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1.	Abelleira Fernandez, J.L., et al. (författare) A Large Hadron Electron Collider at CERN 2012 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract This document provides a brief overview of the recently published report on the design of the Large Hadron Electron Collider (LHeC), which comprises its physics programme, accelerator physics, technology and main detector concepts. The LHeC exploits and develops challenging, though principally existing, accelerator and detector technologies. This summary is complemented by brief illustrations of some of the highlights of the physics programme, which relies on a vastly extended kinematic range, luminosity and unprecedented precision in deep inelastic scattering. Illustrations are provided regarding high precision QCD, new physics (Higgs, SUSY) and electron-ion physics. The LHeC is designed to run synchronously with the LHC in the twenties and to achieve an integrated luminosity of O(100) fb−1. It will become the cleanest high resolution microscope of mankind and will substantially extend as well as complement the investigation of the physics of the TeV energy scale, which has been enabled by the LHC.
2.	Abelleira Fernandez, J.L, et al. (författare) On the Relation of the LHeC and the LHC 2012 Rapport (övrigt vetenskapligt/konstnärligt)abstract The present note relies on the recently published conceptual design report of the LHeC and extends the first contribution to the European strategy debate in emphasising the role of the LHeC to complement and complete the high luminosity LHC programme. The brief discussion therefore focuses on the importance of high precision PDF and αs determinations for the physics beyond the Standard Model (GUTs, SUSY, Higgs). Emphasis is also given to the importance of high parton density phenomena in nuclei and their relevance to the heavy ion physics programme at the LHC.
3.	Anchordoqui, Luis A., et al. (författare) The Forward Physics Facility : Sites, experiments, and physics potential 2022 Ingår i: Physics reports. - : Elsevier. - 0370-1573 .- 1873-6270. ; 968, s. 1-50 Tidskriftsartikel (refereegranskat)abstract The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acceptance of the existing large LHC experiments and will observe rare and exotic processes in an extremely low-background environment. In this work, we summarize the current status of plans for the FPF, including recent progress in civil engineering in identifying promising sites for the FPF and the experiments currently envisioned to realize the FPF's physics potential. We then review the many Standard Model and new physics topics that will be advanced by the FPF, including searches for long-lived particles, probes of dark matter and dark sectors, high-statistics studies of TeV neutrinos of all three flavors, aspects of perturbative and non-perturbative QCD, and high-energy astroparticle physics.
4.	Arhrib, Abdesslam, et al. (författare) Identifying a light charged Higgs boson at the LHC Run II 2017 Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 774, s. 591-598 Tidskriftsartikel (refereegranskat)abstract We analyse the phenomenological implications of a light Higgs boson, h, within the CP-conserving 2-Higgs Doublet Model (2HDM) Type-I, for the detection prospects of the charged H± state at Run II of the Large Hadron Collider (LHC), assuming s√=13 TeV as energy and O(100 fb−1) as luminosity. When sufficiently light, this h state can open up the bosonic decay channel H±→W±(∗)h, which may have a branching ratio significantly exceeding those of the H±→τν and H±→cs channels. We perform a broad scan of the 2HDM Type-I parameter space, assuming the heavier of the two CP-even Higgs bosons, H, to be the observed SM-like state with a mass near 125 GeV. Through these scans we highlight regions in which mH±
5.	Banerjee, Avik, et al. (författare) Vector-like quarks: status and new directions at the LHC 2024 Tidskriftsartikel (refereegranskat)abstract Experimental searches for vector-like quarks have until now only considered their decays into Standard Model particles. However, various new physics scenarios predict additional scalars, so that these vector-like quarks can decay to new channels. These new channels reduce the branching ratios into Standard Model final states, significantly affecting current mass bounds. In this article, we quantitatively assess the relevance and observability of single and pair production processes of vector-like quarks, followed by decays into both standard and exotic final states. We highlight the importance of large widths and the relative interaction strengths with Standard Model particles and new scalars. Then, we review the post-Moriond 2024 status of these models in light of available LHC data and discuss potential future strategies to enhance the scope of vector-like quark searches.
