报告题目：Performance characterization of the Micromegas detector for the New Small Wheel upgrade of the ATLAS Detector at CERN and study of lepton universality, performed by measuring the ratio of the branching fractions of the B⁰ →K^*e⁺e⁻ and B⁰ →K*μ⁺μ⁻ decays,R(K^*)

报告人：Maria Perganti，National Technical University of Athens

报告时间：2023年5月8日（周一）19:00

报告地点：#ZOOM会议号：629 4164 6635　密码：237353

报告摘要

　　The world’s largest and most powerful particle accelerator, the Large Hadron Collider will dramatically increase the rate of collisions as it is heading towards to the High- Luminosity (HL-LHC) era. Almost a year ago the new collision energy world record of 13.6 TeV was displayed, providing greater precision and potentially more possibilities to discover physics beyond the Standard Model (SM), more than ever before. The ATLAS experiment, follows nearly a decade of design and construction, welcomes a new detector system, the New Small Wheels, which replaced the old forward end-caps of the ATLAS Muon Spectrometer. The NSW deploys two innovative gaseous detector technologies: Micro-Mesh Gaseous Detectors - Micromegas (MM) and small-strip Thin Gap Chambers (sTGC) for improved tracking and trigger capabilities at increased collision rates introduced by the HL-LHC upgrade. One crucial part of the integration procedure concerns the installation, testing and validation of the on-detector electronics and readout chain for 128 MM detectors, with more than 2.1 million readout channels in total. The achievement of the requirements for these detectors was a challenging and time-consuming process, more than expected. Performance studies, as analyzing the charge and tracks reconstruction by fitting signals from cosmic muons, and efficiency measurements were of crucial importance. Also main goal was the reducing of the noise levels, as well as the definition of the optimal channel thresholds per NSW readout boards. Furthermore, studies using early RUN3 data are ongoing.

In the first two operation runs of the LHC, which took place from 2010 to 2013, several B-physics experiments were conducted to search for evidence of physics beyond the SM (BSM). In recent years, general-purpose experiments, such as ATLAS, have enabled to perform similar measurements. In the SM, the electroweak couplings of leptons to gauge bosons are independent of their flavour and the model is referred as Lepton Flavour Universality (LFU). Flavour-changing neutral-current (FCNC) processes, where a quark changes its flavour without altering its electric charge, provide an ideal laboratory to test LFU. The measurement of the ratio of the branching fractions of the B⁰ →K^*e⁺e⁻ and B⁰ →K*μ⁺μ⁻ decays,R(K^*) in LHC pp collision data recorded by the ATLAS detector at centre of mass energies = 13 TeV in 2018 is in full swing. Firstly, the definition of all background Monte Carlo samples - considering all possible background processes that could contribute to the observed signal - was necessary. Additionally, splots production of all the useful variables to extract the distributions of signal and background were done. Finally, the improvement and optimization of the analysis preselections in the signal and control regions, helps to raise the rejection of fake leptons and maximize the signal significance.

报告人简介

　　Maria Perganti is an experimental particle physics PhD working on the ATLAS experiment at CERN. She worked for the New Small Wheel upgrade project, the innermost end-caps of the ATLAS Muon Spectrometer. She currently studies the Lepton Flavour Universality and searches for new physics beyond the Standard Model, with ATLAS data collected during Run2 of the LHC. Maria was born and raised in Greece. She received her B.Sc. degree from the Physics Department of the National University of Athens. After finishing her undergraduate studies, she completed a Master's degree and currently writing her Doctorate thesis in Physics at the School of Applied Mathematical and Physics Science at the National Technical University of Athens.

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