TGFC – Past Achievements
Task Group Achievements, 2018-21
In January 2018, a short summary paper and a detailed paper of the CODATA 2017 Special Ajustment of the fundamental constants for the exact values of the Planck constant h, the elementary charge e, the Boltzmann constant k, and the Avogadro constant NA to be considered for the new International System of Units (SI) were published:
An invited presentation titled “The CODATA 2017 Special Adjustment for the revision of the SI” was given at the 2018 Conference for Precision Electromechanical Measurements (CPEM), 9 July, describing how these numbers were determined. These values were adopted as the foundation of the SI by the 26th meeting of the General Conference on Weights and Measures (CGPM) on November 16, 2018 by a unanimous vote of the member states.
During the 2018 meeting of the TGFC held 7 July, 2018 at the Laboratoire national de métrologie et d’essais, Paris, France, the available data and analysis for the 2018 CODATA adjustment of the fundamental constants was discussed. This was a unique adjustment for it was the first with the SI based of the defining constants. The coding and analysis were heavily modified since many of the constants are now exact and others have much smaller uncertainties.
On World Metrology Day, 20 May, 2019, at 12:00 am local time Paris, France, the values of the 2018 CODATA Adjustment of the Fundamental Constants within the new SI were posted on the NIST Fundamental Constants Data Center website:
By late June 2019, the 2018 CODATA adjustment wallet cards were made available for distribution, with the front side showing the defining constants and a subset of fundamental constants that are exact:
The 2019 TGFC meeting was held on 7 October, just before the 24th meeting of the Consultative Committee on Units (CCU) 8 – 9 October, 2019. Discussions focused on newly available input data for the 2018 CODATA adjustment, including new results for the Gravitational constant, a new determination of the fine-structure constant from Caesium recoil measurements, improved hydrogen spectroscopy measurements, and the first inclusion of muonic-hydrogen Lamb shift measurements. The later resolves the discrepancies in the proton charge radius input data that has existed since 2010. The TGFC Co-chairs at that time, David Newell and Krzysztof Pachucki, presented the 2018 CODATA adjustment of the fundamental constants at the 2019 CCU. A manuscript of the 2018 CODATA Adjustment was published in Reviews of Modern Physics and the Journal of Physical and Chemical Reference Data and has been accepted for publication:
The 2020 TGFC meeting was to be held 19 – 20 October, 2020 at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany, but like most all meetings for 2020 was held virtually on 19 October, 2020. Newly available input data for the 2022 CODATA adjustment was discussed, including another determination of the fine-structure constant from Rubidium recoil measurements and the possible inclusion of theoretical determinations of the muon magnetic moment. Major discussions centered on the determinations of relative atomic masses.
The International Committee for Weights and Measures (CIPM) has agreed on a Memorandum of Understanding (MoU) between the BIPM and CODATA. It was signed by Dr Martin Milton, Director of the BIPM and by Dr Simon Hodson, Executive Director of CODATA on 11 October 2021: https://www.bipm.org/en/-/2021-10-11-mou-bipm-codata. Because of the TGFC’s role in the determination of the values of the fundamental constants and in particular the exact values of the defining constants of the revised SI, the CODATA TGFC was an official member of the BIPM’s Consultative Committee for Units (CCU) from 2007 until 2017, when it, along with all other international committees were reclassified as liaisons.
Main Activities to October 2019
The 2019 TGFC meeting will be 7 October, before the 24th meeting of the Consultative Committee on Units (CCU) 8 – 9 October, 2019. TGFC Co-chairs David Newell and Krzysztof Pachucki will present the 2018 CODATA adjustment of the fundamental constants to the CCU.
Challenges or Concerns
No major concerns. The TGFC membership is transitioning to meet the new challenges of determining the best values and uncertainties of the fundamental constants in the revised SI – please see list of members below. Past members Terry Quinn and Barry Taylor are now Emeritus status and we have added Randolf Pohl as a new member. Randolf’s expertise on laser spectroscopy of hydrogenic and muonic systems as they relate to the determination of the proton radius and Rydberg constant are invaluable to us as we perform future adjustments of the fundamental constants and deal with the ‘proton radius puzzle.’
A slight challenge will be identifying the appropriate future venues for the TGFC meetings. On odd years, the meetings have been held at the BIPM in conjunction with CCU meetings and this will continue. On even years, the meetings have been associated with the CPEM conferences due to the importance of the electrical quantities, however this is no longer the case with the revised SI. Venues that has been suggested are the International conference on Precision Physics of Simple Atomic Systems and the Internaitonal Conference on Precision Physics and Fundamental Physical Constants since they cover fields relevant to the constants that need to be determined in the revised SI.
Deliverables by October 2020
The TGFC is presently preparing detailed review articles for Reviews of Modern Physics and Journal of Physical and Chemical Reference Data on the 2018 CODATA adjustment of the fundamental constants.
Task Group Achievements, 2017-18
For the period of 2017 and 2018, the TGFC will have two important deliverables: the 2017 special CODATA adjustment and the 2018 CODATA adjustment of the fundamental constants.
