Quark Flavor Physics Research Articles

Quark flavor physics: Status and future prospects

Quark flavor physics is the study of hadrons, their properties, and their decays into other particles. As a discipline, it simultaneously catalogues the nature of physical states within the Standard Model of particle physics, and in doing so tests the consistency and completeness of the Standard Model’s description of reality. Following the discovery of the Higgs field, it is more essential than ever to critically examine the Standard Model’s own coherence. Precision studies of quark flavor are one of the most sensitive experimental instruments for this task. I give a brief and necessarily selective overview of recent developments in quark flavor physics and discuss prospects for the next generation of experiments and facilities, with an emphasis on the energy scales of beyond Standard Model physics probed by these types of measurements.

Flavour bounds on the flavon of a minimal and a non-minimal {mathcal {Z}}_2 times {mathcal {Z}}_N symmetry

We investigate flavour bounds on the {mathcal {Z}}_2 times {mathcal {Z}}_5 and {mathcal {Z}}_2 times {mathcal {Z}}_9 flavour symmetries. These flavour symmetries are a minimal and a non-minimal forms of the {mathcal {Z}}_2 times {mathcal {Z}}_N flavour symmetry, that can provide a simple set-up for the Froggatt–Nielsen mechanism. The {mathcal {Z}}_2 times {mathcal {Z}}_5 and {mathcal {Z}}_2 times {mathcal {Z}}_9 flavour symmetries are capable of explaining the fermionic masses and mixing pattern of the standard model including that of the neutrinos. The bounds on the parameter space of the flavon field of the {mathcal {Z}}_2 times {mathcal {Z}}_5 and {mathcal {Z}}_2 times {mathcal {Z}}_9 flavour symmetries are derived using the current quark and lepton flavour physics data and future projected sensitivities of quark and lepton flavour effects. The strongest bounds on the flavon of the {mathcal {Z}}_2 times {mathcal {Z}}_5 symmetry come from the D^0 - {{bar{D}}}^0 mixing. The bounds on the {mathcal {Z}}_2 times {mathcal {Z}}_9 flavour symmetry are stronger than that of the minimal {mathcal {Z}}_2 times {mathcal {Z}}_5 symmetry. The ratio R_{mu mu } provides rather robust bounds on the flavon parameters in the future phase-I and phase-II of the LHCb by leaving only a very small region in the allowed parameter space of the models.

Particle identification at FCC-ee

Equipping 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.

Leptoquarks and real singlets: A richer scalar sector behind the origin of dark matter

We investigate scenarios with $\mathcal{O}(1\mathrm{\,TeV})$ scalar leptoquarks that act as portals between the Standard Model and Dark Matter. We assume that Dark Matter is a scalar singlet $S$ which couples to a scalar leptoquark $\Delta$ and the Higgs boson via the terms in the scalar potential. In addition, the leptoquark is endowed with Yukawa couplings to quarks and leptons that may address the anomalies in $B$ meson decays. We consider the $SS$ annihilation cross sections to estimate the Dark Matter relic abundance and explore the interplay between astrophysical, collider and flavour physics bounds on such models. In the heavy Dark Matter window, $m_S > m_\Delta$, the leptoquark portal becomes the dominant mechanism to explain the Dark Matter abundance. We find that the leptoquark Yukawa couplings, relevant for quark and lepton flavour physics, are decoupled from the dark matter phenomenology. By focussing on a scenario with a single leptoquark state, we find that relic density can only be explained when both $\Delta$ and $S$ masses are lighter than $\mathcal{O}(10\mathrm{\,TeV})$.

New perspective in searching for axionlike particles from flavor physics

We propose new perspective in searching for axion-like particles (ALPs) from quark and lepton flavor physics: measurements of the time-dependent CP asymmetry in $B^0 \to K_S^0 \pi^0 \gamma$ and the branching ratio of $B_s \to e^\pm \mu^\mp$ decay possess, along with the anomalous magnetic moment of muon. In the mass range of sub-GeV, accessible by the flavorful ALPs search, the experimental sensitivity for these flavor observables reaches the maximum at around the pion mass scale (called the {\it sweetest} spots), where a couple of loopholes (unexplored regions) for the ALP parameter space have heretofore been present, because of an unavoidable contamination with pion background events. The proposed complementary probes can precisely determine the ALP coupling to photon at these {\it sweetest} spots/loopholes, and will significantly help cover whole parameter spaces in the ALP search including the present loopholes in the future.

