10/14/14

1000 Events
1 pi+ per Event
500 MeV pT (so approximately MIP energy)

IST simplified to air.  IBMO + IBAM, and that is it.

IBMO placed in CAVE as ONLY.  /// this reduces number of steps by order of magnitude.
IBAM placed in IBMO as ONLY.

Figure 1 -- LEFT: Location of each G3 tracking step (entrance or exit) plotting Y vs X in cm.  RIGHT:  Radius of each entrance or exit. 



How much energy do we expect to lose in air?

Density = 1.205E-3 g/cm3.
dEdx|min = 1.815 MeV cm2/g * dens = 2.187 keV / cm.

Mean distrance traveled: 6.66 cm.  (Indicates possible demonic posession).

Expected energy lost in crossing these air volumes:  2.187 * 6.66 keV = 14.57 keV.

Figure 2 -- Observed energy lost in tracking through IBAM volumes.  I expect 14.56 keV.  I see 1.368E-5 GeV = 13.7 keV.



CONCLUSION:  We expect approximately 14.6 keV to be lost crossing through the geant volumes representing the IST mother volumes.  We see about 13.7 keV.  I see no issue with Geant energy loss.

Closer inspection of figure 1 shows that the first step is into a cylindrical volume, whereas the IBAM volumes are overlapping set of boxes.  Thus we expect to see a circular, sawtooth pattern on the inside of the region just like we do on the outside.  Running the overlap checker doesn't show an issue *unless* we switch the placement of IBAM to ONLY.  Then we see that the IBAM volumes are extruding the IBMO mother volume.  The reason this doesn't show up as an extrusion is that it is a perfectly legal intersection in G3.  Probably not what was intended.

Figure 3 -- Reduced inner radius of IBMO to 11 cm, to match the outer radius of the PIXL detector.  We now see the expected sawtooth.



Repeating the dEdx exercise...  we see the expected energy loss in the volumes.

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07/30/14

100 Events
50 pi+ per event
400 MeV pion momentum (approx minimum ionizing)
Thrown perp to beam

Plot dE w/in the 0.0762 cm beam pipe.

Expectations based on PDB for a minimum ionizing pion--

dE/dx|min = 1.595 MeV cm2/g
density   = 1.848 g/cm3
dE/dx|min = 2.938 MeV/cm
dEstep    = 2.938 MeV/cm * 0.0762 cm = 0.2463 MeV 

Plot below shows 0.000226 GeV = 0.226 MeV.

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In pixel detector, sensitive silicon PLAC--

dE/dx|min = 1.664 MeV cm2/g
density   = 2.330 g/cm3
dy (half)        = 0.0008 cm
dEstep    = 1.664 MeV cm2/g * 2.330 g/cm3 * 2 * 0.0008 cm = 6.2 keV

From G3:
7.52 keV (full distribution)
5.65 keV (truncated at 3 sigma)

Conclusion -- The dEstep stored in the track history tree is storing reasonable value... w/in ~15% of the value expected for a MIP passing through the material based back-of-the-envelope calculations.