We study the production of the four-lepton final state $l^+ l^- l^+ l^-$, predominantly produced by a pair of electroweak Z bosons, ZZ. Using the LoopSim method, we merge NLO QCD results for ZZ and ZZ+jet and obtain approximate NNLO predictions for Z
Z production. The exact gluon-fusion loop-squared contribution to the ZZ process is also included. On top of that, we add to our merged sample the gluon-fusion ZZ+jet contributions from the gluon-gluon channel, which is formally of N^3LO and provides approximate results at NLO for the gluon-fusion mechanism. The predictions are obtained with the VBFNLO package and include the leptonic decays of the Z bosons with all off-shell and spin-correlation effects, as well as virtual photon contributions. We compare our predictions with existing results for the total inclusive cross section at NNLO and find a very good agreement. Then, we present results for differential distributions for two experimental setups, one used in searches for anomalous triple gauge boson couplings, the other in Higgs analyses in the four charged-lepton final state channel. We find that the approximate NNLO corrections are large, reaching up to 20% at high transverse momentum of the Z boson or the leading lepton, and are not covered by the NLO scale uncertainties. Distributions of the four-lepton invariant mass are, however, stable with respect to QCD corrections at this order.
VBFNLO is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), double and triple vector boson (plus jet) production as well as QCD-induced single and double vector boson production plus two jets in hadronic col
lisions at next-to-leading order (NLO) in the strong coupling constant. Furthermore, Higgs boson plus two jet production via gluon fusion at the one-loop level is included. This note briefly describes the main additional features and processes that have been added in the new release -- VBFNLO Version 2.7.0. At NLO QCD several new processes are available. These are $W^pmgamma$ and $HH$ production in VBF, the QCD-induced single and double vector boson plus two jets processes $W^pm jj$, $W^pm Zjj$, $W^pmgamma jj$, same-sign $W^pm W^pm jj$, and the Higgs-strahlung process $W^pm H$ (plus jet) production. Anomalous couplings are now available for all VBF, diboson and triboson (plus jet) processes including the new VBF $W^pmgamma jj$ implementation, as well as in the Higgs-strahlung (plus jet) process. Semi-leptonic decay modes are supported for the following diboson, triboson and VBF processes: $VV$, $VVV$, $VVgamma$ production and $VV$ production via VBF, where $V$ denotes a massive gauge boson, i.e. $W^pm$ or $Z$. Additionally, the VBF-Higgs production process with decay into $WW$ or $ZZ$ supports semi-leptonic decays of the gauge bosons. All these semi-leptonic processes contain the possibility to include anomalous gauge boson couplings.
Vbfnlo is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), double and triple vector boson (plus jet) production in hadronic collisions at next-to-leading order (NLO) in the strong coupling constant, as well
as Higgs boson plus two jet production via gluon fusion at the one-loop level. This note briefly describes the main additional features and processes that have been added in the new release -- Vbfnlo Version 2.6.0. At NLO QCD diboson production (Wgamma, WZ, ZZ, Zgamma and gammagamma), same-sign W pair production via vector boson fusion and the process Wgammagamma j have been implemented (for which one-loop tensor integrals up to six-point functions are included). In addition, gluon induced diboson production can be studied separately at the leading order (one-loop) level. The diboson processes WW, WZ and Wgamma can be run with anomalous gauge boson couplings, and anomalous couplings between a Higgs and a pair of gauge bosons is included in WW, ZZ, Zgamma and gammagamma diboson production. The code has also been extended to include anomalous gauge boson couplings for single vector boson production via VBF, and a spin-2 model has been implemented for diboson pair production via vector boson fusion.
