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<p>Hi all,</p>
<p>An update from the trenches of the generator writing:</p>
<p>1) G4SBS seems to agree on the definition of F2. Would be nice if
somebody who knows what they are doing (Tim, Wally?) can double
check though. So if there is no other effect, I'm pretty sure we
see ~5 times more than we thought.<br>
</p>
<p>2) G4SBS also agrees with my estimate of the total DIS rate. It's
actually slightly higher, but I think that's because the simulated
e-arm acceptance is slightly bigger. I'll update my analysis with
that. I'm pretty sure it's very close to 2 times what the
proposal has, so I'd hazard a guess and a factor of 2 comes from
the number of molecules to the number of protons. It's also
assuming that we run at 77K -- I think we talked about running at
room temperature, that makes it 4 times worse of course. (2 times
worse than what is in). Can somebody (Carlos?) run g4sbs in DIS
configuration and see the total rate between x 0.05 and 0.2? I
assume a particle is accepted if Harm.SBSGem.Track.P[0]>1 (for
very few it's not track 0).</p>
<p>So I think, if we run room temp, we'll get half the DIS rate we
assumed, but about 2.5 times the TDIS rate (but in a different
distribution, as far as I can tell). I'll make some updated reach
plots, but I don't have background numbers. Does anyone have those
for all bins? <br>
</p>
<p>Best,</p>
<p>Jan<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 8/6/2020 11:43 AM, Jan C. Bernauer
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:cf44dd71-a72e-721e-44f4-a2bdbbb8de99@t-online.de">Hi
Tim, Hi Wally, Hi TDIS,
<br>
<br>
Sorry for the lengthy email.
<br>
<br>
Some updates and questions to my talk:
<a class="moz-txt-link-freetext" href="https://hallaweb.jlab.org/wiki/images/2/2f/TDIS_sim.pdf">https://hallaweb.jlab.org/wiki/images/2/2f/TDIS_sim.pdf</a> where I
found what I believe are internal inconsistencies, and differences
to my own implementation of F_2, f_\pi, and a full MC.
<br>
<br>
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.
<br>
<br>
<br>
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!
<br>
<br>
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.
<br>
<br>
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.
<br>
<br>
Some things which I found in the code which do not match the
experiment:
<br>
<br>
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.
<br>
<br>
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)
<br>
<br>
With these changes, I match exactly (on a log scale :) ) my own
implementation and the plots in the new proposal.
<br>
<br>
3) BUT the ratio was still off. I traced it down to F_2^p. The
relevant lines are here:
<br>
<br>
CALL SETCTQ6(1) ! CTEQ 'MS-bar' SCHEME.
<br>
u_pro = CTQ6PDF (1, REAL(x), SQRT(REAL(Q2)))
<br>
ubar_pro = CTQ6PDF (-1, REAL(x), SQRT(REAL(Q2)))
<br>
d_pro = CTQ6PDF (2, REAL(x), SQRT(REAL(Q2)))
<br>
dbar_pro = CTQ6PDF (-2, REAL(x), SQRT(REAL(Q2)))
<br>
<br>
F2neu = 2.*x * ((4./9.)*(d_pro + dbar_pro)
<br>
& + (1./9.)*(u_pro + ubar_pro))
<br>
<br>
<br>
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.
<br>
<br>
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.
<br>
<br>
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?
<br>
<br>
( 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)
<br>
<br>
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).
<br>
<br>
<br>
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.
<br>
<br>
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)?
<br>
<br>
TLDR: If all my assumptions are correct, we see indeed 5.5 times
more TDIS events (per DIS event) than we thought!
<br>
<br>
Let me know what you think!
<br>
<br>
Best,
<br>
<br>
Jan
<br>
<br>
<br>
Attached: TDIS_orig.f, code I got from Carlos. TDIS.f: Code with
my modifications.
<br>
<br>
<br>
<br>
<br>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
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</blockquote>
<pre class="moz-signature" cols="72">--
Dr. Jan C. Bernauer
Assistant Professor
Department of Physics and Astronomy
Stony Brook University
Stony Brook, NY 11794-3800 </pre>
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