CDF ZZ Event Display: Lepton 1 Ambiguity

[touqra]

I was looking at this event display from CDF on their discovery of ZZ production. Why is lepton 1 having an ambiguity of either an electron or muon ?
http://fcdfwww.fnal.gov/physics/ewk/2007/ZZ/evd/r211311_e233113.html

 

[ahrkron]

I don't know the details of CDF electron identification, but I assume electrons are id'd based on calorimeter depositions, while muons depend on the muon chambers. If so, then the extra "debris" from the ppbar collision could have deposited enough energy in the calorimeter to pass the electron id. It is also possible that they are using this candidate even when one muon did not leave hits on the muon chambers (maybe went through a region without detector elements), in an attempt to increase the number of candidates on their sample.

 

[drpsycho]

Probably they label it e/mu because it is consistent both with the electron hypothesis (since it leaves some energy in the electromagnetic calorimeter, see the purple block) and with the muon hypothesis (since it has hits in the muon chambers).

My 2 cents: it is a muon which by chance is superimposed to a jet(*). There are three quite stiff tracks pointing in the same directions, which could justify the presence of a signal in the hadronic calorimeter (see the blue block over the purple block), and if it is a jet it's probable that you also have some neutral pions; neutral pions don't leave tracks but they decay into photons, and so give signal in the electromagnetic calorimeter.

(*) or maybe a jet from the fragmentation of a b quark, with the B meson decaying muonically. In this case this event would belong to the background and not to the signal.

 

[drpsycho]

ops, I essentially repeated the answer by ahrkron.