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<p>Hi Wally,</p>
<p><br>
</p>
<p>Thank you for looking into this. <br>
</p>
<p><br>
</p>
<p>Your suggestion to write my own implementation is a very good
one, and exactly what I did. This is where I found the
discrepancies to the proposal (except the ones in the proposal
itself). I think there are two questions left for that:</p>
<p>1) Is my formula for F2p correct, or the one in the code I
attached. I.e, is F2 = x * Sum quarkcharge_i^2
quarkdistributionfunction_i(x,Q^2) (what I think) or is there an
additional factor 2 (what the old code says).</p>
<p>2) Are there some other cuts I didn't realize</p>
<p><br>
</p>
<p>I think all other points I raised are simple mistakes in the
original proposal or otherwise understood artifacts. <br>
</p>
<p><br>
</p>
<p> Other than that, your code + my code produce the same results.
Q2 can probably only be answered by the person who originally came
up with the table in the proposal. But if you could write down
what you think the formula for F2p is, it would be a good cross
check that I didn't just misunderstand the textbooks. <br>
</p>
<p><br>
</p>
<p>Best,</p>
<p>Jan<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 8/11/2020 12:30 AM, Wally
Melnitchouk wrote:<br>
</div>
<blockquote type="cite"
cite="mid:BL0PR0901MB3011E57EAA1A81D4584309A0A8450@BL0PR0901MB3011.namprd09.prod.outlook.com">
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Hi Jan,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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Thanks for your emails, and apologies for the delay.</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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The programs you appended look familiar -- I think I wrote the
core of them back in the 1990s -- and Tim developed them some
half dozen years ago (and possibly other people before and
since) when we were working on some related applications.</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
The best suggestion I would give anyone interested in
implementing the meson exchange contributions to the DIS
structure functions would be to write some script yourself from
scratch. The formulas are actually very simple, if you look at
the analytic expressions. The original ancient Fortran could
probably now be written in a few lines of python code and done
much more efficiently, and writing it yourself would give you a
much clearer idea of what is being computed.</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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I am happy to discuss the formulas with you or anyone else if
you have any questions -- maybe more efficiently over
bluejeans/zoom.</div>
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<br>
</div>
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Best regards,</div>
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Wally</div>
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<br>
</div>
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<br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt"
face="Calibri, sans-serif" color="#000000"><b>From:</b> Jan C.
Bernauer <a class="moz-txt-link-rfc2396E" href="mailto:jan.bernauer@stonybrook.edu"><jan.bernauer@stonybrook.edu></a><br>
<b>Sent:</b> Monday, August 10, 2020 2:03 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:tdis@jlab.org">tdis@jlab.org</a> <a class="moz-txt-link-rfc2396E" href="mailto:tdis@jlab.org"><tdis@jlab.org></a>; Hobbs, Timothy
<a class="moz-txt-link-rfc2396E" href="mailto:TJHobbs@mail.smu.edu"><TJHobbs@mail.smu.edu></a>; Wally Melnitchouk
<a class="moz-txt-link-rfc2396E" href="mailto:wmelnitc@jlab.org"><wmelnitc@jlab.org></a><br>
<b>Subject:</b> Re: [Tdis] [EXTERNAL] Inconsistencies in the
TDIS proposal: Some things I found</font>
<div> </div>
</div>
<div>
<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="x_moz-cite-prefix">On 8/6/2020 11:43 AM, Jan C.
Bernauer wrote:<br>
</div>
<blockquote type="cite">Hi Tim, Hi Wally, Hi TDIS, <br>
<br>
Sorry for the lengthy email. <br>
<br>
Some updates and questions to my talk: <a
class="x_moz-txt-link-freetext"
href="https://hallaweb.jlab.org/wiki/images/2/2f/TDIS_sim.pdf"
moz-do-not-send="true">
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>
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</blockquote>
<pre class="x_moz-signature" cols="72">--
Dr. Jan C. Bernauer
Assistant Professor
Department of Physics and Astronomy
Stony Brook University
Stony Brook, NY 11794-3800 </pre>
</div>
</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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