[Hallcsw] [Shms_users] Hall C 12 GeV software update (mailing list & request for additional info)

[Ole Hansen]

On 8/23/2011 14:53, Brad Sawatzky wrote:
> On Tue, 23 Aug 2011, Eric Christy wrote:
>
>> I think it is well covered now from this discussion that the HRS VDC
>> algorithms should not be expected to work for the Hall C chambers.  I
>> am sorry that I was not able to attend these discussions during the
>> Hall C meeting last week.  I don't know what the BigBite tracking
>> methodology is, but I do know that the HMS code has been optimized
>> over the last decade to
> The "Hall A" tracking algorithm I was discussing was one used with the
> BigBite HDCs, not the HRS VDCs.  That HDC code is an implementation of
> an algorithm developed at HERMES (DellOrso et al., NIM A 287, 436
> (1990)).  It is robust and designed to scale well over a large range of
> chamber conditions.
>
>

The BigBite "TreeSearch" code is a good starting point if

(1) There is no track bending/magnetic field in the tracking region. It
only works with straight tracks.
(2) There are least three wire directions (e.g. x, u, v) in the system,
and _each_ wire direction/projection has at least three planes. So you
need at least 9 wire planes total. The planes can be ordered and
positioned arbitrarily (within reason - you need sufficient z-separation
to get good resolution). The exact wire angles do not matter, they must
only be sufficiently different. Obviously like axes of different planes
must be parallel.

Some examples of what would work:

(x1-u1-v1) --- (x2,u2,v2) --- (v3,x3,u3)

(u1-v1) --- (x1) --- (x2) --- (u2,v2) ---- (u3,v3,x3)

where "---" means, in practice, perhaps ">= 20 cm" (more is better), and
(a-b) means that "a" and "b" wires share a physical chamber within which
the wire planes are pretty close (few cm).

If you have a system like this, all you need to do is to adapt the
Decode routine and put geometry data and parameters into a plaintext
database file. If you have common-stop TDCs, the decoder may even work
more or less out of the box.

We wrote this code specifically to be as generic as possible. There is
very little BigBite-specific code in there.

Ole