Quirks in Quark Flavour Physics

Croatia (Zadar, Croatia)


Zadar, Croatia

Alexander Lenz (Siegen U), Blazenka Melic, Danny van Dyk (TU München), Thomas Mannel (Siegen U)

We will discuss the state of the current anomalies, puzzles, and quirks in quark flavour physics. Participants will contribute in the fields of experimental physics, phenomenology, and lattice field theory.


Quark flavour physics has been instrumental in creating the standard model of particle physics. The comparison of precise theory predictions and  corresponding precise measurements enabled the prediction of the charm and top quark and their masses prior to their discovery. In 2022 we might be in an  even more exciting position: the currently observed B anomalies could point towards the existence of new degrees of freedom that make up the long  sought-after extension of the Standard model at higher energies. In this workshop we will bring together experts in Quark Flavour Physics working in experiment, phenomenology, and lattice QCD to review the field of quark flavour physics and to pave the way for future developments.


The workshop will take place in the beautiful coastal city of Zadar, Croatia.

Light Installation in Zadar

Sunset in ZadarChurch of St. DonatusZadar, Porta Terraferma

  • Aleksey Rusov
  • Alessandro Barone
  • Alexander Lenz
  • Alexei Pivovarov
  • Aliaksei Kachanovich
  • Andreas Juettner
  • Andrej Lozar
  • Anja Novosel
  • Benjamin Grinstein
  • Blazenka Melic
  • Christoph Schwanda
  • Christopher Sachrajda
  • Daniel Moreno
  • Danny van Dyk
  • Gael Finauri
  • Gustavo C. Branco
  • Ilja Doršner
  • Ivan Nisandzic
  • J Tobias Tsang
  • James Gratrex
  • Javier Virto
  • Jernej F. Kamenik
  • Joaquim Matias
  • Johannes Albrecht
  • Karol Adamczyk
  • Kevin Olschewsky
  • Luka Leskovec
  • Luka Santelj
  • Luka Senekovič
  • Marcel Wald
  • Marco Fedele
  • Margarida Nesbitt Rebelo
  • Maria Laura Piscopo
  • Maria Smizanska
  • Marko Bračko
  • Marko Starič
  • Marvin Zanke
  • Matthew Black
  • Matthew Wingate
  • Michele Tammaro
  • Mikhail Shifman
  • Muslem Rahimi
  • Méril Reboud
  • Nico Gubernari
  • Oliver Witzel
  • Paolo Gambino
  • Philip Lüghausen
  • Philipp Böer
  • Stephan Kürten
  • Sébastien Descotes-Genon
  • Thomas Mannel
  • Ulrich Nierste
  • Vladyslav Shtabovenko
  • William Parrott
Conference Dinner & Excursion
Conference Fee: Billing Information
    • Day 1: Morning 1
      • 1
        Speakers: Alexander Lenz (Siegen University), Blazenka Melic, Danny van Dyk (TU München)
      • 2
        Status of the Global Fits and Next Steps

        In this talk I will present the most updated status of the global fits to all b->sll data. An anatomy of the main observables involved will be discussed together with their theoretical aspects. The most relevant scenarios of New Physics will be presented showing the degeneracy we observe systematically in all these years. I will present a full understanding of the reason of this degeneracy of scenarios and more importantly how to break it in the (very) near future. This proposal will constitute a fundamental path to identify the scenario of New Physics that is realized in Nature.

        Speaker: Prof. Joaquim Matias (Universitat Autonoma de Barcelona and IFAE)
      • 3
        Improved Global Theory Analysis of b → sll data

        We parametrize nonlocal contributions in $b\to s\ell\ell$ transitions using a $z$-expansion fitted on theory inputs steaming from a light-cone operator product expansion and experimental measurements. This approach allows us to update the Standard Model predictions of experimental observables in the $B\to K\ell\ell$, $B \to K^*\ell\ell$ and $B_s\to\phi\ell\ell$, with a unprecedented control on the hadronic uncertainties. We finally use these predictions for a new physics fit, confirming the discrepancy of these channels with respect to the Standard Model.

        Speaker: Méril Reboud (TUM)
      • 4
        Form factors for Semileptonic B(s) decays

        Exclusive semileptonic $B_{(s)}$ decays are theoretically described by scalar and vector form factors. Combining experimental branching fraction measurements with theoretical form factor predictions, the CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$ can be extracted. In addition $R$-ratios testing lepton flavor universality can be derived to directly compare standard model predictions to experimental results.

