Deep Inelastic Cross Sections Research Articles

Limits on contact interactions and leptoquarks at HERA

High-precision HERA data corresponding to a luminosity of around 1 fb$^{-1}$ have been used in the framework of $eeqq$ contact interactions (CI) to set limits on possible high-energy contributions beyond the Standard Model to electron-quark scattering. Measurements of the inclusive deep inelastic cross sections in neutral and charged current $ep$ scattering were considered. The analysis of the $ep$ data has been based on simultaneous fits of parton distribution functions including contributions of CI couplings to $ep$ scattering. Several general CI models and scenarios with heavy leptoquarks were considered. Improvements in the description of the inclusive HERA data were obtained for a few models. Since a statistically significant deviation from the Standard Model cannot be established, limits in the TeV range were set on all models considered.

Light-front spin-dependent spectral function and nucleon momentum distributions for a three-body system

Poincare' covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian-Thomas construction of the Poincare' generators, that allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, like the ones needed for evaluating the EMC effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, since remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. It is also shown a straightforward generalization of the definition of the light-front spectral function to an A-nucleon system.

Limits on the effective quark radius from inclusive ep scattering at HERA

The high-precision HERA data allows searches up to TeV scales for Beyond the Standard Model contributions to electron-quark scattering. Combined measurements of the inclusive deep inelastic cross sections in neutral and charged current $ep$ scattering corresponding to a luminosity of around 1 fb$^{-1}$ have been used in this analysis. A new approach to the beyond the Standard Model analysis of the inclusive $ep$ data is presented; simultaneous fits of parton distribution functions together with contributions of "new physics" processes were performed. Results are presented considering a finite radius of quarks within the quark form-factor model. The resulting 95% C.L. upper limit on the effective quark radius is $0.43\cdot 10^{-16}$ cm.

Proton structure and parton distribution functions from HERA

The H1 and ZEUS collaborations at the electron-proton collider HERA collected e ± p scattering data corresponding to an integrated luminosity of about 1 fb −1 . The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV, with different electric charges and longitudinal polarisation of the electron beam. Using these data inclusive neutral and charged current deep inelastic cross sections were measured over six orders of magnitude in negative four-momentum-transfer squared, Q 2 , and Bjorken x . A combination of all inclusive cross sections, published by the H1 and ZEUS collaborations at HERA, was performed. Using these combined HERA data and the individual H1 and ZEUS data taken using the polarised electron beams, the proton structure functions F 2 , F γZ 2 , x F γZ 3 and F L were obtained, and scaling violations, electroweak unification, and polarisation effects in the charged current process were demonstrated. The combined cross sections were used as a sole input to QCD analyses at leading, next-to-leading and next-to-next-to-leading orders, providing a new set of parton distribution functions, denoted as HERAPDF2.0. An extension of the analysis by including HERA data on charm and jet production allowed a simultaneous determination of parton distributions and the strong coupling.

Combination of measurements of inclusive deep inelastic $${e^{\pm }p}$$ e ± p scattering cross sections and QCD analysis of HERA data

A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current $e^{\pm}p$ scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb$^{-1}$ and span six orders of magnitude in negative four-momentum-transfer squared, $Q^2$, and Bjorken $x$. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in $\alpha_s(M_Z)=0.1183 \pm 0.0009 {\rm(exp)} \pm 0.0005{\rm (model/parameterisation)} \pm 0.0012{\rm (hadronisation)} ^{+0.0037}_{-0.0030}{\rm (scale)}$. An extraction of $xF_3^{\gamma Z}$ and results on electroweak unification and scaling violations are also presented.

A-Dependence of diffraction dissociation phenomenon in neutrino interactions with nuclei

We present results on A-dependence of diffraction dissociation (DD) phenomenon in interactions of muonic neutrino with nuclei at various values of momentum transfer. Calculations were done within the two-gluon exchange model by Nikolaev-Zakharov-Zoller(NZZ). Comparison with experimental data obtained in interactions of muonic neutrino with photoemulsion nuclei is carried out. All data are presented as ratio of the DD cross section to the deep inelastic cross section.

