The CERN experiment reports the first evidence for an ultra-rare process that could lead to new physics

The NA62 experiment is 270 m long and includes a 120 m long vacuum tank, shown here, housing several of the particle detectors. (Note: The experiment axis is a straight line, the curvature of the tank is an optical effect of the photo.) Credit: C.

Scientists at CERN report on their first significant evidence for the process predicted by the theory, paving the way for the discovery of new physics evidence in particle processes that may explain the universe’s dark matter and other mysteries.

Today the CERN NA62 collaboration, partially funded by the UK’s Science and Technology Facilities Council (STFC) and comprised of several UK scientists, was presented at the ICHEP 2020 conference in Prague, the first for the ultra-rare decay There is significant experimental evidence. The charged cation consists of one charged pion and two neutrinos (ie+ → π+νν).

The decay process is important in cutting-edge physics research because it is sensitive to deviations from theoretical predictions. This means that it is one of the most interesting things for physicists looking for evidence to support alternative theoretical models in particle physics.

Professor Mark Thomson, particle physicist and executive chairman of STFC, said it was exciting progress because the results showed how accurate measurement of this process gave rise to new physics beyond the standard model of particle physics developed in the 1970s Can:

“The Standard Model describes the fundamental forces and building blocks of the universe. This is a highly successful theory, but there are many mysteries of the universe that the Standard Model does not explain, such as the nature of dark matter and the origin of matter in the universe as a substance-repellent. Imbalance.

“Physicists are searching for theoretical extensions to standard models. Measurements of ultra-rare processes provide an exciting avenue for discovering these possibilities, with the hope of discovering new physics beyond standard possibilities.”

UK participants in this research are from the University of Birmingham, Bristol, Glasgow and Lancaster, and funded by STFC which is part of the UK Research and Innovation as well as the Royal Society and European Research Council (ERC).

The CERN experiment reports the first evidence for an ultra-rare process that could lead to new physics

High-level development of theoretical predictions (red areas) and experimental boundaries (black triangles). There are 3 measurements in blue: the first is from an experiment in the US. The following two are from NA62 with earlier data, and are the measurements. The increased accuracy of current measurements can be clearly seen. Sincerely: NA62 Support

The NA62 experiment has been designed and constructed with a significant contribution from the UK, specifically for the measurement of these ultra-rare con desses, the cones produced by a unique high-intensity proton beam provided by the CERN accelerator complex. From Cones are made from CERN’s super proton synchrotron (SPS) by converting high-energy protons into stable beryllium targets. It forms a beam of secondary particles consisting of about one billion particles per second and about 6%, of which there are cones. The main purpose of NA62 is to precisely measure how a charged particle decreases in a lion and a neutrino-antinutrino pair. The UK has a strong leading role in K+ → π+νν decay analysis.

“This kaon decay process is called the ‘Golden Channel’ because the combination of both ultra-rare and excellent form in standard models makes it very difficult for scientists searching for new physics to hold and hold true promise.” Christina Lezeroni, particle physicist at the University of Birmingham and spokesperson for NA62.

“This is the first time we have been able to obtain significant experimental evidence for this decay process. This is an exciting moment because it is a fundamental step towards capturing accurate measurements of caries and identifying potential deviations from standard models. is.

“In turn, this will enable us to find new ways of understanding our universe. The tools and techniques developed in the NA62 experiment will lead to the next generation of rare Kaon experiments.”

The new result, measured to 30% precision, gives the most accurate measurement to date of this process. The result is in line with the expectation of the standard model, but still leaves room for new particles to exist.

More data is required to reach a definitive conclusion on the presence of new physics or not.

STFC Ernest Rutherford Fellow of Lancaster University Drs. Giuseppe Ruggiero has been the lead analyst for this measurement since 2016, and helped create this experiment. he said:

The CERN experiment reports the first evidence for an ultra-rare process that could lead to new physics

17 events from the 2018 data set appear inside the red boxes (the red boxes have been blinded during the analysis, and their contents have only been revealed as the last step). Other black dots outside the red box are mainly due to the background, ie from other processes. Sincerely: NA62 Support

“Analyzing the data from the experiment posed a real challenge. We had to suppress a huge amount of unwanted data about a thousand billion times. And we had to do this without losing the small signal we wanted to detect. That’s a lot Something is more challenging. Finding needles in a million hastacks! We used a method called blind analysis technique. So called, because analysis is done without looking in the field, or “blind box”, where the signal is perceived. goes. “

STFC funded two Ernest Rutherford Fellowships, one at the University of Liverpool and then Lancaster and one at the University of Birmingham. In addition, three doctoral students at the University of Birmingham received support from STFC and one is now working on the project as a postdoctoral researcher. All five ‘early career’ physicists have worked on the project.

The data used in the research were taken between 2016-2018 at the Cनrn Privèsin site in France, and the research includes more than 200 scientists from 31 institutions. A new period of data taking will begin in 2021 and NA62 will allow cooperation to provide more definitive answers to the new physics question.

The conclusion

The new result comes from a detailed analysis of the full NA62 data set collected so far corresponding to a 6 × 10 risk12 konon decays. Because the process being measured is so rare, the team must be especially careful not to do anything that may bias the outcome. For that reason, the experiment was performed as a ‘blind analysis’, where physicists initially look at the background only to see that their understanding of the various sources is correct.

Only once they are satisfied with this, they look at the field of data where the signal is expected to be; This is called “blind analysis”. After a blind analysis, seventeen+ → π+Candidates for νν have been observed in the main dataset collected in 2018, revealing a significant addition over the expected background of only 5.3 events.

This addition is the first evidence for this process (with a statistical significance above the “three sigma” level). The decay rate, measured to 30% precision, gives the most accurate measurement to date of this process. The result is in line with the expectation of the standard model, but still leaves room for new physics effects. More data is required to reach a definitive conclusion on the presence of new physics or not.

The possibility of this process, known as the “branching ratio”, for ultra-rare+ → π+The νν decay is very small and predicted within the standard model of particle physics to a high precision: (8.4) 1.0) × 10-1 1. This leads to exceptional sensitivity to potential events beyond the standard model description, which makes this decay a “golden mode”, namely one of the most interesting observatories on the exact frontier of particle physics. Experimental studies however are extremely challenging due to the small rate, a neutrino pair in the final state and the huge potential background processes. Due to its characteristics, the NA62 experiment has an excellent sensitivity to a variety of rare kaon decays and foreign processes.

The NA62 collaboration is preparing to take a larger dataset in 2021–24 when CERN will resume SPS operation, taking data at higher beam intensities with an improved beam line and detector setup. The next goal is K’s “Five Sigma” overview.+ → π+The νν decay, after which the decay rate is measured to be 10%, provides a powerful independent test for the standard model of particle physics. Horizon of a new physics program with sensitivity to decay rates well below 10-1 1 The level is now in sight.

For the long-term future, a high-intensity kion beam program with possibilities to measure k is starting to take shape+ → π+νν decay to some degree of precision, to address the decay corresponding to the neutral particle, KL → π0νν, and to reach extreme sensibility reach a huge variety of rare kaon decks that compliment the investigation into the aesthetic quark field.

Ultra-rare kaon decay may give evidence for new physics

QuotesThe CERN experiment presents the first evidence for an ultra-rare process that was introduced in New Physics (2020, 28 July) on 28 July 2020 from Can receive. physics.html

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