Eur. Phys. J. C (1998) 1: 81-96
https://doi.org/10.1007/BF01245799

Measurement of the diffractive structure functionF ₂ ^D(4) at HERA

¹ Argonne National Laboratory, Argonne, IL, USA
² Andrews University, Berrien Springs, MI, USA
³ University and INFN Bologna, Bologna, Italy
⁴ Physikalisches Institut der Universität Bonn, Bonn, Germany
⁵ H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK
⁶ Physics Department and INFN, Calabria University, Cosenza, Italy
⁷ Chonnam National University, Kwangju, Korea
⁸ Nevis Labs., Columbia University, Irvington on Hudson, N.Y., USA
⁹ Institute of Nuclear Physics, Cracow, Poland
¹⁰ Faculty of Physics and Nuclear Techniques, Academy of Mining and Metallurgy, Cracow, Poland
¹¹ Department of Physics, Jagellonian Univ., Cracow, Poland
¹² Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
¹³ DESY-IfH Zeuthen, Zeuthen, Germany
¹⁴ University and INFN, Florence, Italy
¹⁵ Laboratori Nazionali di Frascati, INFN, Frascati, Italy
¹⁶ Fakultät für Physik der Universität Freiburg i.Br., Freiburg i.Br., Germany
¹⁷ Department of Physics and Astronomy, University of Glasgow, Glasgow, UK
¹⁸ Hamburg University, I. Institute of Experimental Physics, Hamburg, Germany
¹⁹ Hamburg University, II. Institute of Experimental Phsyics, Hamburg, Germany
²⁰ Imperial College London, High Energy Nuclear Physics Group, London, UK
²¹ Physics and Astronomy Department, University of Iowa, Iowa City, USA
²² Forschungszentrum Jülich, Institut für Kernphysik, Jülich, Germany
²³ Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japan
²⁴ Korea University, Seoul, Korea
²⁵ Depto de Física Teórica, Universidad Autónoma Madrid, Madrid, Spain
²⁶ Department of Physics, McGill University, Montréal, Québec, Canada
²⁷ Faculty of General Education, Meiji Gakuin University, Yokohama, Japan
²⁸ Moscow Engineering Physics Institute, Moscow, Russia
²⁹ Institute of Nuclear Physics, Moscow State University, Moscow, Russia
³⁰ NIKHEF and University of Amsterdam, Amsterdam, Netherlands
³¹ Physics Department, Ohio State University, Columbus, Ohio, USA
³² Department of Physics, University of Oxford, Oxford, UK
³³ Dipartimento di Fisica dell' University and INFN, Padova, Italy
³⁴ Department of Physics, Pennsylvania State University, University Park, PA, USA
³⁵ Polytechnic University, Sagamihara, Japan
³⁶ Dipartimento di Fisica, Univ. ‘La Sapienza’ and INFN, Rome, Italy
³⁷ Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK
³⁸ University of California, Santa Cruz, CA, USA
⁴⁰ Fachbereich Physik der Universität-Gesamthochschule, Siegen, Germany
⁴¹ Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, Tel-Aviv University, Tel-Aviv, Israel
⁴² Department of Physics, University of Tokyo, Tokyo, Japan
⁴³ Department of Physics, Tokyo Metropolitan University, Tokyo, Japan
⁴⁴ Dipartimento di Fisica Sperimentale and INFN, University di Torino, Torino, Italy
⁴⁵ II Faculty of Sciences, Torino University and INFN, Alessandria, Italy
⁴⁶ Department of Physics, University of Toronto, Toronto, Ont., Canada
⁴⁷ Physics and Astronomy Department, University College London, London, UK
⁴⁸ Institute of Experimental Physics, Warsaw University, Warsaw, Poland
⁴⁹ Institute for Nuclear Studies, Warsaw, Poland
⁵⁰ Department of Particle Physics, Weizmann Institute, Rehovot, Israel
⁵¹ Department of Physics, University of Wisconsin, Madison, WI, USA
⁵² Department of Physics, York University, North York, Ont., Canada

Received: 17 September 1997
Published online: 27 February 2005

Abstract

This paper presents the first analysis of diffractive photon dissociation events in deep inelastic positron-proton scattering at HERA in which the proton in the final state is detected and its momentum measured. The events are selected by requiring a scattered proton in the ZEUS leading proton spectrometer (LPS) with χ _L > 0.97, where xL is the fraction of the incoming proton beam momentum carried by the scattered proton. The use of the LPS significantly reduces the contamination from events with diffractive dissociation of the proton into low mass states and allows a direct measurement of t, the square of the four-momentum exchanged at the proton vertex. The dependence of the cross section ont is measured in the interval 0.073 < |t| < 0.4 GeV² and is found to be described by an exponential shape with the slope parameterb = 7.2 ± 1.1(stat.) _−0.9 ^+0.7 (syst.) GeV⁻². The diffractive structure function FD (4) is presented as 0.9 a function of χ _H ≃ 1 − χ _L and β, the momentum fraction of the struck quark with respect to χ _H , and averaged over thet interval 0.073 < |t′ < 0.4 GeV² and the photon virtuality range 5 <Q ² < 20 GeV². In the kinematic range 4 × 10⁴ < χ _p < 0.03 and 0.015 < β < 0.5, the χ _p dependence ofF ^D(4) is fitted with a form (1/χ _p )^α , yieldinga − 1.00 ± 0.09 (stat.) _−0.05 ^+0.11 (syst.). Upon integration overL, the structure functionF ₂ ^D(3) is determined in a kinematic range extending to higher χ _p and lower β compared to our previous analysis; the results are discussed within the framework of Regge theory.