PhD defense Siim Tolk @ Groningen University

08 - 04 - 2016 om 14:30 tot 08 - 04 - 2016 om 16:30


“Discovery of Rare B Decays”

Siim Tolk, promovendus aan het Nikhef, verdedigt zijn proefschrift vrijdag 8 april 2016 aan de Universiteit van Groningen.

“The matter we know constitutes around 5% of the mass of the Universe. What the rest of the Universe is made of is still unknown. We know that it cannot be made of the the particles we have seen so far and must therefore entail new type of physics. The dissertation describes a search for New Physics.

The signs of various New Physics models were looked for in extremely rare decays of subatomic particles, called neutral B mesons (B_s and B^0). In the established theory of elementary particles (The Standard Model) only around three in a billion B_s mesons decay into two muons (heavier cousins of electrons). Measuring more decays than expected would be a clear sign of New Physics.

The main result of the dissertation is the first ever observation of B_s meson decays into two muons. This is a result of a combination of the results from the CMS and LHCb experiments. The observation is a milestone for rare B decays, and represents the end of searches that started already three decades ago.

The measured number of B_s meson decays to two muons is very close to the Standard Model expectation.
The uncertainties, however, are large and mild New Physics effects cannot be excluded.

Surprisingly, the same analysis also showed evidence for an even rarer decay: a B^0 meson decay to two muons. The result has still large uncertainties, but the current number of measured B^0 decay candidates exceeds the expectations by almost 4 times. Physicists are hoping the new data will clarify whether this could be a sought-after sign of New Physics.”

“Discovery of Rare B Decays” (pdf)

De promotie vindt plaats op vrijdag 8 april, om 14.30 in het academiegebouw  van de Universiteit Groningen.

Promotor: prof. dr. A. Pellegrino
Co-promotor: dr. Francesco Dettori

Contact: Siim Tolk