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Precision jet physics from effective field theory

English title Precision jet physics from effective field theory
Applicant Becher Thomas
Number 153294
Funding scheme Project funding
Research institution Institut für Theoretische Physik Universität Bern
Institution of higher education University of Berne - BE
Main discipline Theoretical Physics
Start/End 01.04.2014 - 31.03.2016
Approved amount 250'442.00
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Keywords (7)

effective field theory; particle physics; quantum chromodynamics; collider physics; soft-collinear effective theory; resummations of perturbation theory; large hadron collider

Lay Summary (German)

Lead
Um die Daten, welche der Large Hadron Collider (LHC) am CERN sammelt, zu interpretieren und darin nach Spuren von neuartigen Teilchen und Wechselwirkungen zu suchen, braucht es präzise theoretische Vorhersagen für die Streuprozesse, welche bei Teilchenkollisionen auftreten. Solche Vorhersagen sind wichtig, weil schwere, neue Teilchen innert kürzester Zeit wieder in leichte, bekannte Teilchen zerfallen. Die Effekte neuer Physik sind deshalb in der Regel nur indirekt nachweisbar, als Abweichung einer Messung von den theoretischen Vorhersagen im Rahmen des Standard Modells der Teilchenphysik. Prozesse an Hochenergiebeschleunigern können mittels Störungsrechnung näherungsweise berechnet werden, in einer systematischen Entwicklung in der Stärke der Wechselwirkungen zwischen den Teilchen.
Lay summary

Das vorliegende Projekt entwickelt neue Methoden, um genauere Vorhersagen für Streuprozesse am LHC zu erhalten, insbesondere für Probleme bei denen mehrere, verschiedene physikalische Skalen relevant sind. In solchen Fällen sind Korrekturen durch grosse Logarithmen des Verhältnisses der verschiedenen Skalen erhöht. Diese Sudakovlogarithmen können zu einem Zusammenbruch der Störungsrechnung führen. Um Vorhersagen auch für solche Fälle zu erhalten, wird im Rahmen des Projekts eine effektive Quantenfeldtheorie benutzt, um die Physik bei verschiedenen Skalen zu trennen. Im Rahmen dieser Soft-Kollinearen Effektiven Theorie (SCET) können Sudakovlogarithmen mittels Renormierungsgruppen-Methoden summiert werden. Ziel des Projektes sind einerseits präzisere Vorhersagen für einige fundamentale Prozesse, wie etwa die Produktion von Higgs-Bosonen, und andererseits die Weiterentwicklung der Methode auf komplexere Prozesse, insbesondere auf solche, welche Jets von stark wechselwirkenden Teilchen im Endzustand aufweisen. 

Direct link to Lay Summary Last update: 01.04.2014

Responsible applicant and co-applicants

Employees

Publications

Publication
An Effective Field Theory for Jet Processes
Becher Thomas, Neubert Matthias, Rothen Lorena, Shao Ding Yu (2016), An Effective Field Theory for Jet Processes, in Physical Review Letters, 116(19), 192001.
Automated NNLL  $$+$$ +  NLO resummation for jet-veto cross sections
Becher Thomas, Frederix Rikkert, Neubert Matthias, Rothen Lorena (2015), Automated NNLL  $$+$$ +  NLO resummation for jet-veto cross sections, in The European Physical Journal C, 75(4), 154.
Introduction to Soft-Collinear Effective Theory
Becher Thomas, Broggio Alessandro, Ferroglia Andrea (2015), Introduction to Soft-Collinear Effective Theory, Springer International Publishing, Cham.
Enhanced nonperturbative effects through the collinear anomaly
Becher Thomas, Bell Guido (2014), Enhanced nonperturbative effects through the collinear anomaly, in Phys.Rev.Lett., 112(18), 182002-182002.
The transverse-momentum spectrum of Higgs bosons near threshold at NNLO
Becher Thomas, Bell Guido, Lorentzen Christian, Marti Stefanie (2014), The transverse-momentum spectrum of Higgs bosons near threshold at NNLO, in JHEP, 1411, 026-026.
Transverse-momentum spectra of electroweak bosons near threshold at NNLO
Becher Thomas, Bell Guido, Lorentzen Christian, Marti Stefanie (2014), Transverse-momentum spectra of electroweak bosons near threshold at NNLO, in JHEP, 1402, 004-004.

