Measurement of long-range two-particle azimuthal correlations in Z-boson tagged pp collisions at $$\sqrt{s}=8$$ and 13 TeV
M. Aaboud, G. Aad, B. Abbott, D. C. Abbott, O. Abdinov, B. Abeloos, D. K. Abhayasinghe, S. H. Abidi, O. S. AbouZeid, N. L. Abraham, H. Abramowicz, H. Abreu, Y. Abulaiti, B. S. Acharya, S. Adachi, L. Adámek, C. Adam Bourdarios, L. Adamczyk, L. Adamek, J. Adelman, M. Adersberger, A. Adıgüzel, T. Adye, A. A. Affolder, Y. Afik, C. Agapopoulou, C. Agheorghiesei, J. A. Aguilar–Saavedra, F. Ahmadov, G. Aielli, S. Akatsuka, T. P. A. Åkesson, E. Akilli, A. V. Akimov, G. L. Alberghi, J. Albert, M. J. Alconada Verzini, S. Alderweireldt, M. Aleksa, I. N. Aleksandrov, C. Alexa, D. Alexandre, T. Alexopoulos, M. Alhroob, B. Ali, G. Alimonti, J. Alison, S. P. Alkire, C. Allaire, B. M. M. Allbrooke, B. Allen, P. P. Allport, A. Aloisio, A. Alonso, F. Alonso, C. Alpigiani, A. A. Alshehri, M. I. Alstaty, B. Álvarez González, D. Álvarez Piqueras, M. G. Alviggi, Y. Amaral Coutinho, A. Ambler, L. Ambroz, C. Amelung, D. Amidei, S. P. Amor Dos Santos, S. Amoroso, C.S. Amrouche, F. F. An, C. Anastopoulos, N. Andari, T. Andeen, C. F. Anders, J. K. Anders, A. Andreazza, V. Andrei, C. R. Anelli, S. Angelidakis, I. Angelozzi, A. Angerami, A. V. Anisenkov, A. Annovi, C. Antel, M. T. Anthony, M. Antonelli, D. J. A. Antrim, F. Anulli, M. Aoki, J. A. Aparisi Pozo, L. Aperio Bella, G. Arabidze, J. P. Araque, V. Araujo Ferraz, R. Araujo Pereira, A. T. H. Arce, F. A. Arduh, J-F. Arguin, S. Argyropoulos, J.-H. Arling
Abstract
Abstract Results are presented from the measurement by ATLAS of long-range ( $$|\Delta \eta |>2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:mi>Δ</mml:mi><mml:mi>η</mml:mi><mml:mo>|</mml:mo><mml:mo>></mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math> ) dihadron angular correlations in $$\sqrt{s}=8$$ <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>8</mml:mn></mml:mrow></mml:math> and 13 TeV pp collisions containing a Z boson. The analysis is performed using 19.4 $$\mathrm {fb}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>fb</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:math> of $$\sqrt{s}=8$$ <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>8</mml:mn></mml:mrow></mml:math> TeV data recorded during Run 1 of the LHC and 36.1 $$\mathrm {fb}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>fb</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:math> 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 data recorded during Run 2. Two-particle correlation functions are measured as a function of relative azimuthal angle over the relative pseudorapidity range $$2<|\Delta \eta |<5$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:mo><</mml:mo><mml:mo>|</mml:mo><mml:mi>Δ</mml:mi><mml:mi>η</mml:mi><mml:mo>|</mml:mo><mml:mo><</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:math> for different intervals of charged-particle multiplicity and transverse momentum. The measurements are corrected for the presence of background charged particles generated by collisions that occur during one passage of two colliding proton bunches in the LHC. Contributions to the two-particle correlation functions from hard processes are removed using a template-fitting procedure. Sinusoidal modulation in the correlation functions is observed and quantified by the second Fourier coefficient of the correlation function, $$v_{2,2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>,</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math> , which in turn is used to obtain the single-particle anisotropy coefficient $$v_{2}$$ <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> . The $$v_{2}$$ <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> values in the Z -tagged events, integrated over $$0.5<p_{\mathrm {T}}<5$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>0.5</mml:mn><mml:mo><</mml:mo><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub><mml:mo><</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:math> GeV, are found to be independent of multiplicity and $$\sqrt{s}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt></mml:math> , and consistent within uncertainties with previous measurements in inclusive pp collisions. As a function of charged-particle $$p_{\mathrm {T}}$$ <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> , the Z -tagged and inclusive $$v_{2}$$ <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> values are consistent within uncertainties for $$p_{\mathrm {T}}<3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub><mml:mo><</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:math> GeV.