10 pages, 7 figures, proceedings of the 12th International Conference on B-Physics at Hadron Machines - BEAUTY 2009, September 07-12, 2009, Heidelberg, Germany
The possible role of precision flavour physics, and particularly of B physics, in the next decade is briefly discussed. Few 2--3$σ$ deviations from the Standard Model found in present $B$ data are reviewed as potential forerunners of new physics signals to be looked for in next-generation experiments. The perspectives for theoretical calculations, in particular those based on lattice QCD, to match the expected progress in experimental precision are also discussed.
We study (semi)leptonic rare charm decays and its opportunities in searches for physics beyond the Standard Model (BSM). In particular, we analyse the impact of potential BSM physics in $c\to ull'$ transitions, notably branching ratios, angular observables, asymmetries and Lepton Flavour Violating (LFV) decays. Testable effects are worked out model-independently and within Leptoquark models supplemented with flavour patterns to link $K$/$B$ decays.
In these proceedings we provide a brief overview of the status of flavour physics, with focus on opportunities to discover New Physics in flavour-violating decays at current and future colliders.
We discuss two theoretical motivations of precision measurements of oscillation parameters. One is the guidance for flavour model building with flavour symmetries, and the other is the connection with the origin of matter-antimatter asymmetry. We also present our recent progress in these aspects, a new approach of flavour model building based on cross coupling in the flavon potential and a novel mechanism of leptogenesis via phase transition.
We present a global likelihood function in the space of dimension-six Wilson coefficients in the Standard Model Effective Field Theory (SMEFT). The likelihood includes contributions from flavour-changing neutral current B decays, lepton flavour universality tests in charged- and neutral-current B and K decays, meson-antimeson mixing observables in the K, B, and D systems, direct CP violation in K -> ππ, charged lepton flavour violating B, tau, and muon decays, electroweak precision tests on the Z and W poles, the anomalous magnetic moments of the electron, muon, and tau, and several other prec…
The understanding of flavour dynamics is one of the key aims of elementary particle physics. The last 15 years have witnessed the triumph of the Kobayashi-Maskawa mechanism, which describes all flavour changing transitions of quarks in the Standard Model. This important milestone has been reached owing to a series of experiments, in particular to those operating at the so-called $B$ factories, at the Tevatron, and now at the LHC. We briefly review status and perspectives of flavour physics, highlighting the results where the LHC has given the most significant contributions, notably including t…
Based on recent HQET sum rule and lattice calculations we present updated Standard Model predictions for the mass differences of neutral $B$ mesons: $ΔM_s^{\rm SM} = \left(18.4^{+0.7}_{-1.2} \right) \mbox{ps}^{-1}$ and $ΔM_d^{\rm SM} = \left(0.533^{+0.022}_{-0.036} \right) \mbox{ps}^{-1}$ and study their impact on new physics models that address the present hints of anomalous data in $b \to s \ell \ell$ transitions. We also examine future prospects of further reducing the theory uncertainties and discuss the implications of a 2025 scenario with $ΔM_s^\text{SM 2025} = \left(18.4 \pm 0.5\right) …
flavio is an open source tool for phenomenological analyses in flavour physics and other precision observables in the Standard Model and beyond. It consists of a library to compute predictions for a plethora of observables in quark and lepton flavour physics and electroweak precision tests, a database of experimental measurements of these observables, a statistics package that allows to construct Bayesian and frequentist likelihoods, and of convenient plotting and visualization routines. New physics effects are parameterised as Wilson coefficients of dimension-six operators in the weak effecti…
We present precision lattice calculations of the pseudoscalar decay constants of the charmed sector as well as determinations of the bottom quark mass and its ratio to the charm quark mass. We employ Nf=2+1+1 dynamical quark gauge configurations generated by the European Twisted Mass Collaboration, using data at three values of the lattice spacing and pion masses as low as 210 MeV. Strange and charm sea quark masses are close to their physical values.