6.	Benbrik, R., et al. (författare) Signatures of vector-like top partners decaying into new neutral scalar or pseudoscalar bosons 2020 Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2020:5 Tidskriftsartikel (refereegranskat)abstract We explore the phenomenology of models containing one Vector-Like Quark (VLQ), t′, which can decay into the Standard Model (SM) top quark, t, and a new spin-0 neutral boson, S, the latter being either a scalar or pseudoscalar state. We parametrise the underlying interactions in terms of a simplified model which enables us to capture possible Beyond the SM (BSM) scenarios. We discuss in particular three such scenarios: one where the SM state is supplemented by an additional scalar, one which builds upon a 2-Higgs Doublet Model (2HDM) framework and another which realises a Composite Higgs Model (CHM) through partial compositeness. Such exotic decays of the t′ can be competitive with decays into SM particles, leading to new possible discovery channels at the Large Hadron Collider (LHC). Assuming t′ pair production via strong interactions, we design signal regions optimised for one t′ → S t transition (while being inclusive on the other t¯ ′ decay, and vice versa), followed by the decay of S into the two very clean experimental signatures S → γ γ and S → Z (→ ℓ+ℓ−)γ. We perform a dedicated signal- to-background analysis in both channels, by using Monte Carlo (MC) event simulations modelling the dynamics from the proton-proton to the detector level. Under the assumption of BR(t′ → S t) = 100%, we are therefore able to realistically quantify the sensitivity of the LHC to both the t′ and S masses, assuming both current and foreseen luminosities. This approach paves the way for the LHC experiments to surpass current VLQ search strategies based solely on t′ decays into SM bosons (W±, Z , h). © 2020, The Author(s).
7.	Bergström, Johannes, 1985- (författare) Predictions of Effective Models in Neutrino Physics 2011 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Experiments on neutrino oscillations have confirmed that neutrinos have small, but non-zero masses, and that the interacting neutrino states do not have definite masses, but are mixtures of such states.The seesaw models make up a group of popular models describing the small neutrino masses and the corresponding mixing.In these models, new, heavy fields are introduced and the neutrino masses are suppressed by the ratio between the electroweak scale and the large masses of the new fields. Usually, the new fields introduced have masses far above the electroweak scale, outside the reach of any foreseeable experiments, making these versions of seesaw models essentially untestable. However, there are also so-called low-scale seesaw models, where the new particles have masses above the electroweak scale, but within the reach of future experiments, such as the LHC.In quantum field theories, quantum corrections generally introduce an energy-scale dependence on all their parameters, described by the renormalization group equations. In this thesis, the energy-scale dependence of the neutrino parameters in two low-scale seesaw models, the low-scale type I and inverse seesaw models, are considered. Also, the question of whether the neutrinos are Majorana particles, \ie , their own antiparticles, has not been decided experimentally. Future experiments on neutrinoless double beta decay could confirm the Majorana nature of neutrinos. However, there could also be additional contributions to the decay, which are not directly related to neutrino masses. We have investigated the possible future bounds on the strength of such additional contributions to neutrinoless double beta decay, depending on the outcome of ongoing and planned experiments related to neutrino masses.
8.	Bhattacharya, Atri, et al. (författare) Charm decay in slow-jet supernovae as the origin of the IceCube ultra-high energy neutrino events 2015 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 6 Tidskriftsartikel (refereegranskat)abstract We investigate whether the recent ultra-high energy (UHE) neutrino events detected at the IceCube neutrino observatory could come from the decay of charmed mesons produced within the mildly relativistic jets of supernova-like astrophysical sources. We demonstrate that the 5.7σ excess of neutrinos observed by IceCube in the energy range 30 TeV--2 PeV can be explained by a diffuse flux of neutrinos produced in such slow-jet supernovae, using the values of astrophysical and QCD parameters within the theoretical uncertainties associated with neutrino production from charmed meson decay in astrophysical sources. We discuss the theoretical uncertainties inherent in the evaluation of charm production in high energy hadronic collisions, as well as the astrophysical uncertainties associated with slow-jet supernova sources. The proton flux within the source, and therefore also the produced neutrino flux, is cut off at around a few PeV, when proton cooling processes become dominant over proton acceleration. This directly explains the sudden drop in event rates at energies above a few PeV. We incorporate the effect of energy dependence in the spectrum-weighted charm production cross-section and show that this has a very significant effect on the shape, magnitude and cut-off energies for the neutrino flux.
