| 1. |
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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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Quark Asymmetries in the Proton from a Model for Parton Densities
- 2005
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Ingår i: Physical Review D. ; 71:094015
-
Tidskriftsartikel (refereegranskat)abstract
- Based on quantum fluctuations in momentum and of the proton into meson-baryon pairs, we develop a physical model for the non-perturbative x-shape of parton density functions in the proton. The model describes the proton structure function and gives a natural explanation of observed quark asymmetries, such as the difference between the anti-up and anti-down sea quark distributions and between the up and down valence distributions. An asymmetry in the momentum distribution of strange and anti-strange quarks in the nucleon is found to reduce the NuTeV anomaly to a level which does not give a significant indication of physics beyond the standard model.
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| 5. |
- Alwall, Johan, 1975-
(författare)
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Quark Distributions and Charged Higgs Boson Production : Studies of Proton Structure and New Physics
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Standard Model describes all elementary particles known today, but at larger energies it will have to be complemented with new particles and interactions. To be able to distinguish new physics at proton colliders such as LHC at CERN, it is essential to have an appropriate description of the colliding protons and their interactions. The study of the proton is important also in itself, to get a better understanding of the non-perturbative aspects of the strong interaction.In paper I-IV of this thesis, a model for the non-perturbative dynamics of quarks and gluons is developed, based on quantum fluctuations in hadrons. The parton distributions of the proton are given by momentum fluctuations, with sea quark distributions generated by fluctuations into baryon-meson pairs. This model can reproduce proton structure function data, as well as measured asymmetries between up and down valence quark distributions and between the anti-up and anti-down sea. It provides an intrinsic charm quark component as indicated by data. It also predicts an asymmetry in the strange sea of the proton, which can explain the NuTeV anomaly first attributed to new physics beyond the Standard Model.Charged Higgs bosons are predicted by several theories for new physics, including Supersymmetry. At proton colliders, the predicted dominant production mechanism is in association with top and bottom quarks. In paper V-VII, different contributions to this production are studied, and an algorithm is developed for combining the two dominant processes gb -> tH+/- and gg -> tbH+/-. The algorithm gives a smooth transition from small to large transverse momenta of the b-quark, which is important when the b-quark is observed. It also gives arguments for the choice of factorisation scale in the process.
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| 6. |
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| 7. |
- Alwall, Johan, et al.
(författare)
-
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)-
-
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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| 8. |
- Andersen, J. R., et al.
(författare)
-
Small-x phenomenology - Summary of the 3rd Lund small-x workshop in 2004
- 2006
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 48:1, s. 53-105
-
Forskningsöversikt (refereegranskat)abstract
- A third workshop on small-x physics, within the Small-x Collaboration, was held in Hamburg in May 2004 with the aim of overviewing recent theoretical progress in this area and summarizing the experimental status.
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| 9. |
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| 10. |
- Andersson, Bo, et al.
(författare)
-
ON HIGH-ENERGY LEPTOPRODUCTION
- 1981
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Ingår i: Zeitschrift für Physik C Particles and Fields. - 0170-9739. ; C9, s. 233-233
-
Tidskriftsartikel (refereegranskat)
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| 11. |
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| 12. |
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| 13. |
- Armesto, N., et al.
(författare)
-
Heavy-ion collisions at the LHC-Last call for predictions
- 2008
-
Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 35:5, s. 054001-
-
Forskningsöversikt (refereegranskat)abstract
- This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.
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| 14. |
- B, Mariotto Cristiano, et al.
(författare)
-
Hard and soft QCD in charmonium production
- 2000
-
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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| 15. |
- Barlow, R., et al.
(författare)
-
Report of the heavy flavors working group
- 1991
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 17:10, s. 1605-1623
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- After a brief discussion of the statistics available to the four LEP experiments at the time of writing and an overview of B-event characteristics, the authors consider in particular the theory, practice and potential pitfalls of neural networks, a new approach to B tagging which attracted a great deal of interest. They then consider some of the QCD aspects of heavy flavour physics. Finally there is a brief discussion of the prospects for heavy flavour physics at HERA.
