One type of this particle can be confused with photons when they decay inside and contaminate the electromagnetic calorimeter in the ATLAS Inner Detector.
Along with a nucleon, one or two of these particles decay from the Roper resonance, and the Drell-Yen experiment gave evidence that there is not an excess of these particles in the nucleus. One type of this particle can be confused with photons when they decay inside and contaminate the electromagnetic calorimeter in the ATLAS Inner Detector. The neutral type of this molecule is able to undergo Dalitz decay into a photon and an electron- positron pair, but usually the neutral type decays into a pair of photons. These spin-0 particles have a mass of approximately 140 mega-electron volts, and were first detected by Cecil Powell. For 10 points, name these lightest mesons that were also the first to be discovered.
Along with a nucleon, one or two of these particles decay from the Roper resonance, and the Drell-Yen experiment gave evidence that there is not an excess of these particles in the nucleus.
{pion}s [also accept {pi} mesons]