WW scattering in ATLAS.
Our goal is measure WW scattering vs CM energy from threshold up to as high as possible.
Organisational Stuff
- 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 You can
browse the archived mails (but at the moment only from UCL machines).
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?
Reply from Jon (second attempt, 22 Oct) I think we should use the same as the Rome sample; this is a reasonable set of parameters which was derived from Tevatron data. Other sensible options would be to use whatever is approved for the new production (is this decided yet?), or to use PYTHIA Tune A from Rick Field (as described in the
HERALHC TeV4LHC workshops. The reason I say go with the Rome parameters is that is will facilitate conmparison between ATLFast and full simulation results, and yet we don't have to wait for the new DC3 parameters. If the new DC3 parameters are already known, I would suggest using them, for the same reason.
We were using: ?
Rome used:
the parameters given on this page
ACTION Sarah and Simon
- Text to be checked and finalised ACTION Jon, Brian and Sarah
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.
detector simulation
how much with
AtlFast, how much needs full simulation?
Signal Generation
Sarah and Stathes can both generate signal with the modified pythia routine.
Continuum is the best default but we can look at other scenrios too.
PYTHIA Signal Production:
- Stathis has produced 60K events of the 1 TeV Scalar and Continuum Signal channels.
- The evens were generated using PYTHIA and the modified FORTRAN routine.
- There are 15 files of 4K events each in pool format. There can be in simple ntuples. If someone needs it let Stathis know.
- The files are located at UCL under: /unix/atlas1/sstef/wwScattering/Gene/ We must decide a common place to store them together with the Manchester samples.
- In the same directory you can find the jobOptions file (sampleJobOptions_pythia.py) for generating these events.
We'd also like some high PT hadronic Ws Foundation samples
Action: Sarah to ask SM and Exo convenors
Stathis is looking at it. Will report on that as soon as there is an action.
Maybe we should we aim for someone to give a talk at next UK SM meeting (November 30).
Useful Links
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JonButterworth - 29 Sep 2005
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SarahAllwood - 13 Oct 2005
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StathisStefanidis - 18 Oct 2005