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Challenging the Standard Model with the scrutiny of b to qll transitions

Project description

Rare decays of b hadrons could hint at new physics beyond the Standard Model

The EU-funded Chiaroscuro project seeks to discover new physical phenomena not predicted by the Standard Model of particle physics. Researchers will conduct precision measurements to find discrepancies between the predictions of the Standard Model and experimental observations that could hint the manifestation of new particles or unknown physics. Using the Large Hadron Collider beauty detector, designed to capture hadrons containing b quarks (b hadrons), researchers will try to detect the rare transitions from b quarks to s or d quarks. Researchers will study for the first time the angular properties of the decay products of these transitions for a variety of b hadrons.


Today, Particle Physics is in an unusual situation with a theory, the Standard Model (SM), able to accurately describe a very large number of precise measurements but at the cost of ad hoc features in the fermionic sector. Furthermore, the SM is unable to answer key questions raised by cosmological observations. Consequently, the ball is now on experiment side to search for signs of non-SM physics (NP). The most straightforward way to hunt for NP particles is to seek for their signatures directly in the data, but none of them has been found today. Therefore, this project focuses on indirect searches which rely on the quantum nature of particles. Since b-hadrons study is an ideal field for this type of searches, I propose to explore the Flavour-Changing Neutral Currents b-> sll and b-> dll transitions to draw the identity card of the NP particles which may be at play. Due to experimental constraints, our current knowledge is limited: the published results are mostly related to the b-> s mumu transitions and the observations of b-> see are rare. With the Chiaroscuro project, I will be able to study for the first time the angular properties of the decay products of the b-> s ee transitions over the full kinematical domain for a variety of b-hadrons to investigate the NP couplings to the electron (e) and muon (mu) particles. Another important question is the coupling of NP with the quarks of the first and second families: are the b->sll and b->dll transitions impacted the same way by NP? In order to answer this interrogation, I will study Lb and Bc hadrons decays - uniquely accessible at the LHC - using cutting edge reconstruction techniques.
The project will use the LHCb detector running at the LHC to benefit from the huge b-hadron production rate. In order to cope with the increasingly challenging data-taking conditions, the project will develop innovative techniques in the electron reconstruction and precise calibration of the LHCb electromagnetic calorimeter.

Host institution

Net EU contribution
€ 2 221 993,00
75794 Paris

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Ile-de-France Ile-de-France Paris
Activity type
Research Organisations
Total cost
€ 2 221 993,00

Beneficiaries (1)