Project

Back to overview

NNLO calculations for leptons

Applicant Signer Adrian
Number 178967
Funding scheme Project funding
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Theoretical Physics
Start/End 01.10.2018 - 31.03.2022
Approved amount 577'397.00
Show all

All Disciplines (2)

Discipline
Theoretical Physics
Particle Physics

Keywords (4)

Next-to-next-to leading order calculations; Lepton-flavour violation; Regularization schemes; Search for physics beyond the Standard Model

Lay Summary (German)

Lead
Das Hauptziel der Teilchenphysik in den kommenden Jahren ist die Suchenach Physik jenseits des Standard Modells (SM). Das SM istäusserst erfolgreich in der Beschreibung von Prozessen anTeilchenbeschleunigern. Gegenwärtig gibt es jedoch eine Reihe vonMessungen, die nicht vollständig mit den Vorhersagenübereinstimmen. Insbesondere Prozesse mit Leptonen (Elektronen, Myonenund Tau-Leptonen) zeigen interessante Abweichungen. Das Ziel diesesProjektes ist es, die theoretischen Vorhersagen einer Klasse vonProzessen mit Leptonen derart zu verbessern, dass ein präzisererVergleich von Theorie mit Experiment ermöglicht wird.
Lay summary
Das Projekt umfasst zwei Hauptbereiche.

Im ersten Bereich geht es darum, die Zuverlässigkeit der theoretischen
Vorhersage für das anomale magnetische Moment des Myons zu
verifizieren. In dieser Grösse wurde eine mögliche Abweichung vom SM
gemessen.

Um zu klären, ob diese Abweichung tatsächlich durch neue Physik
verursacht wird, muss neben dem experimentellen Fehler auch der
theoretisch Fehler reduziert werden.  Die theoretische Vorhersage von
hadronischen Beiträgen für diese Grösse ist sehr heikel. In einer
verwandten Grösse, der Streuung vom Myonen an Elektronen, können diese
Beiträge unabhängig extrahiert werden. Voraussetzung dazu ist, dass
die restlichen Beiträge sehr präzise berechnet werden. Das Ziel dieses
Projektes ist es, den theoretischen Fehler dieser Berechnung auf 0.001
Prozent zu verbessern.

Der zweite Aspekt des Projektes befasst sich mit seltenen Zerfällen
des Tau-Leptons. In vielen Modellen jenseits des SM ist die
Wahrscheinlichkeit, dass ein solcher Zerfall auftritt, stark
erhöht. Deshalb eignen sich solche Prozesse, um mehr Information über
verschiedene Erweiterungen des SM zu erhalten und gewisse Szenarien
auszuschliessen. Im Rahmen dieses Projektes werden eine grosse Anzahl
von seltenen Tau Zerfällen systematisch analysiert und auf ihre
Kompatibilität mit Physik jenseits des SM überprüft.

Direct link to Lay Summary Last update: 27.07.2018

Responsible applicant and co-applicants

Employees

Publications

Publication
Universal structure of radiative QED amplitudes at one loop
Engel T., Signer A., Ulrich Y. (2022), Universal structure of radiative QED amplitudes at one loop, in Journal of High Energy Physics, 2022(4), 97-97.
Møller scattering at NNLO
Banerjee Pulak, Engel Tim, Schalch Nicolas, Signer Adrian, Ulrich Yannick (2022), Møller scattering at NNLO, in Physical Review D, 105(3), L031904-L031904.
Bhabha scattering at NNLO with next-to-soft stabilisation
Banerjee Pulak, Engel Tim, Schalch Nicolas, Signer Adrian, Ulrich Yannick (2021), Bhabha scattering at NNLO with next-to-soft stabilisation, in Physics Letters B, 820, 136547-136547.
May the four be with you: novel IR-subtraction methods to tackle NNLO calculations
Torres Bobadilla W. J., Sborlini G. F. R., Banerjee P., Catani S., Cherchiglia A. L., Cieri L., Dhani P. K., Driencourt-Mangin F., Engel T., Ferrera G., Gnendiger C., Hernández-Pinto R. J., Hiller B., Pelliccioli G., Pires J., Pittau R., Rocco M., Rodrigo G., Sampaio M., Signer A., Signorile-Signorile C., Stöckinger D., Tramontano F., Ulrich Y. (2021), May the four be with you: novel IR-subtraction methods to tackle NNLO calculations, in The European Physical Journal C, 81(3), 250-250.
QED at NNLO with McMule
Banerjee Pulak, Engel Tim, Signer Adrian, Ulrich Yannick (2020), QED at NNLO with McMule, in SciPost Physics, 9(2), 027-027.
Global Fit to Modified Neutrino Couplings and the Cabibbo-Angle Anomaly
Coutinho Antonio M., Crivellin Andreas, Manzari Claudio Andrea (2020), Global Fit to Modified Neutrino Couplings and the Cabibbo-Angle Anomaly, in Physical Review Letters, 125(7), 071802-071802.
handyG—Rapid numerical evaluation of generalised polylogarithms in Fortran
Naterop L., Signer A., Ulrich Y. (2020), handyG—Rapid numerical evaluation of generalised polylogarithms in Fortran, in Computer Physics Communications, 253, 107165-107165.
Theory for muon-electron scattering @ 10 ppmA report of the MUonE theory initiative
Banerjee P., Carloni Calame C. M., Chiesa M., Di Vita S., Engel T., Fael M., Laporta S., Mastrolia P., Montagna G., Nicrosini O., Ossola G., Passera M., Piccinini F., Primo A., Ronca J., Signer A., Torres Bobadilla W. J., Trentadue L., Ulrich Y., Venanzoni G. (2020), Theory for muon-electron scattering @ 10 ppmA report of the MUonE theory initiative, in The European Physical Journal C, 80(6), 591-591.
A subtraction scheme for massive QED
Engel T., Signer A., Ulrich Y. (2020), A subtraction scheme for massive QED, in Journal of High Energy Physics, 2020(1), 85-85.
Charged lepton flavour violating processes
Signer Adrian (2019), Charged lepton flavour violating processes, in SciPost Physics Proceedings, (1), 014-014, SciPost Foundation, Amsterdam(1), 014-014.
Small-mass effects in heavy-to-light form factors
Engel T., Gnendiger C., Signer A., Ulrich Y. (2019), Small-mass effects in heavy-to-light form factors, in Journal of High Energy Physics, 2019(2), 118-118.

