Dr. Carla Marín, a researcher at the Experimental Particle Physics Group at the Institute of Cosmos Science of the University of Barcelona (ICCUB), has been awarded an ERC Starting Grant with more than 1.6M€ to carry out her project “Challenging the Standard Model with suppressed b to d ll decays (CLIMB)”.

ERC Starting Grants, which are part of the program Horizon Europe, are designed to help talented researchers who want to establish their research teams in Europe. The awarded candidates must have an excellent scientific track record showing scientific talent and an excellent research proposal for the next five years. These are evaluated on the basis of excellence as the sole criterion by selected international peer reviewers.

 About the CLIMB project 

The Standard Model of Particle Physics is one of the most complete scientific theories we have developed so far. Despite its hugely successful predictive power, it still fails to explain some observations that are key to understanding our Universe, such as the dominance of matter over antimatter. In the Large Hadron Collider (LHC) at CERN, the LHCb experiment studies decays of b quarks, which result from the proton collisions. The CLIMB project focuses on the rare decays which are those that occur less than once in every million decays. The scarcity of these decays makes them very sensitive to the existence of new particles and forces beyond the Standard Model, which can modify their properties. In recent years, a set of deviations from the predictions of the Standard Model have been observed in the decays of b quarks to an s quark and two leptons, electrons or muons, (b -> s ll), which could be an indication of the existence of new physics.

 The CLIMB project will explore even rarer decays of the b quark to a d quark and two leptons (b -> d ll), which occur once in 100 million. The b -> dll transitions are related to the b -> s ll transitions through the Cabibbo–Kobayashi–Maskawa (CKM) matrix that describes quark mixing in the Standard Model, but their hierarchy is not well understood. Explaining the origin of this hierarchy is the motivation for many new physics models, and therefore, accurately measuring the relationship between b -> sll and b -> dll decays is key information for these models. Due to its suppression, to this day we have very little experimental information on b -> dll transitions. CLIMB aims to radically change this situation. To this end, Dr. Marín’s team will use unique data from the LHCb experiment which contain billions of b quarks, and develop new reconstruction and analysis techniques in order to observe and measure the properties of these sneaky decays.

In the words of Dr. Marín, “due to the rarity of these decays and the difficulty of measuring electrons at the LHCb experiment, new techniques of particle reconstruction and data analysis need to be developed, and here is where the challenge really lies. If we succeed, we will be able to compare transitions with muons and electrons, which should occur exactly the same number of times but which recent experiments indicate may not be the case. This would be clear evidence for the existence of Physics beyond the Standard Model.”

About Dr. Carla Marín

Carla Marín joined the Experimental Particle Physics Group at the Institute of Cosmos Sciences of the University of Barcelona in 2013 to initiate her doctoral thesis with prof. Lluís Garrido.

After obtaining her doctorate, she was a postdoctoral researcher at the Laboratoire de l'Accélérateur Linéaire, Orsay (2018-2021) and CERN (2021-2022).

In 2022, she rejoined the ICCUB where she is currently a tenure-track lecturer.

Outside Particle Physics, Carla Marin enjoys chess and playing football with colleagues from the Physics faculty at the regular weekly matches.