Deep Inelastic Data Research Articles

Extraction of the strong coupling with HERA and EIC inclusive data

Sensitivity to the strong coupling αS(MZ2)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha _S(M^2_Z)$$\\end{document} is investigated using existing Deep Inelastic Scattering data from HERA in combination with projected future measurements from the Electron Ion Collider (EIC) in a next-to-next-to-leading order QCD analysis. A potentially world-leading level of precision is achievable when combining simulated inclusive neutral current EIC data with inclusive charged and neutral current measurements from HERA, with or without the addition of HERA inclusive jet and dijet data. The result can be obtained with substantially less than one year of projected EIC data at the lower end of the EIC centre-of-mass energy range. Some questions remain over the magnitude of uncertainties due to missing higher orders in the theoretical framework.

Extending nuclear PDF analyses into the high- x , low- Q2 region

We use the nCTEQ analysis framework to investigate nuclear Parton Distribution Functions (nPDFs) in the region of large x and intermediate-to-low $Q$, with special attention to recent JLab Deep Inelastic Scattering data on nuclear targets. This data lies in a region which is often excluded by $W$ and $Q$ cuts in global nPDF analyses. As we relax these cuts, we enter a new kinematic region, which requires new phenomenology. In particular, we study the impact of i) target mass corrections, ii) higher twist corrections, iii) deuteron corrections, and iv) the shape of the nuclear PDF parametrization at large-$x$ close to one. Using the above tools, we produce a new nPDF set (named nCTEQ15HIX) which yields a good description of the new JLab data in this challenging kinematic region, and displays reduced uncertainties at large $x$, in particular for up and down quark flavors.

Sensitivity of strange quark polarization to flavor SU(3) symmetry breaking

The polarized strange quark puzzle concerns the fact that the polarized strange quark density extracted from polarized inclusive deep inelastic scattering data is significantly negative, whereas it is zero or slightly positive when extracted from a combined analysis of polarized semi-inclusive and inclusive deep inelastic data. SU(3) flavor symmetry, which, it is generally accepted, is not an exact symmetry, plays an important role in the inclusive analysis, and all the extracted polarized quark densities depend, to some extent, on the level of symmetry breaking introduced. But by far the most sensitive to the breaking is the strange quark density. In this paper we present a NLO QCD analysis of the world data on polarized inclusive DIS data on protons, neutrons and deuterons, including the final JLAB CLAS/EG1b data on the proton and deuteron, and study the sensitivity of the strange quark polarization to the breaking of flavor SU(3).

New study of the Boer-Mulders function: Implications for the quark and hadron transverse momenta

In series of papers the Boer-Mulders function for a given quark flavour has been extracted: (i) from data on semi-inclusive deep inelastic scattering, using the simplifying, but theoretically inconsistent, assumption that it is proportional to the Sivers function for each quark flavour and (ii) from data on Drell-Yan reactions. In earlier papers, using the semi-inclusive deep inelastic COMPASS deuteron data on the $\langle\cos\phi_h\rangle$ and $\langle\cos 2 \phi_h\rangle$ asymmetries, we extracted the collinear $x_{_{\!B}}$ dependence of the Boer-Mulders function for the sum of the valence quarks $Q_V=u_V + d_V$ using a small number of model dependent assumptions and found a significant disagreement with the analysis in (i). In the present paper, we provide a more complete analysis of the semi-inclusive deep inelastic scattering reaction, including a discussion of higher twist and interaction-dependent terms, and also a comparison with the Boer-Mulders function extracted from data on the Drell-Yan reaction. We confirm that the proportionality relation of the BM function to the Sivers function, for each quark flavour, fails badly, but find that it holds rather well if applied to the nonsinglet valence-quark combination, $Q_V$. We also find good agreement with the results of the Drell-Yan analysis. Furthermore, we obtain interesting information on the quark transverse momentum densities in the nucleon and on the hadron transverse momentum dependence in quark fragmentation.

