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Topic: General Monthly FCC-ee physics meeting
29-Nov-21 general FCC physics meeting
https://indico.cern.ch/event/1092025/
Maximum participants: 44
[Indico problems throughout the meeting. Problems should be fixed now, and people can access the slides from the agenda]
(1) News (Alain Blondel)
Slides: https://indico.cern.ch/event/1092025/contributions/4592043/attachments/2354946/4018874/news-AB-2021-11-29.pdf
Plenary ECFA meeting on 19 November, see interesting presentations and full agenda at:
https://indico.cern.ch/event/1085137/
FCC layout: Study has converged on 1 baseline layout (and 2 fallback solutions). Circumference at 91.173 km (cf. CDR value of 97km)
- 1 RF point for Z, WW, HZ in separate RF cavities
After an upgrade, the FCC-ee will have two RF stations with RF shared between e+ and e- (same energy gain for e+ and e- at two different places)
- 2 RF points for HZ, tt in same RF cavities
Upcoming events:
- Snowmass 21: https://indico.fnal.gov/category/1098/
- FCC France workshop (Annecy): 30 Nov – 2 Dec: https://indico.in2p3.fr/event/22887
- Lepton-Photon Symposium Manchester: early registration extended till 10 December
- FCC accelerators & beam energy (2 Dec):
https://indico.cern.ch/event/1090005/
- 5th FCC physics, experiments, detector workshop (Liverpool, 7-11 Feb): https://cern.ch/FCCPhysics2022
- FCC Week 2022, Paris, 30-May - 3-June 2022
Q: Is the location for the FCC France workshop finalised?
A: Not yet.
Q: Are the FCC ring parameters likely to change in the future?
A: I think we can assume they are fixed
(2) Summary from ECFA e+e- Generator workshop (Fulvio Piccinini)
Slides: https://indico.cern.ch/event/1092025/contributions/4633792/attachments/2355031/4018888/piccinini.pdf
First topical meeting on generators (9-10 November at CERN):
https://indico.cern.ch/event/1078675/
Software specifically designed for e+e- machines has reached 10^-4 precision level (NNLO)
Very recent developments o?n QED ISR
Discussion on beamstrahlung (relevant for all machines, not only linear ones)
Plan to follow-up with seminar-style, half-day events
(3) Measuring the CP state of tau lepton pairs from Higgs decays at e+e- colliders (Daniel Jeans)
Slides: https://indico.cern.ch/event/1092025/contributions/4599011/attachments/2354638/4018132/FCCee_higgscp.pdf
Precision studies of the Higgs sector, and in particular CPV, are of great interest as a probe to physics beyond SM
Study on prospects for measurement of CP in Yukawa coupling using full simulation at ILC and ILD detector. Work based on two papers:
- Phys.Rev. D98 (2018) no.1, 013007 arXiv:1804.01241 [hep-ex]
- Nucl.Instrum.Meth.A 810 (2016) 51-58 arXiv:1507.01700 [hep-ex]
Tau reconstruction can be tricky, especially if decay products include neutrino(s).
The CP even-odd mixing angle of tau+ tau- from Higgs decay can be determined to 75 mrad ≈ 4.3° at ILC250 (assuming an integrated luminosity of 2 ab^-1). Previous efforts in this channel give a sensitivity of about 20° (e.g. see CMS papers).
IP is one of the most important factors affecting sensitivity.
Scope for further improvement: Better tau reconstruction, polarimeter reco., BG suppression, additional tau decay modes.
Comment: would be useful to extend these studies to different Higgs masses beyond 125 GeV
Q: Re: the significant improvement in the sensitivity of the mixing angle measurement (from to 20° down to ~4°), is there a desired/target sensitivity because of theoretical motivations?
A: Cannot give a numerical answer, but this could be relevant for EWK baryogengesis, CP-violating 2HDMS, etc.
(4) Long-lived light mediators from Higgs boson decays (Biplob Bhattacherjee)
Slides: https://indico.cern.ch/event/1092025/contributions/4608831/attachments/2355168/4019138/Higgs_LLP.pdf
Talk based on recent paper: e-Print: 2111.02437 [hep-ph]
Production of Long-lived scalar mediator from the on-shell decay of Higgs at LHC and 100-TeV FCChh collider.
Dedicated detectors placed far away (Mathusla and CODEX-b) offer sensitivity complementary to that achieved via muon spectrometer: see e.g. plot on pg. 19 comparing performance of MATHUSLA vs CMS.
LLPs tend to be more in forward direction for lower c*tau values when decay is restricted within the muon spectrometer, therefore a forward detector offers better sensitivity for smaller decay lengths.
Proposal of 3 detector designs for dedicated LLP searches at periphery of FCChh collider (DELIGHT).
Q: What would be the background for an LLP process?
A: Very difficult to comment on potential FCChh backgrounds without detailed simulations, but the expectation is that it should be small.
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