Phenomenology of inclusive overline{B}to {X}_s{mathrm{ell}}^{+}{mathrm{ell}}^{-} for the Belle II era

With the first data being recorded at Belle II, we are at the brink of a new era in quark flavour physics. The many exciting new opportunities for Belle II include a full angular analysis of inclusive overline{B}to {X}_s{mathrm{ell}}^{+}{mathrm{ell}}^{-} which has the potential to reveal new physics, in particular by its interplay with the exclusive b → sℓ+ℓ− counterparts studied extensively at LHCb. In this paper, we present fully updated Standard Model predictions for all angular observables necessary for this endeavour. These predictions are tailored to Belle II and include an elaborate study of the treatment of collinear photons which become crucial when aiming for the highest precision. In addition, we present a phenomenological study of the potential for Belle II to reveal possible new physics in the inclusive decay channel, both in an independent manner and in combination with exclusive modes.

Opportunities for Lattice QCD in quark and lepton flavor physics

This document is one of a series of whitepapers from the USQCD collaboration. Here, we discuss opportunities for lattice QCD in quark and lepton flavor physics. New data generated at Belle II, LHCb, BES III, NA62, KOTO, and Fermilab E989, combined with precise calculations of the relevant hadronic physics, may reveal what lies beyond the Standard Model. We outline a path toward improvements of the precision of existing lattice-QCD calculations and discuss groundbreaking new methods that allow lattice QCD to access new observables.

Modeling theoretical uncertainties in phenomenological analyses for particle physics

The determination of the fundamental parameters of the Standard Model (and its extensions) is often limited by the presence of statistical and theoretical uncertainties. We present several models for the latter uncertainties (random, nuisance, external) in the frequentist framework, and we derive the corresponding p values. In the case of the nuisance approach where theoretical uncertainties are modeled as biases, we highlight the important, but arbitrary, issue of the range of variation chosen for the bias parameters. We introduce the concept of adaptive p value, which is obtained by adjusting the range of variation for the bias according to the significance considered, and which allows us to tackle metrology and exclusion tests with a single and well-defined unified tool, which exhibits interesting frequentist properties. We discuss how the determination of fundamental parameters is impacted by the model chosen for theoretical uncertainties, illustrating several issues with examples from quark flavor physics.

Flavour physics: Status and perspectives

The pattern of quark flavour violation predicted by the Standard Model agrees within theoretical and experimental uncertainties with the available data except for a number of intriguing anomalies that require further investigation. In the coming flavour precision era a multitude of new observables will be measured and the accuracy of the measurements of quark flavour violating rare processes and of the relevant lattice QCD calculations will be significantly improved. This will allow us not only to clarify these anomalies but also hopefully to discover new physics (NP). On the other hand a discovery of charged lepton flavour violation and of non‐vanishing electric dipole moments (EDMs) of particles would be a clear signal of NP. Most importantly the unique role of quark and lepton flavour physics and of EDMs in the coming years will be to allow us to get insight into the dynamics well beyond the reach of high energy processes at the LHC. In fact scales as short as 10−21 m (Zeptouniverse) corresponding to energy scale of 200 TeV or even shorter distance scales can be explored in this manner. We discuss the requirements that have to be met for such a flavour expedition to the Zeptouniverse to be successful. In particular we emphasize the power of correlations between flavour observables in the search for NP. In this context the proposed DNA charts allow for a clear distinction between various alternatives for the new dynamics at the LHC scales and at much shorter distance scales. image

An explicit Z ′-boson explanation of the B → K ∗ μ + μ − anomaly

A global fit to the recent B->K*mu+mu- data shows indications for a large new-physics contribution to the Wilson coefficient of the semi-leptonic vector operator. In this article we consider a simple Z'-boson model of 3-3-1 type that can accommodate such an effect without violating any other constraint from quark-flavour physics. Implications for yet unobserved decay modes such as B->Xsnunubar and longstanding puzzles like B->piK are also discussed. The Z'-boson masses required to address the observed anomaly lie in the range of 7 TeV. Such heavy Z' bosons evade the existing bounds from precision data and direct searches, and will remain difficult to discover even at a high-luminosity LHC. The potential of an ILC as well as the next generation of low-energy parity-violation experiments in constraining the Z'-boson parameter space is also examined.

Colloquium: New physics search with flavor in the LHC era

We give a status report on quark flavour physics in view of the latest data from the B factories and the LHC, and discuss the impact of the latest experimental results on new physics in the MFV framework. We also show some examples of the implications in supersymmetry.

