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Strong interaction at low energy, flavour physics and the search for new physics

English title Strong interaction at low energy, flavour physics and the search for new physics
Applicant Colangelo Gilberto
Number 149272
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 01.11.2013 - 31.10.2015
Approved amount 352'658.00
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Keywords (6)

CP violation; effective field theories; dispersion relations; chiral perturbation theory; flavour mixing; isospin symmetry breaking

Lay Summary (Italian)

Lead
In fisica delle particelle si cerca da molti anni di scoprire dei segnali di nuova fisica: effetti incompatibili con il "modello standard" delle interazioni fondamentali. Questa ricerca procede lungo due direttrici principali: alta energia e alta precisione. Aumentando l'energia di collisioni ad acceleratori si cercadi produrre nuove particelle, mentre aumentando la precisione nello studio di fenomeni noti, si cercano piccole deviazioni rispetto allepredizioni del modello standard.
Lay summary
Obiettivo di questo progetto è un miglioramento della precisione di
calcoli teorici relativi a osservabili che sono già stati misurati o
che verranno misurati con precisione crescente. Solo con questo
miglioramento sul fronte teorico sarà possibile ottenere la prova
di effetti di nuova fisica da nuove misure sperimentali più precise.
La difficoltà dei calcoli teorici è tutta legata alla presenza
delle cosiddette interazioni forti. Nonostante esista una teoria che
le descrive con successo (la cromodinamica quantistica o QCD), ci è
spesso impossibile calcolare delle grandezze all'interno di questa
teoria con il desiderato livello di precisione. Per questa teoria non
è possibile applicare uno degli strumenti principali e più efficaci
nell'effettuare calcoli in teoria dei campi: la teoria delle
perturbazioni.

Metodi alternativi a questo e che useremo all'interno di questo progetto
sono le teorie di campo effettive, le relazioni di dispersione e i metodi
numerici collegati alla formulazione della QCD su reticolo.

Uno degli obiettivi principali di questo progetto è il miglioramento
dei calcoli del momento magnetico anomalo (detto il g-2) del muone ,
ed in particolare dei contributi adronici a questa grandezza. Recenti
sviluppi sperimentali hanno portato a raggiungere la precisione di
0.6 parti per milione nella misura del g-2 del muone, e si è evidenziata
una differenza rispetto alle predizioni teoriche all'interno del
modello standard di più di tre deviazioni standard. Sul fronte teorico
le difficoltà maggiori e il maggior contributo all'incertezza vengono
dal contributo adronico, ed è su questo che concentreremo i nostri sforzi.

Direct link to Lay Summary Last update: 06.11.2013

Lay Summary (English)

Lead
Since long the particle physics community is trying to findevidence of effects not explained by the "standard model" of particle interactions. This effort is carried out along two main alleys: the high-energy and the high-precision ones. By increasingthe energy of collisions at accelerators one tries to produce new,yet unseen particles. By increasing the precision of measurements of known phenomena one tries to see tiny deviations from what the standard model predicts.
Lay summary

The efforts carried out at the LHC have so far lead to the discovery of the only missing particle in the standard model: the Higgs boson. Signs of completely new particles, however, are still missing.

The goal of this project is to improve the precision of the theoretical calculations of quantities which have been and will be measured with increasing accuracy. Only in this manner one can obtain convincing evidence of new effects from precise experimental measurements. The difficulty of the theoretical calculations lies in the presence of strong interactions -- although we have a theory which we believe describes them exactly (quantum chromodynamics, QCD), often we are not yet able to calculate observables, within this theory, to the desired level of precision.

We will use methods like effective field theories or dispersion relations
and collaborate with colleagues which use the numerical approach to deal
with the strong interactions (lattice QCD).