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| 16. |
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| 17. |
- Danielsson, Ulf, et al.
(författare)
-
Heavy photophilic scalar at the LHC from a varying electromagnetic coupling
- 2017
-
Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213 .- 1873-1562. ; 919, s. 569-582
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the phenomenology of a heavy scalar ϕ of the type involved in Bekenstein's framework for varying electromagnetic coupling theories, with the difference that the scalar in our model has a large mass. The model has only two free parameters, the mass Mϕ of the scalar and the scale Λ of new physics. The scalar is dominantly produced through photon-photon fusion at the LHC and leads to a diphoton final state. It can also be produced by quark-antiquark fusion in association with a photon or a fermion pair. Its dominating decay is to diphotons, but it also has a large three-body branching to a fermion pair and a photon, which can provide an interesting search channel with a dilepton-photon resonance. We derive exclusion limits on the Mϕ−Λplane from the latest 13 TeV LHC diphoton resonance search data. For a benchmark mass of Mϕ∼1 TeV, we find a lower limit on Λ of 18 TeV. We discuss the more complex possibility of varying couplings in the full electroweak theory and comment on the possibility that the new physics is related to extra dimensions or string theory.
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| 18. |
- Danielsson, Ulf, et al.
(författare)
-
Varying gauge couplings and collider phenomenology
- 2019
-
Ingår i: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 100:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate a natural extension of the Standard Model that involves varying coupling constants. This is a general expectation in any fundamental theory such as string theory, and there are good reasons for why new physics could appear at reachable energy scales. We investigate the collider phenomenology of models with varying gauge couplings where the variations are associated with real singlet scalar fields. We introduce three different heavy scalar fields that are responsible for the variations of the three gauge couplings of the Standard Model. This gives rise to many interesting collider signatures that we explore, resulting in exclusion limits based on the most recent LHC data, and predictions of the future discovery potential at the high-luminosity LHC.
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| 19. |
- Dittmar, M, et al.
(författare)
-
Parton distributions: Summary report for the HERA - LHC workshop
- 2005
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- We provide an assessment of the impact of parton distributions on the determination of LHC processes, and of the accuracy with which parton distributions (PDFs) can be extracted from data, in particular from current and forthcoming HERA experiments. We give an overview of reference LHC processes and their associated PDF uncertainties, and study in detail W and Z production at the LHC. We discuss the precision which may be obtained from the analysis of existing HERA data, tests of consistency of HERA data from different experiments, and the combination of these data. We determine further improvements on PDFs which may be obtained from future HERA data (including measurements of $F_L$), and from combining present and future HERA data with present and future hadron collider data. We review the current status of knowledge of higher (NNLO) QCD corrections to perturbative evolution and deep-inelastic scattering, and provide reference results for their impact on parton evolution, and we briefly examine non-perturbative models for parton distributions. We discuss the state-of-the art in global parton fits, we assess the impact on them of various kinds of data and of theoretical corrections, by providing benchmarks of Alekhin and MRST parton distributions and a CTEQ analysis of parton fit stability, and we briefly presents proposals for alternative approaches to parton fitting. We summarize the status of large and small x resummation, by providing estimates of the impact of large x resummation on parton fits, and a comparison of different approaches to small x resummation, for which we also discuss numerical techniques.
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| 20. |
- Dombey, S., et al.
