Periodic Reporting for period 4 - DIMO6FIT (DIMO6FIT: Extending the Standard Model -- Global Fits of Optimal Variables in Diboson Production)
Reporting period: 2021-08-01 to 2022-07-31
Is the Standard Model complete?
Particle physicists seek to describe how the fundamental building blocks of nature – the elementary particles – interact with each other to form the universe as we know it. Our current understanding is encoded in one single equation: The Standard Model Lagrangian. Its predictions have been confirmed by thousands of experimental data points. However, we are absolutely that the Standard Model is not the final theory describing the development of the universe from the Big Bang until now. To find hints of what is missing, is one of the aims of the DIMO6Fit project: Looking at the high energy data from the LHC, we might find small deviations from the SM as we know it that help to close the gaps in our knowledge. The ultimate aim is to understand the universe in itself – but what we learn on the way is equally important: Large scale systematic data analysis with special scrutiny, innovative usage of computing methods and last but not least friendly collaboration and cooperation with thousands of other researchers around the globe who also use the ATLAS detector and work together to run this huge endeavour.
Particle physicists seek to describe how the fundamental building blocks of nature – the elementary particles – interact with each other to form the universe as we know it. Our current understanding is encoded in one single equation: The Standard Model Lagrangian. Its predictions have been confirmed by thousands of experimental data points. However, we are absolutely that the Standard Model is not the final theory describing the development of the universe from the Big Bang until now. To find hints of what is missing, is one of the aims of the DIMO6Fit project: Looking at the high energy data from the LHC, we might find small deviations from the SM as we know it that help to close the gaps in our knowledge. The ultimate aim is to understand the universe in itself – but what we learn on the way is equally important: Large scale systematic data analysis with special scrutiny, innovative usage of computing methods and last but not least friendly collaboration and cooperation with thousands of other researchers around the globe who also use the ATLAS detector and work together to run this huge endeavour.
The DIMO6Fit Team has been the driving force behind two the observation of two important processes at the LHC with the ATLAS detector: The scattering of two same-sign W bosons as well as the production of two W bosons from the scattering of two photons. Whilst not entirely surprising - these processes are predicted in the SM - these observations were the result of years of hard work (and two pictures of candidate events are attached below). The team has been very involved with the data taking and has taken the lead in making sure, that the detector can detect electrons well, which are used in the measurements. But it's not enough to just hunt for the new - more precise measurements of tried and trusted can reveal on closer look something surprising. In line with this, the DIMO6Fit team studied closely the production of two opposite-sign W bosons in proton collisions, . Both has led to a better understanding of these two processes within the Standard Model framework. On top of that, we have started to used these measurements to looks for signs of small, additional interactions not described by the SM. Combined with new predictions and innovative ways to determine backgrounds, the most precise measurements of WW production up to date have been carried - with results in the pipeline that remove any restrictions on the number of additional quarks or gluons production in the event. Together with other results, these measurements were taken by the DIMO6Fit team and turned into a stringent test of how well the Standard Model work. In a combination with other final states, small deviations would be amplified in noticeable signals. These fits were the first of their sort that looked simultaneously at results of diboson production, Higgs and top quark production. So far – with no result. But this is interesting and important in itself: The SM is still the best theory we have. Despite this, there are facts that it cannot explain, Dark Matter, Antimatter-Asymmetry and the large mass differences between otherwise very similar elementary particles. We will continue to look for cracks in the SM to see where we can start to look beyond it.
The project has lead the way to the first observation of the scattering of two same-sign W bosons and the photon-induced production of two W bosons at the ATLAS experiment - these processes have never been observed before. Detailed studies on the production of opposite-sign W bosons with or without quarks and gluons have been performed. First constraints on dimension-6 parameters have been set and combinations with other measurements have been carried out.. These combinations where the first using the full information available to the experimental collaborations and they are a powerful constrain on dimension-6 operators shedding light on possible beyond the Standard Model physics.