SciPost Submission Page
Modelling the underlying event in photon-initiated processes
by Jon Butterworth, Ilkka Helenius, Juan Jose Juan Castella, Bradley Pattengale, Shahzad Sanjrani, Matthew Wing
Submission summary
| Authors (as registered SciPost users): | Matthew Wing |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202409_00015v1 (pdf) |
| Date submitted: | 2024-09-12 19:09 |
| Submitted by: | Wing, Matthew |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Experimental, Computational, Phenomenological |
Abstract
Modelling the underlying event in high-energy hadronic collisions is important for physics at colliders. This includes lepton colliders, where low-virtuality photons accompanying the lepton beam(s) may develop hadronic structure. Similarly, photon-induced collisions also occur in proton or heavy-ion beam experiments. While the underlying event in proton-proton collisions has been the subject of much study at the LHC, studies of hadronic-photon-induced underlying event are now of increasing interest in light of planned future lepton and lepton-hadron colliders, as well as the photon-induced processes in ultra-peripheral collisions at the LHC. Here we present an investigation of the underlying event in photon-initiated processes, starting from the \pythia models used to describe LHC and Tevatron data, and revisiting HERA and LEP2 data. While no single tune describes all the data with different beam configurations, we find that a good agreement can still be found within the same model by adjusting the relevant parameters separately for $\gamma\gamma$, $\gamma p$ and $pp$. This suggests that the basic model of multiparton interaction implemented in \pythia can be applied for different beam configurations. Furthermore, we find that a reasonable agreement for $\gamma\gamma$ and $\gamma p$ data, and for $pp$ data at an LHC reference energy, can be found within a single parametrization, but $pp$ collisions would prefer a stronger energy dependence, leading to too many multiparton interactions in lower energy photon-induced collisions. On this basis, we make some recommendations for simulations of photon-induced processes, such as $\gamma \gamma$ events at the LHC or FCC and $ep$ or $eA$ collisions at the EIC, and suggest possibilities for improvements in the modelling.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
Reports on this Submission
Strengths
1- important first step towards a consistent treatment of the underlying event/multi-parton interactions in preparation for the upcoming EIC and for photon physics at the LHC
2- timely
3- well written
Weaknesses
1- none
Report
This is an extremely well written clear paper with interesting results. It is important to pick up the issue of multi-parton interactions in processes with resolved photons, i.e. in processes, where the hadronic structure of the photon becomes experimentally visible and - quite often - dominant.
A first attempt to systematically scrutinise the Pythia model and to elucidate tensions between different data for processes with incoming protons and/or photons and parameters of the model will certainly pave the way for further studies. The observed tensions indicate a clear preference for some scaling laws etc. and it is not inconceivable that further studies may, possibly, highlight issues with the model itself.
I therefore recommend publication of the paper.
Requested changes
1- none
Recommendation
Publish (surpasses expectations and criteria for this Journal; among top 10%)