(författare)
-
QCD evolution of jets in the quark-gluon plasma
- 2008
-
Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 808, s. 178-191
-
Tidskriftsartikel (refereegranskat)abstract
- The quark-gluon plasma (QGP) can be explored in relativistic heavy ion collisions by the jet quenching signature, i.e. by the energy loss of a high energy quark or gluon traversing the plasma. We introduce a novel QCD evolution formalism in the leading logarithm approximation, where normal parton radiation is interleaved with scattering on the plasma gluons occuring at a similar time scale. The idea is elaborated in two approaches. One extends the DGLAP evolution equations for fragmentation functions to include scatterings in the medium, which facilitates numerical solutions for comparison with data and provides a basis for a Monte Carlo implementation. The other approach is more general by including also the transverse momentum dependence of the jet evolution, which allows a separation of the scales also for the scattering term and provides a basis for analytical investigations. The two approaches are shown to be related and give the same characteristic softening of the jet depending on the temperature of the plasma. A substantial effect is found at the RHIC energy and is further enhanced at LHC. Systematic studies of data on the energy loss could, therefore, demonstrate the existence of the QGP and probe its properties.
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| 21. |
- Edin Anders, Ingelman Gunnar
(författare)
-
A model for parton distributions in hadrons
- 1999
-
Ingår i: NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS. - : ELSEVIER SCIENCE BV. ; , s. 189-191
-
Konferensbidrag (refereegranskat)abstract
- The non-perturbative parton distributions in hadrons are derived. from simple physical arguments resulting in an analytical expression for the valence parton distributions. The sea partons arise mainly from pions in hadronic fluctuations. The model gives
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| 22. |
- Edin Anders, Ingelman Gunnar
(författare)
-
A model for the parton distributions in hadrons
- 1998
-
Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 432:3-4, s. 402-410
-
Tidskriftsartikel (refereegranskat)abstract
- A simple model is presented for the parton distributions in hadrons. The parton momenta in the hadron rest frame are derived from a spherically symmetric, Gaussian, distribution having a width motivated by the Heisenberg uncertainty relation applied to th
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| 23. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
LEPTO 6.5 - A Monte Carlo generator for deep inelastic lepton-nucleon scattering
- 1997
-
Ingår i: COMPUTER PHYSICS COMMUNICATIONS. - : ELSEVIER SCIENCE BV. - 0010-4655. ; 101:1-2, s. 108-134
-
Tidskriftsartikel (refereegranskat)abstract
- Physics and programming aspects are discussed for a Fortran 77 Monte Carlo program to simulate complete events in deep inelastic lepton-nucleon scattering. The parton level interaction is based on the standard model electroweak cross sections, which are f
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| 24. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
Quarkonium production at the Fermilab Tevatron through soft color interactions
- 1997
-
Ingår i: PHYSICAL REVIEW D. - : AMER INST PHYSICS. - 0556-2821. ; 56:11, s. 7317-7320
-
Tidskriftsartikel (refereegranskat)abstract
- The direct charmonium and bottomonium production rate observed at high p(perpendicular to) in p (p) over bar collisions at the Fermilab Tevatron is factors of 10 larger than predictions based on conventional perturbative QCD. We show that this excess can
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| 25. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
Rapidity Gaps in DIS through Soft Colour Interactions
- 1995
-
Ingår i: In proc. of workshop `DIS and QCD', Paris, April 1995.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a new mechanism for the creation of large rapidity gaps in DIS events at HERA. Soft colour interactions between perturbatively produced partons and colour-charges in the proton remnant, modifies the colour structure for hadronization giving col
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| 26. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
Soft Colour Exchanges and the Hadronic Final State
- 1999
-
Ingår i: Proc. of workshop Monte Carlo Generators for HERA Physics. ; , s. 280-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The models for soft colour interactions and colour string re-interactions, implemented in the Monte Carlo program LEPTO, are investigated regarding hadronic final states in inclusive and diffractive deep inelastic scattering.
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| 27. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
Soft colour interactions and the diffractive structure function
- 1996
-
Ingår i: JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS. - : IOP PUBLISHING LTD. ; , s. 943-946
-
Konferensbidrag (refereegranskat)abstract
- We discuss our model for soft colour interactions and present results on the diffractive structure function F-2(D)(beta, x(P), Q(2)) and inclusive transverse energy flows, which agree with available HERA data.
