Semileptonic Decays of Strange Beauty Mesons at Belle
Semileptonic Decays of Strange Beauty Mesons at Belle
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DissertationPrüfungsdatum
19.06.2015Datum der Veröffentlichung
16.07.2015Erstgutachter
Dingfelder, Jochen ChristianZweitgutachter
Desch, KlausMetadaten
Zur Langanzeige
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Inhalt
Semileptonic decays of b-flavoured mesons are an important tool for the determination of the CKM matrix element |Vcb|. In this thesis, measurements of semileptonic Bs meson decays are presented. They provide complementary information to the precision measurements of B meson decays and serve as a test of QCD-calculations predicting SU(3) flavour symmetry for the partial decay widths and form factors. The semi-inclusive and inclusive analyses of semileptonic Bs decays are based on the 121.4 fb-1 dataset collected by the Belle detector at the KEKB asymmetric-energy e+ e- collider in Tsukuba, Japan. The sample recorded at a centre-of-mass energy √s = 10.86 GeV, which corresponds to the Y(5S) resonance, contains (7.1 ± 1.3) million Bs pair events.
To measure the semi-inclusive Bs → Ds X l ν and Bs → Ds* X l ν branching fractions, Ds and Ds* candidates are reconstructed and are paired with an oppositely charged lepton, l+ = e+, μ+. The yields of correctly reconstructed Ds and Ds* mesons are determined by fits to their respective invariant mass distributions. The signal yield and the yields of the remaining backgrounds are extracted using kinematic distributions of the reconstructed decay products and the constraint from the known initial state of the e+ e- collision. The measured branching fractions are: Bf(Bs → Ds X l ν) = (8.2 ± 0.2 (stat) ± 0.6 (syst) ± 1.4 (ext)) % and Bf(Bs → Ds* l ν) = (5.4 ± 0.4 (stat) ± 0.4 (syst) ± 0.9 (ext)) % , where the first two uncertainties are the statistical and systematic uncertainties of the measurement and the last uncertainty is due to external parameters. Making an assumption about the Bs → Ds X l ν branching fraction, the measurement of the Bs → Ds X l ν yield is also used to obtain the current best estimate of the Bs pair production cross-section at a centre-of-mass energy √s = 10.86 GeV: σ(e+ e- → Bs pairs) = (57.1 ± 1.5 (stat) ± 4.3 (syst) ± 4.2 (ext) ) pb.
The semi-inclusive measurements are complemented by an analysis of the inclusive decay Bs → X l ν, which has a particularly simple signature of only a charged, high-momentum track. A measurement of this decay mode has to cope, however, with substantial background from B0 and B+ decays, which have a four times higher production rate at the Y(5S) resonance compared to Bs mesons. Therefore, the sample is enhanced in Bs pair events by reconstructing an additional Ds+ meson in the event with same-sign electric charge as the signal lepton, l+. The same-sign requirement ensures that the Ds+ meson and the lepton, l+, stem from decays of different Bs mesons in the event. The Bs → X l ν branching fraction is determined from the measured ratio of the number of Ds+ l+ to the number of Ds+ events. The remaining contribution from B0 and B+ decays is estimated using measured Bs and B meson production rates and branching fractions. The result, Bf(Bs → X l ν) = (9.6 ± 0.4 (stat) ± 0.7 (syst)) % , is the most precise measurement of the inclusive semileptonic Bs branching fraction to date.
To measure the semi-inclusive Bs → Ds X l ν and Bs → Ds* X l ν branching fractions, Ds and Ds* candidates are reconstructed and are paired with an oppositely charged lepton, l+ = e+, μ+. The yields of correctly reconstructed Ds and Ds* mesons are determined by fits to their respective invariant mass distributions. The signal yield and the yields of the remaining backgrounds are extracted using kinematic distributions of the reconstructed decay products and the constraint from the known initial state of the e+ e- collision. The measured branching fractions are: Bf(Bs → Ds X l ν) = (8.2 ± 0.2 (stat) ± 0.6 (syst) ± 1.4 (ext)) % and Bf(Bs → Ds* l ν) = (5.4 ± 0.4 (stat) ± 0.4 (syst) ± 0.9 (ext)) % , where the first two uncertainties are the statistical and systematic uncertainties of the measurement and the last uncertainty is due to external parameters. Making an assumption about the Bs → Ds X l ν branching fraction, the measurement of the Bs → Ds X l ν yield is also used to obtain the current best estimate of the Bs pair production cross-section at a centre-of-mass energy √s = 10.86 GeV: σ(e+ e- → Bs pairs) = (57.1 ± 1.5 (stat) ± 4.3 (syst) ± 4.2 (ext) ) pb.
