Examining the Higgs boson potential at lepton and hadron colliders: A comparative analysis

We investigate inclusive Standard Model Higgs boson pair production at lepton and hadron colliders for Higgs boson masses in the range 120 GeV #<=# m_H #<=# 200 GeV. For m_H #<=# 140 GeV we find that hadron colliders have a very limited capability to determine the Higgs boson self-coupling, #lambda#, due to an overwhelming background. We also find that, in this mass range, supersymmetric Higgs boson pairs may be observable at the LHC, but a measurement of the self coupling will not be possible. For m_H > 140 GeV we examine Z H H and H H #nu# anti #nu# production at a future e"+e"- linear collider with center of mass energy in the range of #sq root#(s) = 0.5 - 1 TeV, and find that this is likely to be equally difficult. Combining our results with those of previous literature, which has demonstrated the capability of hadron and lepton machines to determine #lambda# in either the high or the low mass regions, we establish a very strong complementarity of these machines. (orig.)Available from TIB Hannover: RA 2999(03-035) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Next-to-leading order QCD predictions for W+2 jet and Z+2 jet production at the CERN LHC

We present cross sections and differential distributions for QCD radiative corrections to the QCD processes pp #-># W + 2 jets and pp #-># Z + 2 jets at the CERN LHC. Calculations are performed with the Monte Carlo program MCFM. Cross section dependence on the renormalization and factorization scales is greatly reduced, except for the heavy-flavor case of W"#+-#b anti b, which has new features at next-to-leading order at the LHC. We also present cross sections for W"#+-#b anti b and Z + 2 jets in kinematic configurations relevant for Higgs boson searches. (orig.)Available from TIB Hannover: RA 2999(03-036) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

TeV resonances in top physics at the LHC

We consider the possibility of studying novel particles at the TeV scale with enhanced couplings to the top quark via top quark pair production at the LHC and VLHC. In particular we discuss the case of neutral scalar and vector resonances associated with a strongly interacting electroweak symmetry breaking sector. We constrain the couplings of these resonances by imposing appropriate partial wave unitarity conditions and known low energy constraints. We evaluate the new physics signals via WW#->#tt for various models without making approximation for the initial state W bosons, and optimize the acceptance cuts for the signal observation. We conclude that QCD backgrounds overwhelm the signals in both the LHC and a 200 TeV VLHC, making it impossible to study this type of physics in the tt channel at those machines. (orig.)Available from TIB Hannover: RA 2999(03-002) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Determining the Higgs boson self coupling at hadron colliders

Inclusive Standard Model Higgs boson pair production at hadron colliders has the capability to determine the Higgs boson self-coupling, #lambda#. We present a detailed analysis of the gg #-># HH #-># (W"+W"-)(W"+W"-) #-># (jjl"#+-##nu#)(jjl'"#+-##nu#) and gg#-># HH #-># (W"+W"-)(W"+W"-) #-># (jjl"#+-##nu#)(l'"#+-##nu#l"'"'"-"+#nu#) (l, l', l"'"' = e, #mu#) signal channels, and the relevant background processes, for the CERN Large Hadron Collider, and a future Very Large Hadron Collider operating at a center-of-mass energy of 200 TeV. We also derive quantitative sensitivity limits for #lambda#. We find that it should be possible at the LHC with design luminosity to establish that the Standard Model Higgs boson has a non-zero self-coupling and that #lambda#/#lambda#_S_M can be restricted to a range of 0 - 3.8 at 95% confidence level (CL) if its mass is between 150 and 200 GeV. At a 200 TeV collider with an integrated luminosity of 300 fb"-"1, #lambda# can be determined with an accuracy of 8 - 25% at 95% CL in the same mass range. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(02-183) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

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. (orig.)Available from TIB Hannover: RA 2999(03-102) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Pseudo-axions in little Higgs models

Little Higgs models have an enlarged global symmetry which makes the Higgs boson a pseudo-Goldstone boson. This symmetry typically contains spontaneously broken U(1) subgroups which provide light electroweak-singlet pseudoscalars. Unless such particles are absorbed as the longitudinal component of Z' states, they appear as pseudoscalars in the physical spectrum at the electroweak scale. We outline their significant impact on Little Higgs phenomenology and analyze a few possible signatures at the LHC and other future colliders in detail. In particular, their presence significantly affects the physics of the new heavy quark states predicted in Little Higgs models, and inclusive production at LHC may yield impressive diphoton resonances. (orig.)Available from TIB Hannover: RA 2999(04-137) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Probing the Higgs self-coupling at hadron colliders using rare decays

We investigate Higgs boson pair production at hadron colliders for Higgs boson masses m_H #<=#140 GeV and rare decay of one of the two Higgs bosons. While in the Standard Model the number of events is quite low at the LHC, a first, albeit not very precise, measurement of the Higgs self-coupling is possible in the gg#->#HH#-># b anti b#gamma##gamma# channel. A luminosity-upgraded LHC could improve this measurement considerably. A 200 TeV VLHC could make a measurement of the Higgs self-coupling competitive with a next-generation linear collider. In the MSSM we find a significant region with observable Higgs pair production in the small tan #beta# regime, where resonant production of two light Higgs bosons might be the only hint at the LHC of an MSSM Higgs sector. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-103) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Extracting Higgs boson couplings from LHC data

We show how LHC Higgs boson production and decay data can be used to extract gauge and fermion couplings of Higgs bosons. We show that very mild theoretical assumptions, which are valid in general multi-Higgs doublet models, are sufficient to allow the extraction of absolute values for the couplings rather than just ratios of the couplings. For Higgs masses below 200 GeV we find accuracies of 10-40% for the Higgs boson couplings and total width after several years of LHC running. Slightly stronger assumptions on the Higgs gauge couplings even lead to a determination of couplings to fermions at the level of 10-20%. We also study the sensitivity to deviations from SM predictions in several supersymmetric benchmark scenarios as a subset of the analysis. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(04-089) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman