Kosuke Odagiri

HERWIG 6 : 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 initialand 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.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.

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.

Exploring small extra dimensions at the Large Hadron Collider

Many models that include small extra space dimensions predict graviton states which are well separated in mass, and which can be detected as resonances in collider experiments. It has been shown that the ATLAS detector at the Large Hadron Collider can identify such narrow states up to a mass of 2080 GeV in the decay mode G→e+e−, using a conservative model. This work extends the study of the e+e− channel over the full accessible parameter space, and shows that the reach could extend as high as 3.5 TeV. It then discusses ways in which the expected universal coupling of the resonance can be confirmed using other decay modes. In particular, the mode G→γγ is shown to be measurable with good precision, which would provide powerful confirmation of the graviton hypothesis. The decays G→μ+μ−, W+W −, Z0Z0 and jet-jet are measurable over a more limited range of couplings and masses. Using information from mass and cross-section measurements, the underlying parameters can be extracted. In one test model, the size of the extra dimension can be determined to a precision in length of 7 × 10−33 m.

Production of charged Higgs bosons of the minimal supersymmetric standard model in b quark initiated processes at the large hadron collider

We study integrated and differential rates for the production of charged Higgs bosons H{sup {plus_minus}} of the minimal supersymmetric standard model via b-quark-initiated subprocesses in pp collisions at the CERN Large Hadron Collider. In detail, we compute cross sections and distributions of the reactions bU{r_arrow}bDH{sup +}{r_arrow}bD{tau}{sup +}{nu}{sub {tau}}{circle_plus}c.c. and bU{r_arrow}bDH{sup +}{r_arrow}bDt{bar b}{r_arrow}bDb{bar b}jj{circle_plus}c.c., for a H{sup {plus_minus}} scalar in the intermediate (i.e., M{sup {plus_minus}}{lt}m{sub t}+m{sub b}) and heavy (i.e., M{sup {plus_minus}}{gt}m{sub t}+m{sub b}) mass range, respectively (U and D represent generic u- and d-type light quarks). In the former case, charged Higgs boson masses up to about 145 GeV can be covered for both large and small tan{beta}{close_quote}s. In the latter case, charged scalars can be detected for values of M{sub H{sup {plus_minus}}} up to about 500 GeV, especially if tan{beta} is large, and provided that either excellent b-tagging performances can be achieved or the high luminosity option becomes available. {copyright} {ital 1997} {ital The American Physical Society}

Colour connection structure of (supersymmetric) QCD (2→2) processes

The colour connection structure of QCD (2→2) processes is discussed, with emphasis on its application to the supersymmetric 2 parton → 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→2 matrix elements and their colour decompositions is presented.

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.

Single top production at future

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

e p

We consider the production process e−e+→Gγ of invisible gravitons (G) at future linear colliders. We discuss whether the angular distribution of the photon (γ) can be used to measure the spin of the invisible graviton, or of any other invisible objects produced. We propose a method based on the Fourier expansion of the transverse energy squared moment distribution of the photon. We provide justification for this method, and confirm, especially for the case of two extra dimensions, that the method is valid within a realistic setup, which includes the simulation of the Standard Model background, beamstrahlung, bremsstrahlung, calorimeter resolution and calorimeter coverage. When the number of extra dimensions is increased, the angular distribution does not provide sufficient information to extract the spin, but this method still offers a useful parameterization of the single photon cross section using which the nature of the missing object can be studied.

colliders

We show that quadratic divergences in top-quark condensation are cancelled when the tadpoles cancel. This latter cancellation is naturally implemented as the cancellation among the top-quark, Goldstone and Higgs contributions. We also calculate the bosonic correction terms to Gribovs mass formula for the Higgs boson. These reduce the prediction for M_H from 167 GeV to 132 GeV. The tadpole cancellation condition by itself is an independent condition on the mass of the Higgs boson which, in Gribovs U(1)_Y scenario, yields M_H \approx 117 GeV with large theoretical uncertainty. More generally, we are able to obtain all three masses, M_W, m_t and M_H, in 100 MeV to 10 TeV energy range as a function of the cut-off scale and the gauge couplings only.

Measuring the Spin of Invisible Massive Graviton Excitations at Future Linear Colliders

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