20 research outputs found
Limits on a gravitational field dependence of the proton-electron mass ratio from H2 in white dwarf stars.
Spectra of molecular hydrogen (H2) are employed to search for a possible proton-to-electron mass ratio (μ) dependence on gravity. The Lyman transitions of H2, observed with the Hubble Space Telescope towards white dwarf stars that underwent a gravitational collapse, are compared to accurate laboratory spectra taking into account the high temperature conditions (T∼13 000  K) of their photospheres. We derive sensitivity coefficients Ki which define how the individual H2 transitions shift due to μ dependence. The spectrum of white dwarf star GD133 yields a Δμ/μ constraint of (-2.7±4.7stat±0.2syst)×10(-5) for a local environment of a gravitational potential ϕ∼10(4) ϕEarth, while that of G29-38 yields Δμ/μ=(-5.8±3.8stat±0.3syst)×10(-5) for a potential of 2×10(4) ϕEarth.This work was supported by the FOM-Program \Bro-
ken Mirrors & Drifting Constant", Science and Technol-
ogy Facilities Council, Templeton Foundation and Aus-
tralian Research Council (DP110100866).This is the accepted manuscript. The final version is available from APS at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.123002
Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra
Theories unifying gravity with other interactions suggest spatial and
temporal variation of fundamental "constants" in the Universe. A change in the
fine structure constant, alpha, could be detected via shifts in the frequencies
of atomic transitions in quasar absorption systems. Recent studies using 140
absorption systems from the Keck telescope and 153 from the Very Large
Telescope, suggest that alpha varies spatially. That is, in one direction on
the sky alpha seems to have been smaller at the time of absorption, while in
the opposite direction it seems to have been larger.
To continue this study we need accurate laboratory measurements of atomic
transition frequencies. The aim of this paper is to provide a compilation of
transitions of importance to the search for alpha variation. They are E1
transitions to the ground state in several different atoms and ions, with
wavelengths ranging from around 900 - 6000 A, and require an accuracy of better
than 10^{-4} A. We discuss isotope shift measurements that are needed in order
to resolve systematic effects in the study. The coefficients of sensitivity to
alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis
Precision measurements and test of molecular theory in highly excited vibrational states of H2 (v = 11)
Search for cosmological mu variation from high redshift H2 absorption; a status report
Observations of H2 spectra in the line-of-sight of distant quasars may reveal
a variation of the proton-electron mass ratio mu=m_p/m_e at high redshift,
typically for z>2. Currently four high-quality systems (Q0347-383, Q0405-443,
Q0528-250 and J2123-005) have been analyzed returning a constraint Dmu/mu < 1 x
10^{-5}. We present data and a mu-variation analysis of another system,
Q2348-011 at redshift z_{abs}=2.42, delivering dmu/mu = (-1.5 \pm 1.6) x
10^{-5}. In addition to observational data the status of the laboratory
measurements is reviewed. The future possibilities of deriving a competitive
constraint on Dmu/mu from the known high-redshift H2 absorbers is investigated,
resulting in the identification of a number of potentially useful systems for
detecting mu-variation.Comment: 13 Pages, 4 Figures, JENAM conference (Lisbon); accepte
Quantum cascade laser frequency stabilisation at the sub-Hz level
Quantum Cascade Lasers (QCL) are increasingly being used to probe the
mid-infrared "molecular fingerprint" region. This prompted efforts towards
improving their spectral performance, in order to reach ever-higher resolution
and precision. Here, we report the stabilisation of a QCL onto an optical
frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and
10-14, respectively. The comb is stabilised to a remote near-infrared
ultra-stable laser referenced to frequency primary standards, whose signal is
transferred via an optical fibre link. The stability and frequency traceability
of our QCL exceed those demonstrated so far by two orders of magnitude. As a
demonstration of its capability, we then use it to perform high-resolution
molecular spectroscopy. We measure absorption frequencies with an 8x10-13
relative uncertainty. This confirms the potential of this setup for ultra-high
precision measurements with molecules, such as our ongoing effort towards
testing the parity symmetry by probing chiral species
High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level
Recently we reported a high-precision optical frequency measurement of the (v, L): (0, 2)→ (8, 3) vibrational overtone transition in trapped deuterated molecular hydrogen (HD+) ions at 10 mK temperature. Achieving a resolution of 0.85 parts-per-billion (p.p.b.), we found the experimental value [ν0 = 383, 407, 177.38 (41) MHz] to be in agreement with the value from molecular theory [νth 383, 407, 177.150 (15) MHz] within 0.6 (1.1) p.p.b. (Biesheuvel et al. in Nat Commun 7:10385, 2016). This enabled an improved test of molecular theory (including QED), new constraints on the size of possible effects due to ‘new physics,’ and the first determination of the proton–electron mass ratio from a molecule. Here, we provide the details of the experimental procedure, spectral analysis, and the assessment of systematic frequency shifts. Our analysis focuses in particular on deviations of the HD+ velocity distribution from thermal (Gaussian) distributions under the influence of collisions with fast ions produced during (laser-induced) chemical reactions, as such deviations turn out to significantly shift the hyperfine-less vibrational frequency as inferred from the saturated and Doppler-broadened spectrum, which contains partly unresolved hyperfine structure