arXiv subjects

K. Odagiri

Publications and source records attributed to K. Odagiri.

At least 37 records · Page 2Linked to original sources

arXiv2002

HERWIG 6.5: an event generator for Hadron Emission Reactions With Interfering Gluons (including supersymmetric processes)

HERWIG is a general-purpose Monte Carlo event generator, which includes the simulation of hard lepton-lepton, lepton-hadron and hadron-hadron scattering and soft hadron-hadron collisions in one package. It uses the parton-shower approach for initial- and final-state QCD radiation, including colour coherence effects and azimuthal correlations both within and between jets. This article updates the description of HERWIG published in 1992, emphasising the new features incorporated since then. These include, in particular, the matching of first-order matrix elements with parton showers, a more correct treatment of heavy quark decays, and a wide range of new processes, including many predicted by the Minimal Supersymmetric Standard Model, with the option of R-parity violation. At the same time we offer a brief review of the physics underlying HERWIG together with details of the input and control parameters and the output data, to provide a self-contained guide for prospective users of the program. This version of the manual (version 3) is updated to HERWIG version 6.5, which is expected to be the last major release of Fortran HERWIG. Future developments will be implemented in a new C++ event generator, HERWIG++.

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arXiv2002

Implementation of supersymmetric processes in the HERWIG event generator

We describe the implementation of supersymmetric processes in the HERWIG Monte Carlo event generator. We define relevant parameter and mixing conventions and list the hard scattering matrix elements. Our implementation is based on the Minimum Supersymmetric Standard Model, with the option of R-parity violation. The sparticle spectrum is completely general. Both hadron-hadron and lepton-lepton collisions are covered. This article supplements a separate publication in which the general features of HERWIG 6.2 are described, and updates the treatment of supersymmetry to version 6.4.

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arXiv2002

HERWIG 6.4 Release Note

A new release of the Monte Carlo program HERWIG (version 6.4) is now available. The main new features are: spin correlations between the production and decay of heavy fermions, i.e. top quarks, tau leptons and SUSY particles; polarization effects in SUSY production processes in lepton-lepton collisions; an interface to TAUOLA for tau decays; MSSM Higgs processes in lepton-lepton collisions.

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arXiv2001

HERWIG 6.3 Release Note

A new release of the Monte Carlo program HERWIG (version 6.3) is now available. The main new features are new (MRST) built-in parton distribution functions, more SM gauge boson production processes, 2 to 3 MSSM Higgs production processes, an option to handle negative event weights, and an interface to the CIRCE beamstrahlung program.

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arXiv2001

Heavy charged Higgs boson production at next generation $e^\pmγ$ colliders

We assess the potential of future electron-positron linear colliders operating in the $e^\pmγ$ mode in detecting charged Higgs bosons with mass around and larger than the top quark mass, using Compton back-scattered photons from laser light. We compare the pair production mode, $e^-γ\to e^- H^+H^-$, to a variety of channels involving only one charged Higgs scalar in the final state, such as the tree-level processes $e^-γ\to ν_e H^- Φ^0 $ ($Φ^0=h^0,H^0$ and $A^0$) and $e^-γ\to ν_e f\bar f H^-$ ($f=b,τ$ and $ν_τ$) as well as the loop-induced channel $e^-γ\to ν_e H^-$. We show that, when the charged Higgs boson mass is smaller than or comparable to half the collider energy, $\sqrt s_{ee}\gsim 2M_{H^\pm}$, single production cross sections are of the same size as the pair production rate, whereas, for charged Higgs boson masses larger than $\sqrt s_{ee}/2$, all processes are heavily suppressed. In general, production cross sections of charged Higgs bosons via $e^\pmγ$ scatterings are smaller than those induced at an $e^+e^-$ collider and the latter represents a better option to produce and analyse such particles.

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arXiv2000

Single charged Higgs boson production at next generation linear colliders

We study the single production of charged Higgs bosons in e+e- collisions, chiefly in the Minimal Supersymmetric Standard Model. Our analysis complements foregoing studies of the pair production channel especially in regions where the kinematic constraint suppresses pair production. We present cross sections relevant to experiments at the next generation linear colliders and some brief discussions of their phenomenology. Our analysis shows that the single production is a useful alternative channel for studying the phenomenology of charged Higgs bosons, and there are regions of parameter space where it is accessible beyond the kinematic limit for pair production.

