Diffractive Parton Distribution Functions Research Articles

Determination of diffractive PDFs from a global QCD analysis of inclusive diffractive DIS and dijet cross-section measurements at HERA

We present an updated set of {\tt SKMHS} diffractive parton distribution functions (PDFs). In addition to the diffractive deep-inelastic scattering (diffractive DIS) data sets, the recent diffractive dijet cross sections measurements by the H1 experiment from the HERA collider are added to the data sample. The new set of diffractive PDFs, entitled {\tt SKMHS23} and {\tt SKMHS23-dijet}, are presented at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) accuracy in perturbative QCD. Since the gluons directly contribute to jet production through the boson-gluon fusion process, the data on diffractive dijet production in inclusive DIS help to constrain the gluon density, allowing for the determination of both the quark and gluon densities with better accuracy. The NLO and NNLO theory predictions calculated using both {\tt SKMHS23} and {\tt SKMHS23-dijet} are compared to the analyzed data showing excellent agreements. The effect arising from the inclusion of diffractive dijet data and higher order QCD corrections on the extracted diffractive PDFs and data/theory agreements are clearly examined and discussed.

Global QCD analysis of diffractive parton distribution function considering higher twist corrections within the xFitter framework

We present {\tt SKMHS22}, a new set of diffractive parton distribution functions (PDFs) and their uncertainties at next-to-leading-order accuracy in perturbative QCD within the {\tt xFitter} framework. We describe all available diffractive DIS data sets from HERA and the most recent high-precision H1/ZEUS combined measurements considering three different scenarios. First, we extract the diffractive PDFs considering the standard twist-2 contribution. Then, we include the twist-4 correction from the longitudinal virtual photons. Finally, the contribution of subleading Reggeon exchange to the structure-function $F_2^D$ is also examined. For the contribution of heavy flavors, we utilize the Thorne-Roberts general mass variable number scheme. We show that for those corrections, in particular, the twist-4 contribution allows to include the high-$\beta$ region and leads to a better description of the diffractive DIS data sets. We find that the inclusion of the subleading Reggeon exchange significantly improves the description of the diffractive DIS cross-section measurements. The resulting sets are in good agreement with all diffractive DIS data analyzed, which cover a wider kinematical range than in previous fits. The {\tt SKMHS22} diffractive PDFs sets presented in this work are available via the {\tt LHAPDF} interface. We also make suggestions for future research in this area.

Diffractive gamma gamma production in pp collisions at the LHC

In this letter we estimate the contribution of the double diffractive processes for the diphoton production in pp collisions at the large hadron collider (LHC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity and, transverse momentum distributions are presented. A comparison with the predictions for the light-by-light (LbL) scattering and exclusive diphoton production is performed. We demonstrate that the events associated to double diffractive processes can be separated and its study can be used to constrain the behavior of the diffractive parton distribution functions.

Role of higher twist effects in diffractive DIS and determination of diffractive parton distribution functions

The current analysis aims to present the results of a QCD analysis of diffractive parton distribution functions (diffractive PDFs) at next-to-leading order (NLO) accuracy in perturbative QCD. In this new determination of diffractive PDFs, we use all available and up-to-date diffractive deep inelastic scattering (diffractive DIS) datasets from H1 and ZEUS Collaborations at HERA including the most recent H1/ZEUS combined measurements. In this analysis, we consider the heavy quark contributions to the diffractive DIS in the so-called framework of {\tt FONLL} general mass variable flavor number scheme (GM-VFNS). The uncertainties on the diffractive PDFs are calculated using the standard "Hessian error propagation" which served to provide a more realistic estimate of the uncertainties. This analysis are enriched, for the first time, by including the nonperturbative higher twist (HT) effects in the calculation of diffractive DIS cross sections which are particularly important at large-$x$ and low $Q^{2}$ regions. Then, the stability and reliability of the extracted diffractive PDFs are investigated upon inclusion of HT effects. We discuss the novel aspects of the approach used in this QCD fit, namely, optimized and flexible parameterizations of diffractive PDFs, the inclusion of HT effects, and considering the recent H1/ZEUS combined dataset. Finally, we present the extracted diffractive PDFs with and without the presence of HT effects, and discuss the fit quality and the stability upon variations of the kinematic cuts and the fitted datasets. We show that the inclusion of HT effects in diffractive DIS can improve the description of the data which leads, in general, to a very good agreement between data and theory predictions.

