STAR HardProbes PWG

[Rosi Reed <rosijreed AT lehigh.edu>]

Hi Nihar,

Just a few comments here:

> 1. You don't need to put description of "ALCIE sys bands like correlated
> and uncorrelated etc" One green circle is enough to represent ALICE
> results.

I think it's better to keep their descriptions here - otherwise it is STAR telling ALICE what their data should look like.  The correlated vs uncorrelated is important for making a statement about the comparison, if everything was uncorrelated the significance of the apparent agreement is much stronger, so I would be worried that by changing their results we would be misleading our audience a little on this very interesting result.

>Can you please elaborate how we draw the conclusion of " jet
>modification is path-length dependent" in Isobar ?
>We don't have any hard-core jet RAA/RCP measurement in isobar. Do we
>have?

We don't have RAA/RCP, but I don't see why this is necessary for the statement, we know that jet RAA will < 1 in the isobar system due to other measurements made by STAR (and PHENIX).  You could have a path-length dependent modification that averages out to precisely RAA = 1, though that would be unlikely in a collision with a center of mass energy greater than ~40 GeV judging by the RCP measurement made by Stephen from the BES data.  With a signal at 3.5 sigma, we can state that there is evidence for non-zero jet v2 at RHIC.  There must be some geometrical physics process causing this - if there was not, then the v2 would be close to zero.  In the paradigm of heavy ion collisions we have a choice of initial state effects (so some MPI), pressure gradients and path-length dependent suppression (i.e LPM effect).  We know we can exclude the middle term due to the high Q^2 and the QGP formation time.  There is no evidence for the former term as of yet, so within the paradigm of jets in heavy ion collisions the latter is the assumption for the interpretation of the data that remains.  I certainly don't think we can overturn a decades long paradigm on the basis of a single statistics hungry measurement.

> I would be careful on this statement, as I mentioned we have not done
> any dijet Aj study in Isobar to support of the surfaced bias jet
> selection. It could be correct but we have not done any measurement so
> we should abstain mentioning this.

I don't believe that we have to measure AJ to state this basic fact of nuclear physics.  The surface bias of selecting hard fragmentation has been discussed since the earliest papers on jet quenching (https://physics.fjfi.cvut.cz/files/predmety/02RQGP/zs1617/GyulassyPluemer.pdf for example), and has been mentioned many times by STAR itself in a variety of high pt and jet based measurements.  In fact, not mentioning it after STAR spent so much time discussing jet geometry evolution in the earlier AJ measurements would actually be akin to walking back our earlier statements since we're using the same process in this measurement.

I have also made some comments on Tristan's talk that he'll follow up on, and the official practice of his talk before the council member will happen on Monday so there will be a little bit of tweaking, even after he submits a draft v5.  One quick point on the uncertainties, Rongrong was quite correct in the meeting on Thursday that the uncertainty on the tracking efficiency only plays a role in the uncertainty if we're unfolding.  So there are no further effects that will change the systematics for this non-unfolded measurement - rather we're waiting on this as a last cross-check.

Cheers,

Rosi

On Sun, Oct 9, 2022 at 4:14 AM Nihar Sahoo via Star-hp-l <star-hp-l AT lists.bnl.gov> wrote:

Hello Tristan,

Thank you for implementing my comments and your reply.
Please find my further comments and reply to your response.
All my comments on your recent version (v4).
Please don't remove your old version; that can be done after finishing
our discussion otherwise it is difficult to follow the slide numbers
with new version.

1) Have you updated your remaining sys uncertainty that we were waiting
for?

2)Comments on Figures:
Slide18 fig:
1. You don't need to put description of "ALCIE sys bands like correlated
and uncorrelated etc" One green circle is enough to represent ALICE
results.
2. Please include instead STAR sys box's description  in legend

Slide17 fig:
_ Can you include v2 value (with uncertainty) in this figure that you
get from the fitting?


3) Additional comment:
I think EPD is used for the first time in jet v2 measurement.
It would be good to include EP resolution plot that you get from this
measurement.
For that you can combine slide15-16 to make a story for EPD and EP
calculation.