9.	Bhattacharya, Atri, et al. (författare) Energy-dependent flavour ratios in neutrino telescopes from charm 2024 Ingår i: Journal of Cosmology and Astroparticle Physics. - : Institute of Physics Publishing (IOPP). - 1475-7516. ; 2024:3 Tidskriftsartikel (refereegranskat)abstract The origin of the observed diffuse neutrino flux is not yet known. Studies of the relative flavour content of the neutrino flux detected at Earth can give information on the production mechanisms at the sources and on flavour mixing, complementary to measurements of the spectral index and normalisation. Here we demonstrate the effects of neutrino fluxes with different spectral shapes and different initial flavour compositions dominating at different energies, and we study the sensitivity of future measurements with the IceCube Neutrino Observatory. Where one kind of flux gives way to another, this shows up as a non-trivial energy dependence in the flavour compositions. We explore this in the context of slow-jet supernovae and magnetar-driven supernovae – two examples of astrophysical sources where charm production may be effective. Using current best-fit neutrino mixing parameters and their projected 2040 uncertainties, we use event ratios of different event morphologies at IceCube to illustrate the possibilities of distinguishing the energy dependence of neutrino flavour ratios.
10.	Bhattacharya, Atri, et al. (författare) Perturbative charm production and the prompt atmospheric neutrino flux in light of RHIC and LHC 2015 Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; 6 Tidskriftsartikel (refereegranskat)abstract We re-evaluate the prompt atmospheric neutrino flux, using the measured charm cross sections at RHIC and the Large Hadron Collider to constrain perturbative QCD parameters such as the factorization and renormalization scales, as well as modern parton distribution functions and recent estimates of the cosmic-ray spectra. We find that our result for the prompt neutrino flux is lower than previous perturbative QCD estimates and, consequently, alters the signal-to-background statistics of the recent IceCube measurements at high energies.
11.	Bhattacharya, Atri, et al. (författare) Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects 2016 Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; 11 Tidskriftsartikel (refereegranskat)abstract We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, kT factorization including low-x resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at 7 TeV and at 13 TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from 10% to 35% at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.
12.	Camargo-Molina, José Eliel, et al. (författare) A new perspective on the electroweak phase transition in the Standard Model Effective Field Theory 2021 Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2021 Tidskriftsartikel (refereegranskat)abstract A first-order Electroweak Phase Transition (EWPT) could explain the observed baryon-antibaryon asymmetry and have a detectable gravitational wave signature, but this is not possible in the Standard Model. We therefore study the EWPT in the Standard Model Effective Field Theory (SMEFT) including dimension-six operators. A first-order EWPT has previously been shown to be possible in the SMEFT in scenarios with a tree-level barrier between minima, which requires a negative Higgs quartic coupling and a new physics scale low enough to raise questions about the validity of the EFT approach. In this work we show that a first-order EWPT is possible in a novel scenario where the barrier between minima is generated radiatively, the quartic coupling is positive, the scale of new physics is higher, and there is good agreement with experimental bounds. Our calculation is done in a consistent, gauge-invariant way, and we carefully analyze the scaling of parameters necessary to generate a barrier in the potential. We perform a global fit in the relevant parameter space and explicitly find the points with a first-order transition that agree with experimental data. We also briefly discuss the prospects for probing the allowed parameter space using di-Higgs production in colliders.
13.	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.
14.	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.
15.	Edsjö, Joakim, et al. (författare) High energy neutrinos from cosmic ray interactions in the Sun 2017 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Cosmic rays hitting the outer parts of the Sun result in showers of high energy particles. The shower particles propagate through the solar atmosphere and interact further or decay. Among the shower particles are high energy neutrinos, after production these oscillate between flavours and interact with the solar material while propagating out of the Sun to the Earth. The result is a high energy neutrino flux at the Earth that may be detectable by modern neutrino detectors such as IceCube. Such a neutrino flux will furthermore act as a background in searches for neutrinos coming from annihilations of weakly interacting massive particles, often suggested to be the dark matter in the Universe. We perform an updated calculation of the solar atmospheric neutrino flux using the code MCEq for the cascade evolution in the solar atmosphere and WimpSim for the propagation of the neutrinos from the Sun to the detector on Earth, including full three-flavour treatment of neutrino oscillations and interactions in the Sun.
