16 research outputs found

    Distinguishing models of new physics at the LHC

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    The work presented in this thesis explores ways of distinguishing models of physics beyond the Standard Model at the Large Hadron Collider (LHC). The focus is puton supersymmetric models, in particular the Minimal Supersymmetric Standard Model (MSSM) and the E6-inspired Supersymmetric Standard Model (E6SSM), which are wellknown and well motivated models.The muon decay channel of the pseudoscalar and heavy Higgs bosons in the MSSM is studied. It is shown that these decays to muons, in some scenarios, make it possible to measure the widths of these Higgs bosons at the LHC. This is the only known way of measuring this width at the LHC. The decays to muons also allow for the mass to be measured accurately which together with the width measurement offers a uniqueopportunity to pin down the value of the model parameter tan Beta, which could be used to distinguish different scenarios within the MSSM and potentially in its extensions.Gluino cascade decays are investigated as a tool to distinguish the MSSM from more complex models, with the E6SSM as an example. It is shown that the longer cascadedecays of the E6SSM gluinos provide less missing transverse momentum and higher lepton multiplicity, implying the higher importance of multi-lepton searches at the LHC in models with a richer low-energy particle content. The three-lepton channel is shown to be a good discriminator between the models. In the case of a gluino discovery one would typically expect a signal in this channel if it is an E6SSM gluino but not if it is an MSSM gluino.Furthermore, the implications of limits from dark matter and Z' searches on the Higgs sector and other collider phenomenology are discussed. These implications are important to constrain and differentiate models. In addition, the contribution to fine-tuning from the Z' mass is discussed as an important measure of how attractive a model is, which should be considered by model builder

    Exploring neutralino dark matter resonance annihilation via bA,bH -> b mu^+ mu^- at the LHC

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    One of the main channels which allows for a large rate of neutralino dark matter annihilation in the early Universe is via the pseudoscalar Higgs A-resonance. In this case, the measured dark matter abundance can be obtained in the minimal supergravity (mSUGRA) model when tan(beta)\sim 50 and 2m_{\tz_1}\sim m_A. We investigate the reaction pp\to b\phi\to b\mu^+\mu^- +X (where \phi =A or H) at the CERN LHC where requiring the tag of a single b-jet allows for amplification of the signal-to-background ratio. The rare but observable Higgs decay to muon pairs allows for a precise measurement of the Higgs boson mass and decay width. We evaluate signal and background using CalcHEP, with muon energy smearing according to the CMS detector. We find that the Higgs width (\Gamma_A) can typically be determined with the accuracy up to \sim 8% (\sim 17%) for m_A\sim 400 (600) GeV assuming 10^3 fb^{-1} of integrated luminosity. Therefore, the pp\to b\phi\to b\mu^+\mu^- +X process provides a unique possibility for direct \Gamma_A measurement at the LHC. While the Higgs width is correlated with the parameter \tan\beta for a given value of m_A, extracting \tan\beta is complicated by an overlap of the A and H peaks, radiative corrections to the b and \tau Yukawa couplings, and the possibility that SUSY decay modes of the Higgs may be open. In the case where a dilepton mass edge from \tz_2\to\ell^+\ell^-\tz_1 is visible, it should be possible to test the relation that 2m_{\tz_1}\sim m_A.Comment: 19 pages with 25 .eps figure

    E6SSM vs MSSM gluino phenomenology

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    The E6SSM is a promising model based on the group E6, assumed to be broken at the GUT scale, leading to the group SU(3)\times SU(2)\times U(1)\times U(1)' at the TeV scale. It gives a solution to the MSSM {\mu}-problem without introducing massless axions, gauge anomalies or cosmological domain walls. The model contains three families of complete 27s of E6, giving a richer phenomenology than the MSSM. The E6SSM generically predicts gluino cascade decay chains which are about 2 steps longer than the MSSM's due to the presence of several light neutralino states. This implies less missing (and more visible) transverse momentum in collider experiments and kinematical distributions such as M_eff are different. Scans of parameter space and MC analysis suggest that current SUSY search strategies and exclusion limits have to be reconsidered.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 7 figure

    Solving the taxonomic identity of Pseudotomentella tristis s.l. (Thelephorales, Basidiomycota) – a multi-gene phylogeny and taxonomic review, integrating ecological and geographical data

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    P. tristis is an ectomycorrhizal, corticioid fungus whose name is frequently assigned to collections of basidiomata as well as root tip and soil samples from a wide range of habitats and hosts across the northern hemisphere. Despite this, its identity is unclear; eight heterotypic taxa have in major reviews of the species been considered synonymous with or morphologically similar to P. tristis, but no sequence data from type specimens have been available. With the aim to clarify the taxonomy, systematics, morphology, ecology and geographical distribution of P. tristis and its morphologically similar species, we studied their type specimens as well as 147 basidiomata collections of mostly North European material. We used gene trees generated in BEAST 2 and PhyML and species trees estimated in STACEY and ASTRAL to delimit species based on the ITS, LSU, Tef1α and mtSSU regions. We enriched our sampling with environmental ITS sequences from the UNITE database. We found the P. tristis group to contain 13 molecularly and morphologically distinct species. Three of these, P. tristis, P. umbrina and P. atrofusca, are already known to science, while ten species are here described as new: P. sciastra sp. nov., P. tristoides sp. nov., P. umbrinascens sp. nov., P. pinophila sp. nov., P. alnophila sp. nov., P. alobata sp. nov., P. pluriloba sp. nov., P. abundiloba sp. nov., P. rotundispora sp. nov. and P. media sp. nov. We discovered P. rhizopunctata and P. atrofusca to form a sister clade to all other species in P. tristis s.l. These two species, unlike all other species in the P. tristis complex, are dimitic. In this study, we designate epitypes for P. tristis, P. umbrina and Hypochnopsis fuscata and lectotypes for Auricularia phylacteris and Thelephora biennis. We show that the holotype of Hypochnus sitnensis and the lectotype of Hypochnopsis fuscata are conspecific with P. tristis, but in the absence of molecular information we regard Pseudotomentella longisterigmata and Hypochnus rhacodium as doubtful taxa due to their aberrant morphology. We confirm A. phylacteris, Tomentella biennis and Septobasidium arachnoideum as excluded taxa, since their morphology clearly show that they belong to other genera. A key to the species of the P. tristis group is provided. We found P. umbrina to be a common species with a wide, Holarctic distribution, forming ectomycorrhiza with a large number of host species in habitats ranging from tropical forests to the Arctic tundra. The other species in the P. tristis group were found to be less common and have narrower ecological niches

    Taxonomic annotation of public fungal ITS sequences from the built environment - A report from an April 10-11, 2017 workshop (Aberdeen, UK)

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    The UNITE database community gratefully acknowledges support from the Alfred P. Sloan Foundation. HN and CW gratefully acknowledges financial support from Stiftelsen Olle Engkvist Byggmästare, Stiftelsen Lars Hiertas Minne, Kapten Carl Stenholms Donationsfond, and Birgit och Birger Wålhströms Minnesfond. CW gratefully acknowledges a Marie Skłodowska-Curie post doctoral grant from the ERC. Leho Tedersoo is gratefully acknowledged for providing helpful feedback on an earlier draft of this manuscript.Peer reviewedPublisher PD