https://doi.org/10.1140/epjc/s10052-008-0544-3
Regular Article - Experimental Physics
Three- and four-jet production at low x at HERA
1
I. Physikalisches Institut der RWTH, Aachen, Germany
2
Vinca Institute of Nuclear Sciences, Belgrade, Serbia
3
School of Physics and Astronomy, University of Birmingham, Birmingham, UK
4
Inter-University Institute for High Energies ULB-VUB, Brussels, Universiteit Antwerpen, Antwerpen, Belgium
5
National Institute for Physics and Nuclear Engineering (NIPNE), Bucharest, Romania
6
Rutherford Appleton Laboratory, Chilton, Didcot, UK
7
Institute for Nuclear Physics, Cracow, Poland
8
Institut für Physik, Universität Dortmund, Dortmund, Germany
9
Joint Institute for Nuclear Research, Dubna, Russia
10
CEA, DSM/DAPNIA, CE-Saclay, Gif-sur-Yvette, France
11
DESY, Hamburg, Germany
12
Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany
13
Max-Planck-Institut für Kernphysik, Heidelberg, Germany
14
Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany
15
Kirchhoff-Institut für Physik, Universität Heidelberg, Heidelberg, Germany
16
Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic
17
Department of Physics, University of Lancaster, Lancaster, UK
18
Department of Physics, University of Liverpool, Liverpool, UK
19
Queen Mary and Westfield College, London, UK
20
Physics Department, University of Lund, Lund, Sweden
21
CPPM, Univ. Mediterranee, CNRS/IN2P3, Marseillem, France
22
Departamento de Fisica Aplicada, CINVESTAV, Merida, Yucatan, Mexico
23
Departamento de Fisica, CINVESTAV, Mexico
24
Institute for Theoretical and Experimental Physics, Moscow, Russia
25
Lebedev Physical Institute, Moscow, Russia
26
Max-Planck-Institut für Physik, München, Germany
27
LAL, Univ Paris-Sud, CNRS/IN2P3, Orsay, France
28
LLR, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
29
LPNHE, Universités Paris VI and VII, IN2P3-CNRS, Paris, France
30
Faculty of Science, University of Montenegro, Podgorica, Montenegro
31
Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic
32
Faculty of Mathematics and Physics, Charles University, Praha, Czech Republic
33
Dipartimento di Fisica Università di Roma Tre and INFN Roma 3, Roma, Italy
34
Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
35
Institute of Physics and Technology of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia
36
Paul Scherrer Institut, Villigen, Switzerland
37
Fachbereich C, Universität Wuppertal, Wuppertal, Germany
38
Yerevan Physics Institute, Yerevan, Armenia
39
DESY, Zeuthen, Germany
40
Institut für Teilchenphysik, ETH, Zürich, Switzerland
41
Physik-Institut der Universität Zürich, Zürich, Switzerland
* e-mail: obehnke@mail.desy.de
Received:
16
November
2007
Revised:
18
December
2007
Published online:
22
February
2008
Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q2 with the H1 detector using an integrated luminosity of 44.2 pb-1. Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of and and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the calculation. Too few events are predicted at the lowest x∼10-4, especially for topologies with two forward jets. This hints to large contributions at low x from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.
© Springer-Verlag , 2008