Measurement of the angular distribution in pbar p → ψ (2 S) →e+e-
Abstract
We present the first measurement of the angular distribution for the exclusive process pbar p → ψ (2 S) →e+e- based on a sample of 6844 events collected by the Fermilab E835 experiment. We find that the angular distribution is well described by the expected functional form dN/dcosθ∗ ∝ 1 + λcos2θ∗, where θ∗ is the angle between the antiproton and the electron in the center of mass frame, with λ = 0.67 ± 0.15 (stat) ± 0.04 (sys). The measured value for λ implies a small but non-zero ψ (2 S) helicity 0 formation amplitude in pbar p, comparable to what is observed in J / ψ decays to baryon pairs.
- Publication:
-
Physics Letters B
- Pub Date:
- March 2005
- DOI:
- 10.1016/j.physletb.2005.01.093
- arXiv:
- arXiv:hep-ex/0412007
- Bibcode:
- 2005PhLB..610..177A
- Keywords:
-
- High Energy Physics - Experiment
- E-Print:
- Accepted by Phys. Lett. B