Phenomenology of diffractive DIS in the framework of fracture functions and determination of diffractive parton distribution functions

The goal of this study is to determine a set of diffractive parton distribution function (diffractive PDFs) from a QCD analysis of all available and up-to-date diffractive deep inelastic scattering (diffractive DIS) data sets from HERA $ep$ collider, including the most recent H1 and ZUES combined inclusive diffractive cross section measurements. This extraction of diffractive PDFs, referred to as {\tt HK19-DPDF}, is performed at next-to-leading (NLO) and next-to-next-to-leading (NNLO) in perturbative QCD. This new determination of diffractive PDFs is based on the fracture functions methodology, a QCD framework designed to provide a statistically sound representation of diffractive DIS processes. Heavy quark contributions to the diffractive DIS are considered within the framework of the FONLL general mass variable flavor number scheme (GM-VFNS) and the "Hessian approach" is used to determine the uncertainties of diffractive PDFs. We discuss the novel aspects of the approach used in the present analysis, namely an optimized and flexible parametrization of the diffractive PDFs as well as a strategy based on the fully factorization theorem for diffractive hard processes. We then present the diffractive PDFs, and discuss the fit quality and the stability upon variations of the kinematic cuts and the fitted data sets. We find that the systematic inclusion of higher-order QCD corrections could improves the description of the data. We compare the extracted sets of diffractive PDFs based on the fracture functions approach to other recent sets of diffractive PDFs, finding in general very good agreements.

First global next-to-leading order determination of diffractive parton distribution functions and their uncertainties within the xFitter framework

We present GKG18-DPDFs, a next-to-leading order (NLO) QCD analysis of diffractive parton distribution functions (diffractive PDFs) and their uncertainties. This is the first global set of diffractive PDFs determined within the xFitter framework. This analysis is motivated by all available and most up-to-date data on inclusive diffractive deep inelastic scattering (diffractive DIS). Heavy quark contributions are considered within the framework of the Thorne–Roberts (TR) general mass variable flavor number scheme (GM-VFNS). We form a mutually consistent set of diffractive PDFs due to the inclusion of high-precision data from H1/ZEUS combined inclusive diffractive cross sections measurements. We study the impact of the H1/ZEUS combined data by producing a variety of determinations based on reduced data sets. We find that these data sets have a significant impact on the diffractive PDFs with some substantial reductions in uncertainties. The predictions based on the extracted diffractive PDFs are compared to the analyzed diffractive DIS data and with other determinations of the diffractive PDFs.

Dijet production in s=7 TeV pp collisions with large rapidity gaps at the ATLAS experiment

A $6.8 \ {\rm nb^{-1}}$ sample of $pp$ collision data collected under low-luminosity conditions at $\sqrt{s} = 7$ TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with $p_\mathrm{T} > 20$ GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in $\Delta\eta^F$, the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, $\tilde{\xi}$, of the fractional momentum loss of the proton assuming single diffractive dissociation ($pp \rightarrow pX$). Model comparisons indicate a dominant non-diffractive contribution up to moderately large $\Delta\eta^F$ and small $\tilde{\xi}$, with a diffractive contribution which is significant at the highest $\Delta\eta^F$ and the lowest $\tilde{\xi}$. The rapidity-gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton distribution functions.

