In my paper "Nonlinearity of quantum mechanics and the solution of the problem of wave function collapse". Communications in Theoretical Physics. 2015. V.64, No. 1, 47-53. I argue that quantum mechanics is nonlinear.
Any scattering of particles (for example, obtained in a Large Hadron Collider) is a nonlinear process.
Article Nonlinearity of Quantum Mechanics and Solution of the Proble...