Absorptive effects and power corrections in low x DGLAP evolution

We address a long standing problem concerning the scale behaviour of parton densities in the low x, low Q^2 domain. We emphasize the important role of absorptive corrections at low x and use knowledge of diffractive deep inelastic scattering to exclude the absorptive effect from conventional deep inelastic data. In this way we obtain a significantly different low x behaviour of the gluon density, which is now much better described by linear DGLAP evolution. Accounting also for a second power correction, which arises from the freezing of alpha _s at low Q^2, leads to an essentially flat behaviour of the low x gluon density.

Precise QCD Predictions for the Production of Dijet Final States in Deep Inelastic Scattering.

The production of two-jet final states in deep inelastic scattering is an important QCD precision observable. We compute it for the first time to next-to-next-to-leading order (NNLO) in perturbative QCD. Our calculation is fully differential in the lepton and jet variables and allows one to impose cuts on the jets in both the laboratory and the Breit frame. We observe that the NNLO corrections are moderate in size, except at kinematical edges, and that their inclusion leads to a substantial reduction of the scale variation uncertainty on the predictions. Our results will enable the inclusion of deep inelastic dijet data in precision phenomenology studies.

Geometric Scaling Analysis of Deep Inelastic Scattering Data Including Heavy Quarks**Supported by the National Natural Science Foundation of China under Grant Nos 11305040, 11375071 and 11447203, the Education Department of Guizhou Province Innovation Talent Fund under Grant No [2015]5508, the Education Department of Guizhou Province Innovation Team Fund under Grant No [2014]35, the Guizhou Province Science Technology Foundation under Grant

An analytic massive total cross section of photon-proton scattering is derived, which has geometric scaling. A geometric scaling is used to perform a global analysis of the deep inelastic scattering data on inclusive structure function F2 measured in lepton–hadron scattering experiments at small values of Bjorken x. It is shown that the descriptions of the inclusive structure function F2 and longitudinal structure function FL are improved with the massive analytic structure function, which may imply the gluon saturation effect dominating the parton evolution process at HERA. The inclusion of the heavy quarks prevent the divergence of the lepton–hadron cross section, which plays a significant role in the description of the photoproduction region.

Problems with the perturbative QCD interpretation of HERMES data on semi-inclusive leptoproduction of pions

A theoretical analysis has been performed of the HERMES semi-inclusive deep inelastic data on the difference between $\pi^{+}$ and $\pi^{-}$ multiplicities. It turns out that the application of a standard perturbative QCD analysis, using, as usual, isospin symmetry for the fragmentation functions, leads to a poor description of the deuteron data at small z values. If one allows a breaking of isospin invariance, a good fit to both proton and deuteron data can be achieved for all measured z, but the level of isospin violation, especially at small values of z, is simply not credible. We suspect that the problem is a consequence of using the factorized QCD treatment in a kinematic region where it is unjustified.

Hard to soft pomeron transition in small-x deep inelastic scattering data using optimal renormalization.

We show that it is possible to describe the effective Pomeron intercept, determined from the HERA deep inelastic scattering data at small values of Bjorken x, by using next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution together with collinear improvements. To obtain a good description over the whole range of Q(2), we use a non-Abelian physical renormalization scheme with the Brodsky-Lepage-Mackenzie optimal scale, combined with a parametrization of the running coupling in the infrared region.

Precision NNLO determination of [formula omitted] using an unbiased global parton set

We determine the strong coupling αs at NNLO in perturbative QCD using the global dataset input to the NNPDF2.1 NNLO parton fit: data from neutral and charged current deep-inelastic scattering, Drell–Yan, vector boson production and inclusive jets. We find αs(MZ)=0.1173±0.0007stat, where the statistical uncertainty comes from the underlying data and uncertainties due to the analysis procedure are negligible. We show that the distribution of αs values preferred by different experiments in the global fit is statistically consistent, without need for rescaling uncertainties by a “tolerance” factor. We show that if deep-inelastic data only are used, the best-fit value of αs is somewhat lower, but consistent within one sigma with the global determination. We find that the shift between the NLO and NNLO values of αs is Δαspert=0.0018, and we estimate the uncertainty from higher-order corrections to be ΔαsNNLO∼0.0009.

