Analytical and numerical tools for vacuum systems

Modern particle accelerators have reached a level of sophistication which require a thorough analysis of all their sub-systems. Among the latter, the vacuum system is often a major contributor to the operating performance of a particle accelerator. The vacuum engineer has nowadays a large choice of computational schemes and tools for the correct analysis, design, and engineering of the vacuum system. This paper is a review of the different type of algorithms and methodologies which have been developed and employed in the field since the birth of vacuum technology. The different level of detail between simple back-of-the-envelope calculations and more complex numerical analysis is discussed by means of comparisons. The domain of applicability of each method is discussed, together with its pros and cons

Les Houches Guidebook to Monte Carlo Generators for Hadron Collider Physics

Recently the collider physics community has seen significant advances in the formalisms and implementations of event generators. This review is a primer of the methods commonly used for the simulation of high energy physics events at particle colliders. We provide brief descriptions, references, and links to the specific computer codes which implement the methods. The aim is to provide an overview of the available tools, allowing the reader to ascertain which tool is best for a particular application, but also making clear the limitations of each tool.Comment: 49 pages Latex. Compiled by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, May 2003. To appear in the proceeding

Probing for Invisible Higgs Decays with Global Fits

We demonstrate by performing a global fit on Higgs signal strength data that large invisible branching ratios Br_{inv} for a Standard Model (SM) Higgs particle are currently consistent with the experimental hints of a scalar resonance at the mass scale m_h ~ 124 GeV. For this mass scale, we find Br_{inv} < 0.64 (95 % CL) from a global fit to individual channel signal strengths supplied by ATLAS, CMS and the Tevatron collaborations. Novel tests that can be used to improve the prospects of experimentally discovering the existence of a Br_{inv} with future data are proposed. These tests are based on the combination of all visible channel Higgs signal strengths, and allow us to examine the required reduction in experimental and theoretical errors in this data that would allow a more significantly bounded invisible branching ratio to be experimentally supported. We examine in some detail how our conclusions and method are affected when a scalar resonance at this mass scale has couplings deviating from the SM ones.Comment: 32pp, 15 figures v2: JHEP version, ref added & comment added after Eq.

Next-to-leading order jet distributions for Higgs boson production via weak-boson fusion

The weak-boson fusion process is expected to provide crucial information on Higgs boson couplings at the Large Hadron Collider at CERN. The achievable statistical accuracy demands comparison with next-to-leading order QCD calculations, which are presented here in the form of a fully flexible parton Monte Carlo program. QCD corrections are determined for jet distributions and are shown to be modest, of order 5 to 10% in most cases, but reaching 30% occasionally. Remaining scale uncertainties range from order 5% or less for distributions to below +-2% for the Higgs boson cross section in typical weak-boson fusion search regions.Comment: 19 pages, 8 figure

Robust LHC Higgs Search in Weak Boson Fusion

We demonstrate that an LHC Higgs search in weak boson fusion production with subsequent decay to weak boson pairs is robust against extensions of the Standard Model or MSSM involving a large number of Higgs doublets. We also show that the transverse mass distribution provides unambiguous discrimination of a continuum Higgs signal from the Standard Model.Comment: 12p, 2 figs., additional comments on backgrounds, version to appear in PR

Observation of the Dynamic Beta Effect at CESR with CLEO

Using the silicon strip detector of the CLEO experiment operating at the Cornell Electron-positron Storage Ring (CESR), we have observed that the horizontal size of the luminous region decreases in the presence of the beam-beam interaction from what is expected without the beam-beam interaction. The dependence on the bunch current agrees with the prediction of the dynamic beta effect. This is the first direct observation of the effect.Comment: 9 page uuencoded postscript file, postscritp file also available through http://w4.lns.cornell.edu/public/CLNS, submitted to Phys. Rev.

Higgs decay to dark matter in low energy SUSY: is it detectable at the LHC ?

Due to the limited statistics so far accumulated in the Higgs boson search at the LHC, the Higgs boson property has not yet been tightly constrained and it is still allowed for the Higgs boson to decay invisibly to dark matter with a sizable branching ratio. In this work, we examine the Higgs decay to neutralino dark matter in low energy SUSY by considering three different models: the minimal supersymmetric standard model (MSSM), the next-to-minimal supersymmetric standard models (NMSSM) and the nearly minimal supersymmetric standard model (nMSSM). Under current experimental constraints at 2-sigma level (including the muon g-2 and the dark matter relic density), we scan over the parameter space of each model. Then in the allowed parameter space we calculate the branching ratio of the SM-like Higgs decay to neutralino dark matter and examine its observability at the LHC by considering three production channels: the weak boson fusion VV->h, the associated production with a Z-boson pp->hZ+X or a pair of top quarks pp->htt_bar+X. We find that in the MSSM such a decay is far below the detectable level; while in both the NMSSM and nMSSM the decay branching ratio can be large enough to be observable at the LHC.Comment: Version in JHE