Bounding elastic photon-photon scattering at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt><mml:mo>ā</mml:mo><mml:mn>1</mml:mn></mml:math> MeV using a laser-plasma platform
/ Authors
R. Watt, B. Kettle, E. Gerstmayr, B. King, A. Alejo, S. Astbury, C. Baird, S. Bohlen, M. Campbell, C. Colgan
and 29 more authors
D. Dannheim, C. Gregory, H. Harsh, P. Hatfield, J. Hinojosa, D. Hollatz, Y. Katzir, J. Morton, C. Murphy, A. Nurnberg, J. Osterhoff, G. P'erez-Callejo, K. Poder, P. P. Rajeev, C. Roedel, F. Roeder, F. Salgado, G. M. Samarin, G. Sarri, A. Seidel, C. Spindloe, S. Steinke, M. Streeter, A. Thomas, C. Underwood, W. Wu, M. Zepf, S. Rose, S. Mangles
/ Abstract
We report on a direct search for elastic photon-photon scattering using x-ray and $\gamma$ photons from a laser-plasma based experiment. A gamma photon beam produced by a laser wakefield accelerator provided a broadband gamma spectrum extending to above $E_\gamma = 200$ MeV. These were collided with a dense x-ray field produced by the emission from a laser heated germanium foil at $E_x \approx 1.4$ keV, corresponding to an invariant mass of $\sqrt{s} = 1.22 \pm 0.22$ MeV. In these asymmetric collisions elastic scattering removes one x-ray and one high-energy $\gamma$ photon and outputs two lower energy $\gamma$ photons. No changes in the $\gamma$ photon spectrum were observed as a result of the collisions allowing us to place a 95% upper bound on the cross section of $1.5 \times 10^{15}\,\mu$b. Although far from the QED prediction, this represents the lowest upper limit obtained so far for $\sqrt{s} \lesssim 1$ MeV.
Journal: Physics Letters B