The size of the proton and the deuteron Pohl, Randolf; Amaro, Fernando D; Antognini, Aldo ...
Journal of physics. Conference series,
01/2011, Letnik:
264, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We have recently measured the 2S1/2F=1 − 2P3/2F 2 energy splitting in the muonic hydrogen atom μp to be 49881.88 (76) GHz. Using recent QED calculations of the fine-, hyperfine, QED and finite size ...contributions we obtain a root-mean-square proton charge radius of rp 0.84184 (67) fm. This value is ten times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of rp 0.8768 (69) fm. The source of this discrepancy is unknown. Using the precise measurements of the 1S-2S transition in regular hydrogen and deuterium and our value of rp we obtain improved values of the Rydberg constant, R 10973731.568160 (16) m−1and the rms charge radius of the deuteron rd 2.12809 (31) fm.
The long quest for a measurement of the Lamb shift in muonic hydrogen is over. Last year we measured the
2S
1/2
F=1
-2P
3/2
F=2
energy splitting (Pohl et al., Nature,
466
, 213 (2010)) in μp with an ...experimental accuracy of 15 ppm, twice better than our proposed goal. Using current QED calculations of the fine, hyperfine, QED, and finite size contributions, we obtain a root-mean-square proton charge radius of r
p
= 0.841 84 (67) fm. This value is 10 times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of r
p
. The origin of this discrepancy is not known. Our measurement, together with precise measurements of the 1S-2S transition in regular hydrogen and deuterium, gives improved values of the Rydberg constant, R
∞
= 10 973 731.568 160 (16) m
-1
and the rms charge radius of the deuteron r
d
= 2.128 09 (31) fm.
The Lamb shift in muonic hydrogen Pohl, Randolf; Antognini, Aldo; Nez, Francois ...
Canadian journal of physics,
01/2011, Letnik:
89, Številka:
1
Journal Article
Recenzirano
The long quest for a measurement of the Lamb shift in muonic hydrogen is over. Last year we measured the energy splitting (Pohl et al., Nature, 466, 213 (2010)) in μp with an experimental accuracy of ...15 ppm, twice better than our proposed goal. Using current QED calculations of the fine, hyperfine, QED, and finite size contributions, we obtain a rootmean-square proton charge radius of r.sub.p = 0.841 84(67) fm. This value is 10 times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of r.sub.p. The origin of this discrepancy is not known. Our measurement, together with precise measurements of the 1S--2S transition in regular hydrogen and deuterium, gives improved values of the Rydberg constant, R.sub.∞ = 10973 731.568160(16) m.sup.-1 and the rms charge radius of the deuteron r.sub.d = 2.128 09 (31) fm.
It is now recognized that the International System of Units (SI units) will be redefined in terms of fundamental constants, even if the date when this will occur is still under debate. Actually, the ...best estimate of fundamental constant values is given by a least-squares adjustment, carried out under the auspices of the Committee on Data for Science and Technology (CODATA) Task Group on Fundamental Constants. This adjustment provides a significant measure of the correctness and overall consistency of the basic theories and experimental methods of physics using the values of the constants obtained from widely differing experiments. The physical theories that underlie this adjustment are assumed to be valid, such as quantum electrodynamics (QED). Testing QED, one of the most precise theories is the aim of many accurate experiments. The calculations and the corresponding experiments can be carried out either on a boundless system, such as the electron magnetic moment anomaly, or on a bound system, such as atomic hydrogen. The value of fundamental constants can be deduced from the comparison of theory and experiment. For example, using QED calculations, the value of the fine structure constant given by the CODATA is mainly inferred from the measurement of the electron magnetic moment anomaly carried out by Gabrielse's group. (Hanneke et al. 2008 Phys. Rev. Lett. 100, 120801) The value of the Rydberg constant is known from two-photon spectroscopy of hydrogen combined with accurate theoretical quantities. The Rydberg constant, determined by the comparison of theory and experiment using atomic hydrogen, is known with a relative uncertainty of 6.6×10−12. It is one of the most accurate fundamental constants to date. A careful analysis shows that knowledge of the electrical size of the proton is nowadays a limitation in this comparison. The aim of muonic hydrogen spectroscopy was to obtain an accurate value of the proton charge radius. However, the value deduced from this experiment contradicts other less accurate determinations. This problem is known as the proton radius puzzle. This new determination of the proton radius may affect the value of the Rydberg constant . This constant is related to many fundamental constants; in particular, links the two possible ways proposed for the redefinition of the kilogram, the Avogadro constant NA and the Planck constant h. However, the current relative uncertainty on the experimental determinations of NA or h is three orders of magnitude larger than the 'possible' shift of the Rydberg constant, which may be shown by the new value of the size of the proton radius determined from muonic hydrogen. The proton radius puzzle will not interfere in the redefinition of the kilogram. After a short introduction to the properties of the proton, we will describe the muonic hydrogen experiment. There is intense theoretical activity as a result of our observation. A brief summary of possible theoretical explanations at the date of writing of the paper will be given. The contribution of the proton radius puzzle to the redefinition of SI-based units will then be examined.