The semi-inclusive measurements are complemented by an analysis of the inclusive decay Bs → X l ν, which has a particularly simple signature of only a charged, high-momentum track. A measurement of this decay mode has to cope, however, with substantial background from B0 and B+ decays, which have a four times higher production rate at the Y(5S) resonance compared to Bs mesons. Therefore, the sample is enhanced in Bs pair events by reconstructing an additional Ds+ meson in the event with same-sign electric charge as the signal lepton, l+. The same-sign requirement ensures that the Ds+ meson and the lepton, l+, stem from decays of different Bs mesons in the event. The Bs → X l ν branching fraction is determined from the measured ratio of the number of Ds+ l+ to the number of Ds+ events. The remaining contribution from B0 and B+ decays is estimated using measured Bs and B meson production rates and branching fractions. The result, Bf(Bs → X l ν) = (9.6 ± 0.4 (stat) ± 0.7 (syst)) % , is the most precise measurement of the inclusive semileptonic Bs branching fraction to date.
Schlagwörter
Semileptonischer Zerfall, Verzweigungsverhältnis, B-Meson, Ypsilon-Teilchen, Wirkungsquerschnitt, Bottom mesons, leptonic decay
Klassifikation (DDC)
530 PhysikOswald, Christian: Semileptonic Decays of Strange Beauty Mesons at Belle. - Bonn, 2015. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-40522
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-40522
@phdthesis{handle:20.500.11811/6493,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-40522,
author = {{Christian Oswald}},
title = {Semileptonic Decays of Strange Beauty Mesons at Belle},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2015,
month = jul,
note = {Semileptonic decays of b-flavoured mesons are an important tool for the determination of the CKM matrix element |Vcb|. In this thesis, measurements of semileptonic Bs meson decays are presented. They provide complementary information to the precision measurements of B meson decays and serve as a test of QCD-calculations predicting SU(3) flavour symmetry for the partial decay widths and form factors. The semi-inclusive and inclusive analyses of semileptonic Bs decays are based on the 121.4 fb-1 dataset collected by the Belle detector at the KEKB asymmetric-energy e+ e- collider in Tsukuba, Japan. The sample recorded at a centre-of-mass energy √s = 10.86 GeV, which corresponds to the Y(5S) resonance, contains (7.1 ± 1.3) million Bs pair events.
To measure the semi-inclusive Bs → Ds X l ν and Bs → Ds* X l ν branching fractions, Ds and Ds* candidates are reconstructed and are paired with an oppositely charged lepton, l+ = e+, μ+. The yields of correctly reconstructed Ds and Ds* mesons are determined by fits to their respective invariant mass distributions. The signal yield and the yields of the remaining backgrounds are extracted using kinematic distributions of the reconstructed decay products and the constraint from the known initial state of the e+ e- collision. The measured branching fractions are: Bf(Bs → Ds X l ν) = (8.2 ± 0.2 (stat) ± 0.6 (syst) ± 1.4 (ext)) % and Bf(Bs → Ds* l ν) = (5.4 ± 0.4 (stat) ± 0.4 (syst) ± 0.9 (ext)) % , where the first two uncertainties are the statistical and systematic uncertainties of the measurement and the last uncertainty is due to external parameters. Making an assumption about the Bs → Ds X l ν branching fraction, the measurement of the Bs → Ds X l ν yield is also used to obtain the current best estimate of the Bs pair production cross-section at a centre-of-mass energy √s = 10.86 GeV: σ(e+ e- → Bs pairs) = (57.1 ± 1.5 (stat) ± 4.3 (syst) ± 4.2 (ext) ) pb.
