1,374,828 research outputs found
Parton distributions
No full textParton distributions, α(χ,μ(^₂) are essential ingredients for almost all theoretical calculations at hadron colliders. They give the number densities of the colliding par- tons (quarks and gluons) inside their parent hadrons at a given momentum fraction χand scale μ(^₂). The scale dependence of the parton distributions is given by DGLAP evolution, while the X dependence must be determined from a global analysis of deep-inelastic scattering (DIS) and related hard-scattering data. In Part I we introduce ‘doubly-unintegrateď parton distributions, fa(x, z, k(^₂),μ(^₂)), which additionally depend on the splitting fraction z and the transverse momentum (k) associated with the last evolution step. We show how these distributions can be used to calculate cross sections for inclusive jet production in DIS and compare the predictions to data taken at the HERA ep collider. We then calculate the transverse momentum distributions of พ and z bosons at the Tevatron pp collider and of Standard Model Higgs bosons at the forthcoming LHC. In Part II we study diffractive DIS, which is characterised by a large rapidity gap between the slightly deflected proton and the products of the virtual photon dissociation. We perform a novel QCD analysis of recent HERA data and extract diffractive parton distributions. The results of this analysis are used to investigate the effect of absorptive corrections in inclusive DIS. These absorptive corrections are due to the recombination of partons within the proton and are found to enhance the size of the gluon distribution at small X. We discuss the problem that the gluon distribution decreases with decreasing X at low scales while the sea quark distribution increases with decreasing X, whereas Regge theory predicts that both should have the same small-X behaviour. Our study hints at the possible importance of power corrections at low scales of around 1 GeV
Multi-Parton Interactions at the LHC.
No full textWe review the recent progress in the theoretical description and experimental observation of multiple parton interactions. Subjects covered include experimental measurements of minimum bias in- teractions and of the underlying event, models of soft physics implemented in Monte Carlo generators, developments in the theoretical description of multiple parton interactions and phenomenological studies of double parton scattering. This article stems from contributions presented at the Helmholtz Alliance workshop on ”Multi-Parton Interactions at the LHC”, DESY Hamburg, 13-15 September 2010
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Dolly parton, songteller ::my life in lyrics /
No full textDolly Parton, Songteller: My Life in Lyrics is a landmark celebration of the remarkable life and career of a country music and pop culture legend. As told by Dolly Parton in her own inimitable words, explore the songs that have defined her journey. Illustrated throughout with previously unpublished images from Dolly Parton's personal and business archives. Mining over 60 years of songwriting, Dolly Parton highlights 150 of her songs and brings readers behind the lyrics. Packed with never-before-seen photographs and classic memorabilia Explores personal stories, candid insights, and myriad memories behind the songs Dolly Parton, Songteller: My Life in Lyrics reveals the stories and memories that have made Dolly a beloved icon across generations, genders, and social and international boundaries. Containing rare photos and memorabilia from Parton's archives, this book is a show-stopping must-have for every Dolly Parton fan. Learn the history behind classic Parton songs like "Jolene," "9 to 5," "I Will Always Love You," and more. The perfect gift for Dolly Parton fans (everyone loves Dolly!) as well as lovers of music history and country Add it to the shelf with books like Coat of Many Colors by Dolly Parton, The Beatles Anthology by The Beatles, and Born to Run by Bruce Springsteen
Monte Carlo simulations of hard QCD radiation
No full textMonte Carlo event generators, such as Herwig++, provide a full simulation of events at collider experiments. They give a fully exclusive description of hadronic final states and are therefore crucial tools for the planning of future experiments and analysing of data from existing experiments.
The key component that allows this description of high-multiplicity final states is the parton shower. There has been much recent progress improving the parton shower description of hard radiation using exact matrix elements. This thesis describes research into implementing and improving such methods within the Herwig++ event generator.
In Chapter 1, the parton-shower formalism is reviewed and the structure of event generators described. Chapter 2 details the specifics of the \textsf{Herwig++} parton shower.
In Chapters 3 and 4, the POWHEG next-to-leading-order matching procedure is described, and work implementing the scheme within Herwig++ is presented. The method is implemented for the processes e+e- to hadrons and Drell-Yan vector boson production and the results are compared to experimental data from LEP and the Tevatron. This work includes the first full implementation of the truncated shower.
