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| 2. |
- Alwall, Johan, et al.
(författare)
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Interpretation of electron-proton scattering at low Q2
- 2004
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 596, s. 77-83
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Tidskriftsartikel (refereegranskat)abstract
- Low-Q2 photons do not resolve partons in the proton, which gives problems when applying the deep inelastic scattering formalism, such as an unphysical, negative gluon density extracted from data. Considering instead hadronic fluctuations of the photon, we show that the generalised vector meson dominance model (GVDM) gives a good description of the measured cross section at low Q2, i.e., reproduces F2(x,Q2), using only few parameters with essentially known values. Combining GVDM and parton density functions makes it possible to obtain a good description of F2 data over the whole range of x and Q2.
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| 3. |
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| 4. |
- Alwall, Johan, et al.
(författare)
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Strange quark asymmetry in the nucleon and the NuTeV anomaly
- 2004
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Ingår i: Physical Review D. - 0556-2821. ; 70, s. 111505(R)-
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Tidskriftsartikel (refereegranskat)abstract
- The NuTeV anomaly of a nonuniversal value of the fundamental parameter sin2thetaW in the electroweak theory has been interpreted as an indication for new physics beyond the standard model. However, the observed quantity depends on a possible asymmetry in the momentum distributions of strange quarks and antiquarks in the nucleon. This asymmetry occurs naturally in a phenomenologically successful physical model for such parton distributions, which reduces the NuTeV result to only about 2 standard deviations from the standard model.
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| 5. |
- B, Mariotto Cristiano, et al.
(författare)
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Hard and soft QCD in charmonium production
- 2000
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We show that both hard perturbative and soft non-perturbative QCD effects are important in hadroproduction of charmonium. Observed $x_F$ and $p_\perp$ distributions of J/psi in fixed target experiments can be well described by our Monte Carlo model based
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| 6. |
- Enberg, Rikard, et al.
(författare)
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Diffractive Higgs Boson Production at the Fermilab Tevatron and the CERN Large Hadron Collider
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 89:8, s. 081801-
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Tidskriftsartikel (refereegranskat)abstract
- Improved possibilities to find the Higgs boson in diffractive events, having less hadronic activity, depend on whether the cross section is large enough. Based on the soft color interaction models that successfully describe diffractive hard scattering at DESY HERA and the Fermilab Tevatron, we find that only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the CERN Large Hadron Collider.
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| 7. |
- Enberg, Rikard, et al.
(författare)
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Diffractive Higgs bosons and prompt photons at hadron colliders
- 2003
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 67, s. 011301-
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Tidskriftsartikel (refereegranskat)abstract
- Models for soft color interactions have been successful in describing and predicting diffractive hard scattering processes in ep collisions at DESY HERA and pp̅ at the Fermilab Tevatron. Here we present new comparisons of the model to recent diffractive dijet data, also showing good agreement. The topical issue of diffractive Higgs boson production at the Tevatron and CERN LHC hadron colliders is further investigated. For H⃗γγ the irreducible background of prompt photon pairs from qq̅ →γγ and gg⃗γγ is always dominating, implying that higher branching ratio decay modes of the Higgs boson have to be used. However, such prompt photons can be used to test the basic prediction for Higgs boson production since gg⃗γγ involves a quark loop diagram similar to gg⃗H.
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| 8. |
- Enberg, Rikard, et al.
(författare)
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Hard colour singlet exchange and gaps between jets at the Tevatron
- 2002
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Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 524:3-4, s. 273-282
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Tidskriftsartikel (refereegranskat)abstract
- The new kind of events with a rapidity gap between two high-ET jets, observed in high energy collisions at the Tevatron, is found to be well described by the exchange of a colour singlet gluon system in the BFKL framework. This requires going beyond the conventional asymptotic Mueller–Tang approximation, which results in qualitatively different features of the basic parton–parton scattering amplitude. Non-leading corrections to the BFKL equation are included by incorporation of the consistency constraint and the running QCD coupling. Hadronisation and other non-perturbative QCD effects are treated through a complete Monte Carlo simulation, providing a gap survival probability that varies event-by-event, facilitating comparison with experimental results.
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| 9. |
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| 10. |
- Enberg, Rikard
(författare)
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Quantum chromodynamics and colour singlet exchange in high energy interactions
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantum chromodynamics (QCD) is the fundamental theory in elementary particle physics that describes the strong interaction in terms of exchanges of force-carrying, colour-charged particles known as gluons. Although well-established through experimental verifications, there are fundamental unsolved problems in the theory. In this thesis, some novel aspects of strong interaction dynamics are studied in the context of colour singlet exchange processes — interactions where complex systems of gluons with no net colour charge are exchanged. Both perturbative and non-perturbative QCD methods are used, as well as Monte Carlo computer simulations. Soft colour interactions in the final state of a high energy collision can lead to effective colour singlet exchange. Non-perturbative models for such interactions are shown to give a good description of diffractive production of W, Z, bb, J/ψ and jets in pp collisions at the Tevatron. Predictions are given for diffractive Higgs boson and prompt photon production at hadron colliders. Rapidity gaps between jets is a new phenomenon which is studied with an improved perturbative calculation of hard colour singlet exchange using the BFKL equation, taking into account previously neglected contributions and non-leading logarithmic corrections. Including also underlying soft rescattering effects, the complete model reproduces well data from the Tevatron. Diffractive vector meson production through hard colour singlet exchange in γp collisions is studied in the framework of the conformal invariant non-forward solution of the BFKL equation. Expressions for helicity-dependent amplitudes are derived, and the results show good agreement with data on J/ψ and ρ production from the ep collider HERA. These studies lead to a deeper knowledge of complex gluon dynamics, and therefore advance our understanding of QCD.
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