A first look at H -> A first look at H -> Catherine Wright University of Glasgow Glasgow Atlas Meeting 19/01/06

H -> H -> The decay mechanism for H ->. Ideal decay channel for low mass discovery. 100 < m H < 150 GeV If discovered via different channel, ideal for accurate mass measurement. Requires excellent calorimetry. Need good photon efficiency, high jet rejection.

H -> H -> There are four main channels via which the higgs is generated. The production mechanism studied can have an effect on our ability to find the higgs via H ->

Production Mechanism Selection of production mechanism leads to different triggers and event selection requirements for H ->.

The Backgrounds The backgrounds for this decay are different depending on the production channel being analysed. Irreducible Background: real continuum from quark bremsstrahlung, born and box mechanism – direct production. W, Z, tt, bb - associated production. Reducible Background: jet/, e/ - for direct production l/jet, /jet, /jet/jet, l/jet/jet - for associated production Need excellent background reduction algorithms!

Initial Analysis The significance of this channel was below 5 in initial studies of only one production channel -> NOT a discovery channel!

Combined Analysis Different MC generators are used to produce various aspects of the signal and background. Researchers at Wisconsin focussing on this channel and on combined production channel analysis! In particular they are looking at H-> + jet(s). e.g. used to generate g-g fusion Events then face pre- selection cuts!

Combined Analysis cont d Currently: Fixed jet rejection applied. Results show not only VBF important but gg-fusion also significant. What are the effects of this analysis on the significan ce of the H -> channel?

The Significance This new combined analysis has lead to an improvement in the significance for the channel.

The Comparator Original Photon plot at low eta ( <1,4) Tuned Photon plot at low eta ( <1,4) Developed by Chris Collins-Tooth Designed to optimise, via 2 analysis, the fast simulation – forcing it towards the full simulation. Provides a set of parameter values that minimises 2 for your data sets. Opposite: Example of comparator run for photons.

Future Analysis (??) Future analysis should include better statistical determination of combined backgrounds, via e.g. cousins- huygens approximation. Plus investigation into systematic errors in this channel required. Further studies of rejection of g/q initiated jets needed. Effects of pile-up on mass reconstruction at low luminosity. Use of Event Views in Analysis – this is the future of data analysis and therefore H-> should move in this direction. Introduction of comparator for generating accurate, fast large backgrounds e.g. continuum.

Conclusions Plan to investigate this channel further as a first year project and as part of a combined low mass Higgs analysis. There is still much to be done with this low significance channel. By using combined analysis methods the significance is raised above the all critical 5 level – one can further extend this idea to include other decay channels! Thank you!!