Collaboration

Group / person Country
Types of collaboration
Prof. M. Neubert/Universität Mainz Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Dr. G. Bell/University of Oxford Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. M. Schwartz/Harvard University United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Dr. B. Pecjak/IPPP, Durham U. Great Britain and Northern Ireland (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
Rencontres de Moriond - QCD and High Energy Interactions Talk given at a conference Theoretical summary talk 19.03.2016 La Thuile, Italy Becher Thomas;
Threshold Logarithms Beyond Leading Power Talk given at a conference An Effective Theory for Jet Processes 25.01.2016 Edinburgh, Great Britain and Northern Ireland Becher Thomas;
Aspen Winter Conference on Particle Physics on the Verge of Another Discovery? Talk given at a conference Resummation and SCET 11.01.2016 Aspen, United States of America Becher Thomas;
QCD@LHC 2015 Talk given at a conference Automated NNLL+NLO Resummation for Jet-Veto Cross Sections 01.09.2015 London, Great Britain and Northern Ireland Rothen Lorena;
Parton Showers, Event Generators and Resummation (PSR15) Talk given at a conference Progress in SCET 26.05.2015 Krakau, Poland Becher Thomas;
MIT Individual talk NNLL Resummation for Transverse Thrust 18.03.2015 Cambridge, United States of America Becher Thomas;
Harvard University Individual talk Momentum Modes in SCET — and a Strategy to Avoid Double Counting 11.03.2015 Cambridge, United States of America Becher Thomas;
QCD@LHC 2014 Talk given at a conference The transverse-momentum spectra of electroweak and Higgs bosons near threshold at NNLO 25.08.2014 Suzdal, Russia Marti Stefanie;
LoopFest XIII: Radiative Corrections for the LHC and Future Colliders Talk given at a conference Resummation for W/Z/H production at large and small p_T 18.06.2014 New York, United States of America Becher Thomas;


Associated projects

Number Title Start Funding scheme
165786 Precision jet physics from effective field theory 01.04.2016 Project funding
140978 Precision collider physics from effective field theory 01.04.2012 Project funding

Abstract

To fully exploit the potential of the LHC, in particular of the upcoming run with higher energy and luminosity, it is important to develop new methods to increase the accuracy of the theoretical predictions. Our project focuses on processes which are sensitive to soft and collinear emissions. For such observables, higher-order corrections are enhanced by large logarithms of the ratio of the collision energy over the scales associated with the soft and collinear radiation. The factorization of the physics associated with the different scales and the resummation of the enhanced contributions can be performed in the framework of Soft-Collinear Effective Theory (SCET). The goal of our project is twofold. On the one hand, we will increase the accuracy of some key collider observables by resumming logarithmically enhanced terms to all orders. On the other hand we will attack an outstanding theoretical problem which limits the applicability of higher-log resummations to a fairly restricted class of observables. The specific processes we will study are Higgs and diboson production with a jet veto, W and Z production at large transverse momentum and jet broadening, an event shape variable. The theoretical problem we will investigate as part of this project are so-called non-global logarithms.An example of observables with enhanced higher-order corrections are cross sections in the presence of a jet veto. They play an important role for the Higgs measurement in the WW and the \tau\tau channels because the background composition is quite different in different if energetic jets are present and most of the signal arises in the zero-jet case. The same is true in the search for anomalous gauge couplings in the weak boson pair production (WW, WZ, W photon, etc.), where the large NLO corrections to the tree-level process make it impossible to search for anomalous gauge couplings without a jet veto. Imposing a jet veto induces a small scale into these processes and leads to enhanced higher-order corrections. In the past two years, there has been a lot of progress in the theoretical treatment of such veto processes, but there are still open questions and uncertainties relating to terms enhanced by logarithms of the jet radius. In addition to improving the predictions for Higgs production with a jet veto, we also want to apply the resummation to weak-boson pair production as part of our project.The factorization theorems for transverse momentum dependent variables, such as p_T spectra of electroweak bosons, jet veto cross sections, or jet broadening suffer from a collinear anomaly which generates additional dependence on the hard momentum scale in the collinear and soft parts of the process. This collinear anomaly should also affect the structure of non-perturbative power corrections. As part of our project, we will study the enhancement of power corrections in jet broadening due to the anomaly and will then use our precise resummed results for this observable to perform an extraction of the strong coupling constant from a fit to the precise data available for this event-shape observable. We have recently improved the prediction for W and Z production at large transverse momentum in two ways. First of all, we have computed the threshold cross section at NNLO, which includes the full NNLO virtual corrections as well as soft and collinear real-emission corrections. Secondly, we have computed electroweak Sudakov effects in the spectrum. As a final step, we will now perform a detailed phenomenological analysis of the process, including both QCD and electroweak effects. An important limitation for the all-order resummation of logarithmically enhanced contribution is the fact that existing methods only work for global observables, i.e. observables which are sensitive to emissions everywhere in phase space. In practice, no measured observable is completely global, in particular at hadron colliders where radiation close to the beam directions is not measured and the observables are thus not sensitive to radiation at high rapidities. For non-global observables, additional logarithmically enhanced contributions arise, so called non-global logarithms, which are not resummed by the usual soft-collinear factorization. This effect has been discovered quite some time ago, but beyond the large N_c limit it is currently still not known how to resum such contributions. In our project, we will investigate such logarithms in the context of SCET. As a first step, we will develop an efficient method to compute non-global logarithms, based on the strategy of region expansion technique. In a second step, we will then try to construct an operator formulation of these effects with an appropriate version of SCET. Such an operator formulation would naturally lead to evolution equations which could then be used to resum such contributions to all orders.
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