detector review notes

[Elton Smith <elton@jlab.org>]

Detector Review Notes by Elton.
------------------------------

Below is a non-systematic set of notes taken during the review for future
reference. I pass them on so that we can consider some of the issues
raised, as appropriate for each subsystem. Others may have recorded other
comments.

---------------------

GlueX overview - Alex
- should emphasize 4pi trigger for a 4pi detector

Detector overview - Curtis
- need to include simulation of background channels in acceptance studies
- study of missing mass when particles are missed down the beam hole
- acceptance when proton is lost due to missidentification?

Photon beam - Richard
- dead space between fibers in micros-scope?

LGD - Alex
- Rate of backgrounds in Pb glass near hole (Richard has shown plots to
address this).
- requirement for time resolution? compatible with rise time of pmts?

Bcal - George
- how much light is lost during light collection?
- fast SiPMs pulses and sampling of FADC?
- modeling needed to guide/optimize design
- HPMTs discarded due to difficulty in adequate compromise between rise
time and amplification. This decision should be revisited.

UPV - Paul
- option for use wavelength shifting fibers embedded in scintillator
- look into MINOS design for calorimeter
- check sensitivity of wavelength shifting scheme, and low light output,
for low energy photons

FADC - Paul
- parameters of FADC options needs to be explored in more detail

CDC - Curtis
- material in end-plate: effect of showers on background downstream,
especially LGD
- vertexing: first measurements of z-position are far from target.
Investigate arrangement of stereo/axial arrangement.
- Bill indicated that the dynamic range for BABAR was for counts between
400 and 15,000 (with some saturation corrected using FADCs). Mike  Kelsy a
resource for correcting saturation of individual FADC samples.
- over/under pressure capability of chambers?
- alignment: use of cosmics? need pixel detectors at low angles to help
calibration of forward drift chambers?

FDC - Dan
- frame material needed to support cathodes needs to evaluated.
- Bill Dunwoodie: LASS used 3 mil mylar, wished they had used 5 mil.
Accuracy achieved was 185 microns after survey corrections for stretching
of the cathode strips (600 microns without corrections). Present plans of
using 2 mils should be studied.
- Large-scale prototype for mechanical studies is very important for
evaluating full design.
- Variations in geometry over the cathode planes was calibrated out by
LASS intercalibrating pulses with different "center" strips.
- Should include the option of injecting charge into the electronics for
calibration of pulse heights.
- dependence of capacitance of cathodes planes on circular geometry of
detectors, i.e. different length strips?
- use of timing of cathode strips only instead of anodes?

PID - Ryan
- smearing of track lengths by 1% is probably too large (fine for
momentum)
- Bernhard: simulate g p -> 4pi p events and check to see how many events
satisfy the g p -> K pi K pi p hypothesis.
- In comparing effectiveness of PID one needs to compare specific
reactions to the total rate for the inelastic cross section (i.e. signal
to background for kaon reactions)

TOF - Alex
- check out reflective material used in our start counter - very high
reflectivity and very thin.

DIRC - Paul
- Acceptance of particles into DIRC is taken to be geometric +/- 12
degrees, but compound angles (of spiraling particles) can yield much
larger angles.
- Are there cost savings by tailoring the geometry of the DIRC to the
circular aperture of the magnet?
- Bill: new developments to replace pmts with pixel detectors.

DAQ - Dave
- time sampling of software filters in L3?

Start Counter - Werner
- Is this counter needed at all?
- if used, thickness of 5 cm should be reduced and minimized
- should one use the real estate of the start counter for tracking?


Elton Smith
Jefferson Lab
elton@jlab.org
(757) 269-7625