The proton radius puzzle Antognini, A; Amaro, F D; Biraben, F ...
Journal of Physics: Conference Series,
09/2011, Letnik:
312, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
By means of pulsed laser spectroscopy applied to muonic hydrogen (μ− p) we have measured the 2SF 11/2 – 2PF 23/2 transition frequency to be 49881.88(76) GHz 1. By comparing this measurement with its ...theoretical prediction 2, 3, 4, 5, 6, 7 based on bound-state QED we have determined a proton radius value of rp 0.84184(67) fm. This new value differs by 5.0 standard deviations from the COD ATA value of 0.8768(69) fm 8, and 3 standard deviation from the e-p scattering results of 0.897(18) fm 9. The observed discrepancy may arise from a computational mistake of the energy levels in μp or H, or a fundamental problem in bound-state QED, an unknown effect related to the proton or the muon, or an experimental error.
The Lamb-shift experiment in muonic hydrogen (μ
-
p) aims to measure the energy difference between the
atomic levels to a precision of 30 ppm. This would allow the r.m.s. proton charge radius r
p
to ...be deduced to a precision of 10
-3
and open a way to check bound-state quantum electrodynamics (QED) to a level of 10
-7
. The poor knowledge of the proton charge radius restricts tests of bound-state QED to the precision level of about 6 × 10
-6
, although the experimental data themselves (Lamb-shift in hydrogen) have reached a precision of × 10
-6
. Values for r
p
not depending on bound-state QED results from electron scattering experiments have a surprisingly large uncertainty of 2%. In our Lamb-shift experiment, low-energy negative muons are stopped in low-density hydrogen gas, where, following the μ
-
atomic capture and cascade, 1% of the muonic hydrogen atoms form the metastable 2S state with a lifetime of about 1 μs. A laser pulse at λ ≈ 6 μm is used to drive the 2S → 2P transition. Following the laser excitation, we observe the 1.9 keV X-ray being emitted during the subsequent de-excitation to the 1S state using large-area avalanche photodiodes. The resonance frequency and, hence, the Lamb shift and the proton charge radius are determined by measuring the intensity of the X-ray fluorescence as a function of the laser wavelength. The results of the run in December 2003 were negative but, nevertheless, promising. One by-product of the 2003 run was the first observation of the short-lived 2S component in muonic hydrogen. Currently, improvements in the laser-system, the experimental apparatus, and the data acquisition are being implemented. PACS Nos.: 36.10.Dr, 14.20.Dh, 42.62.Fi
By means of pulsed laser spectroscopy applied to muonic hydrogen (μ− p) we have measured the 2S F=1 1/2−2PF=2 3/2 transition frequency to be 49881.88(76) GHz. By comparing this measurement with its ...theoretical prediction based on bound-state QED we have determined a proton radius value of rp=0.84184 (67) fm. This new value is an order of magnitude preciser than previous results but disagrees by 5 standard deviations from the CODATA and the electronproton scattering values. An overview of the present effort attempting to solve the observed discrepancy is given. Using the measured isotope shift of the 1S-2S transition in regular hydrogen and deuterium also the rms charge radius of the deuteron rd=2.12809 (31) fm has been determined. Moreover we present here the motivations for the measurements of the μ 4He+and μ 3He+2S-2P splittings. The alpha and triton charge radii are extracted from these measurements with relative accuracies of few 10−4. Measurements could help to solve the observed discrepancy, lead to the best test of hydrogen-like energy levels and provide crucial tests for few-nucleon ab-initio theories and potentials.