The Fermilab Proposal P996: Precision Measurement of [formula omitted

The high precision measurement of the ultra-rare K + → π + ν ν ¯ decay at Fermilab would be one of the most incisive probes of quark flavor physics this decade. The dramatic physics reach of a precision measurement of K + → π + ν ν ¯ is due to three factors. 1) The Standard Model prediction for the K + → π + ν ν ¯ and K L 0 → π 0 ν ν ¯ branching fractions are broadly recognized as theoretically robust to the 2-4% level. No other loop-dominated quark process can be predicted with this level of certainty. 2) The K + → π + ν ν ¯ branching fraction is highly suppressed in the Standard Model to the level of less than 1 part in 10 billion. This suppression allows physics beyond the Standard Model to contribute noticeably to the branching fraction with enhancements of up to factors of 5 above the Standard Model level. 3) The certainty with which the Standard Model contribution to K + → π + ν ν ¯ is known permits a 5 σ discovery potential for new physics even for enhancements of the branching fraction as small as 20%. This sensitivity is unique in quark flavor physics and probes essentially all models of new physics that couple to quarks within the reach of the LHC. Further, precision measurement of K + → π + ν ν ¯ is sensitive to many models of new physics far beyond the direct mass reach of the LHC. The experimental challenge of measuring K + → π + ν ν ¯ at the 1 in 10-billion Standard Model rate has been met successfully. Several events of the K + → π + ν ν ¯ process have been clearly observed at BNL. Operating the Tevatron after Run-II as a 120 GeV high-duty factor synchrotron “Stretcher” offers the opportunity to reach more than two orders of magnitude greater sensitivity yielding a 1000-event experiment based on incremental improvements to the techniques refined and firmly demonstrated at BNL. The Fermilab Stretcher would be a unique facility that would provide ideal properties for such rare-decay experiments, allowing the demonstrated performance of the AGS experiment to be extrapolated with confidence to an experiment driven by the Fermilab Stretcher.

Overview of the LHCb calorimeters

LHCb, one of the four LHC experiments, is dedicated to the study of CP violation and rare decays in the B meson sector. It aims at completing the understanding of the quark flavor physics and at revealing signs of new physics beyond the standard model. The goal of the LHCb calorimeter is twofold. On the one hand, the calorimeter system has to provide a fast response for the first level trigger (L0) on the nature of the meson decay. Thus, the scintillator pad detector and the preshower provide a good γ / charged particle and electron/ π 0 separation and the electromagnetic and hadronic calorimeters give a fast transverse energy determination. On the other hand, it provides offline precision measurements and particle identification. The calorimeter system consists of four sub-detectors. They are described in the first section, emphasising the technical choices and the similarities among those components. The second part concerns the monitoring and calibration tools and procedures that will be applied to have a satisfactory running of the detector.

Charm Physics with BES-III at BEPC-II

We report on the charm physics potential at BES-III at BEPC-II which will make significant contribution to quark flavor physics this decade. The charm physics program will include studies of leptonic, semileptonic and hadronic charm decays, and tests for physics beyond the Standard Model. Event samples of the order of 30 million $\DD$ pairs, 2 million $\DspDsm$ pairs at threshold and $10\times 10^9$ $J/\psi$ decays will be produced with one year design luminosity. High precision charm data will enable us to validate forthcoming Lattice QCD calculations at the few percent level. These can then be used to make precise measurements of CKM elements, $V_{cd}$, $V_{cs}$, $V_{ub}$, $V_{cb}$ and $V_{ts}$, which are useful to improve the accuracy of test of the CKM unitarity.

CP Violation and the CKM Matrix

▪ Abstract Our knowledge of quark-flavor physics and CP violation has increased tremendously over the past five years. It is confirmed that the Standard Model correctly describes the dominant parts of the observed CP-violating and flavor-changing phenomena. Not only does CP violation provide some of the most precise constraints on the flavor sector, but several measurements performed at the B-factories achieved much better precision than expected. We review the present status of the Cabibbo-Kobayashi-Maskawa (CKM) matrix and CP violation, recollect the relevant experimental and theoretical inputs, display the results from the global CKM fit, and discuss their implications for the Standard Model and some of its extensions.

Status of Lattice Flavor Physics

This talk reviews recent lattice QCD calculations relevant for quark flavor physics. Since lattice results must be accurate and precise to play a definitive role in phenomenology, the focus is on unquenched results of quantities which can be calculated most reliably.

On the electron–positron energy asymmetry in KL→π0e+e−

Motivated by some new experimental and theoretical efforts, we update the theoretical analysis of the electron–positron energy asymmetry, which arises, in KL→π0e+e−, from the two-photon intermediate state in the Standard Model. It is found that the measurement of this asymmetry in future experiments may increase our understanding of the KL,S→π0e+e− decays, which would thus provide some useful information on quark flavor physics. Meanwhile, in the Standard Model the electron–positron energy asymmetry in the decay of KS→π0e+e− is expected to be vanishingly small, therefore the asymmetry in KS→π0e+e− might be a very interesting quantity to explore new physics scenarios.

CLEO-c and CESR-c: A new frontier in strong and weak interactions

We report on the physics potential of a charm and QCD factory, based on a proposal for the conversion of the existing CESR machine and CLEO detector: “CESR-c and OLEO-c”. Such a facility will make major contributions to the field of quark flavor physics in this decade. It may also provide the best chance for understanding non-perturbative QCD, which is essential to understanding the strongly-coupled sectors of the new physics that lies beyond the Standard Model.

Aspects of Soft and Spontaneous CP Violation(quark flavor physics)

Aspects of Soft and Spontaneous CP Violation(quark flavor physics)