Measurement of dijet production in diffractive deep-inelastic ep scattering at HERA

A measurement is presented of single- and double-differential dijet crosssections in diffractive deep-inelastic $ep$ scattering at HERA using datacollected by the H1 experiment corresponding to an integrated luminosity of 290pb^{-1}. The investigated phase space is spanned by the photon virtuality inthe range of 4<Q^{2}<100 GeV^{2} and by the fractional proton longitudinalmomentum loss x_pom<0.03. The resulting cross sections are compared withnext-to-leading order QCD predictions based on diffractive parton distributionfunctions and the value of the strong coupling constant is extracted.

A global analysis of diffractive events at HERA

We extract diffractive parton distribution functions (DPDFs) and diffractive structure functions from the most recent H1 and ZEUS diffractive deep inelastic scattering data obtained by various methods. We consider the Pomeron as an object with PDF, evolving according to the next-to-leading order DGLAP equations within the framework of the ‘fixed flavour number scheme’. Having performed a global fit analysis, we achieve a very good description of all available measurements by introducing a new set of quark distribution forms for the Pomeron. We predict longitudinal and charm proton diffractive structure function as well. Our results are compared with other analyses from the literature.

Heavy quark production inγPinteractions at hadronic colliders

The diffractive heavy quark cross sections are estimated considering photon-Pomeron ($\gamma \pom$) interactions in hadron - hadron at RHIC, Tevatron, and CERN LHC energies. We assume the validity of the hard diffractive factorization and calculate the charm and bottom total cross sections and rapidity distributions using the diffractive parton distribution functions of the Pomeron obtained by the H1 Collaboration at DESY-HERA. Moreover, we compare our predictions with those obtained using the dipole model. We verify that this process is a good test of the different mechanisms for diffractive heavy quark production at hadron - hadron colliders.

The study of heavy contribution in diffractive parton distribution functions

In this paper we give a brief introduction to the description of QCD analysis in order to determine the diffractive parton distribution functions (DPDFs) at the next-to-leading order (NLO) approximation. We focus on key features of analysis for all available diffractive HERA data and outline challenges for considering heavy quark contributions within the framework of the fixed flavour number scheme (FFNS) which is in full agreement with the diffractive heavy quarks experimental data.

QCD COUPLING CONSTANT FROM DIFFRACTIVE DEEP INELASTIC SCATTERING

Determination of αs is one of the most important issue in high energy physics. Measurements of deep inelastic diffraction provide a chance to study this parameter besides diffractive parton distribution functions (DPDFs). Regarding the fact that LHC data is coming, it is hoped that precision measurements of diffraction in Deep Inelastic Scattering (DIS) provide a more complete understanding of strong coupling constant. We performed advanced theoretical calculations to determine Λ and DPDFs.

An independent estimate of the triple-Pomeron coupling

The value of the important triple-Pomeron coupling is estimated by an unorthodox procedure using the known diffractive parton distribution functions. The result is g3P≃0.2gN, where gN is the Pomeron–nucleon coupling. This is in excellent agreement with an independent determination, g3P≃0.2gN, previously obtained by analysing the available data in the triple-Regge region with absorptive effects taken into account.

Diffractive Structure Functions from the H1 and ZEUS Experiments at HERA

The cross section of inclusive diffractive process ep -> eXp was measured within a wide kinematic range in the H1 and ZEUS experiments at HERA. Results obtained by different experiments and methods are compatible within measurement uncertainties. The measurements were subjected to DGLAP next-to-leading order QCD global fits and the diffractive parton distribution functions (DPDFs) of the proton were determined with noticeably reduced uncertainties due to very high precision of the data. The gluon density precision was much improved in fits which also included data on dijet production in diffractive DIS. Predictions based on the determined DPDFs are in agreement with the measured inclusive cross-section of diffractive dijet photoproduction and charm production in diffractive DIS at HERA. The longitudinal diffractive structure function $F^D_L$ was measured directly for the first time.

A QCD analysis of ZEUS diffractive data

ZEUS inclusive diffractive-cross-section measurements have been used in a DGLAP next-to-leading-order QCD analysis to extract the diffractive parton distribution functions. Data on diffractive dijet production in deep inelastic scattering have also been included to constrain the gluon density. Predictions based on the extracted parton densities are compared to diffractive charm and dijet photoproduction data.