Hydrogen-like light muonic ions, in which one negative muon replaces all the electrons, are extremely sensitive probes of nuclear structure, because the large muon mass increases tremendously the ...wave function overlap with the nucleus. Using pulsed laser spectroscopy we have measured three 2S-2P transitions in the muonic helium-3 ion (\(\mu^3\)He\(^+\)), an ion formed by a negative muon and bare helium-3 nucleus. This allowed us to extract the Lamb shift \(E(2P_{1/2}-2S_{1/2})= 1258.598(48)^{\rm exp}(3)^{\rm theo}\) meV, the 2P fine structure splitting \(E_{\rm FS}^{\rm exp} = 144.958(114)\) meV, and the 2S-hyperfine splitting (HFS) \(E_{\rm HFS}^{\rm exp} = -166.495(104)^{\rm exp}(3)^{\rm theo}\) meV in \(\mu^3\)He\(^+\). Comparing these measurements to theory we determine the rms charge radius of the helion (\(^3\)He nucleus) to be \(r_h\) = 1.97007(94) fm. This radius represents a benchmark for few nucleon theories and opens the way for precision tests in \(^3\)He atoms and \(^3\)He-ions. This radius is in good agreement with the value from elastic electron scattering, but a factor 15 more accurate. Combining our Lamb shift measurement with our earlier one in \(\mu^4\)He\(^+\) we obtain \(r_h^2-r_\alpha^2 = 1.0636(6)^{\rm exp}(30)^{\rm theo}\) fm\(^2\) to be compared to results from the isotope shift measurements in regular He atoms, which are however affected by long-standing tensions. By comparing \(E_{\rm HFS}^{\rm exp}\) with theory we also obtain the two-photon-exchange contribution (including higher orders) which is another important benchmark for ab-initio few-nucleon theories aiming at understanding the magnetic and current structure of light nuclei.
To establish the predictive value of the QRESEARCH risk estimator version 3 (QRISK3) algorithm in identifying Spanish patients with ankylosing spondylitis (AS) at high risk of cardiovascular (CV) ...events and CV mortality. We also sought to determine whether to combine QRISK3 with another CV risk algorithm: the traditional SCORE, the modified SCORE (mSCORE) EULAR 2015/2016 or the SCORE2 may increase the identification of AS patients with high-risk CV disease.
Information of 684 patients with AS from the Spanish prospective CARdiovascular in ReuMAtology (CARMA) project who at the time of the initial visit had no history of CV events and were followed in rheumatology outpatient clinics of tertiary centers for 7.5 years was reviewed. The risk chart algorithms were retrospectively tested using baseline data.
After 4,907 years of follow-up, 33 AS patients had experienced CV events. Linearized rate=6.73 per 1000 person-years (95 % CI: 4.63, 9.44). The four CV risk scales were strongly correlated. QRISK3 correctly discriminated between people with lower and higher CV risk, although the percentage of accumulated events over 7.5 years was clearly lower than expected according to the risk established by QRISK3. Also, mSCORE EULAR 2015/2016 showed the same discrimination ability as SCORE, although the percentage of predicted events was clearly higher than the percentage of actual events. SCORE2 also had a strong discrimination capacity according to CV risk. Combining QRISK3 with any other scale improved the model. This was especially true for the combination of QRISK3 and SCORE2 which achieved the lowest AIC (406.70) and BIC (415.66), so this combination would be the best predictive model.
In patients from the Spanish CARMA project, the four algorithms tested accurately discriminated those AS patients with higher CV risk and those with lower CV risk. Moreover, a model that includes QRISK3 and SCORE2 combined the best discrimination ability of QRISK3 with the best calibration of SCORE2.
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