NuHepMC: A standardized event record format for neutrino event generators

The authors have developed and documented a valuable tool for the study of neutrino interactions with matter using the various existing event generators, setting a standard for future developments.

I have only a number of minor comments and questions to be addressed. See below.

I am in favor of the publication in SciPost.

- To deal with the fact that only in some cases the averaged cross section is known at the beginning of the simulation, the mixed solution of G.C.5 and E.C.4 is proposed. However, the association of unrealistic <sigma> to events generated early in the run could lead to confusion and mishandling among the users. I wonder if <sigma> could be stored by a procedure analogous to G.C.5 but at the end of the run, rather than at the beginning. Probably, there are reasons why a solution of this kind is not possible/feasible/convenient but perhaps a short explanation, not just for this referee but for the readers and potential users would be useful.
- In G.R.8, the authors refer to “generator-specific quasiparticles”, presumably with unresolved nuclear remnants in mind. However, the name “quasiparticle” has a different meaning in physics, which could lead to misunderstanding. It is therefore advisable to find a different name. For example, if no other “quasiparticles” than nuclear remnants are expected, the later term could be directly used.
- In connection to the previous point, in P.C.2, “the new particle number 2009900000 to correspond to a nuclear remnant pseudo-particle” is defined. On the other hand, in a given simulation there might be more than one kind of such remnants, for instance when there are different targets. Wouldn’t it then be convenient to have a range rather than a single number associated to these states?
- The authors strongly recommended adopting picobarns as cross section unit but they are certainly aware that its use is practically inexistent in the neutrino cross section literature.
- In table 1, ID ranges are associated with process categories. The latter correspond to the common classification adopted in the field but it is not necessarily a good choice because it is model dependent and, in some cases, there is no consensus about the kinematic boundaries of each region. Furthermore, not all generators provide information in these terms in their output. In my opinion it would be wise to be able to redefine this structure in the future.
- The beginning of Sec. 4 refers to “preliminary tools for converting proprietary neutrino event formats to the NuHepMC standard”. Such tools would be highly valuable for potential users. I understand the authors are not yet in the position to include these tools in this release but a sentence promising them (soon) would be encouraging.
- In connection to the MARLEY prediction in Fig 1 (right) it is stated that “adding future data points to the plot would be easily achieved with the present NuHepMC-based workflow.” It is not clear in which way the new format would help in this comparison. I would naively say that once the results of the simulation have been obtained, adding (future) data to the plot should be straightforward no matter the format.
- Finally, with the font chosen for Fig. 1, characters “I” and “1” look strange.

Ask for minor revision

This manuscript presents a new format for the output of neutrino generators, aimed at establishing a community-wide standard. The authors argue that the format will facilitate comparisons across various event generators. The format builds on the structures developed for the HepMC3 event record library, which is already in use in other HEP-ex fields.

The authors should address some points, listed in the "Requested changes."

Overall, I find this to be a valuable contribution that deserves publication. However, I believe the authors should address some points for clarity and completeness.

General comments:

Repository: It would be highly beneficial to include a link to a repository. Specifically, I recommend that the authors provide the scripts used to generate Figure 1. This will greatly enhance the utility of the manuscript for readers.

Dependencies: The authors should clarify the dependencies that the proposed format introduces for event generators. For instance, does this imply that generators need to install HepMC3? Does this limit the format to C++-based generators, or are there options for Python-based codes? Are there Python bindings for the NuHepMC structures? A detailed explanation of how to integrate this format into existing generators and any associated limitations would be helpful.

Specific comments:

- Page 8: The attributes for "Beam Energy Distribution Description" are not well-suited for atmospheric neutrino experiments, which involve multiple energies and baselines. The manuscript should clarify how such information can be incorporated.

- Page 9: The term "Nevents" should be clarified—does it refer to the number of generated events or the number of interactions?

- Page 9: Currently, "ParticleStatusInfo" is labeled as a "Suggestion". Why not formalize this as a "Convention"?

- Page 9: It might be useful to include a label that informs users about the reference frame used for all the provided data.

- Page 11: Table 1 lists several processes. The difference between SIS and DIS should be clearly explained for better understanding.

- Page 13: The link between "outgoing real particle" and "observable" is unclear. For instance, particles like taus, which can decay but are observable at high energy, could fit this category. This distinction should be explained in more detail.

- Page 21-22: Figures 2, 3, and 4 are difficult to read. Please enlarge these figures for better legibility.

Publish (meets expectations and criteria for this Journal)