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We consider sample of inclusive [gamma] + 3 jet events collected by the D0 experiment. The double parton fraction (f{sub DP}) and effective cross section [sigma]{sub eff}, a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in p{sub T}) jet transverse momentum p{sub T}{sup jet2} within the 15 ≤ p{sub T}{sup jet2} ≤ 30 GeV range. Also we measured cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (p{sub T}) of the [gamma] + leading jet system and p{sub T} of the other jet for [gamma] + 2 jet, or p{sub T} sum of the two other jets for [gamma] + 3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the PYTHIA and SHERPA Monte Carlo (MC) generators.
Here, we present the results of studies of multiparton interactions done by the DØ collaboration using the Fermilab Tevatron at a center of mass energy of 1.96 TeV. We also present three analyses, involving three distinct final signatures: (a) a photon with at least 3 jets ([gamma] + 3jets), (b) a photon with a bottom or charm quark tagged jet and at least 2 other jets ([gamma] + b/c + 2jets), and (c) two J/ [psi] mesons. The fraction of photon + jet events initiated by double parton scattering is about 20%, while the fraction for events in which two J/ [psi] mesons were produced is 30 ± 10. While the two measurements are statistically compatible, the difference might indicate differences in the quark and gluon distribution within a nucleon. Finally, this speculation originates from the fact that photon + jet events are created by collisions with quarks in the initial states, while J/ [psi] events are produced preferentially by a gluonic initial state.
Samples of inclusive [gamma] + 2 jet and [gamma] + 3 jet events collected by the D0 experiment with an integrated luminosity of about 1 fb−1 in p{bar p} collisions at √s = 1.96 TeV are used to measure cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (p{sub T}) of the [gamma] + leading jet system (jets are ordered in p{sub T}) and p{sub T} of the other jet for [gamma] + 2 jet, or p{sub T} sum of the two other jets for [gamma] + 3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the pythia and sherpa Monte Carlo (MC) generators. The data indicate a contribution from events with double parton (DP) interactions and are well described by predictions provided by the pythia MPI models with p{sub T}-ordered showers and by sherpa with the default MPI model. The [gamma] + 2 jet data are also used to determine the fraction of events with DP interactions as a function of the azimuthal angle and as a function of the second jet p{sub T}.
Many high-energy collider experiments (including the current Large Hadron Collider at CERN) involve the collision of hadrons. Hadrons are composite particles consisting of partons (quarks and gluons), and this means that in any hadron-hadron collision there will typically be multiple collisions of the constituents — i.e. multiple parton interactions (MPI). Understanding the nature of the MPI is important in terms of searching for new physics in the products of the scatters, and also in its own right to gain a greater understanding of hadron structure. This book aims at providing a pedagogical introduction and a comprehensive review of different research lines linked by an involvement of MPI phenomena. It is written by pioneers as well as young leading scientists, and reviews both experimental findings and theoretical developments, discussing also the remaining open issues.
This book constitutes the proceedings of the XVIII International Symposium on Lepton-Photon Interactions. It contains 30 review papers on the latest developments by experts in the field. The subjects cover the structure of photons and hadrons, progress in QCD and diffraction, heavy quark (c, b, t) physics, electroweak precision measurements and tests, CP violation, neutrino physics, searches for new particles and phenomena, cosmology, progress in theory and physics at future colliders.
We have used a sample of photon+3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb−1 to determine the fraction of events with double parton scattering (f{sub DP}) in a single ppbar collision at √s = 1.96 TeV. The DP fraction and effective cross section (sigma{sub eff}), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in p{sub T}) jet transverse momentum pT{sub jet2} within the range 15
This book mainly focuses on the study of photon + 3 jets final state in Proton-Proton Collisions at √s = 7TeV, searching for patterns of two (or more) distinct hard scatterings in the same collision, i.e the so-called Double Parton Scattering (DPS). A new method by using Monte Carlo generators was performed and provides higher order corrections to the description of the Single Parton Scattering (SPS) background. Further it is investigated whether additional contributions from DPS can improve the agreement between the measured data and the Monte Carlo predictions. The current theoretical uncertainties related to the SPS background are found to be larger than expectation. At the same time a rich set of DPS-sensitive measurements is reported for possible further interpretation.
The main focus of this book is on experimental results from electron-positron and electron-proton colliders and related theoretical questions, particularly on hadron production at energies from 1 to 100 GeV and higher. The topics discussed include photo- and electroproduction of heavy flavours, the photon structure function, total cross section, jet production and resonance production. The future of the field is also discussed, notably experiments at linear photon-photon colliders.
The thesis is devoted to the study of processes with multiple parton interactions (MPI) in a ppbar collision collected by D0 detector at the Fermilab Tevatron collider at sqrt(s) = 1.96 TeV. The study includes measurements of MPI event fraction and effective cross section, a process-independent parameter related to the effective interaction region inside the nucleon. The measurements are done using events with a photon and three hadronic jets in the final state. The measured effective cross section is used to estimate background from MPI for WH production at the Tevatron energy.