16.	Edsjö, Joakim, et al. (författare) Neutrinos from cosmic ray interactions in the Sun 2017 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :06 Tidskriftsartikel (refereegranskat)abstract Cosmic rays hitting the solar atmosphere generate neutrinos that interact and oscillate in the Sun and oscillate on the way to Earth. These neutrinos could potentially be detected with neutrino telescopes and will be a background for searches for neutrinos from dark matter annihilation in the Sun. We calculate the flux of neutrinos from these cosmic ray interactions in the Sun and also investigate the interactions near a detector on Earth that give rise to muons. We compare this background with both regular Earth-atmospheric neutrinos and signals from dark matter annihilation in the Sun. Our calculation is performed with an event-based Monte Carlo approach that should be suitable as a simulation tool for experimental collaborations. Our program package is released publicly along with this paper.
17.	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.
18.	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.
19.	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.
20.	Enberg, Rikard (författare) A Monte Carlo study of diffractive W production at the Tevatron 1998 Rapport (övrigt vetenskapligt/konstnärligt)abstract The ratio of diffractive W production in ppbar collisions at sqrt(s)=1.8 TeV measured by the CDF Collaboration is reproduced using Monte Carlo simulations in the Soft Colour Interaction model (SCI). The fraction of diffractive events containing jets measu
21.	Enberg, Rikard, et al. (författare) Associated central exclusive production of charged Higgs bosons 2011 Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 83:9, s. 095020- Tidskriftsartikel (refereegranskat)abstract We propose central exclusive production of a charged Higgs boson in association with a W boson as a possible signature of certain types of extended Higgs sectors. We calculate the cross section and find that the rate at the LHC could be large enough to allow observation in some models with two-Higgs doublets, where the charged Higgs and at least one of the neutral scalars can be light enough. We use the two-Higgs doublet model as a prototype and consider two distinct regions of parameter space, but we also briefly discuss the prospects for the next-to-minimal supersymmetric standard model, where the charged Higgs may very well be quite light.
22.	Enberg, Rikard, et al. (författare) Charged Higgs boson in the W± Higgs channel at the Large Hadron Collider 2015 Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213 .- 1873-1562. ; 893, s. 420-442 Tidskriftsartikel (refereegranskat)abstract In light of the recent discovery of a neutral Higgs boson, Hobs, with a mass near 125 GeV, we reassess the LHC discovery potential of a charged Higgs boson, H±, in the W±Hobs decay channel. This decay channel can be particularly important for a H± heavier than the top quark, when it is produced through the pp→tH± process. The knowledge of the mass of Hobsprovides an additional handle in the kinematic selection when reconstructing a Breit-Wigner resonance in the Hobs→bb¯ decay channel. We consider some extensions of the Standard Model Higgs sector, with and without supersymmetry, and perform a dedicated signal-to-background analysis to test the scope of this channel for the LHC running at design energy (14 TeV), for 300/fb (standard) and 3000/fb (high) integrated luminosities. We find that, while this channel does not show much promise for a supersymmetric H± state, significant portions of the parameter spaces of several two-Higgs doublet models are testable.
23.	Enberg, Rikard, et al. (författare) Constraints on the X17 boson from IceCube searches for non-standard interactions of neutrinos 2024 Tidskriftsartikel (refereegranskat)abstract We explain the ATOMKI anomaly with a very light Z′ state that features non-anomalous and non-flavour-universal vector and axial-vector couplings to all leptons. This Z′ comes from a theoretical framework with a spontaneously broken U(1)′ symmetry in addition to the Standard Model (SM) gauge group and is compliant with current measurements of the anomalous magnetic moments of the electron and the muon as well as beam dump experiments. The lepton flavour structure of this model allows for Z′ couplings to all light neutrinos, suggesting the possibility of Z′-mediated Non-Standard Interactions (NSIs) of neutrinos in matter, so that measurements of the strength parameters of the NSIs can constrain the value of the couplings. We use experimental constraints on NSIs of neutrinos using older TEXONO data and newer IceCube data. The IceCube data, in particular, strongly constrain the flavour universality of the leptonic vector current. The constraints enable us to define the region of parameter space of this theoretical scenario that can be pursued in further phenomenological analyses.