HERA Inclusive Neutral and Charged Current Cross Sections and a New PDF Fit, HERAPDF 2.0

In this talk, I present the brand new results from the H1 and ZEUS Collaborations on the combination of all previously published inclusive deep inelastic cross sections at HERA for neutral and charged current $e^\pm p$ scattering for zero beam polarisation and the corresponding parton distributions functions, HERAPDF 2.0, at up to next-to-next-to-leading order (NNLO). The results also include a new precise determination at next-to-leading order (NLO) of the strong coupling constant $\alpha_s(M^2_Z)=0.1184\pm 0.0016$ (excluding scale uncertainties) based on a simultaneous fit to the combined inclusive cross section data and jet production data.

Deep inelastic cross-section measurements at largeywith the ZEUS detector at HERA

The reduced cross sections for $e^{+}p$ deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, $318$, $251$ and $225$ GeV. The cross sections, measured double differentially in Bjorken $x$ and the virtuality, $Q^2$, were obtained in the region $0.13\ \leq\ y\ \leq\ 0.75$, where $y$ denotes the inelasticity and $5\ \leq\ Q^2\ \leq\ 110$ GeV$^2$. The proton structure functions $F_2$ and $F_L$ were extracted from the measured cross sections.

Precision QCD measurements at HERA

A review of recent experimental results on perturbative QCD from the HERA experiments H1 and ZEUS is presented. All inclusive deep inelastic cross sections mea- sured by the H1 and ZEUS collaborations in neutral and charged current unpolarised ep scattering are combined. They span six orders of magnitude in negative four-momentum- transfer squared, Q 2 , and in Bjorken x. This data set is used as the sole input to NLO and NNLO QCD analyses to determine new sets of parton distributions, HERAPDF2.0, with small experimental uncertainties and an estimate of model and parametrisation un- certainties. Also shown are new results on inclusive jet, dijet and trijet differential cross sections measured in neutral current deep inelastic scattering. The precision jet data is used to extract the strong coupling αs at NLO with small experimental errors.

QCD rescattering mechanism for diffractive deep inelastic scattering

We present a QCD-based model where rescattering between final state partons in deep inelastic scattering leads to events with large rapidity gaps and a leading proton. In the framework of this model the amplitude for multiple gluon exchanges is calculated in the eikonal approximation to all orders in perturbation theory. Both large and small invariant mass ${M}_{X}$ limits are considered. The model successfully describes the precise HERA data on the diffractive deep inelastic cross section in the whole available kinematical range and gives new insight into the density of gluons at very small momentum fractions in the proton.

Combined measurement and QCD analysis of the inclusive e ± p scattering cross sections at HERA

A combination is presented of the inclusive deep inelastic cross sections measured by the H1 and ZEUS Collaborations in neutral and charged current unpolarised ep scattering at HERA during the period 1994-2000. The data span six orders of magnitude in negative four-momentum-transfer squared, Q^2, and in Bjorken x. The combination method used takes the correlations of systematic uncertainties into account, resulting in an improved accuracy. The combined data are the sole input in a NLO QCD analysis which determines a new set of parton distributions, HERAPDF1.0, with small experimental uncertainties. This set includes an estimate of the model and parametrisation uncertainties of the fit result.

Investigation of Neutrino-Nucleon Interaction through Intermediate Vector Boson (IVB)

This work deals with the interaction of neutrino with the nucleon considering data taken from different experiments. It is assumed that the interaction of neutrino with nucleons go through the intermediate vector boson (IVB) which may be the W or Z with effective mass of the order of 80 GeV. The neutrino wave function is obtained via perturbation technique to calculate the weak leptonic current. On the other hand, the quark current is estimated using the measured experimental data of deep inelastic scattering of neutrino-nucleon interaction. Eventually the total interaction transition matrix is calculated as a function of momentum transfer square, q2 and qualitatively compared with the available experimental data. Besides, a comparative study is also done to explore the influence of the target composition during the neutrino weak interactions. In this context an investigation of neutrino-proton and neutrino-neutron interactions are carried out to calculate the deep inelastic cross section in both cases.

Charged particle multiplicity produced in neutrino- nucleon interactions at high energies

The multi-particle productions in neutrino-nucleon collisions at high energy are investigated through the analysis of the data of the experiment CERN-WA-025 at neutrino energy less than 260GeV and the experiments FNAL-616 and FNAL-701 at energy range 120-250 GeV. The general features of these experiments are used as base to build a hypothetical model that views the reaction through a Feynman diagram of two vertices. The first of which concerns the weak interaction between the neutrino and the quark constituents of the nucleon. At the second vertex, a strong color field is assumed to play the role of particle production, which depends on the momentum transferred from the first vertex. The wave functions of the nucleon constituent quarks are determined using the variation method and relevant boundary conditions are applied to calculation the deep inelastic cross sections of the virtual diagram. PACS: 13.15. +g Key words: Weak interaction, feynman diagrams, multiparticles.