        We present our lattice quantum chromodynamics calculation to determine form factors for $B_s\to D_s \ell\nu$, $B_s\to K \ell\nu$, and $B\to \pi\ell \nu$ decays. Starting with the lattice calculation to extract the form factors, we detail how the full error budget is obtained and discuss the challenges to cover the full range of allowed momentum transfer ($q^2$) by performing a kinematical $z$ extrapolation.

        Our calculations are based on RBC-UKQCD's set of 2+1 flavor domain wall Iwasaki gauge field configurations featuring three lattice spacings of $a^{-1}$ = 1.78, 2.38, and 2.78 GeV. We simulate up/down, strange, and charm quarks using domain-wall fermions and use the relativistic heavy quark action for the bottom quarks.

        Speaker: Oliver Witzel (Universität Siegen)
    • 10:30 AM
      Discussion with Coffee/Tea/...
    • Day 1: Morning 2
      • 5
        Asymmetric Leptoquark Pair Production @LHC

        I will introduce two novel mechanisms to produce pairs of leptoquarks at Large Hadron Collider and present several case studies to discuss the associated phenomenological implications.

        Speaker: Ilja Doršner (University of Split)
      • 6
        $(g-2)_\mu$, B anomalies and DM: a loop model tale

        In this talk I will review how the anomalous magnetic moment of the muon and the B anomalies can be addressed by a combined explaination, by means of loop models characterized by minimal field content. Moreover, I will show how some of these model can also provide a viable DM candidate, accounting for the measured relic density while evading direct and indirect DM constraints.

        Speaker: Marco Fedele (KIT)
    • 12:30 PM
      Lunch and Swimming
    • Day 1: Afternoon 1
      • 7
        The search for new physics in $B \to K \ell^+\ell^-$ and $B \to K \nu\bar{\nu}$ using precise lattice QCD form factors

        We present HPQCD's improved scalar, vector and tensor form factors for $B \to K$ decay using the Highly Improved Staggered Quark formalism for more accurate normalisation of the weak currents and working on very fine lattices to cover the full physical $q^2$ range. Our uncertainties at $q^2=0$ are a factor of three better than earlier work.

        We compare Standard Model observables using our form factors to experimental measurements for the rare FCNC processes $B \to K \ell^+\ell^-$ and $B \to K \nu\bar{\nu}$ and discuss the significance of the tensions that arise.

        Speaker: William Parrott (University of Glasgow)
      • 8
        Recent Belle II results on electroweak and radiative penguins

        Decays of B mesons that proceed through electroweak and radiative penguin amplitudes attract significant attention due to a number of observed discrepancies between the standard-model predictions and the results. Belle II is expected to perform measurements on channels closely related to those exhibiting anomalies and that are uniquely available to Belle II. These include b -> s(d) nu nubar and b -> s(d) tau+ tau- transitions. We present recent results on b -> s l+ l- , and b-> s nu nu transitions. In addition, decays of B mesons that proceed through radiative penguin amplitudes are probes of a large class of generic non-SM models for which Belle II has unique reach. We present recent results from an inclusive b -> s gamma analysis

        Speaker: Jim Libby (IIT Madras)
    • 4:00 PM
      Discussion with Coffee/Tea/...
    • Day 1: Afternoon 2
      • 9
        $B$-meson decay into a proton and dark antibaryon from QCD light-cone sum rules

        The recently developed $B$-mesogenesis scenario predicts the decays of $B$ mesons into a baryon and a hypothetical dark antibaryon in the final state. In this work, we suggest to apply QCD light-cone sum rules to estimate the partial width of the simplest exclusive decay mode $B^+\to p \Psi$, where $\Psi$ is a dark antibaryon. We consider two sample models of $B$-mesogenesis and identify the three-quark effective operators relevant for these decays. Furthermore, we calculate the $B\to p$ hadronic matrix elements of these operators applying light-cone sum rules with nucleon light-cone distribution amplitudes in the leading order and to leading twist accuracy. Our main result is the partial width of $B^+\to p \Psi$ decay as a function of the $\Psi$ mass and the four-fermion quark-$\Psi$ coupling.

        Speaker: Marcel Wald (University of Siegen)
    • Day 2: Morning 1
      • 10
        Recent Belle II results related to anomalies in semileptonic and hadronic B decay

        The rate of semitauonic B decays has been consistently above theory expectations since these decays were first measured. Recently significant differences between the forward-backward asymmetry in B -> Denu and B -> Dmunu were also reported. Belle II data are well suited to probe these anomalies. The low-background collision environment along with the possibility of partially or fully reconstructing one of the two B mesons in the event offer high precision. This talk presents recent Belle II results on lepton flavor universality tests based on B->D(*)ell nu decays. We also discuss anomalies in hadronic B decay such as the $K\pi$ puzzle and the $b\to D^{(*)}h$ branching fractions.

