Periodic Reporting for period 2 - LARNUEXP (Searching for new physics with liquid argon time projection chambers and developing the technology for the future of neutrino physics)
Periodo di rendicontazione: 2020-06-01 al 2021-05-31
The primary objective of the project is to search for New Physics which may be hiding within the data taken by short baseline neutrino (SBN) experiments currently operating in the USA. Secondary objectives are to be trained in the operation of a liquid argon time projection chamber (LArTPC), to aid in the construction of LArTPC components for the future DUNE experimnent, and to incorporate results from a DUNE prototype that has been running at CERN into the SBN analyses. The LArTPC technology has been chosen as the next generation technology for the USA-based long baseline neutrino oscillation experiment that will begin operating in the upcoming decade, and the University of Manchester is a member of a consortium to build components for the LArTPC that will be used. The DUNE experiment is a large international endeavour with over 1000 members across over thirty countries, and so is important for society for fostering international collaboration, and also for extending humanity’s understanding of physical reality. The currently running SBN experiment, MicroBooNE, has been taking data with a LArTPC for over five years now, and is mainly investigating whether there is a fourth type of neutrino (hints of which have been seen by older experiments). The experiment may be sensitive to new forces that affect neutrino interactions on argon, which will modify the rate of electron-positron production in the detector. The experiment is also potentially exposed to a high-intensity beam of new particles, such as dark matter, which could be being created in the same proton collisions that are producing neutrinos. The main aim of this project is to search for evidence of these new forces or dark matter being produced in the beams. The primary conclusion of the action is that we performed the first ever search in a LArTPC for electron-positron production from a dark scalar boson (close cousin of the Higgs boson), and found no evidence for it. We were able to exclude the new physics model parameters that could explain an anomalous underestimate of certain particle decays seen at an experiment in Japan called KOTO. This also pioneers similar studies that will be performed in the future at other LArTPC detectors at FermiLab.
I have been trained in the operations of a liquid argon time projection chamber, by being the ‘Run Coordinator’ of the MicroBooNE experiment for a six-month term, a position analogous to ‘chief operating officer’ in the corporate world. I was in charge of the operations of the MicroBooNE experiment, on call 24/7 for the regular shifters to contact if things broke down, and interfacing with the experts familiar in the various subsystems of the detector, to bring things back up again. This experience has led to me being trained in the operations of a LArTPC, fulfilling that objective of the project. In terms of the main physics goals, we publicised and disseminated (first at the ICHEP 2020 conference) our first result for the search for New Physics. We have searched for evidence of a dark sector scalar boson which mixes with the Higgs boson, where we would see its decays to electron-positron pairs inside the detector. We have ruled out this model as explaining an observation of neutral kaon decays occurring too fast, made by the independent KOTO experiment running in Japan. We have released this result as a publication, and disseminated it in talks to at least four conferences (ICHEP 2020, NeuTel 2021, APS-DPF 2021, EPS-HEP 2021) and a poster at a workshop (FermiLab users meeting 2020), with the result also being disseminated at other conferences and meetings by collaborators on the experiment but external this project (e.g. FermiLab PAC 2021). This result has also been reinterpreted by theorists to set limits on other new physics models, so is already impactful. We have begun to search for electron-positron pairs being produced by dark matter scattering off the argon nuclei, and expect to have first results of this search out within the next few years. Also we are supervising a new PhD student who will develop an analysis based on our work, to search for "millicharged" particles (dark matter candidates with a tiny fraction of the electronic charge). We have also begun construction of the DUNE (the next generation, large-scale neutrino LArTPC detector) components, setting up a factory at the Daresbury Laboratory in the UK.
The search for a dark sector scalar decaying to electron-positron pairs is the first ever search for Beyond-the-Standard-Model production of dilepton pairs using a LArTPC, and it will inform similar searches that will be done by the future SBND, ICARUS and even DUNE experiments. It will also impact theorists building models to explain the KOTO anomaly. This result is now publicised as a scientific article, and has already been used by theorists to inform other new physics models. In the near future we will also publish the search for dark matter scattering to electron-positron pairs, with potential impacts on humanity’s understanding of dark matter, if a signal is observed.