LATTICE FLAVOUR QCD

Flavour physics from lattice QCD at the physical point

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 Obiettivo del progetto (Objective)

'The matrix elements of the electro-weak mixing matrix, the Cabibbo-Kobayashi-Maskawa matrix, are of importance to many experimental and phenomenological applications in flavour physics. We will address the particular matrix element V(us), which can be extracted from experimental measurements once the kaon semi-leptonic form factors for the K(l3) decay is known. Therefore, we will provide quantitative results for that form factor using numerical simulations of Quantum Chromodynamics on the lattice, i.e. lattice QCD.

The hadronic matrix element for the K to pi decay will be measured on gauge configurations produced by the QCDSF collaboration. Those lattice QCD simulations are performed with 2 and 21 quark flavours of various masses, where the light quark masses eventually will approach the physical point realized in Nature. The non-perturbative clover improved fermion action is used to simulate the dynamical quark effects. Results for the kaon semi-leptonic form factor at different simulated quark masses will be compared with predictions from chiral perturbation theory.'

Introduzione (Teaser)

Recent progress in large scale simulations provided unprecedented accuracy in estimating properties of elementary particles such as quarks and leptons. EU-funded researchers are now working on elucidating some of the mysteries of the Universe.

Descrizione progetto (Article)

Scientists working on the 'Flavour physics from lattice QCD at the physical point' (LATTICE FLAVOUR QCD) project aim to obtain missing quantities relevant for quantum chromodynamics (QCD). QCD is the theory that describes the strong force that binds quarks together to form particles like protons and neutrons.

The combination of QCD and the theory of the weak interaction between leptons is referred to as the Standard Model. According to the Standard Model, the electromagnetic force is mediated by photons and the weak force by the W and Z bosons. However, the Standard Model does not answer all questions.

The electromagnetic and weak forces are very different at low energies and become similar at very high energies. This behaviour during the transition from high to low energies is called symmetry breaking.

Another aspect of the Standard Model is that the eigenstates of the strong and the electroweak theories do not coincide but are mixed between each other. These mixings are described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The project members focus on the hadronic form factor for a specific decay of a kaon into a pion and other elementary particles, which is in particular suited to extract one leading element of the CKM-matrix from the experimentally measured decay rate. The LATTICE FLAVOUR QCD scientists seek to estimate the form factor by means of numerical simulations of QCD.

An alternative approach explored during the course of this project is the chiral perturbation theory (ChPT). ChPT provides analytical tools for the description of static kaon properties such as mass and decay constant. Simulations are used to test the predictions of ChPT by varying the mass of simulated quarks to obtain low-energy constants.

The LATTICE FLAVOUR QCD has two more years of funding, providing the opportunity to search for new physics. The leading researcher has joined the 'Hadron Physics from Lattice QCD' programme. Efforts are ongoing to acquire through simulations, information complementary to direct searches in colliders, such as the Large Hadron Collider.