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| 28. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
Soft colour interactions as the origin of rapidity gaps in DIS
- 1996
-
Ingår i: PHYSICS LETTERS B. ; 366:1-4, s. 371-378
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce soft colour interactions as a novel mechanism to understand the observed events with large rapidity gaps in $ep$ collisions at HERA. Colour exchanges between produced partons and colour-charges in the proton remnant modifies the colour struct
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| 29. |
- Edin Anders, Ingelman Gunnar, Rathsman Johan
(författare)
-
Unified description of rapidity gaps and energy flows in DIS final states
- 1997
-
Ingår i: ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. - : SPRINGER VERLAG. - 0170-9739. ; 75:1, s. 57-70
-
Tidskriftsartikel (refereegranskat)abstract
- We show that the 'orthogonal' characteristics of the observed rapidity gaps and large forward energy flows in deep inelastic scattering at HERA, can be described within a single framework. Our Monte Carlo model is based on perturbative QCD matrix elements
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| 30. |
- Edin Anders, Ingelman Gunnar, Torokoff Kristel
(författare)
-
Non-perturbative Parton Distributions in the Proton
- 1999
-
Ingår i: Proc. of workshop Monte Carlo Generators for HERA Physics. ; , s. 263-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A model for the parton distributions in hadrons is derived from simple physical arguments leading to an analytical expression for the valence distributions. The sea parton distributions arise mainly from pions in hadronic fluctuations. Evolving from a low
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| 31. |
- Ekstedt, Andreas, et al.
(författare)
-
Constraining minimal anomaly free U(1) extensions of the Standard Model
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; 1611
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a class of minimal anomaly free U(1) extensions of the Standard Model with three generations of right-handed neutrinos and a complex scalar. Using electroweak precision constraints, new 13 TeV LHC data, and considering theoretical limitations such as perturbativity, we show that it is possible to constrain a wide class of models. By classifying these models with a single parameter, κ, we can put a model independent upper bound on the new U(1) gauge coupling gz. We find that the new dilepton data puts strong bounds on the parameters, especially in the mass region MZ′≲3 TeV.
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| 32. |
- Ekstedt, Andreas, et al.
(författare)
-
Hard color singlet BFKL exchange and gaps between jets at the LHC
- 2017
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We explore the perturbative QCD dynamics of hard parton-parton scattering through the exchange of a color singlet two-gluon ladder as described by the BFKL equation, resulting in a rapidity gap between two high transverse momentum jets. Implementing this in a complete Monte Carlo event simulation that also accounts for additional QCD processes at softer scales provides dynamical modeling of gap survival probabilities, which makes possible a detailed comparison with data on such jet-gap-jet events. New data from CMS at the LHC extend the dynamic range of the previous Tevatron data, and can be reproduced reasonably well provided that the Soft Color Interaction model is modified based on the idea of reduced resolution power of softer gluon exchanges. This indicates the need for further theoretical developments in connection with other color exchange processes related to rapidity gaps in the hadronic final state.
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| 33. |
- Ekstedt, Andreas, et al.
(författare)
-
Minimal anomalous U(1) theories and collider phenomenology
- 2018
-
Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; 1802, s. 152-
-
Tidskriftsartikel (refereegranskat)abstract
- We study the collider phenomenology of a neutral gauge boson Z′ arising in minimal but anomalous U(1) extensions of the Standard Model (SM). To retain gauge invariance of physical observables, we consider cancellation of gauge anomalies through the Green-Schwarz mechanism. We categorize a wide class of U(1) extensions in terms of the new U(1) charges of the left-handed quarks and leptons and the Higgs doublet. We derive constraints on some benchmark models using electroweak precision constraints and the latest 13 TeV LHC dilepton and dijet resonance search data. We calculate the decay rates of the exotic and rare one-loop Z′ decays to ZZ and Z-photon modes, which are the unique signatures of our framework. If observed, these decays could hint at anomaly cancellation through the Green-Schwarz mechanism. We also discuss the possible observation of such signatures at the LHC and at future ILC colliders.
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| 34. |
- Ekstedt, Andreas, et al.