4) Slide18(in vesrion4):
"Suggests that jet modification is path-length dependent, even in medium
sized systems!"
Can you please elaborate how we draw the conclusion of " jet
modification is path-length dependent" in Isobar ?
We don't have any hard-core jet RAA/RCP measurement in isobar. Do we
have?

We can only say so far (from this preliminary study) what you have
mentioned in conclusion slide19 (with slight modification "hint…")
"Hint of non-zero v2^ch jet is observed in a medium sized system "

Please bring this statement in slide18


5) Slide19(v4 version)
_"A very different system!" -> "A very different kinematic range and
system size"
_"v2ch jet is observed despite the introduced surface bias" -> "v2ch jet
is observed despite the possible surface bias"
    I would be careful on this statement, as I mentioned we have not done
any dijet Aj study in Isobar to support of the surfaced bias jet
selection. It could be correct but we have not done any measurement so
we should abstain mentioning this.
If you want, then need to do Aj measurement for this hard core jet
selection in Isobar.

_"Our picture of jet quenching is not complete - there is still much to
discover"
       Sounds a vague statement. Please mention 1) what is not completed
relating to jet quenching? 2) what do you think that needs to be
discovered?  Please elaborate this.


Remaining reply can be found inline.

On 2022-10-09 07:56, Tristan Protzman via Star-hp-l wrote:
> Hello Nihar,
>
> A new draft has been uploaded to Drupal.
>
> Note: it should be written as $p$+$p$ and $p$+Au, etc, which is
> different from the guidance.
>
> Fixed.
>
> Slide:2
> _Second bullet seems out of context here. Coupling is large at low Q^2
> then why  is it relevant for the QGP and your jet anisotropy
> measurements? This part is not clear here.
> It motivates the need for a perturbative object like jets to probe
> what we actually want to study, the QGP.  Changed text to clarify.

Still it is not clear and confusing for 1st and 3rd bullets.
If you want to motivate jet (which pQCD calculable) and this is used to
probe QGP (which is asymptotic region of coupling); then what is the
point to mention "alpha_s ~ O(1) at low Q^2."
I would suggest to rephrase;
"Since running coupling is asymptotically small at high Q^2,  pQCD
calculable probes are used to study the QGP medium"
Then you don't need 3rd bullet.


>
> _ Give reference to the running coupling plot. And you could replace
> with most updated version where LHC measurements (very highQ2 region)
> are included if you want to start with it.
> Changed.
>
> __GIve a reference or credit for left cartoon._
>
> Figure removed, I felt it did not add to the message.
>
> Slide:4
> _3rd bullet: "Leads to path length…"  this is not the only effect;
> it
> could be various other contributions like color factor, Temp of QGP,
> initial gluon density, etc. But you need to mention Your motivation is
> to study "path length dependence".
> __ same comment for 4th bullet_
> I have adjusted this section to clarify that the aspect of jet
> modification I am trying to study is the path length dependent nature
> of jet energy loss
>
Slide4 (current  v4)
_ "We are interested in understanding the path-length dependence of
these processes" -> "We are interested in understanding the path-length
dependence of jet quenching"

_"Both collisional and radiative" -> "Both collisional and radiative
energy loss" or "Parton energy loss via both collisional and radiative
processes"


> _ 5th Bullet ("Both collisional and radiative") you need to provide
> reference to the theory calculation for this L/L^2 dependence. These
> are
> model calculations.
>
Slide4 (current v4)
_"Both collisional and radiative" -> "Both collisional and radiative
energy loss" or "Parton energy loss via both collisional and radiative
processes"


