Simulation of a Cross Section and Mass Measurement of a SM Higgs Boson in the H->WW->lvlv Channel at the LHC

The potential to discover a Standard-Model-like Higgs boson at the LHC in the mass range from 150-180 GeV, decaying into a pair of W bosons with subsequent leptonic decays, has been established during the last 10 years. Assuming that such a signal will eventually be observed, the analysis described in this paper investigates how accurate the signal cross section can be measured and how the observable lepton pt spectra can be used to constrain the mass of the Higgs boson. Combining the signal cross section with the analysis of the lepton pt spectra and assuming the SM Higgs cross section is known with an accuracy of +-5%, our study indicates that an integrated luminosity of about 10 fb-1 allows to measure the mass of a SM Higgs boson with an accuracy between 2 and 2.5 GeV.Comment: 19 pages, 11 Figure

NNLO QCD predictions for the H -> WW -> l l nu nu signal at the LHC

We present a first computation of the NNLO QCD cross section at the LHC for the production of four leptons from a Higgs boson decaying into W bosons. We study the cross section for a Higgs boson mass Mh = 165 GeV; around this value a Standard Model Higgs boson decays almost exclusively into W-pairs. We apply all nominal experimental cuts on the final state leptons and the associated jet activity and study the magnitude of higher-order effects up to NNLO on all kinematic variables which are constrained by experimental cuts. We find that the magnitude of the higher-order corrections varies significantly with the signal selection cuts. As a main result we give the value of the cross section at NNLO with all selection cuts envisaged for the search for the Higgs boson.Comment: typos corrected, version accepted in JHE

Combining Monte Carlo generators with next-to-next-to-leading order calculations: event reweighting for Higgs boson production at the LHC

We study a phenomenological ansatz for merging next-to-next-to-leading order (NNLO) calculations with Monte Carlo event generators. We reweight them to match bin-integrated NNLO differential distributions. To test this procedure, we study the Higgs boson production cross-section at the LHC, for which a fully differential partonic NNLO calculation is available. We normalize PYTHIA and MC@NLO Monte Carlo events for Higgs production in the gluon fusion channel to reproduce the bin integrated NNLO double differential distribution in the transverse momentum and rapidity of the Higgs boson. These events are used to compute differential distributions for the photons in the pp \to H \to \gamma \gamma decay channel, and are compared to predictions from fixed-order perturbation theory at NNLO. We find agreement between the reweighted generators and the NNLO result in kinematic regions where we expect a good description using fixed-order perturbation theory. Kinematic boundaries where resummation is required are also modeled correctly using this procedure. We then use these events to compute distributions in the pp \to H \to W^+W^- \to l^+l^- \nu\bar{\nu} channel, for which an accurate description is needed for measurements at the LHC. We find that the final state lepton distributions obtained from PYTHIA are not significantly changed by the reweighting procedure.Comment: 18 pages, 14 fig

Suitability of high-pressure xenon as scintillator for gamma ray spectroscopy

In this paper we report the experimental study of high-pressure xenon used as a scintillator, in the context of developing a gamma ray detector. We measure a light yield near 2 photoelectrons per keV for xenon at 40 bar. Together with the light yield, we also measured an energy resolution of ~9% (FWHM) at 662 keV, dominated by the statistical fluctuations in the number of photoelectrons.Comment: 15 pages, 11 figure

Silicon photomultiplier readout of a scintillating noble gas detector for homeland security

Detectors based on scintillation by high pressure 4He are a viable technology for instruments against the illicit trafficking of nuclear material. A design based on the use of solid state photodetectors is presented in this paper and the preliminary qualification discussed

Perturbative QCD effects and the search for a H->WW->l nu l nu signal at the Tevatron

The Tevatron experiments have recently excluded a Standard Model Higgs boson in the mass range 160 - 170 GeV at the 95% confidence level. This result is based on sophisticated analyses designed to maximize the ratio of signal and background cross-sections. In this paper we study the production of a Higgs boson of mass 160 GeV in the gg -> H -> WW -> l nu l nu channel. We choose a set of cuts like those adopted in the experimental analysis and compare kinematical distributions of the final state leptons computed in NNLO QCD to lower-order calculations and to those obtained with the event generators PYTHIA, HERWIG and MC@NLO. We also show that the distribution of the output from an Artificial Neural Network obtained with the different tools does not show significant differences. However, the final acceptance computed with PYTHIA is smaller than those obtained at NNLO and with HERWIG and MC@NLO. We also investigate the impact of the underlying event and hadronization on our results.Comment: Extra discussion and references adde

A First Comparison of the responses of a He4-based fast-neutron detector and a NE-213 liquid-scintillator reference detector

A first comparison has been made between the pulse-shape discrimination characteristics of a novel $^{4}$He-based pressurized scintillation detector and a NE-213 liquid-scintillator reference detector using an Am/Be mixed-field neutron and gamma-ray source and a high-resolution scintillation-pulse digitizer. In particular, the capabilities of the two fast neutron detectors to discriminate between neutrons and gamma-rays were investigated. The NE-213 liquid-scintillator reference cell produced a wide range of scintillation-light yields in response to the gamma-ray field of the source. In stark contrast, due to the size and pressure of the $^{4}$He gas volume, the $^{4}$He-based detector registered a maximum scintillation-light yield of 750~keV$_{ee}$ to the same gamma-ray field. Pulse-shape discrimination for particles with scintillation-light yields of more than 750~keV$_{ee}$ was excellent in the case of the $^{4}$He-based detector. Above 750~keV$_{ee}$ its signal was unambiguously neutron, enabling particle identification based entirely upon the amount of scintillation light produced.Comment: 23 pages, 7 figures, Nuclear Instruments and Methods in Physics Research Section A review addresse

Soft-gluon effects in WW production at hadron colliders

We consider QCD radiative corrections to WW pair production in hadron collisions. We perform a calculation that consistently combines next-to-leading order predictions with soft-gluon resummation valid at small transverse momenta ptWW of the WW pair. We present results for the ptWW distribution at the LHC up to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect of resummation on the charged-lepton distributions. Soft-gluon effects are typically mild, but they can be strongly enhanced when hard cuts are applied. The relevant distributions are generally well described by the MC@NLO event generator.Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW transverse-mass distribution. Results unchange

Massive particle production to NNLO in QCD

We discuss the recent derivation of the one-loop squared virtual QCD corrections to the W boson pair production in the quark-anti-quark-annihilation channel in the limit where all kinematical invariants are large compared to the mass of the W boson. In particular, we elaborate on the combined use of the helicity matrix formalism with the Mellin-Barnes representations technique.Comment: Presented at "Loops and Legs in Quantum Field Theory", Sondershausen, 20-25 April 2008, 5 page