Collaboration

Group / person Country
Types of collaboration
Pavia, Profs Montagna, Piccinini, Carloni Calame Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
TU Dresden, Prof Stöckinger Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Pisa Prof A.Papa Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Strong2020 Workshop Talk given at a conference Monte Carlo developments towards NNLO 24.11.2021 Rome / Zoom, Italy Ulrich Yannick; Signer Adrian; Engel Tim; Banerjee Pulak;
ILC Workshop on Potential Experiments Talk given at a conference High precision QED calculations 26.10.2021 Tokyo / Zoom, Japan Signer Adrian;
MUonE Collaboration Meeting Talk given at a conference Towards an NNLO Monte Carlo for MUonE 12.02.2020 CERN, Switzerland Signer Adrian; Ulrich Yannick;
Work- Stop/ThinkStart 3.0: paving the way to alternative NNLO strategies Talk given at a conference The FKS^2 subtraction scheme: status and future 04.11.2019 GGI Florence, Italy Engel Tim; Signer Adrian; Banerjee Pulak; Ulrich Yannick;
PSI 2019 Talk given at a conference High-precision QED prediction for low-energy lepton experiments 21.10.2019 PSI Villigen, Switzerland Signer Adrian; Ulrich Yannick; Engel Tim;


Use-inspired outputs

Software

Name Year
McMule 2020


Associated projects

Number Title Start Funding scheme
160156 Lepton flavour violation in an effective-field theory approach with dimension 6 operators 01.04.2015 Project funding
163466 Muon Decays 01.11.2015 Project funding
193383 Hadronic Corrections to Muon Anomalies 01.10.2020 Ambizione
207386 Precision calculations for lepton scattering 01.04.2022 Project funding

Abstract

With the completion of the Standard Model (SM) through the discoveryof the Higgs boson, particle physics has reached a very peculiarpoint. On the one hand we have an extremely successful theory that isable to explain all (?) data from collider and low-energy precisionexperiments. On the other hand, we know that the theory cannot becomplete, as it fails to explain e.g. the abundance of matter overantimatter, neutrino masses, dark matter and dark energy.Hence, the main thrust of particle physics in the coming years is tosearch for deviations from the SM that can be produced in laboratoryexperiments, using high-energy colliders and low-energy precisionmeasurements. In fact, some rather intriguing hints for possibledeviations from the SM have been reported already (hence the questionmark above). There are some indications of possible lepton-flavouruniversality (LFU) violations from $B$~decays and there is a longstanding discrepancy between theory and experiment for the anomalousmagnetic moment of the muon, $a_\mu$. This project contributes to thescrutiny of these hints, focussing on leptonic processes. It followstwo lines.First, computational techniques are developed and adapted to calculateprocesses at next-to-next-to leading order (NNLO) in quantumelectrodynamics (QED). In particular a completely differentialcalculation of the muon decay at NNLO will be performed for a masslessand a massive electron. The corresponding phase-space integration willbe analysed in different regularization schemes and the relationbetween the massive and massless results as well as resummation oflarge logarithms will be studied. The project also contributessubstantially to the international effort of computing muon-electronscattering at NNLO. The main motivation for this is to extract theleading hadronic contribution to $a_\mu$.Second, the project is concerned with searches for physics beyond theSM related to processes with charged lepton-flavour violation(LFV). The connection to LFU makes this more topical than ever. Themain focus will be on a systematic analysis of LFV in taudecays. Apart from a detailed phenomenological investigation thisinvolves the calculation of some selected two-loop anomalous dimensionswithin an effective field theory approach that parametrizes newphysics in a model independent way. The possibility to find some lightnew particles like dark photons using very precisely measured andcalculated observables with muons will also be investigated.
-