If positive charged particles curve in the presence of a magnetic field does that mean the particles colliding in ATLAS create magnetic fields? I ask this because some of the detected particles curve perpendicular to the collision in ATLAS. From what I observed the trajectory maintains a constant curve from the collision. So if it was a magnetic field from an outside source being the accelerator tunnel why are the detected trajectories curved from both sides of the collision. If the magnetic force acting on the charged particles was generated from the tunnel, it would increase the velocity because the particles direction is the same as the force. Where the tunnel on the opposite direction to the collision could be seen to act on the particle moving in the opposite direction,but its force is dismissed because of its opposite equal magnetic force. This to me looks like R is defined from the centre of the collision. Please help me to understand this better. Is the magnetic field from the collision?