1 Properties of hadronic final states in diffractive deep inelastic ep scattering at HERA ZEUS Collaboration

Characteristics of the hadronic final state of diffractive deep inelastic scattering events, ep → eXp, were studied in the kinematic range 4 < MX < 35 GeV, 4 < Q < 150 GeV, 70 < W < 250 GeV and 0.0003 < xIP < 0.03 with the ZEUS detector at HERA using an integrated luminosity of 13.8 pb. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state, X, were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow and “seagull” distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qq̄g states at the parton level. The ZEUS Collaboration S. Chekanov, M. Derrick, D. Krakauer, S. Magill, B. Musgrave, A. Pellegrino, J. Repond, R. Yoshida Argonne National Laboratory, Argonne, Illinois 60439-4815 M.C.K. Mattingly Andrews University, Berrien Springs, Michigan 49104-0380 P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, G. Levi, A. Margotti, T. Massam, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi University and INFN Bologna, Bologna, Italy G. Aghuzumtsyan, I. Brock, S. Goers, H. Hartmann, E. Hilger, P. Irrgang, H.-P. Jakob, A. Kappes, U.F. Katz, R. Kerger, O. Kind, E. Paul, J. Rautenberg, H. Schnurbusch, A. Stifutkin, J. Tandler, K.C. Voss, A. Weber, H. Wieber Physikalisches Institut der Universität Bonn, Bonn, Germany D.S. Bailey, N.H. Brook, J.E. Cole, B. Foster G.P. Heath, H.F. Heath, S. Robins, E. Rodrigues, J. Scott, R.J. Tapper, M. Wing H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom M. Capua, A. Mastroberardino, M. Schioppa, G. Susinno Calabria University, Physics Department and INFN, Cosenza, Italy e H.Y. Jeoung, J.Y. Kim, J.H. Lee, I.T. Lim, K.J. Ma, M.Y. Pac Chonnam National University, Kwangju, Korea A. Caldwell, M. Helbich, W. Liu, X. Liu, B. Mellado, S. Paganis, S. Sampson, W.B. Schmidke, F. Sciulli Nevis Laboratories, Columbia University, Irvington on Hudson, New York 10027 o J. Chwastowski, A. Eskreys, J. Figiel, K. Klimek, K. Olkiewicz, M.B. Przybycień, P. Stopa, L. Zawiejski Institute of Nuclear Physics, Cracow, Poland B. Bednarek, I. Grabowska-Bold, K. Jeleń, D. Kisielewska, A.M. Kowal, M. Kowal, T. Kowalski, B. Mindur, M. Przybycień, E. Rulikowska-Zarȩbska, L. Suszycki, D. Szuba, J. Szuba Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, Cracow, Poland