Periodic Reporting for period 2 - COLORFREE (High-Precision Global Analysis of Color-Free LHC Processes at Small Recoil)
Période du rapport: 2023-04-01 au 2024-09-30
The Large Hadron Collider (LHC) is the world’s largest and most powerful particle accelerator. Situated at CERN, the European Organization for Nuclear Research, it collides protons at the highest currently possible energies. With the large datasets from previous Run 2 and the ongoing Run 3, the precision of LHC measurements will significantly improve over the next years. Colour-free processes (for which the final state of the hard interaction is colour neutral) are of central importance to several high-priority areas of the LHC precision physics programme, e.g. measurements of the W-boson mass, of the couplings of the Higgs boson, and searches for the elusive dark matter particles.
The EU-funded COLORFREE project obtains precise theoretical predictions and combines different colour-free processes in order to unlock the full potential of existing and future precision measurements. The key innovation of COLORFREE is to combine many different colour-free processes into a new type of global analysis in which the dominant theory uncertainties are either eliminated or constrained by the experimental data itself, thereby improving the theoretical precision up to an order of magnitude to the 1-2% level and below.
This is achieved
1) by developing a ground-breaking new method to reliably quantify perturbative theory uncertainties leading to precision theory predictions with built-in uncertainties and correlations, and
2) by developing innovative new effective-field theory methods to account for all effects that are relevant at this precision but have been neglected before.
Important outcomes of COLORFREE are:
1) Determinations of fundamental parameters at the highest possible precision, and stringent tests for possible effects beyond the Standard Model.
2) A new type of precision theory predictions with built-in uncertainties and correlations, which solve a long-standing problem at the interface of theory and experiment. In particular, precision measurements often avoid theory limitations by relying on theory uncertainties to cancel between different control and signal regions, but until now have had no means to reliably quantify the remaining theory uncertainties.
The EU-funded COLORFREE project obtains precise theoretical predictions and combines different colour-free processes in order to unlock the full potential of existing and future precision measurements. The key innovation of COLORFREE is to combine many different colour-free processes into a new type of global analysis in which the dominant theory uncertainties are either eliminated or constrained by the experimental data itself, thereby improving the theoretical precision up to an order of magnitude to the 1-2% level and below.
This is achieved
1) by developing a ground-breaking new method to reliably quantify perturbative theory uncertainties leading to precision theory predictions with built-in uncertainties and correlations, and
2) by developing innovative new effective-field theory methods to account for all effects that are relevant at this precision but have been neglected before.
Important outcomes of COLORFREE are:
1) Determinations of fundamental parameters at the highest possible precision, and stringent tests for possible effects beyond the Standard Model.
2) A new type of precision theory predictions with built-in uncertainties and correlations, which solve a long-standing problem at the interface of theory and experiment. In particular, precision measurements often avoid theory limitations by relying on theory uncertainties to cancel between different control and signal regions, but until now have had no means to reliably quantify the remaining theory uncertainties.
The project work has been carried out in parallel in several directions. In the context of Drell-Yan production, state-of-the-art precision predictions have been obtained for Drell-Yan production at 3rd resummed order, with a systematic treatment of nonperturbative effects based on moment expansions and the inclusion of lattice quantumchromodynamics (QCD) results, a novel consistent treatment of quark flavor thresholds and quark-mass effects, and a groundbreaking new approch for estimating theory uncertainties and correlations using theory nuisance parameters (TNPs). This newly developed method of TNPs has been successfully applied to estimate theoretical uncertainties in the extraction of the strong coupling constant from Drell-Yan mreasurements. The TNP-based predictions have been implemented in the SCETlib C++ library. They have served as the theoretical basis enabling the determination of the W-boson mass by the CMS experiment with the highest precision achieved at the LHC so far. In the context of Higgs production, state-of-the-art resummed predictions have been obtained for the Higgs pT spectrum in quark annihilation and jet-vetoed Higgs+jet production in gluon fusion. The implementations of single Higgs production in gluon fusion, the simultaneous production of two Higgs bosons (di-Higgs production), and W+W- production interfaced to parton showers in the Geneva Monte-Carlo were completed. Other important theory developments include the study of quark mass effects for the first time in the context of quark fragmentation with important implications for the planned electron-ion collider (EIC) as well as detailed investigations on parton distribution functions (PDFs) as an important and nontrivial source of uncertainty in particular for extracting the strong coupling constant and more generally for the planned global fit of colour-free processes.
The above-mentioned predictions for Drell-Yan and Higgs production are the most precise predictions to date, going well beyond the previous state of the art. The successful implementation of theory nuisance parameters (TNPs) can be considered a major breakthrough, demonstrating for the first time the feasibility of correctly accounting for theory correlations and consistently constraining perturbative theory uncertainties in fits to experimental data. The Drell-Yan predictions will be used next for a high-precision determination of the strong coupling constant with reliable perturbative theory uncertainties and a systematic and consistent treatment of nonperturbative and PDF uncertainties. The TNP-based estimation of theory uncertainties and correlations will be extended next to the predictions for Higgs production in gluon-fusion and quark annihilation, which will subsequently be used to determine the Higgs Yukawa couplings from a fit to existing and future measurements of Higgs production.