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Measuring Flavor Mixing with Minimal Flavor Violation at the LHC

Gudrun Hiller, Yosef Nir

TL;DR

The paper analyzes whether MFV can be tested at the LHC by measuring the flavor-changing decay $\tilde t\to c\chi^0$ of the lightest stop, under the scenario where decays to third-generation quarks are kinematically forbidden due to near-degeneracy with the LSP. It derives the stop–charm–neutralino coupling $Y$ within MFV, showing it is CKM- and Yukawa-suppressed and depends on the stop/neutralino composition and $\tan\beta$, with predicted ranges $Y \sim 10^{-10}-10^{-4}$ (strong MFV) or $Y \sim 10^{-8}-10^{-2}$ (weak MFV). The authors assess LHC prospects for extracting the decay rate from a potential secondary vertex, including the impact of four-body decays when $m_{ ilde t}-m_{ ilde\chi^0}>m_b$ and the presence of a light chargino, and contrast MFV predictions with non-MFV alignment models where $Y$ can be orders of magnitude larger, implying prompt decays. They conclude that under favorable MFV conditions, a measurable stop lifetime could provide direct information on the size of flavor-violating couplings and help distinguish MFV from alignment scenarios, thereby addressing fundamental flavor puzzles in supersymmetry.

Abstract

The mixing between third and second (or first) generation squarks is very small in supersymmetric models with minimal flavor violation such as gauge-, anomaly- or gaugino-mediation. An opportunity to measure this mixing will arise if the lightest stop is close enough in mass to the lightest neutralino, so that the decays into third generation quarks are kinematically forbidden. We analyze under which circumstances it might become possible to measure at the Large Hadron Collider (LHC) the rate of the flavor changing stop decays.

Measuring Flavor Mixing with Minimal Flavor Violation at the LHC

TL;DR

The paper analyzes whether MFV can be tested at the LHC by measuring the flavor-changing decay of the lightest stop, under the scenario where decays to third-generation quarks are kinematically forbidden due to near-degeneracy with the LSP. It derives the stop–charm–neutralino coupling within MFV, showing it is CKM- and Yukawa-suppressed and depends on the stop/neutralino composition and , with predicted ranges (strong MFV) or (weak MFV). The authors assess LHC prospects for extracting the decay rate from a potential secondary vertex, including the impact of four-body decays when and the presence of a light chargino, and contrast MFV predictions with non-MFV alignment models where can be orders of magnitude larger, implying prompt decays. They conclude that under favorable MFV conditions, a measurable stop lifetime could provide direct information on the size of flavor-violating couplings and help distinguish MFV from alignment scenarios, thereby addressing fundamental flavor puzzles in supersymmetry.

Abstract

The mixing between third and second (or first) generation squarks is very small in supersymmetric models with minimal flavor violation such as gauge-, anomaly- or gaugino-mediation. An opportunity to measure this mixing will arise if the lightest stop is close enough in mass to the lightest neutralino, so that the decays into third generation quarks are kinematically forbidden. We analyze under which circumstances it might become possible to measure at the Large Hadron Collider (LHC) the rate of the flavor changing stop decays.

Paper Structure

This paper contains 8 sections, 21 equations, 1 figure, 4 tables.

Table of Contents

  1. Introduction
  2. The $\tilde{t}\to c\chi^0$ Decay Rate
  3. Third generation flavor mixing with MFV
  4. Measuring flavor changing decay rates at the LHC
  5. $m_{\tilde{t}}-m_{\chi^0}>m_b$ and four body decays
  6. A light chargino
  7. Third generation flavor mixing without MFV
  8. Conclusions

Figures (1)

  • Figure 1: Interesting regions in the $Y-\Delta m/M$ plane: (i) The single curved line separates the regions where a secondary vertex appears (below) or does not appear (above); (ii) The triplet of curved lines distinguishes the region where the stop two-body decay dominates (left and above) from the region where the four-body decays dominate (below and right); (iii) The horizontal dashed line marks the lower bound on the region accessible to models with alignment; (iv) The horizontal solid line marks the lower bound if the up squark flavor parameters are anarchical. The plot is shown for fixed $m_{\tilde{t}}=100$ GeV and $m_{\chi^+}=500$ GeV. For details see text.