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A study of ''underlying event'' in Run 2 at CDF is presented. Several PYTHIA 6.2 tunes (with multiple parton interactions) are examined and compared with HERWIG (without multiple parton interactions) and with the ATLAS PYTHIA tune (with multiple parton interactions) and they are extrapolated to the LHC.
We present recent studies about the ''underlying event'' which originates mostly from soft spectator interactions. First Run II data results are compared to published Run I results and to QCD Monte Carlo models.
Soft, non-perturbative, interactions are poorly understood from the theoretical point of view even though they form a large part of the hadronic cross section at the energies now available. We review the CDF studies on minimum-bias ad underlying event in p{bar p} collisions at 2 TeV. After proposing an operative definition of 'underlying event', we present part of a systematic set of measurements carried out by the CDF Collaboration with the goal to provide data to test and improve the QCD models of hadron collisions. Different analysis strategies of the underlying event and possible event topologies are discussed. Part of the CDF minimum-bias results are also presented: in this sample, that represent the full inelastic cross-section, we can test simultaneously our knowledge of all the components that concur to form hadronic interactions. Comparisons with MonteCarlo simulations are always shown along with the data. These measurements will also contribute to more precise estimates of the soft QCD background of high-p{sub T} observables.
Improving our understanding and modeling of the underlying event in high energy collider environment is important for more precise measurements at the LHC. CDF Run II data for the underlying event associated with Drell-Yan lepton pair production and early ATLAS data measuring underlying event activity with respect to the leading transverse momentum track are presented. The data are compared with several QCD Monte Carlo models. It is seen that no current standard Monte Carlo tune adequately describes all the early ATLAS data and CDF data simultaneously. The underlying event observables presented here are particularly important for constraining the energy evolution of multiple parton interaction models. One of the goals of these analyses is to provide data that can be used to test and improve MC models for current and future physics studies at the LHC. The underlying event observables presented here are particularly important for constraining the energy evolution of multiple partonic interaction models, since the plateau heights of the underlying event profiles are highly correlated to multiple parton interaction activity. The data at 7 TeV are crucial for MC tuning, since measurements are needed with at least two energies to constrain the energy evolution of MPI activity. PYTHIA tune A and tune AW do a good job in describing the CDF data on the underlying-event observables for leading jet and Drell-Yan events, respectively, although the agreement between predictions and data is not perfect. The leading-jet data show slightly more activity in the underlying event than PYTHIA Tune A, although they are very similar - which may indicate the universality of underlying event modeling. However, all pre-LHC MC models predict less activity in the transverse region (i.e in the underlying event) than is actually observed in ATLAS leading track data, for both center-of-mass energies. There is therefore no current standard MC tune which adequately describes all the early ATLAS data. However, using diffraction-limited minimum bias distributions and the plateau of the underlying event distributions presented here, ATLAS has developed a new PYTHIA tune AMBT1 (ATLAS Minimum Bias Tune 1) and a new HERWIG+ JIMMY tune AUET1 (ATLAS Underlying Event Tune 1) which model the p{sub T} and charged multiplicity spectra significantly better than the pre-LHC tunes of those generators. It is critical to have sensible underlying event models containing our best physical knowledge and intuition, tuned to all relevant available data.
We study the behavior of the "underlying event" in hard scattering proton-antiproton collisions at 1.8 TeV and compare with the QCD Monte-Carlo models. The "underlying event" is everything except the two outgoing hard scattered "jets" and receives contributions from the "beam-beam remnants" plus initial and final-state radiation. The data indicate that neither ISAJET or HERWIG produce enough charged particles (with pt > 0.5 GeV /c) from the "beam-beam remnant" component and that ISAJET produces too many charged particles from initial-state radiation. PYTHIA which uses multiple parton scattering to enhance the "underlying event" does the best job describing the data.
This proceedings volume contains pedagogical lectures on theoretical and experimental particle physics, cosmology and atomic trap physics. It also includes additional contributions that provide up-to-date information on new experimental results from accelerators, underground laboratories, and nuclear astrophysics. This combination of pedagogical talks and topical short talks provides comprehensive information to researchers in the fields of particle physics, cosmology and atomic trap physics. Sample Chapter(s). Chapter 1: New Physics in B and K Decays (1,704 KB). Contents: Cosmic Ray Velocity and Electric Charge Measurements in the AMS Experiment (L Arruda); Flavor and Chiral Oscillations with Dirac Spinors (A E Bernardini); Modification of the Casimir Effect Due to a Minimal Length Scale (U Harbach); Parton Energy Loss, Saturation, and Recombination at BRAHMS (E-J Kim); Spatial Confinement and Thermal Deconfinement in the Compactified Gross-Neveu Model (J M C Malbouisson); Currents on Superconducting Strings in an Unusual Environment (M A Metlitski); QCD Results at CDF (O Norniella); Quantization of Galilean Covariant Fields (E S Santos); Physics of Heavy Flavour at CDF (S Torre); Resonance Production at STAR (H Zhang); and other papers. Readership: Graduate students, researchers and academics in high energy physics, particle physics and astrophysics.
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 gathers the proceedings of The Hadron Collider Physics Symposia (HCP) 2005, and reviews the state-of-the-art in the key physics directions of experimental hadron collider research. Topics include QCD physics, precision electroweak physics, c-, b-, and t-quark physics, physics beyond the Standard Model, and heavy ion physics. The present volume serves as a reference for everyone working in the field of accelerator-based high-energy physics.