24.	Enberg, Rikard, et al. (författare) Diffractive heavy vector meson production from the BFKL equation 2002 Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 26:2, s. 219-228 Tidskriftsartikel (refereegranskat)abstract Diffractive heavy vector meson photoproduction accompanied by proton dissociation is studied for arbitrary momentum transfer. The process is described by the non-forward BFKL equation, for which a complete analytical solution is found, giving the scattering amplitude. The impact of non-leading corrections to the BFKL equation is also analysed. Results are compared to the HERA data on production.
25.	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.
26.	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.
27.	Enberg, Rikard (författare) Diffractive vector meson production 2004 Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474. Konferensbidrag (refereegranskat)abstract This is a brief introduction to diffractive vector meson production, both exclusive γ p → V p and large momentum transfer γ p → V X processes. I overview the theoretical basis for the perturbative description and some recent developments.
28.	Enberg, Rikard, et al. (författare) Diffractive vector meson production with a large momentum transfer 2003 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract We summarise recent progress in the computation of helicity amplitudes for diffractive vector meson production at large momentum transfer and their comparison to data collected at the HERA collider.
29.	Enberg, Rikard, et al. (författare) Diffractive vector mesons at large momentum transfer from the BFKL equation 2002 Konferensbidrag (refereegranskat)abstract Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation, for which an analytical solution is found for all conformal spins, giving the scattering amplitude. Results are compared to HERA data on \rho production.
30.	Enberg, Rikard, et al. (författare) Electroweak production of Higgs boson pairs in 2HDMs 2017 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract One of the main features of a Two-Higgs Doublet Model (2HDM) is the presence of two additional neutral Higgs states, besides the one mimicking the ~125 GeV state observed at the LHC. The three Higgs bosons of a 2HDM can be produced at the LHC either singly via gluon fusion or in pairs with each other. When analyzing their pair production, the emphasis is laid on gluon-initiated processes, and the electroweak (EW) production is generally not treated on the same footing, assuming its contribution to be highly subleading. We show here that when the sum of the masses of the lightest scalar and pseudoscalar Higgs bosons in the Type-I 2HDM is smaller than the Z-boson mass, their EW pair production can dominate over QCD pair production by orders of magnitude.
31.	Enberg, Rikard, et al. (författare) Electroweak production of light scalar-pseudoscalar pairs from extended Higgs sectors 2017 Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 764, s. 121-125 Tidskriftsartikel (refereegranskat)abstract In models with extended Higgs sectors, it is possible that the Higgs boson discovered at the LHC is not the lightest one. We show that in a realistic model (the Type I 2-Higgs Doublet Model), when the sum of the masses of a light scalar and a pseudoscalar (h and A) is smaller than the Z boson mass, the Electroweak (EW) production of an hA pair, which is generally neglected, can dominate over QCD production by orders of magnitude. This is because in the gg-initiated process, hA production via a resonant Z in the s-channel is prohibited according to the Landau-Yang theorem, which is not the case for the qq-initiated process. We explore the parameter space of the model to highlight regions giving such hA solutions while being consistent with all constraints from collider searches, b-physics and EW precision data. We also single out a few benchmark points to discuss their salient features, including the hA search channels that can be exploited at Run II of the LHC.
