A first look at H -> A first look at H ->

Catherine WrightUniversity of Glasgow

Glasgow Atlas Meeting19/01/06

H -> H ->

The decay mechanism for H ->.

• Ideal decay channel for low mass discovery.

100 < mH < 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 MechanismProduction MechanismSelection of production mechanism leads to Selection of production mechanism leads to different triggers and event selection different triggers and event selection requirements for H -> requirements for H -> ..

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

Combined AnalysisCombined 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. MC@NLO used to generate g-g fusion events.

Events then face pre-selection cuts!

Combined Analysis cont’dCombined Analysis cont’dCurrently:

• Fixed jet rejection applied.

• Results show not only VBF important but gg-fusion also significant.

What are the

effects of this

analysis on the

significance of the H ->

channel?

The SignificanceThe Significance

This new combined

analysis has lead to an

improvement in the

significance for the

channel.

The ComparatorThe 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 (??)

• 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.

ConclusionsConclusions

• 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!!