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Guy Wilkinson

Publications and source records attributed to Guy Wilkinson.

At least 19 recordsLinked to original sources
arXiv2026

First comments on a descoped/staged FCC-ee

In response to its remit, the European Strategy Group (ESG) recommended the electron-positron Future Circular Collider (FCC-ee) as the preferred option for the next flagship collider at CERN; and a descoped FCC-ee as the preferred alternative option (with reduced synchrotron radiation (SR) power, without a run at the $\rm t \bar t$ threshold, and with only two interaction regions) in the event that the preferred option turns out not to be feasible. Upon request of the ESG, a basic comparison of the physics potential of the descoped option with that of the baseline version is presented in this short note. Our first observations about the alternative proposal of a descoped FCC-ee are that (i) the same performance as the baseline, apart from $\rm t \bar t$-run related, is achieved with the longer proposed period of operation; and (ii) the top run remains essential, but can be staged at a later date. The full appraisal of the consequences of descoping and a proposal for the best way to integrate possible staging wherever feasible, and possible improvements, will need further joint studies by the physics and accelerator groups.

hep-ex↗
arXiv2025

The FCC integrated programme: a physics manifesto

The FCC integrated programme comprises an $\rm e^+e^-$ high-luminosity circular collider that will produce very large samples of data in an energy range $88 \le \sqrt{s} \le 365$ GeV, followed by a high-energy $\rm pp$ machine that, with the current baseline plan, will operate at a collision energy of around 85 TeV and deliver datasets an order of magnitude larger than those of the HL-LHC. This visionary project will allow for transformative measurements across a very broad range of topics, which in almost all cases will exceed in sensitivity the projections of any other proposed facility, and simultaneously provide the best possible opportunity for discovering physics beyond the Standard Model. The highlights of the physics programme are presented, together with discussion on the key attributes of the integrated project that enable the physics reach. It is noted that the baseline programme of FCC-ee, in particular, is both flexible and extendable, and also that the synergy and complementarity of the electron and proton machines, and the sharing of a common infrastructure, provides a remarkably efficient, timely and cost-effective approach to addressing the most pressing open questions in elementary particle physics.

hep-ex↗
arXiv2025

Luminosity measurement with the LHCb RICH detectors in Run 3

The LHCb Ring-Imaging Cherenkov detectors are built to provide charged hadron identification over a large range of momentum. The upgraded detectors are also capable of providing an independent measurement of the luminosity for the LHCb experiment during LHC Run 3. The modelling of the opto-electronics chain, the application of the powering strategy during operations, the calibration procedures and the proof of principle of a novel technique for luminosity determination are presented. In addition, the preliminary precision achieved during the 2023 data-taking year for real-time and offline luminosity measurements is reported.

hep-ex↗
arXiv2024

Higgs Factory options for CERN: A comparative study

``All future $e^+e^-$ Higgs factories have similar reach for the precise measurement of the Higgs boson properties.'': this popular statement has often led to the impression that all $\rm e^+e^-$ options are scientifically equivalent when it comes to choosing the future post-LHC collider at CERN. More recently, the concept of sustainability has been added in attempts to rank Higgs factories. A comparative analysis of the data currently available is performed in this note to clarify these issues for three different options: the future circular colliders (FCC), and two linear collider alternatives (CLIC and ILC@CERN). The main observation is as follows. For the precise measurement of already demonstrated Higgs decays (b\=b, $\tau^+\tau^-$, gg, ZZ, WW) and for $\rm H \to c\bar c$, it would take half a century to CLIC and ILC@CERN to reach the precisions that FCC-ee can achieve in 8 years thanks to its large luminosity and its four interactions points. The corresponding electricity consumption, cost and carbon footprint would also be very significantly larger with linear colliders than with FCC-ee. Considering in addition that (i) [...]; (ii) [...]; (iii) [...]; and {\it (iv)} the vast experimental programme achievable with both FCC-ee and FCC-hh is out of reach of linear colliders; it is found that FCC-ee is a vastly superior option for CERN, and the only first step en route to the 100\,TeV hadron collider.

hep-ph↗
arXiv2024

Charming Darwin: the evolution of QCD parameters across different species

We explore the prospects of measurements of spectral moments of inclusive charm decays with BESIII. The rich and uniquely clean data set of charm mesons and baryons at BESIII offers a unique laboratory to study the evolution of Heavy Quark Expansion (HQE) parameters across different charm hadron species and to shed light on the interplay between heavy quark dynamics and light quark effects. The HQE in terms of inverse powers of the heavy meson mass is well-established in beauty decays, however due to the lighter charm mass its applicability to charm remains an open question. To date no determination of the HQE parameters, the kinetic energy, chromomagnetic moment and Darwin terms, has been attempted. A particularly important role here is given to the Darwin and weak annihilation operators, whose values are important to predict lifetimes of heavy hadrons. Using a fast simulation for the BESIII detector response and predictions for spectral moments, we investigate the sensitivity to HQE parameters with today's and possible future data sets. In addition, we discuss the theory challenges for the HQE in charm and the experimental limitations. We further investigate the sensitivity of determining the CKM matrix element $|V_{cs}|$ with inclusive semileptonic charm decays.

