ATLAS reveals hidden structure in W boson collisions at record precision
Physicists have made the first complete measurement of how W bosons behave in high-energy collisions, capturing their full angular fingerprints. The findings test quantum theory predictions and could refine models used to hunt for rare particles or physics beyond the Standard Model—critical for future collider experiments and discoveries.
Originaltitel: Measurement of the W-boson angular coefficients and transverse momentum in $$p\!p$$ collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Abstract The angular distributions of Drell–Yan lepton pairs provide sensitive probes of the underlying dynamics of quantum chromodynamics (QCD) effects in vector-boson production. This paper presents for the first time the measurement of the full set of angular coefficients together with the differential cross-section as a function of the transverse momentum of the W boson, in the full phase space of the decay leptons. The measurements are performed separately for the $$W^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:math> and $$W^+$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:math> channels. The analysis uses proton–proton collision data recorded by the ATLAS experiment at the Large Hadron Collider in 2017 and 2018, during special low-luminosity runs with a reduced number of interactions per bunch crossings (pile-up). The data correspond to an integrated luminosity of 338 pb $$^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:math> at a centre-of-mass energy of $$\sqrt{s} = 13$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> </mml:mrow> </mml:math> TeV. The low pile-up environment provides excellent experimental conditions for high-precision measurements of W -boson production. All results agree with theoretical predictions incorporating finite-order QCD corrections up to order $$\alpha _S^2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>α</mml:mi> <mml:mi>S</mml:mi> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> .