1. Experimental Observation of a Heavy Particle J
N.takada

2. Experiments
This experiment used a slow extracted beam from the Brookhaven National Laboratory’s alternating-gradient synchrotron.
The observation was made from the reaction p + Be → e+ + e- + x by measuring the e+ e- mass spectrum.
AGS

3. Detector The cherenkov counter is Co and Ce.
The counters Co and Ce are decoupled by magnets M1 and M2.
There are eleven plates(2xA0, 3xA, 3xB, 3xC) of proportional chambers rotated approximately 20o width respect to each other to reduce multitrack confusion.
Eight vertical and eight horizontal hodoscope counters are placed behind chambers A and B.
Lead Glass counters( x 2)
Side View
Lead Lucite counters

4. Observed
It shows the time-of-flight spectrum between the e+ and e- arms in the mass region 2.5 < m < 3.5 GeV.
A clear peak of 1.5 n-sec width is observed.

5. Observed
It shows the shower and lead-glass pulse height spectrum for the events in the mass region 3.0 < m < 3.2 GeV.

6. Observed
There is a clear sharp enhancement at m = 3.1 GeV. Without folding in the105 mapped magnetic points and the radiative corrections, we estimate a mass resolution of 20 MeV.

7. Conclusion
J particle was discovered by S.C.C.Ting’s group in P + Be →　J + X, J → e+ + e-
The same time, ψ particle was discovered by B.Richter’s group at SLAC. e+ + e- → ψ → hadron.
These particles are the same particle, and was called J/ψ particle.
S.C.C.Ting