Exotic Tetraquarks at the HL-LHC with JETHAD: A High-Energy Viewpoint

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors made a comprehensive review on  the  hybrid high-energy and collinear factorization framework regarding  the semi-inclusive hadron production of  heavy-light tetraquark. The review is clear and instructive, with the theoretical setups being well described and the results being well organized and depicted.  I would like to recommend its publication. 

Author Response

I thank the Referee for her/his careful reading, for her/his valuable comments, and for recommending the publication of my manuscript in this journal.

Reviewer 2 Report

Comments and Suggestions for Authors

The author reviews the hadroproduction of tetraquarks at the High Luminosity - LHC.

He uses leading-twist fragmentation functions and provides predictions of differential distributions with JETHAD.  

The topic is original and relevant. It addresses an issue of interest for the scientific program of the HL-LHC. The report does contribute to future observations of differential distributions for exotic states.

Their study provides calculations of distributions that would be measured experimentally and would probe high energy dynamics of QCD at hadron colliders. 

My only one observation would be:

It would be great if the author compares his results to other analyses and/or comments on other approaches. This would keep the spirit of a review (the report is presented as a review).

All predictions given in the article are obtained with the JETHAD computer program. It would be great if the author could comment on other approaches as well as on the reasons why he considers of particular importance the analysis presented.

Otherwise:

The author provides a very complete set of references, quite extensive.

The plots show the differential distributions. In case the journal keeps a record of numerical tables that support the plots it would be good to have them (in case a reader wants to reproduce the calculations). This is, however, a matter of the journal data storage and support capabilities. 

Author Response

I thank the Referee for her/his careful reading and for her/his valuable comments.

I agree with the Referee that it would be very useful and instructive comparing predictions taken within the NLL/NLO+ hybrid factorization from JETHAD with results obtained by the hands of other approaches. 

I particularly refer to standard collinear factorization or transverse-momentum-dependent factorization, well-suited to probe the inner dynamics of exotic-matter formation from low- to moderate- and large-pT regimes.

To reach this level of comparison, however, we should turn our attention from tetraquark-plus-jet observables, suited to probe the BFKL dynamics, to semi-inclusive emissions of a single particle.

However, to perform such analyses via BFKL, one should rely upon the small-x unintegrated gluon density (UGD) in the proton. However, our current knowledge of the UGD is very qualitative and comes mostly from model-dependent studies.

I have added a paragraph in the Conclusions section to emphasise this point.

Finally, concerning a record of numerical tables that can serve as a quantitative support for the plots, I would be happy to provide them, in the case that the journal requests it.

In any case, all numerical results will be made available by myself to any interested colleague, upon a reasonable request.

Reviewer 3 Report

Comments and Suggestions for Authors

I congratulate the Author on this very interesting work. I found the work easy to read and well researched. I particularly appreciated the historical perspective and the thorough review of previous results and literature.

After the historical perspective, the paper describes in detail techniques and software used to compute cross sections of tetraquarks. Tetraquarks and other exotic quark matter have gained a lot of attention in recent years as LHC experiments measure their properties.

Within this context, this work has a very high intellectual merit of providing novel results in the computation of cross section for the production of tetraquarks in specific processes of interest at the LHC collider and its upcoming upgrade the high-luminosity LHC (HL-LHC).

The main suggestion I have on this work is, since the HL-LHC program is specifically mentioned in the title of the paper, to add a more in-depth discussion of the potential for connecting the results of this work to experiment. In the current state, other than the fact the cross sections are computed at 14 TeV center-of-mass energy for proton-proton collisions, there is no other particular connection to experiment. 

There are a few ways one could improve this:

1. The “Final remarks” chapter could be expanded discussing potential for measurements of the processes described in the paper at the HL-LHC.

2. I believe most of the results presented are applicable to current LHC parameters so they could be adapted and a comparison of the results could be made with current data.

3. Producing results in a format easily readable by experiments and adding realistic acceptance criteria.

The above suggestions would also greatly increase visibility of the work, in my opinion.

Other than that I highly recommend the paper for publication.

Author Response

I thank the Referee for her/his careful reading and for her/his valuable comments.

I welcome the kind suggestion, made by the Referee, to add a more in-depth discussion of the potential for connecting the results of this work to experiment.

More in detail:

1. [Referee]: "The Final remarks chapter could be expanded discussing potential for measurements of the processes described in the paper at the HL-LHC."

1. [Answer]: As for future tetraquark studies within high-energy QCD, a step forward would come out from investigations on single-forward tetraquark detections within our hybrid-factorization formalism.
These channels would give us a direct access to the small-x proton UGD, whose current knowledge is very qualitative and is mainly based on models. Once a more precise description of the UGD becomes available, it will enable a direct comparison with upcoming data collected at the HL-LHC. Here I mainly refer to semi-inclusive final states sensitive to the single-inclusive production of tetraquark states in central rapidity regions covered by ATLAS or CMS barrels, or in forward regions at LHCb Accessing a wider range of transverse momentum will also permit to probe kinematic sectors where different formation mechanisms for our tetraquark are supposed to be at work, ad possibly establish a data-driven hierarchy among them.
I have added a new paragraph in the Final remarks to emphasize this aspect.

2. [Referee]: "I believe most of the results presented are applicable to current LHC parameters so they could be adapted and a comparison of the results could be made with current data."

2. [Answer]: In connection with the previous point, I believe that a proper comparison with data could be double for semi-inclusive final states sensitive to the emission of a single tetraquark state, not accompanied by any jet. But to do such a comparison, we need to rely upon a more precise description of the small-x UGD in the proton. We plan to address this aspect in the medium-term future.

3. [Referee]: "Producing results in a format easily readable by experiments and adding realistic acceptance criteria."

3. [Answer]: In connection with the suggestion made by the second Referee, I would be happy to provide a record of numerical tables that can serve as a quantitative support for the plots, in the case that the journal requests it. In any case, all numerical results will be made available by myself to any interested colleague, upon a reasonable request.