Search for the dark neutrino at the NA62 experiment at CERN

Project Information

TheDarkNeutrino

Grant agreement ID: 893101

DOI

10.3030/893101

Project terminated on 30 November 2021

EC signature date 28 March 2020

Start date 1 April 2020

End date 31 March 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 166 320,00

EU contribution

€ 166 320,00

Coordinated by

UNIVERSITE CATHOLIQUE DE LOUVAIN
Belgium

Periodic Reporting for period 1 - TheDarkNeutrino (Search for the dark neutrino at the NA62 experiment at CERN)

Reporting period: 2020-04-01 to 2022-03-31

Summary of the context and overall objectives of the project

The fundamental particles that make up everything in our universe, and the interactions between them, are described by the Standard Model of particle physics. One type of fundamental particle is the neutrino, and the Standard Model contains 3 of them. Recent experimental observations have proven that the neutrinos are not massless, contradicting the predictions of the Standard Model. Understanding the mechanism that generates the neutrinos masses is one of the key goals of modern particle physics.
Solutions to the neutrino mass puzzle often predict ‘heavy neutrinos’. A special type of heavy neutrino, which interacts with hypothetical ‘dark’ particles, is known as the dark neutrino. Dark neutrinos could be produced in copious amounts in the decays of kaons produced using the proton accelerators at CERN.

The NA62 experiment at CERN collected an enormous sample of kaon decays in 2017-2018. By using novel experimental methods this sample can be analysed to seek the signature of dark neutrinos. Moreover, the NA62 experiment started a new data-taking period that will extend from 2021-2024, including new detector systems such as the ANTI0 detector. The limiting factor to dark neutrino searches at NA62 is the amount of kaon decays that can be collected, which is dictated by the trigger system. Improvements to the trigger system for the 2021-2024 data-taking will allow more kaon decays to be collected, providing a larger sample with which to seek the dark neutrino in the future.

A discovery of the dark neutrino would be a redefining moment for particle physics. The discovery would solve the puzzle of neutrino mass generation, would require a fundamental re-write of the Standard Model, and would pave the way for investigation of new ‘dark’ particles. In particular, the discovery would lead us towards an understanding of Dark Matter as well as the matter-dominance of the universe. It will be a huge leap in our understanding of the universe at its most fundamental level.

The objectives of the project are: to seek the dark neutrino in the sample of kaon decays collected by NA62 in 2017-2018; to commission NA62 for its 2021-2024 data-taking period, including improvements to the trigger system; and to stimulate discussion and collaboration between experimental physicists at NA62 and theoretical physicists working on heavy/dark neutrino models.

The conclusions of the project are: that novel data-analysis techniques were developed and employed to seek the dark neutrino at NA62; that NA62 was successfully commissioned for its 2021-2024 data-taking period, including the initial set-up of the ANTI0 detector and new developments to the trigger system; and that new connections between NA62 and key theorists working on dark neutrino models were established.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In Spring 2020 the NA62 simulation software was extended to accommodate dark neutrino signatures, and large samples of simulated events were produced. A procedure to isolate potential dark neutrino events from the NA62 2017-18 data was developed, requiring several novel techniques to be designed. The efficiency of the selection was evaluated using the simulated events prepared earlier in the project. A detailed understanding of the low-level trigger of the NA62 calorimeters (used to measure particle energies) was established as it proved vital for the analysis. The sensitivity of the analysis (how many dark neutrino events can be isolated in the data, over the background of other processes) was evaluated, proving that the discovery of the dark neutrino is feasible in the 2017-2018 NA62 data. Strategies to improve the selection were investigated in order to optimise the analysis and further improve the sensitivity.

In spring 2021, the simulation of the calorimeter trigger was extended to facilitate the design of a new trigger algorithm, which included a software routine to decode new data expected from 2021. In addition, simulated data was examined to identify a potential trigger to exploit data from the new ANTI0 detector.

In summer 2021 the secondment at CERN began. The initial secondment lasted for 6 months, however the stay was extended for another 3 weeks to cover the full duration of the 2021 data-taking. During that time, the new ANTI0 detector was set-up, and all other aspects of the NA62 experiment were successfully commissioned. Running NA62 for around 6 months included work as an NA62 operator, an on-call expert for several NA62 systems, and taking charge of NA62 operations for 4 weeks as ‘run coordinator’, a position of major responsibility within NA62. As the 2021 data was collected, the data was examined in detail to ensure it was of high quality.

The trigger algorithms for the calorimeter and ANTI0 could not be used during 2021 due to issues outside of the project. These issues were highlighted as risks in the original proposal. As a result, alternative developments of the trigger were designed and implemented, leading to an improved trigger for dark neutrinos during 2021. After returning from CERN, developments were made to the NA62 “data preparation” software, which converts the raw data to a form suitable for analysis.

The project was instrumental in fostering discussions between NA62 experimentalists and theorists that are experts in heavy/dark neutrinos. Interactions between the two groups took place in private communications, at weekly meetings of the host group, as invited speakers at NA62 meetings, and at seminars at the host institute.

Social media accounts for NA62 were created in Spring 2021, in time to announce a major result from NA62. The accounts were maintained throughout the project, with some posts reaching more than 1000 people. An article for a CERN newsletter was prepared, plus outreach at a school in the UK.

The key results of the project (so far) include a new data set containing kaon decays collected by NA62 in 2021. Moreover, the researcher produced 7 journal papers in the context of the NA62 collaboration, with a particular contribution to one of the papers. Recent NA62 results were presented at two international conferences (QCD20 and EPS-HEP 2021), each with proceedings contributions.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The first dedicated search for the dark neutrino has been developed, including new experimental techniques in NA62. New trigger algorithms were designed and deployed, with further algorithms prepared for 2022. NA62 was commissioned for its new data-taking period in 2021-2024, including the first set-up of the ANTI0 detector. Discussions were fostered between NA62 physicists and relevant theoretical physicists.

The scientific impact of the project has been 7 journal publications plus two conference talks each with a proceedings contribution. New contacts have been made with key theoretical physicists. The project was terminated 4 months early to begin a new position, where the researcher has become leader of the NA62 high-level trigger, and convenor of a detector working group. Successful NA62 social media accounts were created and maintained. An article for a CERN newsletter was prepared. An outreach activity a school in the UK was carried out.

The potential discovery of the dark neutrino has wide implications in several scientific disciplines. Moreover, the understanding of the fundamental particles helps us know more about the universe and our place in it.