Maximal Efficiency of Collisional Penrose Process with Spinning Particles

We analyze collisional Penrose process of spinning test particles in an extreme Kerr black hole. We consider that two particles plunge into the black hole from infinity and collide near the black hole. For the collision of two massive particles, if the spins of particles are $s_1 \approx 0.01379\mu M$ and $s_2 \approx -0.2709\mu M$, we obtain the maximal efficiency is about $\eta_{max} = (\text{extracted energy})=(\text{input energy}) \approx 15.01$, which is more than twice as large as the case of the collision of non-spinning particles ($\eta_{max} \approx 6.32$). We also evaluate the collision of a massless particle without spin and a massive particle with spin (Compton scattering), in which we find the maximal efficiency is $\eta_{max} \approx 26.85$ when $s_2 \approx -0.2709\mu M$, which should be compared with $\eta_{max} \approx 13.93$ for the nonspinning case.