Abstract
We have searched for axion-like resonance states by colliding optical photons in a focused laser field (creation beam) by adding another laser field (inducing beam) for stimulation of the resonance decays, where frequency-converted signal photons can be created as a result of stimulated photon-photon scattering via exchanges of axion-like resonances. A quasi-parallel collision system (QPS) in such a focused field allows access to the sub-eV mass range of resonance particles. In past searches in QPS, for simplicity, we interpreted the scattering rate based on an analytically calculable symmetric collision geometry in both incident angles and incident energies by partially implementing the asymmetric nature to meet the actual experimental conditions. In this paper, we present new search results based on a complete parameterization including fully asymmetric collisional geometries. In particular, we combined a linearly polarized creation laser and a circularly polarized inducing laser to match the new parameterization. A 0.10 mJ/31 fs Ti:sapphire laser pulse and a 0.20 mJ/9 ns Nd:YAG laser pulse were spatiotemporally synchronized by sharing a common optical axis and focused into the vacuum system. Under a condition in which atomic background processes were completely negligible, no significant scattering signal was observed at the vacuum pressure of 2.6 × 10−5 Pa, thereby providing upper bounds on the coupling-mass relation by assuming exchanges of scalar and pseudoscalar fields at a 95% confidence level in the sub-eV mass range.
Highlights
The XENON1T experiment recently reported an excess of electron recoil events compared with the defined background level [16]
Focusing on sub-eV ALPs, we have proposed to utilize quasi-parallel collision system (QPS) between two photon pairs with equal energy ω by combining and focusing twocolor lasers along a common optical axis [26] as illustrated in figure 1
The corresponding center-of-mass system (CMS) energy in the QPS is expressed as ECMS = 2ω sin θ, (1.2)
Summary
The polarization information is normally useful for distinguishing whether ALPs are scalar or pseudoscalar fields. Note here that due to the rotating nature of the incident reaction plane in the focused geometry, even if the experimentally prepared linear polarization state is limited to {2}, polarization states defined on individual p1 − p2 planes can contain both {1} and {2} components with different projection weights, resulting in sensitivities to both scalar and pseudoscalar fields. This situation is implemented quantitatively in the vertex factors as follows. This is because vertex factors combining opposite circular polarization states always vanish, counter-intuitively, in both scalar and pseudoscalar exchanges based on eqs. (2.13) and (2.14)
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