One of the goals of the project is to improve the evaluation of hadronic
contributions to the gyromagnetic ratio of the muon. This quantity has been
measured with very high accuracy (to about $0.6$ parts per million for
$(g-2)_\mu$) and is different by more than three standard deviations from
what the standard model predicts. The most delicate part of the
standard-model calculations is precisely the hadronic contributions, whose
evaluation we aim to improve.
Direct link to Lay Summary Last update: 06.11.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
A dispersive treatment of Kℓ4 decays
Colangelo Gilberto, Passemar Emilie, Stoffer Peter (2015), A dispersive treatment of Kℓ4 decays, in Eur. Phys. J., C75, 172-172.
Dispersion relation for hadronic light-by-light scattering: theoretical foundations
Colangelo Gilberto, Hoferichter Martin, Procura Massimiliano, Stoffer Peter (2015), Dispersion relation for hadronic light-by-light scattering: theoretical foundations, in JHEP, 09, 074-074.
Light stops, blind spots, and isospin violation in the MSSM
Crivellin Andreas, Hoferichter Martin, Procura Massimiliano, Tunstall Lewis C. (2015), Light stops, blind spots, and isospin violation in the MSSM, in JHEP, 07, 129-129.
Accurate evaluation of hadronic uncertainties in spin-independent WIMP-nucleon scattering: Disentangling two- and three-flavor effects
Crivellin Andreas, Hoferichter Martin, Procura Massimiliano (2014), Accurate evaluation of hadronic uncertainties in spin-independent WIMP-nucleon scattering: Disentangling two- and three-flavor effects, in Phys.Rev., D89(5), 054021-054021.
Dispersive analysis of the pion transition form factor
Hoferichter Martin, Kubis Bastian, Leupold Stefan, Niecknig Franz, Schneider Sebastian P. (2014), Dispersive analysis of the pion transition form factor, in Eur.Phys.J., C74(11), 3180-3180.
Dispersive Approach to Hadronic Light-by-Light
Colangelo Gilberto, Hoferichter Martin, Procura Massimiliano, Stoffer Peter (2014), Dispersive Approach to Hadronic Light-by-Light, in EPJ Web Conf., 80, 00056-00056.
Dispersive approach to hadronic light-by-light scattering
Colangelo Gilberto, Hoferichter Martin, Procura Massimiliano, Stoffer Peter (2014), Dispersive approach to hadronic light-by-light scattering, in JHEP, 1409, 091-091.
Dispersive approach to hadronic light-by-light scattering and the muon ɡ − 2
Stoffer Peter, Colangelo Gilberto, Hoferichter Martin, Procura Massimiliano (2014), Dispersive approach to hadronic light-by-light scattering and the muon ɡ − 2, in EPJ Web Conf., 81, 05026-05026.
Improved predictions for μ→e conversion in nuclei and Higgs-induced lepton flavor violation
Crivellin Andreas, Hoferichter Martin, Procura Massimiliano (2014), Improved predictions for μ→e conversion in nuclei and Higgs-induced lepton flavor violation, in Phys.Rev., D89(9), 093024-093024.
Isospin Breaking Effects in Kℓ4 Decays
Stoffer Peter (2014), Isospin Breaking Effects in Kℓ4 Decays, in Eur.Phys.J., C74, 2749-2749.
New Constraints on Dark Matter Effective Theories from Standard Model Loops
Crivellin Andreas, D'Eramo Francesco, Procura Massimiliano (2014), New Constraints on Dark Matter Effective Theories from Standard Model Loops, in Phys.Rev.Lett., 112, 191304-191304.
Remarks on higher-order hadronic corrections to the muon g-2
Colangelo Gilberto, Hoferichter Martin, Nyffeler Andreas, Passera Massimo, Stoffer Peter (2014), Remarks on higher-order hadronic corrections to the muon g-2, in Phys.Lett., B735, 90-91.
Review of lattice results concerning low-energy particle physics
Aoki Sinya, Aoki Yasumichi, Bernard Claude, Blum Tom, Colangelo Gilberto, Della Morte Michele, Durr Stephan, El-Khadra Aida, Fukaya Hidenori, Horsley Roger, Juttner Andreas, Kaneko Takeshi, Laiho John, Lellouch Laurent, Leutwyler Heinrich, Lubicz Vittorio, Lunghi Enrico, Necco Silvia, Onogi Tetsuya, Pena Carlos, Sachrajda Christopher, Sharpe Stephen, Simula Silvano, Sommer Rainer, van de Water Ruth + three more (2014), Review of lattice results concerning low-energy particle physics, in European Physical Journal C, 74, 2890.
Roy-Steiner equations for piN scattering
Ruiz de Elvira J., Ditsche C., Hoferichter M., Kubis B., Meissner U.G. (2014), Roy-Steiner equations for piN scattering, in EPJ Web Conf., 73, 05002-05002.
The multiple-scattering series in few-nucleon systems
Baru V., Epelbaum E., Hanhart C., Hoferichter M., Kudryavtsev A.E., others (2014), The multiple-scattering series in few-nucleon systems, in EPJ Web Conf., 73, 06005-06005.
Towards a data-driven analysis of hadronic light-by-light scattering
Colangelo Gilberto, Hoferichter Martin, Kubis Bastian, Procura Massimiliano, Stoffer Peter (2014), Towards a data-driven analysis of hadronic light-by-light scattering, in Phys.Lett., B738, 6-12.