随着B、K介子和中微子物理实验的进行，味道物理学在今天的粒子物理学中占据了中心地位。我们讨论了这些实验提供的机会，在我们寻找新的物理超越SM，并讨论其互补性对撞机物理。我们专注于罕见的B和K介子衰变，突出显示特定的可观测的示范模式。我们还评论了所谓的B --> pi pi和B --> K pi谜题。此外，我们还简要地讨论了长距离强相互作用的限制作用和一些新的工具，如QCD因式分解和SCET。
Low-scale leptogenesis is most efficient in the limit of an extreme mass degeneracy of right-handed neutrino flavours. Two variants of this situation are of particular interest: large neutrino Yukawa couplings, which boost the prospects of experimental scrutiny, and small ones, which may lead to large lepton asymmetries surviving down to T < 5 GeV. We study benchmarks of these cases within a "complete" framework which tracks both helicity states of right-handed neutrinos as well as their kinetic non-equilibrium, and includes a number of effects not accounted for previously. For two right-hande…
The calculations for the production of heavy quarks in deeply inelastic scattering (DIS) can be seen as an illustrative example in the framework of perturbative Quantum Chromo Dynamics (pQCD). In this thesis, I give an overview of all steps that are required for this computation. First, I give an introduction to the fundamental theoretical basics. Next, I present the calculation of the matrix elements which are a main part of the work. The next-to-leading order (NLO) pQCD corrections for polarized DIS have been obtained here for the first time. Then, I discuss two different phase space decompo…
Electric dipole moments and charged-lepton flavour-violating processes are extremely sensitive probes for new physics, complementary to direct searches as well as flavour-changing processes in the quark sector. Beyond the "smoking-gun" feature of a potential significant measurement, however, it is crucial to understand their implications for new physics models quantitatively. The corresponding multi-scale problem of relating the existing high-precision measurements to fundamental parameters can be approached model-independently to a large extent; however, care must be taken to include the unce…
We explain the many reasons for the interest in flavor physics. We describe flavor physics and the related CP violation within the Standard Model, and explain how the B-factories proved that the Kobayashi-Maskawa mechanism dominates the CP violation that is observed in meson decays. We explain the implications of flavor physics for new physics, with emphasis on the "new physics flavor puzzle", and present the idea of minimal flavor violation as a possible solution. We explain why the values flavor parameters of the Standard Model are puzzling, present the Froggatt-Nielsen mechanism as a possib…
The measurements carried out at LEP and SLC projected us into the precision era of electroweak physics. This has also been relevant in the theoretical interpretation of LHCb and Belle measurements of rare $B$ semileptonic decays, paving the road for new physics with the inference of lepton universality violation in $R_{K^{(*)}}$ ratios. The simplest explanation of these flavour anomalies -- sizeable one-loop contributions respecting Minimal Flavour Violation -- is currently disfavoured by electroweak precision data. In this work, we discuss how to completely relieve the present tension between…
While the LHC has not directly observed any new particle so far, experimental results from LHCb, BELLE and BABAR point towards the violation of lepton flavour universality in $b\to s\ell^{+}\ell^{-}$ and $b\to c\ellν$. In this context, also the discrepancy in the anomalous magnetic moment of the muon can be interpreted as a sign of lepton flavour universality violation. Here we discuss how these hints for new physics can also be explained by introducing leptoquarks as an extension of the Standard Model. Indeed, leptoquarks are good candidates to explain the anomaly in the anomalous magnetic mo…
