Outstanding issues

• 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. This is now stated in the text. I guess though we should apply the threshold at 2 GeV for all the data.

• The smearing will be done on cells (twoers, surely?). What value should we to use for the constant term, since we want it to be comparable to smearing on jets? Reply from Jon: I don't think one can completely correctly reproduce smearing on jets by smearing towers whatever one does. And in fact, smearing cells is a better approximation to reality. If we take the radius-proportional term (by the the way, this proportionality seems to be based on a straight line drawn through two points, see page 272 of the TDR) and apply it to the tower radius, that should get the noise etc ok in that twoer, but it will neglect the noise in other towers with no true energy which may have contributed to the jet. I think the noise suppression threshold saves us - it should remove this as wellas the constant term. And Sarah has also tried increasing the constant term and shown we are insensitive to it. So I think this argument and holds and is the best that can be done at present, until there is an approved cell smearing in ATLFast.

• 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

• • We were using: ?

• • Rome used: the parameters given on this page

• The efficiencies as purities need to be discussed/clarified.

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