Master Thesis

Investigation of Final States with Light Antinuclei at the Belle Experiment


At the Belle experiment nuclei or anti-nuclei come into existence in rare cases during e+e-collisions. The detection of these particles is very difficult, as they are overlaid with background. During this thesis a method was developed for the first time to identify nuclei and anti-nuclei within the Belle experiment. Charge and mass of the particles are calculated with the assistance of the energy loss in the detector, the time of flight and the momentum. Other detectors help supressing background.

With this method candidates for deuterons, tritons and anti-deuterons are identified. Most deuterons and tritons don’t origin from e+e-collisions, but rather from interaction with the rest gas or the beam pipe. For this reason they shall not be analysed any further. The following analysis is limited to anti-deuterons, because they origin from e+e-collisions exclusively.

A fraction of the Belle data is taken at the continuum beyond the Υ(4S)-threshold. With this data the inclusive cross section of the anti-deuteron production in the continuum is set to (33 ± 16 ± 1.8) fb. In order to receive the resonant fraction, this contribution of the continuum needs to be subtracted. The results clearly show that the Υ(1S)-, Υ(2S)- and Υ(3S)-resonance can decay into anti-deuterons. A branching ratio can be given for the Υ(3S)- resonance for the first time. The inclusive branching ratio for the Υ(1S)-resonance is set to (3.6 ± 2.2 ± 0.20)·10−5 , for the Υ(2S)-resonance to (3.7 ± 2.4 ± 0.21)·10−5 and for the Υ(3S)-resonance to (6.7 ± 4.3 ± 0.38)·10−5 .

Furthermore, states which would decay into anti-deuterons were searched for. It was not possible to prove such a decay channel. The upper limits were then calculated. The possible decay of the kaonic anti-cluster S+d + p + π+ produced a height with a significance of 2.9σ. The upper limit for the combined cross section of the creation of the anti-cluster S+ and this particular decay is set to 0.45 fb. Upper limits for the hypothetic decay of the anti-hypernucleus 3ΛHd + p + π+ and the exited 3Hed + p are given.

B-decays into deuteron-anti-deuteron-pairs were also searched for. The known decay B± → J/Ψ + K± → p + p + K± was studied additionally as double check. Not a single candidate was observed for the decay B± → d + d + K± and the upper limit for the branching ratio was set to 4.7·10−8 . However, there was one candidate for the decay B0 → d + d, which sets the upper limit of the branching ratio to 2.5·10−7 .