hep-ex↗
arXiv2021

Charming synergies: the role of charm-threshold studies in the search for physics beyond the Standard Model

Measurements performed with pairs of charm mesons produced at threshold from the decay of the $\psi(3770)$ resonance are of great value in flavour physics. The quantum correlation that exists between the two mesons allows unique access to strong-phase information, which is essential input to flavour-physics studies conducted in other environments. An excellent example from the BESIII collaboration is a recent determination of the strong-phase difference between $D^0$ and $\bar{D}^0$ mesons in the decay $D^0 \to K^0_S\pi^+\pi^-$, which has enabled recent measurements to be performed of the $C\!P$-violating phase $\gamma$ and $D^0-\bar{D}^0$ oscillations by the LHCb experiment at CERN. These $\psi(3770)$ data, and also those collected just above the thresholds for $D_s^+$ and $\Lambda_c^+$ production, can also be exploited in many other ways that are of benefit to flavour-physics studies. These synergies are reviewed, and the need for larger threshold data samples in the near future is emphasised.

hep-ex↗
arXiv2021

Particle Identification at FCC-ee

Equipping an experiment at FCC-ee with particle identification (PID) capabilities, in particular the ability to distinguish between hadron species, would bring great benefits to the physics programme. Good PID is essential for precise studies in quark flavour physics, and is also a great asset for many measurements in tau, top and Higgs physics. The requirements placed by flavour physics and these other applications are surveyed, with an emphasis on the momentum range over which PID is necessary. Possible solutions are discussed, including classical RICH counters, time-of-flight systems, and d$E$/d$x$ and cluster counting. Attention is paid to the impact on the global detector design that including PID capabilities would imply.

physics.ins-det↗
arXiv2021

Heavy-quark opportunities and challenges at FCC-ee

The abundant production of beauty and charm hadrons in the $5 \times 10^{12}$ $Z^0$ decays expected at FCC-ee offers outstanding opportunities in flavour physics that in general exceed those available at Belle II, and are complementary to the heavy-flavour programme of the LHC. A wide range of measurements will be possible in heavy-flavour spectroscopy, rare decays of heavy-flavoured particles and $C\!P$-violation studies, which will benefit from the low-background experimental environment, the high Lorentz boost, and the availability of the full spectrum of hadron species. This essay first surveys the important questions in heavy-flavour physics, and assesses the likely theoretical and experimental landscape at the turn-on of FCC-ee. From this certain measurements are identified where the impact of FCC-ee will be particularly important. A full exploitation of the heavy-flavour potential of FCC-ee places specific constraints and challenges on detector design, which in some cases are in tension with those imposed by the other physics goals of the facility. These requirements and conflicts are discussed.

hep-ex↗
arXiv2020

Mixing and $CP$ violation in the charm system

In recent years charm physics has undergone a renaissance, one which has been catalysed by an unexpected and impressive set of experimental results from the $B$-factories, the Tevatron and LHCb. The existence of $D^0\bar{D}{}^0$ oscillations is now well established, and the recent discovery of $CP$ violation in $D^0$ decays has further renewed interest in the charm sector. In this article we review the current status of charm-mixing and $CP$-violation measurements, and assess their agreement with theoretical predictions within the Standard Model and beyond. We look forward to the great improvements in experimental precision that can be expected over the coming two decades, and the prospects for corresponding advances in theoretical understanding.

hep-ph↗
arXiv2020

Improved sensitivity to the CKM phase $γ$ through binning phase space in $B^- \to DK^-$, $D \to K^+π^-π^-π^+$ decays

A binning scheme is proposed for $D^0 \to K^+π^-π^-π^+ $ phase space that will improve the sensitivity of a $B^- \to DK^-$ analysis to the angle $γ$ of the Cabibbo-Kobayashi-Maskawa Unitarity Triangle. The scheme makes use of amplitude models recently reported by the LHCb collaboration. Assuming that a four-bin scheme optimised on the models retains a similar sensitivity when applied in data, it is estimated that the statistical uncertainty on $γ$ from the $B$-meson sample so far collected by the LHCb experiment will be as low as 5 degrees. This will be one of the most precise results available for any single decay mode in a $B^- \to D K^-$ measurement. Quantum-correlated $D\bar{D}$ data accumulated by the CLEO-c experiment are analysed to provide first constraints on the coherence factors and average strong-phase differences in the four bins, which are necessary inputs for the measurement. These constraints are compared with the predictions of the model, and consequences for the measurement of $γ$ are discussed.

