[Paper Review] Is Super-$B$ Sufficiently Superb? -- On the Motivation for a Super-$B$ Factory

I. I. Bigi, A. I. Sanda|ArXiv.org|Jan 1, 2004

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper argues that a Super-$B$ factory—producing $10^{10}$ $B\bar{B}$ pairs annually via $e^+e^-$ collisions at $\sim10^{35}$ cm$^{-2}$s$^{-1}$ luminosity—is essential for precision tests of the Standard Model and diagnosis of New Physics, particularly in the context of flavor physics and supersymmetry. It proposes that such a facility would enable high-precision measurements of CKM parameters, rare decays, CP asymmetries, and $B_s\bar{B}_s$ transitions, offering unique sensitivity beyond hadron colliders.

ABSTRACT

Despite the great success of the $Υ(4S)$ $B$ factories at KEK and SLAC and the guaranteed addition of high sensitivity measurements on beauty decays to be performed at the Tevatron and LHC, a strong case can be made for an $e^+e^-$ Super-$B$ factory yielding data samples of order $10^{10}$ $B \bar B$ pairs as a necessity rather than luxury. It has to be justified through its ability to not only establish deviations from the Standard Model, but also diagnose and interpret those in terms of specific features of the New Dynamics. The role to be played by a Super-$B$ factory is thus analogous {\em and even in parallel} to that of a linear collider. The latter's goal is to provide more detailed information on previously discovered New Physics involved in the electroweak phase transition. Likewise a Super-$B$ factory would provide precision probes for analyzing whether such New Dynamics has an impact on heavy flavour dynamics -- a need particularly manifest if the New Physics is housed under the `big tent' of SUSY. The huge statistics of a Super-$B$ factory and the comprehensive body of accurate measurements uniquely possible there would be harnessed in several classes of studies, among them more precise extractions of $V(ub)/V(cb)$ and $V(td)/V(ts)$, more detailed analyses of $B o γX_{s,d}, l^+l^-X$ and novel data on $B o τν, τνD, ν\bar νX$ and maybe even on $Υ(5S) o B_s \bar B_s$ -- all in addition to a host of CP asymmetries.

Motivation & Objective

• To establish the scientific necessity of a Super-$B$ factory beyond the success of existing $B$ factories.
• To address the limitations of hadron colliders in achieving the required precision for testing CKM parameters and rare decays.
• To enable comprehensive, high-statistics studies of $B$, $D$, and $\tau$ decays to probe New Physics in flavor-changing processes.
• To provide a unique environment for diagnosing New Physics features, especially in the context of supersymmetry.
• To meet the '1% challenge'—achieving $\mathcal{O}(1\%)$ uncertainty in key observables for interpretation of New Physics.

Proposed method

• Proposes an asymmetric $e^+e^-$ collider operating at $\sqrt{s} \approx m_{\Upsilon(4S)}$ with luminosity $\sim10^{35}$ cm$^{-2}$s$^{-1}$, yielding $\sim10^{10}$ $B\bar{B}$ pairs per year.
• Utilizes high-statistics, clean $e^+e^-$ events to enable precision measurements of inclusive and exclusive $B$ decays, including $B \to \gamma X$, $l^+l^-X$, $B \to \tau\nu$, and $B \to \nu\bar{\nu}X$.
• Employs time-dependent CP asymmetry analyses in $B^\pm \to D^{\rm neut}K^\pm$ to extract $\gamma = \phi_3$, with emphasis on minimizing $x_D$ and $y_D$ biases.
• Applies Dalitz plot analyses and T-odd correlations to detect CP violation in charm and $\tau$ decays at $\mathcal{O}(10^{-4})$ to $10^{-3}$ levels.
• Leverages the $\Upsilon(5S)$ resonance to access $B_s\bar{B}_s$ pairs for $B_s$ physics, including $B_s \to \tau\nu$ and $B_s$ mixing.
• Combines data from $B$, charm, and $\tau$ decays to form a network of cross-checked observables for diagnosing New Physics.

Experimental results

Research questions

• RQ1 Can a Super-$B$ factory provide the precision needed to diagnose New Physics in flavor-changing neutral currents and rare decays?
• RQ2 To what extent can $B \to \gamma X$ and $B \to l^+l^-X$ decays probe New Physics beyond the Standard Model?
• RQ3 How can $B_s\bar{B}_s$ production at $\Upsilon(5S)$ improve the determination of $B_s$ mixing and rare decays?
• RQ4 Can CP asymmetries in $D^0 \to K^+K^-$, $\pi^+\pi^-$, and $K_S\phi$ reach the $\mathcal{O}(10^{-4})$ sensitivity needed to detect New Physics?
• RQ5 What is the role of $\tau$ decays in probing lepton-number violating processes and CP violation in the lepton sector?

Key findings

• A Super-$B$ factory with $\sim10^{10}$ $B\bar{B}$ pairs per year would provide a uniquely clean environment for precision flavor physics, surpassing hadron colliders in control and systematic uncertainty.
• The $\sin 2\phi_1 = 0.736 \pm 0.049$ world average from $B_d \to J/\psi K_S$ at $B$ factories demonstrates the power of high-precision $e^+e^-$ data, justifying further upgrades.
• High-precision extraction of $V_{cb}$, $V_{ub}$, $V_{td}$, and $V_{ts}$ is feasible with $\mathcal{O}(1\%)$ uncertainty, enabling stringent tests of the CKM matrix.
• Measurements of $B \to \tau\nu$, $B \to \tau\bar{\nu}D^{(*)}$, and $B \to \nu\bar{\nu}X$ at $\sim10^{-5}$ branching fractions are accessible with $\sim10^{10}$ $B\bar{B}$ pairs.
• The $\Upsilon(5S) \to B_s\bar{B}_s$ mode offers a unique path to study $B_s$ mixing and rare decays, with potential for $\sim10^9$ $B_s\bar{B}_s$ pairs per year.
• CP asymmetries in $D^0$ decays down to $\mathcal{O}(10^{-4})$ and direct CP violation in $D^\pm \to K_{S/L}\pi^\pm$ at $\mathcal{O}(10^{-3})$ are critical probes of New Physics.