Comments from Yosuke

2.1 Electron identification with TPC+EMCal

• You mention "the hadron contamination was statistically subtracted". You simply used the numbers in Fig. 6 or did you do some smoothing?
  • smoothing (actually used Eval in TGraphErrors)

2.2.1 background from photon and neutral meson

• I would like to confirm my understanding of you procedure. You obtain the photonic electron spectrum by (ULS-LS)/epsilon, where epsilon is the efficiency of the photonic electron. You show the efficiencies for eta and pion separately in Fig. 9, but what you actually use is the average of them? What is the eta/pi0 ratio you used? Is the ratio from HIJING shown in Fig. 7? Is the ratio consistent with data (https://aliceinfo.cern.ch/Figure/node/8265)?
  • Yes, by (ULS-LS)/epsilon
  • average by taking into account eta/pi0 ratio (0.45)
• Could you add a figure showing the inclusive electron pT spectrum and the photonic electron spectrum that you subtract? (also their ratio, if possible)
  • done
• What decays of pi0 and eta are implemented in LHC16i3b? All decays in PYTHIA or some channels are enhanced?
  • Those are decayed by following the brunching ratio
• Fig. 9: are these with the full statistics of the MC?
  • no, updated with full stat.
• check fake tracks at high pT by using ..." mentioned in Outlook seems very important to me. The reason is the following based on my understanding of the procedure. I think this procedure ignores the effect of momentum mis-reconstruction. For example, think of a case when an electron from photon conversion with p_T^true steals hits in the ITS and is reconstructed as an electron with p_T^reco. If p_T^true and p_T^reco are different significantly, the electron cannot find a partner satisfying mee < 0.1 GeV/c^2. So, the "fake" electron is not used to construct the photonic electron spectrum. Therefore, the electron should affect the inclusive electron spectrum at p_T^reco, but this procedure will subtract the contribution at p_T^true. This effect might be negligible, but it would be interesting to see the stability of the final results to the fraction of shared ITS clusters, chi^2 of ITS divided by the number of ITS clusters and golden chi2. (I mentioned these variables looking at a dielectron analysis note, https://aliceinfo.cern.ch/Notes/sites/aliceinfo.cern.ch.Notes/files/note...)
  • photonic contribution at high pT is very small, so it's not important in the discussion for fake track at high pT. In addition, if low pT photonic electrons are reconstructed as high pT photonic electrons, such electrons are removed by E/p matching.

2.3 background from W

• Shouldn't it be Section 2.2.2?
• Fig. 10 (left panel) Black squares are from data, right?
  • yes, it's measured HFE spectrum

3.1 Reconstruction efficiency

• Does MC reproduce E/p and the shower shape variable distributions in data?
  • the peaks of E/p were different in data and MC (there was 0.04 shift), and it was corrected. Concerning the shower shape cut, it was confirmed by comparing the efficiency from data and MC.

3.2 Trigger normalization

• Table 2: The EGA/MB ratio seems strongly depending on centrality. So even in a centrality bin, I think the ratio is changing about 50%. Thus, the 30-40% bin in MB and the 30-40% bin in EGA triggered data are not the exactly same. Do you think the difference is negligible?
  • This is because electron yields is centrality dependence in MB (more yields in 30-40%). On the other hand, the trigger records the event above the threshold (10 GeV). Thus such centrality dependence isn't in EMCal trigger event. And as the result, the rejection factor have the centrality dependence.

4.1 Systematic uncertainty from eID

• When you vary the n_{\sigma}^{TPC}, you also re-estimate the hadron contamination?
  • No, but re-estimating by applying titler E/p cuts to increase the purity.
• "not subtracted hadron contaminations": what do you mean by this? Since we know there is hadron contamination, I think this uncertainty is not needed.
  • I mean, when I made the ratio, I compared the spectrum without subtracting hadron contaminations.
• No uncertainty from W-> e subtraction ?
  • it's about ~1%

5. Results

• Fig. 25: RAA is above one for pT > 20 GeV/c (30-40%) and for pT > 15 GeV/c (40-50%). We do not see such a behavior in the forward muon measurement. (https://aliceinfo.cern.ch/Figure/node/9806). Do you have any idea how to interpret this?
  • I think this is due to fake tracks at high pT. Applying strong ITS chi2, such tracks reject (or reduce). At least RAA at high pT (>20 GeV/c)in 0-10%, the results are consistent with D meson result in CMS.
• Fig. 25: legend is wrong.
  • fixed

6. Outlook

• Are J/psi and Upsilon negligible?
  • Yes, the maximum contribution from J/psi was 3% (pT = 3 GeV/c) in PbPb 2.76 TeV. And Upsilon cross section is smaller than J/psi and the contribution should be much smaller.

-- ShingoSakai - 2016-12-22