2018-02-26-scattering¶

http://mice.iit.edu/phonebridge.html

Monday 26th Feb, MICE meeting room, 14:00 GMT

Scattering note: MCSNote.pdf

Notes¶

Present:

John Nugent
John Cobb
Alan Young
Paul Jurj
Chris Rogers
Mariyan Bogomilov

General discussion:-

• Still discussing the analysis not the wording
• Some of the wording was not consistent with plots
• Tackle table/plots first
• Add PID/contamination to systematic uncertainty

Table 1:

• "Total" uses PDG RMS formula and adds in quadrature for each of the materials. Should change to use the sum of the radiation lengths

Fig. 1

• Legend is too small; it is (blue) G4 (green) Moliere (red) Cobb
• Should add error bars; consider enhancing statistical sample to make error bars negligible. Chase JHC if JN needs to know bin content/etc to do the calculation.
• Ensure that the Geant4 beam is monoenergetic and axial (don't use a realistic beam or anything). Note beam impurities were already rejected. This is like a "theory" section/discussion.
• Add to the text that models are consistent.

Table 2(b)

• Note the TOF2 column is number of digit coincidences
• John N should fix the caption; TOF1 is the triggering detector, so TOF2 "triggers" is wrong word.

Line 58-60:

• Should make comment quantitative
• Should use column density, not volume density
• Comment relates to theory, not to measurement; correct text
• "Spell out" the X_0 calculation
• Decide what the paragraph is trying to say

Figure 2:

• Comparison is for sum of momentum settings; should make a comparison on a "setting-by-setting" basis
• Note discrepancy between MC and data in Fig.2a. We don't think it is significant; consider making a comparison of scattering with left hand side of the beam vs right hand side of the beam to determine whether position distribution can contribute to uncertainties/etc.

Table 3:

• Mark \Delta z on the Fig. 3; some dimensions (numbers) would be useful.
• r_0 should be 140 mm not 150 mm.
• Diffuser cut should be between "Upstream track selection" and "TOF timing selection"
• Caption should be changed; more than just 240 MeV/c. Remove "and simulation". Clarify what each row means relative to the previous row.
• Write "overflow bin" rather than 45^degrees in the fiducial cut row.

Fig. 3

• Move up towards beginning; e.g. section 1.3
• More dimensions; definition of axes; Lithium Hydride absorber; consider which detectors/etc to include; remove coils

Fig. 4

• Discuss why we separate x and y; noting that the tracker mixes x and y but the beamline magnets do treat x and y independently (and deliver interesting correlations accordingly). Should present the logic later on.
• Note that fit line is not used.
• Should check that the uncertainties in the efficiencies are correctly taken into account.
• Should add plot with theta and theta^2
• Should enhance statistical sample in MC

Fig. 5

• Needs units

Fig. 6a

• Note that the electron peak is shifted by 200 ps; concern that there may be impact on momentum validation

Fig. 6b

• We were confused about what was shown; this is the (x^2+y^2)^0.5 as defined in Table 3 line 4; it seems like a harsh cut. The normalisation is unclear and should be clarified.
• Should explain what an "event" is? What cuts are switched on?
• The "12 mrad" scatter should be described as applying to the absorber and applied at the absorber; and should be 24 mrad

Fig. 6c

• Nb: it's plotted at the upstream edge of the diffuser; clarify

Fig. 7

• Should explain what "track acceptance" is

Table 4

• Clarify what does RMS really mean? What do the +/- values mean? There is a measurement error and a bin width.
• What z-position do the momentum measurements refer to
• Discuss; how should the momentum bins be presented? Answer: we should just list each bin from the start
• It is worth making more of the momentum measurement; study of different contributions to resolution and their significance (e.g. straggling, TOF resolution, path length discrepancy can all contribute to resolution).

Fig. 8

• Note it is a placeholder; more work needed

Fig. 9

• Fit could/should use eqn 14

Fig. 10 11 12 13

• Note tracks outside the tracker fiducial volume; add a cut rejecting events outside the tracker fiducial volume
• Describe the z-position of the track - where in TKU is this plotted

Fig. 14:

• Note change of slope at 30 mrad; could be tied to the features of the tracker acceptance fig. 4 (stats/behaviour gets different around 30 mrad; enhanced stats may help)
• Need error bars in Fig. 14b
• Add theta y plots

Fig. 15

• Check tracker alignment is correct; speak to Durga and Francois

Fig. 16

• Since making the plot, John N discovered that the deconvolution had not yet converged. Work continues
• Add description of the RooUnfold deconvolution algorithm
• Add chi2 and KS test between red and blue plot

Section 5.1

• Expect 0.003/0.694 = 0.2 % uncertainty in density; => 0.1 % uncertainty in X_0; how does this tie to the 10^-6 quoted?
• Density is not the interesting value; it is column density (how much material per unit area?); fix.

Note that there can be a systematic bias due to no momentum loss in the (empty) absorber; which produces a different scattering effect in TKD compared to full absorber

Fig. 17

• This seems a fairly significant effect
• It should be treated as a systematic; that becomes of order the dominant systematic
  • Hence worth chasing

Fig. 18

• What is normalised residuals? Clarify.
• Why does Moliere not agree better with CC.

Section 7
Eqn 22 - why not just use the analytical formula?

Fig. 19: this is the main result; worth adding more TOF bins

• Add Geant4 result
• Check effect of "2.61 mrad bin" vs Cobb-Carlisle bin size
  • Has the rebinning had an effect?
  • Use John Cobb MC binning

• Eq 13 - check expression

Tab. 10/Fig. 19/Fig. 18
Comment:- as it stands, we are claiming an asymmetry in the MCS distribution with large statistical significance. This is clearly not physical and needs to be addressed.

Fig. 20

• Check horizontal error bars; what is being plotted? Should be the RMS width of the momentum distribution (not the error on the mean, which has an additional factor of 1/sqrt(N))