Gluon jet in deep inelastic muon scattering

We study the quark and gluon final state in deep inelastic μ-scattering. For a hadron observed at sufficiently large angleθ _h with respect to the virtual photon direction, and sufficiently large energy fractionz _h , this final state dominates the cross-section. Moreover, at the same time, most events in this regime are due to the fragmentation of the quark. In such cases the position of the gluon in phase space is determined, the quark acting as a trigger for gluon jet detection. We demonstrate that in the rest frame of the final quark and gluon, the gluon is energetic and well separated from quark and target fragments. We study the boost from the lab to this frame, and give expressions for the most probable boost in terms ofθ _h andz _h . This study should lead to a convenient visualization of the gluon jet.     

Multijet production in neutral current deep inelastic scattering at HERA and determination of $\alpha_s$

Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson virtualities . The data were taken at the ep collider HERA with centre-of-mass energy using the ZEUS detector and correspond to an integrated luminosity of . Jets were identified in the Breit frame using the k_T cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential dijet and trijet cross sections are presented as functions of jet transverse energy ( ), pseudorapidity ( ) and Q² with and . Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant , determined from the ratio of the trijet to dijet cross sections, is . Received: 1 April 2005, Revised: 28 June 2005, Published online: 30 August 2005     

Forward jet production in deep inelastic scattering at HERA

The inclusive forward jet cross section in deep inelastic e⁺pe^+p scattering has been measured in the region of x-Bjorken, 4.5 ·10^-44.5 \cdot 10^{-4} to 4.5 ·10^-24.5 \cdot 10^{-2}. This measurement is motivated by the search for effects of BFKL-like parton shower evolution. The cross section at hadron level as a function of x is compared to cross sections predicted by various Monte Carlo models. An excess of forward jet production at small x is observed, which is not reproduced by models based on DGLAP parton shower evolution. The Colour Dipole model describes the data reasonably well. Predictions of perturbative QCD calculations at the parton level based on BFKL and DGLAP parton evolution are discussed in the context of this measurement.     

Forward jet production in deep inelastic scattering at HERA

The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken scaling variable (x_Bj) and as triple differential cross sections d³σ/dx_BjdQ² , where Q² is the four momentum transfer squared and is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets. The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models.     

Quark jet as a trigger for gluon jet in deep inelastic muon scattering

We calculate, to first order in QCD, the probability for a fast hadron observed at laboratory angle θ _h from the virtual photon directionq, to originate from the quark of a quark-gluon final state. Given this probability, the average gluon energy and angle with respect toq are then calculated. This approach provides a method for gluon jet direction in forthcoming experiments.     

Double Diffractive Process Factorization from ηc and γ Associated Production at Tevatron and LHC

We present a study of associated ηc and γ double diffractive production in pp^- collision based on Ingelman-Schlein model, and the framework of non-relativistic QOD factorization formalism for quarkonia production. The prediction of ηc and γ is more reliable than J/ψ production, because the associated ηc and γ production is a pure color-octet process, and the dominant contribution comes from color octet ^1S0^(8) subprocess, which is related to the color octet matrix element of ^1S0(8) of J/ψ by the heavy quark spin symmetry and the large PT J/ψ production data. We find that the ratio of diffractive to inclusive cross sections is independent of the values of color octet matrix elements, but is sensitive to the gluon factor of the Pomeron and renormalized Pomeron flux factors. So experimental measurement of this ratio can give us more information of the nature of Pomeron and test the assumption of hard diffractive factorization in hadron-hadron collisions.     

A new global analysis of deep inelastic scattering data

A new QCD analysis of deep inelastic scattering (DIS) data is presented. All available neutrino and antineutrino cross sections are reanalyzed and included in the fit, along with charged-lepton DIS and Drell–Yan data. A massive factorization scheme is used to describe the charm component of the structure functions. Next-to-leading-order parton distribution functions are provided. In particular, the strange-sea density is determined with a higher accuracy with respect to other global fits. Received: 16 March 1999 / Published online: 8 December 1999     

Results from a QCD analysis of the new deep inelastic scattering data

Results from a numerical evolution of the Altarelli-Parisi equations are presented, covering the full range 0<x<1. The predictions of leading order and next-to-leading order in perturbative QCD, are compared with the most precise currently available data. All necessary assumptions are quantitatively discussed.     