        Speaker: Jim Libby (IIT Madras)
      • 11
        NLO QCD corrections to inclusive $b \rightarrow c \ell \bar{\nu}$ decay spectrum up to $1/m_b^3$

        We present analytical results for higher order corrections to the decay spectrum of inclusive semileptonic heavy hadron weak decays using the heavy quark expansion (HQE). We describe the analytical computation of the spectrum of the leptonic invariant mass for $B \rightarrow X_c \ell \bar{\nu}$ up to terms of order $1/m_b^3$ within the HQE at next-to-leading order (NLO) in $\alpha_s$. The full dependence of the differential rate on the mass of the final-state quark is taken into account. We discuss the implications of our results for the precise determination of the CKM matrix element $|V_{\rm cb}|$.

        Speaker: Dr Daniel Moreno (Siegen University)
      • 12
        Inclusive semileptonic decays on the lattice

        I will describe the first results of a new method to compute inclusive semileptonic decays on the lattice and the future perspectives.

        Speaker: Paolo Gambino
    • 10:30 AM
      Discussion with Coffee/Tea/...
    • Day 2: Morning 2
      • 13
        New Light-Cone Sum Rules for b-quark Decays

        QCD light-cone sum rules (LCSRs) are a method to calculate the relevant hadronic matrix elements in exclusive $b$-quark decays. I focus on the LCSRs with $B$ or $\Lambda_b$ distribution amplitudes. The versatility of this method allows to apply it to a wide variety of decays, especially to those where lattice QCD calculations are not available yet.
        In this spirit, I present a first calculation of the $B\to D^{**}$ form factors, and an estimate of the ``annhilation-like'' contributions in $\Lambda_b\to\Lambda \ell\ell$ using LCSRs.

        Speaker: Nico Gubernari (technische universität münchen)
      • 14
        Systematic Parametrization of the Leading $B$-meson Light-Cone Distribution Amplitude

        Processes involving the $B$-meson require non-perturbative input due to the nature of the strong interaction;
        one kind of input are the light-cone distribution amplitudes (LCDA).
        For the first time, we constructed a systematic parametrisation for leading-power LCDA.
        I present the construction itself as well as some demonstrations at the hand of common models and finally a pseudo-phenomenological inference procedure.

        Speaker: Philip Lüghausen (TUM)
    • 12:30 PM
      Lunch and Swimming
    • Day 2: Afternoon 1
      • 15
        A lattice QCD study of $B \to \rho \ell \nu$

        The CKM matrix element $V_{ub}$ is both the smallest and least known of all CKM matrix elements; its current value has been determined in many ways, but directly primarily through the exclusive process $B\to\pi\ell\nu$. In this talk, we will present our progress towards a lattice QCD determination of the $V_{ub}$ matrix element from a novel transition - $B\to \rho \ell \nu$. On this ensemble, with $N_f=2+1$ clover fermions with masses corresponding to $m_\pi$ ~ $320$ MeV and $L=3.6$ fm, the $\rho$ appears as a resonance in $\pi\pi$ scattering. We will briefly introduce the theoretical framework and discuss some preliminary results.

        Speaker: Luka Leskovec (Jozef Stefan Institute)
      • 16
        Analysis of lattice data for heavy-light semileptonic form-factors

        In this talk I will discuss the analysis of lattice form-factor data for the exclusive decay of heavy-light mesons containing a bottom quark. Using simulation data from the RBC/UKQCD collaboration for $B_s\to K$, $B\to\pi$ and $B_s\to D_s$. I will address a number of questions arising and ideas for how to improve the analysis.

        Speaker: Andreas Juettner
    • 4:00 PM
      Discussion with Coffee/Tea/...
    • Day 2: Afternoon 2
      • 17
        Dispersive treatment of $B\to \gamma^{(*)}\ell\bar\nu$

        We discuss the Lorentz decomposition of $B \to \gamma^*$ matrix elements in terms of hadronic form factors, which are needed for a theory description of $B^- \to \ell^- \bar{\nu}_\ell \ell' \bar{\ell'}$ decays.
        Our approach closely follows the Bardeen–Tung–Tarach procedure and ensures freedom from kinematic singularities, which is needed to apply dispersion relations in the photon momentum. We compare our approach to others in the literature and point out that a complete basis of structures is important for phenomenological applications, even for the case of massless leptons. In particular, we explicitly show that the supposed “collinear enhancement” for small photon momentum transfer is due to an inconsistent treatment of finite lepton masses. For a prediction of the decay rate, we link the $B \to \gamma^*$ form factors to the well-established $B \to V$ form factors.