We investigate the information that can be gained by including flavour data in fits of the Standard Model Effective Field Theory (SMEFT) with the assumption of Minimal Flavour Violation (MFV), allowing - as initial conditions at the high scale - leading terms in spurionic Yukawas only. Starting therefore from a theory with no tree level flavour changing neutral currents at the scale of new physics, we calculate effects in flavour changing processes at one loop, and the resulting constraints on linear combinations of SMEFT coefficients, consistently parameterising the electroweak parameters and…
We perform a phenomenological analysis of simplified models of light, feebly interacting particles~(FIPs)that can provide a combined explanation of the anomalies in $b\to s l^+ l ^-$ transitions at LHCb and the anomalous magnetic moment of the muon. Different scenarios are categorised according to the explicit momentum dependence of the FIP coupling to the $b-s$ and $μ-μ$ vector currents and they are subject to several constraints from flavour and precision physics. We show that viable combined solutions to the muon $g-2$ and flavour anomalies exist with the exchange of a vector FIP with mass …
Precision measures of electroweak and flavour observables, at both low and high energies, are highly complementary to direct searches for New Physics at high-energy colliders. Despite the discovery of the Higgs boson at the Large Hadron Collider, and of the overwhelming successes of the Standard Model, several observational and theoretical problems remain to be addressed. In addition to neutrino oscillation phenomena, the Standard Model fails to explain the baryon asymmetry of the Universe, and does not offer a viable dark matter candidate. In recent years, numerous deviations between the Stan…
The Anatomy of Quark Flavour Observables in 331 Models in the Flavour Precision Era
即将到来的味道精确时代将允许在不同的新物理（NP）场景中发现各种味道违反模式，这些场景目前被强子和实验不确定性所淘汰。基于规范群SU（3）_C X SU（3）_L X U（1）_X，我们通过对331个模型中的味破坏进行解剖来说明这一点，这些模型是具有新的味源和CP破坏的最简单的NP场景之一。后者主要起源于普通夸克和轻子与新的重Z '规范玻色子的味破坏相互作用。在对这些模型作了一般性的讨论之后，我们在假定CKM和强子参数的不确定性比现有模型小得多的情况下，详细研究了特定的β = 1/\sqrt{3}模型（以后称之为overline {331}模型）中Delta F = 2的可观测量和稀有的K、B介子衰变。在我们的分析中，最突出的作用是B_s-> mu ^+ mu ^-中的δ_K、Δ M_q（q = d，s）、混合诱导的CP不对称性S_{psi K_S}和S_{psi phi}、稀有衰变B_{s,d}-> mu ^+ mu ^-，特别是CP不对称性S_{mu^+ mu^-} ^s。我们确定了一些不同的CMFV模型已知的各种观测值之间的相关性。虽然，Delta F = 2观测值仍然允许在新的参数空间中的四个绿洲，我们演示了如何包含Delta F = 1观测值可以在未来确定该模型的最佳绿洲。对于1 TeV <= M_{Z'} <= 3 TeV，超线{331}模型与B ^+-> tau ^+…
In this talk I discuss the role of heavy quarks in new physics searches with tau leptons. I focus on new physics effects associated to the scalar sector which are naturally enhanced for the heaviest fermions due to the large hierarchy of the fermion masses. I will discuss two topics within this context: lepton flavour violation in the $τ- \ell$ ($\ell=e,μ$) sector and violations of lepton universality in tauonic $B$ decays.
Heavy flavour physics provides excellent opportunities to indirectly search for new physics at very high energy scales and to study hadron properties for deep understanding of the strong interaction. The LHCb experiment has been playing a leading role in the study of heavy flavour physics since the start of the LHC operations about ten years ago, and made a range of high-precision measurements and unexpected discoveries, which may have far-reaching implications on the field of particle physics. This review highlights a selection of the most influential physics results on CP violation, rare dec…
We comprehensively examine precision predictions for scalar leptoquark pair production at the LHC. In particular, we investigate the impact of lepton $t$-channel exchange diagrams that are potentially relevant in the context of leptoquark scenarios providing an explanation for the flavour anomalies. We also evaluate the corresponding total rates at the next-to-leading order in QCD. Moreover, we complement this calculation with the resummation of soft-gluon radiation at the next-to-next-to-leading logarithmic accuracy, hence providing the most precise predictions for leptoquark pair production …
