Developement of a likelihood-based top quark mass measurement using semileptonically decaying events with the full Run 2 ATLAS dataset

Alberto Ibanez
Tuesday, October 17, 2023
10:00 am


The top quark is the most massive elementary particle in the SM, which makes it play an important role in this theory and many of its extensions. In this presentation, I will present the current development status of a measurement of the top quark mass in the on-shell renormalization scheme, the top quark pole mass ($m_{t}^{\mathrm{pole}}$), using semileptonically decaying top quark pair events produced in association with at least one energetic jet ($t\bar{t}\text{+jet}$). Additionally, the top quark mass parameter in the Monte Carlo simulation ($m_{t}^{\text{MC}}$), is determined using semileptonically decaying top quark pair events produced in the lepton+4 jets channel, without additional jets ($t\bar{t}$). The measurement is performed using the proton-proton collision data at $13 \medspace TeV$ collected by the ATLAS experiment at the LHC during Run 2 (2015-2018), corresponding to an integrated luminosity of $140 \medspace \text{fb}^{-1}$. Candidate $t\bar{t}$/$t\bar{t}\text{+jet}$\ events are required to contain one electron or muon, a significant amount of missing transverse momentum, and four or more jets, from which at least one is identified as jet originating from the hadronization of a $b$-quark. To reconstruct the observables used in this analysis, $\rho_s= 340 \medspace \text{GeV} / \sqrt{s_{t\bar{t}\text{+jet}}}$ and $M_{lb}$, a machine learning model implemented within the \textsc{SPA-Net} framework is used. The value of $m_{t}^{\mathrm{MC}}$, and the corrected distribution of the parton level normalized cross section with respect to $\rho_s$ are determined with a statistical model based on a profile likelihood fit. For the top quark pole mass, the methodology outlined in presentation achieves an expected precision level of $\Delta m_{t}^{\text{pole}} (\text{total}) \simeq \medspace ^{0.88}_{0.78} \medspace \text{GeV}$, while the top quark Monte Carlo mass parameter in the simulation is expected to be determined with a precision of $\Delta m_{t}^{\text{MC}} (\text{total}) \simeq 0.41 \medspace \text{GeV}$. At this precision, the top quark mass values extracted using this methodology would be positioned among the most precise determinations of these quantities to date.

Speaker Bio: Alberto Prades Ibañez, PhD student from the University of Valencia (Spain) conducting his research at IFIC



Daniel Whiteson