SciPost Submission Page
Physics case for low-$\sqrt{s}$ QCD studies at FCC-ee
by David d'Enterria, Pier Francesco Monni, Peter Skands, Andrii Verbytskyi
Submission summary
| Authors (as registered SciPost users): | Andrii Verbytskyi |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/2503.23855v1 (pdf) |
| Date submitted: | April 9, 2025, 5:37 a.m. |
| Submitted by: | Andrii Verbytskyi |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Experimental, Phenomenological |
Abstract
Measurements of hadronic final states in $e^{+}e^{-}$ collisions at centre-of-mass (CM) energies below the Z peak can notably extend the FCC-ee physics reach in terms of precision quantum chromodynamics (QCD) studies. Hadronic final states can be studied over a range of hadronic energies $\sqrt{s_\mathrm{had}} \approx 20\mbox{--}80\,\mathrm{GeV}$ by exploiting events with hard initial- and final-state QED radiation (ISR/FSR) during the high-luminosity Z-pole run, as well as in dedicated short (about one month long) $e^{+}e^{-}$ runs at CM energies $\sqrt{s} \approx 40\,\mathrm{GeV}$ and $60\,\mathrm{GeV}$. Using realistic estimates and fast detector simulations, we show that data samples of about $10^{9}$ hadronic events can be collected at the FCC-ee at each of the low-CM-energy points. Such datasets can be exploited in a variety of precision QCD measurements, including studies of light-, heavy-quark and gluon jet properties, hadronic event shapes, fragmentation functions, and nonperturbative dynamics. This will offer valuable insights into strong interaction physics, complementing data from nominal FCC-ee runs at higher center-of-mass energies, $\sqrt{s} \approx 91, 160, 240,$ and $365\,\mathrm{GeV}$.
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- timely 2- predicts important input for FCC program 3- written clearly, briefly and comprehensively
Report
The authors offer two possible avenues to achieve these data sets at the FCC-ee. One is the usage of events with initial- or final state photon radiation at the dedicated high luminosity run at the Z pole. Reasonable simulation of events shows that selected data sets will contain still well over a billion events at a number of low energy bins of 5 GeV size, which will cover the CM energy range between 20 and 91 GeV. The second avenue would be to have dedicated runs at lower energies. The latter option would clearly benefit from pure data samples that might be easier to compare systematically to existing observables from LEP and other colliders.
Still, the study shows that both avenues should lead to very interesting physics results and would give very important input to understanding QCD effects of various kinds.
Recommendation
Publish (easily meets expectations and criteria for this Journal; among top 50%)
Strengths
2-Two different avenues (ISR/FSR and low energy runs) are explored
Weaknesses
Report
The projections are based on the extrapolation of an L3 paper for the ISR/FSR approach and on a some assumption for the FCC-ee luminosity at low energies. In both cases the sensitivities are assessed merely in terms of the HFS event statistics but no detailed studies involving simulated detector performance have been carried out.
So, I would say this paper is interested for getting a first idea of the sensivity of FCC-ee for QCD studies at intermediate energies but clearly more research using full simulation is necessary to establish the physics case. I would judge that the acceptance criterium "Opens a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work" is met. The paper itself is well written (clarity, level of detail, relevant references, abstract/conclusion, reproducibility ). I therefore recommend publication after the detailed comments below have been considered by the authors.
Requested changes
1-p. 5, Table 2: Are the expected yields at FCC-ee for one experiment, for all for 4 together? This should be clarified.
2-p. 8, last paragraph: Luminosity scales as sqrt(s). As this is a key assumption for the results you present in this section, is there no way to find a more rigorous justification than a 'private communication'?
3-p. 9, first paragraph: It should be added that the time estimate of 1-3 weeks plus 1 week for setup is *for every c.m. energy point*.
Recommendation
Ask for minor revision