Robust limit on a varying proton-to-electron mass ratio from a single H₂system

Abstract

Context. The variation of the dimensionless fundamental physical constant μ = m p /m e can be checked through observation of Lyman and Werner lines of molecular hydrogen in the spectra of distant QSOs. Only few, at present four, systems have been used for the purpose providing different results between the different authors. Aims. Our intention is to asses the accuracy of the investigation concerning a possible variation of the fundamental physical constant μ = m p /m e and to provide more robust results. The goal in mind is to resolve the current controversy on variation of μ and devise explanations for the different findings. Methods. The demand for precision requires a deep understanding of the errors involved. Self-consistency in data analysis and effective techniques to handle unknown systematic errors are essential. An analysis based on independent data sets of QSO 0347-383 is put forward and new approaches for some of the steps involved in the data analysis are introduced. In this work we analyse two independent sets of observations of the same absorption system and for the first time we apply corrections for the observed offsets between discrete spectra mainly caused by slit illumination effects. Results. Drawing on two independent observations of a single absorption system in QSO 0347-383 our detailed analysis yields Δμ/μ = (15 ± (9 stat + 6 sys )) × 10 −6 at z abs = 3.025. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of Δμ measurements to ∼300 m s −1 , consisting of roughly 180 m s −1 due to the uncertainty of the absorption line fit and about 120 m s −1 allocated to systematics. Conclusions. Current analyses tend to underestimate the impact of systematic errors. This work presents alternative approaches to handle systematics and introduces methods required for precision analysis of QSO spectra available in the near future.

QSO 0347-383 and the invariance ofmp/mein the course of cosmic time

“…The residuals therein do not take into account the known inaccuracy of the estimated flux error (see Wendt & Molaro 2011;King et al 2011).…”

Fundamental constants and high‐resolution spectroscopy

“…This method has been frequently used in the literature for constraining the variation of µ (see Cowie & Songaila 1995;Levshakov et al 2002;Malec et al 2010;van Weerdenburg et al 2011;Varshalovich & Levshakov 1993;Wendt & Molaro 2011b. However, at present measurements of ∆µ/µ using H 2 is limited to 6 H 2 -bearing DLAs at z ≥ 2.…”

“…The best reported constraints based on a single system being ∆µ/µ = +(0.3 ± 3.7) × 10 −6 reported by King et al (2011) towards Q 0528−250. Among the developments in the field since then we must signal a number of high precision measurements of ∆µ/µ both using UV lines (Malec et al 2010;van Weerdenburg et al 2011;Wendt & Molaro 2011b At z ≤ 1.0 a stringent constraint on ∆µ/µ is obtained using inversion transitions of NH 3 and rotational molecular transitions (Henkel et al 2009;Kanekar 2011;Murphy et al 2008). The best reported limit using this technique is ∆µ/µ = −(3.5 ± 1.2) × 10 −7 (Kanekar 2011).…”

Molecular hydrogen in thezabs = 2.66 damped Lyman-αabsorber towards Q J 0643−5041

“…At present, measurements of ∆µ/µ, using H 2 at z ≥ 2, are limited to six H 2 -bearing DLAs (see Varshalovich & Levshakov 1993;Cowie & Songaila 1995;Levshakov et al 2002;Ivanchik et al 2005;Reinhold et al 2006;Ubachs et al 2007;Thompson et al 2009;Wendt & Molaro 2011Rahmani et al 2013). All these measurements are consistent with ∆µ/µ being zero at the level of 10 ppm.…”

“…Relative shifts between different lines could be an evidence of µ abs µ lab , where µ lab is the laboratory measured value 1 and µ abs is its value at the absorbing system. This method has been used several times in the past (Varshalovich & Levshakov 1993;Cowie & Songaila 1995;Levshakov et al 2002;Ivanchik et al 2005;Reinhold et al 2006;Ubachs et al 2007; Thompson et al 2009;Wendt & Molaro 2011King et al 2011;Rahmani et al 2013). At present, measurements of ∆µ/µ using H 2 have been performed in seven H 2 -bearing DLAs at z > 2 and suggest that ∆µ/µ < 10 −5 at 2 < z < 3.…”