Progress has been made in the preparation method of relativistic spin-polarized positron source

The team of Professor Li Jianxing of the School of Physics of Xi’an Jiaotong University has cooperated with Associate Researcher Lu Chong of the Institute of Nuclear Physics of the China Institute of Atomic Energy to make important progress in the research of the preparation method of relativistic spin polarization positron source, and proposed for the first time a new scheme to generate high-density and high-polarizability positron source by interacting with a single-shot ultra-short and ultra-intense laser pulse and a solid foil target. Recently, the results were published online in Physical Review Letters.


(a) Schematic diagram of spin-polarized positron source generated by interacting with a single-shot laser pulse with an obliquely placed solid foil target (b) Direct laser acceleration process (c) Nonlinear Compton scattering (d) Nonlinear Breit-Wheeler positron pair generation process (Photo courtesy of the research group)

Relativistic spin-polarized positrons have important applications in the fields of materials physics, nuclear physics, high-energy physics, and laboratory astrophysics. The traditional preparation method has the limitation of beam density and efficiency to a certain extent. In recent years, with the rapid development of ultra-short and ultra-intense laser technology, ultra-short and ultra-intense laser pulses with a peak light strength of 1023W/cm2 have been experimentally realized. The use of such laser interaction with matter to produce spin-polarized positrons has become one of the hot research topics in the world. However, these schemes require precise spatiotemporal synchronization of the laser pulse with the electron beam or gamma-ray beam, which is difficult to experiment. In addition, the polarizability of the positron source in these schemes is only about 30%-40%, whereas related high-energy physics experiments often require a positron source with a polarizability greater than 60%.

In view of the above key scientific problems, Professor Li Jianxing’s team used the self-developed spin-resolved laser plasma interaction simulation program SLIPs to simulate and propose a scheme to generate high-density and high-polarizability positron sources by irradiating oblique foil targets with a single ultra-short and ultra-strong laser pulse. In addition, by changing the direction of polarization of the driving laser, the polarization of the gamma photon as an intermediate product can be manipulated, which greatly increases the polarizability of the positron source. Based on this scheme, a high-density (about 1018cm-3) spin-polarized positron source with an average spin polarizability of more than 70% can be generated numerically by using an ultra-strong ultrashort laser pulse with a peak light intensity of 1023W/cm2.

This research will provide an efficient all-optical research method for generating high-energy and high-polarizability positron sources, and is expected to be applied to experiments such as simulating the cosmic environment, searching for supersymmetric particles, verifying the Standard Model, and searching for new physics beyond the Standard Model. (Source: Yan Tao, China Science News)

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