VBFNLO is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), QCD induced single and double vector boson production plus two jets, and double and triple vector boson production (plus jet) in hadronic collision
s at next-to-leading order (NLO) in the strong coupling constant, as well as Higgs boson plus two jet production via gluon fusion at the one-loop level. For the new version -- Version 2.7.0 -- several major enhancements have been included into VBFNLO. The following new production processes have been added: $Wgamma jj$ in VBF, $HHjj$ in VBF, $W$, $Wj$, $WH$, $WHj$, $ppto text{Spin-2}jj$ in VBF (with $text{Spin-2}to WW/ZZtotext{leptons}$) and the QCD induced processes $WZjj$, $Wgamma jj$, $W^pm W^pm jj$ and $Wjj$ production. The implementation of anomalous gauge boson couplings has been extended to all triboson and VBF $VVjj$ processes, with an enlarged set of operators yielding anomalous couplings. Finally, semileptonic decay modes of the vector bosons are now available for many processes, including $VVjj$ in VBF, $VVV$ and $VVgamma$ production.
We compute the complete supersymmetric next-to-leading order corrections to the production of a light Higgs boson in weak boson fusion. The size of the electroweak corrections is of similar order as the next-to-leading order corrections in the Standa
rd Model. The supersymmetric QCD corrections turn out to be significantly smaller than their electroweak counterparts. These higher--order corrections are an important ingredient to a precision analysis of the (supersymmetric) Higgs sector at the LHC, either as a known correction factor or as a contribution to the theory error.
The search for Higgs bosons and extensions of the Standard Model of Elementary Particle Physics are main tasks of the Large Hadron Collider (LHC) at CERN which will start operation mid-2008. In this thesis processes which can be used to detect supers
ymmetric Higgs bosons at the LHC were considered. First a computer program was written which completes the toolbox for automatic calculations of hadronic cross sections. Using this program, the supersymmetric QCD corrections to associated H-W+-production and h0-production via vector-boson fusion and in association with heavy quarks were calculated. The corrections partly give significant contributions to the total cross section. Additionally, the possibility to measure the quartic Higgs self-coupling via triple-Higgs production was investigated and found to be challenging.
If new physics is found at the LHC (and the ILC) the reconstruction of the underlying theory should not be biased by assumptions about high--scale models. For the mapping of many measurements onto high--dimensional parameter spaces we introduce SFitt
er with its new weighted Markov chain technique. SFitter constructs an exclusive likelihood map, determines the best--fitting parameter point and produces a ranked list of the most likely parameter points. Using the example of the TeV--scale supersymmetric Lagrangian we show how a high--dimensional likelihood map will generally include degeneracies and strong correlations. SFitter allows us to study such model--parameter spaces employing Bayesian as well as frequentist constructions. We illustrate in detail how it should be possible to analyze high--dimensional new--physics parameter spaces like the TeV--scale MSSM at the LHC. A combination of LHC and ILC measurements might well be able to completely cover highly complex TeV--scale parameter spaces.
We have conducted a long slit search for low surface brightness Lyman-alpha emitters at redshift 2.67 < z < 3.75. A 92 hour long exposure with VLT/FORS2 down to a 1-sigma surface brightness detection limit of 8x10^-20 erg/cm2/s/sqarcsec yielded a sam
ple of 27 single line emitters with fluxes of a few times 10^-18 erg/s/cm2. We present arguments that most objects are indeed Lyman-alpha. The large comoving number density, the large covering factor, dN/dz ~ 0.2-1, and the often extended Lyman-alpha emission suggest that the emitters be identified with the elusive host population of damped Lyman-alpha systems (DLAS) and high column density Lyman limit systems. A small inferred star formation rate, perhaps supplanted by cooling radiation, appears to energetically dominate the Lyman-alpha emission, and is consistent with the low metallicity, low dust content, and theoretically inferred low masses of DLAS, and with the relative lack of success of earlier searches for their optical counterparts. (abridged)
Once supersymmetry is found at the LHC, the question arises what are the fundamental parameters of the Lagrangian. The answer to this question should thereby not be biased by assumptions on high-scale models. SFitter is a tool designed for this task.
Taking LHC (and possibly ILC) data as input it scans the TeV-scale MSSM parameter space using its new weighted Markov chain technique. Using this scan it determines a list of best-fitting parameter points. Additionally a log-likelihood map is calculated, which can be reduced to lower-dimensional Frequentists profile likelihoods or Bayesian probability maps.
