Re: TPC track analysis

[Claude Petitjean <claude.petitjean@psi.ch>]

Dear Tom,

let me repeat here the points which we wanted to make on last
Tuesdays teleconf:

1) the muon stop definition: we think it's absolutely ok
    (and in fact essential) that a strip cathode signal in time
    coinc to the anode muon stop signal has to be requested in
    order to qualify for a valid muon stop. The problem of
    a possible lifetime dependent influence of charges from
    the decay electron we see on the anodes if nearby signals
    could kill further processing of the particular muon stop.

2) electron tracks going parallel to the anode wires: most
    tracks, especially muons, go perpendicular to anode wires,
    i.e. the ionisation charges of 4 mm length are collected
    by individual anodes. However, of parallel electron tracks
    the charge of up to 120 mm length can arrive simultaneously
    on the anode (average length 60 mm depending on the muon
    stop location). Therefore the height of such mip signals
    can be increased up to 30-fold.

3) threshold length of seeing mips (minimum ionizing particles):
    from our tests in 2003 with 5.5 MeV muons (to simulate
    Alvarez muons) we know that at a cathode voltage 5.0 kV
    they just show barely up in the tpc, i.e. their charge
    over 4 mm is just on the E_low threshold. Alvarez muons
    produce an ionization density which is 6.3 times the one
    of mips (in Carbon: 11 MeV/g/cm3 vs. 1.75 MeV/g/cm3).
    Therefore, mip charges to be on our E_low threshold
    need to be collected over >= 6.3 * 4 mm = 25 mm.

4) from this our conclusion is, that electrons sufficiently
    parallel to anode wires MUST show up in the tpc with a
    good probability as E_low signals. Since typically only
    one anode (+ possibly the neighbour one) is involved
    they will typically produce only one or two neighboring
    pixels which are located in the event display on the
    right side of the muon stop. The distance is defined by
    the mu-e decay time (5mm/usec * t_mu_e), so they are
    easy to locate.

5) our suggestion for the analysis group is to pick out
    parallel-to-anode events by using the theta and phi
    definitions from the epc chambers and check whether
    the probability of appearance of such e-tracks is
    independent of the mu-e decay time, or whether muon
    stop definitions might be influenced by nearby tracks.

    Of course the e-tracks can only be seen on the anodes,
    but from the cathode signal of the muon stop one can
    even calculate the length of the e-track in the tpc
    and therefore find the threshold length of visibility
    for mips.

That's all we wanted to say. We wish you good luck for
finding them!

With best regards

Malte and Claude



Tom Banks wrote:
> Dear Peter et al.,
> 
> after our teleconference discussion yesterday, I eliminated *all*
> remaining TPC track cuts from the Berkeley software--namely, the
> enforcement of coincident strip hits--and modified the code to pass the
> strip information downstream to the Ntuples.  Fred has informed me that
> a new analysis production is now underway on merlin.  However, I just
> remembered that Fred's skimming algorithm made a strip cut!  Thus, even
> though my analysis software is no longer making strip cuts, the skimmed
> data being analyzed has already undergone a strip cut of some sort.  Fred,
> can you remind us of the nature of your skimmer's strip cut?
> 
> One other thing: Claude mentioned during the teleconference that he and
> Malte agreed that it should be possible to see electron effects in the
> vicinity of the muon stop.  Unfortunately, the conversation veered off
> without any further discussion of the subject.  Claude and/or Malte, can
> you describe what we should expect to see from electron effects?  Should
> there be a definite signature, or just some additional EL pixels, or what?
> 
> Regards,
> Tom