(författare)
-
Nucleon parton distributions from hadronic quantum fluctuations
- 2019
-
Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 100:3
-
Tidskriftsartikel (refereegranskat)abstract
- A physical model is presented for the nonperturbative parton distributions in the nucleon. This is based on quantum fluctuations of the nucleon into baryon-meson pairs convoluted with Gaussian momentum distributions of partons in hadrons. The hadronic fluctuations, here developed in terms of hadronic chiral perturbation theory, occur with high probability and generate sea quarks as well as dynamical effects also for valence quarks and gluons. The resulting parton momentum distributions f(x,Q20) at low momentum transfers are evolved with conventional Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equations from perturbative QCD to larger scales. This provides parton density functions f(x,Q2) for the gluon and all quark flavors with only five physics-motivated parameters. By tuning these parameters, experimental data on deep-inelastic structure functions can be reproduced and interpreted. The contribution to sea quarks from hadronic fluctuations explains the observed asymmetry between ¯u and ¯d in the proton. The strange-quark sea is strongly suppressed at low Q2, as observed.
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| 35. |
- Ekstedt, Andreas
(författare)
-
Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Higgs particle was first predicted in 1964, and was discovered in the summer of 2012 at the Large Hadron Collider (LHC). This discovery was the latest in a long list of successful Standard Model predictions spanning the last fifty years. However, some of the Standard Models predictions, such as massless neutrinos, are not in agreement with experiment. Thus, extensions of the Standard Model should be considered. Furthermore, some issues, such as how quarks are bound within the proton, are difficult to study from first principles.In paper I and II of this thesis, a class of models that contains a new TeV scale neutral vector boson is studied. The parameter space of this class of models is constrained using electroweak precision constraints and 13 TeV LHC data. Gauge anomalies are cancelled both by choosing appropriate fermion charges, and by adding Green-Schwarz terms.The Higgs mechanism is often studied at leading order, but there are also important radiative corrections. These radiative corrections, which change the ground state energy, can both be IR divergent and gauge dependent. In paper III it is shown how to solve both of these problems. In particular, IR divergences are shown to be spurious.In paper IV of this thesis, rapidity gaps at the LHC are explained by using a colour singlet two-gluon ladder exchange (BFKL). These exchanges, together with a soft-gluon model, are implemented in a complete Monte Carlo simulation, and reproduce observed rapidity gaps at the LHC.The momentum distributions of bound partons, quarks and gluons, are described by parton distribution functions (PDFs). In paper V and VI of this thesis, a physically motivated model for PDFs is presented. This model can reproduce proton structure function data, and gives a possible solution to the proton spin puzzle.
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| 36. |
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| 37. |
- Enberg, Rikard, et al.
(författare)
-
Diffractive Higgs Boson Production at the Fermilab Tevatron and the CERN Large Hadron Collider
- 2002
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 89:8, s. 081801-
-
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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| 38. |
- Enberg, Rikard, et al.
(författare)
-
Diffractive Higgs bosons and prompt photons at hadron colliders
- 2003
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 67, s. 011301-
-
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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| 39. |
- Enberg, Rikard, et al.
(författare)
-
Hard colour singlet exchange and gaps between jets at the Tevatron
- 2002
-
Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 524:3-4, s. 273-282
-
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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| 40. |
|
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| 41. |
- Enberg, Rikard, et al.
(författare)
-
Hard diffraction and parton rescattering
- 2011
-
Ingår i: 40th International Symposium on Multiparticle Dynamics (ISMD 2010): Antwerp, Belgium, September 21-25, 2010. ; , s. 251-256
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a new model where hard diffraction is an effect of soft gluon rescattering between partons emerging from the hard interaction and the color field of the proton. A resummation to all orders of multiple gluon exchanges leads to an overall color singlet exchange amplitude which reproduces the precise HERA data on diffractive deep inelastic scattering
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| 42. |
- Enberg, Rikard
(författare)
-
Quantum chromodynamics and colour singlet exchange in high energy interactions
- 2003
-
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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| 43. |
- Enberg, Rikard, et al.