Precision determination of [formula omitted] using an unbiased global NLO parton set

We determine the strong coupling αs from a next-to-leading order analysis of processes used for the NNPDF2.1 parton determination, which includes data from neutral and charged current deep-inelastic scattering, Drell–Yan and inclusive jet production. We find αs(MZ)=0.1191±0.0006exp, where the uncertainty includes all statistical and systematic experimental uncertainties, but not purely theoretical uncertainties, which are expected to be rather larger. We study the dependence of the results on the dataset, by providing further determinations based respectively on deep-inelastic data only, and on HERA data only. The deep-inelastic fit gives the consistent result αs(MZ)=0.1177±0.0009exp, but the result of the HERA-only fit is only marginally consistent. We provide evidence that individual data subsets can have runaway directions due to poorly determined PDFs, thus suggesting that a global dataset is necessary for a reliable determination.

Semi-inclusive DIS cross sections and spin asymmetries in the quantum statistical parton distributions approach

We consider the extension of the statistical parton distributions to include their transverse momentum dependence, by using two different methods, one is based on our quantum statistical approach, the other on a relativistic covariant method. We take into account the effects of the Melosh-Wigner rotation for the polarized distributions. The results obtained can be compared with recent semiinclusive Deep Inelastic Scattering data on the cross section and double longitudinal-spin asymmetries from JLab. We also give some predictions for future experiments on electron-neutron scattering.

High-energy strong interactions: from ‘hard’ to ‘soft’

We discuss the qualitative features of the recent data on multiparticle production observed at the LHC. The tolerable agreement with Monte Carlos based on LO DGLAP evolution indicates that there is no qualitative difference between `hard' and `soft' interactions; and that a perturbative QCD approach may be extended into the soft domain. However, in order to describe the data, these Monte Carlos need an additional infrared cutoff k_min with a value k_min ~ 2-3 GeV which is not small, and which increases with collider energy. Here we explain the physical origin of the large k_min. Using an alternative model which matches the `soft' high-energy hadron interactions smoothly on to perturbative QCD at small x, we demonstrate that this effective cutoff k_min is actually due to the strong absorption of low k_t partons. The model embodies the main features of the BFKL approach, including the diffusion in transverse momenta, lnk_t, and an intercept consistent with resummed next-to-leading log corrections. Moreover, the model uses a two-channel eikonal framework, and includes the contributions from the multi-Pomeron exchange diagrams, both non-enhanced and enhanced. The values of a small number of physically-motivated parameters are chosen to reproduce the available total, elastic and proton dissociation cross section (pre-LHC) data. Predictions are made for the LHC, and the relevance to ultra-high-energy cosmic rays is briefly discussed. The low x inclusive integrated gluon PDF, and the diffractive gluon PDF, are calculated in this framework, using the parameters which describe the high-energy pp and p\bar{p} `soft' data. Comparison with the PDFs obtained from the global parton analyses of deep inelastic and related `hard' scattering data, and from diffractive deep inelastic data looks encouraging.

A method for tuning parameters of Monte Carlo generators and its application to the determination of the unintegrated gluon density

A method for tuning parameters in Monte Carlo generators is described and applied to a specific case. The method works in the following way: each observable is generated several times using different values of the parameters to be tuned. The output is then approximated by some analytic form to describe the dependence of the observables on the parameters. This approximation is used to find the values of the parameter that give the best description of the experimental data. This results in significantly faster fitting compared to an approach in which the generator is called iteratively. As an application, we employ this method to fit the parameters of the unintegrated gluon density used in the CASCADE Monte Carlo generator, using inclusive deep inelastic data measured by the H1 Collaboration. We discuss the results of the fit, its limitations, and its strong points.

