39 research outputs found
Probing the standard model and beyond at high-energy colliders
The thesis covers the following topics: Assuming a partonic structure of the Pomeron we give predictions for diffractive heavy flavour production at the Tevatron and the LHC and diffractive Higgs production at the LHC in leading-order approximation. For the latter the dominant background processes are also considered. We obtain results on single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor. Measurements of the single inclusive jet cross section at the Tevatron by the CDF Collaboration maybe suggest a modified picture of QCD in the large E(_T) range. A parameter fit of a neutral heavy vector boson Z(^1) to the CDF data, in leading order perturbation theory, is performed, and the question of how the corresponding single inclusive jet cross-sections and the dijet angular distributions at the LHC are affected by this additional Z' is discussed. We test a model, motivated by the former R(_b) and R(_c) "crisis", which contains extra vector fermions. We suggest an alternative indirect test of the possible existence of new heavy quark flavours at the LEP2 collider, which turns out to give the clearest signal. We calculate qq cross sections within this framework, including one loop corrections. Hadronic antenna patterns can provide a valuable diagnostic tool for probing the origin of the reported excess of high x, Q(^2) events at HERA. We present quantitative predictions for the distributions of soft particles and jets in standard deep inelastic scattering eq → eq events and in events corresponding to the production of a narrow colour-triplet scalar resonance. We also study the patterns corresponding to Higgs production and decay in high- energy hadron-hadron collisions. In particular, the signal gg → H → bb and background gg → bb processes are shown to have very different radiation patterns, and this may provide a useful additional method for distinguishing Higgs signal events from the QCD background. The process eq → eq + γ exhibits radiation zeros, i.e. configurations of the final-state particles for which the scattering amplitude vanishes. We study these zeros for both e(^+)u and e(^+)d scattering. The latter exhibits a new type of zero which to our knowledge has not previously been identified. The observability of radiation zeros at HERA is discussed. In the framework of this new type of zero we also study the process e(^+)e(^-) → qqγ. We calculate the positions of these zeros for u-quark and d-quark production and assess the feasibifity of identifying the zeros in experiments at high energies. The radiation zeros are shown to occur also for massive quarks, and we discuss how the bbγ final state may offer a particularly clean environment in which to observe them
Costituent Quark Picture out of QCD in two dimensions - on the Light-Cone
Using DLCQ as a nonperturbative method, we test Fock-space truncations in
by studying the mass spectra of hadrons in colour SU(2) and
SU(3) at finite harmonic resolution . We include states
for mesons and up to states for baryons. With this truncation, we
give `predictions' for the masses of the first five states where finite
effects are minimal.Comment: 13 pages, uses elsart.sty 2 Postscript figures, uses epsf.sty
'elsart.sty' and 'elsart12.sty' are available via anonymous-ftp at
ftp://ftp.tex.ac.uk/tex-archive/macros/latex/contrib/supported/elsevie
Topology of Hadronic Flows for Higgs Production at Hadron Colliders
Hadronic radiation provides a tool to distinguish different topologies of
colour flow in hard scattering processes. We study the structure of hadronic
flow corresponding to Higgs production and decay in high-energy hadron-hadron
collisions. In particular, the signal gg -> H -> b anti-b and background gg ->
b anti-b processes are shown to have very different radiation patterns, and
this may provide an useful additional method for distinguishing Higgs signal
events from the QCD background.Comment: 24 pages, 13 figures, uses epsfig.sty. High resolution pictures may
be obtained via email from [email protected]
Diffractive Higgs Production at the LHC
We use diffractive parton distributions obtained from fits to the diffractive
structure function measured at HERA to predict cross sections for single
diffractive Higgs production at the LHC. The dominant background processes are
also considered. Although some 5% - 15% of Higgs events are predicted to be
diffractive in this model, the ratio of signal to background is not
significantly improved.Comment: 14 pages, LaTeX, incl. 6 postscript figures, uses epsf.st
Weak Boson Production Amplitude Zeros; Equalities of the Helicity Amplitudes
We investigate the radiation amplitude zeros exhibited by many Standard Model
amplitudes for triple weak gauge boson production processes. We show that
production amplitudes have especially rich structure in terms of
zeros, these amplitudes have zeros originating from several different sources.
It is also shown that TYPE I current null zone is the special case of the
equality of the specific helicity amplitudes.Comment: 27 pages, 12 figures, 2 table
Higgs boson production via Double Pomeron Exchange at the LHC
We study Higgs boson production via Double Pomeron Exchange allowing for the
presence of Pomeron remnants. We estimate the number of events produced at the
LHC collider, as a function of the Higgs boson mass and its decay channel. The
model which successfully describes the high mass dijet spectrum observed at
Tevatron (run I) is used to predict rates of events with tagged protons for the
acceptance range of the CMS/Totem experiments. Sizeable cross-sections and
encouraging event selection signals are found, demonstrating especially for
smaller Higgs boson masses the importance to study the diffractive channels.
Tagging of the Pomeron remnants can be exploited to achieve a good resolution
on the Higgs boson mass for inclusive diffractive events, by optimizing an
intermediary analysis between higher cross-sections of the fully {\it
inclusive} mode (all Pomeron remnants) and cleaner signals of the {\it
exclusive} mode (without Pomeron remnants).Comment: 6 pages, 4 eps.figure