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arXiv2000

Searching for Narrow Graviton Resonances with the ATLAS Detector at the Large Hadron Collider

A spectrum of massive graviton states is present in several recent theoretical models that include extra space dimensions. In some such models the graviton states are well separated in mass, and can be detected as resonances in collider experiments. The ability of the ATLAS detector at the Large Hadron Collider to identify such states and measure their properties is considered, in the case that the resonances are narrow compared to the experimental resolution. The discovery limits for the detection of the decay mode G->e+e- are derived. The angular distribution of the lepton pair is used to determine the spin of the intermediate state. In one specific model, the resonance can be detected up to a graviton resonance mass of 2080 GeV, while the angular distribution favours a spin-2 hypothesis over a spin-1 hypothesis at 90% confidence for resonance masses up to 1720 GeV.

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arXiv2000

Summary of the SUSY Working Group of the 1999 Les Houches Workshop

The results obtained by the Working Group on Supersymmetry at the 1999 Les Houches Workshop on Collider Physics are summarized. Separate chapters treat "general" supersymmetry, R-parity violation, gauge mediated supersymmetry breaking, and anomaly mediated supersymmetry breaking.

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arXiv2000

The QCD and Standard Model Working Group: Summary Report from Les Houches

The Les Houches Workshop on Physics at TeV Colliders took place from June 8-18, 1999. One of the three working groups at Les Houches concentrated on QCD issues, both at the Tevatron Collider and at the LHC. Besides the interest in QCD in its own right, QCD dynamics plays an important role in the production mechanisms for any new physics process that might be observed at either collider, as well as any processes that may form backgrounds to the new physics. This writeup serves both as a pedagogical overview of QCD as well as an update on the current status of the field.

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arXiv2000

The Higgs Working Group: Summary Report

Report of the Higgs working group for the Workshop "Physics at TeV Colliders", Les Houches, France 8-18 June 1999. It contains 6 separate sections: 1. Measuring Higgs boson couplings at the LHC. 2. Higgs boson production at hadron colliders at NLO. 3. Signatures of Heavy Charged Higgs Bosons at the LHC. 4. Light stop effects and Higgs boson searches at the LHC. 5. Double Higgs production at TeV Colliders in the MSSM. 6. Programs and Tools for Higgs Bosons.

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arXiv1999

HERWIG 6.1 Release Note

A new version of the Monte Carlo program HERWIG (version 6.1) is now available. This note gives brief details of the new features relative to the previous version (5.9). A fully updated manual will follow shortly. The main new features are: supersymmetric processes (both R-parity conserving and R-parity violating) in hadron-hadron collisions; the new process e+e- to 4 jets; matrix element corrections to top decay and Drell-Yan processes; new soft underlying event options; updates to particle data tables; new LaTeX and html printout options.

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arXiv1999

Searching for heavy charged Higgs bosons in the neutrino-tau decay mode at LHC

We discuss the search for the heavy charged Higgs bosons H^\pm, implicitly of the Minimal Supersymmetric Standard Model, in the tau-nu decay mode at the LHC. Compared to the dominant decay mode H^\pm\to bt, the channel suffers from suppression due to the branching ratio and the lack of direct mass reconstruction, but the reduced QCD background makes it a feasible channel especially in the large tan(beta) region. We study the production in `bt fusion' via bg\to tH^-, and the leading irreducible background bg\to tW^-. Our results indicate that for the H^\pm mass of greater than 200 GeV and up to 1 TeV and higher, they can be discovered in this channel for a vast range of the parameter space, down to at least tan(beta)\sim3 and potentially the whole range of tan(beta) down to 1.5 if the signal selection efficiency can be improved fourfold. Our analysis is sensitive to top quark identification at large rapidity, and should be supplemented with a full study including jet showering and detector effects.

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arXiv1999

The phenomenology of top quark polarisation in the decay of heavy charged Higgs bosons at LHC and beyond

It has recently been shown that through the $τν$ decay mode the heavy charged Higgs bosons $H^\pm$ can be discovered at LHC over a vast region of the parameter space previously thought unaccessible. If the charged Higgs bosons are discovered in this decay mode and the measurements of its mass and $\tanβ$ are made, it allows us to make greater use of the dominant but QCD background contaminated $bt$ decay mode by cuts suppressing phase space for the background. In this paper we study the top quark polarisation in the $bt$ decay mode. When $\tanβ$ is either moderately large ($\tanβ\gtrsim9$) or small ($\tanβ\lesssim4), the correlation effects can be used as a signal of $H^\pm$ production. We outline the analysis procedure for various decay signatures. As an example, we demonstrate the application of our procedure to the dominant production process $gb\to tH^-$ at LHC. The effect is clearly observable for $H^\pm$ mass between 200 GeV and 500 GeV in both leptonic and hadronic channels, but at 500 GeV the boost on the top quark starts to prevent the reconstruction of invariant masses, and hence the observation of the correlation effect, in the hadronic decay channel.

