Beam-beam effects on the luminosity measurement at LEP and the number of light neutrino species

Voutsinas, Georgios Gerasimos; Pérez, E.; Dam, M.; Janot, P.

doi:10.1016/j.physletb.2019.135068

Cited by 20 publications

(26 citation statements)

References 17 publications

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“…Interestingly, as recently pointed out in Ref. [22], this effect was already present at LEP, where it led to an underestimation of the luminosity measurement by about 0.1%, significantly larger than the originally reported experimental uncertainties.…”

Section: Other Sources Of Systematicsmentioning

confidence: 53%

Challenges for FCC-ee luminosity monitor design

Dam¹

2022

Eur. Phys. J. Plus

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For cross section measurements, an accurate knowledge of the integrated luminosity is required. The FCC-ee physics programme at and around the Z pole sets the ambitious precision goal of $$10^{-4}$$ 10 - 4 on the absolute luminosity measurement and one order of magnitude better on the relative measurement between energy scan points. The luminosity is determined from the rate of Bhabha scattering, $$\mathrm {e^+e^- \rightarrow e^+e^-}$$ e + e - → e + e - , where the final state electrons and positrons are detected in dedicated monitors covering small angles from the outgoing beam directions. The constraints on the luminosity monitors are multiple: (i) they are placed inside the main detector volume only about 1 m from the interaction point; (ii) they are centred around the outgoing beam directions and do not satisfy the normal axial detector symmetry; (iii) their coverage is limited by the beam pipe, on the one hand, and by the requirement to stay clear of the main detector acceptance, on the other; (iv) the steep angular dependence of the Bhabha scattering process imposes a precision on the acceptance limits at about 1 $$\upmu $$ μ rad, corresponding to an absolute geometrical precision of $${\mathcal {O}}(1\,\upmu \text {m})$$ O ( 1 μ m ) on the monitor radial dimensions; and v) the very high bunch-crossing rate of 50 MHz during the Z-pole operation calls for fast readout electronics. Inspired by second-generation LEP luminosity monitors, which achieved an experimental precision of $$3.4 \times 10^{-4}$$ 3.4 × 10 - 4 on the absolute luminosity measurement (Abbiendi et al. in Eur Phys J C 14:373–425, 2000), a proposed ultra-compact solution is based on a sandwich of tungsten-silicon layers. A vigorous R&D programme is needed in order to ensure that such a solution satisfies the more challenging FCC-ee requirements.

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Section: Other Sources Of Systematicsmentioning

confidence: 53%

Challenges for FCC-ee luminosity monitor design

Dam¹

2022

Eur. Phys. J. Plus

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“…In the context of the studies reported here, it has been realised that, despite the smaller charge density of the bunches, the focusing of the leptons emerging from a Bhabha interaction induced by the opposite charge beam was already impacting the luminosity measurement at the LEP collider. This is quantified in a separate paper [19] in which possible corrections of this effect in the absence of an effective collision crossing angle are also outlined.…”

Section: Discussionmentioning

confidence: 99%

Beam-beam effects on the luminosity measurement at FCC-ee

Voutsinas

Pérez

Dam

et al. 2019

J. High Energ. Phys.

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The first part of the physics programme of the integrated FCC (Future Circular Colliders) proposal includes measurements of Standard Model processes in e + e − collisions (FCCee) with an unprecedented precision. In particular, the potential precision of the Z lineshape determination calls for a very precise measurement of the absolute luminosity, at the level of 10 −4 , and the precision on the relative luminosity between energy scan points around the Z pole should be an order of magnitude better. The luminosity is principally determined from the rate of low-angle Bhabha interactions, e + e − → e + e − , where the final state electrons and positrons are detected in dedicated calorimeters covering small angles from the outgoing beam directions. Electromagnetic effects caused by the very large charge density of the beam bunches affect the effective acceptance of these luminometers in a nontrivial way. If not corrected for, these effects would lead, at the Z pole, to a systematic bias of the measured luminosity that is more than one order of magnitude larger than the desired precision. In this note, these effects are studied in detail, and methods to measure and correct for them are proposed.

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“…The Z-pole data at the LEP experiments have been updated recently in ref. [48], based on a sophisticated calculation of the Bhabha cross section, including beam-induced effects [52], for the measurement of the integrated luminosity. The fit is carried out with the HEPfit package [53], which is based on the Markov Chain Monte Carlo provided by the Bayesian Analysis Toolkit (BAT) [54].…”

Section: Jhep08(2020)004mentioning

confidence: 99%

Muon g − 2 and CKM unitarity in extra lepton models

Endo

Mishima

2020

J. High Energ. Phys.

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We investigate the impact of extra leptons on observed tensions in the muon g − 2 and the first-row CKM unitarity. By introducing a new SU(2) L doublet lepton and a SU(2) L triplet lepton, we find that both of the tensions can be explained simultaneously under constraints from electroweak precision observables and Higgs-boson decays. Our model could be tested by measurements of h → µµ at future collider experiments.

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Beam-beam effects on the luminosity measurement at LEP and the number of light neutrino species

Cited by 20 publications

References 17 publications

Challenges for FCC-ee luminosity monitor design

Challenges for FCC-ee luminosity monitor design

Beam-beam effects on the luminosity measurement at FCC-ee

Muon g − 2 and CKM unitarity in extra lepton models

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