The Underlying Event in Large Transverse Momentum Charged Jet and Z-boson Production

The Underlying Event in Large Transverse Momentum Charged Jet and Z-boson Production
Author:
Publisher:
Total Pages:
Release: 2000
Genre:
ISBN:

The authors study the behavior of the underlying event in large transverse momentum charged jet and Z-boson production at 1.8 TeV and compare with the QCD Monte-Carlo models. The data indicate that neither ISAJET or HERWIG produce enough charged particles (with p{sub T}> 0.5 GeV/c) from the beam-beam remnant component and that ISAJET produces too many charged particle from initial-state radiation. PYTHIA which uses multiple parton scattering to enhance the underlying event does the best job describing the data.

Jet and Underlying Event Properties as a Function of Charged-particle Multiplicity in Proton-proton Collisions at Sqrt(s)

Jet and Underlying Event Properties as a Function of Charged-particle Multiplicity in Proton-proton Collisions at Sqrt(s)
Author:
Publisher:
Total Pages: 41
Release: 2013
Genre:
ISBN:

Characteristics of multi-particle production in proton-proton collisions at sqrt(s) = 7 TeV are studied as a function of the charged-particle multiplicity, N[ch]. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity abs(eta) 2.4 and transverse momentum pt 0.25 GeV. Jets are reconstructed from charged-particles only and required to have pt> 5 GeV. The distributions of jet pt, average pt of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of N[ch] and compared to the predictions of the PYTHIA and HERWIG event generators. Predictions without multi-parton interactions fail completely to describe the N[ch]-dependence observed in the data. For increasing N[ch], PYTHIA systematically predicts higher jet rates and harder pt spectra than seen in the data, whereas HERWIG shows the opposite trends. At the highest multiplicity, the data-model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients.

60 Years Of Cern Experiments And Discoveries

60 Years Of Cern Experiments And Discoveries
Author: Herwig Schopper
Publisher: World Scientific
Total Pages: 452
Release: 2015-07-13
Genre: Science
ISBN: 9814644161

The book is a compilation of the most important experimental results achieved during the past 60 years at CERN - from the mid-1950s to the latest discovery of the Higgs particle. Covering the results from the early accelerators at CERN to those most recent at the LHC, the contents provide an excellent review of the achievements of this outstanding laboratory. Not only presented is the impressive scientific progress achieved during the past six decades, but also demonstrated is the special way in which successful international collaboration exists at CERN.

Studying Z/?*+Jet Production in Proton-antiproton Collisions at {u221A}s

Studying Z/?*+Jet Production in Proton-antiproton Collisions at {u221A}s
Author:
Publisher:
Total Pages: 189
Release: 2009
Genre:
ISBN:

The production of jets in association with a Z/?* boson is an example of an important class of processes at hadron colliders, namely vector boson + jet (V + jet) production. Comparisons of measurements of this class of processes with theory predictions constitute an important, fundamental test of the Standard Model of particle physics, and of the theory of QCD in particular. While having a smaller cross section than other V +jet processes, Z/?*(→ e+e-) + jets production, with Z/?* → e+e-/?+?-, has a distinct experimental signature allowing for measurements characterized by low backgrounds and a direct, precise measurement of the properties of the decay products of the Z/?* boson. In this thesis, several new measurements of the properties of jets produced in association with a Z/?* boson in p$ar{p}$ collisions at √s = 1.96 TeV are presented. The cross section for Z/?*(→ e+e-) + N jet production (N ≤ 3) is measured, differential in the transverse momentum of the Nth jet in the event, normalized to the inclusive Z/?* cross section. Also, the cross section for Z/?*(→e+e-) + N jets (N ≥ 1) is measured, differential in the difference in azimuthal angle between the di-electron system and any jet in the event, normalized to unity. The data used in the measurements were collected by the D0 experiment located at the Tevatron Collider of the Fermi National Accelerator Laboratory and correspond to an integrated luminosity of 1.04 fb-1. The measured jet transverse momentum spectra are compared with the predictions of perturbative calculations at the next-to-leading order in the strong coupling constant. Given the low sensitivity of the calculations to model parameters, these comparisons represent a stringent test of perturbative QCD. One of the main goals currently being pursued in particle physics is the discovery of the only particle predicted by the Standard Model which has so far no been detected experimentally, namely the Higgs boson. It is assumed that the ATLAS and CMS experiments located at the Large Hadron Collider (LHC), a proton-proton collider at √s = 14 TeV, will be able to detect the Higgs boson, or rule out its existence, within the next few years. The collisions delivered by the LHC will also be used to perform a long range of searches for other new particles, for instance particles predicted by models based on the principle of supersymmetry. The associated production of vector bosons with jets has relatively large production rates at the LHC and can produce a long list of different final states which can include charged leptons, missing transverse energy, as well as light- and heavy-flavour jets. This makes V + jet production a major source of background events to many searches for new particles. Most techniques used for estimating the expected number of background events to searches rely on passing the stable final-state particles of simulated hadron collisions generated using a so-called event generator code, through a simulation of the experimental detector system. The development of event generators which are capable of reliably predicting the properties of jets produced in association with a core process, e.g. the production of a vector boson, has been the subject of a large amount of research activity during the last ten years. These efforts have led to the appearance of the CKKW and MLM algorithms which are implemented in several event generators, among them SHERPA and ALPGEN + PYTHIA. The large data sample collected by the D0 experiment during Run II offers an excellent opportunity for validating these new event generators against experimental measurements of V + jet production. As argued above, the Z/?*(→ e+e-) + jets process offers the combination of a clean experimental signature and large production rates, making it the process of choice for these studies.

