Eur. Phys. J. C (2024) 84: 785
https://doi.org/10.1140/epjc/s10052-024-13115-8

Regular Article - Experimental Physics

Measurement of the 1-jettiness event shape observable in deep-inelastic electron-proton scattering at HERA

¹ I. Physikalisches Institut der RWTH, Aachen, Germany
² University of Michigan, 48109, Ann Arbor, MI, USA
³ LAPP, Université de Savoie, CNRS/IN2P3, Annecy-le-Vieux, France
⁴ Inter-University Institute for High Energies ULB-VUB, Brussels and Universiteit Antwerpen, Antwerp, Belgium
⁵ Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
⁶ Department of Physics, University of the Basque Country UPV/EHU, 48080, Bilbao, Spain
⁷ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
⁸ Horia Hulubei National Institute for R &D in Physics and Nuclear Engineering (IFIN-HH), Bucharest, Romania
⁹ University of Illinois, 60607, Chicago, IL, USA
¹⁰ STFC, Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK
¹¹ Institut für Physik, TU Dortmund, Dortmund, Germany
¹² Institute for Particle Physics Phenomenology, Durham University, Durham, UK
¹³ CERN, Geneva, Switzerland
¹⁴ IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France
¹⁵ II. Physikalisches Institut, Universität Göttingen, Göttingen, Germany
¹⁶ Institut für Theoretische Physik, Universität Göttingen, Göttingen, Germany
¹⁷ Deutsches Elektronen-Synchrotron DESY, Hamburg and Zeuthen, Germany
¹⁸ Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany
¹⁹ Rice University, 77005-1827, Houston, TX, USA
²⁰ Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland
²¹ Department of Physics, University of Lancaster, Lancaster, UK
²² Argonne National Laboratory, 60439, Lemont, IL, USA
²³ Department of Physics, University of Liverpool, Liverpool, UK
²⁴ School of Physics and Astronomy, Queen Mary, University of London, London, UK
²⁵ Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France
²⁶ Max-Planck-Institut für Physik, Munich, Germany
²⁷ National Institute of Science Education and Research, Jatni, Odisha, India
²⁸ Joint Laboratory of Optics, Palacký University, Olomouc, Czech Republic
²⁹ IJCLab, Université Paris-Saclay, CNRS/IN2P3, Orsay, France
³⁰ LLR, Ecole Polytechnique, CNRS/IN2P3, Palaiseau, France
³¹ Faculty of Science, University of Montenegro, Podgorica, Montenegro
³² Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
³³ Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
³⁴ University of California, 92521, Riverside, CA, USA
³⁵ Dipartimento di Fisica Universitá di Roma Tre and INFN Roma 3, Rome, Italy
³⁶ Shandong University, Jinan, Shandong, People’s Republic of China
³⁷ Fakultät IV-Department für Physik, Universität Siegen, Siegen, Germany
³⁸ Stony Brook University, 11794, Stony Brook, NY, USA
³⁹ Physics Department, University of Tennessee, 37996, Knoxville, TN, USA
⁴⁰ Institute of Physics and Technology of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
⁴¹ Ulaanbaatar University, Ulaanbaatar, Mongolia
⁴² Brookhaven National Laboratory, 11973, Upton, NY, USA
⁴³ Paul Scherrer Institut, Villigen, Switzerland
⁴⁴ Department of Physics and Astronomy, Purdue University, 47907, West Lafayette, IN, USA
⁴⁵ Fachbereich C, Universität Wuppertal, Wuppertal, Germany
⁴⁶ Yerevan Physics Institute, Yerevan, Armenia
⁴⁷ Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, Mexico
⁴⁸ Institut für Teilchenphysik, ETH, Zurich, Switzerland
⁴⁹ Physik-Institut der Universität Zürich, Zurich, Switzerland
⁵⁰ Affiliated with an institute covered by a current or former collaboration agreement with DESY, Hamburg and Zeuthen, Germany

^dz stefan.schmitt@desy.de

Received: 18 March 2024
Accepted: 10 July 2024
Published online: 7 August 2024

Abstract

The H1 Collaboration reports the first measurement of the 1-jettiness event shape observable ${\tau }_1^b$ in neutral-current deep-inelastic electron-proton scattering (DIS). The observable ${\tau }_1^b$ is equivalent to a thrust observable defined in the Breit frame. The data sample was collected at the HERA ep collider in the years 2003–2007 with center-of-mass energy of $\sqrt{s}=319\text{GeV}$, corresponding to an integrated luminosity of 351.1 ${\text{pb}}^{-1}$. Triple differential cross sections are provided as a function of ${\tau }_1^b$, event virtuality $Q^2$, and inelasticity y, in the kinematic region $Q^2>150{\text{GeV}}^2$. Single differential cross sections are provided as a function of ${\tau }_1^b$ in a limited kinematic range. Double differential cross sections are measured, in contrast, integrated over ${\tau }_1^b$ and represent the inclusive neutral-current DIS cross section measured as a function of $Q^2$ and y. The data are compared to a variety of predictions and include long-standing and more recent Monte Carlo event generators, predictions in fixed-order perturbative QCD where calculations up to $\mathcal{O}({\alpha }_{\text{s}}^3)$ are available for ${\tau }_1^b$ or inclusive DIS, and resummed predictions at next-to-leading logarithmic accuracy matched to fixed order predictions at $\mathcal{O}({\alpha }_{\text{s}}^2)$. These comparisons reveal sensitivity of the 1-jettiness observable to QCD parton shower and resummation effects, as well as the modeling of hadronization and fragmentation. Within their range of validity, the fixed-order predictions provide a good description of the data. Monte Carlo event generators are predictive over the full measured range and hence their underlying models and parameters can be constrained by comparing to the presented data.