Patterns of New Physics in $b\to s\ell^+\ell^-$ transitions in the light of recent data (1704.05340v2)

Abstract: In the Standard Model (SM), the rare transitions where a bottom quark decays into a strange quark and a pair of light leptons exhibit a potential sensitivity to physics beyond the SM. In addition, the SM embeds Lepton Flavour Universality (LFU), leading to almost identical probabilities for muon and electron modes. The LHCb collaboration discovered a set of deviations from the SM expectations in decays to muons and also in ratios assessing LFU. Other experiments (Belle, ATLAS, CMS) found consistent measurements, albeit with large error bars. We perform a global fit to all available $b\to s\ell^+\ell^-$ data ($\ell=e,\mu$) in a model-independent way allowing for different patterns of New Physics. For the first time, the NP hypothesis is preferred over the SM by $5\,\sigma$ in a general case when NP can enter SM-like operators and their chirally-flipped partners. LFU violation is favoured with respect to LFU at the 3-4$\,\sigma$ level. We discuss the impact of LFU-violating New Physics on the observable $P_5^\prime$ from $B \to K^*\mu^+\mu^-$ and we compare our estimate for long-distance charm contributions with an empirical model recently proposed by a group of LHCb experimentalists. Finally, we discuss NP models able to describe this consistent pattern of deviations.

• The paper shows a global fit analysis revealing statistically significant new physics over the Standard Model at a 5σ level.
• It employs a model-independent approach focusing on key observables like P₅′, R_K, and R_K* to quantify deviations from SM predictions.
• The findings indicate lepton flavor universality violations, urging further exploration with future high-energy collider experiments.

Analyzing New Physics in $b\to s\ell^+\ell^-$ Transitions

The paper "Patterns of New Physics in $b\to s \ell^+\ell^-$ transitions in the light of recent data" tackles a significant issue in particle physics by examining deviations from the Standard Model (SM) predictions in $b\to s\ell^+\ell^-$ transitions. This research gains importance due to the potential sensitivity of these transitions to physics beyond the SM. In particular, the paper explores the implications of deviations observed by the LHCb collaboration and other experiments, which indicate possible Lepton Flavour Universality (LFU) violation.

Key Findings and Methodology

The authors perform a comprehensive global fit to existing $b\to s\ell^+\ell^-$ data, using a model-independent approach to test for various patterns of New Physics (NP). This analysis reveals that, for the first time, an NP hypothesis is preferred over the SM at a 5$\sigma$ level. The research identifies a specific preference for NP contributions altering LFU, with a 3-4$\sigma$ significance.

The empirical analysis is articulated around significant observables, notably the angular observable $P_5^\prime$ from $B \to K^*\mu^+\mu^-$ and the LFU-violating ratios $R_K$ and $R_{K^*}$. The statistical evidence suggests coherent patterns of NP that necessitate specific modifications to SM-like operators and their chirally-flipped counterparts.

Numerical Results and Significance

The results section presents the fit outcomes for various NP scenarios and effectively underscores their statistical significance compared to the SM predictions. These scenarios are well-documented, with SM pulls reaching over 5$\sigma$, indicating a robust preference for models beyond the SM that challenge the traditional LFU assumption.

Key numerical deviations are quantified, with observable tensions such as -2.9$\sigma$ for $P_5^\prime_{[4,6]}$, and 2.6$\sigma$ for $R_K^{[1,6]}$. These deviations underpin the hypothesis of NP's existence, providing a compelling argument for further exploration into these parameters.

Implications and Future Prospects

The research has considerable implications both theoretically and practically. Theoretically, the findings propose that our understanding of SM processes must adapt to accommodate observable deviations. Practically, the inquiry into NP could guide future experimental designs, aiming to pinpoint the exact nature of such new physics elements in high-energy particle interactions.

The analysis delineates numerous models capable of explaining the deviations, such as scenarios involving new heavy gauge bosons or leptoquarks. These models extend beyond the SM and offer concrete targets for collider experiments aiming to validate the presence of NP.

Looking forward, changes in theoretical predictions and experimental precision will be essential. Future measurements, particularly from the LHC and its upgrades, are crucial for refining the understanding of b-quark transitions and could lead to groundbreaking discoveries relating to NP.

Conclusion

This document substantially contributes to the ongoing debate regarding the nature of physics beyond the SM by demonstrating statistically significant deviations in $b\to s \ell^+\ell^-$ transitions. The research strengthens the case for NP with its methodological rigor and profound analytical depth, serving as a vital resource for physicists working towards a unified theory of fundamental interactions.