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Precision calculations for lepton scattering

Applicant Signer Adrian
Number 207386
Funding scheme Project funding
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Theoretical Physics
Start/End 01.04.2022 - 31.03.2026
Approved amount 838'219.00
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All Disciplines (2)

Discipline
Theoretical Physics
Particle Physics

Keywords (5)

Quantum electrodynamics; Three-loop effects; Next-to-next-to leading order calculations; Resummation; Electroweak corrections

Lay Summary (German)

Lead
Neben dem Elektron gibt es mit dem Myon und Tau-Lepton zwei weitereelektrisch geladene Leptonen, die sich durch eine grösserer Masseunterscheiden. Insbesondere Prozesse mit Elektronen und Myonen könnenmit grosser Genauigkeit gemessen werden und bilden ein wichtigesStandbein in der Suche nach subtilen Effekten jenseits desStandarmodells der Teilchenphysik.Leptonische Prozesse werden hauptsächlich durch die elektromagnetischeund die schwache Wechselwirkung beeinflusst. Diese Wechselwirkungensind im Prinzip gut verstanden, aber die benötigte Präzision in dentheoretischen Vorhersagen erfordert anspruchsvolle technischeBerechnungen, die oft nur durch das Entwickeln neuer Methoden zubewerkstelligen sind.
Lay summary
Das Hauptziel dieses Projektes ist es, die theoretischen Vorhersagen
solcher Prozesse deutlich zu verbessern und die Resultate durch ein
flexibes, öffentlich zugängliches Computer Programm aufzubereiten.
Dieses Program erlaubt die präzise Berechnung von beliebigen den
Experimenten angepassten Grössen. Dadurch wird ein direkter Vergleich
von Messung und Vorhersage im Standarmodell ermöglicht und die Suche
nach potenziellen kleinen Abweichungen erleichtert.

Insbesondere werden Elektron-Myon Streuung sowie Elekton-Elektron
(Moller) und Elektron-Positron (Bhabha) Streuung mit neuartiger
Genauigkeit implementiert. Für letztere Prozesse werden auch Effekte
der schwachen Wechselwirkung berücksichtigt.


Am Paul Scherrer Institut werden weltweit führende Experimente der
Teilchenphysik mit Myonen gemacht. Dieses Projekt liefert Theorie
Support für diese Forschung und trägt bei zur ganzheitlichen Suche
nach Effekten jenseits des Standardmodells der Teilchenphysik.

Direct link to Lay Summary Last update: 07.04.2022

Responsible applicant and co-applicants

Employees

Project partner

Associated projects

Number Title Start Funding scheme
178967 NNLO calculations for leptons 01.10.2018 Project funding

Abstract

Progress in particle physics relies on ever more precise comparisonsof experimental data with theoretical predictions of the StandardModel (SM) of particle physics. In many cases perturbativecalculations in quantum field theory are the most important tool toobtain theoretical predictions. A huge program is under way toimprove such calculations for processes at the energy frontier, mostnotably for processes dominated by the strong interactions describedthrough quantum chromodynamics (QCD), but comparatively little theorysupport is available for perturbative calculations of leptonicscattering and decay processes, often dominated by quantumelectrodynamics (QED). This proposal focuses on improving theoretical calculations forprocesses at the high-intensity and low-energy frontier where leptonsin general and muons in particular play a fundamental role. In fact,in recent years several processes involving electrons, muons, and taushave led to tensions between the SM theory and experimentaldata. Thus, scrutinising the interactions of muons is arguably one ofthe most promising paths towards discovering new physics. With thisproposal we will boost the theory support for this program.For processes involving leptons, QED is the dominant interaction. Withincreasing energy, also electroweak effects become important. Throughthis proposal the theoretical description of such processes areimproved by including perturbative corrections within QED atnext-to-next-to leading order (NNLO). Where necessary, this iscombined with electroweak corrections. It will also be investigated onhow to go beyond NNLO by including dominant contributions at evenhigher orders, either through analytic computations or through a fullynumerical approach. This will lead to an unprecedented precision forsome particularly important processes, like muon-electron scattering,Bhabha scattering or Moller scattering.In many aspects QED is a simpler theory than QCD and within thisproject the progress that has been made for QCD calculations will befully exploited. However, in QED much more detailed aspects of thefinal state are investigated than in QCD. One important aspect is thatnearly collinear final-state photon radiation off charged leptonsresults in observable large logarithmic corrections in physicalquantities. This leads to a class of problems that is specific tosuch QED computations and requires targeted solutions. All results obtained through this project will be implemented in thepublicly available Monte Carlo code McMule (Monte Carlo for MUonsand other LEptons). This code will be further developed into a verybroad tool, also including effects of physics beyond the SM. Thelatter will be described either through simplified models or throughan effective-field-theory approach. All together, this provides theorysupport for in-house experiments with muons at the Paul ScherrerInstitut and similar facilities world wide at an entirely newlevel. On the high-energy side, state-of-the-art calculations will beperformed for processes used for luminosity measurements atelectron-positron colliders, such as a future circular collider FCC-eeor a linear collider ILC.
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