Prospects for Observing an Invisibly Decaying Higgs Boson in the t anti-t H Production at the LHC

The prospects for observing an invisibly decaying Higgs boson in the t anti-t H production at LHC are discussed. An isolated lepton, reconstructed hadronic top-quark decay, two identified b-jets and large missing transverse energy are proposed as the final state signature for event selection. Only the Standard Model backgrounds are taken into account. It is shown that the t anti-t Z, t anti-t W, b anti-b Z and b anti-b W backgrounds can individually be suppressed below the signal expectation. The dominant source of background remains the t anti-t production. The key for observability will be an experimental selection which allows further suppression of the contributions from the t anti-t events with one of the top-quarks decaying into a tau lepton. Depending on the details of the final analysis, an excess of the signal events above the Standard Model background of about 10% to 100% can be achieved in the mass range m_H= 100-200 GeV.Comment: Final version as accepted by EPJ

A Consistent Prescription for Combining Perturbative Calculations and Parton Showers in Case of Associated Z b anti-b Hadroproduction

This paper presents the method of combining parton shower formalism with perturbative calculations (matrix elements) in form of a Monte-Carlo algorithm for the process g g -> Z b anti-b,consistenlty including the heavy quark masses and overlap removal.Comment: accepted by JHEP, revised according to suggestions from JHEP refere

Measurement of trilinear gauge boson couplings at LEP2

The preliminary results of charged trilinear gauge boson WWV, V identical to Z/ gamma coupling values presented in this paper were obtained by the four LEP2 experiments ALEPH, DELPHI, L3 and OPAL by analysing the data collected at LEP energies ranging from square root s=183 GeV to square root s=202 GeV. At these energies, significantly above the kinematic threshold for W/sup +/W/sup -/ boson pair production, each of the four experiments collected data equivalent to more than L~500 pb/sup -1/ of integrated luminosity. The estimation of trilinear gauge boson couplings based on this data provides an independent check of the gauge nature of the standard model. (20 refs)

Synchrotron Radiation-Induced Desorption from a NEG-Coated Vacuum Chamber

When the whole inner surface of a vacuum chamber is coated with a non-evaporable getter film, very low static and dynamic pressures are expected after activation. In an accelerator environment this could result in a longer beam lifetime, in a lower risk of pressure bumps, and in a lower level of bremsstrahlung radiation due to the beam-gas interactions. To substantiate these favourable characteristics a Ti-Zr-V coated stainless steel chamber has been tested on a dedicated beamline at the ESRF. It is shown that a large reduction of the synchrotron radiation-induced desorption occurs after activation

Improved Phase Space Treatment of Massive Multi-Particle Final States

In this paper the revised Kajantie-Byckling approach and improved phase space sampling techniques for the massive multi-particle final states are presented. The application of the developed procedures to the processes representative for LHC physics indicates the possibility of a substantial simplification of multi-particle phase space sampling while retaining a respectable weight variance reduction and unweighing efficiencies in the event generation process.Comment: Minor stilistic changes, submitted to EPJ

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

Photostimulated desorption performance of the future circular hadron collider beam screen

Synchrotron radiation (SR) originated at superconducting bending magnets is known to be at the origin of several beam detrimental effects related to vacuum instabilities. One of the major challenges in the design of the vacuum beam pipes of high-energy hadron colliders is the SR coping strategy. In the case of the future circular hadron collider (FCC-hh), a Cu-coated beam screen (BS) operating in the range of 40–60 K has been designed with the aim of protecting the superconducting magnet cold bores from direct synchrotron irradiation. In order to experimentally study the FCC-hh BS vacuum and cryogenic performance, two sample prototypes were manufactured and installed in the beam screen test-bench experiment (BESTEX) at the Karlsruhe Research Accelerator (KARA) at the Karlsruhe Institute of Technology (KIT). The emitted SR has a critical energy of 6.2 keV, very similar to the 4.6 keV of FCC-hh. Irradiation at both room (RT) and cryogenic (77 K) temperatures showed a significant reduction of the molecular photostimulated desorption yields (η) of the FCC-hh beam screen compared to those of Cu samples. A first approximation of η and its evolution with the photon dose accumulated on the FCC-hh BS prototype at 77 K allows to estimate that a machine conditioning period of ∼1.2 months would be needed to reduce the photostimulated molecular density at the necessary levels to ensure a 100 h beam lifetime at nominal FCC-hh operation