CLAS Calibration and Commissioning (CALCOM) Working Group
Minutes of Meeting, 7 December 1994

Present:  A. Asryan, S. Boiarinov, W. Briscoe, W. Brooks, V. Burkert, 
D. Cords, P. Dragovitsch, K. Dhuga, A. Freyberger, G. Gilfoyle, 
R. Hicks, M .Kossov, S. Matthews, B. Mecking, M. Mestayer, 
B. Niczyporuk, N. Pivnyuk, P. Rubin, E. Smith, L. C. Smith, 
D. Sober, S. Stepanyan, T.-Y. Tung (23)

1. Initial discussion of goals and scopes

V. Burkert proposed that the scope of the task include the following 
phases:
	I.  	Define and review specifications and means for calibration
		of positioning, energy, timing, efficiency,... of the
		individual subsystems.
	II.	Produce a prelimary document for the calibration of each
		subsystem, including specifications, calibration procedures,
		and a listing of responsibilities.
	III.	Plan the commisioning of Hall B and CLAS as an integrated
		system, including positioning of detectors, cosmic ray
		tests, beam-target interactions for calibration,
		use of specific reactions, etc.

In the ensuing discussion, the following suggestions were made for the role
of the Calibration and Commisioning Group:
i)   To be a clearinghouse for calibrations, to assure that 
resources are not wasted on calibrating one subsystem to a precision that
is not utilizable because of the limitations of other subsystems.
ii)  To work with the the software group in helping to standardize 
certain "pushbutton" calibration procedures that will have to
be repeated frequently.
iii) To help integrate calibration procedures and results into the 
CLAS database.
iv)  To concentrate on identifying those calibration tasks that will
require dedicated hardware, beam time, etc., as opposed to those that 
will automatically result from the reconstruction of preliminary data.
v)   To try to evaluate how much beam time and/or beam-off time
will be needed for each calibration task, and propose redesign of the 
procedure if these times are excessive.
vi)  To plan a specific program for the commisioning period (2 to 6 months),
including analysis as well as data taking.

2.  Requirements for toroid magnetic field measurements

B. Mecking presented calculations of the effect of toroid coil 
misalignments on the CLAS resolution.  He finds that the coil position must
be known to about +-0.5 mm if the worst-case resolution (at 20 deg) 
is not to be degraded.  

B. Nizyporuk presented calculations of the effects of shifts of the
drift chambers with respect to the magnetic field.  He found that a 
2 mm radial shift can introduce momentum shifts of order 0.2%.


3.  Using the tagger for incident energy measurement

D. Sober presented beam transport calculations for the full-energy electron
beam through the tagging magnet.  The dispersion is of order 4 cm/% to the
exit flange of the vacuum chamber and 6 cm/% to the entry to the beam dump
at floor level.  Measurement of beam position to 1 mm would give E0 to 
~0.02% except for the other absolute positioning uncertainties of the
incident beam and the tagger magnet.  With the estimates of the surveying
group that the magnet can be located to better than 1 mm, a measurement
of E0 to better than 0.1% absolute should be attainable.


4.  Formation of subgroups and identification of responsibilities

It was agreed that preliminary writeups for the individual subsystems 
would be submitted by the respective working groups before the next 
CALCOM group meeting, which will be held during the next CLAS 
Collaboration meeting in February.  At that meeting, the main item
on the agenda will be defining the position of the drift chambers.

A subcommittee to consider drift chamber alignment problems was set
up, including M. Mestayer, W. Brooks, V. Burkert, B. Niczyporuk, 
N. Pivnyuk, and at least one representative of CMU/Pitt (R. Magahiz?).

The contact persons for the calibration documents of some of the
subsystems are:
Drift chambers			M. Mestayer et al.
Torus magnetic field 		(William & Mary group)
Mini-torus field		V. Burkert
Tagger - photon energy		D. Sober
Beam energy			D. Sober
Beam current monitors		A. Freyberger, (MIT group)
Beam position monitors		A. Freyberger
Start counters			Rice group
Time-of-flight system		E. Smith
Cherenkov counters		(RPI group)
Forward angle calorimeter	W. Brooks
Large angle calorimeter		(Italian groups)
Target lengths and densities	A. Freyberger, (Saclay group)