>
> Removed L/L^2 statements as I am not comparing to any models in this
> presentation
>
> _ This slide only focus on jet and jet quenching, but it doesn't
> motivate your measurement like why jet anisotropy measurement is
> required? Need to include some text on it.
> I suggest you need to motivate jet anisotropy before you go to any jet
> analysis details like in Slide5  underlying event discussion
>
> The way I have structured my talk is to first motivate that we have
> observed jet quenching.  I am using the dijet analysis to this end.  I
> then want to contrast that with azimuthal anisotropy, which is not a
> dissimilar measurement in that it probes jet modification, but it does
> so in a new way.  Therefore, I think it makes sense to talk about jet
> measurements and then the dijet measurement before introducing the
> idea of anisotropy and motivating how that can get us towards the
> missing path length dependence of a dijet analysis.
>
> SLide:5
> _Not clear, what is that right side plot? Is this data or MC
> simulation.
> What is pT, of track or jet? What is Delta phi?
> I agree, this plot was not particularly clear.  I have removed it.
> __"Soft processes produce a fluctuating background" what is that_
> _background? Is it track or _combinatoric_ jet background?_
> I'm not quite sure I understand what you are asking, it is the tracks
> from soft processes which produce the combinatorial jet background, so
> I suppose both?
Then it would good to mention, "Soft processes produce a fluctuating
uncorrelated background for jet measurement in heavy-ion collisions"
Here "uncorrelated" is important.

Slide5 (current v4), right figure is from STAR data or any model? No
description mentioned there.

> __3rd _bulltet_ (Estimated…) it should _be sub-bullet_ of 2nd bullet
> (Soft_
> _process…)_
> Changed.
> __ what is kT?_
> The k_T jet finding algorithm, clarified.
> __ Jet area -> Jet area(A)_
>
> Changed.
>
> Slide6:
> _Not clear, what is that right side plot? Is this data or MC
> simulation?
> What is pT, eta, and phi?
> This is the total track momentum for eta/phi bins for a collision.
> __"A jet finder… had scattering and other processes" ->" had
> scattering_
> _and combinatorial background in heavy-ion collisions"_
> _2nd bullet is not required if you mention above.
>
> _ _I have merged this with slide 5 and changed this wording
>
> SLide:7
> I would suggest to use jet pT as $p_{\rm T, jet}$ throughout your
> presentation.
> Changed.
> __Used in other STAR analysis -> Proved references_
> __Provide _referecen_ to ALICE measurement_
>
> Done.
>
> Slide:8
> _Move this slide or Isobar jet pT distribution after your slide14
> where
> you discuss about Isobar dataset. It seems the left side plot just
> pop-up. This plot should be part of you results discussion even if it
> is
> a STAR performance plot.
> Figure removed
> __"Statistically unlikely for soft processes…" Please rephrase
> this… not_
> _clear._
> Changed to clarify that it is unlikely for soft processes to produce
> high pt hadrons which look like jets
> __"May bias jet selection towards surface" Not sure the motivation of_
> _this bullet. _why it is_ important? You are not doing jet RAA/RCP
> study_
> _and you do not study trigger jet v2 then why it is important if this
> jet_
> _is trigger biased or not. These jets should be treated as inclusive
> _jet_._
>
> Is it not important to understand the biases we introduce into our
> measurements?  By requiring the high pT hadrons the selected jets are
> biased towards the surface of the QGP.  This is the motivation for one
> of the items we would like to explore next in this analysis, the
> variation of the hard core threshold.
>
> Slide:9
> This slide is not relevant. You could put in Backup. (A distraction)
>
> I disagree, the story I am hoping to tell with this talk is that we
> saw signs of jet quenching with measurements like dijet imbalance, but
> that it doesn't tell the complete story.  We can continue our
> understanding of jet quenching from dijet measurements to jet v2
> measurements.

slide8(in v4)
_ we are doing inclusive hard-core jet v2 measurement here. Is not it?
_I am not convinced to motivate with dijet measurement here. Are we
going to do any dijet measurement in isobar?
_Selecting a hard-core jet may not imply you select surface biased jet.
For that you need to show the same dijet Aj measurement in isobar like
in Au+Au. If you have any result to demonstrate that you are selecting
surfaced bias jet in Isobar, please show those results.
I think we have not done that study.

>
> Slide:10
> _ 1st bullet: Why it is important for Dijet imbalance discussion here?
> You are doing inclusive jet v_n measurement. Not clear to me.
>
> See above.

Please see above my concerns.

