Minutes of the PEP-N 4/10/01 "audio" meeting

Attended (the  ? refers to people that probably were there but we did not hear
them, sorry):

SLAC: E.Solodov, M.Placidi, M.Biagini,M.Sullivan,R.Iverson,J.Va'vra,J.Keller
PD : M.Posocco + ?
FE : P. DalPiaz, R.Calabrese, M.Negrini, V.Azzolini + ?
LNF: A.Zallo, P.Patteri, V.Bidoli, P.Levisandri, E.Pasqualucci + ?
UCI: M. Mandelkern +?


The following was discussed:

1. Muke Sullivan proposed an additional permanent magnet dipole, 0.5 m long at
0.5 m from the IP, arranged in slices, which compensate the influence of the
main field on the VLER beam. This compensation magnet would allow to keep the
main field always constant at 0.3 T independently on the VLER energy.
The cost of it  - the position of the additional magnet at 0.5m in
forward direction and blocking +-7.5 deg of solid angle in the forward
direction.
Mike will make some more detailed drowing and put them into WEB. For the moment
we can think to keep two designs of the IR and take the final decision after the
Workshop (taking into account that we already have a dead angle of +-6.2 deg
in the horizontal plane in the present design and the detector field at present
MUST scale with the VLER energy).

2. Jerry Va'vra presented his calculation of the distorsions in the TPC
depending on gas mixture. It was shown, that using "slow" gas mixture as
He+20%CO2+5%CH4 allows to keep distorsion at the level of 1.5 cm for 60cm
drift length, compare to 7-8 cm for "fast" gas mixture as Ar+20%CH4.
The cost is longer drift time (50 microsec compare to 5-6 microsec).
The 1.5 cm distorsion looks already acceptable.

3. Massimo Placidi presented calcUlations of the magnetic field in the dipole
for different pole shapes, as computed by V.Azzolini with Tosca. The flat 1.6 m
diameter poles give the best field in the TPC region, but make vertical opening
angle smaller. The 1.6 m "tapered" poles give +-35 deg vertical opening angle,
but less uniform field (with this field Jerry made his calculations).
The results of calculations with "tapered-carved" poles remained unclear and to be
investigated, probably after the Workshop.
(It would be good anyhow to have a picture of it and the field distribution
plotted on top of the flat poles field)

4. Mark Mandelkern made some comments on the luminosity measurement. The
ammount of material before the forward tracking (0.1-0.2 rad. l?)should be
taken into account for estimation of multiple scattering which is spoiling
angular resolution. Genia Solodov reminded that we needed absolute
knowlege of track angle of Bhabha events - knowlege of absolute position
of forward tracker.

5. Adriano Zallo presented calculations of efficiency and resolutions of
KLOE type of calorimeter for 6 and 10 cm thickness. The bottom line is
that 10 cm is the minimum thickness of the calorimeter, which gives close
to 100% efficiency starting from 60MeV and resolution dE/E about 25%.
The spatial resolution should be around 1.5 cm (KLOE experience) what in
case of PEP-N with 50 cm distance to IP gives 30 mrad angular resolution.
Is it enough for constrained fit to compensate relatively low energy
resolution?

6. Matteo Negrini presented his first NTUPLE with simulation of weighted
multihadronic events. The variables can be found in the WEB page. He is
currently working on adding aerogel counters information into n-tuple.
The suggestion is for all interested people to look to simulated events
and try to understand if we have all important information stored into
NTUPLE.

7. Genia Solodov presented his view of the detector layout with more
compact locations of detector parts. The general statement is that
"smaller detector -> less cost". But of course real life (light guides, PMTs,
cables ) will make the corrections.
The main concern is to put aerogel counters as much close to central
tracking as possible -> less volume of expensive aerogel.
Similar picture was shown by Frascati people.


Also it was a suggestion to put additional tracking not only in front of
PID, but also before the calorimeter (we should think if we need it) and
between EM calorimeter and NbarN detector - this one is certainly useful,
because
a) veto for neutrons
b)help with muon identification.

>From the general discussion I understood that we should present to the
Workshop more or less realistic detector layout without too many detailes,
but showing the capability of the detector for multihadron study.


There was a suggestion to move next detector meeting to Thursday, April
19 at 8:30 SLAC time.


        Respectively submitted,  E.Solodov