Unit:
Κατεύθυνση Πυρηνική Φυσική και Φυσική Στοιχειωδών ΣωματιδίωνLibrary of the School of Science
Author:
Melachroinos Georgios
Supervisors info:
Βελλίδης Κωνσταντίνος, Αν. Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Σφήκας Παρασκευάς, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Τετράδης Νικόλαος, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Original Title:
Comparison of the decays B→J/ψK, J/ψ → μμ and B→ μμK with the CMS experiment at CERN LHC
Translated title:
Comparison of the decays B→J/ψK, J/ψ → μμ and B→ μμK with the CMS experiment at CERN LHC
Summary:
We present a measurement of the ratio of branching fractions of charged B mesons to
B±→μ+μ−K± and B±→J/ψK ± , with the latter decay followed by J/ψ→μ+μ− . The
direct decay B±→μ+μ−K± involves a Flavor-Changing Neutral Current (FCNC), and
thus, is forbidden at tree level in the Standard Model. Instead, the decay proceeds via
higher-order processes, and is therefore rare, with a branching fraction of ∼10^−7 , which
is four orders of magnitude smaller than the B→ J/ψK decay. FCNC rare decays of B
mesons are particularly interesting, since they probe Lepton Flavor Universality in the Weak
Interactions. In this Master’s thesis, we reconstruct both decay modes, using proton-proton collisions recorded by the CMS experiment at the Large Hadron Collider in 2018. We then
measure the fraction RK(μ) = Br(B±→μ+μ−K±)/Br(B±→J/ψ (μ+μ−)K ±), which is
used in a full CMS analysis of a comparison of RK(μ) with RK(e), with RK(e) being the
same ratio for decays with electrons in the final state.
Main subject category:
Science
Keywords:
CERN, CMS, Leptons, b quarks, Β hadrons, rare decays, Electroweak Interactions, Lepton Flavor Universality.
