Scientists searching for evidence of new physics in particle processes that could explain dark matter and other mysteries of the universe have moved one step closer, with the new result of the NA62 experiment reported today at CERN.
The experiment, led by an international team of scientists, demonstrates a new technique which captures and measures the ultra-rare decay of a sub atomic particle called a kaon.
Their results, presented at a CERN Seminar, show how precise measurements of this process could hint at new physics, beyond the Standard Model. Physicists have been searching for extensions to the Standard Model that can predict new particles or interactions that can explain these phenomena.
The new measurement was made at the CERN particle physics laboratory by a team led by the University of Birmingham. The aim of the experiment, called NA62, is to study the sub-atomic particles kaons, containing the strange quark, and a particular way in which they transform into other types of particles with odds around 1 in 10 billion. This process is predicted in detail by the Standard Model with an uncertainty of less than 10 percent, so any deviation from that prediction is an exciting clear sign of new physics.
This kaon decay process is called the ‘golden channel’ because the combination of being ultra-rare and excellently predicted in the Standard model. It is very difficult to capture, and holds real promise for scientists searching for new physics. By capturing a precise measurement of the decay they can identify deviations from the Standard Model prediction. The new result has still limited statistics but has already enabled them to begin putting constraints on some new physics models.
The experiment took place over three years at CERN’s Prevessin site, in France and involves about 200 scientists from 27 institutions. The aim was to measure precisely how the kaon particle decays into a pion and a neutrino–antineutrino pair using the proton beam from CERN’s Super Proton Synchrotron (SPS). The kaons are created by colliding high energy protons from the SPS into a stationary beryllium target. This creates a beam of secondary particles which contains and propagates almost one billion particles per second, about 6% of which are kaons.
Because the process being measured is so rare, the team had to be particularly careful not to do anything that might bias the result. For that reason, the experiment was carried out as a “blind analysis,” where physicists initially only look at the background to check that their understanding of the various sources is correct. Only once they are satisfied with that, they look at the region of the data where the signal is expected to be. The experiment will analyze further data taken in 2018 and publish it next year.
This is a big step forward for the field of particle physics that will enable us to explore new ways to understand our universe. This has been made possible through a huge team effort from all the institutes that have collaborated with each other and the continuous support from CERN.