[Tdis] [EXTERNAL] Inconsistencies in the TDIS proposal: Some things I found

Jan C. Bernauer jan.bernauer at stonybrook.edu
Tue Aug 11 16:16:58 EDT 2020 

Thank you Dipangkar, Thank you Bogdan!

Ok, with the higher pressure, we compensate the temperature change. But 
in light of the larger cross sections, we should think about reducing 
the luminosity  -- that would help a lot in the backgrounds, and makes 
everything just easier to handle.

Best,

Jan

On 8/11/2020 4:12 PM, Dipangkar Dutta wrote:
> Yes, current plans are to run at room temperature, at 3.5 atm. pressure
> Cheers
> Dipangkar
>
>
> On Tue, Aug 11, 2020 at 3:03 PM Jan C. Bernauer 
> <jan.bernauer at stonybrook.edu <mailto:jan.bernauer at stonybrook.edu>> wrote:
>
>     Hi all,
>
>     Could somebody quickly confirm that we'll indeed run at room temp,
>     so with roughly 0.7e36 instead of 3e36 /cm^2/s?
>
>     Thanks,
>
>     Jan
>
>
>     On 8/6/2020 11:43 AM, Jan C. Bernauer wrote:
>>     Hi Tim, Hi Wally, Hi TDIS,
>>
>>     Sorry for the lengthy email.
>>
>>     Some updates and questions to my talk:
>>     https://hallaweb.jlab.org/wiki/images/2/2f/TDIS_sim.pdf where I
>>     found what I believe are internal inconsistencies, and
>>     differences to my own implementation of F_2, f_\pi, and a full MC.
>>
>>     Wally, Tim, I also send this to you, because I believe you might
>>     have additional insight to the source of some of these
>>     figures/values.
>>
>>
>>     0) Does anybody have the exact bins used for the projected result
>>     figures? Especially the one as a function of t. That would be
>>     very helpful!
>>
>>     1) I do see about a factor of 2 more inclusive CS than in the
>>     proposal. I think it's likely that this error is on my end, I
>>     have to verify with g4SBS. In any case, the code version I got
>>     from Carlos (Thanks!), authored from Tim and Wally, do not
>>     calculate that as far as I can tell. It's not helping us in any
>>     case, we would just need less current I'd assume.
>>
>>     2) It would be great to figure out in which configuration the
>>     code was for the generation of table 6 and 7. I assume it was
>>     this code I attach here?  Is that the code version after a factor
>>     2 has already been found? I believe so, because I can get the
>>     F_2^{\pi p} plots out that are in the new proposal, which are
>>     higher than the old proposal.
>>
>>     Some things which I found in the code which do not match the
>>     experiment:
>>
>>     Theta_e is ~12, not 35 degrees. That only affects the calculation
>>     of Q^2, which is slightly affecting the proton PDFs. Can't
>>     explain a big difference.
>>
>>     The code was set up for pi^+, I'm looking at pi^0, so I changed
>>     the isospin factor  to 1. I changed some other integration ranges
>>     (ymax=1, xmax=0, km1, km2 ), and also implemented a cosph cut
>>     (proton theta<70)
>>
>>     With these changes, I match exactly (on a log scale :) ) my own
>>     implementation  and the plots in the new proposal.
>>
>>     3) BUT the ratio was still off. I traced it down to F_2^p. The
>>     relevant lines are here:
>>
>>              CALL SETCTQ6(1)  ! CTEQ 'MS-bar' SCHEME.
>>              u_pro = CTQ6PDF (1, REAL(x), SQRT(REAL(Q2)))
>>              ubar_pro = CTQ6PDF (-1, REAL(x), SQRT(REAL(Q2)))
>>              d_pro = CTQ6PDF (2, REAL(x), SQRT(REAL(Q2)))
>>              dbar_pro = CTQ6PDF (-2, REAL(x), SQRT(REAL(Q2)))
>>
>>              F2neu = 2.*x * ((4./9.)*(d_pro + dbar_pro)
>>          &             + (1./9.)*(u_pro + ubar_pro))
>>
>>
>>      a) LHAPDF 6 and this code has a different definition for what
>>     PID=1 and 2 are. That stumped me for a while, but I'm pretty sure
>>     u_pro is indeed the proton u PDF.
>>
>>     b) For the neutron, d_neu=u_pro and vice versa, so the line
>>     actually reads 2 *x * ( 4/9 ( u_neu +ubar_neu) + 2/9 ( d_neu
>>     +dbar_neu)). I changed it back to be correct for the proton.
>>
>>     c) BUT: I do not have the 2 there. Where does that come from? I'm
>>     not super versed in PDFs, but it is my understanding that that
>>     shouldn't be there.  If not, can anybody please explain?
>>
>>     ( d) There is also a small difference in the code here and LHAPDF
>>     for x<0.1.  10% or so. That must be in the underlying PDF or Q^2
>>     evolution)
>>
>>     In any case, without the 2, my code and this code essentially
>>     agree on F_2^p (with Q^2=1, very close to the plots in the
>>     proposal. With Q^2 changing, slightly different from the
>>     proposal, maybe 30% at most, but both codes the same way. Makes
>>     me think that the proposal line comes from a different program,
>>     which might explain the discrepancy with the 2).
>>
>>
>>     4) Going back to table 6. We already know that it was not updated
>>     from the first proposal, so it likely already has a factor of 2
>>     missing in the F/F ratio. With this additional factor 2, we are
>>     getting very close to what my program has, 4 is close enough to 5
>>     that I would believe the rest is acceptance, slightly different
>>     cuts, etc, or the first factor 2 was actually 2.5 or something.
>>
>>     With these changes, both my code as well as the code I got from
>>     Carlos, modified as described above, gives a ratio F/F of 550 for
>>     the first line in the text. This assumes we accept k between 60
>>     and 500 Mev, x between 0.05 and 0.2, at around 12 degrees, with
>>     30 to 70 deg proton angle. This is also the number my MC gets,
>>     and roughly what I would get looking at the plots.  Or is there
>>     some other cut that should be applied? Cut on z (y in the code)?
>>
>>     TLDR: If all my assumptions are correct, we see indeed 5.5 times
>>     more TDIS events (per DIS event) than we thought!
>>
>>     Let me know what you think!
>>
>>     Best,
>>
>>     Jan
>>
>>
>>     Attached: TDIS_orig.f, code I got from Carlos. TDIS.f: Code with
>>     my modifications.
>>
>>
>>
>>
>>
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>
>     -- 
>     Dr. Jan C. Bernauer
>     Assistant Professor
>     Department of Physics and Astronomy
>     Stony Brook University
>     Stony Brook, NY 11794-3800
>
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>
-- 
Dr. Jan C. Bernauer
Assistant Professor
Department of Physics and Astronomy
Stony Brook University
Stony Brook, NY 11794-3800

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