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EPOS4: What are the new concepts?
by Klaus Werner
Submission summary
| Authors (as registered SciPost users): | Klaus Werner |
| Submission information | |
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| Preprint Link: | scipost_202410_00042v1 (pdf) |
| Date submitted: | 2024-10-17 19:36 |
| Submitted by: | Werner, Klaus |
| Submitted to: | SciPost Physics Proceedings |
| Proceedings issue: | 22nd International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2024) |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
I explain the new concepts underpinning EPOS4, a novel theoretical framework designed to model hadronic interactions at ultrarelativistic energies. This approach eventually reconciles the parallel multiple scattering scenario (needed in connection with collective effects) and factorization (being the conventional method for high-energy scattering).
Current status:
Reports on this Submission
Strengths
The manuscript is devoted to a popular description of basic physics approaches of the EPOS4 Monte Carlo generator and of the corresponding technical implementation. The author discusses in a pedagogical way the main theoretical concepts of the model, providing also selected numerical results for illustration.
Weaknesses
1) In the Introduction, the author rightfully argues that the initial stage of high energy collisions proceeds on much smaller time-distance scales than final state interactions, which allows one to treat the two stages separately. However, in lines 17-22, he states that while the initial stage takes a long time, the corresponding interaction region is pointlike. This may confuse a potential reader. Generally, the size of the interaction region is defined by the interaction time. What the author probably means is that while the time scale of the initial stage is long enough (and the size of the respective region is large enough) to allow for multiple scattering processes to proceed in parallel, this time is very short, compared to the characteristic time scales of final state interactions. Hence, the interaction region can be considered pointlike, compared to the one relevant for final state interactions.
2) Ref. [7] corresponds to the perturbative treatment ('GL' of 'DGLAP') rather than to the Gribov-Regge approach.
Report
The manuscript is devoted to a popular description of basic physics approaches of the EPOS4 Monte Carlo generator and of the corresponding technical implementation. The author discusses in a pedagogical way the main theoretical concepts of the model, providing also selected numerical results for illustration.
I have only two small technical remarks to the manuscript.
1) In the Introduction, the author rightfully argues that the initial stage of high energy collisions proceeds on much smaller time-distance scales than final state interactions, which allows one to treat the two stages separately. However, in lines 17-22, he states that while the initial stage takes a long time, the corresponding interaction region is pointlike. This may confuse a potential reader. Generally, the size of the interaction region is defined by the interaction time. What the author probably means is that while the time scale of the initial stage is long enough (and the size of the respective region is large enough) to allow for multiple scattering processes to proceed in parallel, this time is very short, compared to the characteristic time scales of final state interactions. Hence, the interaction region can be considered pointlike, compared to the one relevant for final state interactions.
2) Ref. [7] corresponds to the perturbative treatment ('GL' of 'DGLAP') rather than to the Gribov-Regge approach.
Requested changes
The author may consider the remarks listed above.
Recommendation
Publish (meets expectations and criteria for this Journal)
Author: Klaus Werner on 2024-12-14 [id 5041]
(in reply to Report 1 on 2024-11-05)point 1)
No I don't mean that the time scale of the initial stage is long enough to allow
for multiple scattering processes to proceed in parallel. The actual multiple scattering processes proceeds in a very short time interval (considered infinitely small). What takes time is the *preparation*, which at the end provides many partons. The long "preparation" does not allow to have the scatterings one after the other.
I changed the paragraph to make this more clear:
In the diagram, it is evident that a comprehensive representation of space-time must consider the prior splitting of partons (parton evolution). This process (which prepares the actual scattering) takes a long time due to significant $\gamma$ factors. However, the interaction region (depicted in red) is indeed pointlike, necessitating multiple scatterings to occur simultaneously (the long "preparation" does not allow to have the scatterings one after the other). In the EPOS4 approach for primary interactions, one avoids sequential scatterings for both parton-parton and nucleon-nucleon interactions by rigorously conducting multiple scatterings in parallel. This is true for both, the theoretical formalism and the Monte Carlo realization, based on the principle that the Monte Carlo must be derived directly from theory, which is a non-trivial task.
point 2)
I cannot localize the problem. Yes [7] V. N. Gribov and L. N. Lipatov, , Sov. J. Nucl. Phys. 15, 438 (1972) refers to Gribov stuff. I think I use [7] to refer to this