The Physics Beyond Colliders initiative is an exploratory study aimed at exploiting the full scientific potential of the CERN's accelerator complex and scientific infrastructures through projects ...complementary to the LHC and other possible future colliders. These projects will target fundamental physics questions in modern particle physics. This document presents the status of the proposals presented in the framework of the Beyond Standard Model physics working group, and explore their physics reach and the impact that CERN could have in the next 10-20 years on the international landscape.
This paper describes the 25 year effort to measure vacuum magnetic birefringence and dichroism with the PVLAS experiment. The experiment went through two main phases: the first using a rotating ...superconducting magnet and the second using two rotating permanent magnets. The experiment was not able to reach the predicted value from QED. Nonetheless the experiment has set the current best limits on vacuum magnetic birefringence and dichroism for a field of Bext=2.5 T, namely, Δn(PVLAS)=(12±17)×10−23 and |Δκ|(PVLAS)=(10±28)×10−23. The uncertainty on Δn(PVLAS) is about a factor 7 above the predicted value of Δn(QED)=2.5×10−23 @ 2.5 T.
We present a more stringent upper limit on long-range axion-mediated forces obtained by the QUAX-gpgs experiment, located at the INFN – Laboratori Nazionali di Legnaro. By measuring variations of a ...paramagnetic GSO crystal magnetization with a dc-SQUID magnetometer we investigate the possible coupling between electron spins and unpolarized nucleons in lead disks. The induced magnetization can be interpreted as the effect of a long-range spin dependent interaction mediated by axions or Axion Like Particles (ALPs). The corresponding coupling strength is proportional to the CP violating term gpegsN, i.e. the product of the pseudoscalar and scalar coupling constants of electron and nucleon, respectively. Our upper limit is more constraining than previous ones in the interaction range 0.01 m<λa<0.2 m, with a best result on gpegsN/(ħc) of 4.3×10−30 at 95% confidence level in the interval 0.1 m<λa<0.2 m. We eventually discuss our plans to improve the QUAX-gpgs sensitivity by a few orders of magnitude, which will allow us to investigate the ϑ≃10−10 range of CP-violating parameter and test some QCD axion models.
We present a proposal to search for QCD axions with mass in the 200μeV range, assuming that they make a dominant component of dark matter. Due to the axion–electron spin coupling, their effect is ...equivalent to the application of an oscillating rf field with frequency and amplitude fixed by the axion mass and coupling respectively. This equivalent magnetic field would produce spin flips in a magnetic sample placed inside a static magnetic field, which determines the resonant interaction at the Larmor frequency. Spin flips would subsequently emit radio frequency photons that can be detected by a suitable quantum counter in an ultra-cryogenic environment. This new detection technique is crucial to keep under control the thermal photon background which would otherwise produce a too large noise.
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