Eur. Phys. J. C (2024) 84: 1334
https://doi.org/10.1140/epjc/s10052-024-13547-2

Regular Article - Experimental Physics

The azimuthal correlation between the leading jet and the scattered lepton in deep inelastic scattering at HERA

¹ Max-Planck-Institut für Physik, Munich, Germany
² DST-Inspire Faculty, Department of Technology, SPPU, Pune, India
³ Department of Nuclear Physics, National Taras Shevchenko University of Kyiv, Kyiv, Ukraine
⁴ Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
⁵ INFN Padova, Padua, Italy
⁶ Deutsches Elektronen-Synchrotron DESY, Zeuthen, Germany
⁷ Physikalisches Institut der Universität Bonn, Bonn, Germany
⁸ Physics and Astronomy Department, University College London, London, UK
⁹ Dipartimento di Fisica e Astronomia dell’ Università and INFN, Padua, Italy
¹⁰ INFN Bologna, Bologna, Italy
¹¹ School of Physics and Astronomy, University of Glasgow, Glasgow, UK
¹² Department of Physics, York University, M3J 1P3, Toronto, ON, Canada
¹³ The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland
¹⁴ Faculty of Physics, University of Warsaw, Warsaw, Poland
¹⁵ Department of Physics, University of Oxford, Oxford, UK
¹⁶ Affiliated with an Institute Covered by a Current or Former Collaboration Agreement with DESY, Hamburg and Zeuthen, Germany
¹⁷ Physics Department, Lancaster University, Lancaster, UK
¹⁸ Hamburg University, Institute of Experimental Physics, Hamburg, Germany
¹⁹ Physikalisches Institut of the University of Heidelberg, Heidelberg, Germany
²⁰ Department of Particle Physics and Astrophysics, Weizmann Institute, Rehovot, Israel
²¹ Sant Longowal Institute of Engineering and Technology, Longowal, Punjab, India
²² Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
²³ Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, Tel Aviv University, Tel Aviv, Israel
²⁴ Physik-Institut, University of Zurich, Zurich, Switzerland
²⁵ Department of Physics, Indiana University Bloomington, 47405, Bloomington, IN, USA
²⁶ GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
²⁷ Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japan
²⁸ Department of Physics, Temple University, 19122, Philadelphia, PA, USA
²⁹ Institut für Kernphysik, Goethe Universität, Frankfurt am Main, Germany
³⁰ Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow, Poland
³¹ Università del Piemonte Orientale, Novara and INFN, Turin, Italy
³² Department of Physics and Astronomy, University of Sussex, BN1 9QH, Brighton, UK
³³ Department of Physics, Jagellonian University, Krakow, Poland
³⁴ Università di Torino and INFN, Turin, Italy
³⁵ National Centre for Nuclear Research, Warsaw, Poland
³⁶ National Centre for Particle Physics, Universiti Malaya, 50603, Kuala Lumpur, Malaysia
³⁷ Department of Physics, Kobe University, Kobe, Japan
³⁸ University of Bath, Bath, UK
³⁹ Lodz University, Lodz, Poland
⁴⁰ Rockefeller University, 10065, New York, NY, USA
⁴¹ INFN Roma, Rome, Italy
⁴² DESY and University of Hamburg, Hamburg, Germany
⁴³ a Leverhulme Trust Emeritus Fellowship, London, UK
⁴⁴ DESY, Hamburg, Germany
⁴⁵ University of Houston, 77004, Houston, TX, USA
⁴⁶ University of Liverpool, Liverpool, UK
⁴⁷ European X-ray Free-Electron Laser facility GmbH, Hamburg, Germany
⁴⁸ Physikalisches Institut of the University of Heidelberg, Heidelberg, Germany
⁴⁹ DESY, Hamburg, Germany
⁵⁰ Hamburg University, II. Institute for Theoretical Physics, Hamburg, Germany

^a jae.nam@temple.edu

Received: 6 June 2024
Accepted: 27 October 2024
Published online: 29 December 2024

Abstract

The azimuthal correlation angle, $\mathrm{\Delta }\varphi$, between the scattered lepton and the leading jet in deep inelastic $e^{\pm }p$ scattering at HERA has been studied using data collected with the ZEUS detector at a centre-of-mass energy of $\sqrt{s}=318\text{Ge}\text{V}$, corresponding to an integrated luminosity of $326{\text{pb}}^{-1}$. A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality $10{\text{Ge}\text{V}}^2<Q^2<350{\text{Ge}\text{V}}^2$, inelasticity $0.04<y<0.7$, outgoing lepton energy $E_e>10\text{Ge}\text{V}$, lepton polar angle ${140}^{\circ }<{\theta }_e<{180}^{\circ }$, jet transverse momentum $2.5\text{Ge}\text{V}<p_{\text{T,jet}}<30\text{Ge}\text{V}$, and jet pseudorapidity $-1.5<{\eta }_{\text{jet}}<1.8$. Jets were reconstructed using the $k_{\text{T}}$ algorithm with the radius parameter $R=1$. The leading jet in an event is defined as the jet that carries the highest $p_{\text{T,jet}}$. Differential cross sections, $d\sigma /d\mathrm{\Delta }\varphi$, were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity. Perturbative calculations at $\mathcal{O}({\alpha }_s^2)$ accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near $\mathrm{\Delta }\varphi \to \pi$ for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD. The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.