The semi-inclusive measurements are complemented by an analysis of the inclusive decay Bs → X l ν, which has a particularly simple signature of only a charged, high-momentum track. A measurement of this decay mode has to cope, however, with substantial background from B0 and B+ decays, which have a four times higher production rate at the Y(5S) resonance compared to Bs mesons. Therefore, the sample is enhanced in Bs pair events by reconstructing an additional Ds+ meson in the event with same-sign electric charge as the signal lepton, l+. The same-sign requirement ensures that the Ds+ meson and the lepton, l+, stem from decays of different Bs mesons in the event. The Bs → X l ν branching fraction is determined from the measured ratio of the number of Ds+ l+ to the number of Ds+ events. The remaining contribution from B0 and B+ decays is estimated using measured Bs and B meson production rates and branching fractions. The result, Bf(Bs → X l ν) = (9.6 ± 0.4 (stat) ± 0.7 (syst)) % , is the most precise measurement of the inclusive semileptonic Bs branching fraction to date.},
url = {https://hdl.handle.net/20.500.11811/6493}
}
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-40522,
author = {{Christian Oswald}},
title = {Semileptonic Decays of Strange Beauty Mesons at Belle},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2015,
month = jul,
note = {Semileptonic decays of b-flavoured mesons are an important tool for the determination of the CKM matrix element |Vcb|. In this thesis, measurements of semileptonic Bs meson decays are presented. They provide complementary information to the precision measurements of B meson decays and serve as a test of QCD-calculations predicting SU(3) flavour symmetry for the partial decay widths and form factors. The semi-inclusive and inclusive analyses of semileptonic Bs decays are based on the 121.4 fb-1 dataset collected by the Belle detector at the KEKB asymmetric-energy e+ e- collider in Tsukuba, Japan. The sample recorded at a centre-of-mass energy √s = 10.86 GeV, which corresponds to the Y(5S) resonance, contains (7.1 ± 1.3) million Bs pair events.
To measure the semi-inclusive Bs → Ds X l ν and Bs → Ds* X l ν branching fractions, Ds and Ds* candidates are reconstructed and are paired with an oppositely charged lepton, l+ = e+, μ+. The yields of correctly reconstructed Ds and Ds* mesons are determined by fits to their respective invariant mass distributions. The signal yield and the yields of the remaining backgrounds are extracted using kinematic distributions of the reconstructed decay products and the constraint from the known initial state of the e+ e- collision. The measured branching fractions are: Bf(Bs → Ds X l ν) = (8.2 ± 0.2 (stat) ± 0.6 (syst) ± 1.4 (ext)) % and Bf(Bs → Ds* l ν) = (5.4 ± 0.4 (stat) ± 0.4 (syst) ± 0.9 (ext)) % , where the first two uncertainties are the statistical and systematic uncertainties of the measurement and the last uncertainty is due to external parameters. Making an assumption about the Bs → Ds X l ν branching fraction, the measurement of the Bs → Ds X l ν yield is also used to obtain the current best estimate of the Bs pair production cross-section at a centre-of-mass energy √s = 10.86 GeV: σ(e+ e- → Bs pairs) = (57.1 ± 1.5 (stat) ± 4.3 (syst) ± 4.2 (ext) ) pb.
The semi-inclusive measurements are complemented by an analysis of the inclusive decay Bs → X l ν, which has a particularly simple signature of only a charged, high-momentum track. A measurement of this decay mode has to cope, however, with substantial background from B0 and B+ decays, which have a four times higher production rate at the Y(5S) resonance compared to Bs mesons. Therefore, the sample is enhanced in Bs pair events by reconstructing an additional Ds+ meson in the event with same-sign electric charge as the signal lepton, l+. The same-sign requirement ensures that the Ds+ meson and the lepton, l+, stem from decays of different Bs mesons in the event. The Bs → X l ν branching fraction is determined from the measured ratio of the number of Ds+ l+ to the number of Ds+ events. The remaining contribution from B0 and B+ decays is estimated using measured Bs and B meson production rates and branching fractions. The result, Bf(Bs → X l ν) = (9.6 ± 0.4 (stat) ± 0.7 (syst)) % , is the most precise measurement of the inclusive semileptonic Bs branching fraction to date.},
url = {https://hdl.handle.net/20.500.11811/6493}
}
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