Measurement of jet shapes in high-Q^2 deep inelastic scattering at HERA

The shapes of jets with transverse energies, , up to 45 GeV produced in neutral- and charged-current deep inelastic scattering (DIS) at GeV have been measured with the ZEUS detector at HERA. Jets are identified using a cone algorithm in the - plane with a cone radius of one unit. The jets become narrower as increases. The jet shapes in neutral- and charged-current DIS are found to be very similar. The jets in neutral-current DIS are narrower than those in resolved processes in photoproduction and closer to those in direct-photon processes for the same ranges in and jet pseudorapidity. The jet shapes in DIS are observed to be similar to those in interactions and narrower than those in collisions for comparable . Since the jets in interactions and DIS are predominantly quark initiated in both cases, the similarity in the jet shapes indicates that the pattern of QCD radiation within a quark jet is to a large extent independent of the hard scattering process in these reactions. Received: 2 April 1998 / Published online: 7 April 1999     

Implications of new deep inelastic scattering data for parton distributions

We perform a next-to-leading order structure function analysis of μN and νN deep inelastic data in an attempt to resolve the disagreement between recent EMC and BCDMS measurements of F₂ for μp scattering. Equally acceptable QCD fits are obtained including either set of μN data, but a comparison with Drell-Yan data appears to favour the parton distributions derived from the BCDMS data.     

Nuclear binding and deep inelastic scattering

We examine deep inelastic scattering using methods which have been successfully applied to study inclusive scattering of GeV electrons by nuclei. We find that the consistent inclusion of the binding effects allows to describe much better the data on nuclear matter to deuteron cross section ratios in the region of large x where binding fully accounts for the deviation of the cross section ratio from one.     

Evidence for planar events and a forward double jet structure in deep inelastic Muon scattering

The final states of charged hadrons produced in 280 GeV μp scattering are analysed with respect to their planarity and jet structure. Distributions of p_⊥² in and p_{⊥ out}² are presented. A two jet structure in the forward hemisphere is observed for events with high p_⊥ tracks are predicted by QCD models.     

Comparison of asymptotically free theories with high-energy deep inelastic scattering data

Comparison of the predictionsof asymptotically free gauge theories on ? 1n vW₂(x, q²)|? 1n q² in the small x region with recent data on high-energy muon-hadron scattering allows a fairly direct determination of the effective coupling constant. The result is α(q²)?0.21/[1 + 0.14 1n q² (GeV²)]. This is much smaller than previous indirect estimates.     

Shadowing in deep inelastic muon scattering from nuclear targets

Results are presented on the ratio of the inelastic muon-nucleus cross section per nucleon for carbon and calcium relative to that for deuterium. The measurements were made in the kinematic range of low x (0.003–0.1) and low Q² (0.3–3.2 GeV²) at an incident muon energy of 280 GeV. The calcium to deuterium ratio shows a significant x dependence which is interpreted as a shadowing effect. No strong Q² dependence is observed. This suggests that the effect is due at least partially to parton interactions within the nucleus.     

Naive quark model and deep inelastic scattering

It is assumed that nucleon consists of three quarks with no admixture of gluons or strange quarks. Gluons as are seen in deep inelastic scattering, appear only as a result of bremsstrahlung by valence quarks. The model gives unique predictions for observable quantaties and imitates the scaling behavior at Q² ? 2 GeV² provided the coupling constant of strong interactions is relatively small at such values of $\text{Q}{}^2\text{(}\text{g}{}^2\text{(2}\text{GeV}{}^2\text{)}\text{4π ≈}\text{1}\text{4}\text{)}$. The predictions of the model agree with the data within (10 – 20) % accuracy and links consideration of deep inelastic scattering with the most naive quark model. The effect of charmed particles production is estimated within the model developed. It is shown that the standard four-quark model of weak interactions is inconsistent with observed anomalies in ν, $\text{ν}$-interactions.