32.	Enberg, Rikard, et al. (författare) Electroweak production of multiple (pseudo)scalars in the 2HDM 2019 Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79 Tidskriftsartikel (refereegranskat)abstract The two-Higgs Doublet Model (2HDM) is the most minimal extension of the Standard Model (SM) containing extra Higgs doublet fields. Given the multiplicity of Higgs states in a 2HDM, its Higgs potential is significantly more involved than the SM one. Importantly, it contains a multitude of Higgs triple self-couplings, unlike the SM, which only has one. These interactions are key to understanding the phenomenology of the 2HDM, as they uniquely determine the form of the potential. Several studies analysing the prospects of measuring these couplings at the Large Hadron Collider (LHC) have found them to be quite low generally. However, such studies have largely concentrated on Higgs pair-production induced by gluon-gluon scattering, either via direct annihilation or followed by their splitting into b-(anti)quark pairs, which in turn annihilate leaving behind spectator b-(anti)quarks. Both of these channels are therefore governed by QCD dynamics. We compare here the yields of such channels to those initiated by (primarily) valence quarks, which involve Electro-Weak (EW) interactions only, for neutral multi-Higgs final states. We find that EW production can be dominant over QCD production for certain final state combinations. We also illustrate that charged final states, which can only be produced via EW modes, could serve as important probes of some H± triple couplings, that are inaccessible in QCD-induced processes, during Run 2 and 3 of the LHC. Our analysis covers regions of the parameter space of the Type-I 2HDM that have escaped the most up-to-date experimental constraints coming from EW precision data, LHC measurements of the 125 GeV Higgs boson properties, searches for additional Higgs states, and flavour physics.
33.	Enberg, Rikard, et al. (författare) Enhancement of associated (HW -/+)-W-+/- production in the NMSSM 2012 Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368 .- 1550-7998. ; 85:7 Tidskriftsartikel (refereegranskat)abstract We study the associated production of a charged Higgs and a W boson in high-energy pp collisions at the LHC. This is an interesting process for charged Higgs discovery, or exclusion, since the production cross section could depend strongly on the model, offering potential discriminating power between supersymmetric extensions of the standard model with minimal or extended Higgs sectors. We compute the cross section for this process in the next-to-minimal supersymmetric standard model (NMSSM), at the tree level for quark-quark scattering, and at one-loop level for gluon-gluon scattering. The most important corrections beyond leading order are taken into account using an improved Born approximation. We find that the pp -> (HW -/+)-W-+/- cross section can be resonantly enhanced by up to an order of magnitude over its MSSM value (both for root s = 7 TeV and 14 TeV) through the contributions of heavy, neutral, singlet-dominated Higgs bosons appearing in the s-channel. Since such Higgs mass configurations are normally not possible in the MSSM, the observation of associated (HW -/+)-W-+/- production at the LHC could provide a striking, although indirect, signature of a more complicated Higgs sector.
34.	Enberg, Rikard, et al. (författare) H± in the W±h channel at the LHC Run 2 2015 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract We analyse the discovery prospects of the charged Higgs boson, H±, via its decay in the W±h channel in the minimal supersymmetric Standard Model (MSSM) as well as several 2-Higgs Doublet Models (2HDMs). h, the lightest scalar Higgs boson in these models, is identified with the recently discovered ∼125 GeV state, Hobs, at the Large Hadron Collider (LHC). We find that, while it provides an important input in the kinematic selection of signal events, the measured Hobs mass renders this channel inaccessible in the MSSM. In the 2HDMs though, through a dedicated signal-to-background analysis for the pp→t(b¯)H−→ℓ±νℓjjbbb¯(b¯)+h.c process, we establish that some parameter space regions will be testable at the LHC with s√=14 TeV.
35.	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.
36.	Enberg, Rikard, et al. (författare) Hard colour singlet exchange at the Tevatron from the BFKL equation 2002 Ingår i: Deep Inelastic Scattering. DIS 2001 Proceedings of the 9th International Workshop. - 9810247540 ; , s. 820-823 Bokkapitel (övrigt vetenskapligt/konstnärligt)
37.	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
38.	Enberg, Rikard, et al. (författare) Hard pomeron in exclusive meson production at ILC 2005 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract We calculate the exclusive process gamma* gamma* ->rho rho at high energy. The Born order estimate and the leading (LLA) and next to leading order (NLLA) BFKL resummation effects show the feasibility of experimental detection in a quite large range of Q2 values at future high energy e+e- linear colliders.