Factorisation issues in diffraction

The high centre-of-mass energies of the HERA ep collider and of the Tevatron collider allow us to study the diffractive interactions in the presence of a hard scale and to describe them in terms of perturbative QCD. In QCD, the diffractive exchange is described in terms of partons, and the factorisation theorem states that the cross section for hard interactions can be expressed as convolution of universal diffractive parton distribution functions and process-dependent coefficients, perturbatively calculable. The recent experimental data from the H1 and ZEUS Collaborations at HERA are presented for diffractive dijet and D ∗ meson production, in both deep-inelastic scattering (DIS) and the photoproduction regimes and are compared to next-to-leading order QCD predictions using diffractive parton distributions. While good agreement is found for dijets in DIS and for D ∗ production in both DIS and photoproduction, the dijet photoproduction data are overestimated by NLO predictions at lower transverse momentum of the jets, indicating the breaking of QCD factorisation.

Factorisation breaking in diffraction

The high energies of the HERA ep collider and of the Tevatron p p ¯ collider allow for the first time to study diffractive interactions in the presence of a hard scale and to describe them in terms of perturbative QCD. In QCD the diffractive exchange is described in terms of partons, and the factorisation theorem states that the cross section for hard interactions can be estimated as convolution of universal diffractive parton distribution functions and process-dependent coefficients, perturbatively calculable. Recent experimental data from the H1 and ZEUS Collaborations at HERA are presented for diffractive dijet and D ∗ meson production, in both deep-inelastic scattering and photoproduction regime and compared to next-to-leading order QCD predictions using diffractive parton distributions. The validity of the QCD factorisation theorem is investigated.

Inclusive diffraction in DIS at HERA

Measurements of the diffractive deep inelastic scattering processes ep → eXY and ep → eXp at HERA are presented. Events with a measured leading proton, as well as events with a large rapidity gap (LRG) between X and the outgoing proton were analysed. Moreover, the difference in the shape of the MX distribution of diffractive and non-diffractive events was utilised to extract the diffractive component. Diffractive parton distribution functions and their uncertainties were determined from a next-to-leading order DGLAP QCD analysis. The results are presented in terms of the diffractive structure functions, F2D(3) and F2D(4), and the diffractive reduced cross sections, σrD(3) and σrD(4).

Dijet cross sections and parton densities in diffractive DIS at HERA

Differential dijet cross sections in diffractive deep-inelastic scattering are measured with the H1 detector at HERA using an integrated luminosity of 51.5 pb-1. The selected events are of the type ep --> eXY, where the system X contains at least two jets and is well separated in rapidity from the low mass proton dissociation system Y. The dijet data are compared with QCD predictions at next-to-leading order based on diffractive parton distribution functions previously extracted from measurements of inclusive diffractive deep-inelastic scattering. The prediction describes the dijet data well at low and intermediate zpom (the fraction of the momentum of the diffractive exchange carried by the parton entering the hard interaction) where the gluon density is well determined from the inclusive diffractive data, supporting QCD factorisation. A new set of diffractive parton distribution functions is obtained through a simultaneous fit to the diffractive inclusive and dijet cross sections. This allows for a precise determination of both the diffractive quark and gluon distributions in the range 0.05<zpom<0.9. In particular, the precision on the gluon density at high momentum fractions is improved compared to previous extractions.

Diffractive photoproduction of D*±(2010) at HERA

Diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb-1. The D* mesons were reconstructed in the kinematic range: transverse momentum pT(D*) > 1.9 GeV and pseudorapidity |η(D*)|<1.6, using the decay D*+→D0π+ s followed by D0→K-π+(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q2 < 1 GeV2, in two ranges of the Pomeron fractional momentum xIP<0.035 and xIP<0.01. The relative contribution of diffractive events to the inclusive D*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.