>
> SLide12
> _"A jet in plane interacts with less medium than one out of plane" ->
> "A
> jet interacts less with medium in plan than out of plane"
> Changed.
> __"Since jet production is isotropic, differences in yields are a
> result_
> _of medium interactions" Not sure, _what you_ want to say here?
> Please_
> reprhase_._
> Changed.
> __" like flow" Remove this._
> I included this to help give context for the measurement to an
> audience who may be familiar with flow studies, but not jet anisotropy
> studies.  If you feel this is misleading I will remove it.
> __ you do not discuss what is v_{2}^{jet} is?_
> Changed equation to remove \Delta\phi -> \Psi_2 - \Phi_jet
> __"Not a flow effect though!" Can you elaborate this?_
>
> I am stating that although it may be described using the same
> framework as flow measurements, jet v2 is a different process.

I would suggest to give a clear idea what could be that different
process, For example...?
Otherwise do not create unnecessary doubt or make statement just for a
buzz?


>
> SLide13
> _RHIC produces a different, cooler QGP -> "RHIC produces a cooler QGP
> medium than the LHC"
> Changed.
> __"Down to 10 _GeV"_ -> But you are not going to show down to 10 GeV.
> So_
> _just remove this extra quantifier _subbullet. Main bullet is fine.
>
> I do show down to 10 Gev though, my first point is 10-12.5 GeV/c jets.
>
> Slide15:
> - Jet trigger -> You don't use any jet trigger and BEMC info in your
> measurement. If yes, just remove.
> I do use the barrel high tower trigger in my analysis, as detailed in
> the preliminary figure request.  I have clarified this as high tower
> trigger rather than jet trigger.
> _- Right side STAR detector, please indicate where is TPC, BEMC, EPD_
> _- Mention kinematic acceptance of these detectors_
>
> See updated slides, Yi mentioned this as well
>
> Slide16:
> _you did not discuss what is Delta_phi?
> I did not, but I am not sure I need to on this slide.  I will discuss
> it on the next slide.
> __right side plot, _make title_/_lable_ of x-, y-axis bigger so that
> it will_
> _be visible. And also legends _in side_ the plot._
> Changed, made entire plot larger as well
>
> Slide18
> Move this slide after Slide15
>
> Changed.
>
> Slide19
> _INside fig, mention "red line" is fit fun.
> Added.
> __ inside fig, p_T^reco -> p_{\rm T, jet}^{reco} ; 12.5 -> 12.5 GeV/c_
> Changed.
> __ you did not mention anywhere before what is "R"? And what jet _R
> you
> are_ going to _do measurement_?_
> It is labeled on the plot, and I will discuss it further on the
> following slide.
> __ what is v_{2}^ch? Need to mention _it charged_ jet v2. I would
> suggest_
> to use $v_{2}^{\rm ch, jet}$; And the same about v_{2}^ch,abs
>
> Changed.
>
> Slide20:
> Before slide20, you need to discuss different jet v2 (all, hard core,
> matched jet) and their spectra showing side-by-side
>
> I'm not sure I understand why?  I think that was a good check to make
> and certainly worth having in the backup, but the measurement being
> presented is jet v2 using the hard core matching criteria, the need
> for which is motivated earlier in the talk.
>
> Slie21:
> _  "Jet v2 is a exciting measurement for determining the path-length
> dependence of jet quenching" -> This statement is fine to motivate.
> But
> for your conclusion this may not be relevant. Because we don't have
> jet
> v2 measurement for different path length/system size with the same
> kinematic coverage. And you did not discuss what is the strategy for
> your measurement unless you plan to do the same in AU+AU.
>
> _"Jets which are in plane interact with a different amount of the QGP
> than those out of plane" Not sure how do you get this conclusion from
> your measurement.
>
> I have updated my conclusions to better reflect the points I wish to
> make and where I will go next with this analysis.
>



