Abstract
This paper presents the prospects for a precise measurement of the branching fraction of the leptonic {B}_c^{+} → τ+ντ decay at the Future Circular Collider (FCC-ee) running at the Z -pole. A detailed description of the simulation and analysis framework is provided. To select signal candidates, two Boosted Decision Tree algorithms are employed and optimised. The first stage suppresses inclusive boverline{b} , coverline{c} , and qoverline{q} backgrounds using event-based topological information. A second stage utilises the properties of the hadronic τ+→ π+π+π− overline{nu} τ decay to further suppress these backgrounds, and is also found to achieve high rejection for the B+→ τ+ντ background. The number of {B}_c^{+} → τ+ντ candidates is estimated for various Tera-Z scenarios, and the potential precision of signal yield and branching fraction measurements evaluated. The phenomenological impact of such measurements on various New Physics scenarios is also explored.
Highlights
N (Bc+ → τ +ντ )The signal yields expected as a function of NZ, as well as their uncertainties as measured in the pseudoexperiment fits, are summarised in table 1
This paper presents the prospects for a precise measurement of the branching fraction of the leptonic Bc+ → τ +ντ decay at the Future Circular Collider (FCC-ee) running at the Z-pole
A two-stage boosted decision tree (BDT) selection is employed to reduce all sources of hadronic Z background, first using topological event-level information, and the vertex properties of the detached τ + → π+π+π−ντ decay to reduce the rate of b-hadron backgrounds
Summary
The international Future Circular Collider (FCC) study aims at a design of p-p, e+e−, and e-p colliders to be built in a new 100 km tunnel in the Geneva region. The e+e− collider (FCC-ee) has a centre of mass energy range between 91 (Z-pole) and 375 GeV (tt). The FCC-ee offers unprecedented possibilities for measuring the properties of the four heaviest particles of the SM (the Higgs, Z, and W bosons, and the top quark), and those of the b and c quarks and of the τ lepton. Circular colliders have the advantage of delivering collisions to multiple interaction regions, which allow different detector designs to be studied and optimised — up to four are under consideration for FCC-ee. The huge statistics anticipated at the Z peak (the so-called “Tera-Z” run) brings specific challenges, as the systematic uncertainties of the measurements should be commensurate with their small statistical uncertainties
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