2. The agenda of the meeting was reviewed and accepted.

Transcription

1 Report on the Meeting of the CODATA Task Group on Fundamental Constants 18 May 2000, Sydney, Australia Prepared by Peter Mohr and Barry Taylor National Institute of Standards and Technology The subject meeting was held during the year 2000 Conference on Precision Electromagnetic Measurements (CPEM) in Sydney, Australia. In attendance were the following. Task Group members: F. Cabiati, T. Endo, P. Mohr, W. Martienssen, B. Taylor. Task Group member representatives: H. Bachmair for W. Wöger, J. Flowers for B. Petley. Observers: K.-I. Fujii (Japan), U. Keyser (Germany) Z. Lu (P. R. China), L. Pendrill (Sweden) M. Tanaka (Japan), X. Zhang (P. R. China). The agenda of the meeting is attached and the following discussion is numbered according to the corresponding agenda items. 1. The meeting opened at about 6:00 pm, and introductions were made. It was noted that Rumin Liu (P. R. China) had retired from NIM and the Task Group since the meeting one year ago. Also, Werner Martienssen of the University of Frankfurt, Germany was welcomed as a new member of the Task Group. 2. The agenda of the meeting was reviewed and accepted. 3. The report of the previous meeting, held on 8 July 1999, was reviewed. The review of some of the details on preparation of the manuscript of the least-squares adjustment and the work in progress was deferred to the appropriate agenda items that followed. Two typographical corrections to the report were noted. One was in item 7. (iii), muonic helium. should be muonic hydrogen. The other in item 7. (vii), µ e /µ p should be µ e /µ p. 4. The publication of the adjustment of the constants was reviewed. As planned at the previous meeting of the Task Group, the 1998 values of the fundamental constants were made available on the World Wide Web soon after that meeting at the URL physics.nist.gov/constants. The actual release date was 23 July 1999, and an update with minor changes in conventions and corrections was made available on 3 December The convention change was to list properties of the negative muon and tau particle rather than of those of the positive antiparticles, which had the effect of changing the signs of some values of the associated constants. The positive particles were originally listed because they were the ones involved in the most precise experiments (particularly for the muon). However, comments from the community suggested that it would be more consistent to list properties of the primary particles rather than 1

2 those of the antiparticles. In each of three numbers in the tables of values related to the Rydberg constant, the last digit was corrected and shifted by 1. The version history of the Web site lists in detail all of the changes in the 3 December release. More recently, on 27 April 2000, the bibliographic database at the URL physics.nist.gov/constantsbib was updated to include all of the references cited in the 1998 least-squares adjustment article, as well as many others, for a total of 2518 citations. The article on the least-squares adjustment, CODATA Recommended Values of the Fundamental Physical Constants: 1998, by Mohr and Taylor, was submitted to the Journal of Physical and Chemical Reference Data (JPCRD) and the Reviews of Modern Physics (RMP) on 24 September It has recently appeared in print in JPCRD and should soon appear in RMP. The long period between submission and publication was due in part to a number of technical problems in the production, which required about three versions of proofs. One problem was the fact that the journals were not set up to deal with non-italic Greek letters. In the initial proof, all Greek letters were set in italic font. This was corrected and necessitated the purchase of new fonts by the journal. Also, in some cases author lists in references were truncated with the introduction of et al., which led to ambiguities in the citations. The RMP version of the article was produced by the same publisher (AIP), so it was possible for RMP to start with the final electronic version of the JPCRD article. Thus all corrections in the proofs as well as the errata were included in the starting document for RMP. In addition, RMP made some changes of a purely stylistic nature. For example, the sections are labeled with Arabic numbering in JPCRD and with Roman numbering in RMP, and there were some changes in the author list truncation conventions and citation ordering. JPCRD includes a list of tables and figures and RMP does not. Apart from such formal changes, the technical content of the articles is the same. Changes in the content of the article since the last Task Group meeting are as follows. Section 6.2, Some Implications for Physics and Metrology of the 1998 CODATA Recommended Values and Adjustment, was added. The figure with results of experiments on G was modified to have open circles for the preliminary results and filled circles for final results. Standard reference error bars were not included in the figures. The sections from Hyperfine structure to Other Quantities ( ) in the Review of Data section were completed. With regard to Eq. (351) in Other Quantities, the value quoted in the paper for sine squared of the weak mixing angle is based on the onshell scheme. This is the value used in the theoretical calculations quoted in our paper, but is not the most accurate value recommended by the Particle Data Group (PDG), as noted in the text. Our recommended value for the anomalous magnetic moment of 2