hep-ex↗
arXiv2019

Polarization and Centre-of-mass Energy Calibration at FCC-ee

The first stage of the FCC (Future Circular Collider) is a high-luminosity electron-positron collider (FCC-ee) with centre-of-mass energy ranging from 88 to 365 GeV, to study with high precision the Z, W, Higgs and top particles, with samples of $5 \times 10^{12}$ Z bosons, $10^8$ W pairs, $10^6$ Higgs bosons and $10^6$ top quark pairs. A cornerstone of the physics program lays in the precise (ppm) measurements of the W and Z masses and widths, as well as forward-backward asymmetries. To this effect the centre-of-mass energy distribution should be determined with the high precision. This document describes the capacity offered by FCC-ee, starting with transverse polarization of the beams around the Z pole and the W pair threshold. A running scheme based on regular measurements of the beam energy by resonant depolarization of pilot bunches, during physics data taking, is proposed. The design for polarization wigglers, polarimeter and depolarizer is outlined. The $e^\pm$ beam energies will be monitored with a relative precision of $10^{-6}$. The centre-of-mass energy is derived subject to further corrections, related to the beam acceleration, synchrotron radiation and beamstrahlung; these effects are identified and evaluated. Dimuon events $e^+e^- \to μ^+ μ^-$, recorded in the detectors, provide with great precision the beam crossing angle, the centre-of-mass energy spread, and the $e^+$ and $e^-$ energy difference. Monitoring methods to minimize absolute error and relative uncertainties are discussed. The impact on the physics measurements is given. A programme of further simulations, design, monitoring and R&D is outlined.

physics.acc-ph↗
arXiv2017

Quantum-correlated measurements of $D\to K^{0}_{\rm S}π^{+}π^{-}π^{0}$ decays and consequences for the determination of the CKM angle $γ$

We perform quantum-correlated measurements of the decay $D \to K^{0}_{\rm S}π^{+}π^{-}π^{0}$ using a data sample corresponding to an integrated luminosity of 0.82 fb$^{-1}$ collected at the $ψ(3770)$ resonance by the CLEO-c detector. The value of the $CP$-even fraction $F_{+}$ is determined to be 0.238 $\pm$ 0.012 $\pm$ 0.012. The strong-phase differences are also measured in different regions of $K^{0}_{\rm S}π^{+}π^{-}π^{0}$ phase space by binning around the intermediate resonances present. The potential sensitivity of the results for determining the CKM angle $γ$ from $B^{\pm} \to D(K^{0}_{\rm S}π^{+}π^{-}π^{0})K^{\pm}$ decays is also discussed.

hep-ex↗
arXiv2017

Quantum-correlated measurements of $D^{0} \to K^{0}_{\rm S}π^{+}π^{-}π^{0}$ and consequences for the determination of $γ$

Quantum-correlated measurements of the decay $D^{0} \to K^{0}_{\rm S}π^{+}π^{-}π^{0}$ are performed using a data sample corresponding to an integrated luminosity of 818 pb$^{-1}$ collected at the $ψ(3770)$ resonance by the CLEO-c detector. Preliminary results are presented for the $CP$-even fraction $F_{+}$ and the strong-phase differences of this decay. The value of $F_{+}$ is measured to be 0.246 $\pm$ 0.018. The strong-phase differences are measured in different regions of $K^{0}_{\rm S}π^{+}π^{-}π^{0}$ phase space by binning around the intermediate resonances present. The potential sensitivity of the results for determining the CKM angle $γ$ from $B^{\pm}~\to~D(K^{0}_{\mathrm S}π^{+}π^{-}π^{0})K^{\pm}$ decay using the data collected by the Belle detector is also shown.

hep-ex↗
arXiv2011

$D^0-\bar{D}^0$ mixing studies with the decays $D^0 \to K^0_S K^\mp π^\pm$

We demonstrate how a time-dependent analysis of the decays $D^0 \to K^0_S K^\mp π^\pm$ can be used to determine the $D^0-\bar{D}^0$ mixing parameter $y$ with a precision that is competitive with established methods. The proposed analysis is an inclusive study which makes use of the measurements of the coherence factor and mean strong phase difference for these decays recently performed by CLEO.

hep-ph↗
arXiv2009

CP-tagged charm decays: relevance, status and prospects

The analysis of quantum-correlated $D-\bar{D}$ decays produced at the $ψ(3770)$ resonance gives unique insight into quantities such as strong-phase differences and coherence factors. Knowledge of these parameters is invaluable for measurements of the CKM-angle $γ$ ($ϕ_3$) in $B \to DK$ decays. Results from CLEO-c analyses performed at the $ψ(3770)$ resonance in a variety of decay channels are reported, and their consequences for the determination of $γ$ is assessed. Future prospects are given for extensions to the present studies.

hep-ex↗
arXiv2009

Godot and the New Physics

A survey is made of selected topics in flavour physics where real progress is expected in the coming half-decade, paying particular attention to those where New Physics signals may appear.

hep-ex↗
arXiv2008

The Charm Renaissance: D-Physics - a Selective Review

For a long time the significance of charm has been overlooked as an important component of the heavy flavour programme. In recent years the balance has been redressed, and charm studies are quite rightly receiving much more attention. This brief review attempts to explain the motives behind this change in perception, focusing on the contribution of charm measurements to precision CKM tests, and the potential that charm has in its own right as a probe of new physics.

hep-ex↗