[Halld-physics] Solenoid - field and physics

[Mark M. Ito]

Folks,

I went to SPIRES and peeked at the LASS "detector" paper. It give the 
numbers as 22.4 kG (p. 17 as labeled in the text) and 1600 A (p.21).

Find the PDF at 
http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-r-298.pdf . It's a 
SLAC-PUB. The SPIRES entry is at 
http://www.slac.stanford.edu/spires/find/hep/www?r=SLAC-0298 .

  -- Mark

Curtis A. Meyer wrote:
> 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
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>>
>>   
>
>
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