Collaboration

Group / person Country
Types of collaboration
FLAG (Flavour Lattice Averaging Group) Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
PD Dr. Bastian Kubis, University of Bonn Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Urs Wenger, ITP, Uni Bern Switzerland (Europe)
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
High-precision QCD at low energy Talk given at a conference Dispersion theory 02.08.2015 Benasque, Spain Colangelo Gilberto;
The 8th International Workshop on Chiral Dynamics 2015 Talk given at a conference Dispersive treatment of the hadronic light-by-light contribution to (g-2)µ 29.06.2015 Pisa, Italy Colangelo Gilberto;
Wuppertaler Physik-Kolloqium Individual talk Hadronische Beitraege zum Myon g-2 22.06.2015 Wuppertal, Germany Colangelo Gilberto;
Graduate school "Particle physics at highest energy and highest precision" Individual talk Dispersive evaluation of the hadronic light-by-light contribution to (g-2)_mu 24.04.2015 Karlsruhe, Germany Colangelo Gilberto;
HICforFAIR Kolloquium Individual talk Dispersive evaluation of the hadronic light-by-light contribution to (g-2)_mu 23.04.2015 Giessen, Germany Colangelo Gilberto;
Hadrons and Hadron Interactions in QCD 2015 - Effective Theories and Lattice Talk given at a conference Determination of the quark mass ratio Q from eta to 3pi 22.02.2015 Kyoto, Japan Colangelo Gilberto;
CHIPP PhD Winter School 2015 Talk given at a conference Nuclear pairing from realistic forces 18.01.2015 Grindelwald, Switzerland Maurizo Stefano;
QCD@Work - International Workshop on QCD - Theory and Experiment Talk given at a conference Hadronic contributions to (g-2)_\mu: a new approach to light-by-light 16.06.2014 Giovinazzo (Bari), Italy Colangelo Gilberto;
13th International Workshop on Meson Production, Properties and Interaction MESON 2014 Talk given at a conference Vortrag: Dispersive Approach to Hadronic Light-by-Light Scattering and the Muon g-2 / Poster: A Dispersive Treatment of Kl4 Decays 29.05.2014 Krakau, Poland Stoffer Peter;
Nuclear and Particle Theory Group Seminar, College of William & Mary Individual talk Dispersive Approach to Hadronic Light-by-Light Scattering 03.04.2014 Williamsburg, United States of America Stoffer Peter;
Massachusetts Institute of Technology, CTP Seminar Individual talk Dispersive Approach to Hadronic Light-by-Light Scattering 02.04.2014 Boston, United States of America Stoffer Peter;
Workshop on Hadronic contributions to the muon anomalous magnetic moment: strategies for improvements of the accuracy of the theoretical prediction Talk given at a conference Dispersive approach to hadronic light-by-light scattering 01.04.2014 Waldhausen Castle near Mainz, Germany Colangelo Gilberto;
Los Alamos National Laboratory, T-2 Nuclear Theory Seminar Individual talk Dispersive Approach to Hadronic Light-by-Light Scattering 20.03.2014 Los Alamos, United States of America Stoffer Peter;
Workshop on Hadronic Probes of Fundamental Symmetries Talk given at a conference Virtual Photon-Photon Scattering and a_μ 06.03.2014 Amherst, United States of America Colangelo Gilberto;
KEK Flavor Factory Workshop (KEK_FF) Talk given at a conference FLAG 2 report 13.02.2014 Tsukuba, Japan Colangelo Gilberto;


Awards

Title Year
Young Scientist Award 2014 of the Professor Heinrich Greinacher Foundation 2014

Associated projects

Number Title Start Funding scheme
163280 Strong interaction at low energy, flavour physics and the search for new physics 01.11.2015 Project funding
137518 Strong interaction at low energy, flavour physics and the search for new physics 01.11.2011 Project funding

Abstract

The LHC has been recently shut down and therewith its first period ofrunning brought to an end. The highlight of the past three years is thediscovery of the Higgs boson, thus completing the experimental confirmationof the Standard Model (SM) in all its building blocks and structure. Adetailed experimental study of the couplings of the Higgs boson to itselfand to the other SM particles is a future goal of the second phase of theLHC and of future accelerators, but from measurements performed so far, itseems that the SM predictions are confirmed at the current level ofprecision. This great success of the LHC and of its experiments has itscounterpart in the lack of any sign of new physics -- not that theexperiments are to blame for this, since they have worked even better thanexpected. Nature has not fulfilled our (presumably too naive) expectationsand presents us with the problem of thinking with a fresh mind aboutpossible extensions of the SM to higher energy scales.There are however a few puzzles which are left unexplained. One of the mostresistant to theoretical and experimental scrutiny remains that of the$(g-2)$ of the muon. While ten years ago the discrepancy betweenmeasurement and SM prediction has been called a ``harbinger of newphysics'', the increased bounds on all beyond-the-Standard-Model (BSM)particles makes the same discrepancy a true puzzle. For example, the``natural'' explanation of the discrepancy within a supersymmetric (SUSY)extension of the SM has now become very problematic because the bounds onthe SUSY particles -- especially those of the first and second generation,which are those needed to explain the $(g-2)_\mu$ puzzle -- are now toohigh. Some of the other puzzles have been generated at the LHC itself, like themeasurement of CP violation in $D$-meson decays, which seems to be higherthan what the SM predicts -- here a cautious formulation of the puzzle(``seems'') is mandatory, because of the difficulty in making a reliable SMprediction. A difficulty which at present we do not even know how to solvein the near or medium-term future.In summary, after the first running phase of the LHC the confirmations ofthe SM have increased both in precision and in number. The fundamentalscalar assumed to be responsible for electroweak symmetry breaking has beendiscovered and the flavour and CP violations observed are all compatiblewith the SM. The possibility that the SM is valid up to a scale much higherthan the TeV, despite naturalness arguments, has now to be considered moreseriously. In any case, we will not have new insights on this fundamentalquestion for the coming three years.The current situation makes it even more urgent to continue to work onreducing hadronic uncertainties in observables where there is an apparentdiscrepancy between measurement and SM prediction which is not yet fullyunderstood. This will be the main goal of this project.
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