The nucleon's octet axial-charge [formula omitted] with chiral corrections

The value of the nucleon's flavour-singlet axial-charge extracted from polarised deep inelastic scattering is sensitive to the value of the octet axial-charge gA(8) which is usually taken from an analysis of hyperon β-decays within the framework of SU(3) symmetry, namely 0.58±0.03. Using the Cloudy Bag model we find that the value of gA(8) is reduced by as much as 20% below the usual phenomenological value. This increases the value of the flavour-singlet axial-charge (gA(0)|inv) derived from deep inelastic data and significantly reduces the difference between it and gA(8).

Production ofZ0bosons with rapidity gaps: Exclusive photoproduction inγpandppcollisions and inclusive double diffractiveZ0’s

We extend the k{sub perpendicular}-factorization formalism for exclusive photoproduction of vector mesons to the production of electroweak Z{sup 0} bosons. Predictions for the {gamma}p{yields}Z{sup 0}p and pp{yields}ppZ{sup 0} reactions are given using an unintegrated gluon distribution tested against deep inelastic data. We show distributions in the Z{sup 0} rapidity, transverse momentum of Z{sup 0} as well as in relative azimuthal angle between outgoing protons. The contributions of different flavors are discussed. Absorption effects lower the cross section by a factor of 1.5-2, depending on the Z-boson rapidity. We also discuss the production of Z{sup 0} bosons in central inclusive production. Here rapidity and (x{sub IP,1},x{sub IP,2}) distributions of Z{sup 0} are calculated. The corresponding cross section is about 3 orders of magnitude larger than that for the purely exclusive process.

Soft-gluon resummation effects on parton distributions

We gauge the impact of soft-gluon resummation on quark distributions by performing a simple fit of Deep Inelastic Scattering structure function data using next-to-leading order (NLO) and next-to-leading-logarithmic (NLL)-resummed coefficient functions. We make use of NuTeV charged-current data, as well as New Muon Collaboration (NMC) and Bologna-CERN-Dubna-Munich-Saclay (BCDMS) neutral-current results, which probe large values of x. Our results suggest that the inclusion of resummation effects in global fits of parton distributions is both feasible and desirable, in order to achieve at large x the accuracy goals of the LHC physics program.

Parton distributions incorporating QED contributions

We perform a global parton analysis of deep inelastic and related hard-scattering data, including ${\cal O}(\alpha_{\rm QED})$ corrections to the parton evolution. Although the quality of the fit is essentially unchanged, there are two important physical consequences. First, the different DGLAP evolution of u and d type quarks introduces isospin violation, i.e. $u^p \neq d^n$, which is found to be unambiguously in the direction to reduce the NuTeV $\sin^2\theta_W$ anomaly. A second consequence is the appearance of photon parton distributions $\gamma(x,Q^2)$ of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes $e N \to e\gamma X$; our predictions are in agreement with the present data.

Simultaneous QCD analysis of diffractive and inclusive deep-inelastic scattering data

We perform a NLO QCD analysis of deep-inelastic scattering data, in which we account for absorptive corrections. These corrections are determined from a simultaneous analysis of diffractive deep-inelastic data. The absorptive effects are found to enhance the size of the gluon distribution at small x, such that a negative input gluon distribution at Q^2 = 1 GeV^2 is no longer required. We discuss the problem that the gluon distribution is valence-like at low scales, whereas the sea quark distribution grows with decreasing x. Our study hints at the possible importance of power corrections for Q^2 \simeq 1--2 GeV^2.

UNCERTAINTY OF POLARIZED PARTON DISTRIBUTIONS

Polarized parton distribution functions are determined by a χ2 analysis of polarized deep inelastic experimental data. In this paper, uncertainty of obtained distribution functions is investigated by a Hessian method. We find that the uncertainty of the polarized gluon distribution is fairly large. Then, we estimate the gluon uncertainty by including the fake data which are generated from prompt photon process at RHIC. We observed that the uncertainty could be reduced with these data.