Estimation of the Inverse Compton Scattering Background in MeV Gamma-Gamma Collider

TL;DR

This paper introduces GBET, a Monte Carlo simulation tool for accurately estimating inverse Compton scattering backgrounds in MeV gamma-gamma colliders, enhancing fidelity over traditional methods.

Contribution

The paper presents GBET, a novel simulation code that fully models successive inverse Compton scatterings with high physical fidelity, verified against CAIN benchmarks.

Findings

Background photon rate from first scattering: 6.24e7/s below 18 eV.

Background electrons and photons from second scattering: ~52 and 1 per second below 11 MeV.

Breit-Wheeler process produces electrons and positrons at ~1312/s with energies 511-720 keV.

Abstract

The MeV Gamma-Gamma Collider would provide a direct experimental platform for elastic light-by-light scattering ($\gamma\gamma \to \gamma\gamma$) and the Breit-Wheeler process with two real photons ($\gamma\gamma \to e^+e^-$). A Monte Carlo code, the Genie Background Evaluation Tool (GBET), has been developed to fully simulate two successive inverse Compton scatterings in the linear regime, including $e^- + \text{laser} \to e^-+ \gamma$ and $e^- + \gamma \rightarrow e^- + \gamma$. GBET overcomes the inherent information loss in traditional luminosity-spectrum-based chain simulations, preserving full particle-level information and achieving higher physical fidelity. The effectiveness of the code is verified by benchmarking against the simulation results of CAIN. GBET shows that the event rate of background photons generated by the first inverse Compton scattering is $6.24 \times 10^7$/s, with energies below 18 eV; the second inverse Compton scattering generates background electrons at 51.99/s and photons at 0.99/s, both with energies below 11 MeV. In addition, M{\o}ller scattering contributes background electrons at 0.56/s with energies around 200 MeV. The count rates of background electrons and positrons originating from the Breit-Wheeler process are 1312.2/s and 1314.3/s, respectively, with energy distributions ranging from 511 to 720 keV.