A precise mass of the top quark has been found by ATLAS and CMS

Amongst the various known fundamental particles today the quarks take the spotlight, particularly the top quark because it provides indirect constraints on the Higgs boson mass, together with the W boson mass. The production of this quark is important to search for new physics beyond the SM. Till now, it is claimed that the top quark has a mass 184 times that of the proton. Measuring the precise value of the mass of both the top quark as well as the Higgs boson provides vital information about the underpinnings of the SM (Standard Model).

For the first time in history, the ATLAS and CMS have collaborated to measure the mass of this fundamental particle. The result which they have obtained makes an average of 15 other measurements that were made with the LHC Run-1 datasets that were collected around a decade ago. This new result obtained by their 2 organisations is the most precise value of the mass of the top quark till date.

Although the 2 organisations have data samples that are independent of each other, they however do have some shared sources of systematic uncertainties. For example, shared theoretical modelling of the quark, background processes and the presence of many simulation collisions that affect the experiment of both similarly. While collating their measurements, researchers should not double count these uncertainties that are present in both the experiments.

The top quark always decays into a bottom quark and a W boson particle. The bottom quark that is formed produces a unique “jet” of particles that is also known as “b-jet”. Finding the energy scale of this unique jet is done using the simulations that are quite similar to both the experiments. This thereby leads to shared data between ATLAS and CMS that both have to be accounted for.

After collating the data, it was found that the new precise mass of the top quark is: 175.52 ± 0.33 GeV. They have also examined this quark with each of the experiments and confirmed that it was consistent with the results which ultimately gives confidence on the new result obtained.

Source: Press release. CERN. "ATLAS and CMS unite to weigh in on the top quark" https://atlas.cern/Updates/Briefing/top-quark-mass. 02/10/23. [Date accessed: 23/10/23]

Edited by: Ansh Pincha