- I think that 5.02 TeV for the beam energy needs to be explained somewhere because it suggests a three digit accuracy. Perhaps just writing in the introduction that this is the nominal beam energy is enough. Since all interpolations were done to 5.02 TeV there should be a systematic error due to the errors on the three beam energies but this systematic error can probably be ignored, this can then also be mentioned in the introduction.

This is the long-standing issues of the energy value. Maybe Burkhard has now reached a conclusion with the LHC people. Otherwise a sentence saying that this is the NOMINAL energy would be fine for us. On the systematic uncertainty, we believe it should be negligible, but we do not know about uncertainties at 2.76 and 7 TeV. Has anybody an estimate ?

We will add some discussion about the center-of-mass energy to the note and then enter the next round of discussion wink

- Lines 88-90 and 129-130: Assuming random correlations coefficients between systematics needs some explanation in my opinion. If the systematics for the measurements are understood then it should be possible to say which components of the systematics are correlated and which are not.

This is one of the main points. We will try to do some brainstorming and to ask experts. If we adopt the approach proposed by Michael we should indeed add an explanation on why we are not able to precisely estimate the uncertainty correlations.

Of course being quantitative about the correlations would be the right thing to do. On the other hand, it may involve a lot of work and does not really guarantee better results. For example, we assumed that the LHCb luminosity systematics were strongly correlated, whereas according to the luminosity group they are not. So as a stopgap measure I decided to do the study with the random correlations, which I could do without wasting anybody elses time, in order to see whether the correlation are important. My personal conclusion was that they are not, since (even assuming that correlations are never negative) the increase in the total uncertainties is at the same level (O(10%)) as the typical precision of error estimates in general. However, that point can of course be discussed.

- Lines 120+ and 127+: If I understand correctly then the LHCb systematic error 0.15_{model} corresponds to the Alice systematic error 0.10_{inter}. Why are two different notations used for this kind of error?

We propose to use "inter" also in the ALICE value, instead of "model"

fine

- Lines 120+ and 127+: If I understand correctly then both Alice and LHCb use the three functional forms to interpolate the measured cross sections but Alice adds on top of that a systematic error (0.05_{theo}) determined from an interpolation that uses FONLL and CEM. Why does LHCb not need this systematic error (or why does Alice need it)?

This is a question for you guys. Indeed we are not forced to the very same approach, but it is fair in this case to shortly explain why.

Good question - in the end it's related to how conservative one wants to be. In LHCb we never tried to use a specific model to interpolate to 5 TeV. We only used the models to check that the functional forms make sense and that taking that largest difference between the power-law and either of the other fits is a reasonable estimate of the systematic error. In our case that's sort of natural, since we fit two parameters to three data points and thus have some control on the functional form from the data. With only two data points ALICE does not have any redundancy. The only way to get it is to fit the normalization of a full fledged model - but doing that one submits to the intrinsic limitations of the model which results in additional uncertainties.

-- EnricoScomparin - 14 Nov 2013

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Topic revision: r3 - 2013-11-20 - MichaelSchmelling
 
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