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WW scattering in ATLAS.

Our goal is measure WW scattering vs CM energy from threshold up to as high as possible.

We had a meeting on 29 September 2005 and this was the start of a workplan.

Work Plan

ATLAS note

Sarah has pretty much finished this except:

The AtlFast data was lost in a disk crash, but can be regenerated. Simon Head will be asked regenerate it. This should be without pileup, since the pileup is unofficial/undocumented, and not a big effect anyway. We can just make a comment in the text.

Comments from Sarah:

The pileup we used is not a big effect as long as a cell threshold of 1GeV for low luminosity and 2 GeV for high luminosity is applied. Without these it is a big effect.

The smearing will be done on cells, though I don't know what value to use for the constant term, since we want it to be comparable to smearing on jets.

Underlying event model: should we use the same parameters as in the Rome samples? Or our own?

Actually the best thing to do might be to use the CDF tune described by Rick Field in his talks at the HERALHC and TeV4LHC workshops. Basically the Rime parameters were tuned to look like PYTHIA at 14 TeV and the others are tuned to look like data at 1.8 TeV. Ideally we would do both, as this is a study that really should be done by someone on ATLAS at has not yet (for any process) apart from the minimum boas work by Craig, Arthur and Ian.

-- JonButterworth - 16 Oct 2005

We were using:

Rome used:

ACTION Sarah and Simon

Text to be checked and finalised ACTION Jon, Brian and Sarah

Infrastructure

Make accounts at Manchester for code sharing ACTION Brian and Jon

Archive code from note and paper. ACTION Sarah, Jon

We want a shared code repository which allows us to to co-develop in reasonable privacy but also allows the checked out version to build/link against the ATLAS code. Action: Pete

Mailing list now available: atlas-ww@hep.ucl.ac.uk

Theory

We need to check that we are generating W+W-, W+W+. We would also like to generate WZ and ZZ.

We would also like to cross check with the Montreal code.

ACTION Brian and Jeff.

Trigger

(FLT, HLT, offline selection) Document which trigger chains the signal should get through etc here. ACTION Stathes

Selection cuts

Action: Sarah to document what she actually does in the full sim analysis

The code is in ... . It started from the AnalysisExamples package.

electron

The standard preselections available in atlas are here

. For electrons, I currently use:

ET>10GeV,
isolation cut of 5GeV in dR=0.3
isEM() & 0x07FF == 0

muon

To be selected, a muon must be highPt and have

chisquared < 20.0,
Muon Isolation cut of 5GeV.
pT > 5GeV
eta < 2.7

missing ET

The missing ET used is MET_Final, which is calib+muons+cryostat correction.

Hadronic W mass resolution

In full simulation I just use the highest pT jet.

pile up, jet finder dependence.

subjet cuts

cal granularity? How to run it practically - produce an ATHENA algorithm which takes a jet (AOD?) and produces a y cut array. Action: Pete

top mass resolution

pileup and jet finder dependence This works in AtlFast & at hadron level. Not yet working in full simulation.

tag jets

how well are they modelled? how well is the rate known? How can it be checked?

hard pt

how well is it modelled? can it be checked?

minijet veto

is it really useful? how well is it understood? use new underlying event models/tunes.

background generation

what samples do we need? which generators? we need W+jet and ttbar samples with a ptmin of about 250 GeV. However, to get decent luminosity will require a lot of CPU so we should put this in as a standing request to the SM and exotics groups, but not sweat about generating it ourselves just yet - there is a lot of work to do on the signal.