Rare decays in quark flavour physics

AbstractEquipping an experiment at FCC-ee with particle identification (PID) capabilities, in particular the ability to distinguish between hadron species, would bring great benefits to the physics programme. Good PID is essential for precise studies in quark flavour physics and is also a great asset for many measurements in tau, top, and Higgs physics. The requirements placed by flavour physics and these other applications are surveyed, with an emphasis on the momentum range over which PID is necessary. Possible solutions are discussed, including classical RICH counters, time-of-flight systems, and dE/dx and cluster counting. Attention is paid to the impact on the global detector design that including PID capabilities would imply.

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Rare decays

Physics Subject Headings (PhySH) ◽

10.29172/5400cdbb-53f8-47c7-b672-6ba1edef9e87 ◽

2018 ◽

Keyword(s):

Rare Decays

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Long-lived light neutralinos at Belle II

Journal of High Energy Physics ◽

10.1007/jhep02(2021)211 ◽

2021 ◽

Vol 2021 (2) ◽

Author(s):

Sourav Dey ◽

Claudio O. Dib ◽

Juan Carlos Helo ◽

Minakshi Nayak ◽

Nicolás A. Neill ◽

...

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

Parameter Space ◽

Rare Decays ◽

Final States ◽

Charged Pions ◽

Belle Ii ◽

Background Events ◽

Displaced Vertex

Abstract We consider light neutralinos of mass about 1 GeV, produced from τ lepton rare decays at Belle II, in the context of R-parity-violating (RPV) supersymmetry. With large and clean samples of τ leptons produced at the Belle II experiment, excellent sensitivity to such light neutralinos with the exotic signatures of displaced vertices is expected. We focus on two benchmark scenarios of single RPV operators, $$ {\lambda}_{311}^{\prime }{L}_3{Q}_1{\overline{D}}_1 $$ λ 311 ′ L 3 Q 1 D ¯ 1 and $$ {\lambda}_{312}^{\prime }{L}_3{Q}_1{\overline{D}}_2 $$ λ 312 ′ L 3 Q 1 D ¯ 2 , which induce both the production and decay of the lightest neutralino. For the reconstruction of a displaced vertex, we require at least two charged pions in the final states. We perform Monte-Carlo simulations for both signal and background events, and find that Belle II can explore regions in the parameter space competitive with other probes. In particular, for the $$ {\lambda}_{311}^{\prime } $$ λ 311 ′ scenario, it can put limits up to two orders of magnitude stronger than the current bounds.

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Contribution of the Darwin operator to non-leptonic decays of heavy quarks

Journal of High Energy Physics ◽

10.1007/jhep12(2020)199 ◽

2020 ◽

Vol 2020 (12) ◽

Author(s):

Alexander Lenz ◽

Maria Laura Piscopo ◽

Aleksey V. Rusov

Keyword(s):

Standard Technique ◽

Quark Propagator ◽

Leptonic Decay ◽

Leptonic Decays ◽

Interference Contribution ◽

The Standard Model ◽

Strength Tensor ◽

Quark Flavour ◽

Quark Decay ◽

B Quark

Abstract We compute the Darwin operator contribution ($$ 1/{m}_b^3 $$ 1 / m b 3 correction) to the width of the inclusive non-leptonic decay of a B meson (B+, Bd or Bs), stemming from the quark flavour-changing transition b → $$ {q}_1{\overline{q}}_2{q}_3 $$ q 1 q ¯ 2 q 3 , where q1, q2 = u, c and q3 = d, s. The key ideas of the computation are the local expansion of the quark propagator in the external gluon field including terms with a covariant derivative of the gluon field strength tensor and the standard technique of the Heavy Quark Expansion (HQE). We confirm the previously known expressions of the $$ 1/{m}_b^3 $$ 1 / m b 3 contributions to the semi-leptonic decay b → $$ {q}_1\mathrm{\ell}{\overline{\nu}}_{\mathrm{\ell}} $$ q 1 ℓ ν ¯ ℓ , with ℓ = e, μ, τ and of the $$ 1/{m}_b^2 $$ 1 / m b 2 contributions to the non-leptonic modes. We find that this new term can give a sizeable correction of about −4 % to the non-leptonic decay width of a B meson. For Bd and Bs mesons this turns out to be the dominant correction to the free b-quark decay, while for the B+ meson the Darwin term gives the second most important correction — roughly 1/2 to 1/3 of the phase space enhanced Pauli interference contribution. Due to the tiny experimental uncertainties in lifetime measurements the incorporation of the Darwin term contribution is crucial for precision tests of the Standard Model.

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