[Halld-physics] Solenoid - field and physics

[Curtis A. Meyer]

Thanks Mark -

  that is the paper I was trying to find last night --  curtis
Mark M. Ito wrote:
> 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
>>> _______________________________________________
>>> Halld-physics mailing list
>>> Halld-physics at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/halld-physics
>>>
>>>   
>>
>>
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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/