The results are published in The European Physical Journal C (Q1, IF: 4.4).
Luminosity is a key quantity that characterizes the work of charged particle colliders. It gives scientists an idea of the number of particle collisions. Accurate measurement is an important task in collider physics. Van der Meer beam scanning is used to properly calibrate detectors designed to measure luminosity. The overlap of the beams is measured as a function of the distance between the orbits of the beams, and then the calibration constant is calculated using a known procedure that takes into account many influencing factors.
"We are quite active in the luminosity analysis group of the CMS experiment at the Large Hadron Collider. Typically, the models used to extract observables from the Van der Meer scan data assume a Gaussian distribution of particles in the incoming beams with some artificial corrections. While such a method describes the experiment well, it is not derived from the real distribution of particles in the beam," notes Abed Mohamed Atef Mohamed, one of the authors of the study, a graduate student at TPU's School of Nuclear Science and Engineering.
TPU researchers considered a fairly general, non-Gaussian, model of particle density that actually describes the Large Hadron Collider beam, calculated the overlap of the beams, modeled the Van der Meer scan based on this, and tested the new model on real data. The study showed that in some cases the model proposed describes the experimental data 10-20% better.
"Colliding clumps are known to have non-Gaussian tails. The non-Gaussian shape of the tails can be explained by several effects, beam dynamics, and interaction with the accelerator. These combined effects change the population of colliding clumps from tail to core and affect the absolute luminosity. Our work accounts for such non-Gaussian beam tails and provides an estimate of their impact on the luminosity calibration. Our model is already being used at the LHC, but it has a wider potential in collider physics, both for the HL-LHC and for other colliders," adds Anton Babaev, one of the authors of the study, researcher at the TPU Research School of High-Energy Physics .
Scientists will continue to study the non-Gaussian distribution in order to improve the calibration of the collider luminosity.
Reference:TPU scientists participate in several collaborations and departments of the European Organization for Nuclear Research - CERN. For example, in the CMS Collaboration, TPU scientists conduct research on luminosity measurement within the BRIL project.
In the LHCb collaboration, they are working on the modernization of the Sci-Fi track detector, analyzing the decays of beauty and charmed mesons, and searching for exotic particles.
In the NA64 collaboration they are engaged in the search for dark matter, and in the COMPASS experiment they are studying the structure of hadrons. Tomsk Polytechnic University scientists, together with the Department of Accelerator Technologies, are also involved in the development of the latest methods of the collider's proton beam diagnostics and control.