Thank you
Nihar
> On Thu, Oct 6, 2022 at 1:34 PM Yi Yang <yiyang0429 AT gmail.com> wrote:
>
>> Dear Tristan,
>>
>> Thanks a lot for the reply and the updated version.
>> They look very good to me.
>> Let's wait for your study and the decision on the preliminary
>> results!
>>
>> Cheers,
>> Yi
>>
>> On Thu, Oct 6, 2022 at 3:26 AM Tristan Protzman <tlp220 AT lehigh.edu>
>> wrote:
>>
>> Hi Yi,
>>
>> Thank you for the feedback!  I have uploaded an updated version and
>> addressed your comments below.
>>
>> - p4: Are the sub-bullet for the 3rd bullet and the 4th bullet the
>> same?
>>
>> Yes, I have removed that redundancy.
>>
>> - p6: toy mode --> toy model
>>
>> Fixed.
>>
>> - p9: Just for my own education, could you please tell me why A_j
>> can be less than 0 (I am assuming pT^1 and pT^2 are leading and
>> subleading jet pT, respectively, is it correct)?
>>
>> Yes, (pT^1, pT^2) is the (leading, subleading) jet pT.  The red
>> points are the measurement of A_j using only hard cores.  This is
>> where leading and subleading are determined, thus no points below 0.
>> However, after matching is done, leading and subleading are not
>> recalculate, so it is possible for the subleading hard core to match
>> to a jet with more momentum than the leading hard core does,
>> resulting in negative A_j.  There are a few ways this could happen.
>> The subleading jet could contain a larger soft component than the
>> leading jet, thus when added to the hard core the magnitudes flip.
>> Additionally, because of the fluctuating background the leading jet
>> could be over subtracted and the subleading jet under subtracted,
>> again flipping the relative magnitude.  This would not affect the
>> hard core since background subtraction is not done on that
>> collection.
>>
>> - p15: It would be good if you can provide more information for the
>> subdetectors, for example eta and phi coverage...
>>
>> I added more information about each system and labeled the picture.
>>
>> - p18: Jet v2 not feasible --> Jet v2 is not feasible
>>
>> Changed to Jet v2 was not feasible
>>
>> Cheers,
>> Tristan
>>
>> On Wed, Oct 5, 2022 at 1:59 PM Yi Yang <yiyang0429 AT gmail.com> wrote:
>>
>> Hi Tristan,
>>
>> Thanks a lot for the nice slide. I have some suggestions/comments
>> for your consideration.
>> - p4: Are the sub-bullet for the 3rd bullet and the 4th bullet the
>> same?
>> - p6: toy mode --> toy model
>> - p8: Title: Hardcore --> Hard core
>> - p9: Just for my own education, could you please tell me why A_j
>> can be less than 0 (I am assuming pT^1 and pT^2 are leading and
>> subleading jet pT, respectively, is it correct)?
>> - p15: It would be good if you can provide more information for the
>> subdetectors, for example eta and phi coverage...
>> - p18: Jet v2 not feasible --> Jet v2 is not feasible
>> - Since we are not settled with your preliminary results yet, I
>> will comment on p20 and p21 later. :-)
>>
>> Cheers,
>> Yi
>>
>> On Thu, Oct 6, 2022 at 12:36 AM Tristan Protzman via Star-hp-l
>> <star-hp-l AT lists.bnl.gov> wrote:
>>
>> Hi All,
>>
>> I submitted this material for review last week, but it seems to have
>> been lost somehow, so I am resending it.
>>
>> Cheers,
>> Tristan
>>
>> On Wed, Oct 5, 2022 at 12:33 PM webmaster--- via Star-hp-l
>> <star-hp-l AT lists.bnl.gov> wrote:
>> Dear Star-hp-l AT lists.bnl.gov members,
>>
>> Tristan Protzman (tlp220 AT lehigh.edu) has submitted a material for a
>> review,
>> please have a look:
>> https://drupal.star.bnl.gov/STAR/node/61264
>>
>> Deadline: 2022-10-11
>> ---
>> If you have any problems with the review process, please contact
>> webmaster AT www.star.bnl.gov
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--

Rosi Reed
RHIC/AGS UEC member
Associate Professor, Physics Department
Lehigh University
(610)758-3907
16 Memorial Drive East Office 406
Bethlehem, PA 18015
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