Abstract:
Near (${\sim}\,100$ pc) and far (${\sim}\,8.7$ kpc) relative to the Galactic center, the molecular clouds SgrB2(N) and Orion-KL exhibit different values of the fundamental physical constant $\mu=m_{\rm e}/m_{\rm p}$, which is the electron-to-proton mass ratio. Measured frequency difference between the emission lines of methanol (CH$_3$OH), $J_{K_u} \to J_{K_\ell} = 6_3 \to 5_2 A^+$ 542000.981 MHz, $6_3 \to 5_2 A^-$ 542081.936 MHz, and $8_0 \to 7_{-1} E$ 543076.194 MHz, observed with the space observatory Herschel toward SgrB2(N) and Orion-KL corresponds to (Sgr-Ori): $\Delta\mu/\mu = (-3.7 \pm 0.5)\times10^{-7}$ (1$\sigma$ C.L.). At the same time, comparison of the same methanol lines in Orion-KL with laboratory frequencies shows no significant changes in $\mu$ (Ori-lab): $\Delta\mu/\mu = (-0.5 \pm 0.6)\times10^{-7}$, while a comparison between SgrB2(N) and laboratory lines indicates a lower value of $\mu$ near the Galactic center (Sgr-lab): $\Delta\mu/\mu = (-4.2 \pm 0.7)\times10^{-7}$. The reduced value of $\mu$ in SgrB2(N) is not explained by known systematic effects and requires further investigation.
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