Azimuthal asymmetries in hadronic final states at HERA

We provide an experimental and theoretical perspective on the behavior of unpolarized distribution functions for the nucleon and pion on the valence-quark domain; namely, Bjorken-x > ∼ 0.4. This domain is key to much of hadron physics; e.g., a hadron is defined by its flavor content and that is a valence-quark property. Furthermore, its accurate parametrization is crucial to the provision of reliable input for large collider experiments. We focus on experimental extractions of distribution functions via electron and muon inelastic scattering, and from Drell-Yan interactions; and on theoretical treatments that emphasize an explanation of the distribution functions, providing an overview of major contemporary approaches and issues. Valence-quark physics is a compelling subject, which probes at the heart of our understanding of the Standard Model. There are numerous outstanding and unresolved challenges, which experiment and theory must confront. In connection with experiment, we explain that an upgraded Jefferson Lab facility is well-suited to provide new data on the nucleon, while a future electron ion collider could provide essential new data for the mesons. There is also great potential in using Drell-Yan interactions, at FNAL, J-PARC and GSI, to push into the large-x domain for both mesons and nucleons. We argue furthermore that explanation, in contrast to modeling and parametrization, requires a widespread acceptance of the need to adapt theory: to the lessons learnt already from the methods of nonperturbative quantum field theory; and a fuller exploitation of those methods. * Electronic address: holt@anl.gov † Electronic address: cdroberts@anl.gov

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“…The general expression for this cross section (Ahmed and Gehrmann, 1999), written to emphasize the azimuthal dependence, is given by:…”

Section: F Azimuthal Asymmetriesmentioning

confidence: 99%

Nucleon and pion distribution functions in the valence region

2010

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“…In CP-conserving theories like perturbative QCD, asymmetry under naïve T reversal appears through the absorptive part of the scattering amplitudes [1,2], and hence offers a nontrivial test of perturbative QCD at one-and higher-loop levels. Various tests have been proposed in the past, including asymmetries in ϒ decay into three jets [1], e þ e − annihilation production of three jets [3], neutrino (electro) production of two jets [2,4], Drell-Yan production of a high-q T W boson at hadron collisions [5,6], Z-boson decay into three jets [7], and top-quark radiative decays [8]. Although the predictions deserve much interest as probes of the absorptive part of the loop-level QCD amplitudes, no experimental confirmation has been made so far.…”

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confidence: 99%

T-Odd Asymmetry inW+jetEvents at the LHC

et al. 2014

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W bosons produced at high transverse momentum in hadron collisions can have polarization along the direction perpendicular to the production plane, which is odd under naïve T reversal where both the threemomenta and angular momenta are reversed. Perturbative QCD predicts nonzero polarization at the one-loop level, which can be measured as parity-odd components in the angular distribution of charged leptons from the decay of W bosons. We perform a detector-level simulation with the generator MADGRAPH5_AMC@NLO, and demonstrate that the asymmetry can be observed at the 8 TeV LHC with 20 fb −1 of data. If confirmed, it will be the first experimental measurement of the sign of the imaginary part of one-loop QCD amplitudes.

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“…A deviation of sin φ HCM from zero at the level of three standard deviations is observed. The mean values are expected to be at least an order of magnitude smaller than the cos φ HCM term [5]. The values of sin 2φ…”

Section: Resultsmentioning

confidence: 88%

“…The azimuthal dependence for semi-inclusive neutral current (NC) DIS can be written [2][3][4][5] as:…”

Section: Introductionmentioning

confidence: 99%

“…The energy-flow method enhances the contribution of leading hadrons since the direction of each particle in the final state is weighted with its transverse energy [10,11]. Additionally, the values sin φ and sin 2φ were determined, although they are expected [3,5] to be much smaller than cos φ and cos 2φ . This paper presents measurements of cos φ , cos 2φ , sin φ and sin 2φ as a function of the pseudorapidity, η HCM , and minimum transverse energy, E …”

Section: Introductionmentioning

confidence: 99%

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Measurement of azimuthal asymmetries in neutral current deep inelastic scattering at HERA

Chekanov¹,

Derrick²,

Magill³

et al. 2007

Eur. Phys. J. C

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The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral current deep inelastic ep scattering using an integrated luminosity of 45 pb −1 taken with the ZEUS detector at HERA. The measurements were made in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers, they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary to describe these data.

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Azimuthal asymmetries in hadronic final states at HERA

Cited by 27 publications

References 14 publications

Nucleon and pion distribution functions in the valence region

Nucleon and pion distribution functions in the valence region

T-Odd Asymmetry inW+jetEvents at the LHC

Measurement of azimuthal asymmetries in neutral current deep inelastic scattering at HERA

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