The Anatomy of Z' and Z with Flavour Changing Neutral Currents in the Flavour Precision Era
SM的最简单的扩展通常会引入新的味源和CP破坏以及右手流，这就是在SM规范群中加入U（1）规范对称性。如果相应的重规范玻色子Z'介导的FCNC过程中的夸克部门在树级，这些新的物理贡献意味着一种模式的偏差，从SM的预期FCNC过程只取决于Z'耦合到费米子和它的质量。这意味着Δ F=2和Δ F=1观测值之间的严格相关性，这些观测值决定了Z '模型允许的参数空间的景观。预计风味精度时代（FPE）摆在我们面前，我们说明了这一点，通过搜索允许绿洲在这一景观假设显着较小的不确定性CKM和强子参数比目前可用。为此，我们分析了K^0-bar K^0和B^0_{s，d}-bar B^0_{s，d}系统中的Delta F=2观测值，以及罕见的K和B衰变，包括各种组合的左手和右手Z '-夸克耦合。我们确定了各种风味可观察值之间的一些相关性，这些风味可观察值可以测试和区分这些不同的Z'场景。强调了b->s l^+ l^-和b->s nu bar nu跃迁在这些研究中的重要作用。在M_Z '<3 TeV的条件下，在B_{s,d}和K介子系统中，由于施加了现有的味约束，出现了与SM期望值偏离的丰富模式.当M_Z '> 5 TeV时，在罕见的B_{s,d}衰变中发现Z'效应通常低于10%，甚至在FPE中也很难测量，而K->pi nu bar nu和K_L-> pi ^0 l^+ l^-衰变则提供了一个重要的入口…
We analyse the interplay of the constraints imposed on flavour-symmetric Composite Higgs models by Naturalness considerations and the constraints derived from Flavour Physics and Electroweak Precision Tests. Our analysis is based on the Effective Field Theory which describes the Higgs as a pseudo-Nambu-Goldstone boson and also includes the composite fermionic resonances. Within this approach one is able to identify the directions in the parameter space where the $U(3)$-symmetric flavour models can pass the current experimental constraints, without conflicting with the light Higgs mass. We also…
Photon pair production at flavour factories with per mille accuracy
我们提出了一个高精度的QED计算，与0.1%的理论精度，双光子产生的$e^+ e^-$湮灭，要求越来越精确的光度监测在香料工厂。该方法的准确性，这是基于精确的下一个到领先的阶校正与QED Parton Shower算法匹配，证明通过详细分析的辐射校正的各种来源的实验相关的观测量的影响。该计算是在事件发生器BabaYaga的最新版本中实现的，可用于精确模拟中等高能量的$e^+ e^-$对撞机的光子对生产。
We compare the sensitivity of precision measurements of lepton flavour observables to the reach of the LHC in a case study of lepton-flavour violating operators of dimension six with two leptons and two quarks. For light quarks precision measurements always yield the more stringent constraints. The LHC complements precision measurements for operators with heavier quarks. Competitive limits can already be set on the cutoff scale $Λ$ > 600 - 800 GeV for operators with right-handed $τ$ leptons using the LHC run 1 data.
Effective operators provide a model-independent description of physics beyond the stan- dard model that is particularly useful given the absence of any signs of new physics at the Large Hadron Collider (LHC). We recast previous LHC analyses to set limits on lepton-flavour-violating gluonic effective operators of dimension 8 and compare our results to existing limits from low-energy precision experiments. Current LHC data constrains the scale $Λ$ of the effective operators to be larger than $Λ\gtrsim 0.5 - 1.6$ TeV depending on the flavour and thus provides the most stringent limit for all oper…
We present in this work a new calculation of the standard-model benchmark value for the effective number of neutrinos, $N_{\rm eff}^{\rm SM}$, that quantifies the cosmological neutrino-to-photon energy densities. The calculation takes into account neutrino flavour oscillations, finite-temperature effects in the quantum electrodynamics plasma to ${\cal O}(e^3)$, where $e$ is the elementary electric charge, and a full evaluation of the neutrino--neutrino collision integral. We provide furthermore a detailed assessment of the uncertainties in the benchmark $N_{\rm eff}^{\rm SM}$ value, through te…
We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in $b \to c \ell ν$ and $b \to s \ell^+ \ell^-$ decays at BaBar, Belle and LHCb. The model consists of an extended gauge group $\mathrm{SU(2)}_{1} \times \mathrm{SU(2)}_{2} \times \mathrm{U(1)}_Y$ which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector-like fermions give rise to potentially large new physics contributions in flavour transitions mediated by $W^{\prime}$ and $Z^{\prime}$ bosons. This model can ease tensi…
