By Email:

1. Trust MARS above Geant4. Geant4 is a physics model library, and the physics results change significantly depending on the physics model used. MAUS defaults to QGSP; but many other models are available. It is worth browsing the Geant4 documentation or doing some googling or something here.

2. Did you fire protons onto the Titanium? Or did you use whatever is in the MAUS/G4BL model? MAUS/G4BL model IIRC samples a pre-generated momentum distribution for secondary pions based on an ancient Geant4 MC done by Tom Roberts 10 years ago.

Tom ran Geant4; sampled the output protons; looked at the pions that made it to Q1 aperture; plotted the momentum distribution of the resultant pions; did a fit to get a "theoretical" momentum distribution as a sum of Gaussians. Doesn't mean it is wrong, but just be aware.

I can do some digging into whether that is still the situation.

3. You may need to reoptimise the Q123 currents for a lower momentum. Use the magic spreadsheet settings:

http://mice.iit.edu/bl/Documentation/index_doc.html

Try Pion-Muon or Muon spreadsheet...

Hope that helps some,
Chris

On 27/01/16 16:33, Jan Greis wrote:

Hi Chris,

We've been trying to understand why running a pion beam would increase
the number of muons and I had assumed that the reason is that the pion
flux is much higher around 250 MeV than at 400+ and therefore if we set
D1 to ~250MeV we'd have a lot more particles in the beamline. We've
tried to confirm that and I ran G4Beamline (assuming I did it correctly)
to terminate halfway between Q3 and D1. I've attached a plot (pimu.pdf,
x-axis is pz in MeV) and it seems to indicate that there are actually
significantly more pi+ at the higher momenta, and therefore the absolute
particle rate would be a lot lower when both bending magnets are tuned
to ~250 MeV. /Unless most of the pions decay with enough transverse
momentum to leave the beamline and we therefore still end up with more
particles?/

To make sure I'm not crazy, I've also had the particles terminate just
after the target, and the attached plot (pimu-target.pdf) looks a lot
like the GEANT4 plot on page 136 of
http://inspirehep.net/record/776392/files/fermilab-thesis-2007-85.PDF?version=1
though the plots there confused me quite a bit as well, because the
GEANT4 one looks extremely different from the two others.

Do you have some insights that might help make sense of this before the
meeting tomorrow?

Cheers
Jan

Rogers, Chris wrote:

1. Trust MARS above Geant4. Geant4 is a physics model library, and the physics results change significantly depending on the physics model used. MAUS defaults to QGSP; but many other models are available. It is worth browsing the Geant4 documentation or doing some googling or something here.

2. Did you fire protons onto the Titanium? Or did you use whatever is in the MAUS/G4BL model? MAUS/G4BL model IIRC samples a pre-generated momentum distribution for secondary pions based on an ancient Geant4 MC done by Tom Roberts 10 years ago.

Hi Chris,

I ran G4Beamline with standard settings, I'm not quite sure how it generates the pions, I've tried digging into the code a little but don't understand too much of it at present. Are you suggesting that we generate the D1-current/particle distribution data several times for different physics models?

So it seems like what the g4bl configuration would want is the values from the gradient fields in the magic spreadsheet, however, the default values ("q_1":1.066,"q_2":-1.332,"q_3":0.927,"d_1":-1.302,"d_2":-0.396,"d_s":3.837) don't appear to correspond to any of the sheets. I can get similar numbers from the muon sheet if I set P0 to 408 MeV, but then the sign of both bending magnets is wrong and the value of d2 is completely wrong. Do you know what's going on there?

I don't know the details of how the numbers were generated - maybe John knows?

Setting on the "magic table" P(muon)=238MeV/C and P(pion)=408MeV/C (as in MAY09-B1B2-positives-param.in) d_1=1.300 and d_2=0.396 and all the other gradient fields match.
Is just a kind of sign convention for the bending magnets?

This looks great, well done.

Can you add in:

1. Histogram of TOF delta t for each species at TOF1
2. Histogram of p for each species at TOF1
3. How many particles of each species are there in each plot (in a legend maybe)?
4. How many muons within a momentum bite of +/- 10 MeV/c from the peak
5. TOF01 vs MC truth total momentum at, say TOF1 (this gives a hint as to how well we can do with PID using tracker, without bothering with trying to get tracker recon to work).

Can you remind me what are the baseline currents?

ps: I spoke to Paolo last night, but prod can you get some data taking settings for doing a rate normalisation?

by email with Jan:

You suggested producing the same plots at the z of TOF1. I'm guessing
there is no way to run G4BL that far down (?) so I'll have to figure out
how to process the G4BL output in MAUS (I'm hoping this will be
reasonably straightforward).

I believe that Q4-9 are in the G4BL simulation but probably TOF0/1 are not in the right position (they move every so often, as you are probably aware). You might have to read the G4BL input deck and documentation.

How many particles of each species are there in each plot

I'm not
entirely sure what benefit this would bring, given that we don't have
proper normalization at this point?

I want to know how bad the pion impurity is. I can add up histogram bars, but probably it is more reliable if you do it.

The absolute number is not so important, the fraction (muons/pions) is useful. Also I would like to compare the number of muons at different momenta, with knowledge that the pion production model is unreliable. A best guess is useful.

How many muons within a momentum bite of ± 10 MeV/c from the peak

Same issue as above. Also, total p or p_z?

As above. pz is fine (probably not much difference anyway, pt is ~ 10 % of pz, we have a factor 2 error in the pion production model anyway).

TOF01 vs MC truth total momentum at, say TOF1 (this gives a hint as to
how well we can do with PID using tracker, without bothering with trying
to get tracker recon to work).

I'm a little confused about this. I assume you mean the momentum
calculated from the time delay between TOF0 and 1 (for muon mass),
compared with MC truth (you write "total", shouldn't it be p_z, given
that that's what determines DeltaT?). How does this tell us how well the
tracker can give us PID? Did you mean to write "without"?

MC truth total momentum means virtual plane (pz**2+px**2+py**2)**0.5. I agree, pz might be better. Both aren't quite right.

Lastly you asked about the baseline currents. Do you mean for a 408/238
beam? I used
"q_1":1.065,"q_2":-1.330,"q_3":0.926,"d_1":-1.300,"d_2":-0.396, "d_s":3.837

Did you scale Q123 with D1? Did you scale DS?

Cheers,
Chris