Physicists have discovered a new particle composed of three quarks in the Large Hadron Collider (LHC) accelerator in Switzerland, confirming the fundamental assumptions of physics regarding the binding of quarks.
A team at the University of Zurich says that the baryon, known as Xi_b, is a composite subatomic particle made up of three quarks.
All baryons that are composed of the three lightest quarks (“up”, “down”, and “strange” quarks) are known. Only very few baryons with heavy quarks have been observed to date. They can be generated artificially in particle accelerators as they are heavy and very unstable.
In the course of proton collisions in the LHC at Cern, physicists Claude Amsler, Vincenzo Chiochia and Ernest Aguiló from the University of Zurich Physics Institute managed to detect a baryon with one light and two heavy quarks.
The particle Xi_b comprises one “up”, one “strange” and one “bottom” quark , is electrically neutral and has a spin of 3/2 (1.5). Its mass is comparable to that of a lithium atom.
The discovery was based on data gathered in the CMS detector, which the University of Zurich was involved in developing. The new particle cannot be detected directly as it is too unstable to be registered by the detector.
However, Xi_b breaks up in a known cascade of decay products. Ernest Aguiló, a postdoctoral student from Professor Amsler’s group, identified traces of the respective decay products in the measurement data and was able to reconstruct the decay cascades starting from Xi_b decays.