A description of the development and implementation of a modified matrix-element merging scheme is presented in Chapter 5. This scheme is based on CKKW merging but uses an extension of the POWHEG idea to improve the method using truncated showers. The method is implemented first for final-state radiation in e+e- to hadrons and then, in Chapter 6, extended to include initial-state radiation in Drell-Yan vector boson production
HERWIG 6: an event generator for Hadron emission reactions with interfering gluons (including supersymmetric processes)
No full textHERWIG is a general-purpose Monte Carlo event generator, which includes the simulation of hard lepton-lepton, lepton-hadron and hadron-hadron scattering and soft hadron-hadron collisions in one package. It uses the parton-shower approach for initial- and final-state QCD radiation, including colour coherence effects and azimuthal correlations both within and between jets. This article updates the description of HERWIG published in 1992, emphasising the new features incorporated since then. These include, in particular, the matching of first-order matrix elements with parton showers, a more correct treatment of heavy quark decays, and a wide range of new processes, including many predicted by the Minimal Supersymmetric Standard Model, with the option of R-parity violation. At the same time we offer a brief review of the physics underlying HERWIG, together with details of the input and control parameters and the output data, to provide a self-contained guide for prospective users of the program
Measurement of the production cross section of prompt J/ψ mesons in association with a W± boson in pp collisions at p s = 7 TeV with the ATLAS detector
No full textThe process pp → W±J/ψ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb-1 of p s = 7TeV pp collisions at the LHC, the first observation is made of the production of W± + prompt J/ events in hadronic collisions, using W± → μ and J/ψ → μ+μ-. A yield of 27.4±7.5 -6.5 W± + prompt J/ψ events is observed, with a statistical significance of 5.1. The production rate as a ratio to the inclusive W± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated
Measurement of the production of a W boson in association with a charm quark in pp collisions at s√ = 7 TeV with the ATLAS detector
No full textThe production of a W boson in association with a single charm quark is studied using 4.6 fb−1 of pp collision data at s√ = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96+0.26−0.30 at Q 2 = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ(W + + c¯)/σ(W − + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s−s¯ quark asymmetry
Measurement of associated W+ charm production in pp collisions at √s=7 TeV
No full textOpen Access, Copyright CERN, for the benefit of the CMS Collaboration.Measurements are presented of the associated production of a W boson and a charm-quark jet (W + c) in pp collisions at a center-of-mass energy of 7 TeV. The analysis is conducted with a data sample corresponding to a total integrated luminosity of 5 fb−1, collected by the CMS detector at the LHC. W boson candidates are identified by their decay into a charged lepton (muon or electron) and a neutrino. The W + c measurements are performed for charm-quark jets in the kinematic region p jet T > 25 GeV, |ηjet| 25 GeV) and σ(pp → W + c + X)× B (W → ℓν) = 84.1 ± 2.0 (stat.) ± 4.9 (syst.) pb ( p ℓ T > 35 GeV), and the cross section ratios σ(pp → W+ + c ¯ + X)/σ(pp → W− + c + X) = 0.954 ± 0.025 (stat.) ± 0.004 (syst.) ( p ℓ T > 25 GeV) and σ(pp → W+ + c ¯ + X)/σ(pp → W− + c + X) = 0.938 ± 0.019 (stat.) ± 0.006 (syst.) ( p ℓ T > 35 GeV). Cross sections and cross section ratios are also measured differentially with respect to the absolute value of the pseudorapidity of the lepton from the W-boson decay. These are the first measurements from the LHC directly sensitive to the strange quark and antiquark content of the proton. Results are compared with theoretical predictions and are consistent with the predictions based on global fits of parton distribution functions
Measurement of the differential and double-differential Drell-Yan cross sections in proton-proton collisions at root s=7 TeV
No full textMeasurements of the differential and double-differential Drell-Yan cross sections are presented using an integrated luminosity of 4.5 (4.8) fb−1 in the dimuon (dielectron) channel of proton-proton collision data recorded with the CMS detector at the LHC at s√ = 7 TeV. The measured inclusive cross section in the Z-peak region (60–120 GeV) is σ(ℓℓ) = 986.4 ± 0.6 (stat.) ± 5.9 (exp. syst.) ± 21.7 (th. syst.) ± 21.7 (lum.) pb for the combination of the dimuon and dielectron channels. Differential cross sections dσ/dm for the dimuon, dielectron, and combined channels are measured in the mass range 15 to 1500 GeV and corrected to the full phase space. Results are also presented for the measurement of the double-differential cross section d2σ/dm d|y| in the dimuon channel over the mass range 20 to 1500 GeV and absolute dimuon rapidity from 0 to 2.4. These measurements are compared to the predictions of perturbative QCD calculations at next-to-leading and next-to-next-to-leading orders using various sets of parton distribution functions
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