3 the muon is based on the theoretical expression primarily. In response to comments by the BNL group currently measuring this quantity, we emphasized this fact in the text in the discussion surrounding Eq. (368). Appendix E, Method of Least Squares, and Appendix F, Use of the Covariance Matrix, were finalized. The most significant changes were made in Appendix E with the addition of historical background near the beginning of the section and a discussion of the justification for the formulation used for the adjustment, including the treatment of covariances, following Eq. (E15). Both the matrix formulation used and the justification based on making the most accurate predictions follow from the work of Aitken from In the manuscript, equations, cross references, and references were checked by us and confirmed with help from Jonathan Baker, a theoretical physicist at NIST at the time. 5. Other publications on the recommended values were discussed. (a) The CODATA Special Report discussed last year is not likely to materialize. Instead, the JPCRD article will serve as the CODATA Report. A limited number (500) of reprints are in the hands of the CODATA Secretariat for distribution. (b) The August 2000 annual Physics Today Buyer s Guide will publish a short article on the constants together with tables of most of the values. (Physics Today is the magazine received by members of the American Physical Society.) This article has been submitted. (c) An article focusing on the physics of the adjustment has been invited for publication in Physics Today in the Spring of 2001, in conjunction with the 100 year anniversary of the founding of NIST. (d) The Particle Data Group will include some of the CODATA recommended values of the constants in their review of particle properties. (e) The Chemical Rubber Handbook will quote new values of constants based on the CODATA recommended values. (f) Production of wall charts (22 cm 28 cm) with the fundamental constants on one side and a periodic table of the elements on the other side is planned. (g) Production of wallet cards with the recommended values of the fundamental constants is planned. 5. Information on work in progress relevant to the next adjustment was discussed. (a) A measurement of h/m( 133 Cs) in progress at Stanford University could provide a precise value of the fine structure constant α. There have been problems with 3

4 systematic effects that are not yet understood, and the time scale for a result is unknown. (b) A new atomic mass compilation by Audi and Wapstra is in progress, and may be available soon. (c) Measurements of the 1S 2S transition in H at Garching have improved. Hänsch gave a talk at a recent APS meeting in Long Beach, California where he reported a value with a relative standard uncertainty of , or 22 Hz. He expects to reach a relative uncertainty of in about 2 years and has stability at the level of His new and old frequency combs agree to However, the usefulness of this single transition for the Rydberg constant is limited by uncertainty in the proton radius and two-photon theoretical contributions. (d) A measurement of the proton charge radius, from frequency measurements on muonic hydrogen atoms, is in progress at PSI, Switzerland. (e) A measurement of the 1S 3S transition at the LKB/LPTF in Paris is in progress. (f) Progress in measurement of the electron magnetic moment anomaly is expected from both the University of Washington, Seattle, and Harvard University, but there are no new results. (g) The theory of the electron anomalous magnetic moment is being improved by Kinoshita, but there is no new result since the adjustment. (h) Measurements of µ e /µ h and µ e/µ p are in progress at NPL, England. (i) Further measurements of R at BNL are in progress for the determination of the muon magnetic moment anomaly. Marginal improvements in the theory have been made. (j) Improved determinations of the Planck constant from watt balance experiments are in progress at NPL, NIST, and OFMET (Switzerland). (k) Measurements of the silicon molar volume have become consistent, except for the NRLM result. There is presently no evidence for voids in the NRLM crystals. (l) Helium fine-structure measurements are progressing with work by several groups. The ultimate precision of the measurements could provide a value of the finestructure constant α that is competitive with the value from the electron anomalous magnetic moment. However, the theory is not sufficiently precise, and while there has been progress, it will be some time before theory catches up to experiment. (m) Measurement of the Stefan-Boltzman constant σ is in progress at NPL. 4

5 (n) Single electron tunneling may eventually become a new source of competitive values of the fine structure constant α. (o) Penning trap mass spectrometer measurements at the University of Washington, Seattle, have improved. The measurements are at the level of a relative precision of For example, van Dyck quoted a value for the relative atomic mass of deuterium at the APS meeting in Long Beach, California, with an uncertainty about three times smaller than the value employed in the 1998 adjustment. (p) A new measurement of R K based on a calculable capacitor at the BNM-LCIE was reported with a relative uncertainty of The status of measurements of G. On 1 May, 2000, at the APS meeting in Long Beach, California, there was a session devoted to measurements of G in which three new experiments (as well as two speculative future experiments) were described. An experiment at the University of Washington, Seattle, based on the perturbation of a flat plate by masses rotating around it, has led to a preliminary value of (9) m 3 kg 1 s 2. A new experiment, based on displacement of hanging masses, with an anticipated relative uncertainty of to 10 4 is being done at JILA. The anticipated time scale is approximately 2 or more years. An experiment is being done by a group at the University of California, Irvine, based on time of swing. The anticipated relative precision is 10 5 with an expected time scale of about 1 year. A session at the CPEM meeting on the day after the Task Group meeting had presentations by the groups at MSL, BIPM, University of Zurich, the University of Wuppertal, the University of California at Irvine, and JILA. (At this session two results from the BIPM were reported: (14) m 3 kg 1 s 2 and (9) m 3 kg 1 s 2 from experiments based on the compensation method and the fixed deflection method, respectively.) 7. The Task Group was in agreement that there should be adjustments of the constants made at regular intervals, both to stay up-to-date and so that the community could know when to expect new adjustments. The appropriate period should be 4 years. There is a possibility that in a shorter time, a new recommendation for the value of G only could be made. It could be a new value or the same value with a reduced uncertainty, provided the results of experiments that will soon be final generally agree with each other and with previous results (except the PTB result). In such a case, it would be deemed no longer necessary to take the PTB result into account when deciding on an uncertainty of the recommended value. 5

6 8. The possibility of expanding the scope and number of constants was considered. It was mentioned that astronomical constants might be of interest for future adjustments. Task Group members were invited to make specific suggestions, and to provide background information on suggested constants. New constants to consider could be completely new or simply new functions of constants already included in the adjustment. 9. There was no other new business. 10. The next Task Group meeting will be held at the BIPM sometime around June or July of The exact date will be determined in the Fall of 2000, when dates for various CIPM consultative committee meetings are set. If at all possible, the date will be selected to be close in time to another meeting where some Task Group members will be in attendance. 11. The meeting was adjourned at about 9:50 pm. 6