Test Of Perturbative QCD Research Articles

Measurements of W and Z boson production in ATLAS

Precision measurements of the production cross-sections of W and Z boson at LHC provide important tests of perturbative QCD and information about the parton distribution functions for quarks within the proton. We present measurements of cross sections for inclusive W^+W+, W^{-}W− and Z boson production using data collected by the ATLAS experiment at a center-of-mass energy of \sqrt{s}s=2.76 TeV. Measurement of the transverse momentum distribution of Z boson at \sqrt{s}s=13 TeV is also presented. The measurements are corrected for detector effects and compared with state-of-the-art theoretical calculations.

Measurements of the production of prompt photons, jets and vector bosons+jets in pp collisions with the ATLAS detector

The production of jets, photons and gauge bosons in association with jets at hadron colliders provides a stringent test of perturbative QCD and can be used to probe the gluon density function of the proton. In this letter we present recent measurements of the inclusive jet cross section in data collected at center-of-mass energies of 8 TeV and 13 TeV. The measurements have been performed differentially in various kinematic and angular observables and are compared with state-of-the-art predictions at NLO in pQCD. ATLAS has performed precise measurements of the inclusive production of isolated prompt photons in data collected at center-of-mass energies of 8 and 13 TeV, differential in both rapidity and the photon transverse momentum. The measurements are compared with NLO pQCD calculations and with several MC generators. The cross section of photons, W and Z bosons in association with one or more jets have been measured differentially in various observables at center-of-mass energies of 8 and 13 TeV and compared with state-of-the-art pQCD calculations up to NNLO QCD and NLO EWK as well as LO and NLO ME+PS generators. Dedicated phase spaces sensitive to emission of massive bosons collinear with jets or the electroweak production of vector bosons are tested.

Measurements of the production of a vector boson in association with jets in the ATLAS and CMS detectors

The production of a vector boson (V = W, Z) in association with jets is can be used for a precise test of perturbative QCD and is a dominant background process in many searches for physics beyond the Standard Model. The differential cross section measurements from CMS and ATLAS collaborations would be presented, and several theoretical predictions at leading order (LO) and next-to leading order (NLO) are compared to data, after the deconvolution of detector effects, with proton-proton collisions at a center of mass energy of 7, 8 and 13 TeV at LHC.

Z/W + jets production at 8/13 TeV in CMS

The production of vector bosons (Z and W) in association with jets provides a stringent test of perturbative QCD and is a background process in searches for new physics. Differential cross section measurements of vector bosons produced in association with jets and heavy flavour quarks in proton-proton collisions at center of mass energies of 8 TeV and 13 TeV in the CMS experiment at the LHC are presented. The measurements are compared to next-to-leading order calculations and event simulations that devise matrix element calculations interfaced with parton showers.

Measurements of Heavy Flavour Photoproduction at HERA

Recent measurements of open charm and beauty photoproduction with the H1 and ZEUS detectors at the e±p-collider HERA are presented. These measurements reveal valuable details about the inner structure of the proton and the photon, the fragmentation of quarks into jets, and allow tests of perturbative QCD. Various experimental techniques were employed to identify and extract the heavy-quark signal. Their results are discussed, and compared to each other and to NLO QCD calculations. In addition the determination of charm fragmentation fractions is presented.

Jet and photon measurements from ATLAS

Di erential cross-section measurements of inclusive-jet and di-jet production provide stringent tests of perturbative QCD predictions and provide inputs for determination of parton density functions. Ratios of jet multiplicities are sensitive to s and have reduced theoretical uncertainties. Measurements of the inclusive isolated-photon and di-photon cross-sections provide a direct probe of short-distance physics, complementary to that from measurements of jets or vector-bosons and are sensitive to the gluon density in the proton. The measurements are compared to next-to-leading-order or higher-order QCD calculations. 1 Introduction ATLAS is a general purpose detector operating within the LHC experiment. The main goals of ATLAS are searches of the Higgs boson, study of the properties of the top quark and search for new physics. High-precision measurements to make novel tests of perturbative QCD (pQCD) will also be possible due to the higher centre-of-mass energy ( p s) available at LHC than in previous accelerators. In this pa- per, measurements of jets and photons at ATLAS are pre- sented. These measurements are one of the tools that can be used at LHC to increase the understanding of QCD in- teractions. In particular, they allow the testing of pQCD down to the shortest accessible distances. Their sensitivity to the proton parton distribution functions (PDFs) make them adequate to measure the strong coupling constant s and to the improvement of the determination of the PDFs. Photons are colorless probes to QCD and can be used to constrain the proton PDFs. Di-photons processes are in ad- dition an important background for the identification of the Higgs boson in the H ! channel. Comparison of data and next-to-leading-order (NLO) and next-to-next-leading- order (NNLO) QCD theoretical calculations are the main focus of this paper.