        Speaker: Marvin Zanke (HISKP, University of Bonn)
      • 18
        Radiative corrections to leptonic decays

        Lattice QCD computations of a number of physical quantities, including leptonic decay rates, yield sufficiently precise results that electromagnetic corrections need to be implemented to make further progress in determining the parameters of the Standard Model and checking consistency with the corresponding experimental results. After a brief introduction to the framework, I will present the latest results, obtained together with members of the RM123 collaboration, from our long-term project on $P\to\ell\nu_\ell$, $P\to\ell\nu_\ell\gamma$ and $P\to\ell\nu_\ell\ell^{\prime+}\ell^{\prime-}$ decays, where $P$ is a pseudoscalar meson, and $\ell$ and $\ell^\prime$ are charged leptons. The results will be compared to existing experimental measurements.

        Speaker: Christopher Sachrajda (University of Southampton)
      • 19
        Mixing of neutral $B$ mesons at NNLO

        In this talk I will report on the calculation of NNLO QCD corrections to the
        flavor observables in the mixing of neutral $B$ mesons and discuss their
        numerical impact. The physical relevance of this work stems from the fact
        that experimental measurements of e.g. the flavor mixing parameter
        $\Delta \Gamma_{12}^s$ have already achieved per cent level accuracy,
        while theoretical predictions are still affected by large uncertainties
        from uncalculated perturbative corrections. My presentation will be based
        on our recent publications arXiv:2106.05979 and arXiv:2202.12305.

        Speaker: Vladyslav Shtabovenko (KIT)
    • Social Events: Conference Dinner
    • Day 3: Morning 1
      • 20
        Testing the Standard Model with CP asymmetries in flavour-specific non-leptonic decays

        Motivated by recent indications that the rates of colour-allowed non-leptonic channels are in tension with their Standard Model predictions based on QCD factorisation, we investigate the potential to study CP asymmetries with these decays. In the Standard Model, these flavour-specific decays are sensitive to CP violation in $B^0_{(s)}$--$\bar{B}^0_{(s)}$ mixing, which is predicted with low uncertainties and can be measured precisely with semileptonic decays. Allowing beyond Standard Model contributions to the non-leptonic decay amplitudes, we derive explicit expressions for the flavour-specific CP asymmetries in a model-independent way. We find that BSM contributions could lead to significant enhancements to the CP asymmetries. Therefore measurements of these quantities and subsequent comparison with the CP asymmetries measured with semileptonic decays have potential to identify BSM effects without relying on Standard Model predictions that might be affected by hadronic effects. In addition, we discuss the experimental prospects, and note the excellent potential for a precise determination of the CP asymmetry in $\bar{B}_s \to D_s^+ \pi^-$ decays by the LHCb experiment.

        Speaker: Aleksey Rusov (University of Siegen)
      • 21
        Lifetimes of singly charmed hadrons

        I present updated predictions for inclusive charmed hadron lifetimes, focusing particularly on the baryons. These predictions are compatible with recent LHCb measurements, which measured the lifetime of $\Omega_c^0$ to be four times greater than earlier results. I will also discuss areas for potential improvement of the predictions, which will be much-needed in order to compete with experimental precision.

        Speaker: James Gratrex (Rudjer Boskovic Institute)
      • 22
        QED Effects in Exclusive B Decays

        Flavour physics is a precision laboratory for tests of the Standard Model. Although most of the theoretical work is devoted to the understanding of hadronic effects, QED corrections will become increasingly important when higher experimental precision is reached. Traditionally, QED effects in exclusive $B$ decays are computed under the assumption that mesons are pointlike up to small distances of order $1/m_B$. This is not justified as photons with wavelength smaller than the typical meson size $1/\Lambda_{\rm QCD}$ can resolve its partonic sub-structure. A proper treatment therefore requires factorization methods based on the $1/m_B$ expansion, which in QED are fairly new and still under development.
        I discuss the recent theoretical progress in this direction, with a particular focus on non-leptonic two-body B decays into light-light final states.

        Speaker: Philipp Böer (JGU Mainz)
    • 10:30 AM
      Discussion with Coffee/Tea/...
    • Day 3: Morning 2
      • 23
        Revisiting inclusive decay widths of charmed mesons

        I will present a comprehensive analysis of inclusive decay widths of charmed mesons within the framework of the HQE. The theoretical predictions for D-mesons lifetimes and their ratios are found to be in agreement with the current experimental data, albeit with very large uncertainties. Open questions and potential theoretical improvements will also be discussed.

