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J. Michael Roney

Publications and source records attributed to J. Michael Roney.

7 recordsLinked to original sources
arXiv2025

Left-right asymmetry calculation comparisons and projected sensitivity to the weak mixing angle in polarized Bhabha scattering at 10.58 GeV

Consideration is being given to upgrading the SuperKEKB electron-positron collider with the introduction of electron-beam polarization. This would enable a unique precision electroweak physics program that opens new ways to search for physics beyond the Standard Model. The upgrade would enable Belle II to make a number of high precision measurements, one of which is the left-right cross-section asymmetry in the $e^+e^-\rightarrow e^+e^-$ Bhabha scattering process. The expected level of precision in such a measurement will require the theoretical values of the asymmetry to be calculated at least to the next-to-leading order (NLO) level, and the implementation of simulation event generators with a similar level of precision. In this study, we compare the calculations of the ReneSANCe Monte Carlo generator with those of an independent NLO calculation to determine the level of agreement in this process. A 2.3% difference between the calculations is found and attributed to some higher-order effects being accounted for in the ReneSANCe generator. Using the published Belle II efficiency for selecting Bhabha events and assuming a 40 ab$^{-1}$ dataset having 70% polarization, the projected uncertainty on the weak mixing angle, sin$^2θ_W$ , is calculated using ReneSANCe to be $\pm$0.00032 or better. Combining this with left-right asymmetry measurements from muons and taus under the assumption of lepton universality yields a projected overall uncertainty of $\pm$0.00019 on sin$^2θ_W$ with SuperKEKB upgraded to have polarized electron beams.

hep-ph↗
arXiv2022

Towards testing the magnetic moment of the tau at one part per million

If physics beyond the Standard Model (BSM) explains the $4.2σ$ difference between the Standard-Model and measured muon anomalous magnetic moment, $a_μ$, minimal flavor violation predicts a shift in the analog quantity for the $τ$ lepton, $a_τ$, at the $10^{-6}$ level, and even larger effects are possible in generic BSM scenarios such as leptoquarks. We show that this produces equivalent BSM deviations in the Pauli form factor, $F_2(s)$, at $s=(10\,\text{GeV})^2$, and report the first complete two-loop prediction of $\text{Re}\, F_2^\text{eff}(100\,\text{GeV}^2)=-268.77(50)\times 10^{-6}$ for resonant $τ$-pair production in $e^+e^-\rightarrow Υ(nS) \rightarrow$ $τ^+τ^-$, $n=1,2,3$. $\text{Re}\, F_2^\text{eff}$ can be measured from $e^-$-helicity-dependent transverse and longitudinal asymmetries in $τ$-pair events, which requires a longitudinally polarized $e^-$ beam. We discuss how Belle II asymmetry measurements could probe $a_τ^\text{BSM}$ at $10^{-6}$, assuming such a polarization upgrade of the SuperKEKB $e^+e^-$ collider, and conclude by outlining the next steps to be taken in theory and experiment along this new avenue for exploring realistic BSM effects in $a_τ$.

hep-ph↗
arXiv2021

Measurements of Beam Backgrounds in SuperKEKB Phase 2

The high design luminosity of the SuperKEKB electron-positron collider will result in challenging levels of beam-induced backgro\ unds in the interaction region. Understanding and mitigating these backgrounds is critical to the success of the Belle~II experi\ ment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKE\ KB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also repor\ t on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions f\ rom synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds origina\ ting from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV elect\ ron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds for\ ward and conclude it is safe to install the Belle II vertex detector.

physics.ins-det↗
arXiv2019

Electroweak Physics with Polarized Electron Beams in a SuperKEKB Upgrade

Consideration is being given to upgrading the SuperKEKB e$^+$e$^-$ collider with polarized electron beams, which would open a new program of precision electroweak physics at a centre-of-mass energy of 10.58GeV, the mass of the $Υ(4S)$. These measurements include $\sin^2θ_W$ obtained via left-right asymmetry measurements of e$^+$e$^-$ transitions to pairs of electrons, muons, taus, charm and b-quarks. The precision obtainable at SuperKEKB will match that of the LEP/SLC world average and will thereby probe the neutral current couplings with unprecedented precision at a new energy scale sensitive to the running of the couplings. At SuperKEKB the measurements of the individual neutral current vector coupling constants to b-quarks and c-quarks and muons in particular will be substantially more precise than current world averages and the current 3$σ$ discrepancy between the SLC A$_{LR}$ measurements and LEP A$_{FB}^b$ measurements of $\sin^2θ_W^{eff}$ will be addressed. This paper will include a discussion of the necessary upgrades to SuperKEKB. This program opens an exciting new window in searches for physics beyond the Standard Model.

hep-ex↗
arXiv2012

The Pion-Photon Transition Form Factor and New Physics in the Tau Sector

Recent measurement of the $γγ^\ast$ form factor of the neutral pion in the high $Q^2$ region disagrees with {\em a priori} predictions of QCD-based calculations. We comment on existing explanations, and analyze a possibility that this discrepancy is not due to poorly understood QCD effects, but is a result of some new physics beyond the standard model (SM). We show that such physics would necessarily involve a new neutral light state with mass close to the mass of $π^0$, and with stronger than $π^0$ couplings to heavier SM flavors such as $c$, $τ$, and $b$. It is found that only the coupling to the $τ$ lepton can survive the existing constraints and lead to the observed rise of the pion form factor relative to $Q^{-2}$ at high $Q^2$. We perform numerical fits to data and determine the allowed range of masses and couplings for such new particles. This range of masses and couplings could also reduce or eliminate the tension between the $e^+e^-$ and $τ$ decay determinations of the hadronic vacuum polarization. Dedicated experimental analysis of $τ$ pair production in association with such new states should provide a conclusive test of the new physics hypothesis as an explanation to the pion form factor rise. We also comment on the calculations of the pion form factor in the chiral quark model, and point out a possible dynamical origin of the quark mass scale inferred from the form factor measurement.

hep-ph↗
arXiv2011

Status Report from Tau subgroup of the HFAG

The aim of Tau subgroup of the HFAG is to provide average values of the mass and branching fractions of the tau lepton. Using the branching fractions, we present tests of charged current lepton universality and obtain estimates for |Vus|. We also summarize the status of searches for lepton flavor violating decays of the tau lepton.

hep-ex↗