Systematics of geometric scaling

Abstract Using all available data on the deep-inelastic cross-sections at HERA at x ⩽ 10 −2 , we look for geometric scaling of the form σ γ ∗ p ( τ ) where the scaling variable τ behaves alternatively like log Q 2 − λ Y , as in the original definition, or log Q 2 − λ Y , which is suggested by the asymptotic properties of the Balitsky–Kovchegov (BK) equation with running QCD coupling constant. A “Quality Factor” (QF) is defined, quantifying the phenomenological validity of the scaling and the uncertainty on the intercept λ . Both choices have a good QF, showing that the second choice is as valid as the first one, predicted for fixed coupling constant. A comparison between the QCD asymptotic predictions and data is made and the QF analysis shows that the agreement can be reached, provided going beyond leading logarithmic accuracy for the BK equation.

A closer look at the tertiary production of antiprotons in the Galaxy

Antiproton spectrum in cosmic rays, produced by the interactions of cosmic-ray nucleons with interstellar gas, has a peak around 2 GeV with a steep positive slope below 1 GeV at production. During the propagation of antiprotons in the Galaxy, the low energy spectrum gets modified due to ionization loss and by the energy degradation from deep-inelastic interactions. In recent years, it is believed that the latter is a dominant process in creating more low energy antiprotons. In this paper, the available data on total, elastic, annihilation and charge-exchange cross-sections at accelerator energies are carefully examined to show that the above conclusion is based partly due to incorrect parametrization of the data and partly by including charge-exchange cross-section as part of deep-inelastic process. It is shown that the deep-inelastic cross-section in ( p ¯ , p ) interactions starts decreasing faster than for ( p, p) interaction below 10 GeV due to the opening of the annihilation channel. It has a low energy cut-off at the threshold energy for pion production as in the case of protons. Though the charge-exchange process play an important role at low energies, the energy change during this process is marginal as in the case of elastic scattering and hence does not contribute to the production of tertiary antiprotons.

Is simultaneousyandξscaling in the quasielastic region accidental?

We study the $y$ and $\xi$--scaling of the nuclear response at large momentum transfer in order to understand how scaling based on very different descriptions of the elementary interaction can occur simultaneously. We find that the approximate validity of $\xi$-scaling at low energy loss arises from the coincidental behavior of the quasielastic and deep inelastic cross sections.

HADRON PRODUCTION IN NEUTRINO–NUCLEON INTERACTIONS AT HIGH ENERGIES

The multi-particle productions in neutrino–nucleon collisions at high energy are investigated through the analysis of the data of the experiment CERN-WA-025 at neutrino energy less than 260 GeV and the experiments FNAL-616 and FNAL-701 at energy range 120–250 GeV. The general features of these experiments are used as base to build a hypothetical model that views the reaction through a Feynman diagram of two vertices. The first of which concerns the weak interaction between the neutrino and the quark constituents of the nucleon. At the second vertex, a strong color field is assumed to play the role of particle production, which depend on the momentum transferred from the first vertex. The wave functions of the nucleon constituent quarks are determined using the variation method and relevant boundary conditions are applied to calculate the deep inelastic cross sections of the virtual diagram.

Modeling deep inelastic cross sections in the few GeV region

We present preliminary results on simple modifications and corrections to GRV94 leading order parton distribution functions such that they can be used to model electron,muon and neutrino deep-inelastic scattering cross sections at low energies.

Modification of the saturation model: Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution

We propose to modify the saturation model of Golec-Biernat and Wusthoff by including DGLAP evolution. We find considerable improvement for the total deep inelastic cross section, in particular in the large Q^2 region. The successful description of DIS diffraction is preserved.

Experimental estimate of the diffractive-dissociation phenomenon following neutrino interaction with photoemulsion nuclei

The first experimental estimate of the diffractive-dissociation (DD) cross section for muon-neutrino interaction with nuclei is presented. Eleven events that satisfy the DD criteria (xB 2) are found among 207 events induced by neutrino interactions with Ag and Br nuclei of nuclear photoemulsion and borrowed from the database of the E-564 experiment (FNAL). The ratio of the DD cross section to the total deep-inelastic cross section for the charged current is 0.29±0.09. Four of the 11 events proved to be candidates for events of coherent DD.