Heavy Flavour Production Measurements at the CERN-LHC

The study of heavy flavour (charm and beauty) production in proton-proton (pp) collisions at the LHC (Large Hadron Collider) is expected to provide an important test of perturbative QCD (pQCD) calculations in a new energy domain.1),2) In heavy-ion collisions, heavy quarks are, due to their large mass, produced in the early stage and experience the full evolution of the strongly-interacting medium expected to be formed in the collision. Heavy flavour particles should be sensitive to the density of this medium through the mechanism of in-medium energy loss of heavy quarks. This effect is usually studied by means of the nuclear modification factor:

Measurement of forward-rapidity heavy-flavour muons in proton-proton collisions at [formula omitted] with ALICE

We report the first results of the ALICE experiment on heavy-flavour measurements at forward 1 1 In this paper “forward” means in the LHC clockwise stream with respect to the interaction point. rapidity ( − 4 < η < − 2.5 ) in the muonic decay channel. The data have been collected during the proton-proton collisions at s = 7 TeV . In the ALICE program, the heavy-flavour detection in nucleon-nucleon interactions has a central role both as a test of perturbative QCD and as a baseline for the study of matter at high energy densities in heavy-ion collisions. The extraction of the heavy-flavour signal in the inclusive muon spectra requires the subtraction of the contribution from the decay-in-flight of light hadrons and from particles produced in the absorption elements. The details of the analysis and the main results will be discussed in this paper.

Production of Jets and Photons at ATLAS

The measurement of the production of jets and photons in ATLAS will provide ideal tests of perturbative QCD in a kinematic regime never observed before. Gaining a precise quantitative understanding of perturbative QCD is essential to searches for new physics at the LHC. In addition, differential cross-section measurements of jet and photon production can be used to constrain parton density functions. The detection of jets and photons in ATLAS is achieved by using finely segmented calorimeters, which surround an inner tracking system enclosed in a 2T solenoid field.

Tests of QCD at colliders

Measurements at colliders can provide precision tests of perturbative QCD as well as leading the development of nonperturbative QCD techniques. This paper discusses precision tests of pQCD calculations made with data taken at ep, e + e −, and hadron-hadron facilities. Measurements of the fragmentation process are also discussed in the context of nonperturbative models.

Perturbative QCD relations inspired by hypothetical tau leptons

We review our recent works on tests of perturbative QCD, inspired by the relation between the hadronic decay of the τ lepton and the e + e − annihilation into hadrons. First, we present a set of commensurate scale relations that probe the self-consistency of leading-twist QCD predictions for any observable which defines an effective charge. These tests are independent of the renormalization scheme and scale, and are applicable over wide data ranges. As an example we apply this approach to R e + e − . Second, using a differential form of these conmensurate scale relations, we present a method to measure the QCD Gell-Mann-Low Ψ function.

Measuring the QCD Gell-Mann–LowΨfunction

We present a general method for extracting the Gell-Mann--Low logarithmic derivative of an effective charge of an observable directly from data as a mean for empirically verifying the universal terms of the QCD $\ensuremath{\beta}$ function. Our method avoids the biases implicit in fitting to QCD-motivated forms as well as the interpolation errors introduced by constructing derivatives from discrete data. We also derive relations between moments of effective charges as new tests of perturbative QCD.

Testing QCD with hypothetical tau leptons

We construct new tests of perturbative QCD by considering a hypothetical tau lepton of arbitrary mass, which decays hadronically through the electromagnetic current. We can explicitly compute its hadronic width ratio directly as an integral over the e^+ e^- annihilation cross section ratio, R_{e^+e^-}. Furthermore, we can design a set of commensurate scale relations and perturbative QCD tests by varying the weight function away from the form associated with the V-A decay of the physical tau. This method allows the wide range of the R_{e^+e^-} data to be used as a probe of perturbative QCD.