        Speaker: Maria Laura Piscopo (University of Siegen)
      • 24
        QED factorization of two-body non-leptonic and semi-leptonic $B$ to charm decays

        Two-body non-leptonic $B$ decays with heavy-light final states, like $B_s \to D \pi$ and $B \to D K$, are among the theoretically cleanest non-leptonic decays as penguin loops do not contribute. They can be described using QCD factorization which relies on the heavy quark expansion. Advancing the theoretical calculations of such decays requires also a careful analysis of QED effects. In this talk we present a treatment of both virtual and ultrasoft real QED effects within a QCD $\times$ QED factorization framework of the non-leptonic and semi-leptonic $B$ to $D$ decays. In particular, due to recent discrepancies between theory and experimental data, we focus on ratios of non-leptonic over semi-leptonic decay rates, which are theoretically clean observables as the form factor dependence drops significantly. We found QED corrections to the amplitude to be at the sub-percent level, while at the level of the rate, ultrasoft photon effects can produce a correction up to a few percent, requiring a careful treatment of such effects in the experimental analyses.

        Speaker: Gael Finauri (TUM)
    • 12:30 PM
      Lunch and Swimming
    • Social Events: Excursion
    • Day 4: Morning 1
      • 25
        Decay rate of the $B_c$ meson in the Standard Model

        The Standard Model decay rate of the $B_c$ meson is discussed together with a novel approach based on the usage of experimental data in combination with an operator product expansion. In the new method differences of $B$, $D$ and $B_c$ meson widths are considered, for which the free-quark contributions drop out, possibly leading to a reduction of the uncertainty of the theoretical prediction.

        Speaker: Benjamin Grinstein (UCSD)
      • 26
        CP violation in B mixing beyond next-to-leading order

        I discuss the recently finished calculation of the next-to-next-to-leading order corrections to the CP asymmetry in flavour-specific $B_{d,s}$ decays and the phenomenological studies
        which will be possible with better data.

        Speaker: Prof. Ulrich Nierste
    • 10:30 AM
      Discussion with Coffee/Tea/...
    • Day 4: Morning 2
      • 27
        Inclusive semi-leptonic B(s) mesons decay from Lattice QCD

        We address the non-perturbative calculation of the decay rate of the inclusive semi-leptonic B(s) mesons decay from lattice QCD. Precise theoretical Standard Model predictions are key ingredients in searches for new physics. This type of computation may eventually provide new insight into the long-standing tension between the inclusive and exclusive determination of the $V_{cb}$ and $V_{ub}$ CKM matrix elements.
        We perform a pilot lattice computation for $B_s \rightarrow X_c l\bar{\nu}$ and improve on existing techniques. The valence-quark masses in our simulations are approximately physical for the domain-wall strange and charm quarks as well as for the bottom quark, for which we use the relativistic heavy quark action. We report on our progress and discuss future plans towards a first study with fully controlled systematic effects.

        Speaker: Alessandro Barone (University of Southampton)
      • 28
        B meson decay constants from Lattice QCD

        We present the status of ongoing work to extract pseudoscalar and vector decay constants for $B^{(*)}$, $B_s^{(*)}$ and $B_c^{(*)}$ mesons and determine phenomenologically interesting ratios such as $f_{B_s}/f_B$ or $f_{B^*}/f_B$. Our results extrapolated to physical quark masses and the continuum are compared to predictions by other lattice collaborations and QCD sum rules, and are used to test heavy quark symmetry relations.

        Speaker: Matthew Black (University Siegen)
    • 12:30 PM
      Lunch and Swimming
    • Day 4: Afternoon 1
      • 29
        Neutral B-meson mixing from the lattice

        The combination of the experimentally measurable mass differences between the flavour eigenstates of neutral mesons and theoretical predictions of the corresponding hadronic matrix elements provide direct access to the CKM matrix elements $V_{td}$ and $V_{ts}$. Furthermore, the full dimension-6 operator basis provides valuable constraints for New Physics models. I will present the status of the joined RBC/UKQCD/JLQCD lattice QCD computation of the relevant mixing parameters including several lattice spacings, physical pion masses and near physical bottom quark masses.

        Speaker: J Tobias Tsang (CP3-Origins, The University of Southern Denmark)
      • 30
        Past Anomalies
        Speaker: Thomas Mannel (University of Siegen)
    • 4:00 PM
      Discussion with Coffee/Tea/...
    • Day 4: Afternoon 2
      • 31
        Anomalies & Puzzles in Nonleptonic Decays
        Speaker: Descotes-Genon
      • 32
        $B$ Physics at ATLAS
        Speaker: Maria Smizanska
      • 33
        Speaker: Shifman
    • Social Events: Goodbye Drinks