Re: [BLAST_SHIFTS] Target polarization and density

From: Karen Dow (kdow@rocko.lns.mit.edu)
Date: Sat Feb 12 2005 - 15:40:09 EST


Michael,

I'd agree, scattering off the cell walls would look flatter than what we see; that was the argument the other day that even with the old collimator opening, the beam didn't see the cell walls. But what about a flat distribution, folded with acceptance, and also folded with any kind of z-distribution in the beam density that hits the walls? Hard to believe it would make the usual triangle.

On the other hand, ligit (or ligit2, since ligit is presumed to not be trustworthy) doesn't show a factor of 3 increase in the thickness, from what I understood yesterday. Maybe we're cooking ice off the walls? Although that should show up in ligit.

I'll see what Genya or Ernie has to say about the polarization/recoating question.

Karen

---------- Original Message ----------------------------------
From: Michael Kohl <kohlm@mit.edu>
Date: Sat, 12 Feb 2005 12:22:54 -0500 (EST)

>Hi Karen,
>
>the quoted polarization numbers were for all new polD2 runs together
>(hPz are the numbers in the lines starting with A_ed_V).
>The question of coating or replacing goes to Ernie and Genya.
>
>I don't think that a factor 3 is coming from cell wall (think of the
>perfectly triangular shape of ep events in the onlineGUI!). If there was a
>big cell wall contribution the z-distribution would show a more or less
>constant, box-like socket.
>
>Regards,
>
> Michael
>
>On Sat, 12 Feb 2005, Karen Dow wrote:
>
>>
>> Michael,
>>
>> How do we know we're not looking at (e,e'd)and (e,e'p) off the cell walls? That would give us more cross section, lower polarization.
>>
>> What is hPz for the full set of runs?
>>
>> If the cell is cooked, I don't know if we get polarization back just by recoating it, or if we'd have to replace it. There is actually no other 12 mm cell, so if the pol is killed, we HAVE to go to a 15 mm cell.
>>
>> Karen
>>
>>
>> ---------- Original Message ----------------------------------
>> From: Michael Kohl <kohlm@mit.edu>
>> Date: Sat, 12 Feb 2005 01:21:56 -0500 (EST)
>>
>> >Hi,
>> >
>> >evaluation of the target polarizations from all D2-ABS runs 13475-13479
>> >13481-13488 (2 shifts) gives the following results:
>> >
>> >Q=2.03 kC,
>> >A_ed_V Point Asymmetries vs Q2 Sector L: 0.164121 +- 0.0534603
>> >A_ed_V Point Asymmetries vs Q2 Sector R: 0.210649 +- 0.0373942
>> >
>> >Pzz Fitted from L/R difference 0.061237+-0.121475
>> >
>> >Concluding, Pzz is consistent with zero, hPz is really much smaller than
>> >claimed yesterday.
>> >
>> >About the target density:
>> >Running show_deep_asym_all.C on new runs 13475-13479 13481-13488:
>> >Total charge in all files : 2032.37 C
>> >Rate of events passing d(e,e'p)n cuts : 45.9419 events/C
>> >Rate of events passing QE d(e,e'p)n cuts : 10.535 events/C
>> >
>> >Running show_deep_asym_all.C on October runs 12115-12120:
>> >Total charge in all files : 2750.76 C
>> >Rate of events passing d(e,e'p)n cuts : 10.7443 events/C
>> >Rate of events passing QE d(e,e'p)n cuts : 3.54702 events/C
>> >
>> >Concluding, the target density has increased by a factor 3!
>> >
>> >The fact that Genya gets a lower elastic-ed yield may be due to
>> >miscalibration of the timing for ed event selection, while the d(e,e'p)
>> >analysis does not depend on this.
>> >
>> >So, the FOM is still lower than in 2004, however now it is due to a low
>> >polarization (have we cooked the cell already?) and not because of a low
>> >density. The question is if the polarization can be improved before we
>> >rush and replace the cell again. Maybe running with 70% of the present
>> >flow would help (which still provides the aimed factor of 2 in density)?
>> >I suggest to try to tune the beam with empty target until a lifetime of
>> >>30 min is achieved. Then check how much flow can be used such that the
>> >lifetime would not drop below 20 minutes. Then measure the polarization
>> >again.
>> >
>> >Regards,
>> >
>> > Michael
>> >
>> >
>> >--
>> >
>> >+-------------------------------------+--------------------------+
>> >| Office: | Home: |
>> >|-------------------------------------|--------------------------|
>> >| Dr. Michael Kohl | Michael Kohl |
>> >| Laboratory for Nuclear Science | 5 Ibbetson Street |
>> >| MIT-Bates Linear Accelerator Center | Somerville, MA 02143 |
>> >| Middleton, MA 01949 | U.S.A. |
>> >| U.S.A. | |
>> >| - - - - - - - - - - - - | - - - - - - - - -|
>> >| Email: kohlm@mit.edu | K.Michael.Kohl@gmx.de |
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>> >| Fax: +1-617-253-9599 | Mobile: +1-978-580-4190 |
>> >| http://blast.lns.mit.edu | |
>> >+-------------------------------------+--------------------------+
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>
>--
>
>+-------------------------------------+--------------------------+
>| Office: | Home: |
>|-------------------------------------|--------------------------|
>| Dr. Michael Kohl | Michael Kohl |
>| Laboratory for Nuclear Science | 5 Ibbetson Street |
>| MIT-Bates Linear Accelerator Center | Somerville, MA 02143 |
>| Middleton, MA 01949 | U.S.A. |
>| U.S.A. | |
>| - - - - - - - - - - - - | - - - - - - - - -|
>| Email: kohlm@mit.edu | K.Michael.Kohl@gmx.de |
>| Work: +1-617-253-9207 | Home: +1-617-629-3147 |
>| Fax: +1-617-253-9599 | Mobile: +1-978-580-4190 |
>| http://blast.lns.mit.edu | |
>+-------------------------------------+--------------------------+
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