Experimental investigations in elementary particle physics

Field: Physics and Astronomy (Physical Sciences)

<p>An account is given of some of the results of an experiment undertaken by a collaboration of five British and one German Hydrogen Bubble Chamber Groups. A beam of 6 GeV/c K<sup>−</sup> mesons was injected into the British National Hydrogen Bubble Chamber at the proton synchrotron at CKPN, Geneva. A total of 300,000 pictures or 1800 kms, of K<sup>−</sup> track was scanned for interactions. The scanning measuring and identification of two classes of interaction in the Oxford sample of film are described in detail. A scheme which uses a computer to do the book keeping of the scanned information is mentioned - this was developed by the author as a result of experience with this experiment. The treatment of losses, biases and ambiguities is discussed at some length - a new method is used to correct for the lose of sigmas at small decay angles in the laboratory and a discussion of the meaning of the probability associated with a kinematic fit leads to ideas affecting the interpretation of ambiguous fits.</p> <p>Special problems affecting the analysis of antibody final states are discussed and solutions put into practice. Careful treatment is given to final states which derive large weights from losses. A discussion of the optimum way of selecting resonances and choosing histogram bin sizes is to be found in an appendix. From a brief discussion of the theory of Unitary Symmetry we are lead to consider the omega minus and its quantum numbers. An original investigation by the author into the isospin of the omega takes the form of a search for s neutral baryon of strangeness −3. The fact that the state is not found is of even greater interest for the quark model of Unitary Symmetry. The latter is described briefly and a search is made for other states forbidden by the model.</p> <p>A survey is made of final states containing a hyperon and mesons. Evidence in favour of a new Y<sup>&amp;bullet;</sup><sub style="position: relative; left:-.5em;">1</sub> resonance at 1680 MeV decaying to (λπ) supports the findings of W. Derrick et al. at 5.5 GeV/c. A strong forward peak of lambdas in the lambda four pion and lambda five pion final states appears to be associated with strong production of positively charged meson resonances decaying into three pions. These resonances appear at 1100, 1500 and 164O MeV and are identified with A1, A2 and π(1640). The A2 appears to decay to (ρπ) although the data suggests that the A1 does not. Similar features were seen in the lambda four pion state at 3.5 OeV. These findings are important since the A1 has only been seen before in final states confused by "Deck" diffractive effects.</p> <p>The decay correlations of the reaction K<sup>−</sup>p &amp;rightarrow; ρ° are calculated from first principles and compared with experiment. This paves the way for the study of the double peripheral production mechanism. Detailed discussion of two final states (K<sup>−</sup>p &amp;rightarrow; ∑°π<sup>+</sup>π<sup>−</sup> and K<sup>−</sup>p &amp;rightarrow; K<sup>*−</sup>π<sup>&amp;plus;</sup>n) is used to set forth the general features of the model. It is shown that the matrix element for the former may be derived directly from that for the well known reaction π<sup>−</sup>p &amp;rightarrow; ∑°K<sup>*</sup>° by crossing symmetry. Although the data are not definitive, they provide general for the model.</p>