The Study of the Z Boson Transverse Momentum Spectrum Recorded by the Compact Muon Solenoid from 2010 Large Hadron Collider Data

The Study of the Z Boson Transverse Momentum Spectrum Recorded by the Compact Muon Solenoid from 2010 Large Hadron Collider Data
Author: Joseph A. Gartner
Publisher:
Total Pages:
Release: 2011
Genre:
ISBN:

ABSTRACT: This dissertation describes the full details of 2 studies of Z0 bosons performed using the Compact Muon Solenoid detector at the Large Hadron Collider of proton on proton collisions with center of mass energy of 7TeV. The first study searches for physics beyond the Standard Model by looking for an excess in production of Z0 bosons by examining the Z0pT spectrum. As no excess is found, limits on new physics models are presented as a function of mass and other free parameters. The second study focuses on a precision measurement of the Z0pT distribution, and is compared to theoretical calculations for the purposes of testing high order QCD calculations in addition to probing the predictions of various tunes of the underlying event.

The Underlying Event in Hard Scattering Processes

The Underlying Event in Hard Scattering Processes
Author: Richard D. Field
Publisher:
Total Pages: 22
Release: 2002
Genre: Jets (Nuclear physics)
ISBN:

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.

Using Drell-Yan to Probe the Underlying Event in Run II at Collider Detector at Fermilab (CDF)

Using Drell-Yan to Probe the Underlying Event in Run II at Collider Detector at Fermilab (CDF)
Author: Deepak Kar
Publisher:
Total Pages:
Release: 2008
Genre:
ISBN:

ABSTRACT: We study the behavior of charged particles produced in association with Drell-Yan lepton-pairs in the region of the Z-boson in proton-antiproton collisions at 1.96 TeV. We use the direction of the Z-boson in each event to define 'toward', 'away', and 'transverse' regions. For Drell-Yan production (excluding the leptons) both the 'toward' and 'transverse' regions are very sensitive to the 'underlying event', which is defined as everything except the two hard scattered components. The data are corrected to the particle level and are then compared with several PYTHIA models (with multiple parton interactions) and HERWIG (without multiple parton interactions) at the particle level (i.e. generator level). The data are also compared with a previous analysis on the behavior of the 'underlying event' in high transverse momentum jet production. The goal is to produce data that can be used by the theorists to tune and improve the QCD Monte-Carlo models of the 'underlying event' that are used to simulate hadron-hadron collisions.

The Black Book of Quantum Chromodynamics

The Black Book of Quantum Chromodynamics
Author: John Campbell
Publisher: Oxford University Press
Total Pages: 760
Release: 2018
Genre: Science
ISBN: 0199652740

This title provides an in-depth introduction to the particle physics of current and future experiments at particle accelerators. The text provides the reader with an overview of practically all aspects of the strong interaction necessary to understand and appreciate modern particle phenomenology at the energy frontier.