Physicists narrow down top quark's mass with new technique at CERN
Scientists have measured the top quark's mass to within 1.56 GeV using a novel decay method at the Large Hadron Collider, reducing uncertainty in a fundamental constant that underpins particle physics models. The precision measurement matters because the top quark's exact mass constrains theories about the universe's stability and helps calibrate experiments searching for undiscovered particles.
Originaltitel: Measurement of the top-quark mass using decays with a J/ψ meson at $$ \sqrt{s}=13 $$ TeV with the ATLAS detector
A bstract The top-quark mass is measured using top-quark decays producing an isolated lepton and J / ψ meson reconstructed in its μ + μ − decay mode. The data sample was recorded with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $$ \sqrt{s}=13 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> </mml:math> TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb − 1 . The measurement is based on the invariant mass m ( ℓμ + μ − ) of the system made of the isolated lepton ℓ from the W boson decay and the non-isolated μ + μ − pair from a J / ψ decay of a b -hadron, exploiting its sensitivity to the top-quark mass. An unbinned maximum-likelihood fit to the m ( ℓμ + μ − ) distribution is performed to extract the top-quark mass. The top-quark mass is measured to be m top = 172.17 ± 0.80 (stat) ± 0.81 (syst) ± 1.07 (recoil) GeV, with a total uncertainty of 1.56 GeV. The third uncertainty arises from changing the dipole parton shower gluon-recoil scheme used in top-quark decays.