Observation of multiple volume reflection by different planes in one bent silicon crystal for high-energy negative particles

Multiple volume reflection by different planes passing through the ⟨111⟩ axis in a bent silicon crystal was observed for the first time for 150 GeV/c negative particles, π− mesons, at one of the secondary beams of the CERN SPS. The beam of π− mesons was deflected opposite to the crystal bend by an angle of about 48 µrad, which is 4.6 times larger than in a single volume reflection by the (110) bent planes. The one-side deflection efficiency was about 65%. Multiple volume reflection transforms to a single volume reflection when the orientation angle of the ⟨111⟩ axis relative to the beam direction is increased.