STAR HardProbes PWG

[Diptanil Roy <roydiptanil AT gmail.com>]

Hi everyone, thank you for your comments. Please find some of my responses inline below.

Rosi's comments:

I think your slide 4 might be a little confusing - on the left you show the CMS plot which very much agrees with the statement about the lost energy being recovered, but the right plot isn't a ratio (right?), so I had to start at it a while because I was wondering why the STAR results didn't show the same thing

You are right, the right plot isn't a ratio. I have added a small comment below the plot now to make that clearer. The ratio measurement is underway at the moment (I believe Joel's doing this), so this is just to tout that result.

On slide 6, I assume the statement about the dispersion comes from CMS?  It really seems like a much stronger statement than the data shows given that the data points essentially touch 1 in the ratio.

I agree with you on this, however, I just used the statement from their paper. I have made it slightly weaker in the current iteration.

I think it would really be good to maybe explicitly state that the dead cone effect goes in the opposite direction from the normal energy recovery - so for these jets you have somewhat a competing effect if you look at the jet shape.  (Though now you're looking at the distance between the D0 and the jet axis, so the story you're telling here is a little confusing.  Do we really need to discuss the jet shape at all?  How should that be related to the angular distance between the D0 and the jet?)

I added an arrow which explicitly shows the dead cone effect in the plot now. 

I don't think we can compare jet shape with the radial distribution of D0s or the splitting angle distribution. The jet shape results are included to show that jets undergo changes in the medium. At a later point, we would like to look at the jet shape of charm tagged jets as well.

Separate from the jet shape measurements, I mention the dead-cone effect result in pp, which show that the charm quark radiation is different (and suppressed from light quarks and gluons), hence a comparison with inclusive jets could be made later for our jet observables.

I actually think the * is unnecessary - the comment that pythia fragmentation is fine to make, but I think 95% of all jet unfolding uses pythia fragmentation in the response matrix.  Sometimes people play a game with q vs g or something like that, but since this is standard you're going to confuse more people with this notation than educate.

I agree that most jet unfolding uses pythia fragmentation in the response matrix. However, while it might not be a huge issue for inclusive jets, we saw massive differences in the final spectra of D0 jets based on our input fragmentation function. Since PYTHIA fragmentation function is considerably harder for charm quarks than is seen in data, we really have to mention this caveat. What we have been trying in this analysis since QM is to find a way to not bias our final spectra because of the PYTHIA input. It has been surprisingly hard.

It would be nice once you show your nice results to have a slide were you at least put the CMS results on the same slide to at least think about a qualitative comparison.

I agree with you on this. I added two more slides, one comparing the D0 jet RAA from ALICE to our measurement, and the other comparing the radial profiles. Thank you for this excellent suggestion. 

 

Sooraj's comments:

One question, On S4: What do you mean by 'medium-response' here, which is different from multiple scattering and medium induced radiation? Why wouldn't the heavy flavor hadron distributions won't probe the first two?

 My slide was a little unclear there. I meant all the three effects are parton-mass dependent. By medium response, I mean how constituents of the medium change because of the interactions with the jet. The first two are collisional and radiative energy losses for the jets themselves.

I have uploaded a new version here with the suggested changes. (https://drupal.star.bnl.gov/STAR/system/files/HotQuarks_DiptanilRoy_v3.pdf). Yi, thank you for sending it to star-talks.

Please let me know if you have any further questions or comments.

--

~ Neil