Pabellón de rayos cósmicos, Scientific research building in University City, Mexico

The Cosmic Ray Pavilion, known as La Muela, is a 1951 building by Jorge González Reyna, Félix Candela and Rafael M. de Arozarena. Its roof is a hyperbolic paraboloid shell only 15 millimetres thick at the highest point, covering a plan 12 metres long and 10.75 metres wide. The structure stands between the Faculty of Dentistry and the Faculty of Medicine.

Carlos Lazo announced the Nuclear Physics Institute in 1951, with this pavilion as its cosmic-ray measurement centre. Jorge González Reyna first proposed a cylindrical roof, but Félix Candela and his Cubiertas Ala replaced it with two hypar shells. Built with advice from Manuel Sandoval Vallarta and Georges Lemaître, it was finished on 23 August 1951.

The hyperbolic paraboloid roof earned the building its nickname 'La Muela' (the molar), for its resemblance to a tooth. Today the former laboratory serves as a toy library and sports equipment store for the Faculty of Dentistry, which occupies the surrounding complex.

The pavilion stands in the eastern part of the UNAM Central Campus, between the Faculty of Dentistry and the Faculty of Medicine. It now serves as a toy library and sports-equipment store for the Faculty of Dentistry, so it is not open as a research site; view the concrete shell from the campus walkways outside.

The roof employs a mathematical shape that transfers loads directly to the foundation without needing thick material. This innovative approach was a groundbreaking example of modern engineering when it was completed.