New at PRISMA+: Javier Fuentes Martin


Javier Fuentes Martin focuses on searching for New Physics that extends the Standard Model of particle physics. Since October, the 31-year-old theoretical physicist has been conducting research at the Mainz Institute for Theoretical Physics (MITP), an international center for theoretical physics at the PRISMA+ cluster of excellence. There he holds a three-year "Senior Postdoctoral Fellowship". He appreciates the flexibility the fellowship offers him in his research projects as well as the opportunity to network with the worldwide community in theoretical physics under the umbrella of the MITP. After all, this is exactly what MITP's goal is: to keep track of all important developments in view of the numerous research directions and publications in the various fields of theoretical physics and to stay on the ball in all forward-looking topics. To this end, those responsible invite leading physicists from all over the world to submit applications once a year for two- to four-week programs or to organize one-week workshops on topics they consider particularly exciting and relevant to the future. Thus, about 500 guests come to MITP each year, from more than 40 countries around the globe. "Researching and networking here at MITP as a postdoctoral fellow is a unique opportunity for me to decisively advance my scientific career and development," summarizes Javier Fuentes Martin, what prompted him to apply for the fellowship in Mainz.

Javier Fuentes Martin's main field of research is flavour physics. In the Standard Model of particle physics, the elementary building blocks of matter, the so-called quarks and leptons, both appear in six different types or flavours. These are grouped into three families that differ only in the masses of their members and in the way they interact among each other. Why there are exactly three families and why they differ in mass while otherwise having exactly the same properties are questions that remain since long unanswered – this is the so-called Standard Model flavour puzzle. Javier Fuentes Martin approaches these questions from a theoretical and phenomenological perspective, and designs models that can provide an explanation. More precisely, he constructs models beyond the Standard Model influenced by current data, and defines all possible sets of experimental tests that could verify or refute them. "Flavour physics may open a door for us enabling a view to new physics," is how Javier Fuentes Martin describes the fascination that drives him in his research.

Specifically, experimental data from flavor factories such as the LHCb detector of the Large Hadron Collider at CERN and the Belle detector at the accelerator KEK, in Japan, have provided exciting results and indications of such new physics, which now need to be interpreted theoretically. Among other things, these experiments study the decay of B mesons, which are created during particle collisions in the accelerator, into leptons. Mesons are composite particles made of a quark and an antiquark, while B mesons are those containing a b quark – a member of the third or heaviest family of quarks. Contrary to quarks, leptons are elementary particles that do not feel the strong interaction and hence do not form composite particles. The Standard Model predicts that B meson decays into leptons should happen with almost the same frequency regardless of the lepton family – a property that is commonly known as Lepton Flavour Universality. However, LHCb and Belle measurements seem to indicate that such decays occur more frequently to the leptons of the heavier families. “These hints of Lepton Flavour Universality Violation may provide crucial information for the solution of the Standard Model flavour puzzle”, concludes Javier Fuentes Martin.

Javier Fuentes Martin is currently studying these “flavour anomalies" with particular intensity. In his calculations and theoretical considerations, an exotic new particle – the leptoquark – enters the stage. "As a mediator of a new force, the leptoquark would for the first time couple directly the lepton part of the Standard Model with the quark part”, explains Javier Fuentes Martin. Even more: "The leptoquark model that has the right properties to explain the anomalous B meson decays, also unifies quarks and leptons into a single particle multiplet. This idea is very tempting, because both parts of the Standard Model, with their three families, have a suspiciously similar flavour structure – which is similarly poorly understood".

It is not yet clear from the data if the “flavour anomalies” are a true manifestation of new physics. This will require further measurements, which Javier Fuentes Martin and theoretical physicists around the world are eagerly awaiting. In the coming years, the LHCb and Belle II – the successor of Belle – experiments will provide a plethora of new measurements that will shed light on this flavour conundrum. “We are currently living a very exciting time in flavour physics”, concludes Javier Fuentes Martin.

For the next three years in Mainz, further exciting topics are on Javier Fuentes Martin's agenda. For instance, while we await for the forthcoming LHCb and Belle II data, he will search for possible imprints of a model of flavour in the cosmos. These could manifest, for example, in the form of gravitational waves whose signatures may be discovered in the next generation experiments. He is looking forward to an intensive exchange with numerous colleagues and to many inspirations and new approaches and ideas.