UTfit

UTfit
Name	UTfit
Type	Research collaboration
Focus	Flavour physics, CKM matrix, global fits
Established	2000s
Headquarters	Europe
Members	International physicists

UTfit

UTfit is an international collaboration of particle physicists that performs global analyses of flavour observables to constrain the parameters of the Cabibbo–Kobayashi–Maskawa framework. It combines experimental results from collider experiments and flavour factories with theoretical inputs from lattice calculations and effective field theories to produce probability distributions for quark-mixing parameters. UTfit contributions are widely cited alongside results from other groups working on global fits and flavour phenomenology.

Overview

The collaboration focuses on determinations of the Unitarity Triangle within the Cabibbo–Kobayashi–Maskawa matrix framework using inputs from experiments such as Large Hadron Collider, LHCb experiment, ATLAS experiment, CMS experiment, Belle experiment, Belle II, BaBar experiment, and facilities including CERN, SLAC National Accelerator Laboratory, KEK and Fermilab. UTfit integrates theoretical computations from groups such as HPQCD, Fermilab Lattice and MILC collaborations, ETM Collaboration, RBC-UKQCD, and model-building work by individuals affiliated with institutions like INFN, Università di Roma La Sapienza, University of Barcelona, Universität Zürich, and Universidad Autónoma de Madrid.

History and Collaboration

The project emerged in the context of precision flavour physics efforts that include historical milestones such as measurements from the CLEO experiment, analyses influenced by the discovery of CP violation in K meson decays, and theoretical developments following the proposal of the Cabibbo angle and Kobayashi–Maskawa mechanism. UTfit formed through collaboration among researchers connected to universities and institutes like Università di Bari, CERN, Università di Napoli Federico II, Università di Pisa, Università di Roma Tor Vergata, Università di Padova, Universidad de Santiago de Compostela, Universidad de Valencia, Universiteit van Amsterdam, Sorbonne University, and Universität Heidelberg. The group interacts with experimental collaborations including NA62 experiment, KOTO experiment, CLEO-c, and participates in workshops hosted by organizations such as IHEP, IPPP Durham, Les Houches, Moriond, and the European Physical Society.

Methodology and Statistical Framework

UTfit employs Bayesian and frequentist statistical techniques adapted from literature associated with analyses by groups like the CKMfitter Group and methods developed in statistical physics and inference applied in particle phenomenology. It uses likelihood construction informed by inputs from decay-rate measurements at KEKB, angular analyses from LHCb experiment, mixing parameters from CDF experiment, and time-dependent CP asymmetries measured by Belle experiment and BaBar experiment. The framework relies on theoretical inputs from Heavy Quark Effective Theory, Chiral Perturbation Theory, and lattice Quantum Chromodynamics results from collaborations such as MILC Collaboration, HPQCD, ETM Collaboration, and RBC-UKQCD. UTfit integrates constraints from rare processes studied by NA62 experiment and KOTO experiment, radiative decays explored by BaBar experiment and Belle experiment, and electroweak parameters measured at LEP and Tevatron experiments like DØ experiment.

Key Results and Contributions

UTfit has produced probability density functions for parameters such as the apex of the Unitarity Triangle and has provided constraints on angles related to CP violation including measurements associated with processes like B0–B0bar mixing and decays mediated by b → sγ and b → sℓ+ℓ− transitions. The collaboration’s fits are used to compare the Standard Model expectations to potential signals of new physics scenarios including models invoking Minimal Flavor Violation, Supersymmetry, Two-Higgs-Doublet Model, Z′ bosons, and effective operators in Standard Model Effective Field Theory. UTfit outputs complement global electroweak fits performed by groups associated with Particle Data Group and connect with searches documented by collaborations such as ATLAS experiment and CMS experiment. The results have informed interpretations of anomalies reported by LHCb experiment, comparisons with lattice inputs from Fermilab Lattice and MILC collaborations, and assessments of constraints on CKM elements like |Vub| and |Vcb| relevant to works by Heavy Flavor Averaging Group.

Software and Tools

Analyses use dedicated fitting software developed within the collaboration, integrating statistical libraries and numerical packages popular in high-energy physics such as ROOT (software), BAT (Bayesian Analysis Toolkit), and custom code written in languages often used at institutions like CERN and SLAC National Accelerator Laboratory. The group utilizes lattice-data repositories maintained by groups like RBC-UKQCD and MILC Collaboration, and cross-checks with phenomenology tools and Monte Carlo generators developed by communities around Pythia, Herwig, EvtGen, and perturbative toolkits used at DESY and Fermilab. UTfit engages with platforms for public dissemination and comparison such as databases curated by the Particle Data Group and global-fit visualization efforts presented at conferences including EPS-HEP and ICHEP.

Collaborations and Impact on Particle Physics

UTfit collaborates with experimenters from LHCb experiment, Belle II, ATLAS experiment, CMS experiment, and lattice theorists from HPQCD, Fermilab Lattice and MILC collaborations, ETM Collaboration, and RBC-UKQCD. The group’s constraints have influenced model-building at institutions like CERN Theory Department, IPPP Durham, IAS Princeton, and research published in journals associated with societies such as the American Physical Society. UTfit outputs are cited in global interpretations that include results from Tevatron, LEP, low-energy experiments like KOTO experiment and NA62 experiment, and inform future projections for upgrades at facilities including High-Luminosity Large Hadron Collider and proposed machines like the Future Circular Collider and International Linear Collider.

Category:Particle physics collaborations