Alexander: Tests of lepton universality in the rates of inclusive semileptonic B-meson decays at Belle II. - Bonn, 2024. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-77208
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-77208
@phdthesis{handle:20.500.11811/11710,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-77208,
author = {{Henrik Alexander Junkerkalefeld}},
title = {Tests of lepton universality in the rates of inclusive semileptonic B-meson decays at Belle II},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2024,
month = jul,
note = {This thesis presents two precision tests of lepton universality: the first measurement of the ratio of light-lepton branching fractions of inclusive semileptonic B-meson decays, R(Xe/μ) = ℬ(B → Xeν) / ℬ(B → Xμν), and the first successful measurement of inclusive B → Xτν decays, measured in a ratio relative to B → Xℓν decays (ℓ = e, μ), R(Xτ/ℓ) = ℬ(B → Xτν) / ℬ(B → Xℓν).
Experimental data from electron-positron collisions at the ϒ(4S) resonance collected with the Belle II detector is used, that corresponds to an integrated luminosity of 189 fb−1. Continuum e+e− → qq events are constrained using 18 fb−1 of off-resonance data, collected 60 MeV below the ϒ(4S) resonance. One B meson from the ϒ(4S) → BB decay is fully reconstructed in a hadronic decay mode. In the signal or normalization decay of the second B meson, B → X[τ→ℓνν]ν or B → Xℓν, a charged lepton candidate is required. The hadronic system X is left unconstrained, rendering this analysis sensitive to all possible hadronic final states.
The light-lepton ratio R(Xe/μ) is extracted in a binned maximum-likelihood fit to the lepton-momentum spectra above 1.3 GeV. The fit is performed simultaneously for both lepton flavors, resulting in a substantial cancellation of correlated systematic uncertainties. The yields from BB backgrounds are constrained in a fit to control-sample data defined by the presence of two B-meson candidates with the same flavor. The value of
R(Xe/μ) = 1.007 ± 0.009 (stat.) ± 0.019 (syst.)
is obtained, which aligns with the Standard-Model expectation. This is the most precise branching fraction-based test of lepton universality in semileptonic B-meson decays to date.
For the measurement of R(Xτ/ℓ), significant discrepancies between experimental data and simulation, mostly attributed to the modeling of D-meson decays within the hadronic system X, are revealed. A new data-driven method to identify, quantify, and correct these modeling inaccuracies is developed, which simultaneously ameliorates the modeling of several observables that are associated with the hadronic system. This technique enables the extraction of R(Xτ/ℓ) in a two-dimensional binned maximum-likelihood fit to the lepton-momentum spectra and the squared missing mass in the event.
The resulting R(Xτ/ℓ) values for electrons and muons are R(Xτ/e) = 0.232 ± 0.020 (stat.) ± 0.037 (syst.), and R(Xτ/μ) = 0.222 ± 0.027 (stat.) ± 0.050 (syst.), respectively. The combination of lepton flavors in a weighted average of correlated values yields
R(Xτ/ℓ) = 0.228 ± 0.016 (stat.) ± 0.036 (syst.).
The results are in agreement with the Standard-Model predictions and represent a complementary test of the longstanding flavor anomaly observed in the exclusive ratios R(D(*)).},
url = {https://hdl.handle.net/20.500.11811/11710}
}
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-77208,
author = {{Henrik Alexander Junkerkalefeld}},
title = {Tests of lepton universality in the rates of inclusive semileptonic B-meson decays at Belle II},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2024,
month = jul,
note = {This thesis presents two precision tests of lepton universality: the first measurement of the ratio of light-lepton branching fractions of inclusive semileptonic B-meson decays, R(Xe/μ) = ℬ(B → Xeν) / ℬ(B → Xμν), and the first successful measurement of inclusive B → Xτν decays, measured in a ratio relative to B → Xℓν decays (ℓ = e, μ), R(Xτ/ℓ) = ℬ(B → Xτν) / ℬ(B → Xℓν).
Experimental data from electron-positron collisions at the ϒ(4S) resonance collected with the Belle II detector is used, that corresponds to an integrated luminosity of 189 fb−1. Continuum e+e− → qq events are constrained using 18 fb−1 of off-resonance data, collected 60 MeV below the ϒ(4S) resonance. One B meson from the ϒ(4S) → BB decay is fully reconstructed in a hadronic decay mode. In the signal or normalization decay of the second B meson, B → X[τ→ℓνν]ν or B → Xℓν, a charged lepton candidate is required. The hadronic system X is left unconstrained, rendering this analysis sensitive to all possible hadronic final states.
The light-lepton ratio R(Xe/μ) is extracted in a binned maximum-likelihood fit to the lepton-momentum spectra above 1.3 GeV. The fit is performed simultaneously for both lepton flavors, resulting in a substantial cancellation of correlated systematic uncertainties. The yields from BB backgrounds are constrained in a fit to control-sample data defined by the presence of two B-meson candidates with the same flavor. The value of
R(Xe/μ) = 1.007 ± 0.009 (stat.) ± 0.019 (syst.)
is obtained, which aligns with the Standard-Model expectation. This is the most precise branching fraction-based test of lepton universality in semileptonic B-meson decays to date.
For the measurement of R(Xτ/ℓ), significant discrepancies between experimental data and simulation, mostly attributed to the modeling of D-meson decays within the hadronic system X, are revealed. A new data-driven method to identify, quantify, and correct these modeling inaccuracies is developed, which simultaneously ameliorates the modeling of several observables that are associated with the hadronic system. This technique enables the extraction of R(Xτ/ℓ) in a two-dimensional binned maximum-likelihood fit to the lepton-momentum spectra and the squared missing mass in the event.
The resulting R(Xτ/ℓ) values for electrons and muons are R(Xτ/e) = 0.232 ± 0.020 (stat.) ± 0.037 (syst.), and R(Xτ/μ) = 0.222 ± 0.027 (stat.) ± 0.050 (syst.), respectively. The combination of lepton flavors in a weighted average of correlated values yields
R(Xτ/ℓ) = 0.228 ± 0.016 (stat.) ± 0.036 (syst.).
The results are in agreement with the Standard-Model predictions and represent a complementary test of the longstanding flavor anomaly observed in the exclusive ratios R(D(*)).},
url = {https://hdl.handle.net/20.500.11811/11710}
}
The following license files are associated with this item:
