Light Higgs Production at a Photon Collider

We present a preliminary study of the production of a light Higgs boson with a mass between 120 and 160 GeV in photon-photon collisions at a Compton collider. The event generator for the backgrounds to a Higgs signal due to bbbar and ccbar heavy quark pair production in polarized Gamma-Gamma collisions is based on a complete next-to-leading order (NLO) perturbative QCD calculation. For J_z=0 the large double-logarithmic corrections up to four loops are also included. It is shown that the two-photon width of the Higgs boson can be measured with high statistical accuracy of about 2-10% for integrated Gamma-Gamma luminosity in the hard part of the spectrum of 43 fb-1. From this result the total Higgs boson width can be derived in a model independent way.Comment: 12 pages, submitted to International Workshop on High Energy Photon Colliders, June 14 - 17, 2000, DESY Hamburg, German

Sphinx: Monte Carlo Program for Polarised Nucleon-Nucleon Collisions

This program can be used to simulate polarised nucleon - nucleon collisions at high energies. Spins of colliding particles are taken into account. The program allows to calculate cross sections for various processes.Comment: 33pp, LaTe

Two- and three-particle azimuthal correlations of high-pt charged hadrons in Pb-Au collisions at 158A GeV/c

Azimuthal correlations of hadrons with high transverse momenta serve as a measure to study the energy loss and the fragmentation pattern of jets emerging from hard parton-parton interactions in heavy ion collisions. Preliminary results from the CERES experiment on two- and three-particle correlations in central Pb-Au collisions are presented. A strongly non-Gaussian shape on the away-side of the two-particle correlation function is observed, indicating significant interactions of the emerging partons with the medium. Mechanisms like deflection of the initial partons or the evolution of a mach cone in the medium can lead to similar modifications of the jet structure on the away-side. An analysis based on three-particle correlations is presented which helps to shed light on the origin of the observed away-side pattern.Comment: 4 pages, 2 figures, contribution to the Quark Matter conference 200

Precise coupling terms in adiabatic quantum evolution: The generic case

For multi-level time-dependent quantum systems one can construct superadiabatic representations in which the coupling between separated levels is exponentially small in the adiabatic limit. Based on results from [BeTe1] for special Hamiltonians we explicitly determine the asymptotic behavior of the exponentially small coupling term for generic two-state systems with real-symmetric Hamiltonian. The superadiabatic coupling term takes a universal form and depends only on the location and the strength of the complex singularities of the adiabatic coupling function. As shown in [BeTe1], first order perturbation theory in the superadiabatic representation then allows to describe the time-development of exponentially small adiabatic transitions and thus to rigorously confirm Michael Berry's [Ber] predictions on the universal form of adiabatic transition histories.Comment: 30 pages, 1 figur

Colour reconnections in Herwig++

We describe the implementation details of the colour reconnection model in the event generator Herwig++. We study the impact on final-state observables in detail and confirm the model idea from colour preconfinement on the basis of studies within the cluster hadronization model. Moreover, we show that the description of minimum bias and underlying event data at the LHC is improved with this model and present results of a tune to available data.Comment: 19 pages, 21 figures, 2 tables. Matches with published versio

An Introduction to PYTHIA 8.2

The PYTHIA program is a standard tool for the generation of events in high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multiparticle final state. It contains a library of hard processes, models for initial- and final-state parton showers, matching and merging methods between hard processes and parton showers, multiparton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and several interfaces to external programs. PYTHIA 8.2 is the second main release after the complete rewrite from Fortran to C++, and now has reached such a maturity that it offers a complete replacement for most applications, notably for LHC physics studies. The many new features should allow an improved description of data.Comment: 45 page

Ethical deliberations about involuntary treatment: interviews with Swedish psychiatrists

Background: Involuntary treatment is a key issue in healthcare ethics. In this study, ethical issues relating to involuntary psychiatric treatment are investigated through interviews with Swedish psychiatrists. Methods: In-depth interviews were conducted with eight Swedish psychiatrists, focusing on their experiences of and views on compulsory treatment. In relation to this, issues about patient autonomy were also discussed. The interviews were analysed using a descriptive qualitative approach. Results: The answers focus on two main aspects of compulsory treatment. Firstly, deliberations about when and why it was justifiable to make a decision on involuntary treatment in a specific case. Here the cons and pros of ordering compulsory treatment were discussed, with particular emphasis on the consequences of providing treatment vs. refraining from ordering treatment. Secondly, a number of issues relating to background factors affecting decisions for or against involuntary treatment were also discussed. These included issues about the Swedish Mental Care Act, healthcare organisation and the care environment. Conclusions: Involuntary treatment was generally seen as an unwanted exception to standard care. The respondents’ judgments about involuntary treatment were typically in line with Swedish law on the subject. However, it was also argued that the law leaves room for individual judgments when making decisions about involuntary treatment. Much of the reasoning focused on the consequences of ordering involuntary treatment, where risk of harm to the therapeutic alliance was weighed against the assumed good consequences of ensuring that patients received needed treatment. Cases concerning suicidal patients and psychotic patients who did not realise their need for care were typically held as paradigmatic examples of justified involuntary care. However, there was an ambivalence regarding the issue of suicide as it was also argued that risk of suicide in itself might not be sufficient for justified involuntary care. It was moreover argued that organisational factors sometimes led to decisions about compulsory treatment that could have been avoided, given a more patient-oriented healthcare organisation. Electronic supplementary material The online version of this article (doi:10.1186/s12910-015-0029-5) contains supplementary material, which is available to authorized users

Coherent Parton Showers with Local Recoils

We outline a new formalism for dipole-type parton showers which maintain exact energy-momentum conservation at each step of the evolution. Particular emphasis is put on the coherence properties, the level at which recoil effects do enter and the role of transverse momentum generation from initial state radiation. The formulated algorithm is shown to correctly incorporate coherence for soft gluon radiation. Furthermore, it is well suited for easing matching to next-to-leading order calculations.Comment: 24 pages, 3 figure

Matching Tree-Level Matrix Elements with Interleaved Showers

We present an implementation of the so-called CKKW-L merging scheme for combining multi-jet tree-level matrix elements with parton showers. The implementation uses the transverse-momentum-ordered shower with interleaved multiple interactions as implemented in PYTHIA8. We validate our procedure using e+e--annihilation into jets and vector boson production in hadronic collisions, with special attention to details in the algorithm which are formally sub-leading in character, but may have visible effects in some observables. We find substantial merging scale dependencies induced by the enforced rapidity ordering in the default PYTHIA8 shower. If this rapidity ordering is removed the merging scale dependence is almost negligible. We then also find that the shower does a surprisingly good job of describing the hardness of multi-jet events, as long as the hardest couple of jets are given by the matrix elements. The effects of using interleaved multiple interactions as compared to more simplistic ways of adding underlying-event effects in vector boson production are shown to be negligible except in a few sensitive observables. To illustrate the generality of our implementation, we also give some example results from di-boson production and pure QCD jet production in hadronic collisions.Comment: 44 pages, 23 figures, as published in JHEP, including all changes recommended by the refere