New Physics Exploration Through Flavor Tagging at FCC-ee: A Comprehensive Study of Four-Fermion Interactions

Core Concepts

The FCC-ee collider presents a unique opportunity to probe for new physics beyond the Standard Model by precisely measuring hadronic and leptonic cross-section ratios, enabling us to constrain flavor-conserving four-fermion interactions with unprecedented accuracy.

Abstract

• Bibliographic Information: Greljo, A., Tiblom, H., & Valenti, A. (2024). New Physics Through Flavor Tagging at FCC-ee. arXiv preprint arXiv:2411.02485.
• Research Objective: This paper investigates the potential of the Future Circular Electron-Positron Collider (FCC-ee) to uncover new physics beyond the Standard Model (BSM) by precisely measuring ratios of hadronic cross sections.
• Methodology: The authors employ the Standard Model Effective Field Theory (SMEFT) framework to analyze the sensitivity of FCC-ee to flavor-conserving four-fermion (4F) interactions. They focus on observables such as ratios of hadronic cross sections (Rb, Rc, Rs, Rt) and leptonic cross sections (Rτ, Rµ, Re) at different energy stages of the FCC-ee (WW, Zh, and ttbar thresholds). The study leverages advancements in machine learning-based flavor tagging to optimize the analysis and estimate the achievable precision for these observables.
• Key Findings: The study reveals that FCC-ee can achieve sub-permille precision in measuring hadronic ratios, improving upon LEP-II measurements by two orders of magnitude. This precision allows for probing energy-enhanced 4F effects, with each energy stage offering competitive sensitivity. The analysis demonstrates that FCC-ee can effectively probe flavor-conserving 4F operators involving heavy quark flavors and all lepton flavors, significantly improving upon current LEP-II and LHC bounds.
• Main Conclusions: The authors conclude that FCC-ee offers an unprecedented opportunity to explore new physics through precision measurements of hadronic and leptonic cross-section ratios. The study highlights the potential of these measurements to constrain flavor-conserving 4F interactions, offering a powerful tool to test the SM and search for BSM physics.
• Significance: This research is highly significant in the field of particle physics as it explores the potential of a future collider to probe fundamental questions about the nature of matter and forces. The high precision achievable at FCC-ee opens up new avenues for discovering and characterizing new particles and interactions, potentially revolutionizing our understanding of the universe.
• Limitations and Future Research: The study acknowledges the need for further theoretical improvements in calculating radiative corrections for leptonic observables to fully exploit the experimental precision achievable at FCC-ee. Additionally, dedicated experimental analyses are required to assess systematic uncertainties, particularly for forward-backward asymmetries. Future research could explore the potential of other observables and analysis techniques to further enhance the sensitivity to new physics at FCC-ee.

Stats

FCC-ee is projected to have a luminosity of 10 ab−1 at the WW threshold.
The SM predicts σ(¯ee →hadrons) ≈34 pb and Rb ≈0.17 at the WW threshold.
The optimal working points for flavor tagging are ϵb
b = 0.67, ϵs
s = 0.07, and ϵc
c = 0.60 at the WW threshold.
The relative precision achievable for Rb, Rs, and Rc at the WW threshold is 1.7×10−4, 3.7×10−3, and 1.4×10−4, respectively.
The tree-level value of Rt is approximately 0.11 at √s = 365 GeV.
The relative statistical uncertainty for Rt is approximately 1.2×10−3 with 1.5 ab−1 of data.
The relative errors for Rτ,µ are {1.6, 3.5, 9.7} × 10−4 at the WW, Zh, and ttbar thresholds, respectively.

Quotes

"The FCC-ee emerges as the envisioned next stride in high-energy physics, building on the foundational achievements of the Large Electron–Positron Collider (LEP) and the Large Hadron Collider (LHC)."
"This paper focuses on the search for new short-distance physics that could manifest through four-fermion (4F) contact interactions."
"Our results indicate up to a two-order-of-magnitude improvement in precision, providing an unprecedented test of the SM."

Key Insights Distilled From

New Physics Through Flavor Tagging at FCC-ee

by Admir Greljo... at arxiv.org 11-06-2024

https://arxiv.org/pdf/2411.02485.pdf

Deeper Inquiries

How might advancements in quantum computing impact the analysis and interpretation of data from future colliders like FCC-ee?

Advancements in quantum computing hold immense potential to revolutionize the analysis and interpretation of data from future colliders like FCC-ee. Here's how:

Enhanced Monte Carlo Simulations: Quantum computers excel at handling complex probabilistic calculations, making them ideal for improving the accuracy and efficiency of Monte Carlo simulations. These simulations are crucial for modeling particle collisions, understanding detector responses, and estimating backgrounds. Quantum algorithms like Quantum Monte Carlo could significantly speed up these simulations, enabling more precise theoretical predictions and better discrimination between SM processes and potential NP signals.

Advanced Machine Learning: Quantum machine learning algorithms can potentially outperform classical algorithms in analyzing vast datasets, like those expected from FCC-ee. This could lead to improved flavor tagging algorithms, more efficient event reconstruction, and enhanced sensitivity to subtle NP signatures. For instance, quantum-enhanced deep learning could be used to optimize the identification of b-jets, crucial for precise measurements of Rb and other observables.