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arXiv1999

Colour connection structure of (supersymmetric) QCD ($2\to2$) processes

The colour connection structure of QCD ($2\to2$) processes is discussed, with emphasis on its application to the supersymmetric 2 parton $\to$ 2 sparton processes, which are currently being implemented in the HERWIG Monte Carlo event generator. The procedure described by Marchesini and Webber is found to be inadequate, and a new method is proposed. However, this alteration is unlikely to significantly affect the theoretical predictions for soft gluon radiation. A complete list of supersymmetric QCD $2\to2$ matrix elements and their colour decompositions is presented.

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arXiv1998

The phenomenology of $W^\pm H^\mp$ production at the Large Hadron Collider

Barrientos Bendezu' and Kniehl [hep-ph/9807480] recently suggested that $W^\pm H^\mp$ associated production may be a useful channel in the search for the elusive heavy charged Higgs bosons of the 2 Higgs Doublet Model at the Large Hadron Collider. We investigate the phenomenology of this mechanism in the Minimal Supersymmetric Standard Model, with special attention paid to the most likely heavy Higgs decay, $H^\mp\to tb\to b\bar b W^\mp$, and to the irreducible background from top pair production. We find that the semi-leptonic signature `$b\bar b W^+W^-\to b\bar b jj \ell$ + missing momentum' is dominated by top-antitop events, which overwhelm the charged Higgs signal over the heavy mass range that can be probed at the CERN collider

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arXiv1997

Charged Higgs scalar production in single-top mode (and other) at future $ep$ colliders in the Minimal Supersymmetric Standard Model

We study charged Higgs boson production at future electron-proton colliders in the framework of the Minimal Supersymmetric Standard Model. We focus our attention to the case of single-top production and decay through the channel $t\to bH^\pm$ and of vector-scalar fusion via $W^{\pm*} Φ^*\to H^\pm$ (where $Φ=H,h$ and $A$). We consider the signature $H^\pm\to τν_τ$ and compare it to the irreducible background from Standard Model interactions. For $M_{H^\pm}<m_t$, the $H^\pm$ signal is accessible through lepton universality breaking if $M_A<100-120$ GeV at both low and large values of $\tanβ$. Furthermore, although the bulk of the production cross section comes from single-top events, a sizable contribution due to vector-scalar-scalar interactions should be observable at large $\tanβ$, this possibly offering some insights into the structure of the scalar sector of the theory. The possibility of the CERN collider running in the LEPXLHC mode is considered in detail

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arXiv1997

Single-top production at future ep colliders

The production of top quarks in single mode at future ep colliders is studied, the attention being mainly focused to the case of the proposed LEPXLHC collider. We are motivated to reanalyse such a process following the discovery of the top quark at Fermilab. Thanks to the measurement of its mass one is now able to establish more accurately the relevance of single top production for itself and for many other processes to which it may act as a background. In addition, the recent improvement of our knowledge of the quark and gluon dynamics inside the proton now allows one to pin down the dependence of single top production on the partonic structure functions. Both the leptonic and hadronic decay channels of the top quark are studied and compared to the yield of the corresponding irreducible background in presence of b-tagging

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arXiv1997

Gluino signals in 4jet events and vertex tagging at LEP1

Heavy flavour tagging provides a broad range of possibilities in testing QCD features at LEP. We present here a study of 4jets events at LEP I where the so-called light gluinos could be directly produced. We show that microvertex techniques offer a unique chance to exploit simple kinematical distributions in order to optimise the signal coming from gluino production with respect to the background of ordinary QCD events. Our results indicate that experimental analyses along the lines suggested here can exclude or reveal the presence of a gluino for masses up to 10 GeV and lifetimes below 10$^{-9}$ sec. We also point out that a large fraction of gluino events could decay in configurations carrying large missing energy, so to escape the usual selection criteria of 4jet samples. In our study, mass effects of quarks and gluinos have been taken into account exactly. Our results are independent from both the jet algorithm and its resolution parameter.}

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