39.	Enberg, Rikard (författare) HARDCOL: Hard Colour Singlet exchange processes in PYTHIA Annan publikation (övrigt vetenskapligt/konstnärligt)
40.	Enberg, Rikard, et al. (författare) Higgs phenomenology in the Stealth Doublet Model 2015 Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 91 Tidskriftsartikel (refereegranskat)abstract We analyze a model for the Higgs sector with two scalar doublets and a softly broken Z2 symmetry. One of the doublets breaks the electroweak symmetry and has tree-level Yukawa couplings to fermions. The other doublet has no vacuum expectation value and no tree-level couplings to fermions. Because the Z2 parity is broken the two doublets can mix, which leads to a distinct and novel phenomenology. This Stealth Doublet Model can be seen as a generalization of the Inert Doublet Model with a broken Z2 symmetry. We outline the model and present constraints from theory, electroweak precision tests and collider searches, including the recent observation of a Higgs boson at the LHC. The CP-odd scalar A and the charged scalar H± couple to fermions at one-loop level. We compute the decays of A and H± and in particular the one-loop decays A→ff¯, H±→ff¯′, H±→W±Z and H±→W±γ. We also describe how to calculate and renormalize such processes in our model. We find that if one of H± or A is the lightest scalar, H±→W±γ or A→bb¯ are typically their respective dominating decay channels. Otherwise, the dominating decays of H± and Aare into a scalar and a vector. Due to the absence of tree-level fermion couplings for H± and A, we consider pair production and associated production with vector bosons and scalars at the LHC. If the parameter space of the model that favors H±→W±γ is realized in Nature, we estimate that there should be a considerable amount of such events in the present LHC data.
41.	Enberg, Rikard, et al. (författare) Higgs properties in a broken Inert Doublet Model 2013 Ingår i: Journal of High Energy Physics (JHEP). - : Springer Berlin/Heidelberg. - 1126-6708 .- 1029-8479. ; 8 Tidskriftsartikel (refereegranskat)abstract We consider a model for the Higgs sector with two scalar doublets and a softly broken Z2 symmetry, the Stealth Doublet Model. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken Z2 symmetry leads to interesting phenomenology such as mixing between the two doublets and charged and CP-odd scalars that can be light and have unusual decay channels. We present theoretical and experimental constraints on the model and consider the recent observation of a Higgs boson at the LHC. The data on the H→ γγ channel can be naturally accommodated in the model, with either the lightest or the heaviest CP-even scalar playing the role of the observed particle.
42.	Enberg, Rikard, et al. (författare) Higgs properties in a softly broken Inert Doublet Model 2013 Ingår i: Journal of High Energy Physics. - 1029-8479. ; :8 Tidskriftsartikel (refereegranskat)abstract We consider a model for the Higgs sector with two scalar doublets and a softly broken Z(2) symmetry, the Stealth Doublet Model. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken Z(2) symmetry leads to interesting phenomenology such as mixing between the two doublets and charged and CP-odd scalars that can be light and have unusual decay channels. We present theoretical and experimental constraints on the model and consider the recent observation of a Higgs boson at the LHC. The data on the H -> gamma gamma channel can be naturally accommodated in the model, with either the lightest or the heaviest CP-even scalar playing the role of the observed particle.
43.	Enberg, Rikard, et al. (författare) Higgs properties in a softly broken Inert Doublet Model[JHEP, 08, (2013), 079] 2015 Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2015:1 Tidskriftsartikel (refereegranskat)
44.	Enberg, Rikard, et al. (författare) High energy neutrinos from charm in astrophysical sources 2009 Ingår i: Physical Review D. - : The American Physical Society. - 1550-7998 .- 1550-2368. ; 79:5, s. 053006- Tidskriftsartikel (refereegranskat)abstract Charm production gives rise to a flux of very high energy neutrinos from astrophysical sources with jets driven by central engines, such as gamma ray bursts or supernovae with jets. The neutrino flux from semileptonic decays of charmed mesons is subject to much less hadronic and radiative cooling than the conventional flux from pion and kaon decays and therefore has a dominant contribution at higher energies, which is of relevance to future ultrahigh energy neutrino experiments.
45.	Enberg, Rikard (författare) LHC och världens undergång 2009 Ingår i: Folkvett. - : Vetenskap och Folkbildning. - 0283-0795. ; :2, s. 7-30 Tidskriftsartikel (populärvet., debatt m.m.)