As agreed with the Consultative Committee for Units (CCU), the TGFC will perform a special adjustment in 2017 of all available data for the determination of the values of the defining constants that will be the foundation of the revised International System of Units (SI) that is expected to be adopted in 2018. Due to the timeline for adopting the revised SI, to be considered for the 2017 special CODATA adjustment all relevant input data must be published or accepted for publication by 1 July 2017.
In preparation for the 2017 CODATA Special Adjustment, the TGFC has modified the LSA code and is adding new input data as they become available. Drafts of a summary and a detailed report of the 2017 CODATA special adjustment have been circulated among the TGFC members for input and comments concerning the structure, selection, and treatment of input data. The chair of the TGFC has been in communication with the editors of Metrologia and they are expecting submission of the two completed documents by August 1. It is expected that after critical review, the summary and report will be accepted for publication such that they can be posted and made publicly available before the 23rd CCU meeting 5 – 7 September, 2017.
The next regular CODATA four year cycle adjustment of the fundamental constants will be the 2018 adjustment with a closing date for input data of 31 December, 2018, with the relevant data in publication or preprint form as usual. The results will be made available by 20 May 2019 (World Metrology Day) when the revised SI is to be implemented. The 2018 CODATA adjustment is unique in that it will be the first adjustment of the fundamental constants in the revised SI with much more accurate values for almost all the fundamental constants.
Task Group Activities, 2017-2018
- Closing date for special CODATA adjustment. All relevant input data must have been published or accepted for publication to be considered, 1 July 2017
- Task Group meeting at the BIPM in conjunction with the meeting of the CCU. The TGFC will present the results of the 2017 special CODATA adjustment of the fundamental constants, 4 -7 Sept 2017
- Task Group meeting in conjunction with CPEM 2018 in Paris, France. Discussions will focus on new data for the 2018 CODATA adjustment of the fundamental constants, 7 July 2018
- Closing date for 2018 Codata adjustment of the fundamental constants. All relevant input data must be available in publication or preprint form to be considered, 31 Dec 2018
- The TGFC has recently published the detailed review article on the 2014 CODATA adjustment of the fundamental constants in Reviews of Modern Physics (Rev. Mod. Phys. 88, 035009 (2016) and in the Journal of Physical and Chemical Reference Data (J. Phys. Chem. Ref. Data 45, 043102 (2016)). If the revised SI is adopted in 2018, the 2014 CODATA adjustment of the fundamental constants is unique in that it is the last adjustment in the present SI.
- Using the 2014 values as a template, the TGFC also assisted and advised the Consultative Committee for Units (CCU) during the 22nd meeting of the CCU (15 – 16 June, 2016, BIPM) on the draft resolution 1 adopted by the 105th meeting of the International Committee for Weights and Meaures (CIPM) (October, 2016). In particular, the CIPM agreed with the proposal made by the CCU that the number of digits be kept in the numerical values of the defining constants (i.e. within the relative standard uncertainties from the special 2017 CODATA adjustment of the fundamental constants).
The latest recommended set of constants, called the 2010 LSA, was released early in 2011 on the NIST website (http://pml.nist.gov/cuu/Constants/) and published in 2012 (Mohr et al., Rev. Mod. Phys. 84, 1527 (2012) and Mohr et al., J. Phys. Chem. Ref. Data 41043109 (2012)).
- For 2015
1 – 6 February 2015 – Workshop on the determination of the fundamental constants, Eltville, Germany, Organized by the TGFC.
- For 2014
Task Group updates LSA for CCU/CIPM for CIPM meeting held in November. Update discussed within Task Group by email.
30 August 2014 – Task Group meeting in conjunction with the 2014 Conference on Precision Electromagnetic Measurements, Rio de Janeiro, Brazil. Review new data for upcoming normal 2014 LSA, in particular new watt balance results and isotopic abundance measurements associated with the International Avogadro Project.
3-4 November 2014 – Second 2014 Task Group meeting at the BIPM. Final meeting before closing date for new relevant data for 2014 LSA. Focus on decisions on discrepant data. Special session on data associated with the proton charge radius with invited guest speakers in the research fields of QED, electron-proton scattering, and muonic hydrogen.
Collection of new relevant data, entered into the Fundamental Constants Data Center, in preparation for 2014 LSA
- For 2013
Consultative Committee for Electricity and Magnetism (CCEM) meeting, March 2013. Status report from the Task Group on fundamental constants given by Dr. Barry Wood.
Task Group meeting 10 June, 2013, BIPM. Acceptance of status report to be given to the CCU. Status report focused on relevant data impacting the values and uncertainties of h, e, k and NA since these are the four constants to be defined as exact in the new SI. Results of unofficial LSAs on the values and uncertainties of h, e, k and NA presented.
CCU meeting June, 2013, BIPM. Dr. David Newell represented CODATA and submitted status report. Presentation focused on the history and role of the CODATA TGFC, new data relevant to h, e, k and NA, and discrepant data associated with the proton charge radius.
Selected Working documents
The reports on the meeting of the CODATA Task Group on Fundamental Constants,
from 2000 to 2014 are available in open access here.