Tackling Theoretical Challenges: Quantum computing could provide new tools for tackling challenging theoretical calculations in quantum field theory. This could involve developing quantum algorithms for perturbative calculations, lattice QCD simulations, or even exploring non-perturbative regimes. Such advancements could lead to more precise SM predictions for observables like Ra, Rℓ, and reduce theoretical uncertainties, maximizing the sensitivity to NP effects.

Data Storage and Processing: The unprecedented data volume generated by FCC-ee poses significant storage and processing challenges. Quantum computing, combined with classical techniques, could offer novel solutions for handling this data deluge. Quantum algorithms for data compression and efficient search could be employed, while quantum-inspired classical algorithms could optimize data analysis pipelines.
However, it's important to acknowledge that large-scale, fault-tolerant quantum computers suitable for these tasks are still under development. The timeline for their practical application in high-energy physics remains uncertain. Nevertheless, the potential benefits of quantum computing for FCC-ee data analysis are significant and warrant continued research and development.

Could the observed flavor anomalies be explained by alternative mechanisms beyond four-fermion interactions, and how would these be tested at FCC-ee?

While the paper focuses on four-fermion interactions as a potential explanation for flavor anomalies, alternative mechanisms could also be at play. Here are a few examples and how FCC-ee could test them:

Leptoquarks: These hypothetical particles carry both lepton and quark quantum numbers and could mediate flavor-violating transitions. FCC-ee could search for direct production of leptoquarks through their resonant signatures in e+e− collisions. The high luminosity and clean environment would allow for sensitive searches, complementing LHC searches.

Z′ bosons: New heavy neutral gauge bosons, often referred to as Z′ bosons, could couple to quarks and leptons in a non-universal way, leading to flavor anomalies. FCC-ee could indirectly probe Z′ bosons through their contributions to precision electroweak observables. Deviations from SM predictions in observables like Ra, Rℓ, and asymmetries could hint at the presence of a Z′ boson.

Extended Higgs Sector: Models with additional Higgs bosons could also contribute to flavor anomalies. For instance, a Two-Higgs-Doublet Model (2HDM) with flavor-violating couplings could explain some of the observed anomalies. FCC-ee could search for direct production of these additional Higgs bosons, particularly in association with heavy fermions.

Composite Models: In these scenarios, quarks and leptons are considered composite objects, and their interactions are mediated by new strong dynamics. Flavor anomalies could arise from the exchange of composite resonances. FCC-ee could probe these models by searching for deviations in the angular distributions of fermion pair production, which would be sensitive to the compositeness scale.
FCC-ee's ability to perform precision measurements across a wide range of energies and with various final states makes it a powerful tool for disentangling different NP scenarios. By combining information from different observables, including those discussed in the paper and beyond, FCC-ee can provide crucial insights into the nature of flavor anomalies and the underlying physics.

If new physics is discovered at FCC-ee, what implications might it have for our understanding of the fundamental laws of nature and the evolution of the universe?

The discovery of new physics at FCC-ee would be a monumental event with profound implications for our understanding of the universe:

Beyond the Standard Model: A confirmed NP signal would definitively demonstrate the incompleteness of the SM, ushering in a new era in particle physics. It would provide crucial guidance for theoretical model building, pointing towards the correct framework for extending our understanding of fundamental particles and forces.

Hierarchy Problem and Electroweak Symmetry Breaking: New particles or interactions discovered at FCC-ee could shed light on the hierarchy problem, which questions the vast difference between the electroweak scale and the Planck scale. Understanding the mechanism of electroweak symmetry breaking, responsible for giving mass to particles, is intimately tied to this problem, and NP discoveries could provide crucial missing pieces.

Dark Matter and Dark Energy: The nature of dark matter and dark energy, constituting the majority of the universe's energy content, remains one of the biggest mysteries in modern physics. New particles or interactions discovered at FCC-ee could potentially interact with the dark sector, providing insights into the properties of dark matter and its role in the universe's evolution.

Early Universe Cosmology: The high energies probed by FCC-ee correspond to conditions present in the very early universe. Discoveries at this energy scale could have profound implications for our understanding of cosmology, potentially impacting models of inflation, baryogenesis, and the formation of large-scale structures.

Grand Unified Theories: The discovery of new particles or forces could provide evidence for Grand Unified Theories (GUTs), which attempt to unify the fundamental forces of nature into a single framework. FCC-ee's ability to precisely measure gauge couplings could offer hints towards the energy scale at which unification might occur.

Fundamental Symmetries: New physics could reveal unexpected violations of fundamental symmetries, such as CP symmetry, which is closely related to the matter-antimatter asymmetry in the universe. Such discoveries would have profound implications for our understanding of the fundamental laws of nature.
The discovery of new physics at FCC-ee would not only revolutionize particle physics but also have ripple effects across various fields, from cosmology and astrophysics to condensed matter physics. It would open new avenues of exploration, leading to a deeper understanding of the universe's fundamental constituents and its evolution.