Measurement ofαs(Q2)from the Gross–Llewellyn Smith Sum Rule

We extract a set of values for the Gross–Llewellyn Smith sum rule at different values of 4-momentum transfer squared ( Q2), by combining revised CCFR neutrino data with data from other neutrino deep-inelastic scattering experiments for 1<Q2<15GeV2/c2. A comparison with the order αs3 theoretical predictions yields a determination of αs at the scale of the Z-boson mass of 0.114±0.0120.009. This measurement provides a new and useful test of perturbative QCD at low Q2, because of the low uncertainties in the higher order calculations.Received 8 May 1998DOI:https://doi.org/10.1103/PhysRevLett.81.3595©1998 American Physical Society

Phenomenology of forward hadrons in deep inelastic scattering: Fracture functions and itsQ2evolution

We analyze recent data on the production of forward neutrons in deep inelastic scattering at DESY HERA in the framework of a perturbative QCD description for semi-inclusive processes, which includes fracture functions. Using a model estimate for the nonperturbative piece of the fragmentation process, in fairly good agreement with the available data, we analyze the ${Q}^{2}$ dependence of the resulting fracture functions, which is driven by nonhomogeneous evolution equations. We also propose a measurement of the pion production cross section in the target fragmentation region as a new test of perturbative QCD, which in this case predicts also a different ${Q}^{2}$ evolution with respect to the one given by the usual Altarelli-Parisi equations.

PROPERTIES OF THE W BOSON FROM THE FERMILAB TEVATRON

The experimental knowledge of the charged intermediate vector boson, the W, is reviewed. Measurements of the electroweak properties of the W boson, such as its mass, decay width, couplings to fermions, and leptonic branching ratios, are summarized. As well, I review production properties of the W as measured in [Formula: see text] collisions and how they can be used as tests of perturbative QCD. I also discuss new particle searches that make use of the W signature, such as new charged electroweak bosons and the now-confirmed discovery of the top quark.

Tests of perturbative QCD using CCFR data for measurements of nucleon structure functions

We present measurements of nucleon structure functions, F 2( ϰ, Q 2) and xFs( ϰ, Q 2), from the high-statistics, high-energy neutrino-iron scattering experiment at the Fermilab Tevatron. The existing high-statistics xF 3 determination by the CDHSW collaboration is compared to our data. The data presented here constitute the first corroboration of the QCD prediction of xF 3 evolution at low-ϰ, and yields Λ MS =210±28±41 MeV, and a determination of the GLS sum rule at Q 2 = 3 GeV 2, S GLS = ∫ ϰ 1 xF s ϰ =2.50±0.018 (stat.)±0.078 (syst.) . Our value of Λ MS yields α 3( M z ) = .111 ± .002 ± .003 ± .003 (scale). Comparison of the neutrino determination of F 2( ϰ, Q 2) with that obtained from the charged-lepton ( e or μ) scattering leads to a precise test of the mean-square charge prediction by the Quark Parton Model. The SLAC-CCFR and BCDMS structure function provide a consistent and precise set of structure functions over a large range of Q 2.

Tests of Perturbative QCD at LEP

Following a major shortage of 99Mo in the 2009–2010 period, concern grew that the aging reactor production facilities needed to be replaced. Most producers were using highly enriched 235U (HEU) as the target material. The Organisation for Economic Co-...Read More

Tests of QCD at LEP

Recent results on tests of perturbative QCD in hadronic final states of Z 0 bosons are reviewed. Studies of 3- and 4-jet final states provide significant tests of the basic quantum numbers of the theory, as the gluon spin and the number of colours ( N c = 3). The energy dependence of jet production rates provides direct evidence for asymptotic freedom and for the nonabelian nature of QCD. The strong coupling α s is determined, from studies of event topologies and jet production rates, to be α s ( M Z 0 ) = 0.115 ± 0.008 in second order perturbation theory, where the error is dominated by the unknown contribution of higher orders. Combined analyses of Z 0 line shapes and decay asymmetries lead to α s ( M Z 0 ) = 0.131 ± 0.011, which is limited by data statistics. The weighted average is α s ( M Z 0 ) = 0.120 ± 0.006. Studies of soft hadron and gluon coherence phenomena are shortly reviewed.

Tests of Perturbative QCD at LEP

Following a major shortage of 99Mo in the 2009–2010 period, concern grew that the aging reactor production facilities needed to be replaced. Most producers were using highly enriched 235U (HEU) as the target material. The Organisation for Economic Co-...Read More