CERN experiment analysed by Lancaster physicist sees hints of one of the rarest kaon decays

CERN experiment analysed by Lancaster physicist sees hints of one of the rarest

Scientists at Cern say their NA62 experiment has observed what may be an ultra-rare charged kaon decay.

The NA62 experiment is a particle physics experiment at CERN using a 400 GeV proton beam from the SPS (Super Proton Synchrotron) accelerator.

The UK has played a leading role in both the detector construction for NA62 and the data analysis and production of results, with Dr Giuseppe Ruggiero from Lancaster University as the Physics Coordinator.

The main aim of the NA62 experiment is to study rare kaon decays and to pin down possible effects of physics beyond the Standard Model that appear in short distance interactions involving quarks.

Specifically, NA62 will measure the rate at which the charged kaon decays into a charged pion and a neutrino-antineutrino pair. This process is one of the rarest among meson decays, with a probability to happen of about 1 over 10,000,000,000, and it is extremely well predicted by the Standard Model of Physics.

Dr Ruggiero said: “The novelty of NA62 is to use for the first time an experimental technique called “kaon decay in flight” to investigate this process. The advantage of this technique is that up to 50 times fewer protons are required to produce such a decay compared to the past, making this technique scalable to higher statistics. This would open the possibility of a precise measurement of this incredibly rare process.

“We present the first result of NA62 from a small subset of data collected by the experiment in 2016. One event is found among more than 200,000,000,000 kaon decays, with a probability to be a K->pinunu (signal) higher than any other similar process (background), and in agreement with the expectation. Though one event is not statistically enough to say that we see this decay, this result proves that NA62 is able to separate this particular kaon decay from a background that originally is 10,000,000,000 higher.

“In essence we present the experimental proof of concept of NA62 and of its new technique to address the K->pinunu process.”

The NA62 team expects to identify more events of the rare kaon decay in the ongoing analysis of a twenty-fold-larger dataset taken in 2017, and it will begin taking data again in mid-April for a record number of 218 days.

If all goes to plan, the collaboration should be able to measure the branching fraction of the decay with a small enough uncertainty to make a precise test of the Standard Model.

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