Calorimeter R&D for the SuperNEMO Double Beta Decay Experiment

SuperNEMO is a next-generation double beta decay experiment based on the successful tracking plus calorimetry design approach of the NEMO3 experiment currently running in the Laboratoire Souterrain de Modane (LSM). SuperNEMO can study a range of isotopes, the baseline isotopes are 82Se and possibly 150Nd. The total isotope mass will be 100-200 kg. A sensitivity to neutrinoless double beta decay half-life greater than 10e26 years can be reached which gives access to Majorana neutrino masses of 50-100 meV. One of the main challenges of the SuperNEMO R&D is the development of the calorimeter with an unprecedented energy resolution of 4% FWHM at 3 MeV (Qbb value of 82Se).Comment: Presented at 13th International Conference on Calorimetry in High Energy Physics (CALOR08), Pavia, Italy, 26-30 May 200

Prospects for Higgs properties determination at the LHC

The strategies recently developed to study Higgs boson properties at the LHC are reviewed. It is shown how to obtain model-independent determinations of couplings to fermions and gauge bosons by exploiting different production and decay channels. We consider in some detail the case of Weak Boson Fusion Higgs production with H --> b \bar b as well as the prospects for the determination of the Higgs self-coupling at the SLHC.Comment: LaTeX (using npb style), 5 pages, 1 .eps figure. Talk presented at RADCOR and Loops and Legs 2002, 8-13 September 2002, Kloster Banz, Germany. Added one referenc

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.Comment: 12p, 2 figs., additional comments on backgrounds, version to appear in PR

Top Pair Production Beyond Double-Pole Approximation: pp, pp~ --> 6 Fermions and 0, 1 or 2 Additional Partons

Hadron collider cross sections for tt~ production and di-lepton, single-lepton and all-jet decays with up to 2 additional jets are calculated using complete LO matrix elements with 6-, 7- and 8-particle final states. The fixed-width, complex-mass and overall-factor schemes (FWS, CMS & OFS) are employed and the quality of narrow-width and double-pole approximations (NWA & DPA) is investigated for inclusive production and suppressed backgrounds to new particle searches. NWA and DPA cross sections differ by 1% or less. The inclusion of sub- and non-resonant amplitudes effects a cross section increase of 5-8% at pp supercolliders, but only minor changes at the Tevatron. On-shell tt~/Wtb backgrounds for the H --> WW decay in weak boson fusion, the hadronic \tau decay of a heavy H^\pm and the \phi --> hh --> \tau\tau bb~ radion decay at the LHC are updated, with corrections ranging from 3% to 30%. FWS and CMS cross sections are uniformly consistent, but OFS cross sections are up to 6% smaller for some backgrounds.Comment: 20 pages, 6 tables, 1 figur

Heavy Higgs signal-background interference in gg → VV in the Standard Model plus real singlet

For the Standard Model extended with a real scalar singlet field, the modification of the heavy Higgs signal due to interference with the continuum background and the off-shell light Higgs contribution is studied for gg --> ZZ, WW --> 4 lepton processes at the Large Hadron Collider. Interference effects can range from O(10%) to O(1) effects for integrated cross sections. Despite a strong cancellation between the heavy Higgs-continuum and the heavy Higgs-light Higgs interference, the full interference is clearly non-negligible and modifies the heavy Higgs line shape. A |M_VV - M_h2| < Gamma_h2 cut mitigates interference effects to O(10%) or less. A public program that allows to simulate the full interference is presented.Comment: 22 pages, 15 figures, 9 tables; added results and references, improved discussion, corrected v2 results (heavy top approximation was inadvertently active, results deviate by less than 5%), conclusions unchanged, updated gg2VV code, version to appear in EPJ

A threshold-improved narrow-width approximation for BSM physics

A modified narrow-width approximation that allows for O(Gamma/M)-accurate predictions for resonant particle decay with similar intermediate masses is proposed and applied to MSSM processes to demonstrate its importance for searches for particle physics beyond the Standard Model.Comment: 10 pages, 5 figures, version to appear in JHE

Search for a Standard Model Higgs Boson in CMS via Vector Boson Fusion in the H->WW->l\nu l\nu Channel

We present the potential for discovering the Standard Model Higgs boson produced by the vector-boson fusion mechanism. We considered the decay of Higgs bosons into the W+W- final state, with both W-bosons subsequently decaying leptonically. The main background is ttbar with one or more jets produced. This study is based on a full simulation of the CMS detector, and up-to-date reconstruction codes. The result is that a signal of 5 sigma significance can be obtained with an integrated luminosity of 12-72 1/fb for Higgs boson masses between 130-200 GeV. In addition, the major background can be measured directly to 7% from the data with an integrated luminosity of 30 1/fb. In this study, we also suggested a method to obtain information in Higgs mass using the transverse mass distributions.Comment: 26 pages, 22 figure

Prospects for Higgs search at the LHC

The present status of theoretical calculations for signal and background processes relevant to the Higgs boson search at the LHC is reviewed, with special emphasis on recent developments. The issue of Higgs properties determination at the LHC is addressed.Comment: LaTex2e, 5 pag. Talk presented at the 31st International Conference on High Energy Physics ICHEP02, Amsterdam, The Netherlands, 24-31 July, 2002; one reference adde

Inadequacy of zero-width approximation for a light Higgs boson signal

In the Higgs search at the LHC, a light Higgs boson (115 GeV <~ M_H <~ 130 GeV) is not excluded by experimental data. In this mass range, the width of the Standard Model Higgs boson is more than four orders of magnitude smaller than its mass. The zero-width approximation is hence expected to be an excellent approximation. We show that this is not always the case. The inclusion of off-shell contributions is essential to obtain an accurate Higgs signal normalisation at the 1% precision level. For gg (-> H) -> VV, V= W,Z, O(10%) corrections occur due to an enhanced Higgs signal in the region M_VV > 2 M_V, where also sizable Higgs-continuum interference occurs. We discuss how experimental selection cuts can be used to exclude this region in search channels where the Higgs invariant mass cannot be reconstructed. We note that the H -> VV decay modes in weak boson fusion are similarly affected.Comment: 26 pages, 18 figures, 6 tables; added references, expanded introduction, version to appear in JHE

Finite-Width Effects in Top Quark Production at Hadron Colliders

Production cross sections for t\bar{t} and t\bar{t}j events at hadron colliders are calculated, including finite width effects and off resonance contributions for the entire decay chain, t --> bW --> b\ell\nu, for both top quarks. Resulting background rates to Higgs search at the CERN LHC are updated for inclusive H --> WW studies and for H --> \tau\tau and H --> WW decays in weak boson fusion events. Finite width effects are large, increasing t\bar{t}(j) rates by 20% or more, after typical cuts which are employed for top-background rejection.Comment: 32 pages, 11 figures, 7 tables; minor changes, reference added, to be published in Phys. Rev.