(författare)
-
Rapidity gaps at HERA and the Tevatron from soft colour exchanges
- 2000
-
Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 26, s. 712-715
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Tidskriftsartikel (refereegranskat)abstract
- Models based on soft colour exchanges to rearrange colour strings in the final state provide a general framework for both diffractive and non-diffractive events in ep and hadron-hadron collisions. We study two such models and find that they can reproduce rapidity gap data from both HERA and the Tevatron. We also discuss the influence of parton cascades and multiple interactions on the results.
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| 44. |
- Enberg, Rikard, et al.
(författare)
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Soft color interactions and diffractive hard scattering at the Fermilab Tevatron
- 2001
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 64:11, s. 114015-
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Tidskriftsartikel (refereegranskat)abstract
- An improved understanding of nonperturbative QCD can be obtained by the recently developed soft color interaction models. Their essence is the variation of color string-field topologies, giving a unified description of final states in high energy interactions, e.g., diffractive and nondiffractive events in ep and pp̅ . Here we present a detailed study of such models (the soft color interaction model and the generalized area law model) applied to pp̅ , considering also the general problem of the underlying event including beam particle remnants. With models tuned to DESY HERA ep data, we find a good description also of Fermilab Tevatron data on production of W, beauty and jets in diffractive events defined either by leading antiprotons or by one or two rapidity gaps in the forward or backward regions. We also give predictions for diffractive J/ψ production where the soft exchange mechanism produces both a gap and a color singlet cc̅ state in the same event. This soft color interaction approach is also compared with Pomeron-based models for diffraction, and some possibilities to experimentally discriminate between these different approaches are discussed.
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| 45. |
- Enberg, Rikard, et al.
(författare)
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Soft colour interactions and diffractive Higgs production
- 2004
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 33:Suppl. 1, s. 542-544
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Tidskriftsartikel (refereegranskat)abstract
- The topical subject of Higgs production in diffractive hard scattering events at the Tevatron and LHC is discussed. This has been proposed as a Higgs discovery channel with appealing experimental features. Predictions are obtained from the Soft Colour Interaction model, where rapidity gaps are created by a new soft interaction added to the normal hard scattering processes, implemented in the Monte Carlo event generator PYTHIA. A brief review of the successful application of the model to describe all CDF and DØ data on diffractive hard scattering, such as production of W/Z, dijets, beauty and $J/\psi$ is also given.
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| 46. |
- Eriksson, David, et al.
(författare)
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Color rearrangements in B-meson decays
- 2009
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 79:1, s. 014011-
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Tidskriftsartikel (refereegranskat)abstract
- Wepresent a new model, based on color rearrangements, which atthe same time can describe both hidden and open charmproduction in B-meson decays. The model is successfully compared toboth inclusive decays, such as B-->J/psiX and B-->DsX, as wellas exclusive ones, such as B-->J/psiK(*) and B-->D(*)D(*)K. It alsogives a good description of the momentum distribution of directJ/psi's, especially in the low-momentum region, which earlier has beenclaimed as a possible signal for new exotic states.
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| 47. |
- Eriksson, David, et al.
(författare)
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New angles on top quark decay to a charged Higgs
- 2009
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media LLC. - 1126-6708 .- 1029-8479. ; 01:1, s. 024-
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Tidskriftsartikel (refereegranskat)abstract
- To properly discover a charged Higgs Boson (H±) requires its spin and couplings to be determined. We investigate how to utilize t spin correlations to analyze the H± couplings in the decay t → bH+ → bτ+ντ. Within the framework of a general Two-Higgs-Doublet Model, we obtain results on the spin analyzing coefficients for this decay and study in detail its spin phenomenology, focusing on the limits of large and small values for tan β. Using a Monte Carlo approach to simulate full hadron-level events, we evaluate systematically how the H± → τ±ντ decay mode can be used for spin analysis. The most promising observables are obtained from azimuthal angle correlations in the transverse rest frames of t(). This method is particularly useful for determining the coupling structure of H± in the large tan β limit, where differences from the SM are most significant.
