Detecting Linear Breit-Wheeler Signals with a Laser-Foil Setup

TL;DR

This paper proposes a laser-foil experimental setup combined with particle-in-cell simulations to detect linear Breit-Wheeler pair production, distinguishing it from Bethe-Heitler signals through positron energy spectra analysis.

Contribution

It introduces a novel experimental scheme using a 10 PW laser and foil target to identify LBW signals by analyzing positron spectra, even when BH signals dominate.

Findings

LBW positrons are created at the front of the target.

High-energy positron spectra invariance indicates LBW.

Scheme is effective even with dominant BH yield.

Abstract

As a fundamental QED process, linear Breit-Wheeler (LBW) pair production predicted 90 years ago has not yet been demonstrated in experiments with real photons. Here, we propose an experimentally advantageous scheme to detect the LBW signal by irradiating a foil target with a single 10 PW-level laser. Our integrated QED particle-in-cell simulations demonstrate that the LBW signal can be explicitly distinguished from the Bethe-Heitler (BH) signal by comparing positron energy spectra behind the target at varying target thicknesses. The LBW positrons are created at the front of the target and subsequently experience both laser vacuum acceleration and sheath field acceleration to gain high energies, while BH positrons, originating within the target bulk, are only subjected to sheath field acceleration. As a result, the invariance of the high-energy tail of positron spectra with respect to the target thickness serves as a distinct signature of the LBW process. Notably, this scheme remains viable even when the BH yield dominates over the LBW yield.