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

Scattering note: MCSNote.pdf



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))

MCSNote.pdf (1.38 MB) Rogers, Chris, 25 February 2018 19:53

Notes-on-PDG-etc.pdf (111 KB) Cobb, John, 25 February 2018 20:30