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| 48. |
- Eriksson, David, 1977-
(författare)
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Phenomenology of Charged Higgs Bosons and B-meson Decays
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For more than 30 years the Standard Model has been the theoretical foundation for particle physics. The theory has been verified successfully by experimental tests. Its biggest shortcoming is the non-discovery of the Higgs boson,responsible for giving the other particles masses. Despite its success there are hints that the Standard Model is not the complete theory and many extensions of it, such as supersymmetry, have been proposed. Extended theories often predict the existence of a charged Higgs boson and its detection will be a clear sign of physics beyond the Standard Model. The main focus in this thesis is on various phenomenological aspects of the charged Higgs boson. For favorable mass and couplings direct detection is shown to be possible at the Large Hadron Collider in production with an associated W boson. It is also shown how a light charged Higgs can have measurable effects on spin correlations in decays of pair-produced top quarks. The charged Higgs boson can also be seen indirectly, in for example B-meson decays, which can be used to put constraints on its mass and fermion couplings. Exclusion limits in two supersymmetric models are given together with a comparison with the discovery potentials for the LHC experiments. A tool for calculating properties, such as masses and decays, of both charged and neutral Higgs bosons in the Two-Higgs-Doublet Model is also presented. B-meson decays can also be used to test aspects of the strong interaction. Part of this thesis deals with improving and applying phenomenological models to B-meson decays. Although these models are not derived from first principles, their success shows that they capture important features of non-perturbative strong interactions.
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| 49. |
- Falk, Johan
(författare)
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Students' depictions of quantum mechanics : a contemporary review and some implications for research and teaching
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a comprehensive review of research into students’ depictions of quantum mechanics. A taxonomy to describe and compare quantum mechanics education research is presented, and this taxonomy is used to highlight the foci of prior research. A brief history of quantum mechanics education research is also presented. Research implications of the review are discussed, and several areas for future research are proposed. In particular, this thesis highlights the need for investigations into what interpretations of quantum mechanics are employed in teaching, and that classical physics – in particular the classical particle model – appears to be a common theme in students’ inappropriate depictions of quantum mechanics. Two future research projects are presented in detail: one concerning interpretations of quantum mechanics, the other concerning students’ depictions of the quantum mechanical wave function.This thesis also discusses teaching implications of the review. This is done both through a discussion on how Paper 1 can be used as a resource for lecturers and through a number of teaching suggestions based on a merging of the contents of the review and personal teaching experience.
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| 50. |
- Ghaderi, Hazhar
(författare)
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The interplay between quark and hadronic degrees of freedom and the structure of the proton
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We study the low-energy sector of the strong interaction which is the least understood part of the Standard Model, the theory that describes the interactions of all known particles. The ideal particles for this study are the proton and the neutron, collectively called the nucleon. They make up the nucleus of all the atoms of our world and understanding them has been of high priority ever since their discovery. We show that one cannot neglect the effects of other hadrons, such as neutrons and pions when studying the proton. A large part of the proton's hadronic wavefunction is shown to consist of the wavefunctions of other hadrons. In other words, when probing the proton there is a sizeable probability that one is probing some other hadron surrounding the proton as a quantum fluctuation.The nucleon itself consists of elementary particles known as quarks and gluons, collectively called partons. Exactly how the properties of these partons make up the properties of the nucleon has been the subject of active research ever since their discovery. Two main issues are the flavor asymmetry of the proton sea and the spin structure of the nucleon. To address these questions we study the interplay between the partonic and hadronic degrees of freedom. We introduce a model based on a convolution between hadronic quantum fluctuations as described by chiral perturbation theory, and partonic degrees of freedom motivated by a physical model of the nucleon having only few physically constrained parameters.We present the hadronic distribution functions and the parton distribution functions. The results are in agreement with a large set of experimental data. These include the structure functions of the proton and the neutron. Agreement with the sum rules of the spin structure functions offers new insight into the spin structure of the nucleon.
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