46.	Enberg, Rikard (författare) Neutrinos from charm production in the atmosphere 2014 Ingår i: Proceedings of the 6th International Workshop on Very Large Volume Neutrino Telescopes (VLVVT 13). - : AIP Publishing LLC. - 9780735412699 ; , s. 44-49 Konferensbidrag (refereegranskat)abstract Atmospheric neutrinos are produced in interactions of cosmic rays with Earth's atmosphere. At very high energy, the contribution from semi-leptonic decays of charmed hadrons, known as the prompt neutrino flux, dominates over the conventional flux from pion and kaon decays. This is due to the very short lifetime of the charmed hadrons, which therefore do not lose energy before they decay. The calculation of this process is difficult because the Bjorken-$x$ at which the parton distribution functions are evaluated is very small. This is a region where QCD is not well understood, and large logarithms must be resummed. Available parton distribution functions are not known at such small $x$ and extrapolations must be made. Theoretically, the fast rise of the structure functions for small $x$ ultimately leads to parton saturation.This contribution describes the "ERS" calculation of the prompt neutrino flux, which includes parton saturation effects in the QCD production cross section of charm quarks. The ERS flux calculation is used by e.g. the IceCube collaboration as a standard benchmark background. We are now updating this calculation to take into account the recent LHC data on the charm cross section, as well as recent theoretical developments in QCD. Some of the issues involved in this calculation are described.
47.	Enberg, Rikard, et al. (författare) Perturbative Charm Production and the Prompt Atmospheric Neutrino Flux in light of RHIC and LHC 2020 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Prompt neutrinos due to the decay of charmed mesons produced in the atmosphere from cosmic-ray and atmospheric nuclei interactions may be a significant source of background to ultra-high energy neutrino searches above 10 TeV. We re-evaluate this flux using updated charm production cross-sections based on QCD parameters, the charm quark mass, and the range for the factorization and renormalization scales that provide the best description of this data at fixed target experiments, at RHIC, and at LHC. We find that the prompt neutrino flux is reduced from previous results in the literature by a factor between two and eight, depending on the energy. We discuss the implications of our results for current IceCube data.
48.	Enberg, Rikard, et al. (författare) Prompt neutrino fluxes from atmospheric charm 2008 Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 78:4, s. 043005- Tidskriftsartikel (refereegranskat)abstract We calculate the prompt neutrino flux from atmospheric charm production by cosmic rays, using the dipole picture in a perturbative QCD framework, which incorporates the parton saturation effects present at high energies. We compare our results with the next-to-leading order perturbative QCD result and find that saturation effects are large for neutrino energies above 10^6 GeV, leading to a substantial suppression of the prompt neutrino flux. We comment on the range of prompt neutrino fluxes due to theoretical uncertainties.
49.	Enberg, Rikard, et al. (författare) Prospects for higgsino-singlino dark matter detection at IceCube and PINGU 2015 Tidskriftsartikel (refereegranskat)abstract We study neutralino dark matter (DM) with large singlino fractions in the next-to-minimal supersymmetric Standard Model (NMSSM). We perform a detailed analysis of the parameter space regions of the model that yield such DM while satisfying the constraints from the Higgs boson searches at the Large Electron Proton (LEP) collider and the Large Hadron Collider (LHC) as well as from b-physics experiments. We find that this DM can yield a thermal relic density consistent with the Planck measurement in mass regions where the lightest neutralino of the minimal supersymmetric Standard Model (MSSM) generally cannot. This is particularly true for lighter DM masses, either less than 10 GeV or between 60 -100 GeV, and for heavier DM masses, between 500 - 1000 GeV. We then analyse the prospects for indirect detection of such DM at the IceCube neutrino telescope, assuming the complete 86-string configuration including DeepCore. We also consider the added sensitivity to low-mass DM with the proposed PINGU extension. We find that IceCube is sensitive to some regions of the NMSSM parameter space containing singlino-dominated DM and that a subset of such model points are already ruled out by the IceCube one-year data. IceCube will also be sensitive to some parameter space regions that will not be probed by the upcoming ton-scale direct detection experiments.
50.	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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