1. Some introduction
Cosmics events can produce energetic jets and missing energy. They need
to be discriminated from collision events with true MET and jets.
Calorimeter-based cuts to separate QCD jets and cosmics have been
developed (Tokyo, Toronto). Documented in ATL-COM-CAL
and plots approved at last AW.

2. My job
Are the cleaning cuts appropriate (i.e. they do not kill the signal) for the signals we are interested in (W, tt, susy) ?
How can they be used from athena-based analysis ?
Is Inner Detector tracking information useful/needed to reject cosmics ?

3. So far I used run 90272, CaloComm stream
Accessed AOD or prescaled ESD (CALOCOMM_DPD) from an Athena job. Used MissETPerformance package to access/compute the information I needed (jet EM fraction for instance)
I accessed all calorimeter based variables and reproduced the results of the note
Tracking info as it is not appopriate: tracks are not splitted (like they would be with collision-like reconstruction). This is the reason the very simple tracking cuts developed by Tokyo were not accepted for the public results. I will need to split the tracks.
Meanwhile I tried to understand if the cosmic background is relevant at all for the signatures we are interested in (which always include an isolated lepton)
How much remains after calo based cleaning cuts? Do these affect collision events as well ?

4. Some tracking plots
Only to give you a feeling of what cosmics are like. Cosmics tracks not splitted, and not overlaid with min bias MC yet.

5. Muons in cosmics
No event (out of about 300 thousands) contains even a loose electron. Some
(fake) photons which may pick up a track from minimum bias, but it seems that
in electron channels cosmics will be far below the QCD background even
before any cleaning cut.
Lots of muons (STACO, pt>20GeV) instead. Those downward going may be triggered.
I need to ask muon trigger people if there is any estimate of the rate with collision
trigger (do we *really* expect 3 Hz ?). Potentially a significant background.

6. Missing Et
Events with 1 muon reported. If triggered, lots of cosmics (more than W inclusive!)
without cleaning. Much reduced by calo-based event cleaning (not obvious wether
negligible however). Note no jet is required here (next slide).
Calo-based event cleaning ok for ttbar (unaffected).

7. Jets
Only event with MET>20 GeV here. After top selection cut of 3 jets of 40 GeV potentially still large cosmics background. Event cleaning helps (but less so when several jets?). Jet cleaning helps but also affects ttbar signal.
My conclusions is that it is not obvious that cosmics background is
negligible in muon channel after calo-based event cleaning, and deserves
further study.