[Halld-physics] Solenoid - field and physics

[Curtis A. Meyer]

Hi Everyone -

     first a couple of clarifications. At one point in the last year, we 
thought that the magnet
would be able to run at 2.5T. I recall that this was the design value, 
but that value had never
been reached. The 2.2 number is what I was sure LASS ran at back at 
SLAC. Certainly,
at Los Alamos for MEGA, that  field was not reached (they also left one 
of the coils out).
So, are we talking 80-90% of the 2.5T number or 80-90% of the 2.2 number 
(where I thought
LASS ran)?

      In support of the 2.2 number, I enclose a copy of the Cassel 
report from 1999. There is
a table at the end which was compiled by Bill Dunwoodie, one of the main 
physicists on
LASS. In that table, Bill clearly lists the LASS field as 2.24T. Thus, 
at some point in the
past the magnet did run with sufficient current to reach 2.24 T. I also 
went back through the material that had been compiled in 2002 or so on 
the magnet. There it is listed that a current
of 1800A was used in LASS. Thus,  I am fairly confused on what is going 
on here.

    Unfortunately, from home I cannot access LASS papers to see what 
field they published,
but I have no reason to doubt Bill's statement that it was 2.24T. I was 
also   under the
impression that the actual design field for the solenoid was 2.5 T, and 
that it indeed never
reached that value.
  
    My question now is what has changed that causes us to think that 
LASS did not run
at 2.24T  If there is some reason to now think that maximum LASS current 
( 1250A ??)
no longer produces the LASS field of 2.24T, then we certainly need to be 
concerned.

   Perhaps a good starting point is to address this.


    As per the PWA, I think that all the work that we have done recently 
has been with the
all-neutral final states. Sadly, we could have done this in 2000 with 
software that parametrized
the detector, but that stopped working a long time ago and can't really 
be resurrected. 
Presumably, we could take our parametrized Monte Carlo and degrade the 
charged particle
momentum resolutions the scaled field. We could then look at the impact 
of this resolution
on reconstructing complete final states and at least quantify how much 
leakage from background
we get with reduced resolutions.

A classic case where we know that there is a hole in the detector are 
the recations like

  gamma p -> n pi+ pi+ pi-

  gamma p -> Delta-0 pi+ pi+ pi-    Delta0 -> n pi0 

some fraction of the latter throw the pi0 into the backwards hole, so 
simply quantifying
the leakage in the two filed cases would tell us. The level of this 
latter leakage would at
least set some limit on how small signals could be.

  I think that this topic should be put on the Monday Physics meeting 
agenda.


    curtis

Eugene Chudakov wrote:
> Hi,
>
> today we ran through a review of the solenoid project, see:
>
> http://www.jlab.org/Hall-D/reviews/Solenoid_Magnet_Internal_Review_Nov09/
>
> They gave a recommendation to show the physics impact of
> running at 80-90% of the planned field (2.2T at 1500A).
>
> The point is that the magnet may not reach 1500A. Before,
> it ran at not more than 1250A. Also, it turns out that the full 
> axial force on coil 2 changes sign at 1350A, which might become a problem.
> This magnet is not expected to quench, but still, if a piece of 
> conductor  moves it may generate a voltage which would look
> like quenching to the control system, which would power 
> the magnet down. Other problems may occur.
>
> Before the review we discussed this question with Curtis. It seems
> that no hard numbers have been collected in one place to be used
> in such occasions.
>
> We must provide this info before the next Lehman review
> (February?). We should assume the detector design finished
> and not adapted to a lower field. 
> Here I list several possible impacts to consider:
>
> a) Higher EM background close to the beam. Result - running
>     at lower luminosity, losses of small angles.
>
> b) Missing mass resolution. Let us take 3-4 reactions and estimate
>     the contamination from reactions with an additional pion (unseen).
>
> c) Particle identification (pi/K/p) from TOF and kinematic fitting.
>     BG for events with charged kaons and no missing particles.
>
> d) The ultimate parameter is the sensitivity to an exotic wave
>     at a certain confidence level, at least for one "gold" reaction.
>
> While a)-c) are simple, c) is complex, but quite important, 
> since similar questions will be asked in future.
>
> Any numbers or suggestions? Who would work on this?
>
> Eugene
> ------------------------------------------------------
> Eugene Chudakov
> http://www.jlab.org/~gen
> phone (757) 269 6959  fax (757) 269 6331
> Thomas Jefferson National Accelerator Facility
> 12000 Jefferson Ave,
> Newport News, VA 23606 USA
> _______________________________________________
> Halld-physics mailing list
> Halld-physics at jlab.org
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>
>   


-- 
Prof. Curtis A. Meyer		Department of Physics
Phone:	(412) 268-2745		Carnegie Mellon University
Fax:	(412) 681-0648		Pittsburgh PA 15213-3890 
cmeyer at ernest.phys.cmu.edu	http://www.curtismeyer.com/      


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