Measurement of the azimuthal anisotropy of charged particles produced in $$\sqrt{s_{_\text {NN}}}$$ s NN = 5.02 TeV Pb+Pb collisions with the ATLAS detector (2018)

Measurements of the azimuthal anisotropy in lead-lead collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt><mml:msub><mml:mi>s</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mtext>NN</mml:mtext></mml:msub> </mml:msub> </mml:msqrt> </mml:math> = 5.02 TeV are presented using a data sample corresponding to 0.49 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup><mml:mrow><mml:mi>nb</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for "ultra-central" collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:math> - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi> <mml:mn>7</mml:mn></mml:msub> </mml:math> , which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi> <mml:mi>n</mml:mi></mml:msub> </mml:math> over wide ranges of the transverse momentum, 0.5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo><</mml:mo> <mml:msub><mml:mi>p</mml:mi> <mml:mi>T</mml:mi></mml:msub> <mml:mo><</mml:mo></mml:mrow> </mml:math> 60 GeV, the pseudorapidity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo> <mml:mi>η</mml:mi> <mml:mo>|</mml:mo> <mml:mo><</mml:mo></mml:mrow> </mml:math> 2.5, and the collision centrality 0-80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt><mml:msub><mml:mi>s</mml:mi> <mml:msub><mml:mrow></mml:mrow> <mml:mtext>NN</mml:mtext></mml:msub> </mml:msub> </mml:msqrt> </mml:math> = 2.76 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>TeV</mml:mi></mml:math> and 5.02 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>TeV</mml:mi></mml:math> . In particular, the shape of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>p</mml:mi> <mml:mi>T</mml:mi></mml:msub> </mml:math> dependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi> <mml:mi>n</mml:mi></mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>p</mml:mi> <mml:mi>T</mml:mi></mml:msub> </mml:math> values by constant factors over the centrality interval 0-60% and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>p</mml:mi> <mml:mi>T</mml:mi></mml:msub> </mml:math> range 0.5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo><</mml:mo> <mml:msub><mml:mi>p</mml:mi> <mml:mi>T</mml:mi></mml:msub> <mml:mo><</mml:mo></mml:mrow> </mml:math> 5 GeV.