We report a new test of quantum electrodynamics (QED) for the w (1s2p 1 P1 → 1s 2 1 S0) X-ray resonance line transition energy in helium-like titanium. This measurement is one of few sensitive to two-electron QED contributions. Systematic errors such as Doppler shifts are minimised in our experiment by trapping and stripping Ti atoms in an Electron Beam Ion Trap (EBIT) and by applying absolute wavelength standards to calibrate the dispersion function of a curved-crystal spectrometer. We also report a more general systematic discrepancy between QED theory and experiment for the w transition energy in helium-like ions for Z > 20. When all of the data available in the literature forZ = 16 − 92 is taken into account, the divergence is seen to grow as approximately Z 3 with a statistical significance on the coefficient that rises to the level of five standard deviations. Our result for titanium alone, 4749.85(7) eV for the w-line, deviates from the most recent ab initio prediction by three times our experimental uncertainty and by more than ten times the currently estimated uncertainty in the theoretical prediction.PACS numbers: 31.30.jf, 12.20.Fv, 34.50.Fa, 32.30.Rj Quantum electrodynamics (QED) is a cornerstone of modern theoretical physics. New activity on this topic has been stimulated by the announcement of a five-sigma inconsistency between a 15 ppm (parts per million) measurement of an atomic transition frequency in muonic hydrogen [1] and independent measurements of the proton size, linked together by QED calculations. The high sensitivity of such a measurement to QED is derived in part from the large mass of the bound lepton which shrinks the orbital radius. Another way to reduce the orbital radius and study magnified QED effects is to measure transitions in highly charged ions of increasing Z. QED processes scale as various powers of Zα and significantly affect the quantum observable, namely transition energies. Moreover, in the high-Z range, some of the perturbative expansions fail, so that theoretical methods very different from those used for hydrogen are required. Since QED treatment of low-Z and high-Z systems are undertaken with significantly different starting points and mathematical techniques, precise measurements for ions in the mid-Z range will guide the long-pursued development of a unified computational methodology with very accurate predictions for the entire domain Z < 100 [2,3].Advances in QED theory have been sufficient that one can go beyond one-lepton systems (either free or bound) and explore the three-body quantum problem to high precision, including the investigation of helium-like * Electronic address: chantler@unimelb.edu.au atomic systems with two electrons bound to a nucleus. Here the two-electron QED contributions that are entirely absent in one-electron systems can be probed and compared to various theoretical formulations. In this work, we report a measurement of the strongest resonant transition 1s2p1 P 1 → 1s 2 1 S 0 in He-like Ti (Ti 20+ ), and present a divergence that is...
Probably not, but it is interesting nevertheless to investigate just how close Cas A might have come to generating such an event. Focusing on the northeast jet filaments, we analyze the polar regions of the recently acquired very deep 1 Ms Chandra X-ray observation. We infer that the so-called "jet" regions are indeed due to jets emanating from the explosion center, and not due to polar cavities in the circumstellar medium at the time of explosion. We place limits on the equivalent isotropic explosion energy in the polar regions (around 2.3 × 10 52 ergs), and the opening angle of the x-ray emitting ejecta (around 7 degrees), which give a total energy in the NE jet of order 10 50 ergs; an order of magnitude or more lower than inferred for "typical" GRBs. While the Cas A progenitor and explosion exhibit many of the features associated with GRB hosts, e.g. extensive presupernova mass loss and rotation, and jets associated with the explosion, we speculate that the recoil of the compact central object, with velocity 330 km s −1 , may have rendered the jet unstable. In such cases the jet rapidly becomes baryon loaded, if not truncated altogether. Although unlikely to have produced a gamma ray burst, the jets in Cas A suggest that such outflows may be common features of core-collapse SNe.
We have measured the absolute polarization of the 2p 6 1 S 0 Ϫ2p 5 ( 2 P 3/2 o )3s͓3/2͔ 2 o magnetic quadrupole transition in Ne-like barium, excited in an electron-beam ion trap at a variety of energies. We find strong evidence for the existence of resonant excitation processes that are not explained by our collisional-radiative calculations even when the polarization arising from impact excitation is included. At energies well away from where the resonances occur, the agreement between experiment and theory is good.
We report new observations of emission line intensity ratios of Fe XVII under controlled experimental conditions, using the National Institute of Standards and Technology electron beam ion trap (EBIT) with a microcalorimeter detector. We compare our observations with collisional-radiative models using atomic data computed in distorted wave and R-matnx approximations, which follow the transfer of the polarization of level populations through radiative cascades. Our results for the intensity ratio of the 2p6 1S0-2p53d 1P1 15.014 Å line to the 2p61S0-2p53d3D 1 15.265 Å line are 2.94 ± 0.18 and 2.50 ± 0.13 at beam energies of 900 and 1250 eV, respectively. These results are not consistent with collisional-radiative models and support conclusions from earlier EBIT work at the Lawrence Livermore National Laboratory that the degree of resonance scattering in the solar 15.014 A line has been overestimated in previous analyses. Further observations assess the intensity ratio of the three lines between the 2p6-2p53s configurations to the three lines between the 2p6-2p523d configurations. Both R-matrix and distorted wave approximations agree with each other and our experimental results much better than most solar and stellar observations, suggesting that other processes not present in our experiment must play a role in forming the Fe XVII spectrum in solar and astrophysical plasmas
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